GEOLOGY AS APPLIED TO LAND-USE MANAGEMENT ON CUMBERLAND ISLAND, GEORGIA by William H. Mclemore, Charles T. Swann, Perry B. Wigley, Mary C. Turlington, Vernon J. Henry , Gregory J. Nash, J. Martinez, Robert E. Carver, John T. Thurmond Prepared for the United States Department of Interior as part of Contract No. CX5000-8-1563 DEPARTMENT OF NATURAL RESOURCES Joe D. Tanner, Commissioner ENVIRONMENTAL PROTECTION DIVISION J. Leonard Ledbetter, Director GEORGIA GEOLOGIC SURVEY William H. Mclemore, State Geologist Atlanta 1981 GEOLOGY AS APPLIED TO LAND-USE MANAGEMENT ON CUMBERLAND ISLAND GEORGIA by William H. McLemore, Charles E. Swann, Perry B. Wigley, Mary C. Turlington, Vernon J. Henry, Gregory J. Nash; J: Martinez, Robert E. Carver, and John T. Thurmond Prepared for the United States Department of Interior as part of Contract No. CXS000-8-1563 Department of Natural Resources Joe D. Tanner, Commissioner Environmental Protection Division J. Leonard Ledbetter, Director Georgia Geologic Survey William H. McLemore, State Geologist Atlanta 1981 SECTION 1-0 2-0 2-1 2-2 2-3 3-0 3-1 3-2 3-3 3-4 3-5 3-6 4-0 4-1 4-2 4-2-1 4-2-2 4-3 4-4 5-0 5-1 5-2 5-3 5-4 5-5 5-6 5-7 6-0 6-1 6-2 6-3 6-4 6-5 6-6 6-7 6-8 6-9 7-0 7-1 7-2 7-3 TABLE OF CONTENTS SUBJECT PAGE AN INTRODUCTION TO THE CUMBERLAND ISLAND PROJECT 1-1 GEOGRAPHY OF CUMBERLAND ISLAND AND THE SURROUNDING REGION 2-0 Regional geographic setting 2-1 Geography of Cumberland Island 2-2 Climate 2-3 GENERAL GEOLOGY OF THE CUMBERLAND ISLAND REGION 3-1 Introduction 3-1 Holocene-Pleistocene geology 3-2 Pliocene series 3-4 Miocene series 3-5 Upper Eocene sediments 3-5 Structural geology 3-6 STRATIGRAPHY 4-1 Introduction 4-1 Quarternary deposits 4-1 Holocene (Recent) deposits 4-1 Pleistocene deposits 4-1 Pliocene and Miocene deposits 4-2 Summary 4-3 HYDROGEOLOGY OF CUMBERLAND ISLAND 5-1 Introduction 5-1 Previous work on the hydrogeology of Cumberland Island 5-1 Well inventory of Cumberland Island 5-2 Well construction techniques used on Cumberland Island 5-3 Characteristics of the Principal Artesian Aquifer 5-4 Characteristics of shallower aquifers 5-6 General ground-water flow characteristics at Cumberland Island 5-7 LANDFORMS AND NATURAL VEGETATION 6-1 Introduction 6-1 Beach 6-1 Salt marshes 6-2 Foredunes 6-3 Interdune meadow 6-4 Back dunes (rear dunes) and other active dunes 6-5 Stabilized and partially stabilized dunes 6-5 Inland marshes 6-6 Interior forests 6-7 LAND USE ON CUMBERLAND ISLAND 7-1 Introduction 7-1 Marginal marine lands 7-1 Agricultural lands 7-1 SECTION 7-4 7-5 7-6 8-0 8-1 8-2 8-3 8-4 8-5 8-5-1 8-5-2 8-5-3 8-6 8-7 8-8 8-9 8-10 8-11 8-12 8-13 9-0 9-1 9-2 9-3 9-4 9-5 9-6 9-7 10-0 11-0 11-1 11-2 11-2-1 11-2-2 11-2-3 11-2-4 11-2-5 11-2-6 TABLE OF CONTENTS (Continued) SUBJECT PAGE Residential lands 7-2 Recreational lands 7-2 Miscellaneous lands HISTORICAL CHANGES IN THE MEAN HIGH WATER SHORELINE AND NEARSHORE BATHYMETRY OF CUMBERLAND ISLAND History of shoreline changes, 1843-1979, general description Northern segment Central segment Southern segment Hi~torical bathymetric changes in the ebb-tidal deltas and shoal areas General statement St. Andrew Sound St. Marys Entrance Discussion - net shoreline changes Relations of shoreline change to coastal processes Natural causes of erosion and accretion - sea level rise Hydraulic and sedimentary processes at inlets Severe storms and hurricanes Man's influence in the coastal zone Destruction of dunes Summary and conclusions 8-1 8-1 8-1 8-2 8-3 8.:.4 8-4 8-5 8-7 8-10 8-11 8-12 8-13 8-17 8-19 8-20 8-22 ENVIRONMENTAL AND GEOLOGIC HAZARDS ON CUMBERLAND ISLAND 9-1 Introduction 9-1 Flooding 9-1 Erosional hazards 9-4 Accretional hazards 9-5 Dune care and protection 9-7 Cavity collapse hazards 9-8 Suitability for septic tank filter fields 9-9 ECONOMIC MINERALS 10-1 VETEBRATE PALEONTOLOGY OF CUMBERLAND ISLAND Introduction Sharks Caraharias or Odontaspis spp. (sand sharks) Lamnidae Lamna sp. (near L. nasus - porbeagle shark) Isurus sp. (near I. oxyrhincus - mako shark) Carcharodon megalodon (extinct white shark) Carcharidae (requiem sharks) Carcharhinus spp. 11-1 11-1 11-1 11-1 11-2 11-2 11-3 11-3 11-3 SECTION 11-2-7 11-2-8 11-2-9 11-2-10 11-3 11-3-1 11-3-2 11-3-3 11-3-4 11-4 11-4-1 11-4-2 11-5 11-5-1 11-5-2 11-6 11-6-1 11-6-2 12-0 12-1 12-2 12-3 12-4 12-5 TABLE OF CONTENTS (Continued) SUBJECT Galeocerdo cuvieri (tiger shark) Hemipristis serra Physodon sp. Family sphyrnidae (hammerhead sharks) Rays Myliobatis (eagle rays) Rhinoptera (cownose rays) Aetiobatis (spotted eagle rays) Other rays Boney fish - Lepisosteus sp. (gar) Sciaenidae; Pogonias sp. (sea drum) Didon vetus (extinct porcupine fish) Mammals Order perissodactyla; (Unidentified horse) Order ?Cetacea Reptiles Indeterminate turtle ?Alligator sp. GENERAL RECOMMENDATIONS Introduction Recommendations relating to landforms and environments Recommendations relating to ground water Recommendations relating to economic minerals and geologic testing Miscellaneous recommendations PAGE 11-5 11-6 11-6 11-7 11-7 11-8 11-8 11-8 11-8 11-8 11-9 11-9 11-10 11-10 11-10 11-10 11-10 11-11 12-1 12-1 12-1 12-2 12-4 12-5 APPENDIX A: APPENDIX B: APPENDIX C: APPENDIX D: APPENDIX E: APPENDIX F: APPENDIX G: APPENDICES Detailed stratigraphy of Cumberland Island Drilling procedures Lithologic logs Grain size data List of Macrofossils List of Microfossils Miscellaneous photographs 1-0 AN INTRODUCTION TO THE CUMBERLAND ISLAND PROJECT Cumberland Island is the largest and southernmost of Georgia's barrier islands. The majority of Cumberland Island is owned by the National Park Service and operated as a National Seashore under Public Law 92-536, passed on October 23, 1972 (National Park Service, 1977). The acquisition of Cumberland Island was initiated and widely supported by public outcry to save Cumberland Island from commercial exploitation and preserve the island in its natural state. In support of these concerns, the National Park Service has undertaken extensive planning in order to protect the natural environment and simultaneously allow public use. This planning brought to light the fact that very little detailed data concerning present geologic processes and basic hydrologic and geologic resources were available for Cumberland Island. Therefore, on September 28, 1978, the Georgia Geologic Survey agreed, on a contractual basis, to conduct investigations on Cumberland Island to produce these basic data needed for the prudent planning and use of the National Seashore. To meet these ends, the Georgia Geologic Survey has undertaken an extensive subsurface testing program and other on-site investigations. A synthesis of existing geologic, hydrologic, remote sensing, and other pertinent information has been provided as an aid in planning. The Georgia Geologic Survey has drilled 19 stratigraphic test/water monitor wells on Cumberland Island with a cumulative total of 2155 ft. (657 m) drilled. This included a deep stratigraphic test/ monitor well into the Principal Artesian Aquifer. Seismic data offshore from Cumberland Island also has been obtained to aid stratigraphic correlations. As aresult of these test wells and seismic records, "in use" as well as potential aquifers on Cumberland Island have been identified. A number of remote sensing studies have resulted in new and more detailed geologic, landform-natural vegetation, land use and geologic hazards maps. 1-1 The Survey's intent is to present useful and accurate information to those people planning the future of Cumberland Island National Seashore. Therefore, the scope of study is directed more to applied geology rather than the theoretical aspects. In realization that the primary users of this report will probably not be intimately acquainted with geologic nomenclature, the wording has been simplified as much as possible. It is the Survey's belief that a broader and more concise understanding for the users of this report is worth the expense in style. As part of the Georgia Geologic Survey's evaluation of Cumberland Island, great emphasis was placed on evaluating the subsurface stratigraphy of the island. In other words, we were attempting to obtain a good understanding of the . geometry of the various sand, clay, and calcareous strata that underlie the site . Such knowledge is extremely important in assessing the potential impacts of septic disposal, ground-water availability, salt-water infiltration and so forth. And, while the bulk of the text is written in rather general terms, more precise technical back-up is provided in appendices. Drilling procedures, descriptions of cores and cuttings, a list of microfossils, as well as informative photographs also are provided in the appendices. 1-2 2-0 GEOGRAPHY OF CUMBERLAND ISLAND AND THE SURROUNDING REGION 2-1 Regional geographic setting Cumberland Island is part of a chain of barrier islands that extends along much of the Atlantic coast of the United States. These barrier islands are well developed along the entire Georgia coast. In Georgia they are commonly referred to as the "Sea Islands" or as the "Golden Isles". The islands vary in size from that of Cumberland Island, the largest in Georgia, to several islands that are barely above the high tide mark. Jekyll Island lies north of Cumberland Island with St. Andrew Sound between the two. Amelia Island, to the south of Cumberland Island, is separated from Cumberland Island by Cumberland Sound. There are three rivers that flow into the salt marshes landward of Cumberland Island and the Atlantic Intracoastal Waterway west of Cumberland Island. These rivers are the Satilla River entering near the north end of Cumberland, the Crooked River entering near the midpoint of the island, and the St. Marys River entering near the south end of Cumberland Island. All of these rivers are tidally influenced and salt marshes extend several miles inland along their courses. The Crooked River is almost entirely a tidal river and rapidly diminishes in size above the tidal range. Cumberland Island is a portion of Camden County, which is bordered on the north by Glynn County, on the west by Brantley and Charlton counties and on the south by Nassau County (Florida). The St. Marys River forms the Georgia-Florida boun~ary. Woodbine, Kingsland and St. Marys are the major population centers in Camden County. St. Marys is located on the mainland in the extreme southeast portion of Camden County on the banks of the St. Marys River. Kingsland, a smaller town, is located west and further inland from St. Marys. Fernandina Beach, Florida1 is located on Amelia Island, just across Cumberland Sound from Cumberland Island. Cumberland Island is located between two major coastal cities: Brunswick, to the l-1 2-0 GEOGRAPHY OF CUMBERLAND ISLAND AND THE SURROUNDING REGION 2-1 Regional geographic setting Cumberland Island is part of a chain of barrier islands that extends along much of the Atlantic coast of the United States. These barrier islands are well developed along the entire Georgia coast. In Georgia they are commonly referred to as the "Sea Islands" or as the "Golden Isles". The islands vary in size from that of Cumberland Island, the largest in Georgia, to several islands that are barely above the high tide mark. Jekyll Island lies north of Cumberland Island with St. Andrew Sound between the two. Amelia Island, to the south of Cumberland Island, is separated from Cumberland Island by Cumberland Sound. There are three rivers that flow into the salt marshes landward of Cumberland Island and the Atlantic Intracoastal Waterway west of Cumberland Island. These rivers are the Satilla River entering near the north end of Cumberland, the Crooked River entering near the midpoint of the island, and the St. Marys River entering near the south end of Cumberland Island. All of these rivers are tidally influenced and salt marshes extend several miles inland along their courses. The Crooked River is almost entirely a tidal river and rapidly diminishes in size above the tidal range. Cumberland Island is a portion of Camden County, which is bordered on the north by Glynn County, on the west by Brantley and Charlton counties and on the south by Nassau County (Florida). The St. Marys River forms the Georgia-Florida boun:Jary. Woodbine, Kingsland and St. Marys are the major population centers in Camden County. St. Marys is located on the mainland in the extreme southeast portion of Camden County on the banks of the St. Marys River. Kingsland, a smaller town, is located west and further inland from St. Marys. Fernandina Beach, Florida1 is located on Amelia Island, just across Cumberland Sound from Cumberland Island. Cumberland Island is located between two major coastal cities: Brunswick, to the 2-1 north end and Jacksonville, Florida,to the south. Interstate Highway 95 is a major transportation artery in the eastern United States and connects Brunswick, Kingsland, and Jacksonville, Florida. 2-2 Geography of Cumberland Island There are no roads or highways connecting Cumberland Island with the main- land; therefore all transportation to and from the island must be made by boat or airplane. The National Park Service has two major landing points on the west side of Cumberland Island; Dungeness Wharf and Sea Camp Wharf. Plum Orchard Wharf is also a landing point but is not extensively used by the National Park Service. These landing points and some private ones are connected to the rest of the island via the main road, which is also referred to as Grand Avenue. The only landing strip is suitable for light aircraft only. The major population concentrations on Cumberland Island are at High Point, Squaw Town, Little Greyfield and Dungeness. High Point is situated on the northern end of the island on private lands, and the majority of the buildings are private dwellings. Squaw Town and Little Greyfield are located in the middle portion of the island. These areas consist almost exclusively of private dwellings on National Park Service land. Many of these dwellings are being removed when they become unoccupied. Dungeness is located on the southern end of Cumberland Island and is comprised of private dwellings as well as a number of National Park Service buildings) including historic sites such as the Carriage House, the Captain's House and the Dungeness ruins. Greyfield, Stafford and Plum Orchard are the three mansions still intact on the island. Greyfield, which is privately owned, is presently operated as a luxury hotel. Stafford, also privately owned, is unoccupied at the present, although the surrounding buiJdings are used. Plum Orchard is owned by the National Park Service and will be restored a~ a national historic site. It is presently 2-2 being used as a first aid station for the northern camp gites. Cumberland Island also has a number of inland marshes. The majority of these marshes are freshwater and support lush vegetation. Some of the marshes, such as Whitney Lake, Willow Pond and portions of the Sweetwater Complex, are open ponds. The ponds and marshes occur naturally west of stabilized sand dunes. The dunes act as dams, which block the eastward flow of surface waters. Salt marshes are also a significant part of Cumberland Island and are attached to the western edge of the island. The salt marshes generally are not specifically named except for the Raccoon Keys Salt Marsh on the south end of the island. There are also two inland salt marshes connected with the Atlantic Intracoastal Waterway by tidal creeks. Figure 2-1 illustrates the major geographic features of Cumberland Island. 2-3 Climate The regional climate is generally characterized by short, mild winters and warm, humid summers. The Atlantic Ocean has a moderating effect on the coastal weather, producing cooler summers and warmer winters. Cumberland Island is subject to violent storms, such as tropical storms and hurricanes. There is a special threat to the barrier island because of the effects of torrential rains, high winds and surge tides produced by these storms. The Cumberland Island area, however, does not appear to be as susceptible to hurricanes as some other portions of the Atlantic and Gulf coast. Since 1881, only nine very destructive hurricanes have passed in the immediate area of Cumberland Island (N.P.S. 1977). 2-3 0 I 2 ~ 4 MILES ~N [),1 LOCATJON MAP Figure 2-1. Major geographic features of Cumberland Island, Georgia. 3-0 GENERAL GEOLOGY OF THE CUMBERLAND ISLAND REGION 3-1 Introduction * Cumberland Island is located in the portion of the Coastal Plain which contains the youngest sediments in Georgia. These sediments represent modern and ancient barrier islands and related environments, which have moved eastward in response to a falling sea level since early Pleistocene time (Table 3-1, Figure 3-1, and Plate 1). Only Holocene and Pleistocene aged sediments are exposed at the surface of the island. The Pliocene series is represented in the subsurface on Cumberland Island by a sandy equivalent to the Duplin Formation. These sands were deposited under marine conditions when the shoreline was .inland from the present coast. The sands are stratigraphically below clays of the basal Pleistocene and above calcareous sediments of Miocene age. The Miocene series comprises two formations; a lower Hawthorne Formation that consists predominantly of sands and clays with minor carbonate beds and an upper Charlton Formation that consists predominantly of carbonates with minor sands and clays. These sediments underlie the Pliocene sediments and, in turn, overlie the Ocala Group. The Ocala Group is composed of limestones of upper Eocene age in unconformable contact with the suprajacent Miocene series. No Oligocene sediments have been recognized on Cumberland Island or in the southeastern area of Georgia. According to the Florida Bureau of Geology, the Ocala Group is divided into three formations: the lower Inglis, the Williston, and the upper Crystal River Formations. Stratigraphic test well CI-01, drilled on Cumberland Island by the Georgia Geologic Survey, established the presence of the Crystal River Formation, but did not penetrate through the formation. I * A detailed description of the stratigraphy of the Cumberland Island area is provided in Appendix A. 3-1 3-2 Holocene-Pleistocene Geology The Holocene deposits on Cumberland Island consist primarily of fine-grained sands situated along the eastern edge of the island and clays of the salt marshes on the western edge (Plate 1). This pattern is typical of barrier islands of the Georgia coast. The Holocene deposits of the eastern side of the island represent dune, interdune deflation areas and beach environments. Fresh water ponds and marshes, which are receiving sediments, are scattered over the island. These marshes are exceptionally well developed west of the dunes. Here the dunes act as dams impounding the eastward drainage which results in marshes and ponds. Other fresh water marshes occupy slight depressions in the land surface and appear to be receiving modern sedimentation. The salt marshes typically are located on the western edge of the island although there are some tidally influenced marshes in the island interior. Both the salt and interior marshes are characterized by clay and silt size grains with interbedded, fine-to very fine-grained quartz sands. The Holocene age deposits are easily distinguished from the upper Pleistocene Satilla Formation in that the Satilla Formation lacks significant clay units. The Holocene sands also may be differentiated from the Pleistocene sands by the presence of a soil profile and the absence of calcareous shell debris in the Satilla Formation. The Pleistocene sediments of the Georgia coast also are situated in "terraces" which parallel the present coast. These "terraces" we:re first noted by William Bartram in his excursions through coastal Georgia and were subsequently described in the account of his travels published in 1791. Each "terrace" is composed of a barrier island and its related marsh or lagoon deposits landward of the barrier. The marsh deposits lje within a given range of elevations which differ for each barrier-marsh complex (Table 3-1). The older "terraces" occupy positions of higher 3-2 elevation than the younger ones. This results in a series of "steps" or "terraces" which terminate at the present coast. Table 3-1 is a synopsis of the elevations of the Pleistocene shorelines recognized in Georgia. Table 3-1 - Recognized Shorelines of the Lower Georgia Coastal Plain SHORELINE ELEVATIONS ABOVE MSL AGE Present day or Holocene coast Silver Bluff Princess Anne Pamlico Talbot Penholoway Wilcomico 0 Approximately 4~ ft (1.4 m) Approximately 13 ft (4.0 m) Approximately 24~ ft (7.5 m) 39 - 46 ft. (12-14 m) 69 - 75~ ft. (21-23 m) 95 - 102 ft. (29-31 m) Holocene Late Pleistocene Late Pleistocene Pleistocene Pleistocene Pleistocene Early Pleistocene (Adapted from Hails and Hoyt, 1969) These obvious topographic features have led to each shoreline and its associated environments being assigned a formal lithostratigraphic name which corresponds to the name of ' the shoreline. For example, the Wilcomico barrier/ marsh complex is referred to as the Wilcomico Formation. The mapping of these formations is based largely on elevation. Theoretically, each barrier/marsh complex represents a stabilization of the shoreline followed by a regression and trans- gression which stabilizes at a lower elevation than the previous barrier/marsh complex. Two lithologic units in the Pleistocene sediments are recognizable in drill holes on Cumberland Island: The upper unit is a barrier island facies con- sisting of a sand composed of predominantly fine-grained quartz; whereas the lower unit is a back barrier facies composed of silts and clays. The upper sand unit is assigned to the Silver Bluff shoreline deposits. The lower, fine-grained terrestrial unit has not been assigned to any shoreline or formation. This unit suggests a restricted marine environment such as a modern-day salt marsh. 3-3 A review of existing literature that relates to the Pleistocene sediments of the Cumberland Island region reveals that the upper sand unit present throughout Cumberland Island fits the stratigraphic position and lithologic description of the Satilla Formation described in Veatch and Stephenson (1911). Therefore, the Satilla Formation is adopted as the name of the upper sand unit of Pleistocene age on Cumberland Island. The name is applied as described in Veatch and Stephenson (1911) on Cumberland Island with the exception of the river deposits which are omitted (Plate 1). The type sections for this formation are located on the Satilla River only a few kilometers from Cumberland Island on the mainland. Preliminary results of ongoing research suggest that the term Satilla Formation "may be useful in a regional scale, and is presently being considered for adoption and use by the Georgia Geologic Survey" (Paul Huddlestun, oral commun., 1980) . The lower unit of fine-grained terrestrial sediments that is present on Cumberland Island has not been named. This unit also appears to be a mappable unit on Cumberland Island and on the mainland in southeast Georgia. Both the Satilla Formation and the lower fine-grained terrestrial sediments unit are detailed in the Neogene Stratigraphy section (refer to Appendix A) of this report. 3-3 Pliocene series The Pliocene series is represented on Cumberland Island by one lithostrati- graphic unit equivalent to the Duplin Formation. The Duplin equivalent is not exposed to the surface on Cumberland Island, but is represented in the subsurface by a marine sand which fines upward. In southeastern Georgia, the Pliocene series is covered by Pleistocene sediments. There are few exposures of these sediments at the surface, as the Pliocene shoreline appears to have about the same location as the highest Pleistocene terraces (Paul Huddlestun, oral commun., 1980). The Pliocene sediments on Cumberland Island are described in more detail in the Neo- 3-4 gene Stratigraphy section of this report. 3-4 Miocene series The Miocene series in the southeast Georgia region consists of two units. The upper, calcareous unit is the equivalent of the Charlton Formation and the lower clastic and carbonate sediments comprise the Hawthorn Formation. The Tampa Limestone, which is the basal Miocene unit in east Florida, is not present in southeastern Georgia. In well CI-01 (GGS 3426) the Miocene sediments had a total thickness of 320ft (97.5 m). The Charlton Formation is 210 ft(64 m) in CI-01 with the Hawthorn Formation making up the remainder of the series. The most recent study of the Miocene sediments was made by Watson (1979), but the main emphasis in his paper was groundwater. An isopachous map produced by Watson showed the Miocene sediments to be between 400 ft (120 m) and 500 ft (150 m) thick in the Cumberland Island area. The test drilling on Cumberland Island has shown that Watson's figures for the thickness of the Miocene are too high and should be revised downward closer to the 320ft (97.5 m) of sediments encountered in CI-01. 3-5 Upper Eocene sediments The sediments of late Eocene age are represented in the southeastern Georgia region as the Ocala Group. The Ocala Group consists of a thick sequence of limestones which lie unconformably on the middle Eocene Claiborne Group. The Florida Bureau of Geology recognizes the following formations in ascending order; the Inglis Formation, the Williston Formation, and the Crystal River Formation. Cumberland Island well CI-01 penetrated 113 ft. (34.4 m) of the Crystal River Formation. The lithology of the Crystal River Formation encountered in CI-01 is not typical of the formation. Rather, the formation consists of a fossiliferous (bryzoan-rich), white limestone. This bryzoan facies, nevertheless, is considered to be a member of the Crystal River Formation as yet unnamed (Paul Huddlestun, oral commun., 1980). 3-5 Figure 3-2 is a structure contour map of the top of the Ocala Group in the Cumberland Island region. 3-6 Structural geology Several faults have been proposed north of Cumberland Island in Glynn County (refer to Figure 3-3). These faults are considered to be potential pathways whereby salty ground waters have contaminated portions of the Principal Artesian Aquifer in the vicinity of Brunswick. They are discussed in greater detail in groundwater geology section of this report. 3-6 ITIJ] STREAM ALLUVIUM N CJ HOLOCENE SHORELINE COMPLEX r~:m~ SILVER BLUFF SHORELINE COMPLEX BE PRINCESS ANNE SHORELINE COMPLEX 1:~:::;~:::1 PAMLICO SHORELINE COMPLEX F-d TALBOT SHORELINE COMPLEX 1:'::::.1 PENHOLOWAY SHORELINE COMPLEX 0 WICOMICO SHORELINE COMPLEX ~CHARLTON FORMATION AND ~ DUPLIN MARL 0 10 20M ILES Adapted from the Geologic Map of Georgia,1976 Figure 3-1. Regional geology of southeast Georgia. STRUCTURE CONTOUR Of THE TOP Of THE OCALA GROUP 0 2 8 IOMILES _,\=:<:=i:::==i=i==i===l __!!_ Well number 448 Depth to cup of Ocala group n relalod to sea level Data point ...,.....JJtfJ,.,....... Struc:tur con,our line Conhlar iiiiii'VII 25 loot Figure 3-2. Structure contour of the top of the Ocala Group. --CRAMER and ARDEN, /980 Jekyll Island I Proposed faults 0 2 4 6 8 IOMILES Cumberland Island Figure 3-3. Geologic structure proposed in the Cumberland Island region. 4-0 STRATIGRAPHY 4-1 Introduction Cumberland Island is made of and underlain by layers of sand, clay, silt and limestone which are known to range in age from Miocene to Holocene. The purpose of this section is to present a concise description of the stratigraphic units. Much information on the stratigraphy was obtained from the boreholes (refer to Figure 4-1). For more concise and detailed description of the stratigraphy, the reader is referred to Appendix A. 4-2 Quaternary deposits 4-2-1 Holocene (Recent) deposits: Holocene or recent sediments include those deposited from 25,000 years ago to the present. The oceanward side of Cumberland Island began forming about 5000 years before present (B.P.) when a marked lowering of sea level allowed the formation of a Holocene barrier-island system somewhat seaward of its present location (Henry and others, 1973). As a result of subsequent island retreat, this Holocene barrier system became welded onto the pre-existing Pleistocene Silver Bluff barrier island. Thus Cumberland Island is a composite of relatively recent Holocene and older Pleistocene barrier island complexes (Plate 2). 4-2-2 Pleistocene deposits: Deposits of Pleistocene age are predominantly composed of sand, clayey sand, and sandy clay consisting of a barrier island facies as well as a back barrier facies (refer to Section 3-2). The barrier island facies is characterized by fine, clean sand (refer to Figure 4-9) whereas the back barrier environment is represented by a more clayey facies (Figs. 4-2 through 4-7). 4-1 Macrofossils are uncommon in the Pleistocene deposits, except for abundant plant remains in the upper part of the barrier island facies and a few shells. Ophiomorpha nodosa (Fig. 4-8), the fossil burrow of the shrimp Callianassa major, is also found. 4-3 Pliocene and Miocene deposits These epochs are represented by the Pliocene age Duplin Formation which directly overlies the Miocene Charlton Formation. The Duplin Formation is middle Pliocene in age and consists of yellowish-brown to greenish-gray, fine-grained sand in the upper part and pale green sand in the lower part. The Duplin includes clay and clayey sand interbeds, some of which are cross-bedded. The Duplin fossils include clams, oysters, scallops, sea snails and abundant microfossils. The general distribution and thickness of the Duplin on Cumberland Island is shown on Figures 4-2 through 4-7, which are based on well logs. In addition, Figures 4-10 through 4-15 which are based on seismic studies, show the distribution of the middle Pliocene (and presumably the Duplin). The abundance of marine fossils indicates that the Duplin sediments probably were deposited in shallow marine conditions. The Charlton Formation of middle Miocene age is a well cemented limestone. Because of its hardness, drilling was stopped at the top of the Charlton. The borings which did penetrate the Charlton showed a yellowish-gray, hard, sandy, phosphatic limestone that locally contains chert. In places the Charlton contains enough fossils to be called coquina (beach rock). Fossil impressions of sea snails occur commonly in the Charlton. The Charlton is identified on the seismic profiles (Figs. 4-10 through 4-15) as the middle Miocene. The Charlton was deposited in a shallow marine environment. 4-2 4-4 Summary Sediments on and beneath Cumberland Island consist of sand, mud and limestone deposited in both marine and non-marine environments. The Pleistocene and Holocene deposits show evidence of deposition in a barrier island complex which includes dune and salt marsh deposits. The older deposits, because of their fossil content, are interpreted as being shallow marine. 4-3 + LITTLE \ CUMBERLAND ISLAND A' I BORE HOLE ':I,'AtO_,X SEISMIC LINE ~ 8' 8 ~ CROSS SECTION 0 1 2 3 KILOMETERS 0 % 1 2 NAUTICAL MILES Figure 4-1. Bore hole, seismic line, and cross section locations, Cumberland Island, Georgia. EXPLANATION FINE SAND [ I COARSE SAND TO PEBBLES ~MUD HUMUS II LIMESTONE BARRIER ISLAND FACIES BACK BARRIER FACIES NEARSHORE DELTAIC FACIES Well numbers are located above each well diagram. Explanation for figures 4-2 through 4-7. These figures are presented in metric units to more closely fit with seismic interpretations. A A' Seismic Line 17 16 8 Seismic Line 4 -~~'l&iJW][!i;::~~~lr~~======~~F -8 -12 -16 -20 -24 0 Y2 1 Km 17 8 16 A 18 A' --------?- -12 -16 -20 -24 COLUMNAR SECTIONS OF WELLS SHOWING CORRELATION OF LITHOLOGIES NO HORIZONTAL SCALE IMPLIED Figure 4-2. Geoloqic cross section A-A'. m 8 12 8 - Seismic Line 4 169 0 -4 -8 -12 -16 -20 0 Y2 12 8 8 12 4 0 -4 11 14 14 8' Seismic Line 171 11 8' m COLUMNAR SECTIONS OF WELLS SHOWING CORRELATION OF LITHOLOGIES NO HORIZONTAL SCALE IMPLIED Figure 4-3. Geologic cross section 8-B' . m c 8 Seismic Line 4 169 0- -4 -8 - - -12 -16 0 Y:z 1 Km 8 9 m c 8 9 C' C' Seismic Line 171 COLUMNAR SECTIONS OF WELLS SHOWING CORRELATION OF LITHOLOGIES NO HORIZONTAL SCALE IMPLIED Figure 4-4. Geologic cross section C-C'. m D 8 4 0 -4 -8 -12 -16 -20 0 ~ 1 Km 0' Seismic Line 171 ":,. m 8 D 7 6 5 D' 4 . . I 0 -+---1--~+-------~,.':.,__-1---------1-....~:~.' \' -4 -8 -12 -16 -20 -24 COLUMNAR SECTIONS OF WELLS SHOWING CORRELATION OF LITHOLOGIES NO HORIZONTAL SCALE IMPLIED Figure 4-5. Geologic cross section 0-0'. m E 4 3 E' Seismic Line 171 ~ 1 Km m 1 4 0 -4 4 .f:~~-- :. .. . ... .-.:: . . . -;: .... ,. 3 E' I \ \ \ ' 8 -12 / -16 -20 ....;. ~;~.i; ~~}i~;:~;f{~- .' ~~f:;;;~It;: __ -24 -28 COLUMNAR SECTIONS OF WELLS SHOWING CORRELATION OF LITHOLOGIES NO HORIZONTAL SCALE IMPLIED Figure 4-6. Geologic cross section E-E'. F f' m Seismic Lines 16 8 0 -8 -16 -24 0 1 Km m 12 F 8 4 0 -4 -8 -12 -16 -20 -24 11 9 17 F' COLUMNAR SECTIONS Or WELLS SHOWING CORRELATION OF LITHOLOGIES NO HORIZONTAL SCALE IMPLIED Figure 4-7. Geologic cross section F-F'. Figure 4-8. Ophiomorpha nodosa burrow in boring 3 at 7 m below surface, illustrating well-preserved wall structure. Note smooth mud in the interior surface of burrow. Figure 4-9. Cumberland Island Wharf outcrop . Pleistocene barrier island deposits (foreshore facies) on 12 m high erosional scarp. 20m.sec 15m + 1 Kilometer ~I ...... ' ,; ' ~ : ~ ;: . : Figure 4-10. Seismic profile in Cumberland River, 2 km south of Cumberland Wharf, showing thin Holocene deposits unconformably overlying sediments of Pleistocene crossbedded deposits. The latter overlie middle Pliocene sediments. A horizontal unconformity defines the boundary between Pliocene sediments and the limestone (middle Miocene). 15 m l 'f,.......--- - - - - 1 Kilometer ...." Figure 4-11 . Seismic profile; intersection of seismic line 171 with cross section A-A', showing large channel cut with fill of probably Pleistocene age. The channel is cut into middle Pliocene deposits with the channel bottom on the top of Miocene sediments. ' \. ' ~ . 'i :,l . ~. ... ' half kilometer t ~'- \::,' .. ; fL' Figure 4-12. Seismic profile in Beach Creek (seismic line 188), 1 km southeast of Dungeness, showing Holocene channel deposits unconformably overlying bedded sediments of back barrier facies of Pleistocene age. A strong reflector defines the boundary between the middle Miocene and middle Pliocene sediments. + /~- Kilometer Figure 4-13. Seismic profile in Cumberland River (seismic line 169), in front of Stafford Island. Reworked sediments of Pliocene-Holocene age directly overlie the middle Miocene Charlton limestone. 15m + + '..-.. /,_.,..,..,____ _ _ _ _ _ _ 1 Kilometer o: oe o t o: : ; o \ I ' Figure 4-14. Seismic profile in Cumberland River (seismic line 169), 5 km south of CllJmberland Wharf, showing flat-lying beds of Pleistocene unconformably overlying a thin sequence of Pliocene sediments. The latter overlie the erosional surface of the middle Miocene. ----- - -------~------ -- 20nuec 1 Kilometer . . -~I -- ----' --- ! : Figure 4-15. Seismic profile in southern end ofthe seismic line 171, showing karst. Quaternary deposit overlies coarse material of the Duplin Formation (middle Pliocene). The latter deposits overlie an irregular surface developed by karstification on the limestone (middle Miocene). S-0 HYDROGEOLOGY OF CUMBERLAND ISLAND S-1 Introduction After acquisition of large portions of Cumberland Island by the National Park Service, it became apparent there essentially was no hydrogeologic data available. In response to this need, the Georgia Geologic Survey conducted a geologic and ground-water survey of the island. Such a survey provides the basic data on which planning decisions can be made. The ground-water survey also has resulted in several recommendations listed in Section 12. This study is not a detailed examination of the ground-water systems on Cumberland Island, but rather a general discussion of the most important aspects of them. In this regard, the Georgia Geologic Survey inventoried a majority of the existing water wells on National Park Service property, constructed a deep well into the Principal Artesian Aquifer, constructed 17 shallow wells to monitor the unconfined water table, lithologically logged one private well, and examined shallow seismic data for the area surrounding Cumberland Island. S-2 Previous work on the hydrogeology of Cumberland Island The most prolific aquifer on Cumberland Island is the Principal Artesian Aquifer, also known as the Floridan Aquifer. The Principal Artesian Aquifer has attracted much attention because of the large water withdrawals along the Atlantic coast of Georgia and Florida. These withdrawals have resulted in significant changes in the potentiometric surf~ce of the aquifer, resulting in an increased potential for salt water encroachment. Governmental and public concern over changes in the potentiometric surface have resulted in publication of voluminous regional (but not specific to Cumberland Island) works by the United States Geological Survey, the Georgia Geologic Survey, the Florida Water Management Districts, the 5-1 the Florida Bureau of Geology and private industry. The first study that specifically mentioned wells on Cumberland Island was by McCallie (1898). Warren (1944), in a study of the Principal Artesian Aquifer along the entire Georgia Coast, measured heads on a number of wells on Cumberland Island and in the St. Marys area. A regional study by Stringfield (1966) dealt with many aspects of the Principal Artesian Aquifer including the chemistry and its implications on water quality. Krause and Gregg (1972) documented changes in the potentiometric surface of the Principal Artesian Aquifer from 1880 to 1971. Johnson and others (1980) published 1a regional map of the estimated original potentiometric surface of the Principal Artesian Aquifer. The shallow aquifers of Miocene to Holocene age have had little study. The latest studies are by Watson (1979), who conducted a regional analysis of the shallow aquifers of the coastal area of Georgia, and Beck (1979), whose paper is a discussion of the use of ponds for irrigation and the hydrologic similarities between the ponds and large-diameter wells. Frazee and McClaugherty (1979) of the St. John's Water Management District (Florida) published a comprehensive paper that deals with the major ground water systems in the St. Johns Water Management District, including the shallow aquifers. Portions of their work were conducted across the St. Marys River from Cumberland Island; therefore, the data probably can be applied to Cumberland Island. 5-3 Well inventory- of Cumberland Island An inventory (Table 5-1) of existing wells on Cumberland Island has resulted in the documentation of 48 wells located largely on National Park Service property. The inventory was concentrated on National Park Service properties and included only the most accessible private wells; therefore, 48 wells in considered to be a conservative figure. Figure 5-1 is a location map of,the wells inventoried. 5-2 The inventory resulted in the location of 15 larger-diameter wells that are believed to tap the Principal Artesian Aquifer. The remainder of the wells are from two to three inches (about S-8 em) in diameter and withdraw water from shallower aquifers. 5-4 Well construction techni ques used on Cumberland Island There are three types of well construction used on Cumberland Island; "driven wells", "rock wells", and "deep wells". The modes of construction correlate with well use and depth. Well construction methods used in the unconsolidated sands and clays of the Pleistocene and Pliocene age sediments result in Type 1, usually referred to as "driven wells". These wells are used by the National Park Service in several campgrounds, where only small amounts of water are required. The Type 1 wells are constructed by driving a slotted drive point and casing into the sediments with a hammer mounted on a drill rig. This type of well is restricted to use in soft sediments near the surface and is seldom more than 90 feet (27 m) in depth because of the hard dolostone of the Charlton Formation, which cannot be penetrated by the drive point. Wells constructed by the second type of well construction are commonly referred to as "rock wells". The Type 2 wells are of intermediate depth and typically are used for domestic purposes on Cumberland Island. Standard rotary drilling methodology is used to open a well bore from the surface through the calcareous sediments of the Charlton Formation. The well is then cased from the top of the calcareous sediments to the surface, with open hole construction through the calcareous sediments. Through use of compressed air or water pressure a reservoir is opened in the underlying calcareous sands. Wells made by the third type of well construction are commonly referred to as "deep wells". The Type 3 wells obtain water from the Principal Artesian Aquifer. Standard rotary or cable tool methodology is used to open a well bore from the 5-3 surface to the top of the Principal Artesian Aquifer. This is then cased internally and drilling is continued inside the casing. The portion of the well below the casing is left open to the aquifer. In the majority of the wells on Cumberland Island, the potentiometric surface of the Principal Artesian Aquifer is above the land surface; therefore, these wells flow at the surface without pumping. 5-5 Characteristics of the Principal Artesian Aquifer The Principal Artesian Aquifer consists of hydrologically connected lime- stone from middle Eocene to Miocene in age. This aquifer is the most viable source of fresh water on the island. The earliest recorded well drilled into the Principal Artesian Aquifer on Cumberland Island was constructed in 1887 (McCallie, 1898). This well had a head of 67 ft (20.4 m) above mean sea level and was estimated to flow at a rate of 800,000 gallons (3,000,000 liters) per day (McCallie, 1898). Because of the large amounts of water used by the coastal industries, there has been significant decline in the potentiometric surfa~e of the Principal Artesian Aquifer (Krause and Gregg, 1972). These changes are largely the result of water withdrawal. Cones of depression surrounding Brunswick and the St. MarysFernandina Beach area are of primary concern on Cumberland Island. The southern half of the island is influenced by the St. Marys-~ernandina Beach cone of depression. Figure 5-2 is a map of the potentiometric surface of the Principal Artesian Aquifer at Cumberland Island, based on September 1980 measurements. The map indicates a lowering of the potentiometric surface towards Fernandina Beach. There are no water level measurements for the extreme northern portion of Cumberland Island, but this area may be influenced by pumping in the Brunswick area. Figure 5-3 is a potentiometric map of the Brunswick-Fernandina Beach area (Mitchell, 1980) which was adapted for use in this report. This map suggests that the lowering of the potentiometric surface, illustrated in figure 5-2, is a result of pumpage 5-4 in the St. Marys-Fernandina Beach area. Salt water intrusion also has been a problem in the Principal Artesian Aquifer in Brunswick, as well as Fernandina Beach, Florida. Studies by Wait and Gregg (1973), Gregg and Zimmerman (1974), and Harden and Associates (1979) address the geohydrology of salt water intrusion. These studies indicate that deep zones in the aquifer contain salty connate water under relatively high heads (i.e. high hydrostatic pressures). As a result of the higher heads, saline waters will move up well bores and contaminate the water of the Ocala Group. The remedial measure for this problem has been to terminate wells above these zones of high chloride water. On Cumberland Island, it is recommended that wells drilled into the Ocala Group not exceed 1000 ft (about 300 m) in depth to prevent possible contamination of the aquifer. The water analyses from wells using the Principal Artesian Aquifer on Cumberland Island indicate the water is hard to very hard, but meets the chemical standards for general use as well as drinking water (Table S-2). Table 5-3 is a synopsis of water analyses taken from the Principal Artesian Aquifer on Cumberland Island. The values in Table 5-3 represent the arithmetic mean of all samples. The average chloride (Cl) concentration is 37.25 ppm. This is well below the maximum limit of 250 ppm; therefore, no salt water intrusion into the aquifer is indicated. Fluorides' (F) have an average concentration of 0.7 ppm on Cumberland Island. Fluorjde concentrations between 0.7 ppm and 1.2 ppm are generally considered ideal to help reduce the incidence of tooth decay in young children and 1.5 ppm is considered the maximum allowable concentration. On Cumberland Island a concentration of 0.7 ppm appears to be characteristic of the water from the Principal Artesian Aquifer. The average concentration of CaC03 is 328.0 ppm. Water with a Caco3 concentration of more than 200 ppm is considered very hard water. This high concentration of carbonates may cause scale to form in boilers and water heaters and may also result in the "liming up" of water pipes. 5-5 Total dissolved solids include all material in solution in the water. The total dissolved solids in the water of the Principal Artesian Aquifer averaged 463.5 ppm on Cumberland Island. Generally, total dissolved solids should not exceed 500 ppm although concentrations up to 1000 ppm can be used if no other supplies are available, but concentrations over 1000 ppm are considered unacceptable. Table 5-3 also includes a number of other chemical components, all of which are within acceptable limits. For more detailed information on those chemical components the reader is referred to Hem (1970), Sonderegger and others (1978) and the Rules for Safe Drinking Water published by the Georgia Environmental Protection Division. Sediments overlying the Principal Artesian Aquifer in the vicinity of Cumberland Island are from 400 to 600 feet thick (120-180 m) and consist of clays and sandy clays with lens-shaped bodies of sand, gravel, and thin carbonate layers. These shallow sediments have been largely ignored as potential aquifer because of the proximity to the highly productive Principal Artesian Aquifer. Wells tapping the shallow aquifers require screening and filter packing, and consequently are more expensive to construct per foot of depth. Shallower wells can also be expected to produce less water per foot of depth than wells tapping the Principal Artesian Aquifer. Nevertheless, a water user requiring perhaps 200 gallons (750 liters) of water per minute or less may find a better cost-benefit ratio from a shallow well. Water quality (Table 5-4) in the shallow aquifers is comparable to or better than water quality in the Principal Artesian Aquifer (Watson, 1979). Contamination of unconfined surface aquifers can be a problem, particularly in populated areas. Properly cased shallow wells completed in Pliocene-Miocene sediments are protected from surface contamination by clay interlayered with the water-bearing sands and carbonates. 5-6 5-7 General ground-water flow characteristics at Cumberland Island Figure 5-5 is an idealized cross-section from St. Marys to Cumberland Island, summarizing the relationship of the various water-bearing units and direction of water movement. The most important aspect of this figure is that it clearly points out that the unconfined and Pliocene-Miocene aquifers are somewhat susceptible to contamination. Also in some estuaries, saline surface water may enter the Pliocene-Miocene aquifer system. If this is the case, then the Park Service should not consider constructing wells in these two aquifers; rather, the Miocene Sand Aquifer or the Principal Artesian Aquifer should be utilized. 5-7 TABLE 5-1 WELL INVENTORY OF CUMBERLAND ISLAND Map No. Name Diameter 001 Carriage House 4 inches 002 Dungeness #1 4 inches 003 Grange #1 4 inches 004 Grange #2 2 inches 005 NPS #1 2 inches 006 NPS #2 2 inches 007 Capt. Middleton 3 inches 008 NPS-Brickhill 2 inches 009 NPS-Stafford 2 inches 010 Dungeness #2 4 inches 011 NPS-barracks 012 013 014 Greyfield #1 015 Greyfield #2 2 inches 2 inches 2 inches 3 inches 8 inches 016 4 inches 017 2 inches 018 2 inches 019 2 inches 020 3 x 2 inches 021 3 inches 022 3 inches 023 2 inches 024 2 inches 025 2 inches 026 2 inches 027 4 inches 028 2 inches 029 Dungeness Garden Well 4 inches 030 NPS-Superintendent Well 2 inches 031 032 033 034 Stafford 035 4 inches 4 inches 2 inches 6 inches 2 inches 036 Greyfield Tower 3 inches 037 NPS #3 2 inches 038 NPS #4 2 inches 039 NPS #5 2 inches 5-8 Use none none domestic domestic domestic domestic domestic camp use camp use none domestic domestic none domestic domestic none domestic domestic domestic domestic none domestic domestic domestic domestic domestic domestic none-capped domestic domestic domestic domestic domestic livestock none-capped none none-capped domestic domestic Table 5-1 WELL INVENTORY OF CUMBERLAND ISLAND (Continued) Map No. Name 040 NPS #6 041 NPS #7 042 043 044 NPS #8 045 046 Plum Orchard #1 047 Yankee Paradise 048 Beach Well * casing rusted beneath ground level Diameter 2 inches 2 inches 2 inches 2 inches 2 inches 2 inches 4 inches 4 inches * Use domestic domestic domestic none domestic domestic domestic camp use none S-9 Table 5-2 MAXIMUM CONTAMINANT LEVELS FOR DRINKING WATER (ppm) Primar;r Arsenic Barium Cadmium Chromium Lead Mercury Nitrate (as N) Selenium Silver Inorganic Secondary 0.05 Chlorine (Cl) 1.00 Copper (Cu) 0.01 Iron (Fe) 0.05 Manganese (Mn) 0.05 0.002 Sulfate (S04) Zinc (Zn) 10.00 Total Dissolved Solids 0.01 0.05 Organic Chemicals Chlorinated Hydrocarbons: Endrin Lindane Methoxychlor Toxaphene 0.0002 0.004 0.01 0.005 Chlorophenoxys: 2,4-D 0.1 2,4,5-TP 0.01 250.0 1.0 0.30 0.05 250 5 500 Source: Rules for Safe Drinking Water, Georgia Environmental Protection Division 5-10 TABLE 5-3 ANALYSES OF WATER FROM THE PRINCIPAL ARTESIAN AQUIFER ON CUMBERLAND ISLAND, GEORGIA Silica (Si0 2) Iron (Fe) 28 ppm 0.16 ppm Manganese (Mn) -0- Calcium (Ca) 66.25 ppm Magnesium (Mg) 39.50 ppm Sodium (Na) 24.00 ppm Ul I I-' Potassium (K) 3.00 ppm I-' Sulfate (S04) 165.50 ppm Chloride (Cl) 37.25 ppm Fluoride (F) Nitrate (N03) Phosphate (P04) Sulfide (S) Bicarbonate (HC03) Alkalinity as Caco3 Hardness as Caco3 Dissolved Solids pH .70 ppm -0-020.66 ppm 192.75 ppm 158.25 ppm 328.00 ppm 463.50 ppm 7.47 Ab~ve values represent the mean value of all samples. TABLE 5-4 ANALYSES OF WATER FROM THE PLIOCENE - MIOCENE AQUIFER Silica (Si02) Iron (Fe) Manganese (Mn) Calcium (Ca) Magnesium (Mg) Sodium (Na) Ul I Potassium (K) 1-' N Sulfate (S04) Chloride (Cl) 20.3 ppm .24 ppm -0- 54.3 ppm 8.0 ppm 22.0 ppm 1.9 ppm 6.5 ppm 50.0 ppm Flouride (F) Nitrate (N03) Phosphate (P04) Sulfide (S) Bicarbonate (HC03) Alkalinity as CaC03 Hardness as CaC03 Dissolved Solids pH .16 ppm -0-015.3 ppm 170.6 ppm 140.0 ppm 168.6 ppm 322.2 ppm 7.65 ppm Above values represent the mean value of all samples. 6. 0 LANDFORMS AND NATURAL VEGETATION 6-1 Introduction Cumberland Island is typical of the Georgia barrier islands as are the landforms and the vegetation that cover it. An excellent study of the vegetation on Cumberland Island was published by Hillestad and others (1975) under contract with the National Park Service. This report dealt mainly with the ecology of Cumberland Island, but included geologic considerations which were adapted from previous works. Vegetation and natural environments on Cumberland Island were briefly mentioned in a regional study by Wharton (1978); also a brief study of the landforms on Cumberland Island was published by Henry (1973) under contract with the National Park Service. Roberts (1975), in an investigation of the geologic evolution of the south end of Cumberland Island, correlated vegetation with present landforms. The detailed study by Hillestad and others (1975) can hardly be improved upon; therefore, this study is a review of the vegetation and a more accurate analysis of landforms. Plate 2 is a landform and natural vegetation map produced from aerial photography as well as ground survey. 6-2 Beach A beach is defined as a land area which lies within the normal tidal range. Beaches can be composed of a number of sediments ranging in size from clay size particles to whole oyster valves. The most prominent beaches on Cumberland Island are situated on the eastern side of the island. The fine-grained quartz sand beaches are as much as 300 ft (90 m) wide on the south end of Cumberland Island. The sands contain significant amounts of dark, heavy minerals which make them a darker color than the purer quartz sand beaches of the Gulf Coast. The longshore drift is north to south and therefore transports the byach sands in a southerly 6-1 direction. This is evident from the rapid growth of the south end of Cumberland Island after completion of the jetty. The jetty acts as a sediment trap and causes accretion north of it; the jetty has resulted in the addition of approximately .62 mi. 2 (1.61 2 km ) of land to Cumberland Island since 1881 (Roberts, 1975). This phenomenon was discussed by Roberts (1975) as well as by Nash (1977). There is little to no vegetation growing on the beaches on the eastern side of the island. There are two types of beaches on the western side of the island. Beaches which border the Pleistocene portion of the island are narrow sand beaches that commonly contain appreciable amounts of clay. The sand on these beaches is largely derived from the erosion of the island itself. The clay and organic material are derived from suspended material in the waters west of the island. The most common plants on these beaches are Salicornia ~ and Spartina ~ These plants commonly appear to have reestablished themselves after being eroded from the marsh. The second type of beach is composed of the imbricated valves of the common oyster Crassostrea virginica. These beaches are not extensive and occur only where significant oyster populations exist. The oyster shell beaches are most common in the vicinity of the salt marsh although they are found in isolated patches along the entire length of the western side of the island. Salicornia ~ and Spartina ~ are both common on the oyster shell beaches. Salicornia ~ seems to be especially compatible with this environment. All beaches on the western side of the island are narrow and are too small to plot on the landforms map (Plate 2). 6-3 Salt marshes The salt marshes on Cumberland Island are located on the western side of the island, adjoining the higher Pleistocene portion of the island. These marshes are separated from other salt marshes by the Intracoastal Waterway and Cumberland River, 6-2 although they are very similar in vegetation as well as topography. The marshes on Cumberland Island, as well as the other marshes, can be divided into high marshes and low marshes. Both of these divisions are represented as a single unit on Plate 2~ The low marshes, as the name implies, are topographi- cally lower and commonly have a clay and silt substrate. The most common plant is Spartina alterniflora. The high marshes are topographically higher and are composed of a coarser sandier substrate. On Cumberland Island the high marshes have a fine-to medium-grained, argillaceous sand substrate. This sand is derived j from the Pleistocene core of the island, the dunes of the Holocene portion, or from spoil banks placed. in .the salt marsh. The major plants that vegetate the marsh are listed below: Distichlis spicata, Salicornia virginica Iva frustescens Spartina alterniflora Juniperus virginiana Spartina patens Juncus ~ 6-4 Foredunes The foredunes on Cumberland Island are located directly behind the beaches and extend westward to the edge of the interdune meadow. These dunes vary in size from 1.5 ft (0.5 m) to 3 ft (1 m) high to well-developed dunes 6 or more feet (2 m) high. They are composed of fine-grained, crossbedded, quartz sand with dark, heavy minerals. Because the dunes are located just back of the beach, they are subject to erosion from storms; therefore, these dunes are variable in size and shape and subject to cyclical changes. As a general rule, foredunes are eroded during the winter months because of storms and rebuilt during the summer months. Plants on the foredunes are tolerant to an environment that includes salt spray, wind, drought, sand abrasion, burial, and occasional flooding by salt 6-3 water during storms. The major plants found in this environment are listed below: Croton punctatus Pasaalum vaginatum Hydrocotyle bonariensis Sabatia stellaris Lippia nodiflora Uniola paniculata Myrica cerifera Yucca gloriosa 6-5 Interdune meadow The interdune meadow is a flat to broadly basin-shaped area located between the foredunes and the back or rear dunes. This landform originates from zones of deflation which have subsequently become stabilized by vegetation. Because defla- tion areas and interdune meadows are related, they have been mapped as one unit on Plate 2. Active deflation areas commonly have a shell pavement developed to some extent on the surface, although it becomes less noticeable after vegetation begins to stabilize the area. Interdune meadows received sedimentation from wind- blown sand that originates from the foredunes and the beach as well as from occa- sional wash-over associated with storms. It should be noted tl1at sedimentation takes places in these areas only where there is a vegetative cover. The interdune meadow is protected from salt spray more than the beach or foredunes; therefore, a greater number of plants can survive in this environment. Hillestad and others (1975) divided the interdune meadows on Cumberland Island into several communities, each of which represents a different set of environmental conditions. The major plants found on this landform are listed below: Andropogon virginicus Hydrocotyle 'bonariensis Chenchrus echinatus Iva imbricata Dichromena colorata Myrica cerifera Eremochla ophiuroides Spartina patens Eupaterium capillifolium Yucca gloriosa 6-4 6-6 Back dunes (rear dunes) and other active dunes The back dunes on Cumberland Island form a very prominent sand ridge, which extends almost the length of the island and is as much as 45 ft. (14 m) in height. This landform is composed of crossbedded, fine-grained quartz sand with dark, heavy minerals. Where erosion has exposed the interior of these dunes, pronounced crossbedding can be seen where the dark, heavy minerals mark the cross laminations. The dunes are formed from the prevailing easterly winds and thus migrate in a westward direction. The vegetation over which the dune is migrating affects many aspects of the duneJincluding morphology and migration rate. The rate of dune migration is con- siderably higher where there is sparse or low vegetation. For example, the rates of migration in the Raccoon Keys Salt Marsh and the Beach Fields are higher than in areas where the dune must migrate over the oak-palmetto interior forest. The vegetation over which dunes migrate also influences the shape of the dune. As the dunes migrate over heavy vegetationJthe leeward side of the qune steepens and the dune gains height. The dunes have little vegetative cover to stabilize the sands. The major plants found in the back dune environment are listed below: Croton punctatus Oenothera humifus Uniola panticulata Myrica cerifera Yucca gloriosa 6-7 Stabilized and partially stabilized dunes This landform represents dunes that have been partially or completely stabilized by vegetation. Excellent examples of this landform are located in the Sweetwater Complex (Fig. 2-1) and near Whitney Lake. The stabilized dunes in the Sweetwater Complex have impeded the natural drainage systems, and shallow ponds and marshes have formed at their base. These dunes have a different plant cover from those stabilized without the marshes at their base; therefore, the plant cover I 6-5 is variable in this landform and specific taxa will not be named. In general, the vegetative cover varies from plants described in the back dune environment to that of the oak-palmetto forests. 6-8 Inland marshes The inland marshes on Cumberland Island can be divided into two major groups. The most common inland marsh on Cumberland Island is the freshwater marsh. These marshes form in depressions or where the natural drainge systems have been im- peded. Johnson Pond is an excellent example of an inland marsh that occupies a closed depression in the land surface. Whitney Lake and the Sweetwater Complex are examples of inland ponds and marshes that have formed where sand dunes have impounded natural drainges. None of these marshes are influenced by salt water or tidal action. These marshes contain a large number of plant taxa. The more common plants are listed below. This includes marsh, aquatic and semiaquatic plants. Axolla coaoliniana Panicum hemitomon Cephalanthus occidentalis Pontderia cordata Cladium jamaicense Pontedria laceolata Limnobium spongia Sabatia stellaris Magnolia virginiana Similax auriculata Nelumbo luten Spartina bakeri Nymphoides aquatica Typha latifolia Nyssa sylvatica Ultricularia ~ The second type of inlanJ marsh is a variant of the salt marsh described in 6-3 above and includes those inland marshes influenced by the saline waters of the Intracoastal Waterway and Cumberland River. Because these marshes are connected to the estuarine waters, the water level is influenced by tidal action. 6-6 The influx of salt water also influences the salinity of the marsh, but not uniformly. At high tide the salinity of the water where the estuary enters into the marsh is nearly the same as that in Cumberland Sound, but salinity appears to decrease away from the point of entry. At low tide, the waters running out of the marshes have a decreased salinity, but it is doubtful if the water ever becomes truly fresh water before the tide again floods the marshes. The salinity of water exiting the inland salt marshes at low tide is 6.5 parts per thousand, whereas the salinity of the surrounding unconfined water table is 0.5 parts per thousand as determined from adjacent monitor wells. The vegetation of the inland salt marshes is essentially the same as that of the high salt marsh (refer to Section 6-3). In thil study, the areas of decreasing salt water influence could not be mapped; therefore, the entire marsh was mapped as salt marsh on Plate 2. The substrate is black to dark gray organic clays and silts. 6-9 Interior forests The interior forest is the largest landform mapped. This division covers the flat to rolling sands of the Pleistocene portion of the island. Hillestad and others (1975) divided the forests into several communities, which are con- sidered one unit in this study. This division contain extensive flora. The plants listed below are the more common plants and by no means are a complete listing. Cercis canadensis Quercus laevis !lex vomitoria Quercus nigra Luniperus silicicola Quercus virginiana Lyonia ferruginea Sabal palmetto Nyssa sylvatica Sassafras albidem Pinus palustric Serenoa repens Pinus taeda Vaccinium arboreum 6-7 7-0 LAND USE ON CUMBERLAND ISLAND * 7-1 Introduction Present land use on Cumberland Island is shown on Plate 3. In the compliation of this map, it was discovered that land uses would commonly fit into more than one class. In such cases the category which was most useful in planning was chosen. 7-2 Marginal marine lands These lands include salt marshes and beaches. The marginal marine lands are used largely for recreational purposes; the salt marshes also serve as a nutrient source for marine life important to the local seafood industry. 7-3 Agricultural lands These lands are presently used or were used in the past as agricultural lands. There are no row crops presently being grown on Cumberland Island, although this activity was significant in the past. The present agricultural uses include pastures for livestock, hay production and pine plantations. Among the abandoned agricultural lands are those used for rice and row crops)as well as tree crops such as olives and tung nuts. 7-4 Residential lands These areas include all residential areas in private as well as governmental ownership. Some of the private dwellings have been removed by the National Park Service since completion of the map; therefore, there may be some inaccuracies. The areas owned by the National Park Service and intended for public use have been mapped as a separate unit. * The reader is referr ed to Plate 3. Reference to the plate shows the locations of various classes of lands. Also, the land use map was prepared prior to the extensive forest fires in the summer of 1981. 7-1 7-5 Recreational lands This class of land use overlaps many of the other classes. The recreational areas of Plate 3 are primarily used for recreation. These areas include the interior forests and the sand dune complex,as well as inland marshes and natural areas. Developed campsites are included in recreational areas although there is presently only one. 7-6 Miscellaneous lands Airstrips also are indicated on Plate 3. Only one of those (near Stafford) is still used. 7-2 8-0 HISTORICAL CHANGES IN THE MEAN HIGH WATER SHORELINE AND NEARSHORE BATHYMETRY OF CUMBERLAND ISLAND * 8-1 History of shoreline changes, 1843-1979, general description Cumberland Island is the largest of the Georgia coastal islands. It is nearly 19 miles (30 km) long and has an area of roughly 60 mi 2 (160 km2) of which nearly two thirds are above spring tide. Net erosion and accretion for the periods 1843 to 1974 are shown in Figure 8-1. The curves depicting cumulative changes and rates are illustrated in Figures 8-2 and 8-3 . Figures 8-4 shows the changes in the mean highwater (M.H.W.) shoreline for the northern part of the island for the period 1869 to 1965. Figure 8-5 shows the changes in the M.H.W. shoreline in the central part of the island from 1871 to 1962 and Figure 8-6 shows the changes in the M.H.W. shoreline in the southern part of the island for the period 1873 to 1971. Figure 8-7 shows the various positions of the M.H.W. shoreline during the period 1857 to 1979; Figure 8-8 summarizes net accretion and erosion along the shoreline over that 122-year period. Little Cumberland Island is separated from the main body of the island by marsh and a small, but active, tidal inlet, which for the purposes of this section will be considered collectively with the main island mass. Broad sandy beaches flank the ocean and inlet margins, merging into extensive but discontinuous dune systems of over 65ft (20m) relief that extend inland for approximately 0.6 mi (1 km). Except for the St. Marys Entrance jetties on the south end of the island, no manmade beach structures are present. 8-2 Northern segment The northwestern tip of Cumberland Island has averaged 5 ft (1.5 m)/yr. erosion over the past 100 years. In the vicinity of transect C3 (Figure 8-4) net * Sections 8-2 through 8-10 are rather technical and need not be read for an overall understanding of how shoreline changes may effect the management of Cumberland Island. 8-1 erosion for the 46-year period between 1871 and 1917 was followed by oscillations of accretion and erosion, resultirtg ih a slight net gain for the 103 year period between 1871 and 1974. For the same period, oscillations also were superimposed on the accretional trend of the northeastern tip where a maximum advance of 1260 ft (384 m) adjacent to transect CS (~ig. 8-4) resulted in a net gain of over 0.08 mi 2 (0.2 km 2). Reversals of the erosion and accretion rates illustrate the highly changeable nature of the section of shoreline from transect C6 south to Christmas Creek inlet. Negligible net change has occurred in the vicinity of transect C7, although north of this P?int erosion has been predominant. South of transect C7 the shoreline has prograded 1400 ft (430 m), largely as the result of the formation of a tidal delta by Christmas Creek. Since 1885 accretion has been predominant along the Little Cumberland Isla~d shoreline, although appreciable erosion (approximately 10 ft/yr (3 m/yr)) occurred in the area adjacent to transect C6. The section between transects C3 and C9 (Fig. 8-4) was significantly eroded by Hurricane Dora; however, cumulative curves shown in Figure 8-2 indicate only a slight net effect relative to long-term rates of shoreline change. 8-3 Central segment In the Long Point, area (Fig. 8~4 ) , accretion of approximately 0.4 m1 2 (1 km 2) has occurred since 1869, over 70 percent of which occurred prior to 1924. The section of beach extending approximately 2.5 mi (4 km) south and 1 mi (1.5 km) north of transect C11 (Fig. 8-1) averaged over 160 ft (50 m) of erosion prior to 1924. Since that time the trend has reversed to one of gradual accretion. Along this section of coast, relatively high and stable dunes are situated behind a wide plain of unstable and partially stable dunes. The unstable area approximately corresponds to the zone of beach recovery since 1924. The southern half of the island has a gently curving arcuate shoreline along the northern section of which southeastern progradation has occurred, re- 8-2 sulting in a gain of approximately 0.3 mi 2 (0.8 km2) since 1971. At transect C12 (Figures 8-1 and 8-4) accretion amounted to approximately 22 ft (6.6 m)/yr. The 1871 shoreline in this area closely corresponds to a line of relatively high and unstable dunes that are migrating over a forested area. Further south, at transect C13 (Fig. 8-1) the shore has been accreting since 1924. Approximately 330 ft (100 m) of shoreline that had been eroded prior to 1917 had recovered by 1958; this recovery continued until 1974; between 1974 and 1979, however, significant shoreline retreat has occurred. A comparison of 1962, 1964, and 1965 U.S. Geological Survey aerial photographs shows that the entire central segment of shoreline was eroded during Hurricane Dora in 1964 but had rapidly recovered by 1965. 8-4 Southern segment The shoreline of the southern segment of Cumberland Island has been signifi- cantly influenced by the emplacement of large jetties, extending 2.5 mi (4.1 km) and 1.5 mi (2.4 km) seaward from the southern end of Cumberland Island and the northern end of Amelia Island, respectively. Prior to the initiation of their construction irt 1881, the southeastern end of Cumberland was rapidly eroding. Early reports by the U.S. Army Corps of Engineers (1865 and 1879) described the St. Marys Entrance as having increased in width by 1590 ft (484 m) from 1843 to 1857 and an additional 213 ft (65 m) by 1879. Maximum rate of shoreline loss was 220,000 ft 2 (0.02 km2)/yr along the inlet throat (between transect C16 (Fig. 8-6) and Beach Creek) on Cumberland from 1943 to 1957; shoreline loss had decreased to 75,000 ft 2 (0.007 km 2)/yr from 1857 to 1876. Simultaneous shoaling and shifting of the main channel prompted the Corps of Engineers to initiate jetty construction at the entrance channel in 1881. Figure 8-3 shows the reversal of this erosional trend following the emplacement of the jetties. The southern~ost end of Cumberland Island stabilized and the southeastern segment of the island rapidly accreted. Shoreline advance was greatest at the inlet throat where there was a maximum gain of 1.1 mi (1.75 km) along transect Cl8 (Fig. 8-6) since 1876 at a rate of 60 ft (18 m)/yr. Accretion decreased to the north away from the influence of the jetties. During the period 1888 to 1902, the rate of accretion slowed, possibly reflecting the passage of the severe hurricane of 1898. The now extinct meander of Beach Creek (Fig. 8-6) was cut through to the ocean during this hurricane. This cut separated the island into two parts before a dike was constructed, re-establishing the shoreline. After the dike was constructed, the beach in that area rapidly accreted and the meander was abandoned by the main flow of Beach Creek. Narrow, discontinuous lines of partially stable dunes now approximate the positions of the 1898 and 1917 shorelines which are separated by larger stabilized dune areas. Nearly 0.8 mi 2 (2 km2) of land have been added to the southern end of Cumberland Island since the emplacement of the jetties. Between 1852 and 1974 the southern end of the island accreted, although net loss occurred in the vicinity of transect CIS (Fig. 8-1). Low-lying areas of the highly accretional southern end were typified by free sand or poorly vegetated low foredunes, which were easily inundated by the high water levels associated with Hurricane Dora. Maximum shoreline recession of approximately 650 ft (200 m) occurred at transect C15 (Fig. 8-3) during this minor hurricane. 8-5 Historical bathymetric changes in the ebb-tidal deltas and shoal areas 8-5-1 General statement : A comparison of hydrographic smooth sheets for St. Andrew and St. Marys inlets has provided evidence concerning the historical changes in the position, size, and configuration of the channels and associated shoals. These dynamic environments exert extensive control over the adjacent barrier shorelines. For example, navigational improvements at both St. Simons Sound and St. Marys Entrance exert a strong influence on bathymetric changes in those areas. 8-4 8-5-2 St. Andrew Sound: Transect locations and ebb-tidal delta configurations are shown in Figure 8-9. Bathymetric profiles at each transect are given in Figures 8-10 and 8-11. Volume changes were calculated for the period 1869-71 to 1924. No other complete bathymetric surveys of the St. Andrew ebb-tidal delta were made after 1924. St. Andrew Sound separates Jekyll Island from Cumberland Island and is over 2.5 mi (4 km) wide at its narrowest point. The sound is the largest on the Georgia coast and connects the ocean with the Satilla, Little Satilla, and Cumberland Rivers and Jointer and Jekyll Creeks. Maximum depths in the inlet throat area are approximately 90ft (27m). An extensive system of marginal and distal shoals borders the northern margin of the entrance channel, which continues 7.5 mi (12 km) seaward of the inlet in a gently-curving arc to a point 3.7 mi (6 km) off Long Point on Cumberland Island. For the 55-year period 1869 to 1924, losses in sediment volume below the 1969 M.H.W. shoreline are estimated to be 2.3 x 108 ft 3 (6.4 x 106m3) and shoreline accretion seaward of the 1969 M.H.W. shoreline was 1.1 x 109ft 3 (30.4 x 106m3). Rates of erosion were higher in the entrance channel,which deepened and lengthened seaward. Although no completed survey of the ebb-tidal delta has been done to date, a recent survey (1976) by the U.S. Coast and Geodetic Survey of the north marginal shoals area shows a general increase in the shoal volume along the periphery of the northern-marginal and distal shoals. This survey modified only portions of the original 1924 survey. The three major sound channels shown in transect 5 (Fig. 8-10) merge at the inlet throat. Cross-sections of the northern and middle channels have been reduced in area, largely by accretion along their margins from 1869 to 1935. At transect 6 (Fig. 8-10), major sound channels have merged to form two main channels of which the south channel is considerably larger and acts as the primary drainageway for the sound (Howard, 1971). The south channel has eroded the margins of the centrally located shoal area from 1869 to 1935 and has migrated up to 1300 ft (400 m) to the south 8-5 at a depth of 50ft (15m), resulting in an increase in its cross-sectional area. Although southerly migration of the main channel is not evident on transects 7 and 8 (Fig. 8-10), minor southward migration occurred along the entire length of the entrance channel seaward of the inlet from 1869 to 1924. A funnel-shaped channel, similar in area and running parallel to the main channel, forms the northern boundary of the northern-marginal shoals (Fig. 8-10). This channel, first discernible at the 23 ft (7 m) depth, becomes more conspicuous as it narrows and shoals landward. It eventually transects the marginal shoals off the south end of Jekyll Island and connects with the main channel at the inlet throat. Similar features are present at most Georgia inlets but are not as well developed as the St. Andrew Sound entrance. Transects 7 and 8 cross both the main channels and the funnel channel and show the general deepening and migration of the funnel channel to the south. Because no shoaling occurred on .the north side of the funnel channel, a general widening resulted from 1869 to 1924. During the same period, the funnel channel also deepened and extended landward. A comparison of the 1924 survey with modifications from the 1976 survey indicates that there has been little change in the position of the main channel or the funnel channel. However, there has been a shoaling of the funnel channel and an extension of the distal shoals to the south. The extension of the distal shoals effectively increases the length of the main channel by more than 0.6 mi (1 km) before crossing the shoal system. Marginal shoals along the northern boundary of the main channel have shallowed and migrated south following the trend of the channel. Contemporaneous erosion of their northern flanks, due to the southward migration of the funnel channel, resulted in a net loss in sediment volume primarily below the 6 ft (1.8 m) isobath. The northern shoals were an essentially stable area, although their east-west trend became highly segmented by an increase in the number and size of channels similar 8-6 to those described by Oertel (1975) as "spill-over channels". A comparison of the 1924 survey with the modified 1976 survey shows that two of these channels, which trend northeast, have deepened and cut through the northern marginal shoal system connecting the main channel with the funnel channel. South of the main channel, shoals inside the 18 ft (5.5 m) isobath have deepened nearly uniformly as shown on transect 9 (Fig. 8-11). 8-5-3 St. Marys Entrance: The St. Marys Entrance is bordered by Cumberland Island to the north and Amelia Island to the south. Two large jetties extend 2.5 mi (4.1) km and 1.5 mi (2.4 km) seaward from the southern end of Cumberland Island and the northern end of Amelia Island, respectively. Tida'l flow is confined within the jetties where a depth of about 33 ft (10 m) is maintained by dredging. Maximum depths at the inlet throat are approximately 70ft (21m). The inlet carries tidal flow between Cumberland Sound and the Amelia River, which drain marsh areas behind Cumberland and Amelia IslandsJ and the ocean. The inlet also receives tidal and freshwater flow from the St. Marys River, whose principal drainage originates in the Okeefenokee Swamp. The inlet configurations at St. Marys Entrance before construction of the jetties in 1876 and the present configuration are shown in Figure 8-12. Construction of the jetties at St. Marys Entrance was initiated in 1881 with the laying of the foundation for the north jetty (U.S. Army Corps of Engineers, 1902). At that time, five groins were constructed along the shoreline adjacent to Fort Clinch to retard shoreline erosion. The initial proposal called for twin jetties, the outer end of each jetty to be constructed at a height of half tide and the shore ends to M.L.W. By 1883 it was evident that the jetties needed to be raised to a higher level in response to current-scouring near the shore of Cumberland Island. This scour resulted from the persistence of a flood-oriented funnel channel near the base of Cumberland Island (Fig. 8-12). Erosion persisted also in the vicinity 8-7 of Fort Clinch and two additional groins were constructed. Approximately 330 ft (100 rn) of accretion had occurred at the base of the south jetty by 1886. As work proceeded on the jetties, a southward migration of the northern-marginal shoals, upon which the northern jetty was being constructed, caused shoaling of the project channel to such an extent as to require the opening of a gap in the south jetty (i.e. Amelia Island jetty) along the line of the old main channel to accornodate navigation. To prevent further encroachment of the shoals, the north jetty was extended and raised (U.S. Army Corps of Engineers, 1891). As this work progressed, a new channel began to form inside and adjacent to the north jetty which extended into the shoals. By 1899, flow through the gap in the south jetty was reduced and dredging operations began the removal of shoal material obstructing the jetty entrance seaward of the gap. Lengthening of the north jetty and dredging of the channel shoals permitted closing of the south jetty gap. With the jetties completed, the tidal current flow and the development of a more efficient ebb flow caused the scouring of the channel and the further removal of shoal material (U.S. Corps of Engineers, 1902). As previously mentioned, the major hurricane of October 1898 cut through the beach on the south end of Cumberland Island, connecting the ocean with Beach Creek (Fig. 8-6). This breach in the shoreline rapidly widened and deepened, probably in response to flood tidal and littoral flow now restricted by the north jetty. To close the breach, a pile and stone dike 1.3 rni (2.1 krn) long was constructed in 1904 from the shore end of the jetty and tied to the northwest high ground. Work on the jetties was completed at this time, although between 1905 and 1913 considerable jetty maintenance work was carried out. In 1927 the north jetty was raised to 12 in (35 ern) above the M.H.W. and the south jetty was raised to 2 in (6 ern) below M.H.W. The channel has been subject to periodic maintenance dredging with disposal areas offshore, in tidal creeks and in deep areas of the inlet throat since 1903. The channel was realigned to a 8-8 position within the natural channel near the south jetty in 1956 survey. The U.S. Army Corps of Engineers (1961) estimated an annual rate of shoaling of 4.0 x 106ft 3 4 3 (11.4 x 10m). Records of the entrance channel dredging (U.S. Army Corps of Engineers, 1961) show that between 1903 and 1956 a total of 9.2 x 10 7ft 3 (2.6 x 106m3) has been dredged from the St. Marys Entrance. Dredged channels of the Atlantic Intracoastal Waterway, to the north and south of Cumberland Sound, extend to the deep gorge of the main channel. The ebb delta configuration prior to the construction of the jetties is shown in Figure 8-12. The main channel extended 1.7 mi (2.8 km) seaward of the inlet to a point of bifurcation in 23 ft (7 m) of water. Large, arcuate, marginal shoals bordered the channel on the north; and distal shoals extended around the delta front to the south. The northern channel crossed the distal shoals almost 1.2 mi (2 km) north of the south channel (Fig. 8-12). Although the southern channel was longer and deeper, the northern channel followed a more direct course which continued west from the main channel and crossed the distal shoals with a minimum depth of 10 ft (3 m). At the point of bifurcation, the south channel hooked to the southeast and continued along the inner margin of the shoals before attenuating into distal shoals with a minimum depth of 10ft (3m). Both channels were approximately symmetrical in cross-section as was the main channel seaward of the inlet. Surveys of 1843, 1856, and 1876 show the rapid migration of both channels to the south. From 1843 to 1876 the south channel lengthened and began to parallel the trend of the Amelia Island shoreline. The lengthening was forced by a southern migration of the distal shoal system and resulted in a decrease in flow efficiency for the south channel. A simultaneous migration of the north channel during this period was coupled with an increase in flow capacity as it cut into the distal shoals and extended seaward. Between 1856 and 1876 the ebb-tidal delta volume increased 1 .8 x 108ft 3 (5.1 x 106m3) , pr1.mar1. ly due to enlargement of the d1' stal shoal system and shoaling in the south channel. During this same period a new 8-9 north channel was formed further to the north, which may have been subsequent to the abandonment of the old south channel; or, the new north channel also may have formed after the two older channels had migrated to the south and shoaled to such an extent as to require a more direct route to the sea for efficient ebb flow. The new north channel probably would have then begun to migrate to the south and continued the cyclic pattern of channel migration and abandonment. 8-6 Discussion - net shoreline changes Considering the total ocean shorelines of the barrier islands from St. Simons Island to Little Talbot Island, there has been minor net accretion amounting to approximately 1.5 mi 2 (4 km2) since the mid-nineteenth century. The estimated volumetric increase along the shoreline was based on the empirical relationship that a gain of one square foot (930 cm2) of area along the shoreline is equivalent to a volumetric gain of one cubic yard ( 0.8 m3) of sediment (U.S. Army Corps of m Engineers, 1966). By this relationship approximately 1.1 x 9 10 f t 3 . (32 x .106 3) of ' sediment has been added to the ocean shoreline between the mid-nineteenth century and 1974. Although limited bathymetric evidence does not allow a direct comparison of volume change per time period, the shoreline gains approximate the net volume loss between the 18 ft (5.5 m) depth contour and the mid-nineteenth century M.H.W. shoreline. These data indicate that sediment input roughly equaled sediment loss within the nearshore zone. Accretion above the M.H.W. shoreline has been dominant along the lower Georgia coast; however, when comparing linear distances along the coast, erosional shore- lines approximately equal depositional shorelines (Fig. 8-13). This disparity results from the intensified accretion in a relatively small area adjacent to the St. Marys Entrance jetties, where over 80 percent of the total accretion above the M.H.W. shoreline has occurred. If the erosional and accretional trends in the vicinity of St. Marys Entrance had not been altered by jetty construction, a net 8-10 erosion of roughly .035 mi 2 (0.09 km2) would have resulted. This estimate of net erosion is likely to be high because rate-of-change curves indicate a slowing of rates of erosion on the south end of Cumberland Island prior to the emplacement of the jetties. Shoreline segments experiencing greatest net change and greatest rates of change are the northern and southern thirds of the island and along inlet margins. Maximum rates of accretion occurred on the south end of Cumberland Island south of transect C13 (Fig. 8-1) where almost 640,000 ft 3 (18,000 m3) of sediment per year were deposited for the period 1876 to 1974. However, a recent increase in the rate of erosion has occurred in the south-central portion of Cumberland Island in an area historically characterized by relatively minor shoreline oscillations. Comparing Fig. 8-1 with Figures 8-7 and 8-8 at the approximate location on transect C13, almost 700 ft (200 m) of retreat has occurred between 1974 and 1979. This figure may be somewhat misleading as the 1979 measurement was based on aerial photos taken the day after Hurricane David (September 4, 1979). Significant net erosion also has occurred along small isolated sections of Little Cumberland Island. 8-7 Relations of shoreline change to coastal processes While it is possible to evaluate coastal stability within the study area based on a qualitative knowledge of the sediment transport characteristics and longterm coastal changes, a more accurate evaluation of coastal stability would require quantitative knowledge of the supply of energy and sediment budget. However, sufficient field data to evaluate these factors does not exist. Quantification of the sediment budget would be highly speculatory in nature, and although mathematical formulas have been derived for sediment transport model studies, problems with scale restrict the field use of such formulas to the relatively simple situations. Sediment sources and sinks must be considered in terms of the potential transporting agents such as wind, waves, tidal and non-tidal currents, and the inter- 8-11 relationship of these agents which necessitates their consideration as a system. When the supply and loss of material are equal and constant, the shoreline will eventually attain stability. However, the two principal sources of energy, tides and wave action, are continually changing, which causes the shoreline to be in a state of dynamic equilibrium. That is, even given a constant supply and loss of material, the shoreline will never appear stable within a short time reference of months or years. The shallow shoreface will be continually approaching equilibrium with respect to wave and tidal energy. Sea-level rise short-term trends can also be erratic. For this reason, erosional and accretional trends only can be assessed over periods of decades or perhaps even centuries. 8-8 Natural causes of erosion and accretion - sea level rise A theoretical model for sea-level rise as a cause of shoreline erosion was introduced by Bruun (1962) and favorably evaluated by Schwartz (1967, 1968) from model and field studies. This theory demonstrates how dynamic equilibrium is maintained during sea level rise along relatively straight shorelines where the sediment budget is in longshore quantitative equilibrium. The effective maintenance of equilibrium varies with sediment, wave, current and slope characteristics. Gentle slopes give rise to a phase-difference between "action", or sea-level rise, and "reaction", or shoreline erosion and offshore deposition (Bruun, 1962). However, dominance of tidal inlets on sedimentary processes, a gently sloping nearshore zone, and paucity of severe storms and hurricanes over the past few decades may have obscured this process in the study area. The influence of the nodal tidal cycle, combined with sea-level rise, may have caused significant variations in the vertical positions of M.H.W. and M.L.W. shorelines that could have resulted in erroneous estimates of sediment volume in transport, particularly when suxvey dates fall at different points of the 18.6 year lunar cycle. Of particular significance is the increase in the elevation of the M.L.W. shoreline caused by a rise in sea level, because offshore delta and shoal volumes were based on the position of M.L.W. As an example, the area encompassed by the volume change survey at St. Andrew Sound was over 40 mi 2 (100 km2). Within this area a sea-level rise of approximately 4.3 in (11 em) (Hicks, 1973) from 1929 to 1971 would effectively reduce delta shoal volume by roughly 4.0 x 108ft 3 (11 x 106m3). Although a sea-level rise of this magnitude falls easily within the limits of error when comparing old hydrographic surveys, the effect would be a positive change in volume estimates, possibly as much as 100 percent. Adjusting for known sea-level rise and assuming a constant tidal range for the period 1924 to 1954, volume loss estimates would decrease by 14 percent for St. Marys Entrance. The original volume change estimates, however, may still be considered a net loss in sediment volume because a rise in sea level essentially reduces these shoal areas by submerging them. 8-9 Hydraulic and sedimentary processes at inlets The most readily observable changes during the period covered by this study were southerly channel migrations in the outer portions of the ebb-tidal deltas, where littoral currents become relatively stronger with respect to tidal currents. Because the Coriolis Force can be considered negligible (Bruun and Gerritsen, 1960), wave energy must be the primary force in accomplishing such migrations in the outer ebb-tidal delta. Wave energy also counteracts the seaward movement of sediments by ebb-tidal flow. The dominant influence of relatively high energy waves from the northeast on delta configuration increases away from the axis of the main channel. This effect is augmented and reflected from north to south by: 1) increased rates of channel migration, 2) the decrease in tidal prisms and correspending decrease in the dominance of tidal currents over littoral currents seaward of the inlet throat, and 3) the lesser refraction of waves approaching from the northeast resulting from the alignment of the shoreline, nearshore bathymetry and the bottom gradient. 8-13 Channel migration is a cyclic process in the outer reaches of the ebb-tidal deltas. Both the rate of channel migration and the length of the channel affected are a function of wave and tidal energy, although the process is somewhat modified by the initial direction of the ebb-tidal jet. One complete cycle is on the order of decades for St. Marys Entrance and 100 to 150 years for St. Andrews Sound. It is evident that a southward migration of the outer main ebb-tidal channel eventually results in a reduction of channel flow efficiency. This is seen at St. Marys Entrance where southward channel migration results from the southward development of distal shoals along the outer margin of the channel. The southward growth and development of distal shoals indicates the on-going process of by-passing. At some point in time, this southward shoal development restricts ebb flow efficiency to such an extent that a new channel is formed to re-establish a more direct and efficient ebb-tidal exit. The new channel is located to the north of the old channel and its formation is probably initiated during periods of higher tides. Initially, the channel is relatively small and shares the volume of water jetted seaward during ebb tide. Howeve~, the high efficiency of the new channel eventually results in an increase of its flow capacity while simultaneous shoaling occurs in the old channel. As sediment by~passing is established by wave action, the development of distal shoals begins to force the southward migration of the new channel. Wave refraction plays a significant role in the accumulation of sand at ebbtidal deltas. Waves approaching approximately normal to the shoreline are refracted by the delta shoal system and the resulting littoral drift is directed toward the shoreline on both sides of the inlet. Because there is a dominant direction of wave energy from the northeast, offsets develop on the downdrift or southern sides of the inlets (O'Brien, 1969). This process results from the development of an energy shadow south of the ebb-tidal delta in which material carried by the shoreward component of littoral transport is deposited. Such offsets are clearly evident at St. Marys Entrance and St. Andrew Sound. Erosional and depositional trends at the northernmost parts of the island are indicative of the relationship between sedimentary transport characteristics in these areas and the hydraulics of associated inlet systems. At the north end of Cumberland, net littoral transport to the north results from the sheltering effects of the ebb-tidal deltas which restrict the approach of waves from the north- east. Lower energy southeast waves produce northward littoral movement in concert with flood tidal flow. A centrally located shoal system such as Stafford Shoal off Cumberland Island (Fig. 8-14) may also be related to the influence of tidal hydraulics. Similar features are present along most Georgia barrier islands. The central location of these shoals between inlets suggests a possible formation in response to an energy minimum with respect to tidal flow. During flood tide, tidal currents converge on the inlets from both sides, resulting in an area of relatively slack water near the center of an island. Although tidal flow near the sea flood-tide convergence is probably incapable of inducing significant bedload sediment movement, such currents may be capable of imparting movement to sediment suspended by shoaling waves. Transect C12 (Fig. 8-5) is at the southern extreme of Stafford Shoal on Cumber- land Island, where a net sediment transport to the south has resulted in the develop- S 3 6 3 ment of a prograding foreland and the accretion of 2.3 x 10 ft (6.6 x 10m) of sediment inside the present trend of the M.H.W. shoreline between 1871 and 1974. However, the outer portion of Stafford Shoal is strongly skewed to the north indi- eating that, while alongshore littoral processes clearly impart a net southward drift, the more constant tidal influence may be more important offshore. Upon approaching the south ends of the islands, the dominant southward littoral drift becomes intensified during flood tidal flow. As on the north ends of the island, however, accretion is limited by the proximity of the inlet throat to the associated channels and sediment supply. The positions of flood-dominated funnel channels have considerable control over sedimentary transport characteristics at 8-15 the south ends of the islands. During the period from 1843 to 1976, prior to the construction of the jetties at St. Marys Entrance, an apparently flood-dominated funnel channel crossed the northern marginal shoals near the south end of Cumberland Island (Fig. 8-12). This channel migrated to the northwest and caused the erosion on the south end of the island for that period. Construction of the north jetty eventually terminated tidal flow through this channel. However, the erosion on the south end of Cumberland Island during that period may not have continued if the flood channel was subject to cyclic migrations. The transfer of sand past inlets and the accumulation of sand at inlet-associated shoals and deltas are of extreme importance to an understanding of the sediment budget and related shoreline movement in the study area. Although by-passing actively occurs at these inlets, increases in delta and shoal volumes suggest that these areas still function as vast sediment sinks for material in littoral transport and have not yet attained a balance between the sedimentary and hydraulic characteristics of the inlet and ambient wave forces. This may result primarily from changes in sea level. Brunn and Gerritsen (1960) and Brunn (1962) quantitatively analyzed the important relationship of littoral drift and tidal flow to inlet stability. However, sufficient field data do not yet exist in the study area to determine by-passing stability, locational stability, or cross-sectional stability in the study area. The ratio of "tidal prism" to "mean annual net amount of littoral drift" provides a relative measure of inlet stability (Brunn and Gerritsen, 1960). Accordingly, there is a decrease in stability to the south in the study area. Inlet stability also varies with changes in the tidal prism, minimum cross-sectional area of the inlet and sediment supply. These changes may be brought about by: the filling of estuarine storage areas; the trapping of river sediment; the landward transport of suspended and fine sediment; sea level changes; lateral and vertical marsh expansion; sediment compaction, subsidence or uplift; and man-made alterations such as 8-16 the construction of dams in mainland rivers, the dredging of sounds and intracoastal waterways, shoreline construction, the dredging of entrance channels, or the construction of jetties. Although the relative importance of each of these is difficult to assess, man-made alterations of both St. Marys Entrance and St. Simons Sound are clearly the controlling factors in these areas. At St. Marys Entrance, erosion of the inlet margins and shoaling of the inlet occurred prior to the construction of the jetties. The natural process primarily involved a change in inlet morphology and hydraulics rather than changes in cross-sectional areas of the inlet throat or the tidal prism and may have resulted from: 1) a rapidly increased rate of littoral drift due to the severe hurricanes of the late 1800's and subsequent shoaling of the inlet, 2) the deepening and lengthening of existing channels, or 3) the formation of additional channels. All of the above possibilities would account for the redistribution of tidal flow rather than a change in the tidal prism. 8-10 Severe storms and hurricanes Severe storms and hurricanes may cause significant modification of the coastal zone and inner shelf within relatively short periods of time. These high energy events may also be of greater significance in the geologic record than the predominant lower energy conditions. Equilibrium adjustments in nearshore and inlet areas may be largely accomplished by high energy events. The intensity, duration, and frequency of severe storms significantly determines the rate of shoreline response to a rise in sea level, growth and development of dunes, shoaling, migration of inlet channels, and the response of nearshore areas to man-made alterations of the sediment budget. Beaches are subject to cyclic changes related primarily to transient meteoro- logic conditions. Johnson (1949) found that deepwater wave steepness CHb/lu) was an important factor determining whether a nearshore profile was aggradational or erosional. Numerous field and model studies (Shepard, 1950; Saville, 1957; Iwagaki 8-17 and Noda, 1963; Johnson and Eagleson, 1966; Hayes, 1971; Sonu and Van Beek, 1971; Dean, 1973, and others) have shown the relationship of wave steepness to the development of either a summer/normal or winter/storm profile. Recent coverage of this subject by Dean (1973, 1976) demonstrated the importance of additional factors in onshore-offshore transport, including the fall velocity of sand particles, the breaking wave height, and wind drift currents. Generally, the formation of a winter or storm beach following mild summer conditions involves the removal of sand from the upper beach, which often results in the formation of a scarp at the foot of the dune line. The seaward movement of this eroded material causes a reduction in the slope of the shoreface profile. In conjunction with the offshore transport of sand, a seaward shift in the breaker zone results in the formation of an offshore bar. A return to gentle summer wave conditions generally causes a reversal of these processes. Onshore transport of the material stored in the bar is commonly accomplished by the landward migration of ridge and runnel systems which eventually weld onto the beach face and reestablish the summer profile (Johnson, 1949; Saville, 1957; Dean, 1976). Generally, low wave energy levels in the study area indicate that shoreface profiles should undergo equilibrium adjustments within a relatively shallow nearshore zone. A rise in sea level may cause a sediment deficit to exist seaward of that portion of the profile in which equilibrium is maintained with respect to relatively low energy waves. Tidal flow in conjunction with oscillatory wave motion may also move sediment at depths greater than those to which the shoreface profile can rapidly adjust. Under these conditions, offshore transport during a severe storm or hurricane would supply material to the undernourished portion of the profile and reestablish equilibrium to depth only modified by rare high-energy conditions. Ebb-tidal deltas would significantly modify the effects of a severe storm. Although such modifications would greatly depend on the stage of the tidal cycle 8-18 with respect to the duration and peak intensity of the storm, the delta would probably buffer adjacent shorelines. A portion of the incident wave energy would be dissipated on the shoal systems. Also, the shoal system would supply sediment to undernourished nearshore areas because of an increased rate of littoral drift, possibly intensified by increased flood tidal flow. These factors would further reduce incident wave energy and associated offshore transport. Shoreline accretion in the study area is reflected in development of parallel beach/dune ridge complexes, a process that begins with an excess of sand in the nearshore zone. In many cases, this excess may result from the lateral movement of large volumes of sand during severe storms. As the shoreface profile attains equilibrium, the sediment excess is deposited in the form of low sand ridges. Once established above M.H.W., beach ridges may be altered by eolian processes or perhaps partially or completely eroded by storm surge. The ultimate heightening or deflation of a beach/dune ridge will depend principally on climatic conditions, the development of stabilizing vegetation and the supply of material to the shoreline. High ridges may result from the destruction of the lower ridges and foredune complexes by a severe storm. Major high dune lines on several of the islands correspond to late 19th century shoreline positions and probably reflect significant devegetation by the several hurricanes of that period, particularly the storm of 1898 (Figs. 8-5, and 8-6). 8-11 Man's influence in the coastal zone Barrier island shorelines and inlets in the study area are considered to be in a state of dynamic equilibrium with the nearshore sand prism. Because there exists a delicate balance of opposing forces which control this equilibrium, any manmade alteration of the coastal zone will commonly be reflected in a modification of sediment transport characteristics. Jetty construction, d.redging operations, the destruction of dunes and attempts to stabilize the shoreline by the construction of seawalls and groins have all affected shoreline stability within the study area. 8-19 The construction of jetties at St. Marys Entrance was proposeu to eliminate the problems of shoaling and shifting navigation channels. Side effects to jetty construction are: 1) a drastic alteration of the ebb-tidal deltal system, 2) initially intensified accretion immediately adjacent to the jetties, 3) the probable elimination of by-passing, and 4) the development of a vast sediment sink seaward of the jetties. The apparent intensification of erosional trends along the shoreline of Amelia Island may also be influenced by the construction of the jetties. Although tidal flow is essentially confined within the jetties, a portion of both the ebb and flood flow passes over and through the jetties. This process, evident from a cursory examination of aerial and LANDSAT satellite photographs, is particularly important. Much of the sediment in littoral transport that is transported over and through the jetties is subsequently carried seaward with ebb-tidal flow. Although sediment that has passed through the jetties may have contributed to substantial accretion on the south end of Cumberland Island at transect Cl8 and Cl9 (Fig. 8-6) and on the north end of Amelia Island, most of the sediment has been deposited seaward of the jetties and lost to the littoral system. The extensive shoal area, developed seaward of the jetties and which exhibits only minor southward movement, is far from approaching the dimensions necessary to re-establish sediment transport under normal wave conditions. 8-12 Destruction of dunes Despite a longstanding recognition of the importance of coastal dunes by both scientific and public sectors, much of the dune system on St. Simons, Jekyll and Amelia Islands has been destroyed. The resulting accelerated erosion has prompted the construction of groins and seawalls on St. Simons, Jekyll and Amelia Islands. Such structures are only temporarily effective and not only reduce the recreational value of the shoreline, but often increase the long-term problem of shoreline recession. By destroying the flexibility of the beach, these structures must withstand the full force of storm waves, and this commonly results in an increase in the erosion of sediment from in front of them. This eventually results in their collapse, as has been the case along the south end of St. Simons Island and central areas of Jekyll Island. Furthermore, along sections of shoreline protected by seawalls, there is ,less material available for the development of a storm profile. Adjacent, unstabilized sections of shoreline undergo accelerated erosion to fill this deficit. As is usually the case, the construction of a groin or section of seawall precipitates the construction of another such structure downdrift. Much of the dune system on Cumberland Island has been altered by the early introduction of large grazing animals, primarily hogs and horses. Overgrazing has resulted in the formation of large migrating dunes and deflation areas. An 1870 topographic survey shows extensive dunes already established along the northern half of Cumberland Island. A 1956 survey, however, depicts eroding forests bordering the south central shoreline, a condition similar to that seen on the northern end of Jekyll Island today. A comparison of 1977 and 1956 topographic surveys shows a general widening of the dune system along most of the island. These high migrating dunes not only destroy additional inland vegetation but also function as a vast sediment sink. The dune system along the central and south central sections of the islands increased in size and height to where 50 to 65 ft (15 to 20 m) high dunes migrate over meadows, ponds, and forests, (see Fig. 8-15). Expanses of active and inactive deflation areas front the seaward side of the migrating dunes. Apparently, overgrazing of low areas on Cumberland Island increased their susceptibility to wind deflation and storm attack, which eventually flattened any ridges which may have formed. Areas once similar in appearance to deflation zones on Cumberland Island correlate with large scale erosional losses on north central Jekyll and Amelia Islands for the period 1856 to 1871 and on southern Amelia 8-21 Island for the period 1871 to 1924. Overgrazing may have contributed significantly to the initiation of such losses; the erosion, in turn, probably was enhanced by severe storms or hurricanes. The National Park Service has constructed enclosures in some deflation areas on Cumberland Island. These fenced-off areas prevented grazing by free ranging animals and, within a one-year period, there were significant increases in vegetation within the enclosures. 8-13 Summary and conclusions During the 131-year period between 1843 and 1974, the shoreline and near- shore zone from St. Simons Island, Georgia, to Little Talbot Island, Florida, have experienced significant changes in position and volume, respectively (Fig. 8-13). In terms of net change, accretion has been slightly dominant during the period of study with progradation occurring along approximately 60 percent of the shoreline. Within the past two decades, however, over 50 percent of the shorelines in the study area have undergone net erosion. Shoreline areas experiencing greatest net change and greatest rates of change are the northern and southern thirds of the islands and along the sound margins. Induced by the construction of the St. Marys Entrance jetties, maximum rates of accretion occurred on the south end of Cumberland Island where approximately 640,000 ft 3 (18,000 m3) of sediment per year were deposited during the period 1876 to 1974. Also, the highest rate of shoreline advance, 60 ft (18 m) per year, occurred within this area. The highest long-term rate of shoreline retreat, 43 ft (13 m) per year, was located on the north end of Amelia Island during the period 1871 to 1924. Cumberland Island also experienced shoreline losses though probably never this high. Although the above rates are maxima for the study area, changes of this magnitude are not unexpected in the immediate vicinity of inlets. Shoreline changes are intimately associated with migrating ebb-tidal delta channels and shoals and alterations of the hydrologic regime related to maintenance of navigational channels. The shoreline sections adjacent to tidal inlets, therefore, are the most undesirable locations for development. Ironically, most of the current sites of problem erosion are located in the historically stable central areas of the islands. Although recent erosional trends on Jekyll and Amelia Islands contradict earlier periods of stability, it should be noted that these areas have been heavily influenced by man in the past several decades. Both islands are located south of navigation projects (i.e. St. Simons Sound and St. Marys Entrance). Net rates of erosion and accretion along central island areas rarely amount to more than + 3 ft (1 m) per year when calculated over a 100-year period. Nevertheless, an unusually high number of seasonal northeasterly storms or the passage of a hurricane~ however, may cause 60 to 100 ft (20 to 30 m) of erosion in less than one year's time or in a single event. For example, based on aerial photos taken the day after the passage of Hurricane David, the position of the high water shoreline along the southern bight of Cumberland Island (between C12 and C14 in Figure 8-1) was between 500 and 700 ft (150-200 m) inland from the 1974 shoreline as shown on Fig. 8-7. Because the position of the high water shoreline immediately preceding the hurricane was not known, the actual extent of retreat could not be determined. Nevertheless, relative to historical rates of movement, including the effect of Hurricane Dora (See Figures 8-2 and 8-3), it is concluded that 1nost of this erosion can be attributed to Hurricane David. In areas free of shore protection structures, severe storm erosion is usually followed by beach accretion and low foredune development caused by the more prevalent day-to-day conditions of waves and tides, which tend to deposit material along the coast. Referring to Figures 8-1, 8-3, 8-7, and 8-8, the shoreline segments at C10 and between C12 and C14 will continue to show the greatest change. The changes in the vicinity of ClO are directly related to the inlet dynamics associated with Christmas Creek and probably will not result in any significant net changes. However, net I shoreline trends of a more critical extent in all likelihood will continue in the bight between C12 and Cl4. Furthermore, the island behind this segment is narrow and relatively low, while water depths seaward of the segments are deeper than elsewhere along the island front. These conditions make this portion of the island extremely vulnerable for washover and/or breakthrough by major hurricanes; of particular concern in this regard is the narrowest part of the island in the Beach Creek area, the site of an earlier breakthrough by the 1898 hurricane (Fig. 8-6). Although the highwater shoreline along the central portion of the island shows little net change since 1871, the backshore areas are subject to severe flooding due to the lowered topography following dune migration away from the beach front. Despite the critical conditions described above, no engineering structures or other protective devices are recommended at this t~me. Grazing of dune areas should cease and all vehicular and foot traffic should be closely managed, with dune crossover structures provided at all designated beach access points. Should continued erosion threaten to break through the Beach Creek area, consideration shpuld be given to the effect such breaching would have on the maintenance and operation of the jetty and navigation channel. Finally, over 23 miles (37 km) of navigation channel, with a controlling depth in excess of 42ft (13m) and a bottom width of 400-600 ft (120-180 m), is proposed for the King Bay Submarine Support Base. This project will significantly increase the disequilibrium in sediment source and sink already caused by the St. Marys Entrance Project and the Atlantic Intracoastal Waterway. To what extent this project will adversely effect the ocean and estuarine shoreline of Cumberland Island can only be speculated; however, it is possible that at least the estuarine shoreline adjacent to St. Marys Sound would undergo increased erosion. 8-24 ST. ANDREvi SOUND scale kil omett:rs 1 .s 0 northern segment . . . ..E_ .X_ .P_ _L. _A. . _N. _A. _T_I.O. _ .N_ . _. . . . . .n o r t h e r n net erosion net accret i on ll~M:.f~;~g$~ffj.y] limit of 1843 1973 or 1974 U1.H.W.) shoreline 1843 or 1871 (M.H.W.) shoreline transect locations on Cumberland Island C4-. central segment 1974 southern segment ST. MARYS ENTRAN Figure 8-1 . Net shoreline changes on Cumberland Island, Georgia, 1843 to 1974. YEARS 1840 1860 1880 1900 1920 1940 1960 1980 400 300 200 100 0 -100 -200 -300 -400 (/') 0:: L.LJ t- L.LJ :E 500 400 300 200 100 0 -100 -200 CUMBERLAND ISLAND (northern segment) --- .,.,r.. .. ,-.--- _,C10 ,.---------...........' CUMBERLAND ISLAND ..,' / (central segment ) i 1 ,,I , ,..,. ,................C12 ... ,, ..,...........1, .... ... ... .~ ........ ........ / ..............,................ - ------ .... -~ ~~ -'"-" - 6 0 o' ~~ .... -:., .... ~.... -... ~ "" ~ OCALA GROUP- CRYSTAL RIVER w w z () 0 w TO 64 5' Figure B-1. Geology encountered in well Cl-01 (GGS 3426). WELL CONSTRUCTION DIAGRAM FOR Cl-01 (GGS 3426) 0 1001 2001 TOP FILL GROUT SEAL 4" CASING 3001 4001 GROUT SEAL 5001 6001 -+--- OPEN HOLE 7 0 0 ' - r- -- -- -- - - . - - - - - - - - - , 0 ld' 2 0 11 Figure B-2. Diagram of well construction for Cl-01 (GGS 3426) . . I APPENDIX C LITHOLOGIC LOGS DEPTH BELOW SURFACE (ft.) 0 - 4.0 4.0 - 7.25 7.25- 13 13 - 14.2 14.2 - 16 16 - 22.5 22.5 - 29 29 - 67 67 - 73 73 - 85 85 - 90 90 - 94 94 - 95.5 95;5 - 100 LITHOLOGIC LOG CI-01 DESCRIPTION Sand: Medium to fine; subangular to rounded; slightly argillaceous; with dark heavy minerals. Sand: Fine; subangular; with dark heavy minerals. Sand: Fine-to medium; subangular; with dark heavy minerals. Sand: Fine; subangular; slightly argillaceous; prominent organic staining at top of bed becoming lighter downward. Sand: Fine to very fine; subangular; argillaceous; with dark heavy minerals; phosphatic. Sand: Fine to medium; subangular to rounded; with dark heavy minerals. Sand: Fine; subangular to rounded; argillaceous; micaceous; with dark heavy minerals. Clay: Silty; with finely-bedded sand; micaceous; fossiliferous (bivalves, as original shell material). Sand: Fine; rounded; with dark heavy minerals; fossiliferous (bivalve fragments as original shell material); with clay interbeds. Sand: Fine to medium; subangular to rounded; with dark, heavy minerals; fossiliferous (bivalves as original shell material). Sand: Medium to coarse; rounded to subangular; calcareous; phosphatic; becoming indurated at bottom of bed with calcite cement. Dolostone: Argillaceous; very sandy (fine to very coarse; subangular to well rounded); scattered quartz granules; fossiliferous (bivalves, as molds and casts). Dolostone: Argillaceous; very sandy (fine to coarse; subangular to subrounded); phosphatic; with clasts of clay (silty, micaceous); lighter clay forms rims around a darker core. Dolostone: Argillaceous; very sandy (very fine to coarse; angular to subrounded); sparsley phosphatic; with scattered, rounded quartz granules. C-1 Lithologic Log CI-01 (Cont'd): DEPTH BELOW SURFACE (ft.) 100 - lOS 105 - 110 110 - 111 111 - 120 120 - 130 *130 - 130.5 130.5 - 133.5 133.5 - 144.5 144.5 - 152 152 - 156 156 - 159 159 - 160 160 - 172 172 - 185 DESCRIPTION Dolostone: Argillaceous; very sandy (very fine to coarse; angular to subrounded), sparsely micaceous; phosphatic; with scattered rounded quartz granules. Dolostone: Argillaceous; sandy (fine to coarse; subangular to rounded); with clay interbeds (silty, sandy; sparsely micaceous; of maximum thickness of 2.5 em). Sand: Fine to very coarse; subangular to rounded; phosphatic; fossiliferous (bivalves as original shell fragments); with rounded quartz granules. Sandstone: Fine to very coarse; rounded to subangular; rounded quartz to pebble size; phosphatic; fossiliferous (as molds and casts); dolomite cement. No recovery-lithology appears to be a medium watersaturated sand. (drilling log). Clay: Silty; fossiliferous (original shell material, molds and casts) . Sand: Very fine to very coarse; subangular to rounded with ~ounded quartz granules; silty; micaceous; fossiliferous (original shell material). Dolostone: Sandy; argillaceous; phosphatic; fossiliferous (molds and casts); sand fraction is fine to very coarse; rounded to subangular. Sand: Fine to very coarse; subangular to rounded; argillaceous, phosphatic, calcareous. Dolostone: Sandy; argillaceous; finely phosphatic; sand fraction is very fine to coarse, angular to rounded. Sand: Very fine to very coarse; subangular to rounded; micaceous; phosphatic; with scattered well-rounded quartz granules. Dolostone: Sandy; argillaceous; phosphatic; sand fraction fine to very coarse, angular to subrounded. Sand: Fine to very coarse; subangular to rounded; argillaceous; micaceous; slightly phosphatic; calcareous; with scattered rounded quartz pebbles. Dolostone: Very argillaceous; coarsely phosphatic; sand fraction fine to coarse, subangular to rounded. C-2 Lithologic Log CI-01 (Cont'd): DEPTH BELOW SURFACE (ft). 185 - 210.5 210.5 - 220 220 - 240 240 - 243.5 243.5 - 249.5 249.5 - 252 252 - 260 260 - 269 269 - 275 275 - 282 282 - 288 288 - 291 291 - 364 364 - 374 DESCRIPTION Sand: Fi ne to coarse; subangular t o rounded; arg'l l aceous ; phosphatic; with scattered rounded quartz granules; becomes f ossiliferous at 20 0-203 ft . ; fossil s are or iginal shell mat erial . Dolostone: Sandy; argillaceous, phosphatic; sand fraction is fine to very coarse, subangular to rounded. Sand~ Fine to coarse; angular to rounded; argillaceous; phosphatic; with scattered rounded quartz granules. Sand: Fine to medium; angular to subrounded; phosphatic; with scattered rounded quartz granules. Sand: Fine to very coarse; angular to rounded, argillac~ous; sparsely phosphatic; calcareous; some zones indurated. Limestone: Dolomitic; very sandy, phosphatic; sand fra~tion is fine to medium, rounded to subangular. Sand: Coarse to very coarse; subangular to subrounded; coarsely phosphatic; calcareous; locally indurated; fossiliferous (molds and casts in indurated beds). Sand: Fine to coarse; angular to subrounded; argillaceous; phosphatic. Clay: Faintly laminated; with fine to medium sand partings; phosphatic. Sand: Fine to coarse; subangular to rounded; argillaceous; phosphatic. Sand: Fine to coarse; subangular to rounded; argillaceous; calcareous; micaceous; locally indurated. Dolostone: Sandy; argillaceous; micaceous; sand fraction is medium to fine, subrounded grains. Silt: Laminated to thinly bedded; finely carbonaceous; with sand parting (very fine to coarse sand), fossilferous (original shell material, molds and casts). Sand: Very fine to very coarse; angular to subrounded; argillaceous; very phosphatic; calcareous, glauconitic; sparsely fossiliferous (original shell material). C-3 Lithologic Log CI-01 (Cont'd): DEPTH BELOW SURFACE (ft.) 374 - 376 376 - 390 390 - 400 400 - 410 410 - 410.5 411 - 413 413 - 413.5 413.5 - 419 419 - 449 449 - 456 456 - 457 457 - 482 482 - 485 483 - 493 DESCRIPTION Sandstone; Fine to medium; subangular, argillaceous; micaceous; phosphatic; with scattered rounded quartz granules; calcareous; indurated. Sand: Fine to medium; subrounded; argillaceous; phosphatic; fossiliferous (original shell material and molds and casts); phosphate at top becoming less concentrated downward. Dolostone: Very sand; phosphatic; fossiliferous (original shell material and molds and casts); sand fraction is fine to medium, with occasional rounded quartz granules. Sand: Fine to medium; subangular to subrounded; argillaceous; phosphatic; micaceous. Limestone: Very sandy, finely phosphatic; sand fraction is fine, micaceous. Clay: Silty; sandy; finely lmainated; finely micaceous; sand fraction is very fine. Limestone: Very sandy; argillaceous; finely phosphatic; sand fraction is fine to medium, angular to subrounded. Sand: Very fine to medium; subrounded; argillaceous; phosphatic, calcareous; micaceous. Clay: Silty; sandy; very finely carbonaceous; micaceous; sand fraction is very fine, subrounded. Sand: Fine to coarse; angular to subrounded; argillaceous. Limestone: Sandy; argillaceous; sand fraction is medium to fine, subangular to rounded. Clay: Very sandy, calcareous; sparsely phosphatic; s~nd fraction is very fine to medium, subangular. Silty: Sandy; calcareous; phosphatic; fossiliferous (molds and casts); sand fraction medium to very coarse; subangular. Limestone: Dolomitic, sandy; argillaceous; phosphatic; fossiliferous (molds and casts); sand fraction is fine to very coarse, subangular to rounded. C-4 Lithologic Log CI-01 (Cont'd): DEPTH BELOW SURFACE (ft.) 493 - 510 510 - 531 531 - 532 532 - 580 580 - 600 600 - 645 645 DESCRIPTION No recovery Clay: Sandy; sparsely phosphatic; fossiliferous (shark teeth); sand fraction is very fine-grained. Limestone: Sandy; phosphatic; fossiliferous (original shell material, molds and casts); sand fraction is fine - to medium-grained. Limestone: Sandy at top; fossiliferous (original shell material; bryzoans abundant). No recovery-very loose calcite sand taken from wash sample. Limestone: White; abundantly fossiliferous (original shell material, molds and casts). Total Depth All sand is quartz unless otherwise specified. Formational Tops 0 - 29' 29' 67' 90' 288' 537' 645' Satilla Formation Pleistocene undifferentiated Duplin Marl equivalent Charlton Hawthorn Formation Ocala Group-Crystal River Formation Total Depth *NOTE: The clay logged in the interval 130' - 130.5' contains Pleistocene bivalves. Those bivalves are considered to be cave material from above. Latitude: 30o45'22" Longitude: 81o28'13" Elevation 17 feet above mean sea level. C-5 DEPTH BELOW SURFACE (ft.) 0 - 1.0 1.2 - 3.3 3.3 - 10 10 - 13 13 - 13.8 14 - 20.5 20.5 - 22.5 22.5 - 29.0 29.0 - 40 40 - 67 67 - 73 73 - 75 75 - 80 BORING 1 DESCRIPTION Sand: Pale, yellpwish-brown; fine-grained; very well sorted; subangular to well rounded; heavy minerals 2-3%; feldspar 3-5%. Sand: Light brown; fine-grained; very well sorted; subangular to well rounded; stained quartz grains 90%; heavy minerals 2-3%. Sand: Mottled, very pale-orange and pale yellowishbrown; fine-grained; very well sorted; subrounded grains; heavy minerals 2-3%; feldspar 5-10%. Sand: Very pale-orange; fine-grained; well sorted; subrounded to well rounded grains; slightly phosphatic; feldspar 5%. Sand: Humitic, moderate brown; fine-grained; well sorted; subrounded grains; feldspar 5%. Sand: Very pale-orange; fine-to very fine-grained; scattered very coarse sand 5%; epidote 2-3%; feldspar 10%; other heavy minerals 3%; opaque minerals 2-3%. Sand: Grayish-orange; fine-to medium-grained; scattered very coarse sand 5%; heavy minerals 2-3%; feldspar 5%. Sand: Grayish-orange; medium-grained; well sorted; subrounded grains; very toarse sand S-8%; feldspar 5-7%; heavy minerals 3%. Clayey sand: Greenish-gray; white mica flakes 2%; large shell fragments (Crassostrea virginica). Recovery 3 ft. Clayey sand: Greenish-gray; abundant oyster shell fragments; scattered quartz pebbles in sand. Recovery 1.4 ft. Sand: Light greenish-gray; coarse-grained; very coarse sand 2%; heavy minerals 3%; oriented shell fragments; bored oyster fragments; subangular to rounded quartz grains. Recovery 0.9 ft. Sand: Very light-gray; coarse-grained; well sorted; subangular to well rounded; very coarse sand 2-3%; heavy minerals 2-3%; shell fragments 10%. Recovery 0.8 f Sand: Very light-gray; coarse-grained; oyster shell fragments; scattered pebbles. Recovery 2.4 ft. C-6 Boring 1 (Cont'd) DEPTH BELOW SURFACE (ft. J 80 - 90 90 - 96 0 - 67 67 90 Below 90 DESCRIPTION Sand: Conglomeratic; quartz pebbles 75%; limestone pebbles 25%. The quartz grains size increases to the bottom. Recovery 2.4 ft. Limestone: Yellowish-gray; very coarse quartz grains in fine calcareous mud; phosphate grains 3-5%; chert 1%. Recovery 3.6 ft. INTERPRETATION Pleistocene Middle Pliocene Middle Miocene C-7 DEPTH BELOW SURFACE (ft.) 0 - 0.9 0.9 - 3.0 3.0 - 8.0 8.0 - 10 10 - 12 12 - 15 15 - 18 18 - 20 20 - 21.5 21.5 - 27 27 - 30 30 - so so - 51 51 - 52 BORING 2 DESCRIPTION Sand: Dark yellow-brown; medium to fine-grained; subrounded grains; quartz as aggregates; fine, long roots. Sand: Moderate yellowish-brown; fine-grained; well sorted; heavy minerals 2%; white mica flakes 2%; small roots; subrounded grains. Sand: Grayish-orange; fine-grained; well sorted; subangular to subrounded grains; oxidized stems; epidote 5%; hornblende 3%; pink grains (feldspar?). Sand: Pale yellowish-brown; fine to medium-grained; well sorted; subrounded grains; quartz grains as aggregates. Sand: Grayish-orange; fine-grained; well sorted; subangular to subrounded grains; epidote 2-3%; oxidized plant stems; quartz grains as aggregates; stained quartz grains (less than 5%). Sand: Pale greenish-yellow; very fine-grained; subangular to subrounded grains; fine sand mixed with silty material and very coarse sand; sample partially "washed" during sampling; oxidized stem fragments. Recovery 2.2 ft. Sand: Yellowish-gray; very fine-grained; very well sorted; opaque minerals 2%; sample "washed" during sampling. Recovery 1.9 ft. No recovery. Sand: Yellowish-gray; very fine-grained; well sorted; 5 mm white sand layers forming cross bedding. No recovery. Clayey sand: Yellowish-gray; white mica flakes 1-2%; lignitic stem fragments; stained quartz grains 5-10%; 2-3 mm clay layers; limonitic patches in sand. No recovery. Sand: Dusky-yellow; with clay patches (bioturbation?); abundant oxidized stem fragments. No recovery. C-8 Boring 2 (Cont'd) DEPTH BELOW SURFACE (ft.) 52 - 53 53 - 60 60 - 72 72 - 0 - 50 50 - 72 Below 72 DESCRIPTION Sand: Light olive; fine-to medium-grained; heavy minerals 3%; white mica flakes 2%; Mulinia lateralis, Venericardia sp. (Sample 1). Sand: Greenish-gray; medium-grained; very coarse sand 10%, quartz pebbles 5%; dark gray limestone fragments, 1-2 em diameter; abundant shell fragment$. Sand: Greenish-gray; medium to coarse-grained; subangular to subrounded grains; scattered limestone fragments 2-5%; Mulinia lateralis (Sample 2). Recovery 0.9 ft. Limestone (no recovery). INTERPRETATION Pleistocene Middle Pliocene Middle Miocene C-9 DEPTH BELOW SURFACE (ft. J 0- 2.7 2.7 - 3.4 3.4 - 7 7 - 10 10 - 13 13 - 17 17 - 24 24 - 27 27 - 28 28 - 30 30 - 31 31 - 35 35 - 46 46- 47.5 BORING 3 DESCRIPTION Sand: Pale red; fine- to medium-grained; subangular to subrounded quartz grains; thin sterns of Spartina alterniflora; stained quartz grains. Sand: Dark yellowish-brown; medium-grained; subrounded grains; quartz grains as aggregates. Sand: Moderate yellowish-brown; medium-grained; subangular grains; stem fragments; stained quartz grains 10-20%. Sand: Dark yellowish-brown; fine-to medium-grained; subrounded to rounded quartz grains; coarse grains 2-3%; stem fragments. The quartz grain size increases to the bottom of this interval. No recovery. Sand: Moderate yellowish-brown; fine-grained; moderately sorted; subrounded quartz grains; coarse sand 2-3%. Sand: Grayish-orange; very fine-grained; thin brown layers forming cross-bedding; Ophiomorpha nodosa at 21ft (Sample 20); stained quartz grains. Sand: Yellowish-gray; very fine-grained; subangular to rounded quartz grains; quartz grains partially covered with limonite; thin clay layers forming cross bedding; plant remains. No recovery. Sand: Yellowish-gray; fine-grained; subrounded quartz grains; lignitic plant remains; interbedded thin sand-clay layers. No recovery. Clayey sand: Gray; white mica flakes; oyster fragments; lignitic stern fragments; Ophiomorpha nodosa burrow at 32 ft. Silty clay: Dark greenish-gray; small patches of fine white sand; bioturbation; Rangia cunneiata; Nassarius obsoletus (Sample 4). Recovery 2.8 ft. Silty clay: Dark greenish-gray; patches of fine sand; Mercenaria sp., Mulinia lateralis. C-10 Boring 3 (Cont'd) DEPTH BELOW SURFACE (ft. ) 47.5- 53 53 - 57 57 - 61 63 - 73 73 - 80 80 - 81 81 - 91 91 - 92 0 - 51 51 - 91 Below 91 DESCRIPTION Sand: Olive gray; fine-grained; subangular to subrounded quartz grains; coquina limestone fragments; slightly mottled, with minor amounts of clay (probably due to contamination); carbonaceous wood remains. Recovery 1.2 ft. Sand: Yellowish-gray; fine-grained; 0.5 ft clay layers; epidote 1-2%; opaque minerals 2- 3%; abundant foraminifera; Elphidium gunteri, Ammonia beccarii, Polymorphina guttulina Nonionella sp., Hanzawaia concentrica, Elphidium advena Globigerinoides rubra, Elphidium sp. Recovery 0. 7 ft. Sand: Mottled, light gray and pale green; mediumgrained mixture of clay and sand at the top of this interval, probably due to contamination; Elphidium gunteri, Ammonia beccarii, Elphidium sp., Globorotalia menardii. Recovery 1.0 ft. Sand: Mottled, medimn gray and dusky yellow; mediumgrained; subrounded quartz grains; very coarse sand 2-3%; white mica flakes 3%; Mulinia lateralis Acteocina canaliculata (Sample 6). Recovery 1.3 ft. Sand: Olive gray; medium to coarse-grained; shell fragments 5-10%; limestone fragments 5%; Elphidium sp . , Hanzawaia concentrica, Quinqueloculina sp., Elphid'um gunteri, Ammonia beccarii. Recovery 2.5 ft . Sand: Olive gray; very coarse-grained; poorly sorted; limestone fragments 30%; shell fragments 15%; wood remains; Nassarius obsoletus (Sample 7). Recovery 0. 7 ft. Sand: Light olive gray; coarse to very coarse-grained limestone fragments 5-10%; shell fragments 10%; Mulina lateralis, Acteocina canaliculata (Sample 8). Recovery 1.3 ft. Limestone: Light olive gray; clay-supported framework; fine quartz grains in fine matrix. INTERPRETATION Pleistocene Middle Pliocene Middle Miocene C-ll BORING 4 DEPTH BELOW SURFACE (ft.) 0 - 0.56 0.66 - 2.2 2.2 - 2.7 2.7 - 5.5 5.5 - 10 10 - 32 10 - 17 17 - 22 22 - 32 32 - 41 41 - 42 42 - 50 50 - 62 * (Cut) - Cuttings sample. DESCRIPTION Sand: Medium light gray; fine-grained; well sorted; subangular to rounded grains; large roots. Sand: Very light gray; fine-grained; well sorted. Sand: Brownish-gray; very fine-grained; subrounded to subangular grains; abundant roots and stems. Sand: Yellowish-gray; fine-grained; subangular to rounded grains; oxidized stems; quartz grains as aggregates. Sand: Brownish-gray; fine-grained; stained quartz grains 90%; silty quartz grains 10%; large stems of Spartina alterniflora; phosphate grains 2-3%. No core sample. * (Cut) Sand: Very pale orange; fine-grained; subangular quartz grains; very coarse sand 1-3%; opaque minerals 1-2%; feldspar 2%; epidote less than 1%. *(Cut) Sand: Yellowish-gray; fine to very finegrained subrouned quartz grains.; epid.ote 1-2%; white mica flakes 2%; prismatic grains (sillimanite?) 1%; feldspar 3-5%; shell fragments. *(Cut) Sand: Yellowish-gray; fine to very finegrained; subrounded to rounded quartz grains; white mica flakes 2%; feldspar 3-4%; prismatic grains 2%. Sanp: Dusky yellow; fine-grained; heavy minerals 2-3%. The heavy minerals increase to the bottom; thin clay layers forming cross-bedding. Recovery 1.8 ft. Clay: Greenish-gray; shell fragments; Mercenaria sp., Crassostrea sp. (Sample 10). Recovery 0.2 ft. Clay: Medium bluish-gray; thin sand layers interbedded the clay (1-2 mm thick); small shell fragments. Recovery 3.0 ft. Clayey sand: Mottled olive gray and dark greenishgray; fine-grained; sand 75%; mud 25%; oriented shell fragments; Elph.dium gunteri~ Globigerinoides sacculifer, Elphdum sp ., Globigerinoides obliquus, Cibicides sapeloensis; Elphidiwn poeyanum, Polymorphina sp., Globigerinoides rubra, Hanzawa l a concentrica. Recovery 0.5 ft. C-12 Boring 4 (Cont'd) DEPTH BELOW SURFACE (ft.) 62 - 72 72 - 92 72 - 77 77 - 82 82 - 87 87 - 76 92 - 93 93 - 95 0 - 50 50 - 93 Below 93 * (Cut) - Cutting Samples DESCRIPTION Clay: Bluish-gray; high content of Rhaphaneis an~laris (diatom). Some diatoms are replaced by pyrite; thin sand layers in the clay (2-3 mm thick); thin sand layers forming cross-bedding. Recovery 2 ft. No core sample. * (Cut) Sand: Yellowish-gray; fine-grained; sub- rounded quartz grains; heavy minerals 2-4%; feldspar 8%; scattered shell fragment 2%. * (Cut) Sand: Yellowish gray; fine-to medium-grained; subrounded quartz grains; epidote 2-3%; white mica flakes 1-2%; feldspar 8%; other heavy minerals 3%; shell fragments 10%. * (Cut) Sand: Yellowish gray; fine- to very coarse- grained; subrounded to rounded quartz grains; feldspar 5%; hornblende 1%; white mica flakes 1%; opaque grains 2%; epidote 1%; shell fragments 25%. * (Cut) Sand: White; fine- to very coarse-grained; subrounded to well rounded quartz grains; fine sand 70%; granules 20%; pebbles 5%; opaque minerals 2-3%; feldspar 5-10%; limestone fragments,' Smm diameter; shell fragments and whole shells of Mulinia lateralis. Sand: Light olive gray; fine grained; very coarse sand 2-3%; limestone fragments, 3-4 em diameter; shell fragments. Limestone: Fragments, 7-9 mm diameter; fine quartz grains in fine calcareous mud. INTERPRETATION Pleistocene Middle Pliocene Middle Miocene C-13 DEPTH BELOW SURFACE (ft.) 0 - 0.9 0.9 - 2.0 2.0 - 3.3 3.3- 7.0 7.0 - 10.0 10.0- 11.5 11.5 - 12.0 12 - 16 12 - 16 16 - 20 20 - 35 20 - 22 22 - 27 27 - 32 BORING 5 DESCRIPTION Sand: Dark yellowish-brown; fine-grained; subrounded quartz grains; epidote 1-2%; heavy minerals 2-3%; oxidized roots and stems. Sand: Light brownish-gray; fine-grained; well sorted; sillimanite (?) 1-2%; opaque minerals 3!1:. 0, stem frag- ments 2!10: . Sand: Pale yellowish-brown; fine-to very fine-grained; sdubangular quartz grains; stained quartz grains 80%. The stained quartz grains decrease to the bottom. Sand: Brown; fine-grained; well sorted; subangular to rounded quartz grains; slightly phosphatic; oxidized roots and stems. Sand: Moderate yellowish-brown; fine-grained; subrounded quartz grains; white mica flakes 1%; stained quartz grains 90%; .epidote less than 1%; other heavy minerals 2-3%. Sand: Grayish-orange; fine-grained; subrounded to rounded quartz grains; phosphate grains 5%; epidote 1-2%. Sand: Moderate yellowish-brown; fine-grained; rounded grains; stained quartz grains 15%. No core sample. * (Cut) Sand: Grayish-orange; very fine-grained; subangular to subrounded quartz grains; phosphate grains 2%; feldspar 5-10%; epidote 1-2%; other heavy minerals 3%. No recovery. No core sample. * (Cut) Sand: Grayish-orange; fine-grained; subangular to subrounded quartz grains; feldspar 5-10%; epidote 1-2%; opaque minerals 2%; Mulinia lateralis (Sample 11). * (Cut) Sand: Grayish-orange; fine-grained; sub- angular to subrounded quartz grains; feldspar 5%; opaque minerals 3%. * (Cut) Sand: Very pale orange; fine-grained; very well sorted; subangular to rounded quartz grains; epidote 2%; heavy minerals 2%; white mica flakes 1%. C-14 Boring 5 (Cont'd) DEPTH BELOW SURFACE ft.) 32 - 35 35 - 42 42 - 52 42 - 52 52 - 55 55- 57.5 57.5- 62 62 - 72 72 - 82 0 - 62 62 - 72 Below 72 * (Cut) - Cutting Sample DESCRIPTION * (Cut) Sand: Yellowish-gray; fine-grained; sub- angular to subrounded quartz grains; very coarse sand 3%; phosphate grains 1%; feldspar 5-10%; heavy minerals 2%. Silty clay: Pale green; heavy minerals 2%; white mica flakes 2%; shell fragments forming layers. The shell fragments increase to the bottom; Oliva sayana (Sample 16), Elphidium sp. Recovery 0.7 ft. No core sample. * (Cut) Sand: Yellowish-gray; fine-grained; sub- angular quartz grains; heavy minerals 3%; white mica flakes 2%; feldspar 3-5%; shell fragments 10%. Silty clay: Olive gray; 2 in sand layer interbedded the c,lay; sand- filled burrows. Sand: Light olive gray; fine-grained; subangular to rounded quartz grains. Silty clay: Olive gray; shell fragments, 1-2 em diameter; oxidized stem debris. The plant remains lie parallel to the stratification; pieces of indurated clay with scattered quartz grains. Sand: Pale greenish-yellow; fine-grained; subangular to rounded quartz grains; epidote 2%; white mica flakes 1%; feldspar 5-8%; shell fragments 1%. The coarse sand increases to the bottom. Recovery 0.9 ft. Limestone: Yellowish gray; clastic quartz grains in fine matrix, 0.5 to 3mm diamter; scattered chert grains. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION C-15 DEPTH BELOW SURFACE (ft.) 0 - 1.3 1.3 - 2.8 2.9- 6.7 6.7 - 8.3 8.3 - 8.6 8.6 - 9.8 9.8 - 12.8 12.8 - 42 12.8 - 17 17 - 18.7 18.7- 42 42 - 44.5 44.5 - 46 46 - 52 BORING 6 DESCRIPTION Sand: Light brownish-gray; fine-grained; well sorted; heavy minerals 3-4%; Spart]na alterniflora stems. Sand: Moderate yellowish-brown; fine-grained; subrounded to rounded quartz grains; stained quartz grains 90%. Sand: Very pale orange to grayish-orange; finegrained; well sorted; subrounded quartz grains; stained quartz grains; epidote 2%; other heavy minerals 2-3%. Sand: Moderate brown; fine-grained; rounded quartz grains; hyaline grains 5%; stained quartz grains 95%. Sand: Moderate yellowish-brown; subrounded quartz grains; heavy minerals 3%. Sand: Dark grayish-orange; fine-grained; well sorted; subrounded to rounded quartz grains; heavy minerals 3%. Sand: Dark grayish-orange; fine-grained; subrounded to rounded quartz grains; epidote 2%; other heavy minerals 3%. No core sample. * (Cut) Sand: Grayish-orange; fine-grained; subangu1ar quartz grains; heavy minerals 5%. * (Cut) Sand: Grayish-orange; fine-grained; subrounded to well rounded quartz grains; coarse sand 3%; stained quartz grains 5%; feldspar 5-10%; heavy minerals 2%. * (Cut) Sand: Yellowish-gray; fine-grained; subangular to subrounded quartz grains; feldspar 5%; heavy minerals 1-3%; white mica flakes 3%. Clay: Dark greenish-gray; plant remains lain parallel to the stratification; 8 mm thick sand lenses. Clayey sand: Dusky yellow green; shell fragment layers; whole shells of Mulinia lateralis, Abra aequalis (Sample 12), Elphidium sp. Silty clay: Olive gray; thin sand layers, 1-2 mm thick; mixture of clay and sand, probably due to bioturbation. Recovery 3 ft. for 42-52 ft. interval. C-16 Boring 6 (Cont'd) DEPTH BELOW SURFACE (ft.) 52 - 62 62 - 79 62 - 76 76 - 82 0 - 61.5 61.5 - 79 Below 79 * (Cut) - Cutting sample. DESCRIPTION Silty clay: Olive gray; thin sand layers, 1-2 mm thick; fine dissemination of pyrite in the clay; small plant remains parallel to the stratification; sandfilled burrows, 1.5-2.0 em wide; 5 in sand layers interbedded the mud in the lower part of this interval; Elphidium sp. No core sample. * (Cut) Sand: Yellowish- gray; fine-grained; subangular to rounded quartz grains; very coarse sand 2-3%; epidote 2%; opaque minerals 2-3%; sillimanite (?) 1-2%; white mica flakes 2%; feldspar 5%. Limestone: Yellowish-gray; quartz granules; 5-6 em thick sand layer interbedded in calcareous clay; very coarse grained; finely disseminated pyrite. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION C-17 DEPTH BELOW SURFACE (ft.) 0 - 10 10 - 12 12 - 52 12 - 22 22 - 32 32 - 52 52 - 53 53 - 62 62 - 73.3 73.3 - 75.5 75.5 - 79 BORING 7 DESCRIPTION Sand: Grayish-yellow; fine-grained; very well sorted; subrounded quartz grains; stained quartz grains 70%; heavy minerals 3-4%. Recovery 2 ft. Sand: Grayish-orange; fine-grained; well sorted; subrounded to rounded quartz grains; heavy minerals 5%. No core sample. * (Cut) Sand: pale grayish-yellow; fine-grained; sub- rounded to subangular quartz grains; heavy minerals 4-5%. * (Cut) Sand: Very pale orange; fine-grained; sub- angular to subrounded quartz grains; very coarse sand 10%; heavy minerals 3-5%; white mica flakes 2%; feldspar 6%. * (Cut) Sand: Yellowish-gray; fine-grained; subangular to rounded quartz grains; feldspar 3-6%; sillimanite 2%; white mica flakes 2%; other heavy minerals 3%. Sand: Light olive gray; medium- to coarse-grained; shell fragments 5-10%; rounded limestone fragments; Elphidium sp. Clay: Olive gray; 1-2 mm sand layers interbedded the clay; sand-filled burrows, 2 em wide, 3-4 em long; carbonaceous plant remains; Elphidium sp., Cocconeis superba (diatom). Recovery 3 t. Silty clay: Olive gray; thin sand layers interbedded the clay; scattered wood remains; finely disseminated pyrite in the sand beds. Cocconeis superba (diatom). Recovery 3 ft. Sand: Yellowish-gray; fine-grained; well sorted; subrounded quartz grains; opaque minerals 2-3%; epidote less than 1%; Ammonia beccarii; quartz pebbles. Limestone: Light olive gray; fine quartz grains 5%; chert 3%. C-18 Boring 7 (Cont'd) 0 - 75.5 0 Below 75.5 Pleistocene Middle Pliocene Middle Miocene INTERPRETATION C-19 DEPTH BELOW SURFACE (ft.) 0 - 3. 3 3.3 - 5.4 5.4 - 8.2 8.2 - 8.6 8.6 - 9.8 9.8 - 12 12 - 47 12 - 32 32 - 37 37 - 42 42 - 47 47 - 52 52 - 54.3 54.3 - 60 BORING 8 DESCRIPTION Sand: Yellowish-brown; fine-grained; well sorted; subrounded quartz grains; plant remains; stained quartz grains. Sand: Grayish-orange; fine-grained; subrounded quartz grains; heavy minerals 5%. Sand: White; fine-grained; well sorted; subrounded to rounded quartz grains; heavy minerals 3-5%. Sand: Pale yellowish-brown; fine-grained; very well sorted; subrounded to rounded quartz grains; heavy minerals 2-3%. Sand: Moderate brown to dark greenish-orange; finegrained; well sorted; subrounded grains; slightly phosphatic. No recovery. No core sample. * (Cut) Sand: Yellowish-gray; fine-grained; subangular to subrounded quartz grains; feldspar 5-8%; epidote 2-3%; white mica flakes 3%. * (Cut) Sand: Yellowish-gray; fine to very fine-grained; very well sorted; subrounded grains. * (Cut) Sand: Yellowish-gray; fine to very finegrained; subangular grains; epidote 1-2%; other heavy minerals 3-5%; mud 5-10%; shell fragments 5%. * (Cut) Sand: Yellowish-gray; fine to very finegrained; very well sorted; subangular grains; heavy minerals 5%. Clay: Medium bluish-gray; horizontal thin sand layers interbedded the mud. Recovery 0.4 ft. Sand: Light olive gray; very fine-grained; well sorted; subangular quartz grains; Cibicides sp., Ammonia beccarii, Elphidium sp. Clay: Medium bluish-gray; oyster shell fragments. Recovery 0.2 ft. C-20 Boring 8 (Cont'd) DEPTH BELOW SURFACE (ft.) 60 - 62 62 - 72 72 0 - 52 52 - 72 Below 72 DESCRIPTION Clayey sand: Light olive green, abundant shell fragments; white mica flakes 3-4%; plant remains. Sand: Light gray; very fine-grained; well sorted; sand and clay mixed; sand 85%, mud 15%; epidote 2%; phosphate grains 1%. Limestone: Gray dark; fine quartz grains; white mica flakes; coquina facies in the lower part of this interval; mollusk molds. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION C-21 DEPTH BELOW SURFACE (ft.) 0 - 3.0 3.0 - 6.4 6.4 - 10 10 - 11 11 - 12 12 - 22 12 - 17 17 - 22 22 - 32 32 - 62 32 - 37 37 - 42 42 - 52 52 - 62 BORING 9 DESCRIPTION Sand: Dark yellowish-brown; fine-grained; very well sorted; subrounded quartz grains; heavy minerals 3-5%; stained grains 85%. Sand: Pale yellowish-orange; fine-grained; well sorted; subrounded quartz grains; heavy minerals 3-5%. Sand: White; fine-to medium-grained; well sorted; subrounded quartz grains; epidote 1-2%; opaque minerals 3-5%. Sand: Brownish-gray; fine-grained; well sorted; subrounded to rounded grains. Sand: Grayish-orange; fine -grained; well sorted; subrounded grains. Recovery 0.5 ft. No core sample. * (Cut) Sand: Moderate yellowish-brown; fine-grained; subangular to rounded quartz grains; heavy minerals 3-5%; plant remains 2%; feldspar 5-7%. * (Cut) Sand: Grayish-yellow; fine-grained; subangular to rounded grains; heavy minerals 4%; plant remains 3%. Humitic sand: Dark brown; very fine-grained lignitic plant debris; heavy minerals 2%; white sand lenses. Recovery 0.3 No core sample. * .CCut) Sand: Very pale orange; fine-grained; subrounded grains; feldspar 5%; epidote 1-2%; plant remains 2%. No recovery. * (Cut) Sand: Yellowish-gray; fine-grained; coarse sand 5-10%; heavy minerals 3-5%; white mica flakes 2-3%; shell fragments 5%; clay 20%. k (Cut) Sand : Yellowish-gray; fine-grained; subangular to we~l rounded quartz grains; heavy minerals 3-5%; fel dspar 5-10%; shell fragments 33-40%; c lay 10%; clay interbedded with sand (%?). C-22 Boring 9 (Cont'd) DEPTH BELOW SURFACE (ft) 62 - 71 71 0 - 52 52 - 71 Below 71 DESCRI:PTION Shelly sand: Yellowish-gray; fine-grained; very well sorted; heavy minerals 4%; shell fragments 50-60%. Recovery 53 ft. Lime's tone: Dark gray; fine and rounded quartz grains in calcareous clay; partially dolomitized. Pleistocene I I Middle Pliocene Middle Miocene INTERPRETATION * (Cut) - Cuttings sample. C-23 DEPTH BELOW SURFACE (ft.) 0 - 3.5 3.5 - 4.8 4.8 - 7.5 7.5 - 8.0 8.0 - 10.0 10.0 - 11.8 11.8 - 22 22 - 32 22 - 32 32 - 33.3 33.3 - 42 42 - 46 46 - 52 BORING 10 DESCRIPTION Sand: Light gray; fine-grained; well sorted; subrounded to rounded grains; stained grains 15%. Sand: Pale yellowish-orange; fine-grained; well sorted; subrounded quartz grains; stained grains 95%; oxidized plant remains; heavy minerals 3-4%. Sand: Pale grayish-orange; fine-grained; very coarse sand 5%; heavy minerals 2-3%. Sand: Brownish-black; fine-grained; subrounded quartz grains; stained quartz grains. Sand: Light brown; fine-grained; subrounded grains; heavy minerals 2-3%; sand partially "washed" during sampling. No recovery. Sand: Brownish-black; medium grained; well sorted; subrounded grains; hematitic stains on quartz grains .; Recovery 1.3 ft. No core sample. * (Cut) Sand: Very pale orange; fine-grained; subrounded to well rounded quartz grains; rounded phosphatic grains 3%; epidote 2%; feldspar S-8%; white mica flakes 3%. Sand: Greenish-gray; fine-grained; subrounded to rounded grains; phosphat~ grains 2-3%; white mica flakes 3%; epidote 1-2%. Silty clay: Dark greenish-gray; sand-filled burrows, 0.3 in. wide; horizontal, thin sand layers interbedded the clay. Recovery 2.5 ft. Clayey sand: Greenish-gray; subrounded quart z grains; heavy minerals 3%; epidote 1%; white mi ca fl akes 2- 3%; plant r emains 2%; Elphidi um sp . , Noni onell a sp . , Hanzawaia concentrica, Ammonia be carii, Glob igerinoi des rubra , Nonione ll a sp. Recovery 2. 0 ft . Clayey sand: Light olive gray; well-sorted; subrounded to rounded grains; white mica flakes 3%; heavy minerals 2%; shell fragments 5%; Ammonia beccarii, Elphidium sp. C-24 Boring 10 (Cont'd): DEPTH BELOW SURFACE (ft.) 52 - 62 62 0- 40.7 40.7- 62 Below 62 DESCRIPTION Sand: Very pale orange; fine-grained; subangular to well rounded; stained grains 15%; heavy minerals 3%; shell fragments 5%. Coquina limestone: Pale gray; whole shells of Mulinia sp.; fragments of Turritella sp. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION * (Cut) - Cutting sample. C-25 DEPTH BELOW SURFACE (ft.) 0- 3 3- 6 12 - 32 12 - 17 17 - 32 32 - 42 42 - 62 42 - 47 47 - 62 62 - 66 66 - 72 72 - 83 83 - 92 92 -100 BORING 11 DESCRIPTION Sand: Moderate yellowish-brown; fine-grained; well sorted; subrounded quartz grains; heavy minerals 4%; stems of Spartina alterniflora. Sand: Pale yellowish-orange; fine-grained; well sorted; subrounded grains; heavy minerals 3-4%; No core sample. * (Cut) Sand: Grayish-yellow; fine-grained; sub- angular to well rounded quartz grains; heavy minerals 1-2%. * (Cut) Sand: Very pale orange; fine-grained; sub- angular quartz grains; heavy minerals 4%. Clayey sand: Mottled, olive gray; heavy minerals 3%; stained quartz grains 5%. Recovery 0.2 ft. No core sample. * (Cut) Sand: Very pale orange; fine-grained; subangular grains; heavy minerals 3-5%; wood fragments. * (Cut) Sand: Pale yellowish-gray; fine-grained; subangular to well rounded grains; white mica flakes 3%; feldspar 10%; epidote 2%. Mixture of sand and clay: Sand 75%; clay 25%; abundant shell fragments and whole shells of Mulinia lateralis (Samples 9-13). Elphidium sp. Clay: Greenish-gray; sand layers 1-2 mm thick; plant debris parallel to the stratification; Cocconeis superba; Ammonia beccarii, Elphidium sp., El phid i um poeyanum. Recovery 3.8 ft. Clayey sand: Dark greenish-gray; fine-grained; subrounded quartz grains; epidote 2%; phosphate grains 2-3%; white mica flakes 3%; shell fragments 5%; Elphidium sp. Recovery 1.8 ft. Clay: Greenish-gray; ligritic plant remains; diatoms; sand patches. Recovery 1.8 ft. Sand: Olive gray; fine-grained; well sorted; heavy minerals 3%; feldspar 5%; limestone fragments, 5 em diameter. Recovery 0.7 ft. C-26 Boring 11 (Cont'd): DEPTH BELOW SURFACE (ft.) 100 0 - 92 92 -100 Below 100 DESCRIPTION Limestone: Fragments; very coarse quartz grains in calcareous clay; phosphatic bone fragment, 5 em diameter. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION * (Cut) - Cutting sample. C-27 DEPTH BELOW SURFACE (ft.) 0 - 2.0 2.0 - 6.4 6.4 - 10 10 - 12 12 - 32 12 - 27 27 - 32 32 - 35 35 - 42 42 - 52 42 - 52 ~2 - 62 62 - 72 BORING 12 DESCRIPTION Sand: Dark yellowish-brown; fine-grained; well sorted; rounded grains; epidote 2-3%; sillimanite (?) 1-2%; quartz as aggregates. Sand: Grayish-orange; fine-grained; very well sorted; subrounded quartz grains; feldspar 5%; heavy minerals 3-5%. Sand: Very pale orange; fine-grained; subrounded quartz grains; very coarse sand 5%; heavy minerals 3%; oxidized stem fragments. Sand: Very pale orange; fine-grained; well sorted; subrounded quartz grains; heavy minerals 2%; phosphate grains 1-2%. No core sample. * (Cut) Sand: White; fine-grained; subangular to rounded grains; stained quartz grains 2-3%; heavy minerals 5%. * (Cut) Sand: Yellowish-gray; fine-grained; sub- angular to subrounded grains; very coarse grained 3%; plant remains 1%; heavy minerals 2%; white mica flakes 2-4%; feldspar 5%. Sand: Mottled pale olive and greenish-gray; well sorted; subangular grains; heavy minerals 3%. Clay: Dark greenish-gray; 5 mm sand layers. No core sample. * (Cut) Sand: Yellowish-gray; fine-grained; heavy minerals 4-5%; white mica flakes 2%; feldspar 5-10%; clay 15-20%. This interval is interpreted as silt/clay sequence. Sand: Lig ht ol i ve gray; coarse-grained ; heavy minerals 3% ; Glob igerinoides sacculifer , Han zawaia concentrica , Globor ot alia sp . , Cibi cides duplinensis ( ? ). Recovery 1 .0 ft . Sand: Light - olive gray; calcareous; medium-to coarse- grained; heavy mi nerals 2-3%; quartz pebbles 3%; Cancris sp., Cibicides sapeloensis , Globorotalia menardii , Gl ob igerinoides sacculifer, Shaero idinellopsis subdehis cens, Globiger ino'des ob liquus, Ps eudo polymorfina r uti la , Elphi dium sp., Globigerinoides rubra , Noni on ella sp. ' C-28 Boring 12 (Cont'd): DEPTH BELOW SURFACE (ft.) 72-77 0 - 52 52 - 72 Below 72 DESCRIPTION Coquina limestone: Light olive gray; mollusk external molds; grain supported framework; shell skeletal 90%; clay 10%. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION * (Cut) - Cutting Sample. C-29 DEPTH BELOW SURFACE (ft.) 0 - 4.4 4.4 - 5.0 5.0 - 9.4 9.4 - 32 9.4 - 22 22 - 27 27 - 32 32 - 42 42 - 52 52 - 68 68 0 - 52 52 - 68 Below 68 * (Cut) - Cutting sample. BORING 13 DESCRIPTION Sand: Mottled brown and dark gray; fine-grained; subangular to rounded quartz grains; heavy minerals 2%; large roots and stems of Spartina alterniflora. Sand: Grayish-yellow; fine-grained; subrounded grains; heavy minerals 3%. Sand: Yellowish-gray; fine-grained; well sorted; subrounded to rounded grains; heavy minerals 2-3%. No core sample. * (Cut) Sand: White; fine-grained; subangular grains; epidote 3%; feldspar 5-10%. No recovery. * (Cut) Sand: White; fine-grained; subangular to rounded grains; feldspar 5%; slightly phosphatic; epidote 1-2%; plant remains 2%. Sand: Yellowish-gray; fine-grained; very well sorted; subrounded grains. Recovery 1.0 ft. Clay: Dark greenish-gray; oyster fragments; white mica flakes 2%; the clay is partially m1xed with the sand, clay 85%, sand 15%; Elphidium sp. Recovery 0.2 ft. Sand: Medium-dark gray; calcareous; moderately sorted; very coarse-grained; shell fragments 15%. Limestone: Fragments; scattered quartz granules. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION C-30 DEPTH BELOW SURFACE (ft) 0 - .66 .66- 7.0 7.0 - 17.0 17.0 - 23.4 23.4 - 28 28 - 32 32 - 42 32 - 42 42 - 46.4 46.4 - 49 49 - 52 52 - 62 52 - 62 62 - 65 BORING 14 DESCRIPTION Sand: Medium light gray; fine-to medium-grained; very well sorted; subrounded to rounded grains; heavy minerals 3%; small pieces of roots and stems. Sand: Brownish-gray; fine-grained; very well sorted; subrounded quartz grains; stained quartz grains; heavy minerals 2-3%. Humus: Brownish-black; fine-grained; clayey organic matter. Sand: Yellowish-brown; fine-grained; very well sorted; subrounded to rounded grains; phosphatic grains 2%; epidote less than 1%. Sandy Humus; Brownish-black; fine-grained; abundant organic matter. Sand: Yellowish-brown; fine-grained; well sorted; subrounded quartz grains; slightly phosphatic epidote 1%. No core sample. * (Cut) Sand: Yellowish-brown; subangular grains; white mica flakes 2%; feldspar 5-8%; heavy minerals 3%. Sand: Light olive gray; fine-grained; very well sorted; angular to subangular grains; white mica flakes 3%. Clay: Greenish-gray; small pieces of plant remains; shell fragments 10%; patches of sand. Shelly clayey sand: Dark greenish-gray; fine-grained; abundant shell fragments; whole shells of Mulinia laterlais Elphidium sp., Elphidium poeyanum 1 Polymorphina sp. No core sample. * (Cut) Sand: Pale yellowish-brown; fine-grained; subangular to rounded grains; heavy minerals 2-3%; white mica flakes 2%; shell fragments 10%; clay 10-20%. Sand: Yellowish-brown; fine-grained; well sorted; subrounded to well rounded grains; heavy minerals 2%; shell fragments 5-10%. C-31 Boring 14 (Cont'd): DEPTH BELOW SURFACE (ft.) 65 - 72 72-77 72 - 77 77 - 92 92 - 96 0 - 77 77 - 92 Below 92 * (Cut) - Cutting sample. DESCRIPTION Sand: Yellowish-brown; fine-grained; moderately sorted; oyster fragments; calcareous sandstone fragments; subordinate amounts of clay; Mitrella lunata, Olivella mutica, Mulinia lateralis, Anadora ovalis (Sample 14). No core sample. * (Cut) Sand: Pale yellowish-brown; coarse-grained; subrounded grains; white mica flakes 2%; feldspar 1-2%; heavy minerals 2%. Sand: Light olive gray; fine-grained; well sorted; subrounded to rounded grains; quartz granules 15-20%; shell fragments. Recovery 1.3 ft. Limestone: Pale olive green, sandy; internal gastropod molds; clay supported grains. Recovery 2.0 ft. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION C-32 DEPTH BELOW SURFACE (ft.) 0 - .56 .56 - 4.4 4.4 9.0 9.0 - 10.0 10.0 - 12 12 - 42 12 - 22 22 - 27 27 - 32 32 - 42 42 - 52 52 - 62 BORING 15 DESCRIPTION Sand: Yellowish-gray; fine-gTained; subangular to well rounded grains; epidote 2-3%; other heavy minerals 3%; oxidized quartz grains. Sand: Yellowish-orange; fine-grained; very well sorted; subrounded quartz grains; epidote 1-2%; stained quartz grains. Sand: very light gray; fine-grained; very well sorted; subrounded quartz grains; phosphate grains 2%; heavy minerals 3%. Sand: Yellowish-brown; fine-grained; well sorted; subrounded quartz grains; slightly phosphatic; heavy minerals 3%. No recovery. No core sample. * (Cut) Sand: Grayish-orange; fine-grained; subangular to rounded grains; heavy minerals 3%; feldspar 5%; white mica flakes 2%. k (Cut) Sand: Pal e ye ll owis h- bro wn ; medium-to coarse-gr ained; subangular to well r ounded grains; heavy minerals 2%; white mica flakes 2- 3%; plant remains ,l-2% . * (Cut) Sand: Pale yellowish-brown; fine-grained; subangular grains; heavy minerals 1-3%; white mica flakes 2%. * (Cut) Sand: Pale yellowish-brown; coarse-grained; I subangular grains; epidote 2%; other heavy minerals 3%; shell fragments 4%. Sandy cl ay : Light olive gray; very well sorted ; sub- rounded grains; o. 4 in t hick sand l ayers i nter- bedded with clay in t he lm.,r er part of th i s i nt erval; pl ant remains parall el to the stratifi cation. Ammonia beccarii, Elphi dium sp., Discorbis sp., Hanzawaia c on c e n t ri c a . No core sample. C-33 Boring 15 (Cont'd): DEPTH BELOW SURFACE (ft.) 52 - 62 62 - 71 71 - 92 92 0 - 42 42 - 92 Below 92 DESCRIPTION * (Cut) Sand: Pale yellowish-brown; fine-grained; heavy minerals 3%; white mica flakes 2%; shell fragments 10%; clay 25%. This interval is interpreted as silt/clay sequence. Clay: Dark greenish-gray; small pieces of plant remains parallel to the stratification; large shell fragments of Crassostrea virginica; scattered quartz pebbles. Recovery 0.9 ft. Sand: Light olive gray; coarse-grained; subrounded to rounded quartz grains; quartz pebb~es 15%; phosphatic grains 3%; epidote 1-2%; shell fragments 5%. Recovery 1.2 ft. Bed rock ( ilo recovery) . Pleistocene Middle Pliocene Middle Miocene INTERPRETATION * (Cut) - Cutting sample C-34 DEPTH BELOW SURFACE (ft.) 0 - 2.0 2.0- 7.4 7.4- 9.0 9.0 - 12.4 12.4 - 17 17 - 22 22 - 32 32 - 62 32 - 52 52 - 62 62 - 64 64 - 72 72 - 82 BORING 16 DESCRIPTION Sand: Brownish-gray; fine-grained; subrounded to rounded quartz grains; heavy minerals 2%; thin roots; shell fragments 2%; stained quartz grains. Sand: Light olive gray; fine-grained; very well sorted; subrounded quartz grains; phosphatic grains 3%; epidote 1-2%; hornblende (?) 2%. Humus: Brownish-black; fine quartz grains in organic material. Mixture of brownish-gray sand and black clay, small shell fragments. Clay: Brownish-black; abundant plant debris; patches of sand; high content of organic matter; large lignitic stem debris, 9 em long, 3-4 em diameter. Recovery 3.9 in. Clayey sand: Dark greenish-gray; subrounded quartz grains; heavy minerals 3%. Clay: Dark greenish-gray; thin sand layers interbedded the clay. No core sample. * (Cut) Sand: Very pale orange; fine-to mediumgrained; subangular grains; white mica flakes 2%; heavy minerals 4%; feldspar 5-10%; wood fragments; clay 15-30%. This interval is interpreted as clay/sand sequence. * (Cut) Sand: Pale yellowish-brown; fine-grained; subangular quartz grains; shell fragments 40%; heavy minerals 4%. Clay: Dark greenish-gray; 3-4 mm sand layers; shell fragments 3%; scattered quartz grains. Recovery 2 in. Sand: Dusky yellow; medium-grained; very well sorted; rounded quartz grains; ca1careous sandstone fragments; large shell fragments. Recovery 0.7 ft. Sand: Light olive gray; fine-grained; very well sorted; subrounded to well-rounded quartz grains; shell fragments 5%; the sand in the lower part changes gradually to ~layey sand. Recovery 1.0 ft. C-35 Boring 16 (Cont'd): DEPTH BELOW SURFACE (ft.) 82 - 94 94 0 - 52 52 - 94 Below 94 DESCRIPTION Sand: Light olive gray; fine-grained in the upper part and coarse in the bottom; subrounded quartz grains; heavy minerals 3%; white mica flakes 2%; Pecten sp., Balanus (barnacle) (Sample 17); Cibicides sapeloensis, Ammonia beccarii. Recovery 1.0 ft, Bed rock (no recovery). Pleistocene Middle Pliocene Middle Miocene INTERPRETATION * (Cut) - Cutting sample. C-36 DEPTH BE LOW SURFACE (ft.) 0 - 1.5 1.5 - 2.4 2.4 - 6.0 6.0 - 10 10 - 12 12 - 32 12 - 32 32 - 42 42 - 52 42 - 52 52 - 56 56 - 62 62 - 72 62 - 72 BORING 17 DESCRIPTION Sand: Very light gray; fine-grained; abundant roots and stems; heavy minerals 3-5%. Sand: Yellowish-brown; fine-grained; subangular to well-rounded quartz grains; phosphatic grains 2%; feldspar 10%. Sand: Grayish-orange; fine-grained; subrounded grains; epidote 1-2%; prismatic grains (sillimanite (?)) 1-2 %. No recovery. Sand: Moderate brown; fine-grained; very well sorted; subrounded to rounded quartz grains; heavy minerals 4%; shell fragment 5% . No core sample. * (Cut) Sand: Moderate yellowish-brown; fine-grained; subangular to rounded quartz grains; feldspar 5-10%; white mica flakes 3%. Sand: Mottled yellow and greenish-yellow; fine grained; subrounded quartz grains; heavy minerals 3%; wood fragments 2%. Recovery 0.5 ft. No core sample. * (Cut ) Sand : Pale orange; fi ne- grained ; subround ed quartz grains; dark mineral s 1%; wh ite mica f l akes 2%; clay 5-10% . This interval is i nterpreted as sil t / clay sequence based on clay content. Sand: Light olive gray; very-fine grained; well sorted; subrounded quartz g~ains; white mica flakes 5-10%; epidote 2%; sh ell fragments 3% ; Elphidi um sp., Globigerinoides obliquus, Cibicides sapel oensis . Sandy clay : Dusky yellow green; scattered shell fragments; Ammonia beccarii , Elphidium sp., Hanzawaia concentrica, Globiger ino id es sacculifer. No core sample. * (Cut) Sand: Light olive gray; fine-grained; white mica flakes 2-3%; heavy minerals 2%; shell fragments 15%. C-37 Boring 17 (Cont'd): DEPTH BELOW SURFACE (ft.) 72 - 82 82 - 92 92 - 98 98 DESCRIPTION Mixture of sand and clay: clay 75%; sand 25%; the sand is fine-grained; limestone fragments 5 em diameter; Pecten sp., Anadora ovalis, Mulinia lateralis (Sample 19). Recovery 0.8 ft. Sand: Brownish-yellow; coarse-to very coarse-grained; shell fragments; mixture of sand and clay; Ostrea sp., Crassatella sp. Sand: Greenish-gray; fine-to medium-grained; subangular to rounded grains; white mica flakes 3%; epidote 2%. Recovery 1.0 ft. Bed rock (no recovery). 0 - 52 52 - 98 Below 98 * (Cut) - Cutting sample. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION C-38 DEPTH BELOW SURFACE (ft.) 0 - 2.0 2.0- 7.5 7.5- 10 10 - 12 12 - 32 12 - 32 32 - 42 42 - 52 42 - 52 52 - 62 62 - 72 72 - 79 79 - 82 ' 0 - 42 42 - 79 Below 79 * (Cut) - Cutting sample. BORING 18 DESCRIPTION Sand: Grayish-orange; fine-grained; subrounded to well-rounded quartz grains; feldspar 5%; heavy minerals 2%; root fragments. Sand: Grayish-orange; fine-grained; subrounded quartz grains; prismatic grains (sillimanite (?)) 2%. Sand: Mottled dakr brown and pale brown; fine-grained; well-sorted; rounded to well-rounded quartz grains; phosphatic grains 1-2%. No recovery. No core sample. * (Cut) Sand: Very pale orange; subangular to rounded quartz grains; white mica flakes 3%; epidote 1-2%. Silty clay: Dark greenish-gray; sand layers interbedded the clay, 0.5-1.0 em thick. Recovery 1.2 ft. No core sample. * (Cut) Sand: Yellowish-gray; fine-grained; sub- angular to rounded quartz grains; white mica 2-3%; heavy minerals 4%. Silty clay : Dark greenish-gray; shell fragments 5%; sand patches; lignitic plant remains; Mercenaria sp. (Sample 15). Recovery 0.4 ft. Sandy clay: Shell fragments (interpretation based on field log). Sand: Light olive gray; fine-to coarse-grained; rounded to well-rounded grains; epidote 3%; other heavy minerals 2%; Pecten sp. fragment. Limestone: Light olive gray; medium to very coarse quartz grains in calcareous clay. Recovery 2.1 ft. Pleistocene Middle Pliocene Middle Miocene INTERPRETATION C-39 APPENDIX D GRAIN SIZE DATA GRAIN SIZE DATA DEPTif BELOW SURFACE (m) MEAN (Mz) SKEWNESS (Sk) STANDARD DEVIATION (SD) KURTOSIS (KG) GRAVEL % SAND % SILT % CLAY % SILT & CLAY % BorinL!_ 0.60 2.73 -0.03 1.52 2.53 -0.20 2.74 2.79 0.29 3.65 2.75 0.0 3.96 - 4.26 2. 77 0.29 5.48 2.53 -0.31 6.82 2.75 O.Oi 8.83 3.04 0.31 t::J 9.75 Approx. 3.08 0.56 ..I.... 12.19 5.58 0.30 21.33- 2.10 0.19 25.90 1.03 0.03 0.40 0.56 0.31 0.41 0.27 0.57 0.44 0.59 1. 31- 0.59 0.65 1.38 2.59 2.48 1. 78 2.64 1. 73 2.57 2.65 0.90 2. 34 1.82 0.87 0.90 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.04 13.53 99.20 99.33 99.72 99.43 99.31 99.73 98.29 99.29 89.52 0.0 99.71 86.27 ~ 5.36 85.07 5.02 14.92 0.80 0.67 0.28 0.57 0.69 0.27 1.71 0.71 0.25 0.10 Borin~ 0.20 0.67 1. 31 2.13 2.74 3.35 3.65 4.57 5.18 15.84 16.76 18.59 18.89- 21.94 2.75 2. 77 2. 77 2. 77 2.77 2.79 5.04 4.08 4.26 2.73 2.61 2.51 2.63 -0.27 0.06 0.{)7 0.29 0.06 0.30 0.58 0.53 0.61 -0.13 0.35 -0.37 0.12 0.48 0.39 0.38 0.30 0.39 0.31 2.43 1. 52 1.50 1.16 3. 04 0.73 3.41 3.35 2.54 2.49 1. 79 2.54 1.84 0.47 1.58 2.18 4.25 1. 78 3.08 0.91 0.06 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.44 9. 77 0.04 23.58 97.73 98.83 99.14 99.55 98.98 98.10 53.41 83.01 81.37 88.43 73.57 97.68 51.57 9.18 13.14 4.69 6.87 16.58 - 37.42 3.84 14.06 9.78 88.26 2.21 1.17 0.86 0.45 1.02 1.90 9.12 2.28 DEPTH BELOW SURFACE (rn) Boring 3 0.02 0.30 0.60 0.72 1.01 1. 21 1.62 2.13 0 I 3.04 N 3.96 4.87 5.18 6.09 6.70 7.31 8.22 8.83 9.75 10.78 11.58 12.49 13.41 14.02 16.15 17.06 17.67 18.28 GRAIN SIZE DATA (Continued) MEAN SKEWNESS STANDARD KURTOSIS GRAVEL % SAND % SILT % CLAY % SILT & (Mz) (Sk) DEVIATION (K ) CLAY % (SO) G 2.99 2.99 3.00 2. 77 2.96 2.78 2.95 2.78 4.36 3 . 11 2 . 94 3.14 3.11 3.07 3.05 3.05 3.16 5.62 6.32 7.64 5.32 7.91 2.96 2.07 2.05 4.95 0.02 0.32 0.31 0.36 0.06 0.31 0.06 0.32 0 . 07 0.55 0.46 0.26 0.44 0.50 0.55 0.55 0.56 0. 71 -0.'22 --o. 28 -0.63 -0.50 -0.56 0.28 -0.58 -0.62 0.58 0.51 0.57 0.58 0.56 0.41 0.56 0.41 0.54 0.40 1. 88 0.52 0.50 0.51 0.50 0.50 0.50 0.50 0.98 2.26 2.21 1.47 3.45 1. 35 0.59 1.18 1.32 2.58 1.46 2.49 2.54 2.39 2.64 2.59 2.53 2.56 2.48 0.78 0.59 2.60 0.58 0.59 0.63 0.65 0.67 1.57 0.65 0.57 1. 01 0.75 1.00 2.66 1. 31 o.-59 0.51 1.44 0.13 0.33 0.01 0.0 0.14 o.o 0.06 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.60 0.29 8.87 0.00 o.o 4. 23 7.46 o.o 48.37 98.02 97.20 97.50 97.34 97.43 98.47 97.92 99.80 69.08 98.94 98.10 99.71 99.61 98.16 98.55 98.01 84.70 45.81 29.12 13.51 28.12 5.58 97.15 95.18 91.75 53.92 50.94 22.27 15.15 37.71 26.44 28.53 25.78 25.95 3.24 8.65 0.14 16.49 42.84 57.68 37.23 68.47 42.84 1.85 2.47 2.48 2.66 2.43 1.53 2.01 1.20 1.06 1.90 0.29 0.39 1.84 1.45 1. 99 2.85 0.59 0.79 0.68 GRAIN SIZE DATA (Continued) DEPTII BELOW SURFACE (m) MEAN (Mz) SKEWNESS (Sk) STANDARD DEVIATION (SO) KURTOSIS (KG) GRAVEL % SAND % SILT % CLAY % SILT & CLAY % Borin~ (Cont'd) 18.89 19.20 20.11 22.25 22.86 23.77 24.38 - -24.68 24.68 - 27.73 1. 78 5.58 0.70 3.27 2.84 3.65 0.50 0.51 -0.69 -0.37 0.07 0.26 0.43 0.31 0.56 0.43 1.49 3.10 1.59 2. 71 3.09 3.48 1.25 1.59 0.98 0.64 0.79 1.56 1. 24 0.65 1.31 0.79 8.16 2. 77 21.62 0.98 2.88 2.26 10.61 18.45 90.54 46.12 77.89 79.65 78.58 68.00 87.73 81.42 3.90 11.47 3.59 8.19 47.21 7.99 14.95 21.56 1.30 0.49 1.66 0.13 0 I 0-l Boring 4 0.30 1. 21 2.20 2.99 9.75 - 11.27 App. 11.27 - 12.80 App. 14.02 14.93 15.84 - 18.89 19.81 20.87 28.04 - 28.34 2.76 2. 77 2.78 2.74 3.03 6.25 6.32 5.01 4.51 7.22 7.09 3.00 0.02 0.04 0.29 -0.02 0.31 -0.25 -0.25 0.57 0.50 0.48 0.55 0.17 0.42 0.40 0.31 0.39 0.59 2.14 2.11 2.35 1.98 1.02 0.98 0.75 2.68 2.58 1. 79 2.62 0.94 1.20 1.19 0.50 0.65 0.59 0.65 3.13 0.0 98.73 1.27 0.0 99.39 0.61 0.0 99.25 0.75 0.0 99.23 0. 77 0.0 99.54 0.46 0.0 21.13 47.98 30.89 0.0 18.67 48.20 33.13 0.0 52.91 21.92 25.17 0.0 53.51 32.55 13.94 0.0 2.05 58.58 39.37 0.0 2.54 70.37 27.09 0.0 95.48 4.52 Borin~ 0.12 0.45 2.55 2.75 -0.30 0.01 0.54 0.39 2.51 2.63 0.0 99.33 0.0 99.11 0.67 0.99 GRAIN SIZE DATA (Continued) DEPTif BE LOW SURFACE (rn) MEAN (Mz) SKEWNESS (Sk) STANDARD DEVIATION (SD) KURTOSIS (KG) GRAVEL % SAND % SILT % CLAY % SILT & CLAY % Borin~ (Cont'd) 1.06 2.76 0.04 1.52 2.78 0.30 1.94 2.55 -0.30 2.20 2.78 0.29 2.43 2.89 2.78 2.79 0.30 0.30 3.47 - 3.65 2.79 0.30 3.65 - 12.80 16.47 Approx. 4.53 7.17 0.49 {).10 17.47 Approx. 4.39 0.57 0 I 18.89 - 21. 94 2.98 0.57 """' Boring 6 0.39 0.31 0.54 0.30 0.29 0.30 0.30 1. 96 1.50 1. 94 0.46 2.63 1.81 2.51 1.80 1.86 1.85 1.83 0.67 1.19 0.68 1.77 0.0 98.42 1.58 0.0 98.97 1.03 0.0 99.37 0.63 0.0 99.49 0.51 0.0 98.74 1.26 0.0 99.11 0.89 0.0 99.54 0.46 0.0 53.49 33.60 12.91 0.0 7.95 54.24 37.82 0.0 64.99 23.89 11.12 0.0 98.76 1.24 0.25 1.38 2.74 3.80 13.53 Approx. 15.64 Approx. 18.28 18.71 2. 72 2.78 2. 77 2. 77 3.40 7. 72 7.69 2.79 -0.02 0.30 0.30 0.30 0.01 -0.62 -0.59 0.30 0.42 0.30 0.30 0.29 1. 26 1. 39 1. 36 0.31 2.55 1.80 1.80 1.81 2.32 1. 03 0.99 1.87 0.0 99.31 0.69 0.0 99.42 0.58 0.0 98.80 1.20 0.0 98.93 1.17 o.o 88.03 6.22 5.74 0.0 6.94 33.05 60.01 0.0 5.45 39.05 55.49 0.0 97.63 2.37 Boring 7 0 - 3.0 3.35 - 3.65 15.84 - 18.89 18.89 - 21.94 22.09 Approx. 2. 77 2.74 7.20 7.69 2.73 0.07 -0.01 0.51 -0.41 -0.11 0.38 0.41 1.0 1.01 0.87 2.47 2.54 0.59 0.57 2.97 0.0 99.25 0.75 0.0 99.45 0.55 o.o 0.0 63.19 36.81 0.0 0.0 47.91 52.09 0.51 97.22 2.28 DEPTII BELOW SURFACE (m) Boring 8 0.60 1.67 2.43 2.89 14.32 ~ 15.84 16.45 Approx. 17.82 Approx. 18.. 99 Approx. 19.91 Approx. 0 I U1 Boring 9 0.60 1.52 2.92 3.50 6.70 - 9.75 Boring 10 0.17 1.57 2.28 - 2.43 2.43 - 3.0 3.65 - 6.70 10.05 Approx. 12.49 Approx. 12.80 - 14.02 14.02 - 15.87 GRAIN SIZE DATA (Continued) MEAN (Mz) SKEWNESS (Sk) STANDARD DEVIATION (SD) KURTOSIS (KG) GRAVEL % SAND % SILT % CLAY % SILT & CLAY % 2.74 2.76 2.78 2.75 7.57 3.07 4. 77 2.69 2. 77 0.0 0.03 0.30 0.0 -0.50 0.54 0.31 -0.01 0.30 0.42 0.40 0.31 0.42 1.57 0.52 2.86 0.79 0.31 2.67 2.52 1.80 2.66 1.09 0.53 1.02 0.99 1.84 0.0 0.0 0.0 0.0 0.0 o.o 6.56 0.0 0.0 98.69 99.12 99.21 99.14 15.69 96.67 52.28 98.70 98.11 33.43 24.15 50.88 17.02 1.31 0.86 0.79 0.86 3.33 1.30 1.89 2.73 2.76 2.75 2.78 2 .,75 -0.02 0.29 0.0 0.29 0.01 2.73 2.75 2.78 2.78 2.50 3.03 6.02 4.62 6.12 -0.05 -0.02 0.30 0.07 -0.57 0.30 -0.16 0.54 -0.10 0.41 0.28 0.41 0.30 0.46 0.40 0.36 0.30 0.42 0.46 0.60 2.10 1.93 1.97 2.63 1.72 2.64 1.77 2.53 2.53 2.44 1.83 2.61 1. 73 0.96 0.78 0.80 0.68 0.0 0.03 0.0 0.0 0.0 98.88 99.87 99.57 99.63 98.41 1.12 0.09 0.43 0.37 1.59 0.10 0.04 0.0 0.0 0.0 0.0 0.0 0.0 0.0 99.08 99.74 98.84 96.28 99.86 98.91 40.56 55.63 37.68 37.66 28.59 37.74 21.78 15.78 24.58 0.81 0.22 1.16 3. 72 0.14 1.09 GRAIN SIZE DATA (Continued) DEPTif BELOW SURFACE (m) MEAN (Mz) SKEWNESS (Sk) STANDARD DEVIATION (SD) KURTOSIS (KG) GRAVEL % SAND % SILT % CLAY % SILT & CLAY % Boring 11 0 - 0.60 2.78 0.07 1.52 2.78 0.29 2.74 2.99 0.57 2.65 3.06 0.56 9.75 - 12.80 4.19 0.85 19.37 Approx. 4.54 0.48 20.94 Approx. 7.12 0.12 21.94 - 25.29 6.. 11 -0.23 25.29 - 28.04 7.18 0.53 0 29. 04 - . 30. 0 I Q\ 2.74 -0.01 Boring 12 0.39 0.31 0.46 0.49 2.02 2.00 1.49 2.04 0.99 0.74 2.48 1. 75 1. 74 0.65 0.65 0.66 1.21 0.84 0.60 2.49 0.0 99.12 0.88 0.0 99.70 0.30 0.0 99.23 0. 77 0.0 98.78 1.22 0.0 60.27 24.36 15.37 0.0 52.46 32.11 15.43 0.0 9.45 56.89 33.66 0.0 26.65 53.28 20.09 0.0 0.0 65.55 34.45 0.0 98.72 1.28 2.74 1.82 1.99 3.65 10.86 Approx. 12.19 Approx. 18.89 2.73 2. 77 2.76 2.76 2.78 6.30 2.02 -0.04 0.29 0.03 0.07 0.30 -0.17 0.32 0.40 0.30 0.37 0.37 0.29 1.97 0.61 2.57 1.77 2.52 2.51 1.82 1.03 2.45 0.08 0.0 0.0 0.0 0.0 0.0 0.37 99.18 99.52 99.39 98.60 99.77 22.09 98.82 47.23 30.67 0.74 0.48 0.61 1.40 0.23 0.81 Boring 13 0.35 1.52 1.82- 2.43 9.75 - 12.80 12.80 - 15.84 2.74 2.77 2.78 2.79 7.25 -0.04 0.29 0.29 0.30 0.48 0.38 0.30 0.30 0.30 1.01 2.53 1. 78 1. 79 1.82 0.58 0.0 99.43 0.57 0.0 99.44 0.56 0.0 99.40 0.60 0.0 99.58 0.32 0.0 0.0 58.74 41.26 GRAIN SIZE DATA (Continued) DEPTI-1 BELOW SURFACE (m) MEAN (Mz) SKEWNESS (Sk) STANDARD DEVIATION (SO) KURTOSIS (KG) GRAVEL % SAND % SILT % CLAY % SILT & CLAY % Boring 14 0 - 0.60 2.43 -0.53 1. 52 2.45 -0.53 1.82- 2.13 2.75 -0.01 2.13 - 4. 26 4.07 0.86 4.26- 6.70 2.76 0.05 8.27 Approx. 5.21 -0.37 13.90 Approx. 3.06 0.32 14.98 Approx. 5.92 -0.20 19.77 Approx. 2.73 -0.07 20.42 Approx. 1.05 -0.36 0 21.03 -:- 21.94 0.74 0.03 I -...J 24.99 - 28.04 2.56 -0.28 0.50 0.50 0.40 1.89 0.37 1. 97 0.59 2.37 0.42 1.65 1.69 0.57 0.62 0.63 2.64 0.65 2.49 0.64 0.96 0.54 2.69 0.50 0.48 2.61 0.10 0.0 o.o 0.0 0.0 0.0 0.0 0.0 0.0 23.57 37.16 0.09 99.45 99.39 99.18 66.71 99.86 48.33 99.27 43.80 99.66 75.83 52.23 99.27 26.05 39.11 18.94 0.63 7.24 12.56 37.25 0.44 0.61 0.82 0.14 0.73 0.34 0.61 0.60 Boring 15 0.30 1.33 - 2. 74 2.74- 3.0 12.80 - 15.84 18.89- 21.94 21.94 - 28.04 2.75 2.54 2.74 5.53 7.09 2.15 0.0 -0.29 -0.03 -0.32 0.22 0.32 0.38 0.56 0.36 1.71 1.30 0.83 2.50 2.54 2.45 0.81 1.10 1.19 0.0 99.35 0.65 0.0 99 .34 0.66 0.0 99.57 0.43 0.0 46.74 41.50 11.75 0.0 5.19 66.57 28.24 0.0 95.38 4.62 Boring 16 0.60 1.52 2.25- 2.74 3.12- 3.77 3.77- 5.18 6.1 Approx. 19.50 - 21.94 21. 94 - 24. 99 24.99 - 28.65 2.47 2.75 2.76 2.76 5.32 4.18 2.57 2.75 2.37 -0.56 0.01 0.28 0.0 -0.45 0.86 _-0.03 0.01 -0.45 0.49 0.39 0.27 0.16 1. 98 2.00 1.08 0.82 0.79 0.57 2.61 1.67 0.74 0.64 0.65 1.32 2.17 1.14 0.11 0.12 0.0 0.0 0.0 0.0 1. 24 0.0 0.30 99.57 99.24 98.54 99.70 36.33 58.56 89.62 96.33 98.56 49.99 27.23 13.68 14.21 0.32 0.64 1.46 0.30 9.14 3.67 1.13 GRAIN SIZE DATA (Continued) DEPTII BELOW SURFACE (m) MEAN (Mz) SKEWNESS (Sk) STANDARD DEVIATION (SO) KURTOSIS (KG) GRAVEL % SAND % SILT % CLAY % SILT & CLAY % Boring 17 0.91 2.75 -0.02 1.82 2.75 0.03 3.0 - 3.65 2.75 -0.03 9.75 - 12.80 2. 77 0.29 15.84- 17.06 3.75 0.25 17.06- 18.89 4.22 .0.13 21.94 - 24.99 5.78 -0.34 29.87 0 I 00 Boring 18 3.11 0.15 0.36 0.37 0.36 0.30 0.70 2.49 3.00 0.70 2.48 2.54 2.45 1. 78 5.19 0.96 0.73 0.92 0.0 0.0 0.02 0.0 0.0 2.62 5.59 . 0.09 99.42 99.34 98.90 99.37 89.86 53.77 40.94 95.37 7.45 34.98 16.89 2.69 8.63 36.58 0.58 0.66 1.08 0.63 4.54 0 - 0.03 1.21 2.13 3.00 9.75 - 12.80 15.84 - 18.89 20.23 2.73 2.76 2.75 2.56 6.28 4.50 2.76 -0.07 0.28 0.01 -0.28 -0.25 0.35 0.01 0.38 0.27 0.41 0.56 2.17 2.14 0.42 2.40 1.66 2.67 2.50 0.58 0.73 2.69 0.05 0.0 0.0 0.0 0.0 0.0 0.05 99.28 99.37 99.0 99.13 25.41 50.61 98.98 37.80 36.11 36.79 13.28 0.57 0.63 1.0 0.87 0.97 APPENDIX E LIST OF MACROFOSSILS MACROFOSSILS Abra aequalis (Say) Acteocina canaliculata (Say) Anadora ovalis (Bruguiere) Balanus sp. Chione latirilata (Conrad) Crassatella sp. Crassostrea virginica (Gmelin) Mercenaria sp. Mitrella lunata (Say) Mulinia lateralis (Say) Nassarius obsoletus (Say) Oliva sayana_ (Ravenel) Olivella mutica (Say) Ophiomorpha nodosa Ostrea sp. Pecten sp. Rangia cuneiata (Gray) Turritella sp. Venericardia sp. BORING NUMBER(S) 6 3 14, 17 16 3 17 3, 15 3, 4, 18 14 2, 3, 5, 6, 11, 14, 17 3 5 3, 14, 3 17 16, 17, 18 3 10 2 E-1 FigureG-11. Inland salt marshes located on South Cut road, Cumberland Island . Grass in the foreground is Spartina alterniflora- FigureG-12. Raccoon Keys salt marsh with active back dunes in background. APPENDIX F LIST OF MICROFOSSILS MICROFOSSILS Ammonia beccarii (Linne) Cancris sp. Cibicides sapeloensis (Darby and Hoyt) Cocconeis superba Disc or bis sp . Elphidium advena (Cushman) Elphidium gunteri (Cole) Elphidium poeyanum (d'Orbigny) Globigerinoides obliquus (Bolli) Globigerinoides rubra (d'Orbigny) Globigerinoides sacculifer (Brady) Globorotalia menardii (d'Orbigny) Hanzawaia concentrica (Cushman) Nonionell a sp. Polymor phina guttulina (d'Orbigny) Polymorphina sp. Pseudo polymorphina rutila (Cushman) Quinqueloculina sp. Rhaphaneis angularis Sphaeroidinellopsis subdehiscens (Blow) BORING NUMBER(S) 3, 7, 8, 10, 11, 15, 16, 17 12 4, 12, 16' 17 7, 11 15 3 3, 4 4, 11, 13, 14 4, 12, 17 3, 4, 10, 12 4, 12, 17 3, 12 3, 4, 10, 12, 15, 17 3, 8, 10, 12 3 4 , 14 12 3 3 12 F-1 APPENDIX G MISCELLANEOUS PHOTOGRAPHS Note: The photographs provided in this Appendix are not referenced in the text. Rather the photographs are provided so that the reader can obtain a visual image of several concepts discussed in the narrative. Figure G-1 . Exposure of the Satilla Formation at Terrapin Point, Cumberland Island. FigureG-2. Holocene Dunes advancing over the Pleistocene age Satilla Formation in the Beach Fields, Cumberland Island. FigureG-3. Salicornia sp. (glasswort) located on the high marsh in the Raccoon Keys salt marsh. FigureG-4. Uniola paniculata (see oats) growth on foredunes tends to stabilize the sands and retard erosion. FigureG-5. Stabilizing vegetation on the back dunes near the Little Greyfield dune crossing, Cumberland Island. FigureG-6. Typical vegetation of the interdune meadow near the Little Greyfield dune crossing. FigureG-7. Freshwater marsh on Cumberland Island, notice the vegetation changes from foreground to background. FigureG-8. Lake Whitney, a fresh water pond near the north end of Cumberland Island. Figure G-9. Beach on the south end of Cumberland Island at low tide. RgureG-1Q The jetty located on the south end of Cumberland Island is acting as a sediment trap causing growth of the island. Figure G-13. Dune erosion as a result of Hurricane David, near Willow Pond crossing. FigureG-14. Close up of dune erosion resulting from Hurricane David. FigureG-15_ Erosion of the Pleistocene sands on Terrapin Point, Cumberland Island. FigureG-16. Marsh erosion in the Raccoon Keys salt marsh, Cumberland Island. Figure G-17. Back dune encroachment over I i ve oaks at the edge of the Raccoon Keys salt marsh. . . .) Figure G-18. This house was bu i It west of the back dunes. Subsequent dune migration covered the house and it is now emerging on the east side of the dunes. Nightingale Avenue, Cumberland Island. Figure G-19. Uncontrolled flow of artesian well at Carriage House, Cumberland Island FigureG-20. Hydraulic ram used to pump water without electricity, Dungeness, Cumberland Island.