Brevard Fault Zone in western Georgia and eastern Alabama

BREVARD FAULT ZONE IN WESTERN GEORGIA AND EASTERN ALABAMA
by Thomas J. Crawford and Jack H. Medlin
TERTIARY STRATIGRAPHY OF THE CENTRAL GEORGIA COASTAL PLAIN
by Paul F. Huddleston, William E. Marsalis and Sam M. Pickering, Jr .
GUIDEBOOK 12
Published by the Georgia Geological Survey for the Geological Society of America Southeastern Section Annual Meeting
Georgia Department of Natural Resources Joe D. Tanner, Commissioner Earth and Water Division
The Geological Survey of Georgia Sam M. Pickering, Jr., State Geologist
ATLANTA 1974

I
I.
I

BREVARD FAULT ZONE IN WESTERN GEORGIA AND EASTERN ALABAMA
by Thomas J. Crawford and Jack H. Medlin
FIELD TRIP 1

CONTENTS

Introduction Review Stratigraphy Geochemistry and Mineralogy .
Quartzites Schists . . Granitic gneisses Amphibolites and hornblende gneisses Austell gneiss . .. Yellow Dirt gneiss Purpose Approach Road log . Traverse 1 Traverse 2 Traverse 3 References . .
ILLUSTRATIONS

1-1 1-1 1-9 1-11 1-12 1-12 1-25 1-30 1-37 1-41 1-41 1-46 1-47 1-51 1-57 1-62 1-66

Plate 1. The Brevard Fault Zone in western Georgia and eastern Alabama . . . in pocket

Figure 1. The metamorphic belts of Crickmay compared to the geology of

western Georgia . . . . . . . . . . . . . . . . . . . .

1-2

2. Major structures between the Cartersville and Brevard Fault Zones.

1-3

3. Correlation of stratigraphy

1-5

4. Stratigraphic column . .

1-6

5. Photograph of flinty crush rock derived from the Y~llow Dirt

gneiss . .

1-8

6. Photomicrograph of garnets in quartzite

1-13

7. Photomicrograph of magnetitic quartzite

1-13

iii

Figure 8. Triangular plot of quartz-plagioclase-muscovite + biotite modes from selected schist samples . . . . . . . . . . . . . . . .

9. Photomicrograph of mylonitic schist with muscovite buttons .

10. Photomicrograph of muscovite button

11. Photomicrograph showing crinkle folds in mylonitic schist .

12. Photomicrograph of garnets from mylonitic schist

13. Photomicrograph of garnets from schist . . . .

14. Photomicrograph of garnet from mylonitic schist

15. Photomicrograph of garnet from mylonitic schist

16. Photomicrograph of augen of quartz and feldspar in mylonitic

schist . . . . . .

. . . . . . . . . . . . . .

17. Photomicrograph of blastomylonitic and mortar textures in schist .

18. Ca0-Na20-K20 plot of selected schist samples 19. ACF plot of 81 schist samples . . . . . . .

20. Photomicrograph of mylonitic Yellow Dirt gneiss

21. Photomicrograph of microbreccia in Yellow Dirt gneiss

22. Triangular plot of quartz-microcline-plagioclase modes from selected granitic gneiss samples . . . . . . . . . . . . .

23. Ca0-Na20-K20 plot of selected granitic gneiss samples 24. ALK-F-M composition plot of "granitic" gneisses . .

25. K20 vs. Na20 of amphibolites and hornblende gneisses

26. Na 20 + K20 vs. Si0 2 plot of amphibolites and hornblende gneisses

27. ALK vs. Fe2 0 3 vs. MgO compositional diagram of amphibolites and

hornblende gneisses . . . . . . . . . . . .

. . . . .

28. Triangular plot of quartz-microcline-plagioclase modes for Austell gneiss . . . . . . . . . . . . . . . . . .

29. Na20-K20-Ca0 triangular plot for the Austell gneiss 30. Ca0-Na20-K20 plot for the Yellow Dirt gneiss 31. Field trip route

32. Traverse 1 - map

1-17 1-18 1-19 1-19 1-20 1-20 1-21 1-21
1-24 1-24 1-26 1-27 1-28 1-28
1-31 1-34 1-35 1-38 1-39
1-40
1-42 1-43 1-44 1-48 1-50

iv

Figure 33. Photograph of Dry Creek quartzite 34. Traverse 2 - map . . . . . . . 35. Photograph of Anneewakee graphitic schist-quartzite 36. Photograph of fracturing in the Anneewakee graphitic schistquartzite . 37 . Traverse 3- map

1-53 1-58 1-59
1-60 1-63

TABLES
Table 1. Chemical analyses of quartzites 2. Modes of selected schist samples 3. Chemical analyses of schists 4. Modes of selected "granitic" gneiss samples 5. Chemical analyses of "granitic" gneisses . . 6. Chemical analyses of hornblende genisses and amphibolites 7. Chemical analyses of the Yellow Dirt gneiss

1-14 1-15 1-22 1-29 1-32 1-36 1-45

v

..

THE BREVARD FAULT ZONE IN WESTERN GEORGIA AND EASTERN ALABAMA:
THE STRATIGRAPHY, STRUCTURE, PETROLOGY, AND GEOCHEMISTRY
IN RELATION TO CATACLASIS
by
Thomas J. Crawford and Jack H. Medlin
INTRODUCTION
Our work in the Piedmont of western Georgia and eastern Alabama during the past eight years has yielded a tremendous amount of data. As is often the circumstance when working on different projects with diverse aims, not all of the raw data can be assimilated, interpreted, and published as rapidly as might be desirable in order that others interested in the same or similar problems have full access to the data.
Some of the interpretations and conclusions which we have published during the past few years are reviewed here , and expanded on the basis of additional data.
REVIEW
Lithologic units and sequences of lithologic units are readily distinguishable in the western Georgia Piedmont, and persist as mappable units over long distances.
In western Georgia, between the Cartersville Fault Zone and the Brevard Fault Zone, lithologic sequences are repeated as a result of folding. These sequences have been traced across areas previously separated into different "metamorphic bPlts ' '- Tall Pdega, Wedowee , Ashland, Tallulah, and Brevard (Crickmay, 1952) . The same lithologic sequences are present in different "belts" (Fig. 1) and have been mapped across "belt'' boundaries, continuing from one "belt" into another. Overall metamorphic grade of the various lithologic units increases progressively southeastward from the Cartersville Fault Zone to. and beyond, thE' Brevard Fault Zone (Crawford and Medlin, 1973).
The western Georgia Piedmont has been fold ed into a series of doubly plunging anticlinoria and synclinoria complicated by regional faulting and metamorphism (Fig. 2). Dominant structural features of the Georgia Piedmont west of Atlanta, between the Cartersville and Brevard Fault Zones, are two anticlinoria and two s-ynclinoria (Crawford and Medlin, 1973). Major folds are of two different styles: (1) overturned (northwest) isoclinal and overturned (northwest) asymmetrical folds; and (2) broad, upright open folds. The upright, open folds occupy a central position between the Cartersville and Brevard Fault Zones.
One of these major structures we have mapped for a distanc e of 80 miles (129 km) and named the Austell-Frolona Anticlinorium (Crawford and Medlin, 1973). This anticlinorium is bordered on the southeast by a high-angle reverse fault (Fig. 2), referred to by Hurst (1973) as the Chattahoochee Fault. A stratigraphic section of approximately 3500-4500 feet (10701370 meters) has been cut out by this fault over a strike distance of about 40 miles (64 km )Douglas County to Heard County (Plate 1; Fig. 2).

UNIT Ill & IV UNIT II UNIT I

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BOUNDARY METAMORPHIC
BELTS OF CRICKMAY (1952)

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Figure 1. The metamorphic belts of Crickmay (1952) compared to the geology of western Georgia, between the Cartersville and Brevard Fault Zones.

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MA..JOR STRUCTURES

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Figure 2. Major strudures between the cartersville and Brevard Fault Zones.

Southeast of the Austell-Frolona Anticlinorium is a narrow synclinorium with doubly plunging synclinal folds overturned to the northwest. This synclinorium, which we name here the Centralhatchee Synclinorium (Plate 1; Fig. 2) is bounded on the northwest by the Chattahoochee Fault and on the southeast by the Long Island Fault over a strike of about 50 miles (80 km)-Douglas County to Heard County.
The lithostratigraphic units in the Centralhatchee Synclinorium correlate in part with stratigraphy presented by Higgins (1966, 1968) for the Atlanta area-the Sandy Springs Sequence (Fig. 3). The Sandy Springs Sequence also correlates with rock units which flank the Carroll-Paulding Synclinorium (Crawford and Medlin, 1973); with rock units southeast of the Brevard Fault Zone (Medlin and Crawford, open-file maps, Ga. Geol. Survey); and possibly with rocks adjacent to the Cartersville Fault Zone in Polk. Paulding, and Bartow Counties (Crawford and Medlin, 1970; 1973).
In western Georgia and eastern Alabama, we have used the term "Brevard" to refer to a fault zone, the Brevard Fault Zone, which we define as a "linear zone of penetrative movement". In this area, Lhe Brevard Fault Zone extends from Atlanta southwestward across Georgia and into eastern Alabama near Roanoke, crossing stratigraphic and structural entities (Plate 1).
Work along some 80 miles (130 km) of the Brevard Fault Zone in Cobb, Douglas, Fulton, Coweta, Carroll, and Heard Counties, Georgia and Randolph and Chambers Counties, Alabama has revealed a mappable lithostratigraphy within the fault zone (Medlin and Crawford, 1973b). Detailed lithostratigraphic mapping indicates that the rocks within the "Bremrd belt" in western Georgia and eastern Alabama can be divided into nine lithologic units (Figs. 3 & 4), which define a synclinorium more than 80 miles (130 km) in length, the Centralhatchee Synclinorium (Plate 1). This detailed mapping has outlined overturned, asymmetrical, doubly plunging synclines within the Brevard Fault Zone.
All lithologic units within the Brevard Fault Zone have been regionally metamorphosed to staurolite-kyanite grade, or higher; and subsequently retrograded, in part, by (the Brevard) cataclastic event(s). They are of the same metamorphic grade as that of adjacent rocks outside the Brevard Fault Zone. The presence, abundance, or absence of metamorphic index minerals in individual rock units both within and outside the Brevard Fault Zone reflects not only metamorphic conditions but original rock composition as well (Medlin and Crawford, 1973b).
Retrogressive metamorphism is indicated by the widespread occurrence of chlorite replacement of biotite and amphibole, and muscovite replacement of kyanite and staurolite . Chlorite is particularly abundant in rocks associated with major shear zones and with alteration zones (Hurst and Crawford, 1969). Tourmaline is widespread, in association with major shear zones and with zones of alteration throughout the western Georgia Piedmont, as disseminated euhedral crystals, and as fibrous masses closely associated with vein quartz.
Deformation produced a well-developed catadastic foliation, button schists, phyllonites, mylonites, ultramylonites, and blastomylonites. Zones that have been intensely sheared and granulated alternate with zones that have undergone little or no cataclastic deformation. Within zones of intense shearing, the cataclastic foliation becomes the dominant s-surface, and lithologic differentiation in addition to structural or textural mapping is essential for stratigraphic and structural interpretations (Medlin and Crawford, 1973b).
Megabreccias are present in some areas, but for the most part, cataclasis has resulted in textural changes that include: shredding of the micas; granulation of quartz, garnet,
1-4

Crawford & Medlin This report

Crawford & Medlin & Medlin, 1973 Crawford, 1974

Higgins, 1966, 1968

Hurst, 1973

Mt. Olive Church

Adamson quartzite

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Backbone schist

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Anneewakee graphitic schist- "-0.

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Dry Creek quartzite

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Chapel Hill Church

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Mt. Vernon Church graphitic

schist -q u a r t z i t e

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Yellow Dirt gneiss

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TGneiss, schist, amphibolite

porphyroclastic biotite-quartz feldspar aneiss

Mylonite gneiss

not shown

Bentley & Neathery 1970
Jackson's Gap Group
not mapped

Austell gneiss (includes Union Grove Church schist)
Bill Arp
Frolona

UNIT II UNIT I

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Austell granitic gneiss

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I

not present

A

Ashland Group (part)
Wedowee Formation

not present

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Centralhatchee Formation

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Figure 3 _ Correlation chart of stratigraphy in the field trip area_

Sparks Reservoir I1000-2000)
Dry Creek quartzite (250-300)
Union Grove Church schist (200-300) Austell gneiss (600L:

Mt. Olive Church (950+) Adamson quartzite (200-4501 Backbone schist (500-1600)
Ano~eewakee graphitic schist-quartzite ( 150-250)
vl'll"lll Dirt gneiss Long Island Fault
Chapel Hill Church (1600-2000)
Mt. Vornon Church graphitic ochiot quortzite (250-650) Mt. Vernon Church schist (1500+1
Chattahoochee Fault
Bill Arp (9000+1

Frolona (5000+)
Figure 4. Stratigraphic column for the field trip area. 1-6

microcline, and plagioclase; button-shaped concentrations of graphite in the graphitic schists; changes in the shape of quartz (augen), feldspar (augen), micas (bent), kyanite (bent), garnets (flattened, sheared into thin plates), and staurolite (flattened). It is the combinations of these textural changes, combined with good development of a cataclastic foliation in some places, that has produced button schist, phyllonite, mylonite, ultramylonite, and blastomylonite. These are quite well documented by Higgins (1971). Mineralogically, there is little, if any, difference between rocks within the cataclastic zones and rocks outside the zones (Table 7). Cataclastic deformation was accompanied by little overall chemical change in the affected rocks, although locally there has been considerable addition of silica (Table 7, Fig. 5).
A zone of intense cataclastic deformation (within the Brevard Fault Zone) coincides with a pronounced topographic lineament. It intersects the lithostratigraphic trends at a slight angle. In Douglas County and part of Carroll County, this zone of intense cataclasis is southeast of the Sandy Springs Sequence. Southwestward, this zone of intense cataclasis enters the Sandy Springs Sequence and maintains that position to central Heard County where it crosses to the northwest side of the Sequence (Plate 1 ). There is no evidence to indicate that displacement accompanied cataclasis. To the contrary, where this zone of intense cataclasis crosses lithostratigraphic units and structural entities (faults and fold axes), no offset can be demonstrated (Medlin and Crawford, 1973b).
In Douglas County, Georgia and Randolph County, Alabama, cataclastic deformation of the Brevard Fault Zone is distributed over a broader area than in the intervening 49 miles (80 km). Splaying of the cataclastic zones coincides with the opening of major folds in the Sandy Springs Sequence (opening of the Centralhatchee Synclinorium), and the beginning of closure in the Austell-Frolona Anticlinorium (Plate 1). Recent work (maps on open file at the Ga. Geol. Survey) has shown south-trending splays which depart from the Brevard Shear Zone on the southeast side and continue southward in the vicinity of Campbellton, Whitesburg, Franklin, and Waresville.
Cataclastic deformation in this part of the Piedmont was later than the major folding episode(s), and probably occurred during the waning stages of regional metamorphism. Small-scale folds in mylonites indicate some post-cataclasis compression (Medlin and Crawford, 1973b).
Field data indicate that the orientation of the Brevard Fault Zone, the Cartersville Fault Zone, and major shear zones between these regional zones of breakage were controlled by fold patterns; that regional breaks parallel the flanks of anticlinoria and synclinoria, with spurs or splays departing these regional breaks and extending across saddle areas (Crawford and Medlin, 1973).
Along the Cartersville Fault Zone there are several north-trending departures from the northeast regional structural trend (Crawford and Medlin, 1970; 1973). These changes in trend of the Cartersville Fault Zone coincide, generally, with north-trending major shear zones within the Piedmont and with the alignment of north-trending subsidiary shear zones which branch from the Brevard Fault Zone across the noses of regional folds (Fig. 2; Plate 1 ).
Faulting in this area appears to have been controlled by major fold structures, such as the Austell-Frolona Anticlinorium and the Centralhatchee Synclinorium (Plate 1 ); and not stratigraphically controlled, except to the extent that spatial distribution of stratigraphic units is fold-controlled.
Finally, in the western Georgia-eastern Alabama Piedmont, present data indicate that there is not a great discontinuity across the Brevard Fault Zone.
1-7

Figure 5. Flinty erush roek derived from the Yellow Dirt gneiss; exposure at Mile 52.25.
1-8

STRATIGRAPHY
The stratigraphy of the field trip area has been presented in a rather general fashion in several recent publications (Crawford and Medlin, 1973; Medlin and Crawford, 1973b; Bentley and Neathery, 1970) and, for a part of the field trip area, presented by Higgins in 1966. However, in these publications few formal names, well-defined and specific in delineation, have been forthcoming. In this section of the Guidebook, we attempt to define the lithostratigraphic units in some detail and for purpose of discussion have attached geographic names to them. This should provide workers from adjacent areas with a basis for correlating with a stratigraphy that we have spent some eight years developing and have mapped for a distance of some 80 miles (128 km) along strike in Georgia and Alabama. We hope that it will also provide impetus for further stratigraphic and structural work in these two states during the next few years.
We are aware of the very real problem of proliferation of "names" in geological literature. However, because this is a field trip guidebook, we feel some freedom in the use of unit names to facilitate the presentation of data as clearly as possible. The names are, of course, used informally at this time, and in this guidebook format.
Figure 3 is a correlation chart for the lithostratigraphy in the western Georgia-eastern Alabama Piedmont, showing probable correlations with the units of other workers in the same general areas.
The oldest rocks in the stratigraphic sequence in this part of the western Georgia Piedmont are those comprising the Frolona. This unit is named for the community of Frolona, Heard County, Georgia, where the lithologies are very well developed and exposed. The rocks comprising this unit occupy parts of Carroll and Heard Counties, Georgia and part of Randolph County, Alabama. They have a general northeast strike and compose the core of the Austell-Frolona Anticlinorium which has a length of more than 80 miles (128 km) in the western Georgia-eastern Alabama Piedmont. The thickness of the Frolona is estimated to be approximately 5000 feet (1525 m). It consists of the following rock types, interlayered: graphitic staurolite-kyanite-garnet-feldspar-quartz-muscovite schist, nongraphitic mica schist, feldspathic micaceous quartzite, clean quartzite, and quartz-pebble metaconglomerate. The quartzites are fine to coarse grained, commonly feldspathic and micaceous. Layers of quartz-pebble metaconglomerate contain elongate pebbles as large as 8 x 20 mm in a quartz-feldspar-mica matrix.
Overlying the Frolona is a unit herein designated the Bill Arp. The unit is named for the community of Bill Arp, Douglas County, Georgia, where it is well exposed. The Bill Arp is the most extensive unit in this part of the western Georgia-eastern Alabama Piedmont. From Douglas County it extends southwestward through Carroll and Heard Counties, Georgia and into Randolph County, Alabama. Over most of this outcrop distance it is overturned to the northwest except in Douglas County, Georgia where it is exposed on the nose of the northeasterly plunging Austell-Frolona Anticlinorium which is upright and open in this area. The unit is approximately 9000 feet (2745 m) thi'ck. It consists of several rock types: quartz-muscovite-biotite schist, with some layers composed almost entirely of mica, alternating with muscovite-biotite-quartz-feldspar geniss and schist, sericite schist, and micaceous quartzite; quartzose-feldspathic layers are dominant. Mafic layers are rare, thin and discontinuous where present. Porphyroblastic mica cuts across schistosity and layering, and fractures are filled with coarse mica. Garnets are scarl:e, small where present. Thin layers of sericite schist contain abundant finely disseminated magnetite and ilmenite; coarse ilmenite is associated with vein quartz.
In parts of Douglas County and all of its outcrop in Carroll and Heard Counties, Georgia and in Randolph County, Alabama, the Bill Arp is truncated on the southeast by the Chattahoochee Fault (Crawford and Medlin, 1973; Hurst, 1973).
1-9

Above the Bill Arp and perhaps correlative in part is a rock unit herein designated the Austell Gneiss. The rock is named for the town of Austell in Douglas County, Georgia where it is well exposed. The name is not new except that we substitute the term gneiss for granite gneiss as originally used by Hayes (1901). A detailed description of this rock unit is presented in a discussion of the Austell gneiss. Briefly, the Austell Gneiss is composed of two granitic gneiss units separated by a quartz-muscovite schist unit herein referred to as the Union Grove Church Schist (of the Austell Gneiss). This schist unit is 200 to 300 feet (60 to 90 m) thick and wraps around the nose of the A ustell-Frolona Anticlinorium. It is well exposed at Union Grove Church in Douglas County, Georgia. The Austell Gneiss is approximately 6000 feet (1830 m) in thickness.
Overlying the Austell Gneiss and in fault contact is a unit herein designated the Mt. Vernon Church Schist. This unit is well exposed in the vicinity of Mt. Vernon Church in Douglas County, Georgia. It consists of a tourmaline-garnet-kyanite-muscovite-quartz schist, medium grained, with finely disseminated magnetite; interlayered with plagioclasehornblende gneiss and thin layers of magnetitic quartzite. The magnetitic quartzite is only locally present, and the percentage of the unit comprised of hornblende gneisses varies greatly. The bottom of the Mt. Vernon Church Schist is not exposed because of truncation by the Chattahoochee Fault. The thickness of the exposed part of this unit is approximately 1500 feet (460 m).
Overlying the Mt. Vernon Church schist is the Mt. Vernon Church graphitir~ schistquartzite. This unit consists of garnet-staurolite-kyanite-graphite-quartz-muscovite schist interlayered with quartz-rich muscovite schist, and fine-grained feldspathic quartzite; millimeter-scale layering is well-developed in the quartzites. Minor chloritic quartzplagioclase-hornblende gneiss occurs locally. The thickness of this unit ranges from 250 to 650 feet (75 to 200m).
Above the Mt. Vernon Church graphitic schist-quartzite is the Chapel Hill Church unit. This unit is well exposed in roadcuts south of Chapel Hill Church in Douglas County, Georgia. The following lithologies compose this unit: biotite-quartz-feldspar geniss, fine to medium grained, with feldspar porphyroblasts in part; interlayered with tourmaline-garnet-muscovite schist, muscovite-biotite-quartz schist, and plagioclase-hornblende gneiss. These appear to be intertonguing facies, with lateral variations in dominant facies. Scattered thin pegmatites of garnet, tourmaline, quartz, and feldspar are present. The unit ranges from 1600 to 2000 feet (490 to 610 m) in thickness.
The Dry Creek quartzite overlies the Chapel Hill Chruch unit. This name comes from good exposures south and southeast of Dry Creek, Douglas County, Georgia. The unit consists of quartzite, graphitic garnet-quartz-muscovite schist, muscovite quartzite, and muscovite-quartz schist, interlayered. Also present are thin discontinuous layers of plagioclase-hornblende gneiss. The unit is 250 to 300 feet (76 to 90 m) thick.
Overlying the Dry Creek quartzite is the Sparks Reservoir unit, so named because of the excellent exposure in the vicinity. of the Douglas County (George Sparks) reservoir. This unit consists of the following rock types: garnet-biotite-muscovite-quartz schist and biotitequartz-feldspar gneiss, interlayered with plagioclase-hornblende gneiss. These lithologies grade laterally into quartzose-feldspathic gneiss equivalents and, locally, muscovite schist with small amounts of garnet, quartz, or feldspar. The rock unit is estimated to be 1000 to 2000 feet (300-600 m) thick.
The Anneewakee graphitic schist-quartzite overlies the Sparks Reservoir unit. The name arises from the excellent exposures in the vicinity of the Anneewakee Community in Douglas County, Georgia, particularly along Anneewakee Road. The unit is composed of the
1-10

following rock types: graphitic schist, quartzite, kyanite-garnet-quartz-muscovite schist, and muscovitic quartzite, interlayered; graphite, garnet, kyanite, quartz, and muscovite vary in percentage and size; lateral facies changes are prevalent. Quartzites are fine to medium grained, with well-developed layering. The unit ranges from 150 to 250 feet (45 to 75 m) in thickness.
Above the Anneewakee graphitic schist-quartzite is the Backbone schist. This name is derived from the areas of good exposure along the northwestern side of Backbone Ridge, in southwestern Heard County, Georgia. The unit consists of biotite-garnet-muscovite-quartzfeldspar schist, fine to coarse grained, interlayered with minor fine- to medium-grained garnet-biotite-muscovite-quartz-feldspar gneiss. Kyanite is common. Thin stringers of hornblende-plagioclase gneiss are present, but rare. The estimated thickness of the Backbone schist is 500 to 1600 feet (150-485 m).
The Adamson quartzite is above the Backbone schist. The designation is from the community of Adamson, Heard County, Georgia. This unit consists of graphitic schist, quartzite, muscovitic quartzite, and muscovite-quartz-feldspa.r schist, with scarce hornblendeplagioclase gneiss. Quartzites grade laterally into micaceous quartzites and quartz-rich schists. Kyanite is common. The quartzites are fine to medium grained, thinly layered, and contain graphite. The estimated thickness of the Adamson is 200 to 450 feet (60 to 135m).
The youngest rock unit in the Centralhatchee Synclinorium we refer to herein as the Mt. Olive Church for good exposures near Mt. Olive Church in Heard County, Georgia. This unit is composed of kyanite-quartz-garnet-biotite-muscovite schist, interlayered with biotitequartz-feldspar gneiss, and lesser amounts of hornblende-plagioclase gneiss. The top of the unit is not exposed. Estimated thickness is 950 (+) feet (290+ m ).
One of the most distinctive lithologic units in the field trip area is referred to here as the Yellow Dirt gneiss, named for the community of Yellow Dirt in Heard County, Georgia. A detailed description of this unit is given in the section on granitic gneisses. Briefly, the rock is a biotite-epidote-muscovite-quartz-plagioclase-microcline gneiss; fine to medium grained with local development of microcline porphyroclasts (augen-shaped) which range from 5 to 25 mm across. The rock is normally light gray to pink in color and in much of the field trip area has a well-developed cataclastic foliation. Thickness is estimated to be 250 to 800 (+)feet (7 5 to 240 m) . Structural data indicate that the Yellow Dirt gneiss is equivalent to or younger than the Austell gneiss, and older than the Mt. Vernon Church schist. Probably it is a part of the Sandy Springs sequence, but present data are not sufficient to determine exact position in the sequence. The Yellow Dirt gneiss has been traced for a distance of some 80 miles (50 km) along strike. It includes the mylonitic gneiss of Higgins (1966, p. 36; 1968). We place a fault, the Long Island Fault of Higgins (1966, p. 1517; 1968), along the northwest side of the Yellow Dirt gneiss. Part of the Sandy Springs sequence is faulted out along this boundary.
Ultramafic pods that occur in the metasedimentary-metavolcanic pile are extensively altered to chlorite, serpentine, and anthophyllite.
GEOCHEMISTRY AND MINERALOGY
The lithostratigraphic units in the western Georgia-eastern Alabama area are quite variable, both within particular units as well as laterally in all rock units. Because of this variation and the need for relating mineralogy, metamorphic grade, cataclasis, etc. to chemistry, rock samples were collected and studied both petrographically and chemically. In the following sections, the mineralogy, textures, and chemistry of these samples are
1-11

presented and discussed very briefly. The discussion is presented in part from a regional basis. Therefore, quartzites, schists, "granitic gneisses", and amphibolites/hornblende gneisses from Cobb, Douglas, Carroll, Coweta, and Heard Counties, Georgia and Randolph and Chambers Counties, Alabama are discussed together under the appropriate rock heading. Similar sections are presented on rock units studies in more detail-the Austell gneiss and the Yellow Dirt gneiss. Sample localities are shown on Plate 1. Future work will be directed toward the examination of the mineralogy, textures, and chemistry of each individual rock unit and relating these parameters to original differences both vertically and laterally within rock units; and to changes in mineral chemistry with metamorphism.
QUARTZITES
Microscopically and megascopically the quartzites in the field trip area range from white to dark grey in color. The color and appearance of the rocks apparently reflect the amount of iron present and the degree of weathering. The grain size of the quartzites ranges from fine to medium. The presence or absence of distinct layering is dependent upon the amount of mica present and the degree to which the rocks have been subjected to cataclasis. The most abundant minerals in the rocks are quartz and muscovite. Other minerals present in accessory amounts include epidote, sericitized plagioclase, opaque minerals, chlorite, biotite, garnet, tourmaline and, rarely, zircon.
Sample DCM 351 (Fig. 6) displays anhedral elongate garnets which define the layering in the quartzite. Biotite is normally scarce, but where present it is typically intergrown with chlorite and opaque minerals, suggesting an alteration of the biotite. This is especially noticeable in those rocks that have a cataclastic texture. Muscovite in almost all samples delineates the layering in the quartzites and in most rocks comprises approximately 1 to 5 volume percent of the rock. Epidote, though scarce, commonly occurs in association with biotite and chlorite.
Quartz shows evidence of strain in all specimens, including the noncataclastic samples. Undulose extinction and sutured grain boundaries are common. In the mylonitic quartzites (HCM 262, HCM 269, CACM 827), two S-surfaces are defined by strained and granulated quartz and deformed muscovite. In places (CACM 827) crinkle folds as well as the strain in the quartz define two S-surfaces.
One sample, DCM 228, comes from the magnetitic quartzites previously outlined by Higgins (1966; 1968) in Douglas County. This rock is normally fine grained, black, and_ contains muscovite in addition to magnetite and quartz. In this sample (Fig. 7), magnetite defines the layering.
Chemically, the quartzites (Table 1) contain 82.2 to 97.2 percent Si02 However, with but eight exceptions, all of the analyses show the Si02 content to be greater than 92 percent. Those samples which have Si02 values above approximately 95 percent would have been orthoquartzites before metamorphism according to Pettijohn (1963, cf Table 12). In summary, all samples would be either arkoses or orthoquartzites using Pettijohn's data. A very cursory comparison of the data for those quartzites which have been subjected to cataclasis with data for those which have not suggest that little if any chemical mobilization took place during the cataclasis. Those samples containing higher than normal Al 20 3 , Fe 2 0 3 , Na2 0, and K2 0 contain abnormal amounts of feldspar, muscovite, magnetite, and garnet. This is supported by thin-section studies. On the basis of distribution, mineralogy, and geochemistry, there seems to be little doubt that these rocks were derived from quartz-rich sandstones.
SCHISTS
Modal analyses of selected schist samples show that the rocks are composed mostly of four minerals-quartz, plagioclase, biotite, and muscovite (Table 2 and Figure 8). A cursory
1-12

Figure 6. Anhedral, elongate garnets parallel to layering in quartzite (DCM 351). Other minerals include muscovite (light gray) and quartz (white). Photomicrograph is approximately 4mm wide.
Figure 7. Magnetitic quartzite (DCM 228). Black magnetite defines layering very well. Photomicrograph is approximately 4mm wide. 1-13

Table 1. Chemical analyses of quartzites from the western Georgia-eastern Alabama Piedmont (analyses by atomic absorption).

Sample No. Si02

Al203 TiQ

F~ 0 3 Mno Mgo CaO Na20 K20

SiO Cr2 0 3 Rb20 Total

CBCM 26

97.1

1.50

0.10

0.30

0.03 0.05 0.21 0.46

0.40 0.021

-

0.001 100.17

DCM66

95.9

2.56

0.16

0.37

0.03 0.13 0.19 0.45

0.90 0.020 0.008 0.004 100.72

DCM 85-A 93.4

3.48

0.18

0.29

0.03 0.09 0.18 2.27

0.34 0.019 0.001 0.000 100.28

DCM 108

95.2

1.38

0.20

0.15

0.03 0.04 0.16 0.24

0.17 0.016 0.006 0.000

97.70

DCM 148

84.0

0.25

0.38 14.00

0.05 0.10 0.16 1.52

0.08 0.015 0.014 0.001 100.59

DCM 157

95.0

2.32

0.49

0.24

0.03 0.07 0.10 2.06

0.57 0.017 0.002 0.002 100.50

DCM 218

96.8

0.56

0.27

0.48

0.02 0.09 0.13 1.73

0.13 0.017 0.002 0.001 100.23

DCM228

82.3

0.32

0.42 14.78

0.04 0.08 0.12 1.72

0.09 0.018 0.007 0.001

99.90

DCM 326

95.2

0.92

0.16

0.76

0.03 0.11 0.16 2.01

0.23 0.017 0.000 0.002

99 .69

DCM 330

94.8

1.00

0.34

0.26

0.03 0.12 0.16 2.06

0.30 0.014 0.002 0.001

99.08

DCM 332

96.8

0.22

0.30

0.30

0.04 0.08 0.17 2.04

0.10 0.015 0.001 0.002 100.07

.......
......

DCM 349-2 84.6

7.21

0.42

2.63

0.07 0.37 0.22 2.27

2.13 0.019 0.002 0.008

99.95

DCM 351

84.8

7.02

0.44

4.09

0.06 0.23 0.24 0.54

1.43 0.024 0.010 0.003

9 8 .8 8

~

CACM 827 92.5

2.80

0.37

0.88

0.02 0.24 0.13 1.57

1.22 0.019 0.000 0.004

99.74

HCM64

97.1

1.60

0.16

1.01

0.04 0.02 0.12 0.46

0.08 0.020 0.009 0.002 100.62

HCM65

93.0

1.10

0.22

0.16

0.02 0.06 0.16 0.24

0.32 0.015 0.005 0.000

95 .30

HCM74

97.2

0.98

0.13

0.19

0.03 0.05 0.12 0.49

0.26 0.020 0.009 0.002

99.48

HCM 240A 83.7

7.99

0.36

0.92

0.02 0.40 0.69 4.00

0.14 0.018 0.019 0.001

98.26

HCM 252A 87.9

4.10

0.47

1.21

0.02 0.10 0.16 0.42

0.88 0.017 0.006 0.002

95.29

HCM 262

93.9

0.45

0.38

1.19

0.02 0.05 0.22 0.32

0.08 0.012 0.014 0.002

96 .64

HCM 269

94.5

0.70

0.35

0.11

0.01 0.07 0.13 0.27

0.32 0.10

0.013 0.002

96.49

RCM 213

94.0

3.20

0.05

1.19

0.03 0.11 0.05 0.80

0.16 <0.001 0.006 0 .002

99.41

RCM 214

95.0

2.02

0.18

1.32

0.05 0.08 0.52 0.83

0.48 <0.001 0.006 0.005 100.48

RCM 221

90.9

4.27

0.56

0.11

0.05 0.52 0.01 0.89

0.91 <0.001 0.005 0.004

98.22

RCM 241A 83 .3

9.72

0.21

1.68

0.05 0.54 0.01 0.82

1.98 <0.001 0.006 0.008

98.3Q_

CACM -Carroll Co., Ga. CBCM - Cobb Co., Ga. DCM - Douglas Co., Ga.

HCM -Heard Co., Ga. RCM -Randolph Co., Ala.

Table 2. Modes of selected schist samples from the field trip area (in volume percent)

Sample No. Qtz.

CBCM 10 73.7

CBCM 20-A 56.0

CBCM 33

39.0

DCM 282 44.3

CACM 820 46 .5

CACM 831 64.0

CACM 837-A 52.5

HCM 251-A 41.5

HCM 256-A 44.5

HCM 256-B 32.0

HCM 259

51.5

HCM 261-B 45.0

HCM 261-C 61.0

HCM 261-D 39.0

HCM 261-E 61.5

HCM 273-A 13.0

Plag.
4.0 4.5 17.3 16.5 4.0 15.0 14.5 19.5 42.0 19.5 17.0 7.0 37.0 19.0 20.0

Muse. 23.3 30.0 46.0 22.4 1 9 .0 23 .0 18.5 23.5 9.0 18.5 12.0 17.5 1l.O 2.0 6.5 47.0

Biot. 1.0 5.0 2.5
10.0 1 8 .0
13.5 14.0 26.0
4.5 13.5 18.5 14.5 13.0 11.5
8.5

Gar. 1.0 4.5 6.5 4.0 Tr. 2.5 Tr.
Tr. 1.5 2.5 Tr. 5.5 7.0 Tr. 9.0

Staur. Tr. Tr.
Tr. 3.5
Tr.

Epi. Opaq.+Acc. K-spar.

1.0

.5

1.5

2.0

Tr.

6.5

.5

2.0

1.0

1.0

.5

1.0

1.0

2.0

1.0

2.0

Tr.

Tr.

1.5

1.5

Tr.

1-15

view of Table 2 and Figure 8 indicates that the quartz percentage ranges from around 45 to 75 volume percent. Plagioclase ranges from around 4 to 20 volume percent. The biotite+ muscovite content ranges from around 15 to 40 volume percent. Lesser amounts of green tourmaline, garnet, staurolite, epidote, sphene, opaque minerals, microcline, and zircon occur in some of the rock samples; kyanite and graphite are prevalent in some samples.
Thin-sections reveal that biotite and muscovite are commonly intergrown and have associated intergrowths of opaque minerals and, rarely, epidote. Commonly, the muscovite in the mylonitic rocks occurs as overlapping sheaves which, along with two S-surfaces, define muscovite buttons (Figs. 9, 10, & 11). In the cataclastic rocks, shredding and strewing out of the micas are common. Garnets occur in at least two forms-elongate and rounded to euhedral (Fig. 12). They also show mortar textures locally in the mylonitic specimens. The elongate, poikiloblastic garnets (Figs. 13, 14 & 15) are unusual in that they occur both in rocks subjected to cataclasis and those which occur outside the cataclastic zones. Where affected by cataclasis, the garnets commonly show little evidence of alteration to chlorite or biotite. They are uncommonly fresh.
Staurolite occurs as straw-yellow to tan porphyroblasts commonly associated with muscovite-biotite bundles in the schist. Few specimens reveal any cataclastic deformation of staurolite and it, as the garnets, displays little alteration.
Quartz and the feldspars commonly occur as augen (Fig. 16) in the schist and also as fine-grained layers separated by folia of the micas. Quartz in the unsheared rocks normally displays undulatory extinction and sutured boundaries. These same features also occur in the mylonitic rocks, but quartz is, in addition, granulated and smeared. Commonly two directions of undulatory extinction or smearing of the quartz are observed in those rocks subjected to cataclastic deformation.
Plagioclase is the dominant feldspar in all of the schist; microcline occurs only rarely and then in trace amounts. The plagioclase occurs both in the groundmass of the schist and as porphyroblasts and porphyroclasts (augen-shaped) in the cataclastic rocks. Twinning is common in some specimens. Extinction angle measurements 1x indicate that the composition ranges from An20 to An 30 In the mylonitic rocks, the plagioclase grains display bent twin lamellae, undulatory extinction and a mortar texture (Fig. 17, sample 284). The plagioclase appears to withstand cataclasis to a greater degree than either the quartz or the microcline. This conclusion results from petrographic observations on both feldspars and quartz in the gneisses and schists subjected to cataclastic deformation.
Thin-section examinations also suggest that the feldspars underwent little hydrothermal alteration during cataclasis. This is supported by the near absence of sericite or epidote in the plagioclase and the absence of sericite in or around the K-feldspar. Alternatively, cataclasis took place at temperatures above that at which the feldspars break down to sericite and epidote. The scarcity of chlorite or biotite alteration of the garnets and the rarity of chlorite alteration of the biotite flakes also suggest a near lack of hydrothermal alteration. However, chlorite is a common accessory in the hornblende gneisses and amphibolites, and in all the more mafic and ultramafic rocks which occur in or near the zones of intense cataclasis, even though it appears to be near absent in the more quartzose-feldspathic gneisses and schists.
Within zones of intense cataclasis, garnet, biotite, and graphite commonly form buttons in the deformed rocks. Commonly the garnets are flattened and sheared into thin platelets which, superficially, do not resemble garnets. In many specimens, these garnet buttons are encapsulated in strewn-out mica flakes. Biotite buttons normally are very similar to the muscovite buttons; that is, they are composed of overlapping sheaves of biotite. Graphite buttons are normally of the same shape and dimensions as the otl;ler types of buttons, but in some cases may be more strewn out, producing a streaky texture.
1-16

QTZ











1-'

I
1-' ....::J











PLAG

MU+SC
810

Figure 8. Triangular plot of Quartz-Plagioclase-Muscovite+Biotite modes from selected schist samples in the field trip area.

Figure 9. Photomicrograph of mylonitic schist (HCM 4) showing muscovite buttons. Width of field is approximately 6mm.
1-18

Figure 10. Enlargement of muscovite button shown in Fig. 9. Note the fine grain size of the surrounding constitutents, as well as the sheaves of muscovite flakes forming the button. Width of field is approximately 3mm.
Figure 11. Crinkle folds in mylonitic schist (CACM 837A). Note the two S-surfaces. Width of field is approximately 6mm. 1-19

Figure 12. Flattened and rounded garnets from a mylonitic schist (CACM 837B). Note also the development of quartz augen and the poorly defined mica buttons. Width of field is approximately 6mm.
Figure 13. Elongate, anhedral poikiloblastic garnets from schist sample (CBCM 20A); not associated with cataclasis. Compare with Figures 14 and 15. Width of field is approximately 6mm. 1-20

Figure 14. Elongate poikiloblastic (clastic) garnet from a mylonitic schist (HCM 261B). Width of field is approximately 6mm.
J.

--- _-.,--.;
, ...
Figure 15. Elongate poikiloblastic (clastic) garnet from a mylonitic schist (HCM 261D). Width of field is approximately 6mm. 1-21

Table 3. Chemical analyses of schists in the western Georgia-eastern Alabama Piedmont (analyses by atomic absorption).

Sample No.
CACM 473 CACM 821 CACM 826-B CACM 832 CACM 837-A CACM 837-B CACM 840-B CACM 05 CCM 5-B CCM 6 CCM 103 CCM 128 CCM 128A CCM 131 CCM 142C CCM 153 CCM 154 CCM 157 CBCM 5 CBCM 10 CBCM 19-A CBCM 20-A CBCM 33 CBCM 62-A CBCM 62-E DCM 2-A DCM7-A DCM 14 DCM 15 DCM 22-1 DCM 27-2 DCM 39-2 DCM67 DCM 85-B DCM 100 DCM 105-2 DCM 109 DCM 110 DCM 1 56 DCM 190-A DCM 190-B DCM 258 DCM 282 DCM 284 DCM 298 DCM 302 DCM 333 DCM 334 HCM4 HCM 34-A HCM 123 HCM 148 HCM 177 liCM 251-A HOM 258-A HCM 261-B HCM 261-C

SiO,
60.4 79.9 63.0 57.5 72.3 61.9 61.3 52.7 74.1 75.7 66.2 86.4 86.4 71.6 65.8 76.5 76.7 76.4 65.5 80 .6 69.3 72.5 63.3 59.0 59.3 41.8 42.1 41.9 63.4 52 .5 41.8 46.7 74.5 76.7 41.6 54.3 43.8 57.5 75.2 58.9 69.1 63.5 70.3 39.5 67.1 58.0 62.4 67.2 79.2 59.0 71.1 74.6 63.0 61.1 58.3 69 .0 71.8

AI , 0 3 16.88
9.29 17.40 16.84 12.11 17 .55 17.12 41.50 11.66 11.25 16.01
3.97 5.09 16.62 15.52 12.32 7 .14 12.91 1 5 .6 8 8.92 9.18 10.97 17.70 14.49 17.43 28:80 28.20 29.37 17 .6 4 19.92 27 .71 23 .46 11 .56 13.79 33.66 24 .09 28.04 19.50 15.92 16.50 13.84 15.26 14.81 8.60 15.19 19.56 17.46 14.26 9.44 17.96 9.54 12.42 15.80 17.34 17 .98 12.57 13.03

'J'iO,
0.98 0.73 1.10 1.55 0.84 1.01 1.14 0 .28 1.48 1.30 0.62 0.55 0.44 1.25
.72 0.12 0.36 0.39 0 .82 0.56 0.93 0 .64 1.12 0.71
.84 1.53 1.58 2.02 0.83 1.37 1.80 1.13 0.70 0.58 1.72 1.14 1.33 0.81 0.31
.79 0 .8 7 0.62 0 .7 5 0.30 0.89 1.13
.90 0.87
.49 0.96 0.52 0.37 0.77 1.11 0 .9 9 0.99 0 .73

Fe, O,
8.52 2.54 6.94 8.90 4.55 7 .6 8 6.82 0.82 4.18 4.58 3.33 0.61 1.01 2.14 5.89 1.32 2.72 1.80 6.82 3.99 2.91 6.02 7.39 17.49 7.03 5.60 9.72 5.84 5.63 9.51 8.24 8.15 5.24 1.11 3.48 6.50 12.43 7.54
.49 9.90 2.93 6.00 5 .6 4 12.04 6.39 7.61 6.56 4.98 3.15 7.01 3.84 3.05 7.29 5.37 7.53 5.60 6.57

Mno
0.19 0.04
.11 0.17 0.10 0.11 0.14 0 .0 3 0.09 0.10 0.08 0.03 0.02 0.06
.18 .03 0.09 0 .0 4 0 .0 5 0 .0 6 0.03 .08 .10 .36 .10 .03 .03 .03 .05 .13 .06 .06 .15 .03 .02 .06 0.03 .13 .02 .47 0.05 .17 .06 0.18 .06 .11 .05 0.06 .04 0.11 0.05 0.05 0.07 0 .1 0 0.12 0.08 0.08

Mgo
2.50 0.34
.43 3.30 1.16 2.67 1.65 0.15 1.36 1.16 1.31 0.14 0.24 0.60 1.51 1.10 2.44 0.89 2.97 0 .57 0 .47 1.27
.57 2.28 2 .32 2.17
.91 1.20 1.58 3 .0 8 1.91 1.92 1.05
.40 .90 .83 0.73 2.46 .16 2.21 1.31 1.82 1.49 24.40 1.58 1.91 1.89 1.47 .28 2.70 0 .75 0.57 2.69 2.03 3 .2 3 1.89 1.70

CaO 1.23 0.15
.13 2.30 1.21 0 .26 1.08 0.43 0.66 1.19 3.09 0.11 0.14 0.13 1.67
.12 0.29 0.15 0 .55 0.25 0 .20
.40 .14 1.48 .45 .30 .18 .19 .19 1.98 .22 .12 .71 .12 .19 .26 0.20 .89 .20 1.40 0.21 .68 .49 2.48 .31 .53 .58 0.47 .11 1.55 0.59 1.33 1.91 0.55 i .24 0.85 0.62

Na, o
4.91 1.56
.75 4.22 3.13 2.13 2.42 0.91 1.87 2.28 4.04 0.50 0.54 0.88 5.60 1.19 1.37 0.93 1.42 0.69 0.85 1.18
.95 .76 1.33 2.81 2.67 2.70 2.27 3 .61 2.55 .90 3.20 1.02 3.72 2.98 1.41 .93 2.28 1.47 2.64 1.19 1.97 0.41 3.08 1.47 2.96 1.06 .78 2.05 1.05 5.77 2.57 1.42 1.51 1.60 1.44

K, O
2.84 2.25 3.45 3.43 3.36 4 .14 4 .63 1.98 2.90 1.47 3.55 0.91 0.76 3.04
.12 2.10 1.80 2.70 0 .12 1.64 4.06 2.54 4.62 2.07 4.09 6.98 6.00 7.72 4.41 5.40 8 .0 4 6.96 2.18 3.09 7.46 5.54 7.14 6.22 4.54 4.10 2.03 3 .91 2.98 0 .10 2.93 4.76 3.42 3.23 2.47 4.13 1.96 0.24 3.72 3.42 4 .77 2.72 2.65

SrO .032 .023 .026 .038 .025 .023 .032 .031 .028 .040 .076 .016 .002 .020 .027 .007 .033 .016 .038 .028 .047 .019 .042 .030 .019 .045 .024 .02 2 .019 .035 .029 .024 .023 .020 .033 .032 .043 .025 .018 .016 .025 .021 .024 .013 0.30 .024
.30 0.20 .020 .034 .022 .026 .019 .024 .026 .022 .015

Cr2 O, .008 .005 .001 .010 .oo8 .007 009 .012 .017 .017 .015 .016 .013 .016 .002 .002 .010 .015 .012 .010 .012 .001 .002 .001 .001 .002 .002 .002 .002 .002 .002 .002 .002 .002 .002 .001 .016 .001 .002 .001 .009 .001 .001 .205 .002 .002 .002 .013 .002 .011 .013 .008 .017 .014 .012 .013 .018

Rb, O
.009 .005 .010 .012 .010 .015 .012 .006 .016 .011 .011 .008 .003 .009 .002 .002 .005 .010 .000 .005 .015 .006 .014 .005 .013 .016 .m2 .018 .009 .014 .021 .016 .007 .008 .024 .016 .035 .018 .019 .013 .006 .013 .011 .000 .008 .013 .013 .012 .005 .014 .005 .000 .012 .014 .016 .009 .010

Total '98.60 96.83 98.35 98.27 98.84 97.49 96.35
98.8-5
98.37 99.10 98.34 93 .27 94.65 96.37 97.04 94.78 92.96 96.26 93.98 97 .33 88.01 9 5 .6 3 95.94 9 8 .9 5 92.92 9<L27 91.47 91.01 96.03 97 .55 92 .64 8 9 .4 4 99.3 2 96.87 92.10 95.75 95.21 96.03 9 9 .1 6 95.17 93.03 93 .18 98 .52 88.23 97 .57 95.11 9 6 .2 1 93.64 95.99 95.51 89.45 98.44 99.87 92.48 95.73 95.33 98.67

1-22

Table 3. (continued)

Sample No
HCM 2610 acM 273-A HCM 277-B HCM 278-B RCM3 RCM6 RCMlO RCM28 RCM69 RCM73 RCM74 RCM 79-B RCM 80-A RCM 80-B RCM86 RCM88 RCM 89-B RCM 131 lWM 182-A RCM 136-B RCM 137 RCM 140 RCM l!IZB RCM 152-B RCM 152-C RCM 158 RCM 187 RCM 202-A RCM 202-C RCM 206
RCM 212 RCM 212-B RCM 218 RCM 220 RCM 227 RCM 231 RCM 241-B RCM 241-C RCM 19-23-1A RCM 21-21-1 R.CM 23-201 RCM 1W-105-L-1A RCM 2W-48-Rl RCM .Ht-1 W-105 -L1 RCM 258 RCM 259

70.8 52.1 67.3 61.8 43.4 42.4 75.9 68.1 81.0 78.2 72.0 52.8 64.5 77.5 68.5 64.9 70.9 75.2 70.2 59.2 75.5 90.4 70.8 83.0 82.4 86.1 75.0 70.7 75.0 80.7 75.3 64.5 45 .10 61.6 62.0 70.0 66.8 68.2
63.3 66.3 62.8
81.2
73.8
72.6 75.7 55.7

AI,O, 13.08 22.80 16.96 17.18 15.55 36.30 10.30 11.45
8.35 10.01 12.25 24.96 14.75 10.30 1 2 . 51 14.80 14.80 10.15 14.10 17.04
8.65 6.32 13 .09 6.60 9 .1 2 8.60 12.15 12.90 11.22 12 .3 2 12.00 18.40 33.42 17.35 10.34 14.69 17.55 13.65
15.25 17.98 18.35
8.50
12.90
12.62 11 .82 21.99

Ti 0 2 0.65 1.04 0.93 1.01 1 .28 2.18 0.64 1.10 0.62 0.45 1.49 1.86 1.39 0.74 0.88 1.48 0.88 0.71 0.11 1.47
.22 0 .1 1 0.71 0.37 0.50 0.38 0.13 1.80 0 .15 0.07 0.53 0.86 0.45 0.85 0.77 0.55 0.66 0.71
0.93 0.84 0.96
0.82
0.38
1.21 1.17 1.49

Fe1 0 3 6.11 7 .92 5.22 7 .46 27.16 8.19 5.02 6.92 1.96 2.98 5 .4 6 8 .66 6 .20 4.60 5.05 7 .92 5.86 6.15 1.48 11.55 7.11 1.20 3.48 3.00 .74 1.15 3 .88 4.52 1.40 1.32 5.01 7.20 2.85 7 .85 8.90 3.35 2 .69 5.72

Mno 0.13 0.11 0.07 0.14 0.03 0.03 0.05 0.20 0.03 0.02 0.08 0.05 0.09 0.05 0.10 0.12 0.07 0.04 0.03 .15 .02 0.01 0.03 0.02 .04 0.02 0.06 0.12 0.10 0.05 0.05 0.07 0.02 0.08 0.06 0.06 0.04 0.08

10.42 0.11

7.22

0.14

8 .00

0.09

4.70

0.06

2.60

0.04

3.86

0.10

6.15

0.03

12.04 0.50

Mgo
1.71 2.33 1.19 2.70 0.46 0.86 1.20 1.20 0.69 0.55 1.48 1.93 1.94 1.18 1.33 3 .21 1.26 1.40 0.22
.82 .26 0.33 0.55 0.42 .42 0.29 0.52 2.10 0 .81 0.83 0.59 1.30 0.85 2.68 0.64 0.79 0.44 2.10
1.70 2.08 2.90
0.70
0.59
1.08 0.26 2.06

eao
2.20 0.70 0.63 2.19 0.16 0.20 0.48 1.20 0.14 0.18 0.97 0.52 1.93 0.48 2.32 1.48 0.49 0.45 0.03
.51 .12 0.11 0.10 0.06 .15 0.15 0.01 0.70 0.18 0.01 0.10 0.10 0.07 2.05 0.01 0.01 0.01 0.51
0.21 0.46 0.85
0.88
0.01
0.29 0.12 0.62

Na,O
3.08 1.58 1.77 3.34 0.65 1.55 0.88 1.14 0.46 0.40 2.74 1.02 3.27 2.22 3.48 1.95 1.61 1.75 0.14 1.15
.8 9 0.13 0.22 0.14 1.53 1.30 0 .24 2.86 1.57 0.90 0.89 0.62 1.33 2.77 0.99 0.84 0.97 1.05

K20 1.46 5.60 4.36 3.32 3.32 7.94 2.53 2.87 2.29 2.73 2.74 6.64 2.93 2.92 2.81 2 .3 9 3.65 2.14 4.41 3.51 1.89 1.01 3.65 1.42 3.07 2.00 3.40 2.56 3.74 3.08 3.41 4.30 6.80 3.84 7.40 3.02 2.94 3.78

SrO .024 .028 .040 .054 .026 .035 .004 .006 .020 .008 .029 .028 .031 .006 .032 .023 .022 .008 <. 001 .022 .019 .003 .018 < .001 .022 .003 .004 .017 .014 < .001 .002 .014 .0 11 .029 .002 <.001 .002 .008

Cr,O, .016 .011 .013 .013 <.001 .005 <.001 <.001 <.001 <.001 <.001 .009 <.001 :<:.001 <.001 <.001 <.001 <.001 <.001 .001 .001 .011 <.001 <.001 .001 <.001 <.001 <.001 < .001 .003
.005 .025 .017 <.001 .010 .007 .007 .006

Rb 20 .007 .020 .013 .013 .008 .024 .010 .009 .007 .010 .008 .022 .010 .007 .007 .013 .015 .009 .019 .010 .002 .004 .013 .005 .007 .007 .008 .006 .013 .007
.012 .017 .021 .017 .015 .010 .008 .012

Total 99.27 94.24 98.48 99.21 92.05 99.72 97.00 94.10 99.57 95 .54 99.. 25 98.50 9 7.04 lOO.Ql 97.02 98 .28 99 .56 9 8 .01 99.26 95.42 9 4 .6 8 9 9 .6 3 92.66 95.04 98.00 100.00 95.40 98 .29 95 .12 99.27 97.87 97.41 90.94 99.12 91.1 3 93 .33 92.12 95.83

0.98

3.82

.005

.008

.023

96 .76

1.10

3.75

.020 <.001

.026

99.93

2.45

3.55

.023

.010

.021

1 0 0 .0 0

1.78 1.36

.009 <.001

.006

1 0 0 .0 0

0.63

2.88

.020 <.001

.008

93.86

1.12

2.60

.002

.005

.005

0.09

0.75

.015

.016

.006

1.31

3.60

.024

.016

.020

95.49 96 .14 99.37

CACM - Carroll Co., Ga . CCM -Chambers Co., Ala. CBCM - Cobb Co., Ga. DCM - Douglas Co. , Ga.

HCM - Heard Co., Ga. RCM - Randolph Co. , Ala. COCM- Coweta Co., Ga.

1-23

Figure 16. Augen of quartz and feldspar in mylonitic schist (HCM 256A). Nate also the fine-grained mylonitic groundmass and development of mica buttons. Width of field is approximately 6mm.
Figure 17. Blastomylonitic and mortar textures in schist (HCM 284A) .. Mineral is plagioclase. Note the granulated groundmass. Width of field is approximately 6mm. 1-24

Kyanite normally occurs in trace amounts. Few thin sections show kyanite, but it is quite common as fine grains in the schist residuum throughout the field trip areo. Its color ranges from gray to bluish gray; locally it is black within the graphitic schist-quartzite units. The black color is due to graphite inclusions. Locally, kyanite blades are bent and folded, suggesting a folding episode after kyanite growth. In one place, blades of kyanite were noted to have grown on sheared-garnet platelets.
A compilation of 103 chemical analyses of the various types of schists within the field trip area and the western Georgia-eastern Alabama Piedmont is presented in Table 3. At present, no attempt has been made to separate the graphitic schists from the group. However, they can be generally recognized by their low totals. These low totals occur because the carbon content of the samples has not been determined.
When chemical analyses of schist samples are plotted on a Ca0-Na2O-K 20 triangular diagram, most of the points fall in the lower one-third of the diagram, along the Na 20-K20 base (Fig. 18). This suggests that the samples are low in the calcium component. This is especially well documented when plots of various average shale and slate values taken from the literature are plotted on the same diagram. Most of the average shale values plot much closer to the Ca0-K20 side of the triangle and have much more CaO in them than do the schist samples from the field trip area. A comparison with average graywacke values taken from the literature does not solve the problem; the graywackes are richer in CaO and plot more toward the Na20-Ca0 side of the triangle. With these comparisons, it is evident that either there was some sort of metasomatic activity during the metamorphism of the original rocks, or the schists were derived from rocks of a different composition than that of average shales or graywackes. Possibly they were derived from volcanic rocks or a mixture of volcanic and sedimentary rocks. The presence of probable metabasalts-now hornblende gneisses and amphibolites-within the rock pile or interlayered with the schist lends support to a volcanic origin. In any case, the schists do not plot near the average shale in composition. Thin-section studies do not suggest any textures or mineralogies that would indicate massive metasomatism of Na 20, K20, or CaO. It is very evident from the modal analyses that the high K20 content comes from the presence of much muscovite and biotite. The presence of a lowcalcium, high-sodium plagioclase probably accounts, to a great extent, for the high sodium content and the low calcium values.
An ACF plot of the schist samples (Fig. 19) shows that part of the samples fall within the "Al-rich clays and shales" area of Winkler (1965). However, many fall outside this area, suggesting that if the schists were originally Al-rich shales and clays, they differ considerably from the typical ones presented by Winkle-r. This deviation would be even mote evident if the FeO concentration were known for the samples. The diagram is derived by assuming that all the iron is Fe20 3 The ACF plot and the Ca0-Na20-K20 plot both suggest that the schists were not derived from average shales or clays.
GRANITIC GNEISSES
In the field and in hand specimens studied in detail, rocks placed in this general category, ''granitic gneisses", have a variety of textures, mineralogies and colors. In general, the rocks range from light gray to medium gray in color. They range from fine-grained equigranular to porphyroblastic gneisses with either quartz or the feldspars forming the porphyroblasts in a fine- to medium-grained groundmass. Some of the gneisses have a very poor development of the gneissic texture and could be classified as metagraywackes rather than true gneisses. In places, some of the gneisses have been subjected to cataclasis; effects range from minor granulation to complete granulation and silicification (Figs. 20, 21 ). In the latter case, not only has there been a change in grain size, but a change in .mineralogy and chemistry of the rock. For example, observe the chemical analyses of samples CACM 02 and CACM 03.
1-25

CaO

Schist samples - western Georgia-eastern Alabama
0 Average of Mesozoic and Cenozoic shales (27 samples/1 analysis)
0 Average slate (69 samples) .A. Mudrocks of Russian platform (4030
samples/290 analyses) 0 Average of Paleozoic shales (51 samples/
1 analysis) .6. Mudrocks of Great Caucasus Geosyncline
(11,151 samples/455 analyses)
7'
t-:) (j)

.6.
0 ...


Na,o






.
.... ...,....













e D


~








-'


#

I



K20

Figure 18. Ca0-Na2 O-K2 0 plot of selected schist samples from the field trip area. For comparison, average values for shales, slates, and mudrocks are included (Blatt and others, 1972, Table 11-2, p. 397).

A



..........
















I-'
~
-1

. /









c

F

Figure 19. ACF plot of 81 schist samples from the western Georgia-eastern Alabama Piedmont. For comparison, the area of Al-rich clays and shales from Winkler (1965) is outlined.

Figure 20. Photomicrograph of the myloniti Yellow Dirt gneiss. Note t he microcline porphyroclast in a uniformly granulated ground:mass (CACM 04). Width of field is approximately 6mm.
Figure 21. Photomicrograph of microbreccia formed from the cata lasis and silicifi ation of the Yellow Dirt gneiss. Not ghost-like relicts of th e breccia and the veinlet of quartz. Widt h of field is approximately 6mm. 1-28

Table 4. Modes of selected "granitic" gneiss samples from the field trip area.

Sample No.
CBCM 14 CBCM 16A CBCM 31 CBCM 35 DCM 210 DCM 243 DCM 319 DCM 338 CACM 815 CACM 838 CACM 04 HCM17 HCM19 HCM 231 HCM 273B HCM 288

Qtz.
29.5 38.5 51.5 36.5 30.5 30.5 30.5 45.0 40.0 28.0 38.5 69.5 53.0 36.0 49.5 50.0

Micr; 4 .0 8.0
24.5 4.0 3.0 14.0 17.0 32.0 27 .5 31.5
24.5 40.7
2.5 31.0

Piag.
50.0 34.0 32.0 31.0 47.5 41.0 37.0 12.5 22.0 30.0 28.0 10.0 19.5 20.6 20.0 14.0

Muse.
0.5 2.5 1.0 6.0 4.5 10.5 2.0 8.5 1.5 3.5 1.0 0.7 6.5 1.0

Bio. 13.5 14.5 15.5
17.0 19.5 12.5
9.0 3.5 6.0
17.0 2.0 1.3
24.5 4.0

Epi. Gar. 3.0 5.0
4.5
1.0 6.0 0.5
0.5
0.7 1.0 0.5

Opaq. +Ace. Tr Tr 0.5 1.0
Tr 0.5 Tr Tr Tr Tr Tr Tr Tr 0.5 Tr

CBCM -Cobb County, Georgia DCM - Douglas County, Georgia CACM - Carroll County, Georgia HCM -Heard County, Georgia

1-29

A cursory examination of -the modal analyses of selected "granitic" gneisses given in Table 4 indicates that quartz and plagioclase are the dominant minerals in the rocks; microcline , biotite, and muscovite are prominent phases, also. Varying amounts of epidote, garnet, and opaque minerals comprise the remaining minerals in the rocks. The quartz content ranges from 28 to 69 volume percent; plagioclase from 12 to 50 volume percent; microcline from less than 1 to more than 32 volume percent. Biotite and muscovite occur in amounts ranging up to 24 and 10 volume percent, respectively. When the modes of a select d group of these 'granitic " gneisses is plotted by quartz-microcline-plagioclase content, there js an abundant scatter of samples (Fig. 22). This variability in mineralogy is a reflection of the lumping tog ther of many rocks of variable textures and mineralogies. This ltunping is done in order to give an overview of the "granitic-like" gneisses in the field trip area.
A compilation of 116 chemical analyses of the "granitic" gneisses is given in Table 5. The variation in chemical composition of these gneisses further emphasizes the variation observed in the thin-section studies and in the modal analyses. It should be noted that the cataclastic gneisses, which have been silicified locally, are also included in the compilation and the various plots of the chemical data that follow.
A Ca0-Na20-K20 plot of the granitic gn eiss samples (Fig. 23) shows considerable scatter. For comparison, the fields for quartz-diol"it , granodiorite, granite, quartz monzonite, and Wyomin g graywackes as present d by Condi (1967) are indicated on the diagram. Using Condie's data, t he rocks as a group fall in all of the above categories .
n .Nk-F-M plot of th gn. isses (Fig. 24) reenforces the fact that the gneisses are quite variable in composition . As can be seen, mo t of the samples plot along a trend that is indicative o.f l"O l{S with compositions ranging from granodiorite to granite. Assuming little if any m tasomatism during metamorphism , these data indicate that the source area of these 1ocks was diverse-as diverse as the rock om positions themselves.
AMPHIBOLITES AND HORNBLENDE GNEISSES
Amphibolites and hornblende gneisses are major rock types in the western Georgiaeastern Alabama Piedmont. Although they comprise only a minor part of the total rock section in this area, they are widespread geographically due to repetition by folding. Stratigraphically, the amphibolites and hornblende gneisses occur in the younger lithologic sequences. They are well-exposed in the Carroll-Paulding Synclinorium (Crawford and Medlin, 1973; Hurst, 1973; Hurst and Jones, 1973), and within and to the southeast of the Centralhatchee Synclinorium. These rocks may occur in outcrop either as discontinuous bodies, or as distinct units traceable over a distance of several miles. In places, they are intricately folded as shown by structural attitude readings and outcrop patterns. For the most part, they are pre:;ent in areas which have been metamorphosed to at least the kyanite grade of metamorphism.
The amphibolites and hornblende gneisses are mostly dark green and range from fine to medium grained. For the most part, they are well foliated and locally crinkled. The dominant prograde minerals are plagioclase, blue-green amphibole, and epidote; garnets are scarce; retrograde chlorite is present in minor amounts, particularly in those rocks subjected to cataclastic metamorphism . This cataclastic and retrograde metamorphism is evidenced by a reduction in grain size of the rocks, a development of a good cataclastic foliation, intricate crinkling of the foliation, and the alteration of hornblende to chlorite and epidote, locally.
Table 6 is a compilation of 57 chemical analyses of these metamorphosed mafic rocks in western Georgia-eastern Alabama. Sample locations are shown on Plate 1. A K20 vs.
1-30

QTZ

cto.-",
to-"

MIC

PLAG

Figure 22. Triangular plot of Quartz-Microcline-Plagioclase modes from selected granitic gneiss samples from the field trip area.

Table 5. Chemical analyses of "granitic" gneisses in the western Georgia-eastern Alabama Piedmont (analyses by atomic absorption)

Sample No CACM 815 CACM 817A CACM 8178 CACM 820 CACM 825A CACM 838 CACM 840A CACM 841 GACM 846 CACM 01-A CACM 01-B CACM 02 CACM 03 CACM 04 CACM 103 CCM 114 CCM 139A CBCMH CBCM.lG CBCM 19-B OBCM 31 cacM 35 CBCM 62-B CBCM 62-D CBCM 68 CBCM+ 1-1 CBCM+1-2 CBCM+1-3 COCM 12 GOf!M 1 4 COCM 18 COCM 19 DCM1 DCM 2 DCM4 DCM 5 DCM6 DCM7 DCM 19 DCM 22-2 DCM 27-1 DCM 34 DCM SG DCM 39-l DCM 47 DCM 54 DCM61 DCM 77 DCM88 DCM 89 DCM 101 DCM 102A DCM 102B DCM 105-1 DCM 106 DCM 118 DCM 136

78.2 9].0 66.7 70.9 95.9 66.3 77.8 79.0 73.4 70.3 88.0 78.6 96.0 78.6 7 0 ,6 76.7 66 .4 69.1 73 .7 74.8 76.0 74.7 S.S.O 62.2 71.5 64 .5 65.1 74.4 76.3 78.5 74.9 69 .8 77.0 77.6 73.9 80.8 77.4 76.7 69.3 69.0 85.0 68.1 72.2 65 .8 72.9 72.4 72.9 86.2 74 .5 64.6 74 .1 73.5 75.5 61.2 75.4 76.1 72.8

Al2 0 , 12.00
.77 16.83 13.92
1.25 16.28 10.11 12.15 12.67 14.38
5.26 10.60
0.88 12.40 13 .75 12.66 l '/,'11 15.50 13.50 12.46 10.12 13.15 12.68 13.02 16.82 13.78 14.80 12.25 13.18 11 .52 13.50 13.46 11.88 11.90 12.40
8.45 12.00 12.35 12.60 11 .96
6.08 18.88 11.80 13.22 11.79 10.76 10.80
5.96 11.45 14.67 13.36 13.66 11.62 19.59 1 2 .03 11.71 13.69

'l'i02 0.42
.24 0.45 0.84 0.43 0.57 1.14 0.32 0.43 0.51 0.34 0.27 0.28 0.36 0.20 0.43 0.5!! 0.59 0.51 0.80 0.75 0,45 0.83 0.78 0.22 1.07 0.81 0.36 0.28 0:12 0.38 0.49 0.4 2 0.41 0.40 0.83 0.48 0.48 0.45 1.03 0.36 0.65 0.87 0.90
.77
.62 .80 0.48 0.45 0.75 0.58 0.38
0.34
0.86
0~6
0.16 0.37

f'e, o, Mno

1.20

0.05

5.57

.03

1.42 0.05

5.22 O.D7

1.27

0.06

2.l2 0.0\)

D.20

0.05

1.16

0.04

1.52

0.08

2 .7 9

0.07

o.a4

0.03

1.13

0.04

0 .54 0.02

0.53

0.04

3.25

.09

0.94

0.06

2.70

0.05

2.75

0.06

1.70

0.05

3.97

0.09

3.46 0.13

1.32

0.04

16.24

1.28

1 6 .6 2

0.99

0.91

0.04

8.26

.17

6.26

.10

2.78

.03

1.55

0.11

1.61 _1l. OR

1.36

0.09

5.48 0 .13

1.31

0.06

1.47

0 .06

1.47

0.07

4.32 0.07

1.45

0.08

1.50

0 .0 8

5.97

.10

6.05

.08

2.57

.06

5.61

.15

4.91

0.12

6.92

0.09

5.66

.09

4.82

.11

3 .9 1

.12

2.06

.09

4.47

.10

7.05

.13

2.22 0.07

1.67 0.07

1.24

.05

6.88

.10

1:01

.07

1.2'7

.06

1.!)6

.07

Mgo
0.11 .10 0.36 1.46 0.05 0.69 0 .8 4 0,07 0.30 0.77 0 .0 9 0.08 0.12 0.04 .63 0.20 0 .71 1.29 0.61 0.94 0.94 0.23 1.64 1.90 0.20 4.23 1.98 .43 0.35 0.19 0.28 1.47 0.14 0.22 0.22 1.22 0.23 0.33 1.61 1.57 .40 1.62 1.34 1.95 1.34 .97 1.06 .32 1.11 1,70 0.62 0.47 .26 1.90 .29 .32 .42

CaO

Na,o K2 0

0.58

2.95

4 .96

.14

.54

.13

0.50

2.77

4.95

1.45

3.44

3.10

0 .1 3

0.19

0 .14

1.17

4.41

4.48

0.42

2.57

1.98

0.17

0.99

5.09

1.12

5.26

0.05

0.94

3.77

3.90

0.13

0.60

3.7 7

0.47

1.56

6.89

0.16

1.51

0.25

0.29

2.3_2

5.31

1.63

3.45

4.50

0.81

2.98

4.81

0 .1 3

0.60

3.50

3.49

4.68

2.31

1.06

3.48

3.75

1.16

1.92

1.56

1.20

2.23

1.13

1.40

4.18

4.40

2.32

1.32

1.49

1.54

1.41

2.11

3.18

5.99

1.12

1.29

3.85

2.04

1.88

4 .14

2 .9 0

.26

1.00

6.78

1.74

3.27

2.89

___2,.3.1._ 1--' 8/L_1---ua_

1.04

2.90

5.47

5.25

3.63

1.16

0.71

3 .3 5

4.73

0 .70

3.08

4.85

0.69

3.01

4.88

0 .2 6

0 .3 2

2.13

0.61

2.75

4.93

0.58

3.85

4.07

1.11

4 .34

2.81

1.73

5.78

2.63

.56

3.85

.90

1.96

5.51

2.28

2.02

3 .01

1.23

1.02

1.86

3.38

1.02

3.78

1.79

1.29

4 .27

1.70

2.13

3.41

1.82

.34

1.99

.99

1.07

2.83

2.23

1.85

2.94

3.56

1.51

3.24

4.33

0.58

2.15

5. L8

.5 6

3.01

5.16

.65

3.33

5.27

.73

5.45

4 .64

.85

3.40

5.02

.94

5.66

4 .75

SrO
.023. .021 .026 .0 27 .011 .034 .024 .020 .0 23 .019 .007 .019 .017 .022 .024 .019 .020 ,063 .031 ,024 .030 .029 .042 .043 .082 .027 .036 .024 .037 .044 .039 .049 .022 .023 .024 .022 .025 .025 .028 .031 .021 .026 .031 .035 .029 .027 .0 26 .024 .023 .019 .046 .034 .005 .031 .019 .01)3 .021

Cr, o , <.001
.002 .005 .008 <.001 .005 .00.7 <.001 .005 .013 .012 .004 .007 <.001 .002 .014 .016 .003 .014 .006 .008 .014 .015 .013 .011 .001 .001 .002 .010 .010 .011 .011 <.001 <.001 <.001 < oo1 <.001 <.001 .002 .001 .002 .001 .008 .008 .002 .001 .001 .001 .002 .002 .010 .011 .002 .002 .002 .002 .001

R.b,O Total

.029

100.52

.001

98.54

.015

94.08

.008

100 .45

.002

99.43

.009

96.11

.006 100.14

.0 2 7

99.14

.021

99.48

.014

97 .-t7

.018

98.90

.031

99.69

.002

99 .79

.0 22

99.93

.017

9 8 .1 4

.022

99 .64

.009

92.13

.007

99.89

.OlD

98.40

.QQ5

97.74

.005

96,()1

.013

99 .92

.009

100.87

.013

100.63

.003

100.07

.004

99.22

.008

98.02

.015

98.32

.009

99 .73

. OM -ll.!I.Jlli..

.028

100.00

.002

100.47

.034

99.65

.028 100.34

.030

97.09

.007

97.43

.029

99.01

.01 3

99 .98

.009

98.33

.004

99.86

.002

99.80

.008

99.80

.003

97 .54

.013

95.20

.006

99.18

.004 .007

96~7 96.4~1

.002

98.45

.008

98.24

.01,1

97.28

.016

100.11

.024

98.02

.019

97.77

.017

99.83

.021

9_9.8 2

.019

!:18.91,

.022

99 .77

1-32

Table 5. (continued)

Sample No.

SiO,

DCM 204

64.8

DCM 210 DCM 213 DCM 231

- 70.6 75.0
68.1

DCM 24S

61.6

DCM 292

72.3

DCM 319

68.0

DCM 338

69.8

DCM02

69.1

HCM 17

82.0

HCM 19

75.2

HCM 22

65.6

UCM 34

6!!.0

HCM 56

72.2

HCM 62

75.8

HCM 198

64.3

HCM 210

76.4

HCM 221

72.0

HCM 228

70,6

HCM 231

73.2

HCM 233

77.4

HCM 237

74.7

HCM 241

78 .0

HCM 251-B

72.1

HCM 256-C

78.9

HCM 259

73.3

HCM 261-E

73.4

HCM 273-B

70.J

HCM 277-A

64 .8

ITCM 278-A

68.0

HCM 284-A

67 .8

HCM 288

78.1

RCM 290

78.0

HCM 292

63 .7

HCM 294

76.2

HCM 295

78.4

HCM 296-A

75.7

HCM 296-B

74.2

RCM 87

67.1

RCM 92

85.0

RCM 132-B

76.4

RCM 139

72.5

RCM142-A

75.2

RCM 149

69.0

RCM 162

72.8

ll.CM 170

66.1

RCM 171-A

67.9

RCM 175

75.2

RCM 180

71.8

RCM 186

71.8

RCM 200

69.3

ltCM 209

74.8

RCM 211

73.8

RCM 215

77.0

RCM 226

75.7

RCM 227A

77.6

RCM 229

73.9

RCM 17-24

69.3

RCM Ht-2W-47-L1 68.6

AI,O,
15.57 16.28 11 .7'1 15.46 16.26 11.99 15.36 14.74 Vl..97
8.54 12.14 1 5 .1 5 13.85 13.19 11.17 16.84 13.38 13.38 13.25 13.18 10.96 12.11 13.14 14.29
9.74 13.47 11 .65 1 2 .2 1 16.00 11.92 15.96 11.65 11.86 14.52 12.40 11.26 11.42 11.76 1 3 .7 0 7 .15 10.45 13.75 14.81 16.75 1 2.65 14.83 13.45 12.72 13 .09 1 4 .00 16.10 13.18 11.92 12.10 11.67 11.31 10.78 17.88

TiO,
0.64 0.63 0.69 0.79 0.84 0.25 0.56 0.73 0.55 0.49 0 ,30 0.54 0.99 0.37 0.28 0.75 0.35 0.34 0.35 0.33 0.72 0.26 0.32 0.76 0.64 0.37 0.61 0.71 0.89 1.34 0.48 0.34 0.25 0.92 0.43 0.43 0.32 0.35 1.19 0.45 0.66 0.30 0.45 0.19 0.15 0.22 0.47 0.00 0 ,08 0.18 0.27 0.10 0.17 0.13 0.61 0.39 0.77 1.80

13.50 0.80

CACM ~ Carroll Co., Ga. CBCM - Cobb Co., Ga. CCM -Chambers Co., Ala. COCM - Coweta Co., Ga. DCM -Douglas Co., Ga. HCM - Heard Co., Ga. RCM - Randolph Co., Ala.

Fe,O,
4.78 2.54 2.96 2.81 3.59 2.80 2.93 3.56 2.19 2.30 0.90 3.07 6.68 1.65 4.60 6.92 0.70 2.40 1.05 0.92 4.37 0.47 0.44 5.82 3.25 1.49 4 .54 5.55 5.96 6 .91 3.24 L21 1.15 5.11 1.41 1.01 1.08 1.34 5.05 3.48 4.68 3.00 2.20 3.12 2.48 4.28 3.39 0.60 1.00 3. 39 4.95 0 .80 1.65 0.30 4.70 0.96 2.85 0.95

Mno
0.08 0.07 0.08 . 0.09 0.08
.07 .07 0.07 0.04 0.05 0.06 0.05 0.11 0.07 0.06 0.10 0.07 0.10 0.04 0.05 0.06 0.02 0.03 0.07 0.10 0.06 0.06 0 .07 0.11 0.16 0.07 0.05 0.06 0.09 0.05 0.06 0.04 0.04 0.11 0.05 0.05 0.07 0.04 0.07 0.06 0.10 0.08 0.01 0.07 0.06 0.08 0.05 0.04 0.04 0.08 0.07 0.07 0.01

Mgo
1.83 0.93 1.17 1.11 1.04
.79 .79 1.16 0 .6 6 0 .5 4 0.07 0 .95 1.79 0.20 0 .6 8 2 .6 2 0.09 0 .64 0.23 0 .1 7 1.25 0.10 0.06 1.92 0.82 0.28 1. 3 1 1.66 2.15 1.80 1.15 0.12 0.06 2.42 0 .13 0 .0 8 0.11 0 .1 4 1.61 0 .52 0.95 0.55 0.89 0.75 0.40 1.00 0.85 0.07 0.12 0 .6 8 0.85 0.83 0.19 0.18 1.52 0.06 1.32 0.26

6.08

0.08

2.45

CoO 3.90 2.09 1.27 2.66 1.24 1.91 1.55 2.27 0.12 0.29 0.56 1.94 3.13 1.29 0.56 2.17 0.53 2.33 0.59 0.84 0.72 1.56 0.39 0.56 3.20 0.68 1.11 1.25 2.76 4.13 2.54 0,50 0.29 1.57 0.62 0.32 0.56 0.47 2.94 0.30 0.18 0.97 0.80 3 . 25 1.44 3.19 2.42 1.33 0.38 2.15 1.40 0.23 0.22 0.55 1.08 0.25 0.30 1.28
2.80

Nn,O
5.22 5.60 5.08 4.94 2.02 5.21 5.38 4.33 0.60 0 .78 3 .23. 3.75 4.24 3.75 4.95 3 .00 4.00 3.29 1.32 2.42 1.64 3.01 2.59 1.42 1.82 2.91 2.06 2.21 4.65 3.63 4.10 3.00 3.04 2.12 2.76 3.23 3.41 2 .9 9 4.42 1.52 0.42 2.32 1.90 2.90 2.58 2.64 3.41 3.24 3.47 2.15 0.50 3.03 3 .1 0 2.92 1.74 3.26 1.02 4.25

K1 0 2.10 2.03 1.62 3.58 4.02 3.39 3.91 3.67 4.85 0.83 4.56 3.54 1.17 4.15 0.23 3.45 4.35 3.03 5,62 5.83 1.89 4.17 4.89 2.91 1.51 4.98 1.93 3.15 1.90 0.31 3.56 4.90 4.37 3.55 5.16 4.53 4.63 4.84 1.29 1.03 2.00 4.73 3.63 2.13 2.78 2.20 3.78 4.38 4.21 2.42 2.92 5,38 4.77 4.30 2.00 4.46 2.50 0.09

8rO .037 .029 .034 .031 .043 .036 .045 .085 .020 .024 .019 .065 .037 .010 .022 .029 .003 .028 .020 .029 .024 .031 .009 .012 .020 .011 .023 .027 .047 .057 .073 .023 .016 .033 .016 .012 .013 .008 .047 .011 <.001 .014 .023 .011 .008 .014 .022 .003 .013 .014 .014 <.001 .004 .013 .008 .009 <.001 .034

Cr, 0 1 .005 .005 .007 .006 .005 .002 .001 .011 .014 .006 .006 .017 .016 .017 .014 .016 .016 .004 .014 .005 .013 .018 .018 .018 .018 .017 .014 .016 .019 .008 .018 <. 001 .015 .008 .015 .014 .019 .017 <.001 <.001 .011 < .001 <.001 .011 <.001 <.001 < .001 < .001 <.001 < .001 <.001 .004 .001 <.001 .009 .014 .005 < .001

Rb,O
.008 .008 .006 .010 .012 .011 .012 .014 .016 .002 .033 .008 .004 .013 .002 .014 .015 .009 .023 .022 .005 0.10 .030 .012 .004 .021 .006 .007 .008 .001 .007 .022 .032 .012 .021 .028 .032 .021 .005 .004 .008 .016 .012 .007 .010 .009 .015 .011 .019 .010 .011 .017 .019 .029 .010 .036 .007 .004

Total
98.97 1 0 0 .81
99.62 99.67 90.76 98.76 98.61 100.44 92.13 95 .85 97 .09 94 .69 100.02 96.91 98.36 100.21 99 .91 97 .55 93.10 97.00 99.05 96.46 99.92 99.94 100.03 97 .59 96.71 9 6 .9 7 99.96 98.27 94 .90 99 .91 99.15 94.05 99 .22 99.37 97.33 96 .18 97 .92 99.09 95.81 98 .22 99.97 97.14 95.36 94 .58 9fi .79 97.56 94 .25 96 .85 96.39 97 .84 95.88 97.56 99.13 98.43 93 .52 96 .74

2.52

1.44

.030

.010

.009

98.32

1-33

CaO

_ ? Quartz. diorite

~
I
1

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I

\ ; - ~

Granod i o r i t e

f-l.
6J
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. . l .\, l Wyoming graywac~ \ e ....

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.

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granitic gneiss samples

0 Average oi 7 Sou1h Afr ican graywackes (Pettijohn. 1963)

0 Average of 14 New Zea land illlesozo1c graywackes (Pem)ohn , 19631

A. Average of 17 Harz Mtn. graywackes (Pettijohn , 1963)
o Average oi 12 Precambnan graywackes (Pettijohn , 1963)

/::,. Average of 30 graywackes ITyrrell i11 Pettijohn. 19631

X AveFage of 61 graywackes (Pettijotm, 19631

Figure 23. Ca0-Na2 O-K2 0 plot of selected granitic gneiss samples from the field trip area.

F



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~
01




















ALK

M

Figure 24. ALK-F-M composition plot of the "granitic" gneisses in the western Georgia-eastern Alabama Piedmont (26 analyses not plotted because they would have fallen on previously plotted points).

Table 6. Chemical analyses of hornblende gneisses and amphibolites in the western Georgia-eastern Alabama Piedmont (analyses by atomic absorption).

Sample No CACM 844 CACM 847 COM 124 CCM 129 CCM 135 (lCM 135-A CCM 140-A CCM 140-B COM 142-B CBCM 11 CBCM 20 -B CBCM 22 CBCM 55 CBCM 91 OOCM1 COCM2 COCM 3 COCM 16 UGM 75 DCM 140 DCM 150 DCM 161 lJCM 162 DOM 175 DCM 203 DCM 254 HCM 24 HCM39 HCM 49 UCM 196 HCM 203 I'ICM 236 RCM 239 HCM.240-B HCM 286 HCM 293-A ltCM 24 RCM 26 RCM 31 ROM 71 :ROM 79-A ROM 79-'E RCM 103 RCM 121 R OM 136-A RCM 138 ROM 147 ROM 183 RCM 188 RCM199 -A ROM 199-B EtCM 201 RCM 202-B .R.CM 222 RCM232 ltCM 19-23-1B ltcM 114-L-1

SiO, 52.1 50.0 50.1 60.3 49.8 49.7 50.4 43.0 44.6 48.8 46.7 50.1 67.0 50.2 47.2 49.2 43.7 49.8 53.8 49.3 50.0 47.4 56 .3 49.0 45.3 49.1 51.2 44.0 50.3
48.3 42.9 46.9 54.0 47.6 51.1 36.6 47.4 71.5 48.7 60.1 4 7 .9 1(9 ,8 46.3 50.8 46.2 53.5 47.4 44.1 48.4 4.9 .0 45.6 61.0 78.0 55.3 52.4 11.<1 62.7

A12 0, 15.69 Hi .S l 14..02
9.73 1 3 . 5(; 11..15 14 .06 15.44 15.91 13.40 14.72
7.24 16.05 16.98 14.25 16.70
0.70 9.08 16.96 14.41 15.82 8.75 1.75
~ 4.70
7.91 1.5.32 14.98 16.&2 l fl .OG 1.2.3.1 21.06 33.66 14 .67 13.58 J4 .34 16.87 15.00 11.90 14.70 15.95 14 .85 14,55 16.45 16.40 lll .72 13 . 8 0 1 6 .0 5 14.65 1 4 .3 0 16.60 15.42 14.4-9 10.72 16.68 15.!l'l 18.00 15.::15

CACM - Carroll Co ., Gn .
CJ3CM - Cobb Cl.> .. Ga. C M - Chumbers o ., Ala. C,OCM - Co:wata Co., On .

'1~0 1 1.41 1.25 1.01 0.36 0.96 1.52 0.91 0.53 1.56 lUlll 3.08 2.40 0.42 1 .10 0.52 1.37 0.98 0.95 1.59 1.08 1 .61 0.615 0 .03 1.12 0.62 2.24 1.09 2.16 0.86
1.69 0.43 1.36 0 .98 1.30 1.68 4.12 1.60 1.03 1.42 0.82 1.10 1.47 1.03 0.71 1.94 1.05 0.8 () J.l4 0.99 1.17 1.32 0.29 0.14 0.73 .68 1.56 0.94

Fe,o, 11.74 11.00 L2.34
6.52 1 1.>11 12.83 11.49 12.45 12.77
8.13 20.98 16.24
4.08 il, .67
7.13 J.O.l2 13.36 11.44 12.32 10.42
9.34 10.89
4.05 10.72 11.35 16.02 13.44 14.19 10.46 14.30
5.07 12.80 11 .75 12.12 13.47 16.99 12.98
6.52 13.'13
8 .0 5 J 3.10 l l.95 10.49 11.70 15.62 12.55 11.70 15.00 13. 56
9.38 .!.2. 7 6
9.10 1.45 11.95 12.60 10.91 12.16

MnO 0 .26 0.22 0.21 0.1 fi 0.20 0.23 0.19 0.22 0.19 0.24 0.24 0.25 0.08 0.15
().15
0. 1 7 0 ,15 0.16 0.17 0.20 0.14 0.22 0.12 0.20 0.19 0.26 0.22 0.25 0.21
0.23 0.09 0.24 0.20 0.22 0.22 0.23 0.19 0.13 0.26 0.15 0.19 0.26 0.17 0.18 0.21 0.23 0.18 0.21 0.19 0.14 0.18 O.LI; 0.05 0.2 ) 0.17 O.l8 0.1 1

MgO 5.45 6.75 6.39 6.52 6.32 7.68 G.3$J
10.4() 10.26
5.09 3.49 5.10 1.53 7.80 11.38 11.32 23.78 7.70 4 .01 7.80 5.05 21.20 23.36 7.52 22.80 4.55 5.18 5.31 6.24
7.04 8.01 6.87 5.07 6.40 3.90 5.95 7.40 1.59 7.38 2.08 7.68 7.80 3.52 3.95 6.85 6.25 ll.05 7.26 8.08 8.82 9.57 10.00 0.65 2.52 4.32 6.88 1.62

CaO 8.02
10.34 10.03
8.44 9.75 12.92 9.82 13.24 10.10 9.80 5.01 10.60 3,74 8.02 15.80 10.13 1.4n 9.71 6.68 12.66 9.89 6.42 11.46 11.88 5.05 6.15 8.34 9.73 10.86
8 .34 16.64
9.33 6.53 7.51 7.03 10.70 10.15 3.60 10.99 3.88 10.08 1 0 .34 17.56 7.52 10.28 6.48 10.08 1 6. 7 0 11.95 12.36 12.45 9 .20 0.80 8.79 7.30 8 .1 2 O.LO

DCM - Douglas Co., Ga. HOM - Heard Co., Ga. ROM -Randolph Co., Ala.

Na,O K,O

5.92 4.31 ' 4:99 4..18 2.54 3.98 2..6(1

0 .32 0.27 0.62 3.36 0.60 0.09 0.77

3.56

0.33

4.44

0.25

2.34

0.40

0.84

0.25

2.00

0.20

3.80

2.81

4.66

0.17

1.16 0.46

0.60

0.35

0 .<1 7

0 .13

2.61

0.24

4.23

0 .36

3.88

0.1:l

7.57

0.63

1.07

0.11

2.32

0.10

4.~1- 0.26

1.67

0 .11

6.20

0.15

4 .19

0.24

2.80

0.26

2.49

0 .16

2.55

0.22

0.97

0.29

2.41

0.20

4.21

0.20

3.35

0.21

3.65 1.01 2.35 3.23 2.86 5.56 2.04 3.39 2.68

0.22 1.47 0.15 0.13 0.22 0.06 0.19 0.29 0 .1 2

3.00

0.08

2.18

0.22

3.75 3.70 0.80 2.53 1.04 2.04 Ul8 J) .51J
1.08 3.68 3.92 0.66

0.17 0.06 0.16 O. l (l 0.14 0.26 0.15 0.73 2.63 0.16 0.22 3.90

SrO .018 .029 .011 .1 06 .014 .921 ,016 .016 .019 .051 .054 .052 .038 .024 .051 .037 .018 .026 .033 .029 .033 .008 .024
.oao
.019 .IJ25 .013 .040 .025
.023 .027 .023 .018 .027 .021 .J 51 .026 .027 .030 .020 .021 .030 .046 .022 .04 7 .017 .014 .029 .021 .023 .033 .018 .Olll .011 .014 .032 .020

'CrO 3
.006 .008 .01 3 .012 .012 .016 .014 .010 .016 .Ol5 .018 .016 .002 .024 .013 .032 .111 .020 .017 .012 .004 .DOl .014 .015 .078 .007 .019 .010 .018 .01 6 .052 .014 .018 ,016 .OJ2 .OUl .032 <. DOl <.001 .011 .027 .947 <.001 <. 001 .038 < .001 .035 .031) .035 .035 .040 .050 <.001 .010 .004 .041 <.001

ftb 1 0 .001 <.001 .003 .007 .004 <.001 .002 .000 .002 .001 .003 .002 .009 .002 .000 .001 .001 .002 .002 <.001 .001 .001 .002 < 001 <.001 .001 .001 .000 .001
.000 .000 .000 .001 .000 .000 .006 <.001 .002 .000 <.001 .000 .001 .001 .000 <.001 <.001 .000 .001 .001 .001 <.001 .001 .004 .004 .002 .002 .023

Total 100.95
99.99 99 .73 89 ,69 95.15 100.32 96.66 l00.20 100.12 90.86 95.38 94.20 99.56 100.7!) 98..IJ 100.36
!1.~ . 85
9l.'M 100.17
99.92 100.08
96.67 99.52 100.06 95.13 100.00 9!l.9t 9& . 9 4 97 .70
95.05 95.54 93.80
- -97.6-5
92.34 95.54 94.11 07.28 99.66 99.911 96.68 97.38 99.93 9!! . 3 7. 93 .3G 98.29 97 .79 98.07 1 0 0 .0 9 100.16 98.70 99.67 95 .79 97.10 99.90 97.19 91.16 97.58

1-36

Na20 plot of mafic rocks in the western Georgia-eastern Alabama field trip area, the Cartersville district (Kesler and Kesler, 1971), Paulding and Cherokee Counties, Georgia, and the Stone Mountain-Lithonia area, Georgia was drawn (Fig. 25). This plot shows a distinct clustering into three groups along the Na20 side of the diagram indicating that the rocks are low in potassium. This includes those from the Cartersville district. The Paulding and Cherokee County samples from Crickmay (1952) as well as those from the Stone MountainLithonia area (Hermann, 1954) also plot in the same areas of the diagram.
A plot of Na 20 + K 20 vs. Si02 is shown in Figure 26. Again, a number of other samples are plotted on this diagram in addition to those from the field trip area. The basic diagram is taken from Kuno (1959). As can be seen, the samples fall in both the alkaline and tholeiitic basalt fields. This would suggest that if the mafic metamorphic rocks were derived from igneous rocks, then they have both alkaline as well as tholeiitic basalt affinities.
Figure 27 is a plot of the chemical analyses on a standard Alk vs. Fe203 vs. Mg diagram. With few exceptions, the rocks plot in the fields normal for basaltic and andesitic rocks.
The preceding chemical data when plotted on the various types of diagrams indicate that the amphibolites and hornblende gneisses of the western Georgia-eastern Alabama area have a parentage that can be attributed to igneous rocks-probably basalt flows or basaltic sills. The outcrop patterns of the rocks, discontinuous and mostly concordant, as well as the enclosing lithologies would seem to indicate that the rocks' origins can be explained by an igneous origin. The rocks occupy the same stratigraphic position as those rocks described by Hurst and Jones (1973), who attribute the origin to metabasalts, based on structural, textural, and isotopic work.
AUSTELL GNEISS
Since the initial work by Hayes (1901), several workers have studied the Austell gneiss. Among these are Crickmay (1952), Schepis (1952), and Higgins (1966). However, the stratigraphic and structural nature of the Austell gneiss was not known until the work of Crawford and Medlin (1972). This work has shown that stratigraphically the Austell gneiss is overlain by the Sandy Springs Sequence and underlain by a thick sequence of metagraywacke and schist units which we refer to here as the Bill Arp. A thin unit of muscovite schist which occurs within the Austell gneiss has been designated the Union Church schist. Structurally, the Austell gneiss occurs along the flanks and around the nose of the AustellFrolona anticlinorium (Crawford and Medlin, 1973), one of the major structural features of western Georgia-eastern Alabama. The Chattahoochee Fault (Hurst, 1973) occurs along the southeast flank of the anticlinorium; faulting is also evident along part of the northwest side.
Much of the quantitative information concerning the mineralogy, petrology, and geochemistry presented here is derived from unpublished information and from the work of Coleman and others (1973). Megascopically, the rock is light to dark gray in color. The grain size is quite variable, ranging from fine- to coarse-grained, non-porphyroblastic, equigranular varieties to rocks with fine to coarse groundmass containing feldspar porphyroblasts 5mm to 3cm long. The porphyroblastic texture is dominant and seems to be unrelated to position in the rock unit. The long dimensions of the feldspar porphyroblasts are parallel to the well-developed foliation in the rock. Well-developed layering, lineations, and jointing are prevalent in most outcrops. Commonly, the rock crops out as "pavement" and spheroidal boulders throughout its extent. The outcrop area according to Coleman and others (1973) is 35 square miles.
Microscopic examinations indicate that the dominant minerals are quartz, microcline, plagioclase, biotite, and muscovite. Accessory and secondary minerals include epidote, sericite, chlorite, garnet, ilmenite, sphene, zircon, tourmaline, and magnetite. The epidote, sericite, and chlorite appear to be retrograde minerals.
1-37

3


This paper 0 Cartersville
Paulding & Cherokee Cos. 0 Stone Mountain & Lithonia area 6. Tholeiitic basalts .& Alkali basalts 0 All basalts

2

t-'

~
00

0

N

..

~

0



6.

0





...

0

0







ooe.o.

_


0

0

o

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0



" 0

~~--------------~--------------~----------&---~-------------~

0

2

3

4

Na 20

Figure 25. K2 0 vs. Na2 0 for the amphibolites and hornblende gneisses of the field trip area; compared to similar rocks of other areas.

This paper
0 Paulding & Cherokee Cos. D Stone Mountain & Lithonia area 0 Cartersville



6





s

0



N

~
+ 4



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~

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00

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40

45

50

55

60

Si02

Figure 26. Na2 0 + K2 0 vs. Si02 plot of the amphibolites and hornblende gneisses from the field trip area.

F



~
J,..
0



















..





ALK

M

Figure 27. ALK vs. Fe2 0 3 vs. MgO compositional diagram of the amphibolites and hornblende gneisses of the western Georgia-eastern Alabama Piedmont.

Modes of a representative number of samples show the variation of quartz-microclineplagioclase on the Q-M-P triangular plot (Fig. 28). Though there is scatter of the values, the microcline to plagioclase ratio indicates that the Austell is equivalent to a quartz-monzonite or adamellite. Plots of several samples from Hermann's 1954 study of the Lithonia and Stone Mountain areas are shown for comparison.
Atomic absorption analyses of 23 samples confirm the modal data. A triangular plot of this data, Na20-K20-Ca0, shows that the majority of the samples fall in areas specified for granites and quartz monzonites (Fig. 29) by Condie (1967). The scattering also indicates, as did the modal work, that there is some mineralogical and chemical variation within the Austell gneiss. This is probably related to its original composition.
YELLOW DIRT GNEISS
The Yellow Dirt gneiss has been mapped from Douglas County, Georgia to Randolph County, Alabama (Plate 1). Over this distance it is mostly a light-gray, fine- to mediumgrained muscovite-biotite-plagioclase-microcline-quartz gneiss. In many places, microcline porphyroblasts are conspicuously present in a fine- to medium-grained groundmass of muscovite, biotite, plagioclase, microcline, and quartz. In parts of Carroll County, the gneiss is a silicified micro breccia due to severe cataclasis (Figs. 20 and 21 ); little of the original mineralogy, texture, or geochemistry is recognizable in these areas. In Douglas and Heard Counties, Georgia and Randolph County, Alabama, the rock displays some degree of cataclasis, but deformation is not as severe as in Carroll County.
Chemical analyses of 19 samples of the Yellow Dirt gneiss show that the Si02 values are slightly higher than in a normal granite and the Al 203 values are slightly lower (Table 7). Exceptions to the Si02 values are those samples located in Carroll County, where the gneiss becomes a part of a zone of intense cataclasis. It is obvious that the rock, in addition to being severely granulated, has been silicified during the cataclasis. Thin-section studies (Figs. 20 and 21) and field observations support this conclusion. Samples CACM 825A and CACM 03 are rri1crobreccias. They show little, if any, of the precataclasis mineralogy and texture of the rock which is so well demonstrated in outcrops along strike to the northeast and southwest.
With only few exceptions, both the iron and MgO values are uniformly low, and the Na20 and K2 0 values are approximately that of an arkose. On a Ca0-Na2 0-K20 triangular diagram the majority of the rocks plot near the Na20-K2 0 base (Fig. 30). This suggests, as do the chemical analyses, that the gneiss is fairly uniform in chemical composition with the notable exceptions being those parts affected by cataclasis. The diagram also suggests that there was not a mass movement of either Na20 or K20 during the regional metamorphism. Field observations on this rock and other rocks in the study area suggest that there was pronounced movement of Si02 associated with cataclasis. In the field, "ribbons" of quartz are commonly found along the gneissosity and schistosity planes of the sheared rocks. These "ribbons" are lense-like in shape and occur only in the most intensely deformed mylonitic rocks. The lateral persistence of this gneiss and its mineralogy and geochemistry suggest that the Yellow Dirt gneiss was originally a sedimentary rock. ,Its present structural position suggests that the Yellow Dirt gneiss is a part of the Sandy Springs Sequence, although present data is not sufficient to determine, with certainty, its position within that sequence.
PURPOSE
The purpose of this field trip, as indicated by the title, is to view the stratigraphy, structure, petrology, and geochemistry of the Brevard Fault Zone; specifically, to relate these features to cataclasis; and, in particular, to point out the relationship of a very obvious low topographic lineament (developed along a zone of intense cataclasis) to the overall geology of this area. '
1-41

Q

1-'
,1::..
t-.:1

M

p

Austell gneiss
:J Lithonia & Stone Mountain samples (Hermann, 1954)

Figure 28. Triangular plot of quartz-microcline-plagioclase (Q-M-P) modal data for the Austell gneiss.

CaO

I"".- - '\ Quartz diorite

/

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I

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...... J:.

I

I

c.:

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//--, Granodiorite

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Granite and quartz monzonite

Wyoming graywackes

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Na20
Figure 29. Na2 O-K2 0-CaO triangular plot for the Austell gneiss.

K20

CaO

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Figure 30. Ca0-Na2 O-K2 0 plot of the Yellow Dirt gneiss.

Table 7. Chemical analyses of the Yellow Dirt gneiss in the western Georgia-eastern Alabama Piedmont (analyses by atomic absorption).

Sample No.

Si02

Al203 Ti02 Fe20 3 MnO MgO

CaO

Na2 0 K20

SrO

Cr2 0 3 Rb2 0 Total

CACM 01-A CACM 01-B

70.3

14.4

0.51

2.79

0.07

0.77

0.94

3.77

3.90 0.019 0.013 0.014

97.49

88.0

5.3 I 0.34

0.64

0.03

0.09

0.13

0 .60

3.77 0.007 0.012 0.018

98.94

CACM 02

78.2

10.6

0.27

1.13

0.04

0.08

0.47

1.56

6.89 0:019 0.004 0.031

99.29

CACM03

97.0

0.8

0.28

0.54

0.02

0.12

0.16

1.51

0.25 0.017 0 .007 0.002 100.71

CACM 04

78.0

12.4

0.36

0.53

0 .04

0.04

0 .29

2.32

5.31 0.022 0.000 0.022

99.33

CACM 815

78.2

12.0

0.42

1.20

0.05

0.11

0.58

2.95

4.96 0.023 < 0.001 0.029 100.52

CACM 825A CACM 825B

95.9

1.2

63.0

17.4

0.43

1.27

0 .06

0 .05

0 .13

0.19

0.14 0 .011 <0.001 0 .002

99 .38

1.0

6.94

0.11

0.43

0.13

0.75

3.45 0.026 <o.oo1 I 0.010

93.35

......

CACM 841

79.0

12.1

0 .32

1.16

0.04

0.07

0.27

0.99

5.09 0.020 <0 .001 0.027

99.09

.i>.

DCM1

77.0

11.9

0.42

1.31

0.06

0.14

0.71

3.35

4.73 0.022 <0.001 0 .034

99.69

Ol

DCM2

77.6

11.9

0.41

1.47

0.06

0.22

0.70

3.08

4.85 0.023 <0.001 0 .028 100.34

DCM4

73.9

12.4

0.40

1.47

0.07

0.22

0.69

3.01

4.88 0.024 <0.001 0 .030

97.09

DCM6

76.1

12.0

0.48

1.45

0.08

0.23

0.61

2 .75

4 .93 0.025 <0.001 0.029

98.59

DCM7

75.0

12.3

0.48

1.50

0.08

0.33

0.58

3 .85

4 .07 0.025 <0.001 0.013

98.23

HCM 241

77.2

13.1

0.32

0.44

0.03

0.06

0.39

2.59

4 .89 0.009 0.018 0.030

99.08

HCM 288

78 .0

11.6

0.34

1.21

0.05

0.12

0.50

3.00

4.90 0.023 <0.001 0.022

99.76

HCM 290

79.0

11.8

0.25

1.15

0.06

0.06

0.29

3.04

4.37 0.016 0.015 0.032 100.02

HCM 292

63.7

14.5

0.92

5.11

0.09

2.42

1.57

2.12

3.55 0.033 0.008 0.012

94.03

RCM 209

74.8

13.2

0.10

0 .80

0.05

0.83

0.23

3.03

5.38 <0.001 0.004 0.017

97.86

RCM 211

73.8

11.9

0.17

1.65

0 .04

0.19

0.22

3.10

4.77 0.004 <0.001 0.019

95.86

-

CACM - Carroll Co., Ga. DCM - Douglas Co., Ga. HCM -Heard Co., Ga. RCM - Randolph Co., Ala.

Higgins (1966, 1968) defined the Brevard (Fault) zone in parts of Douglas, Cobb, and Fulton Counties as being bounded on the northwest by a thin mylonite gneiss (coincident with the Long Island Fault), and on the southeast by sheared Palmetto Granite. Using this definition, the Sandy Springs Sequence is northwest of the Brevard zone and the Brevard zone coincides with a zone of intense cataclasis, which is coincident with a low topographic lineament.
Because of the limited amount of detailed work in this area until recently, it seems to have been assumed that the relationship between the Brevard (Fault) Zone (i.e., a (low) topographic lineament with a northeast-southwest tr nd) and "Brevard" lithologies is consistent in western Georgia; that the relationship would be the same as that published for Douglas-Cobb-Fulton Counties. Such is not the case .
Southwestward from Douglas County, the low topographic lineament (coincident with a zone of intense cataclasis) cuts across stratigraphic boundaries, across the Yellow Dirt gneiss (mylonite gneiss of Higgins), and across the Long Island Fault, so that in Carroll and Heard Counties, Georgia and Randolph County, Alabama, this lineament is within and on the northwest side of the Sandy Springs Sequence. Because this northeast-southwest trending lineament is so very conspicuous, it has received much attention from those attempting to intervreL the regional structure and history of the southeastern Piedmont. However, there are numerous broad zones of intense cataclasis which splay off this lineament to the south and to the north, which have received no attention.
To further emphasize the importance of distinguishing between faults, fault zones, cataclastic zones, and topographic lineaments, we will attempt to demonstrate with this field trip that major displacement within the Brevard Fault Zone has occurred along distinct faults within the zone, but that widespread and intense cataclasis occurred later and resulted in little displacement; and that these zones of intense cataclasis are not spatially coincident with major-displacement faults.
If this interpretation is valid, and evidence is sufficient to require consideration that it is, great care should be exercised in projecting (displacement) faults into unmapped areas, particularly on the basis of topographic lineaments, and using such projections as bases for making regional interpretations.
APPROACH
The major part of the field trip will consist of three walking traverses (Fig. 31 ). Each traverse will begin in the same stratigraphic unit, the Yellow Dirt gneiss, and proceed northwestward across the Sandy Springs Sequence.
At Traverse 1, the Yellow Dirt gneiss and the Sandy Springs Sequence lie northwest of a pronounced low topographic lineament which is coincident with a zone of intense cataclasis (Brevard zone of Higgins, 1966, 1968).
At Traverse 2, the Yellow Dirt gneiss and Sandy Springs Sequence lie within this lineament (although a major splay diverges southward toward Franklin).
At Traverse 3, the Yellow Dirt gneiss and Sandy Springs Sequence lie southeast of this lineament.
We have been unable to demonstrate offset of lithologic units, or faults, as a result of movement associated with cataclasis along this lineament.
1-46

CUMULATIVE MILEAGE 0.00
2.50 3.65 4.70
5.85 6.80 7.30
7.85 8.15 8.85 9.30 10.30

ROAD LOG

INTERVAL 0.00
2.50 1.15 1.05
1.15 0.95 0.50 0.55 0.30 0.70 0.45 1.00

Road log begins on Ga. Hwy. 70, at the traffic light immediately southwest of Interstate Hwy. 20; heading south on the Fulton Industrial Blvd.
The roadway follows a (low) topographic lineament developed on a zone of intense cataclasis in the Brevard Fault Zone. In this area, the Chattahoochee River Valley coincides with this lineament.
The rocks exposed here are Palmetto (type) granite (gneiss ? ). Across the river. to the northwest are linear ridges and valleys develop d on r<:>cks of the Sandy Springs Sequence (Higgins, 1966; 1968).
Entrance, Atlanta Gateway Park-double tetrahedra.
Road junction, Ga. Hwy. 154; continue straight ahead.
Road junction, Boatrock Rd.; continue straight ahead. The extensive graded area northwest of the road exposes sheared Palmetto Granite (Watson, 1902, p. 104; Higgins, 1966, p. 36-39), a light gray granite (gneiss) composed of medium- to coarsegrained feldspar, quartz, and biotite (muscovite) with feldspar phenocrysts.
Road junction, Riverside Drive; continue straight ahead. Saprolite of biotite-muscovite-quartzfeldspar gneiss, fine- to medium-grained, sheared.
Phyllonitized garnet-quartz-muscovite schist and mylonitized biotite-quartz-feldspar gneiss.
The buses will stop here (10 minutes) so that you may examine the phyllonite and mylonite which are characteristic of rock underlying the (low) topographic lineament.
Junction, Ga. Hwy. 166; turn right; same rock types as at Mile 6.80.
Approaching the (low) topographic lineament, occupied here by the Chattahoochee River.
Chattahoochee River
Junction, King Drive; turn right.
Yellow Dirt gneiss; southeastern boundary. Begin TRAVERSE 1.

1-47

1-48

1-49

Q

.~.

'
\

-.:\

'I

( ! .

-r )

.--- '\_

Figure 1-50

__ ..........
v---.. ,~.l f'\..... _.. '-<
~. v

TRAVERSE 1

Traverse 1 begins in the Yellow Dirt gneiss, a (garnet) muscovite-biotite-quartz-feldspar gneiss, light gray, with feldspar augen as large a.s 25mm across in a medium-grained groundmass. Mylonitic zones show pronounced streaking. A mineral alignment lineation strikes N30E, plunges 4SW; foliation strikes N30-45E, dips 30SE. Residual soil and saprolite are light gray and quartzose, with abundant quaJ:tz fragments.

The northwestern boundary of the Yellow Dirt gneiss is covered. It is considered to be in fault contact (Long Island Fault) with the Mt. Vernon Church schist, a tourmaline-garnetkyanite-muscovite-quartz schist, medium-grained, with thin (2- to 8-inch) layers of micaceous quartzites and scarce thin (less than 6 inches) hornblendic zones. Soil and saprolite are light tan, micaceous, and quartzose. Opaques are disseminated in the muscovite. Schistosity strikes N42E, dips 47SE. Axes of chevron crinkles, asymmetrical with a steep northwest limb, strike N30E, plunge 15SW.

Continuing to .the northwest, the traverse crosses the Mt. Vernon Chtirch graphitic schist-quartzite. The quartzites here are composed of opaques-muscovite-quartz, fine grained, with very well developed millimeter-scale layering. Interlayered with the quartzites are quartz-rich muscovite schist, graphite-quartz-muscovite schist and quartz-feldspar-hornblende gneiss (minor) with scattered chlorite. Layering is parallel to foliation , strikes N25-35E, and dips 40-60SE. There is no pronounced shearing.

10.70

0.40

Junction, Lower River Road; load on buses, proceed southwestward on Lower River Road.

11.00

0.30

Junction, paved road; turn left.

11.35

0.35

Unload, continue Traverse 1.

The dominant rock type here is a biotite-quartz-plagioclase gneiss, fine to medium grained, with feldspar porphyroblasts, in part interlayered with tourmaline-garnet-muscovite schist.

Thin (1 to 8 inches) garnet-tourmaline-quartz-feldspar pegmatites are scattered. Vein quartz is granulated; tourmaline crystals are broken, offset, and healed with quartz. Garnets up to 5mm across are "rounded ", with face intersections smooth rather than angular. Layering is well-developed, but irregular; foliation is parallel to layering, strikes N40-50E, dips 50-70SE. Mineral alignment lineation strikes N38E, plunges 5NE; crinkle axes strike N35E, plunge 7SW.

11.75

0.40

Pleasant Grove Church; load buses; turn left.

11.85

0.10

Junction, Ga. Hwy. 92; turn right on Ga. Hwy. 92.

12.15

0.30

Junction, Lower River Road; continue on Ga. Hwy.

92.

12.45

0.30

Community Grove Church on right.

12.50

0.05

Junction, Anneewakee Road; turn left on

Anneewakee Road.

12.70

0.20

Dirt road on right; continue on Anneewakee Road.

The road is parallel to outcrop trend of well-

developed quartzites.

1-51

13.00

0.30

Junction, South Anneewakee Road on left; unload

and continue Traverse 1. Proceed southwestward

on Anneewakee Road to Pope Road, turn right and

continue on Pope Road.

Exposures of the Anneewakee graphitic schist-quartzite show quartzites 3 to 8 feet thick, composed of quartz, muscovite, tourmaline, magnetite, and pyrite, fine to medium grained with well-developed layering. They are interlayered with tourmaline-garnet-quartzmuscovite schist; garnets are less than 2mm in diameter, euhedral, and some exhibit flattening. Foliation parallel to layering strikes N45E, dips 62SE. Crinkle axes strike N37E, plunge 7SW.

Exposures of the Backbone schist on Pope Road show garnet-quartz-biotite-muscovite schist, medium to coarse grained, interlayered with gray fine-grained biotite-quartzfeldspar gneiss; layering is very well developed. Foliation parallel to layering strikes N42E, dips 42SE. Shear foliation stril es N52E, dips 67SE. The schist has a poorly developed button textur.e.

According to our interpretations, this is the axial portion of the Centralh11tchee Synclinorium. In contact with the Backbone schist on the northwest is the Anneewakee graphitic schist-quartzite, here a tourmaline-graphite-kyanite-gamet-quartz-muscovite schist; medium to coarse grained, interlayered with thinly layered fine-grained micaceous quartzites. Foliation parallel to layering strikes N42E, dips 42SE; shear foliation strikes N65E, dips 62SE.

Continuing the traverse to the northwest along Pope Road, we cross the Sparks Reservoir unit. Notice deformed kyanite in the schist.

The Dry Creek quartzite is well exposed just southeast of Crooked Creek (Fig . 33). Her it is a clean medium- to coarse-grained quartzite interlayered with graphitegarnetquartz-muscovite schist and micaceous quartzite. Layering parallel to foliation strikes N40E, dips 50SE.

13.85

0.85

Crooked Creek; board buses.

14.15

0.30

Road junction, Lake Monroe Road; continue on

Pope Road.

14.35

0.20

Unload buses; continue Traverse 1.

The Mt. Vernon Church graphitic schist-quartzite

here consists of kyani:te-garnet-graphite-quartz-

muscovite schist, with interlayered muscovitic

feldspathic quartzite, and hornblende gneiss.

Continuing to the northwest, the traverse crosses

the Mt. Vernon Church schist which here includes

thinly layered hornblende gneiss ontaining bands

of magnetitic quartz:it 1 to 4 f et thi k; and

staurolite-garnet-quartz-m usco"rite schist.

14.90

0.55

Junction, Bomar Road. The fault contact (Chatta-

hoochee Fault) of the Mt. Vernon Church schist

and the Austell gneiss is placed just southeast of

the road junction.

Board buses; continue on Pope Road.

1-52

Figure 33. Dry Creek exposed at mile 13.85, Traverse 1. 1-53

15.25
15.55 16.25 16.45 17.05 20.60 22.15 24.25
24.95 25.45 25.85 26.75 27.15 29.00
29.65 29.90 30.55 32.85 33.25

0.35
0.30 0.70 0.20 0.60 3.55 1.55 2.10
0.70 0.50 0.40 0.90 0.40 1.85
0.65 0.25 0.65 2.30 0.40

Junction, dirt lane on left; turn left; unload. Pavement exposure of the Austell gneiss; on the southeast flank of the Austell-Frolona Anticlinorium.
Board buses and retrace route to Bomar Road
Junction, Bomar Road; turn left on Bomar Road.
Pavement ends; continue on dirt road. Traversing Austell gneiss.
Union Grove Church schist (of the Austell gneiss).
Junction, Ga. Hwy. 92; bouldery outcrops of Austell gneiss on the left; turn right on Ga. Hwy. 92.
Junction, Ga. Hwys. 166 and 92; turn right on Ga. Hwys. 166 and 92.
Victory Church on left; outcrop of Yellow Dirt gneiss.
Junction, Ga. Hwys. 166 and 92; turn right on Ga. 166. This is the same (low) topographic lineament and zone of intense cataclasis as at Mile 0.00 and 8.15.
Anneewakee Creek
Pipeline crossing; Yellow Dirt gneiss, southeastern contact.
Yellow Dirt gneiss, northwestern contact (Long Island Fault).
Yellow Dirt gneiss, northwestern contact (Long Island Fault).
Chapel Hill Road; Ga. Hwy. 166 follows trend of the Yellow Dirt gneiss.
Yellow Dirt gneiss, northwestern contact (Long Island Fault) with the Sandy Spring Sequence. Circle-H Ranch on the left.
Fouts Road on right; continue on Ga. Hwy. 166
Anneewakee graphitic schist-quartzite of the Sandy Springs Sequence.
Little Creek; passing across the axial part of the Centralhatchee Synclinorium.
Dog River
Northwestern boundary of the Sandy Springs Sequence; in fault contact (Chattahoochee Fault) with the Bill Arp.
1-54

34.00 35.30 35.75 35.95 37.90 38.65 39.15 39.55
40.65
43.10 45.45 46.75 47.25
48.80 49.70 50.75 51.30 51.95
52.25
53.55

0.75 1.30 0.45 0.20 1.95 0.75 0.50 0.40
1.10
2.45 2.35 1.30 0.50
1.55 0.90 1.05 0.55 0.65
0.30
1.30

Five-notch Road on left; continue on Ga. Hwy. 166.
Capps Ferry Road; continue on Ga. Hwy. 166.
Junction, Ga. Hwy. 5, McWhorter; turn left on Ga. Hwy. 5.
Flint Hill Methodist Church on left.
Wilson Road on right.
Tyree Road on right.
Douglas-Carroll County line; leave Douglas, enter Carroll.
Southeastern boundary of the Bill Arp, in fault contact (Chattahoochee Fault) with the Sandy Springs Sequence.
Southeastern boundary of the Sandy Springs Sequence, in fault contact (Long Island Fault) with the Yellow Dirt gneiss.
Crossroad; continue on Ga. Hwy. 5.
Snake Creek
Whitesburg City limit
Junction, U.S. Hwy. 27 Alt.; continue on Ga. Hwy. 5. Near Whitesburg, a south-trending cataclastic zone departs from the southwest regional trend and passes in the vi inity of (Ga. Power Co.) Plant Yates.
Twin stacks of Plant Yates on left.
Road on left to Mcintosh Reserve; continue on Ga. Hwy. 5.
Rotherwood Methodist Church on right.
Acorn Creek
Road junction on right; excellent exposure of fault zone (Long Island Fault), and flinty crush rock derived from the Yellow Dirt gneiss.
Yellow Dirt gneiss, a flinty crush rock here, in fault contact (Long Island Fault) on the northwest side with the Sandy Springs Sequence.
(BRIEF STOP)
Crossroad; near the northwestern boundary of the Sandy Springs Sequence, in fault contact (Chattahoochee Fault) with the Bill Arp.
1-55

53.80 53.95 54.90 55.65 55.90 56.95 57.80 57.85 59.60 60.45
62.80 63.05
64.40 65.50 65.95 66.20 66.95 67.30 67.65
68.65 70.00
70.15

0.25 0.15 0.95 0.75 0.25 1.05 0.85 0.05 1.75 0.85
2.35 0.25
1.35 1.10 0.45 0.25 0.75 0.35 0.35
1.00 1.35
0.15

Whooping Creek
Railroad overpass; Plant Wansley spur. Traversing the Bill Arp.
Crossroad; continue on Ga. Hwy. 5
Road junction; continue on Ga. Hwy. 5.
Contact between the Bill Arp and the underlying Frolona.
Crossroad, Lowell; continue on Ga. Hwy. 5.
New Lebanon Church on left.
Road junction on right; continue on Ga. Hwy. 5.
Rt.llr Point; crossroad; continue on Ga. Ilwy. 5.
Contact between the Frolona and the overlying Bill Arp; on the northwest flank of the AustellFrolona Anticlinorium.
Roopville City limit.
Junction, U.S. Hwy. 27; turn left on U.S. Hwy. 27; continue south through City of Roopville. The Carroll Syncline is to the right (west) of U.S. Hwy. 27.
Road junction on left; turn left toward Glenloch; traversing Bill Arp.
Dirt road on left.
Contact between the Bill Arp and the underlying Frolona.
Paved road on right; continue straight ahead.
Goshen Church on right.
Dangerous curve.
Dirt road on right; continue straight ahead; traversing the Frolona, across the crest of the Austell-Frolona Anticlinorium.
Crossroad, Glenloch; turn left toward Plant Wansley.
Southeastern boundary of the Bill Arp, in fault contact (Chattahoochee Fault) with the Sandy Springs Sequence.
Plant Wansley, entrance.
1-56

70.80

0.65'

Yellow Dirt Church- LUNCH Begin TRAVERSE 2

TRAVERSE 2
The traverse starts at Yellow Dirt Church, in the Yellow Dirt gneiss which has an outcrop width of approximately 1000 feet at this locality. The weathered rock is pink to light gray, fine grained (due to cataclasis), and is composed of feldspar, quartz, muscovite, and biotite, with microcline porphyroclasts 5 to 10 mm in size; yields a yellow-brown residuum. Shear foliation and mineral alignment are well developed.
Flinty crush rock is exposed approximately 175 feet northwest of the church. In this place, the flinty crush rock was derived from the Yellow Dirt gneiss through extensive granulation and the addition of silica. Along strike to the northeast, a development of microbreccia has occurred in the flinty crush rock (CACM 03, Fig. 5). The addition of silica here is not as great as at other localities. Si0 2 content ranges from about 73 percent in the unsilicified Yellow Dirt gneiss to 97 percent at map station CACM 03.
Stringers of milky and smoky quartz, 1 to 6 inches wide, concordant and discordant, are broken and offset. Jointing is closely spaced.
The contact with the Sandy Springs Sequence (road junction) is interpreted as a fault contact (Long Island Fault). Near the contact, jointing is closely spaced and there is intimate mixing of feldspar-biotite-muscovite-quartz schist and the Yellow Dirt gneiss. The schist contains small pegmatite pods and thin stringers of hornblende gneiss.
There are approximately 400 feet of biotite-quartz-feldspar gneiss (Sparks Reservoir unit) next along the traverse. It is fine to medium grained, locally with feldspar porphyroblasts 3 to 5 mm across. The intensity of cataclasis varies across the outcrop; Next there is approximately 100 feet of silvery gray quartz-garnet-muscovite schist, fine to medium grained. The garnets are euhedral, commonly flattened, and 1 to 10 mm across. This schist contains small pegmatitic pods, and zones of button texture caused by the intersection of S-surfaces. Succeeding this is approximately 100 feet of gneiss, as before, well-foliated and well-lineated, containing discordant tabular pegmatites approximately 9 to 12 inches thick.
The Anneewakee graphitic schist-quartzite unit occupies the next part of the traverse. Here it consists of graphite-quartz-muscovite schist, fine to medium grained; feldspathic muscovitic quartzite, and fine- to medium-grained quartz-garnet-muscovite schist. Garnets are 1 to 6 mm across, euhedral, and commonly flattened. Sheared muscovite-biotite-quartzfeldspar gneiss contains thin layers of chloritic epidote-hornblende-plagioclase gneiss.
The next unit, Backbone schist, consists of quartz-garnet-muscovite schist, fine to medium grained, with euhedral, flattened, elongate garnet porphyroblasts 1 to 10 mm across. Thin zones in the schist contain garnets as large as 2 em in diameter. Interlayered with the schist are scarce, black, fine-grained, dense biotite-quartz-feldspar gneiss layers, and discontinuous zones of hornblende gneiss.
Covered interval- approximately 350 feet.
The Anneewakee graphitic schist-quartzite is exposed for approximately 300 feet northwest of the covered interval. Fine-grained quartzite, graphite-muscovite-quartz schist, thin hornblende gneiss layers (minor), fine-grained quartz-muscovite-biotite-feldspar gneiss, and fine-grained quartz-garnet-muscovite schist with distorted garnet porphyroblasts 1 to 5 mm in diameter comprise the section (Fig. 35). Toward the northwest boundary (Plant Wansley entrance), closely spaced fractures are filled with halloysite, manganese oxide, and graphite (Fig. 36). Some fractures show small-scale movement. Minor folds are overturned to the northwest.
1-57

Figure 34. Traverse 2 1-58

Figure 35. Anneewakee graphitic schist-quartzite; exposure on Traverse 2. 1-59

Figure 36. Fracturing in the Anneewakee graphitic schist-quartzite; Traverse 2. 1-60

Poor exposures near the Plant Wansley entrance show garnetiferous mylonitic schist with thin zones of feldspathic quartzite. The covered interval (to the old road) is considered to be underlain by the Sparks Reservoir unit.
Feldspathic muscovitic quartzite, 3 to 5 feet thick, interlayered with (garnet) quartzmuscovite-schist and thin hornblende gneisses is exposed in the old roadbed northwest of Plant Wansley entrance. This is near the northwest contact of the Dry Creek quartzite unit of the Sandy Springs Sequence in fault contact (Chattahoochee Fault) with the Bill Arp.

71.45
72.95 74.90 76.25 77.25
77.85
81.20 82.65 83.35
83.60
83.65
84.25 87.30 88.35 90.50 91.00 91.25
92.75 93.95

0.65
1.50 1.95 1.35 1.00
0.60
3.35 1.45 0.70
0.25
0.05
0.60 3.05 1.05 2.15 0.50 0.25
1.50 1.20

Plant Wansley entrance; board buses. Retrace route to crossroad at Glenloch.
Glenloch, crossroad; turn left.
Junction, U.S. Hwy. 27; turn left on U.S. Hwy. 27.
Centralhatchee city limit.
Centralhatchee Elementary School; junction, paved road on right; continue on U.S. Hwy. 27.
Southeast boundary of the Sandy Springs Sequence, in fault contact (Long Island Fault) with the Yellow Dirt gneiss.
Centralhatchee Creek.
Franklin city limit
Junction, Ga. Hwys. 34 and 100; turn right on Ga. Hwy. 34W and lOON.
North-trending shear zone in chloritic hornblende gneiss.
Junction, Ga. Hwy. lOON; continue on Ga. Hwy. 34W.
Glover Creek (Hillabahatchee Creek)
Flat Rock Camp Ground; Viola
Junction, Ga. Hwy. 219; continue on Ga. Hwy. 34W.
Crossroad, continue on Ga. Hwy. 34W.
Texas, Georgia
Junction, John T. Mickle Road; turn right (Prospect Church is about 150 yards to the west on Ga. Hwy. 34).
Pipeline crossing
Disembark for TRAVERSE 3.

1-61

TRAVERSE 3
Traverse 3 begins in the Yellow Dirt gneiss, an epidote-biotite-mus ovite-quartz-feldspar gneiss; fine- to medium-grained, with cataclastic foliation. Flattened and smeared feldspar porphyroclasts are common. In places, quartz-feldspar pegmatites l ss than 4 em wide, are sheared and granulated. The gneiss is considered to b in fault contact (Long Island Fault) with the Sandy Springs Sequence. Covered interval - approximately 100 f et.
Northwest of the covered interval is the Dry Creek quartzite: muscovitic quartzite, fine to medium grained, white to yellowish white, sheared; abundant chips of quartzite are conspicuously present in the saprolite. Minor associated lithologies include chlorite-hornblendeplagioclase gneiss, fine grained; muscovite-quartz schist, fine to medium grained, silvery white; quartz-muscovite-feldspar schist, fine grained, very feldspathic; and a varigated feldspathic gneiss. Outcrop width is approximately 100 feet..
Next is the Sparks Reservoir schist, weathered and poorly exposed. The dominant lithology is a l{yanite-garnet-quartz-muscovite schist, fine to mel;lium grained. Coarse kyanite blades, commonly bent, are abundant in the residuum. Garnet porphyroblasts, 1 to 5 mm across, are common. Flattened and sheared garnets (slivers) are abundant in the residuum. Muscovite buttons arc common.
To the northwest is a thin zone of fine- to medium-grained muscovitic quartzite and (garnet) muscovite-quartz schist; both are white and granulated. This unit, the Anneewakee graphitic schist-quartzite, is approximately 50 to 75 feet thick.
In contact on the northwest is the Backbon schist, a kyanite-garnet-quartz-muscovite (biotitic in places) schist, fine to medium grained, silvery gray in color. Garnet porphyroblasts are from 1 to 6 mm in diameter, fiatt ned, with shear slivers common. Kyanite is common in the saprolite. Graphite occurs sparingly in some quartz chips within the schist. Interlayered with the s lust are thin layers of chloritic hornblende gneiss. The schist is very well exposed in th road ditches (NE side of road near its northwest boundary. Here it is well-lineated, the lineations (crinkle axes) striking N25E, plunging 12SW.
Approximately 200 feet southeast of the crossroads is the contact between the Backbone schist and the Adamson graphitic schist-quartzite. Northwestward along the traverse, the following lithologies are xposed: muscovitic quartzite, fine to medium grained, white to yellowish white; in places the quartzite ontains graphite, garnet pyrite, and biotite. Layering is well develop d. Chloritic hornblende gneiss, thinly layered; weathered, but conspicuously present. Quartz-muscovit !feldspar schist gneiss, fine-grained; very weathered and quit variable in color. IUs onspicu usly present and composes a larg portion of the section. Pegmatites are common.
At the ro sroad is a good development of a mixtme of gmphite-garnet-quartz-muscoviteschist and garn tiferous-muscovitic quartzite. Garnets ar euhedral and less than 3 mm in diameter. Some are flattened and sheared. Sh ared muscovite-quartz-feldspar pegmatit and granulated quartz stringers are common. The pegmatitic zones extend over a distance of 3 to 5 feet.
Northwest of the crossroad the rocks are mostly biotite-garnet-quartz-feldspar-muscovite schists interlayered with mus ovite-bi tite-quartz-feldspar gneiss. Both are fine to medium grained. Garnet porphyroblasts range from 1 to 10 mm across; the garnets are euhedral, locally flattened, elongate, and sheared. Quartz stringers, less than 2 inches wide, are common. At or near th northwest conta t of this unit (Adamson graphitic schist-quartzite) is a good aevelopment of graphite-garnet-muscovite-quartz schist and graphitic muscovitic quartzite (subordinate). Graphite is very abundant; gam .t porphyroblasts, less than 3mm across, are euhedral and very common.
1-62

I I
~ .-~-f-l~ -~I 1

0 0
Figure 37. Traverse 3 1-63

The Mt. Olive Church unit, in the center of the Centralhatchee Synclinorium here, is mostly covered along this traverse. Saprolite and scattered residuum show a mixture of chloritic hornblende gneiss, muscovite-biotite-quar tz-feldspar gneiss and kyanite-garnetmuscovite-quartz schist. Kyanite blades and euhedral garnets less than 3 mm across, are conspicuous in the saprolite. Chips of quartz string rs are common on the ground surface.
Continuing to the northwest, the traverse again crosses the Adamson, which here consists of interlayered gtaphitic muscovi.tic quartzite fi ne to medium grained, orange in color thinly layered in places, with scarce graphite; chlorit i (garnetiferous) hornblende gneiss, fin -grained , thinly layered (minor folds ar ammon); muscovite-quartz-feldspar gneiss schist, quite feldspat hic, weathering to a varigated color and scarce garnet-muscovite-quartz schist, fine to medium grain d, with garnet por phyro bJasts from less t han 1 mm to 4 mm across . Garn t s are euh dral , som rounded, some sheared into slivers . Mineral alignment (mn. covite and quartz ) is well developed ; vein quru:tz is grooved.
The contact between the Adamson graphitic schist-quartzite and the Backbone schist is covered. Board the buses for a short ride.
To the northeas t alo ng the road the Backbo ne schist is poorly exposed. The saprolite shows that the unit is composed mmtly n f a garnet-m uscovite quartz schis t. Garnet porphyroblasts in t he saprolite ar euhedral, flattened, and sh ar d; t hey range from 1 to 10 mm across. Thin, sheared layers of chJoriti hornblend gneiss are scarce .
Unload to continue walking traverse.
At t he t op of t he hill and as the r oad cUl'ves bacl< to th northw t, t h (Low) topographic lli1eament developed on a zon of intense cata lasis (and the Cha ttahooche Fault) is quite conspicuous. In t he roadcuts to r own Creek at th e bottom of t b hill are good exp osur s of a kyanite-garnet-quartz- muscovit s hisl (Ba kbone schist) . Th l"oc k is silvery gray, f ine to medium grain d and p mphyroblastic. Gamet por phyrobJasts l to lO mm. a ross, occur as euhedral elongate and shear d grains. The ro ck contains both garnet and muscovite buttons and is mylonitic. Two 8-surfaces are well develop d . Milky q uartz strin gers are normally less than 3 inches wide, but may reach several feet in length . They ar for the most part parallel to the cataclastic schistosity and may be sin uo us in places. F ine grain. of ky anit e are common in the saprolite. Crinkle fold lineations m well develo ped.

95.45 95.80
96.25 97.35 97.40 97.85 101.20

1.50

Town Creek. Board buses and ride across the

cataclastic zone.

0.35

Good exposures of rock in the zone of intense

shearing. The dominant lithology is mylonitic

muscovite-quartz-fe ldspars h.isL very feldspathic;

interlay red wit h less r amounts of mylonitic

epidot -plagio lase-hornblend e gneiss . Well-

developed lineation (crinkle axes) plunge to the

southwest.

0.45

Ridley; road parallels the low topographic linea-

ment developed on zone of intense cataclasis.

1.10

Road junction; turn right

0.05

Hillabahatchee Creek

0.45

Crews Creek

3.35

Junction, Ga. Hwy. 100; turn right on Ga. Hwy.

100.

1-64

103.20 103.55

2.00

Junction, Ga. Hwy. 34; turn left to Franklin; Q!_

turn right to Roanoke, Alabama and points west;

Q!_proceed on Ga. Hwy. 100 to mileage 103.55

0.35

Junction, U.S. Hwy. 27; turn left to Carrollton; Q!_

turn right to Franklin, Newnan, LaGrange, and

points south.

END OF ROAD LOG

1-65

REFERENCES
Bentley, Robert D., and Neathery, Thornton L., 1970, Geology of the Brevard Fault Zone and related rocks of the Inner Piedmont of Alabama: Guidebook for 8th Annual Field Trip of the Ala. Geol. Soc., 120 p.
Blatt, H., Middleton, G., and Murray, R., 1972, Origin of sedimentary rocks: Prentice-Hall, Inc., N.J., 634 p.
Coleman, S. L., Medlin, J. H., and Crawford, T. J., 1973, Petrology and geochemistry of the Austell gneiss in the western Georgia Piedmont (abs.): Geol. Soc. Am. Southeastern Sec. Abstracts with Programs, v. 5, no. 5, p. 388.
Condie, K. C., 1967, Geochemistry of early Precambrian graywackes from Wyoming: Geochem. et. Cosmochem. Acta, v. 31, p. 2135-2149.
Crawford, Thomas J., and Medlin, Jack H., 1970, Stratigraphic and structural features between the Cartersville and Brevard fault zones: Fifth Annual Field Trip, Georgia Geol. Sue., 37 p.
__ 1972, The western Georgia Piedmont between the Cartersville and Brevard fault zones (abs.): Geol. Soc. Am. Southeastern Sec. Abstracts with Programs, v. 4, no. 2, p. 68.
__ 1973, The western Georgia Piedmont between the Cartersville and Brevard fault zones: Amer. Jour. Sci., v. 273, p. 712-722.
Crickmay, Geoffrey W., 1952, Geology of the crystalline rocks of Georgia: Georgia Geol. Survey Bull. 58, 54 p.
Hayes, C. W., 1901, Geological relations of the iron ores in the Cartersville District, Georgia: Am. Inst. Min. Eng., Trans., v. 30, p. 403-419.
Hermann, L. A., 1954, Geology of the Stone Mountain-Lithonia District, Georgia: Georgia Ge9l. Survey Bull. 61, 139 p.
Higgins, Michael W., 1966, Geology of the Brevard lineament near Atlanta, Georgia: Georgia Geol. Survey Bull. 77,49 p.
__ 1968, Geologic map of the Brevard Fault Zone near Atlanta, Georgia: U.S. Geol. Survey Misc. Geol. Inv., MP I-511.
__ 1971, Cataclastic rocks: U.S. Geol. Survey Prof. Paper 687, 97 p.
Hurst, Vernon J., 1973, Geology of the Southern Blue Ridge Belt: Amer. Jour. Sci., v. 273, p. 641-670.
Hurst, Vernon J., and Crawford, Thomas J., 1969, Sulfide deposits, Coosa Valley area, Georgia: Econ. Development Administration, U.S. Dept. of Commerce, Washington, D. C., 190 p.
Hurst, V. J., and Jones, Lois M., 1973, Origin of amphibolites in the Cartersville-Villa Rica area, Georgia: Geol. Soc. Am. Bull., v. 84, no. 3, p. 905-911.
Jones, Lois M., Hurst, Vernon J., and Walker, Raymond L., 1973, Strontium isotope composition of amphibolite of the Cartersville-Villa Rica district, Georgia: Geol. Soc. Am. Bull., v. 84, p. 913-918.
1-66

Kesler, T. L., and Kesler, S. E., 1971, Amphibolites of the Cartersville District, Georgia: Geol. Soc. America Bull., v. 82, p. 3163-3168.
Kuno, Hisashi, 1959, Origin of the Cenozoic petrographic provinces of Japan and surrounding areas: Bull. Volcanologique, v. 20.
Medlin, Jack H., and Crawford, Thomas J., 1973a, Geologic maps, Coweta, Fulton, and Heard Counties, Georgia: Unpublished maps in files of Georgia Dept. of Natural Resources, Earth and Water Division, Atlanta, Ga.
__ 1973b, Stratigraphy and structure along the Brevard Fault Zone-western Georgia and eastern Alabama: Amer. Jour. Sci., v. 273-A, p. 89-104.
Pettijohn, F. J., 1963, Chemical composition of sandstones-excluding carbonate and volcanic sands, in Fleischer, M., ed., Data of geochemistry, 6th edition: U.S. Geol. Survey Prof. Paper 440-S.
Schepis, Eugene L., 1952, Geology of eastern Douglas County, Georgia: Unpublished Master's Thesis, Emory University.
Watson, T. L., 1902, The granites and gneisses of Georgia: Georgia Geol. Survey Bull. 9, 367 p.
Winkler, H. G. F., 1965, Petrogenesis of metamorphic rocks: Springer-Verlag. New York, Inc., New York, 220 p.

TERTIARY STRATIGRAPHY OF THE CENTRAL GEORGIA COASTAL PLAIN
by Paul F. Huddlestun, William E. Musalis and Sam M. Pickering, Jr.
FIELD TRIP 2

.

.

. ..
' A

; .

,t

~' '

. I i,

..r ' .

CONTENTS
Introduction Stratigraphy
Midwayan Stage Clayton Formation Porters Creek Formation .
Sabinian Stage . . . . . . Gravel Creek Member of Nanafalia Formation
Claibornian Stage Lisbon Formation
Jacksonian Stage . . Clinchfield Sand . Tivola Limestone . Twiggs Clay . . "Cooper Marl"
Vicksburgian and Chickasawhayan Stages Neogene undifferentiated References Road Log Measured section .
ILLUSTRATIONS
Figure 1. Location of field trip area 2. Correlation chart . 3. Schematic cross-section of Upper Eocene deposits in Georgia . 4. Field trip itinerary 5. Composite geologic section, Stop 1 . 6. Composite geologic section, Stop 3 .
7. Photograph of west sump, Stop 3
8. Photograph of west quarry, Stop 3
iii

2-1 2-1 2-1 2-1 2-2 2-4 2-4 2-4 2-4 2-6 2-6 2-6
2-8 2-9 2-10 2-11
2-12
2-15 2-33
2-2 2-3 2-7 2-14 2-16 2-18 2-19 2-20

Figure 9. Photograph of west quarry, Stop 3

2-21

10. Photograph of west quarry, Stop 3

2-22

11. Photograph of Twiggs Clay .

2-23

12. Composite geologic section, Stop 4 .

2-25

13. Composite geologic section, Stop 5 .

2-26

14. Stratigraphic cross-section, Clinchfield to Hawkinsville, Ga.

2-27

15. Schematic section of roadcut, Stop 6

2-28

16. Composite geologic section, Stop 7 .

2-32

iv

TERTIARY STRATIGRAPHY OF THE CENTRAL GEORGIA COASTAL PLAIN
by
Paul F. Huddlestun, William E. Marsalis and Samuel M. Pickering, Jr.
INTRODUCTION
Middle Georgia was selected for this field trip because it is a transition area between the Atlantic and Gulf Coastal Plain (Fig. 1 ). Stratigraphic and paleontologic correlations of Tertiary units between these two parts of the Coastal Plain have been difficult and seldom attempted. The updip Middle and Lower Tertiary Gulf Coastal Plain deposits of western Georgia and eastern Alabama have been removed by erosion. All outcrops of that age now occur far downdip from the area covered by the field trip route. Thus, in the past, correlation westward from middle Georgia has been done along a 200-mile outcrop belt of downdip facies, where lithology and faunas differ appreciably from those in the field trip area. The writers have found it far more reliable to relate the updip section in middle Georgia to units of similar facies in middle and western Alabama (Fig. 2).
Correlation of the Tertiary units of middle Georgia with Atlantic Coastal Plain sediments of South Carolina is hampered by the east Georgia section, which is stratigraphically poorly known. Paucity of fossils and the more clastic nature of the units in eastern Georgia have made correlation with outside areas difficult. Accurate identification and correlation of sedimentary deposits is becoming increasingly important, as the demand accelerates for industrial minerals and ground water. In addition, determination of regional and local structural features depends completely on precise stratigraphic determinations.
We hope that this field trip will allow a rapid review of current stratigraphic work on the Georgia Coastal Plain, as well as a chance to visit several classic exposures where abundant fossils may be collected. Roadcut grassing and quarry reclamation have limited the future availability of many localities. To preserve as much as possible of the information contained in these exposures measured sections, lithologic descriptions, and photographs are included.
STRATIGRAPHY
MIDWAYAN STAGE
CLAYTON FORMATION
The Clayton Formation was named by Smith (1892) for exposures near Clayton, Barbour County, Alabama. On the Chattahoochee River (Toulmin and LaMoreaux, 1963), the Clayton consists of sandy limestone, clacareous sand, calcareous sandstone, coquinoid limestone, and silty, microfossiliferous, soft limestone. North of Montezuma, Macon County, Georgia, on the Flint River, the Clayton consists of a coarsely fossiliferous, slightly argillaceous, calcareous sand that contains highly fossiliferous limestone ledges and abundant Ostrea crenulimarginata.
The thickness of the Clayton on the Chattahoochee River ranges from 90 feet to 150 feet as a result of solution on the top of the formation (Toulmin and LaMoreaux, 1963). The Clayton has thinned to only 13112 feet on the Flint River (Stop 7) and it has not been recognized in outcrop further east.
The Clayton Formation unconformably overlies the Providence Sand of Late Cretaceous age.

l .

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GULF

COASTAL \PLAIN

ALABAMA -- "-FloiiioA-- -- -

I '. -- - - - ~
...

GEORGIA

r " '

----FLORiD;.-------- -, )

L

Figure 1. Location of field trip area.
PORTERS CREEK FORMATION
The Porters Creek Formation was originally defined in Hardeman County, Tennessee (Safford, 1864). It has subsequently been recognized in Mississippi and Alabama where it had been referred earlier to the Sucarnoochee Clay. The Porters Creek overlies the Clayton Formation in western Alabama and is believed to grade laterally into Clayton lithology in eastern Alabama (LaMoreaux and Toulmin, 1959; Toulmin and LaMoreaux, 1963). As a result the Porters Creek interval is included in the upper part of the Clayton Formation on the Chattahoochee River.
Typically, the Porters Creek is a tough, dark gray to almost black, blocky, calcareous clay. This lithology is exposed near Andersonville in Sumter County. At Montezuma (Stop 7) on the other hand, the silty calcareous clay lithology exposed above the Clayton is atypical but is more consistent with Porters Creek than with Clayton.
Outcrops of Porters Creek Clay are not known east of the Flint River.
The Porters Creek conformably and gradationally overlies the Clayton Formation at Montezuma.
2-2

g"u

MISSISSIPPI

ALABAMA

UPDIP CENTRAL GEORGIA

FLORIDA

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2-3

SABINIAN STAGE
GRAVEL CREEK MEMBER OF THE NANAFALIA FORMATION
The Gravel Creek Member of the Nanafalia Formation was named by LaMoreaux and Toulmin (1959) for exposures along Gravel Creek, Wilcox County, Alabama. They (Toulmin and LaMoreaux, 1963) later recognized the Gravel Creek Member on the Chattahoochee River where the Gravel Creek forms the basal member of the Nanafalia Formation.
Outcrops of typical marine facies of the Nanafalia Formation in Georgia are restricted to the watershed of the Chattahoochee River. To the east the entire Nanafalia is represented by the marginally marin to nonmarine Gravel Creek Member. In Georgia, this unit is characteristically a sand , wh_ich is massive, thin bedded, or cross bedded, micaceous, and frequently coni-.ains lenses of kaolinite or bauxite. Occasionally these lenses in western Georgia are large enough and pure enough to be of commercial value as a refractory raw material.
The thir.kness of the Gravel Cr ck Member is not now well known along the outcrop belt in Georgia. Along the Chattahooch e River the entire Nanafalia Formation may be as thkk as 80 feet. At Montezuma th Gravel Creek Member is 57 feet thick. The Gravel Creek has been traced as far east as th Ocmulgee River, Houston County, Georgia, but its thickness there is unc rtain. Where th Gravel Creek is underlain by Midwayan marine sediments, or by the Upper Cretaceous Providence Sand, it can be readily distinguished from the "Tuscaloosa Formation". However, where the Gravel Creek rests directly on the "Tuscaloosa", separation is difficult, since the lithologies are almost identical.
The Nanafalia Formation and the Gravel Creek Member unconformably overlie the Clayton Formation on the Chattahoochee River. To the east in Sumter County and Macon County the Porters Cre k Clay appears abov the Clayton and it is overlain unconformably by the Gravel Cre k Member . Further updip and to the east, the marine Lower Paleocene pinches out and th unconformity b tween the Gravel Cr ek Mem ber and older deposits becomes obscured by their lithologic similarity . Tertiary kaolin~containing deposits of east Georgia, descril ed by Buie and Fountain (1 67 , Carver (1966), and others, may be in part equivalent to the Gravel reek Member.
CLAIBORNIAN STAGE
LISBON FORMATION
T. H. Aldrich ( 886) mad first 1 ference to the Lisbon Formation for beds cropping out at"L_isbon Landing on the Alabama River, in Monroe County, Alabama. Although beds of Middle Eocene (Claibornian) age have been recognized in Ge rgia since th last century there has been uncertainty as to which formation to put them into. Vea band Stephenson (1911) established the McBean Formation for Claibornian ag d posits in eastern Georgia. They recognized lithologi similarities with the Lisbon of Alabama but justi fied the er ction of the n w formation name on the difference in formation sequence between the two states. Veatch and Stephenson apparently believed that a formational name was valid only when a unit was in the same sequence as at the type locality. Thus, since neither Gosport nor Tallahatta was evident to them, the name Lisbon was not thought valid. As a result, they recognized only the McBean Formation in Georgia, which they believed equivalent to the combined Tallahatta, Lisbon, and Gosport Formations of Alabama.
2-4

The opinions of subsequent authors have varied. Cooke (1943), like Veatch and Stephenson, recognized only the McBean in state. Pickering (1970), in his study of the stratigraphy of the Houston-Pulaski County area recognized only the McBean Formation. McNeil (1947), however, considered all younger Claibornian deposits in the western half of the state to be Lisbon, restricting the McBean Formation to its type area along the Savannah River. Toulmin and LaMoreaux (1963) and Marsalis (1972) recognized both Tallahatta and Lisbon on the Chattahoochee River.
Herrick (1961) and Herrick and Vorhis (1963) approached the problem differently. They recognized the Lisbon as a shallow subsurface clastic equivalent of the McBean Formation, but did not elaborate on their lithologic distinction. They restricted the McBean to its outcrop belt and considered the two units to be equivalent. They recognized the Lisbon in the subsurface across the entire state, from the Chattahoochee River to the Savannah River.
The authors find it impossible at this time to draw a consistent lithologic distinction between the Lisbon Formation of Alabama and the McBean Formation of Burke County, Georgia. Both units in their marine extent are dominated by quart sand, clay, and calcium carbonate. Limestone beds and shelly debris are common and mica, glauconite, and lignitic fragments are often present. There is no characteristic lithology peculiar to either unit. One can only be certain of the correct identificaiton of these formations by determination of precise stratigraphic position. Consequently the authors feel that until a comprehensive evaluation of the Late Claibornian is made in Georgia, it is prefereable in the field trip area to use the more universally known Lisbon Formation.
On the Chattahoochee River the Lisbon unconformably overlies the Tallahatta Formation. The Tallahatta is not present in outcrop east of the watershed of the Chattahoochee River. Consequently, the Lisbon overlies the older Gravel Creek Member of the Nanafalia or the Tuscaloosa undifferentiated eastward of the Chattahoochee River.
The thickness of the Lisbon in outcrop is variable. It appears to thicken consistently downdip. On the Chattahoochee River the Lisbon is 110 feet thick (Toulmin and LaMoreaux, 1963). Further east on the Flint River at the old site of Danville Ferry, the Lisbon is at least 20 feet thick. At Clinchfield the Lisbon is 37 feet thick. Ten miles to the southeast at Hawkinsville the subsurface Lisbon has thickened to 100 feet.
The outcropping Lisbon in Georgia is equivalent to the upper Lisbon of Alabama (Ostrea sellaeformis Zone), to the Avon Park Limestone of Florida, to at least part of the Santee Limestone of South Carolina, and to the Castle Hayne Limestone of North Carolina.
2-5

JACKSONIAN STAGE
CLINCHFIELD SAND
The Clinchfield Sand was first proposed informally by Vorhis (1965) for strata which had been previously referred to Gosport Sand (LeGrande, 1962). It was first adopted in print by Carver (1966). Pickering (1966, 1970) formally defined the formation and Herrick (1972) discussed its age and correlation.
The Clinchfield Sand is typically a fine to medium grained, massive or bedded, poorly to nonconsolidated fossiliferous, calcareous quartz sand. Locally the top of the Clinchfield may be indurated to a hard, rubbly, porous, calcareous sandstone that is packed with molds and casts of pelecypods and gastropods.
The Clinchfield Sand is a thin deposit and rather variable in thickness. Herrick (1972, p. 6) reports thicknesses ranging from 9 feet in the vicinity of the type locality to as much as 35 feet in wells and shallow cores.
As presently understood, the Clinchfield Sand is of earliest Jacksonian age and is thought to be equivalent to the basal Moodys Branch Formation of Mississippi, to the lower Moodys Branch of Alabama (Huddlestun and Toulmin, 1965), and to the Inglis Limestone of Florida.
Where it is present, the Clinchfield overlies the Lisbon Formation unconformably.
TIVOLA LIMESTONE
In Georgia, any Upper Eocene limestone that contains a characteristic "Ocala" fauna has been called Ocala Limestone, regardless of the particular limestone lithology. Thus Cooke (1915) first recognized the Ocala Limestone of Florida (Dall, 1892) in the Bainbridge, Georgia area. Later, Cooke and Shearer (1918) extended the Ocala Limestone concept into the Houston County area on the basis of the gross lithology and fauna. They proposed it to be a thin extension or tongue of the downdip limestone body into the equivalent, updip clastic body (Barnwell Sand) and called it the Tivola tongue of the Ocala Limestone after the community of Tivola, Houston County, Georgia (Fig. 3). Connell (1959), on the other hand, recognized a lithologic distinction between the Tivola, which he considered to be a member of the Ocala, and the Ocala Limestone of the southwestern part of the state. Subsequent authors, Herrick (1961), Herrick and Vorhis (1963), Carver (1966), and Pickering (1970) have continued the use of the term Ocala in middle Georgia.
Like Connell, the authors of this guidebook recognize a systematic lithologic difference between the Tivola limestone and the Ocala limestone of the southwestern part of the state. In addition, intensive stratigraphic studies now in progress at the Georgia Geological Survey indicate that the limestone tongue concept of Cooke and Shearer is oversimplified and inaccurate, and that the Ocala Limestone as presently used in the state can be subdivided into two or more separate units.
As noted above, the Tivola tongue was thought by Cooke and Shearer to be a simple extension of the Ocala Limestone (Fig. 3). However, from the senior writer's experience, the Jacksonian of the southeast is characterized by two distinct marine transgressive events. The marine inundations left sedimentary deposits of characteristic lithology and are therefore lithostratigraphically distinguishable. In the field trip area, the lithologic units of the earlier transgression are the Clinchfield Sand, Tivola limestone, and Twiggs Clay. The later transgression is represented in the Houston-Pulaski County area only by the "Cooper Marl" and possibly by its updip equivalent, the Irwinton Sand. Downdip however, as will be
2-6

..;

OCALA LIMESTONE

1:..:>

Cooke & Shearer, 1918

~

BARNWELL FORMATION

- - ~

~--

"<::::..

- = c = TWIGGS CLAY MEMBER

--~

Bed Containing 0. G EORG IANN.A.

...c....

.~
~

c

.!

.
;;;
~

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OCALA LIMESTONE

-===

-- 5 n COOPER

MARL "

IRWINTON SAND

~

BARNWELL SAND

I. z
.t"'!iu!

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Huddlestun, Marsalis & Pickering, 1974

TWIGGS CLAY

;

g

- - ~~-

-

-

-

-

--

Figure 3. Schematic cross-section of Upper Eocene deposits in Georgia, as interpreted by Cooke and Shearer (1918), and authors.

discussed later, the "Cooper Marl" grades into what the authors regard as Ocala Limestone. The Tivola on the other hand maintains its lithologic identity in the shallow subsurface, and sediments of similar stratigraphic position and lithology have been identified in outcrop in the southwestern part of the state.
The Tivola is a coarse, uneven, marly, bioclastic limestone. Bryozoan remains are commonly so abundant that the sediment may be regarded as a coquinoid bryozoan limestone. The uneven texture is due to the lack of size sorting of the bioclasti debris. Wher larger fossils such as pectens, echinoids, oysters, and molluscan molds ar abundant, the texture of the limestone is very coarse and rubbly. Impuriti sin the Limeston ar chara teristically clay mineral, glauconite, pyrite, and in the lower part, quartz sand . In fresh exposures the
Tivola is usually a lightly indurated to tm onsolidat d, cal areous sediment with a 6 to 10
foot bed of hard rubbly limestone at the top. Even brief exposure to weathering, however, will case-harden the unconsolidated limestone.
The Tivola limestone is considered to be equivalent to the upper part of the Moodys Branch Formation of Jacl{son Wssissippi; to the Upper Moodys Branch of Alabama (Huddlestun and Toulmin, 1965) ; to the Williston Limestone of Florida and to the upper Sant~P. Tlimestone at the Carolina CianLquarry near Hully Hill, South Carolina. ln eastern Georgia the Tivola appears to grade into a noncalcareous sand that underlies the Twiggs Clay in some areas.
As with most of the other units in the field trip area, the thickness distribution of the Tivola at present is uncertain. Its maximum known thickness appears to be consistently about 40 feet at Clinchfield and in the shallow subsurface. The unit thins updip and is known to be discontinuous in the northeastern part of the field trip area.
The Tivola Limestone conformably and gradationally overlies the Clinchfield Sand.
TWIGGS CLAY
The Twiggs Clay Member of the Barnwell Formation was proposed by Cooke and Shearer (1918) for fuller's earth clay deposits of Jacksonian age in eastern Georgia. Earlier Veatch and Stephenson (1911) referred the calcareous facies of the unit, characteristically developed in the central Georgia Coastal Plain, to Jackson Formation and the siliceous facies characteristically developed in the eastern part of the state to the Congaree Clay of Sloan (1907). Shearer (1917) is given credit for correlating the calcareous and siliceous facies of the unit. Pickering (1970) r omrn nded independent formational status for the Twiggs Clay because of its lithologi distinctiven mappability, wide aerial distribution, and its easily determined upper and low l' boundaries in the central part of the state.
Tb, Twiggs 'lay i a gt nish to bluish-gray, silty clay with hackly, blocky, or conchoidal fra tur . Some b cis c nsist of almost pure montmorillonite clay but characteristically the clay is impme. The impurities may consist of quartz silt or sand, finely disseminated or biogenic cal it. or opal ristobalit occasionally preserved argonitic mollusc shells, glauconite, pyrite, mica, and Decks of arbonaccous matter. Minerals which are normally subordinate may produce the dominant lithologies in this unit. Sand, glauconite, chert, or limestone beds of varying thickness and extent are present.
The maximum known thickness of the Twiggs is approximately 100 feet in Twiggs and Houston Counties. It thins updip in Bibb and Crawford Counties to less than 30 feet. It thins in the shallow subsurface and is not present a short distance downdip (Herrick, 1961).
2-8

The Twiggs Clay is considered to be equivalent to the North Twistwood Creek Clay of Alabama and Mississippi and to the lower part of the Yazoo Clay of Mississippi. The lithology and stratigraphic position of the Twiggs are almost identical to the North Twistwood Creek Clay. The Twiggs and the North Twistwood Creek may well have been continuous at one time. However, no equivalent beds exist now between the Conecuh River of Alabama and the Flint River of Georgia.
"COOPER MARL"
The unit referred to as "Cooper Marl" in this guidebook was originally placed in the Jackson Formation by Veatch and Stephenson (1911). Cooke (194-3} recognized the distinctiveness of this unit and correlated it with the Cooper Marl of South Carolina on the basis of lithology and what was then known of its fauna and stratigraphic position. Subsequent faunal analysis of typical Cooper Marl from its type area (Cooke and MacNeil, 1952) suggested an Oligocene age for the formation. In Georgia, Pickering (1966, 1970) identified Paraster americanus and Brissopsis blanpiedi, both enchinoids beif!g restricted to the Vicksburgian of Alabama and Mississippi. As a result, an Oligocene age has Been incorporated in the literature for the "Cooper Marl" of Georgia (Pickering, 1966, 1970; Herrick and Counts, 1969).
Micropaleontological examinations of the Georgia "Cooper" and the South Carolina Cooper by the senior author show that the "Cooper" of Georgia is Late Eocene in age, based on the presence of the planktonic foraminifers Cribrohantkenina inflata, Globorotalia cerroazulensis, and Hantkenina alabamensis. At present no part of the "Cooper", nor any other sediment so far examined by the authors in Georgia, can definitely be correlated with Early OligocenaRed Bluff Clay of Mississippi and Alabama or its equivalent, the Bumpnose LJmestone of Alabama and Florida. ' The Cooper Marl of South Carolina on the other hand contains planktonic foraminifera of Late Oligocene, Chickasawhayan age and of Early Miocene, Aquitanian age. Only one South Carolina Cooper locality visited by the authors contains a Late Eocene planktonic foraminifer suite, and it is well updip from the type area on the Cooper and Ashley Rivers.
Although the lithology of the "Cooper Marl" in Houston and Pulaski Counties is grossly similar to the South Carolina Cooper, no continuous similar lithology occurs between the Edisto River of South Carolina and the field trip area in central Georgia. Marly sediments equivalent to "Cooper Marl" are known in the vicinity of the Ogeechee and Savannah Rivers of Georgia, but the lithology is not the same as that of the Cooper Marl. In addition, from available cores in the vicinity of the Savannah River, it has been found that these marly sediments grade downdip into a gray, coarsely bioclastic, indurated limestone that is not Ocala and certainly is not Cooper. Therefore, it cannot be maintained that the "Cooper" of Georgia is a tongue of the Cooper of South Carolina.
From this evidence we conclude that there is no true Cooper Marl in the state of Georgia, and that the "Cooper" deposits in Houston and Pulaski Counties have been misnamed. Since a guidebook is not a vehicle for formal designation of new stratigraphic units, the name by which this unit has been known is retained but placed in quotation marks to show the suggested impropriety of its usage.
The typical "Cooper Marl" at the outcrop in the field trip area consists of a basal sandy, glauconitic, indurated limestone overlain by tough, massive-bedded, glauconitic, granular, marly-textured, non-indurated limestone. In the shallow subsurface however, the typical lithology is more argillaceous, marly, and variable than it is in outcrop. This suggests that only the more calcareous, resistant beds in the unit are able to withstand deep weathering and are exposed at the surface. In the shallow subsurface of Houston and Pulaski Counties, the "Cooper" is typically a glauconitic, argillaceous to clayey, even-textured, granular to
2-9

lutitic, very calcareous marl to very marly limestone. Both at the surface and in the shallow subsurface, bryozoans often occur in sufficient abundance to render a coarse, uneven, bioclastic texture to the otherwise even, granular sediment.
The "Cooper Marl" grades very gradually downdip to the south into Ocala lithology that is exposed in the vicinity of Albany, Dougherty County, Georgia. Midway between the Houston-Pulaski County area and Dougherty County, exposures of Ocala Limestone are present on the Flint River west of Cordele, Crisp County, that are intermediate lithologically between "Cooper" and Ocala.
The "Cooper Marl" is biostratigraphically equivalent to the Pachuta Marl and Shubuta Clay of Mississippi and western Alabama, to the upper part of the Yazoo Clay of Mississippi, to the Ocala Limestone of central Alabama (Huddlestun and Toulmin, 1965), to at least part of the Crystal River Formation as currently used in Florida (Puri, 1957), to the Sandersville Limestone of eastern Georgia, and to the oldest part of the Cooper Marl of South Carolina. The available evidence suggests that part of the Irwinton Sand of eastern Georgia is an undip, non-marine, or at least, noncalcareous facies of the "Cooper". In addition, some exposures of traditional Barnwell Sand in Bmke-County_, Georgia, contain silicified "CoopP.r" faunas.
The "Cooper Marl" conformably overlies the Twiggs Clay in the Houston-Pulaski County area. It is overlain abruptly and apparently unconformably by Marianna Limestone in the vicinity of Hawkinsville, Pulaski County. Further updip, both at the surface and in the shallow subsurface, it is overlain with a pronounced unconformity by massive chert of Late Oligocene (Chickasawhayan) age, or by detrital cherty sands, clays., and gravels of probable Miocene age.
VICKSBURGIAN AND CHICKASAWHAYAN STAGES
Limestone exposures along the Ocmulgee River below Hawkinsville, here recognized as the Marianna and Glendon Limestones, are the only Oligocene sediments in the field trip area which have not been reduced by weathering to a chert-clay residue. No other Early Oligocene (Vicksburgian) sediments have been found in the area.
Elsewhere in outcrop, the Late Oligocene (Chickasawhayan) Suwannee Limestone has been weathered to a chert residue. Chert occurs in various forms: as sand- to gravel-size chert detritus; as cobbles and boulders in a matrix of intensely weathered sand and clay; as massive bedded chert; and as massive chert pinnacles surrounded and overlain by younger sands, clays, and gravels of probable Neogene a_ge. Only the pinnacles and massive bedded chert appear to be in situ. These in situ cherts are widespread as large, coherent masses with bedding characteristics occasionally still apparent. Pickering (1966, 1970) used the term Flint River Formation for the in situ chert occurrences in the field trip area. They occur at a consistent stratigraphic horizon, above unweathered Twiggs Clay, "Cooper Marl", or Glendon Limestone, and below intensely weathered Neogene clays, sands, and gravels. Stratigraphically, little can be said at present about the massive chert except that it is altered from limestone and that the fossils included in the chert are considered to be of Late Oligocene (Chickasawhayan) age. Apparently in this area the Late Oligocene marine transgression overlapped both the Vicksburgian and the Late Jacksonian.
Although widespread in outcrop distribution, the massive chert is discontinuous in the Houston-Pulaski County area. It has not been encountered at all in numerous coring or drilling operations, even at locations that are less than a mile from outcrops of bedded, massive chert. As noted above, when it does occur in outcrop, it is a predictable stratigraphic horizon.
2-10

Cooke (1935) assigned the name Flint River Formation to the chert that contained a Chickasawhayan fauna. He recognized chert of other ages but did not include these cherts in the Flint River. We now know that in situ chert occurs in the following units or their equivalents: Clayton Formation, Lisbon Formation, Tivola Limestone, Twiggs Clay, "Cooper Marl", Vicksburgian limestone, and Suwannee Limestone. Evidently there have been one or more silicification events that affected calcareous beds of various ages at or near the surface. We feel at this time that there is no realistic way of grouping all these silicified sediments into one stratigraphic unit or of separating the various altered beds into separate stratigraphic units on the basis of the presence of chert only.
NEOGENE UNDIFFERENTIATED The youngest sediments in the Houston-Pulaski County area are deeply weathered, redbrown to purple to tan clay, sandy clay, sand, bedded and crossbedd d gravelly sand and bedded and crossbedded gravel. These sedim~rtts apparently originated in a fluvial -deltaic to very near shore, lagoonal environment and are characteristically noncalcareous and nonfossiliferous. However, oyster shells and oyster shell fragments have been found in some-of the more clayey deposits at Stop 6. Tentative Neogene age of these deposits is inferred because: 1) they overlie and contain reworked, altered, Upper Oligocene sediments; and 2) the close of the Oligocene epoch throughout the southeast is marked by a general cessation of carbonate deposition, and by an abrupt increase in terrigenous clastic sedimentation. Subdivision of Neogene sediments has not yet been attempted within this area although it appears that there may be more than one unit present. Correlation outside of the area, therefore, is not possible because of the complete lack of stratigraphic control for Neogene sediments. It is interesting to speculate that the lithology at the top of this Neogene sequence is not greatly unlike that of the Miccosukee Formation of north Florida or the apparently equivalent Citronelle Formation of west Florida, Alabama, and Mississippi.
2-11

REFERENCES
Aldrich, T. H., 1886, Preliminary report on the Tertiary fossils of Alabama and Mississippi: Alabama Geol. Surv. Bull. 1, p. 19-29.
Buie, B. F., and Fountain, R. C., 1967, Tertiary and Cretaceous age of kaolin deposits in Georgia and South Carolina (abs): Geol. Soc. America, Southeastern Section.
Carver, R. E., 1966, Stratigraphy of the Jackson Group (Eocene) in central Georgia: Southeastern Geology, v. 7, p. 83-92.
Connell, J. F. L., 1959, The Tivola Member of the Ocala Limestone of Georgia: Southeastern Geology, v. 1, no. 2, p. 59-72.
Cooke, C. W., 1915, Age of the Ocala Limestone: U.S. Geological Survey Prof. Paper 95, p.107-117.
_ _ _ 1935, Notes on the Vicksburg Group: Am. Assoc. Petroleum Geologists Bull., v. 19, p. 1162-1172.
_ _ _ 1943, Geology of the Coastal Plain of Georgia: U.S. Geol. Survey Bull. 941, 121 p.
Cooke, C. W., and MacNeil, F. S., 1952, Tertiary stratigraphy of South Carolina: U.S. Geol. Survey Prof. Paper 243-B, p. 19-29.
Cooke, C. W., and Shearer, H. K., 1918, Deposits of Claiborne and Jackson age in Georgia: U. S. Geol. Survey Prof. Paper 120, p. 41-81.
Dall, W. H., 1892, Correlation Papers- Neocene: U.S. Geol. Survey Bull. 84, p. 103, 104.
Herrick, S.M., 1961, Well logs of the Coastal Plain of Georgia: Georgia Geol. Survey Bull. 70, p. 462.
_ _ _ 1972, Age and correlation of the Clinchfield Sand in Georgia: U.S. Geol. Survey Bull. 1354-E, p. 1-17.
Herrick, S.M., and Counts, H. B., 1969, Late Tertiary stratigraphy of eastern Georgia: Ga. Geol. Society Guidebook.
Herrick, S.M., and Vorhis, R. C., 1963, Subsurface geology of the Georgia Coastal Plain: Georgia Geol. Survey Inf. Circ. 25, p. 25.
Huddlestun, P. F., and Toulmin, L. D., 1965, Upper Eocene- Lower Oligocene stratigraphy and paleontology in Alabama: Gulf Coast Assoc. of Geol. Soc. Trans., v. 15, p. 155-159.
LeGrande, H. E., 1962, Geology and ground-water resources of the Macon area, Georgia: Georgia Geol. Survey Bull. 72, p. 28, 29.
LaMoreaux, P. E., and Toulmin, L. D., 1959, Geology and ground-water resources of Wilcox County, Alabama: Alabama Geol. Survey County Rept. 4, 280 p.
MacNeil, F. S., 1947, Geologic map of the Tertiary and Quaternary formations of Georgia: U. S. Geol. Survey Oil and Gas Investigations Prelim. Map 72.
2-12

Marsalis, W. E., 1972, Preliminary geologic report on Clay County, Georgia (abs.): Georgia Acad. Sci. Bull., v. 30, p. 80.
Pickering, S.M., 1966, Stratigraphy and paleontology of portions of Perry and Cochran Quadrangles, Georgia: University of Tennessee M.S. Thesis, unpublished.
___ 1970, Stratigraphy, paleontology, and economic geology of portions of Perry and Cochran Quadrangles, Georgia: Georgia Geol. Survey Bull. 81, p. 11.
Puri, H. S., 1957, Stratigraphy and zonation of the Ocala Group: Florida Geol. Survey Bull. 38, 248 p.
Safford, J. M., 1864, On the Cretaceous and superior formations of west Tennessee: Am. Jour. Sci., 2nd ser., v. 37, p. 360-372.
Shearer, H. K., 1917, A report on the bauxite and fullers earth of the Coastal Plain of Georgia: Georgia Geol. Survey Bull. 31, p. 158~163.
Sloan, E., 1907, Catalogue of the mineral localities of South Carolina: South Carolina Geol. Survey Bull. 2, p . 460-462.
Smith, E. A., 1892, On the phosphates and marls of Alabama: Alabama Geol. Survey Bull. 2, 82 p;
Toulmin, L. D., and LaMoreaux, P. E., 1963, Stratigraphy along the Chattahoochee River, connecting link between Atlantic and Gulf Coastal Plains: Am. Assoc. Petroleum Geologists Bull., v. 47, p. 385-404.
Veatch, 0., and Stephenson, L. W., 1911, Geology of the Coastal Plain of Georgia: Georgia Geol. Survey Bull. 26, 466 p.
Vorhis, R. C., 1965, Notes on the stratigraphy of Pulaski County, Georgia (abs.): Geol. Soc. Am., Spec. Paper 87.
2-13

Figure 4. Field trip itinerary . 2-14

ROAD LOG

MILEAGE

Interval

Cumulative

0.0

Pierce Avenue, entrance to I-75

2.1

2.1

Exit east to I-16

0.3

2.4

Cross Ocmulgee River. Coastal Plain sediments cap hills, crystalline rocks exposed in river banks and bed.

2.6

5.0

Low, swampy flood plain of Ocmulgee River begins.

2.6

7.6

Cochran Short Route exit. Continue south on I-16.

0.4

8.0

I-16 climbs from Ocmulgee flood plain to Fall Line Sand Hills. Good outcrop of Tuscaloosa Formation on right in borrow pit.

2.6

10.6

Stop 1.

STOP 1.

Section exposed on west side of I-16 on top and sides of hill above Ocmulgee River valley, Bibb County. The exposure consists of, in ascending order, "Tuscaloosa Formation", Gravel Creek equivalent?, and/or Lisbon equivalent?, massive Tivola chert and massive Tivola equivalent sand, Twiggs Clay, and Irwinton Sand.

0.4

11.0

Enter Twiggs County

2.7

13.7

Exit Sgoda Road, turn right

1.1

14.8

Outcrop on right is a very sandy kaolin in mottled red, sandy clay. Probably Tertiary age, may be Gravel Creek equivalent.

0.2

15.0

Huber Kaolin Co. plant visible ahead.

0.1

15.1

Turn left on U.S. 23, 129.

1.5

16.6

Abundant kaolin balls in red sandy clay, overlain by tan eolian sand.

0.6

17.2

Kaolin pit on left.

4.0

21.2

Bullard, Georgia

3.7

24.9

Weathered Twiggs Clay overlain by sandy chert and limonite.

1.5

26.4

Abundant chert with rare Periarchus pileussinensis in Twiggs Clay.

0.9

27.3

Richland Creek. Tivola limestone exposed in ditch on right. Road climbs scarp to Fall Line Red Hills.

2-15

NO!NIMHI

3N3J03 ~3dd0

SOODVl3~;)
~3d dO
I. !N31VIIIfl03 NOIISI

:
.2

1
2
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"-u"

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V)

>-
u 0

1

... ~

' v
' ' ''



2-16

;: :.':.... ,.~ -~
t : ' ' .:
l
\ \
I
I
...-i 0.. 0
2iJ
...01.:,.:
(.) ll) rJl
-..(...).
bll 0 0
~
.~.... rJl
0
s0..
0 C)

0.8 0.5 0.8 1.0 0.3 0.3 0.5 1.3 1.6 1.0 0.3 STOP 2. 2.3
1.9 2.0 1.1 2.0 0.5
0.5 0.9 1.6 0.2
0.1 STOP 3.
0.6 4.4

28.1

Tarversville, Georgia

28.6

Turn right on Ga. 96.

29.4

Red, deeply weathered clastiCs overlying Twiggs Clay.

30.4

Twiggs Clay on left.

30.7

Twiggs Clay on left and right.

31.0

Chert over Twiggs Clay on right

31.5

Twiggs Clay on left

32.8

Enter Ocmulgee River flood plain.

34.4

Cross Ocmulgee River.

35.4

Leave Ocmulgee River flood plain.

35.7

Stop 2.

Kaolin in Gravel Creek Member of Nanafalia Formation? on left and right.

38.0

Bonair. Burn left on Ga. 247. Good outcrop of

Tivola limestone 0.1 mile to right of intersection.

39.9

Gravel Creek? exposed on left.

41.9

Kathleen, Georgia.

43.0

Sand Bed, Georgia, take Ga. 247 spur to right.

45.0

Cross railroad tracks.

45.5

Twiggs Clay overlain by manganese oxide bed and

chert with oysters. Periarchus quinquefarius and

Chlamys cocoana are also present.

46.0

Pabst Brewery

46.9

Turn left on U. S. 341.

48.5

Clinchfield, Georgia

48.7

Railroad overpass, conveyor belt from crusher to

Medusa Cement Company plant.

48.8

Turn right to Medusa west quarry. Stop 3.

Geologic section exposed in Medusa Portland Cement Co., west quarry, measured and logged by Huddlestun, January, 1974.

49.4

Turn right on Limerock Road

53.8

Railroad crossing. Road to left is to Dixie Lime and

Stone Plant. Continue straight on Limerock Road.

2-17

... ,._:.':'

= )J __22._
"

- "-

, .=-..:-=-~=-
Bench "B" , / Co111ad 100 '

Bench "A"
... "' "'
i""T.,_Jr--:;.l"' r
=
Quarry floor

!ZJ Sood
~Chert ~Clay ~Shells
~limestone ~Calcareous
(II] Unconsolidaled limestone (iL1J Glauconile ] Animal 'Burrows
Microfossil Sample

so '
<
-'
0
>
I-

Figure 6. Composite geologic section in west quarry of Medusa Cement Co., Clinchfield, Ga. Stop 3. 2-18

.:..1:..;)
<:.0
Figure 7. West sump, showing top of Clinchfield Sand and lower part of Tivola limestone, Medusa Cement Co., Stop 3.

u 0
2-20

!:>:)
~
I-'
Figure 9. Medusa Cement Co. west quarry; Twiggs Clay between bench "A" and bench "B", Stop 3.

1::-:l
~
1::-:l
Figure 10. Medusa Cement Co. west quarry; upper part of Twiggs Clay between bench "B" and bench "C", Stop 3 .

~
l:\:1 C.:>
Figure 11. Twiggs Clay (Bed 14) showing bedding and characteristic fracturing on fresh surface (1x).

0.1 0.9 1.0 1.2 0.6 STOP 4.
0.1
1.0 0.1
0.2 0.7 1.0 3.4
3.2 1.8 0.2
0.2 STOP 5.
1.6 1.5 0.1 4.3 1.1 1.3

53.9

Gravel Creek Member of Nanafalia on right.

54.8

Perry, Georgia, city limits

55.8

Turn left on Perry-Elko Road

57.0

Cross Flat Creek.

57.6

Stop 4.

Limestone quarry exposing Twiggs Clay and Tivola limestone. Excellent fossil collecting during lunch.

57.7

Twiggs Clay on left and right. Note prominent

glauconite bed dipping into hillside at 2-3.

58.7

Cross Limestone Creek, road climbs escarpment.

58.8

Twiggs Clay on left and right. Glauconite bed again

exposed.

59.0

Oligocene chert on right.

59.7

Church on left

60.7

Turn left on Grovania Road.

64.1

Railroad crossing, Grovania, Georgia. Continue on

main road to left.

67.3

Hayneville, Georgia. Turn right on U. S. 341.

69.1

Cross Dry Creek

69.3

Basal limestone of "Cooper Marl" overlying Twiggs

Clay

69.5

Stop 5.

Outcrops along the highway expose the top of the Twiggs Clay, "Cooper Marl", and undifferentiated Neogene sediments. The exposures of "Cooper Marl" at this locality contain a rich and varied Upper Eocene microfauna.

71.1

Klondike, Georgia

7.2.6

Oligocene chert.

72.7

Cross Buck Creek

77.0

Junction with Ga. 247. Continue south on U.S. 341.

78.1

Turn right on U. S. 341 Truck Route.

79.4

Turn right on Ga. 27 and 257.

2-24

z w
w C)
0
z w
no'
- - - - - 100
90'
so' - - - - - - - - - - -

,_:'_ _5:!_V!_t'_!d_ _

II , ,

I

1T "'='.J...

..L 0 T

..L T .L T ..L

_ .L.?.J....

Figure 12. Composite geologic section, Stop 4. 2-25

60'
so'

Q . Sand
~A Chert -j Clay ~ " Shells g2j l imestane
~..L Calcareous
m.... Unconsolidated
In? !Glauconite

Limestone

40'
0
>

o'

GGS 3106

NO CORE
I
10
20
.
30
POOR RECOVERY

EZJ Sand
~6 Chert
-] Cloy
~~~I Shells
00 Limestone
[g.).. Calcareous [ffi] Unconsolidated Limestone
I 17 r T Glauconite
Microfossil Sample

."cc..'(.

iz=

".I."..l..l''.:.

. ...

Q z
;:)

50

"z '

"~ '

0

.......:..

"z '

40

~:b.-":::.P::i.: .!>-::.;,

1
40

{;t::\:":::;.;y,

0"'
u

I

I COVERED

OgTrr-, - ~ I

-'-

:r

~ ..._7,..

.
30

0 -..,..-.~.L_T.-r:_:.a~..

I
I

I

50 ---- - ....

J..

-

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1 T -.L~T

T

.J...T.l. T..L

... , .f.~...;

o

..L;:.l..+..L

T -

o

60 T.,._T_ r.J o

- 'J.r r-7 o

I I

COVERED

-:l I I I ~T .J..1,- .J.... -.-..L. I ..L~T -..LTT'

~rT .i.. T-J.... T..L

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1

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I I

COVERED

. ..... "<('

20

~

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fl..

0
. 0u
10

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0
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Ill:
a"a..'
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70 -~~"-~~:J.I=T~~----------------------------------------,~...~ ~-_~-~.J..~...1-~7 ::-----------------------L----~

'-=~--:-_=---.=J-..=--_= 0

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- -..L.-- --

u

V)

<.:>

80 :.-:.:.;=_:;:-.==-~-.J-._ 0

<.:>
3:
I-

~~~~~:

Total Depth 85 '

Figure 13. Composite geologic section at Stop 5, compared to drill core taken !A mile south of exposure. 2-26

I-

z

..!

w
... >- ~
~

.;:
c,.:..

0
c "

"<'{
u

0
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GGS

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3058 ,.

0

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HOUSTON CO.

PULASKI CO

-"

u""

-~
-o c:

>-
Ci

0
;<
..-"

.-"
"
u

u

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GGS 3112

..0..

t-:)
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NO . RECOVERY MIDWAYAN
.Figure 14. Stratigraphic cross-section, Clinchfield to Hawkinsville, Ga.

co '
GGS Jill
loo'
200,
oo'
Q

3.3 0.5 STOP 6.

82.7

Cross Big (Tucsawnatchee) Creek.

83.2

Stop 6.

The outcrop along the highway here exposes the tops of Oligocene, massive chert pinnacles, an enveloping Neogene clayey unit, and an overlying gravelly sand unit that is similar lit hologically t o the Citronelle Formation of Alabama and the Miccosukee Formatio n of F lorida.

Figure 15. Schematic section of roadcut at Stop 6. 2-28

CD MASSIVE CHERT PINNACLE

~SILTY CLAY

@ POORLY SORTtD SAND

~ G) GRAVELLY SAND

G) ~

DEEPLY WEATHERED SANDS&CLAYS

0.5

83.7

0.1

83.8

0.8

84.6

0.6

85.2

1.3

86.5

0.3

86.8

1.1

87.9

1.3

89.2

0.1

89.3

0.2

89.5

0.3

89.8

0.2

90.0

0.2

90.2

0.1

90.3

0.3

90.6

6.0

96.6

0.9

97.5

0.1

97.6

0.1

97.7

0.1

97.8

0.1

97.9

0.7

98.6

1.6

100.2

Long Branch Chert Branch of Big Creek Chert on left Lenwood Church on left St. Paul Church on left Stop sign. Intersection of FR 620 and Ga. 230. Turn left. Chert on right. Good outcrop of chert on both sides of road. Intersection of FR 835, S161, and Ga. 230. Turn right on Ga. 230. Chert on right and left. Chert on right and left, good outcrop. South Prong Creek. Chert on right and left. Dooley-Pulaski County line. Unadilla city limits. Unadilla Baptist Church. Railroad crossing. Intersection of Ga. 230 and U. S. 41. Turn left. Go one block, turn right on Ga. 230. Methodist Church on left. Overpass over I-75. Y- fork, junction of Ga. 230 and Ga. 329. Continue west on Ga. 329.

2-29

3.4

103.6

0.3

103.9

1.6

105.5

0.3

105.8

0.6

106.4

0.2

106.6

0.5

107.1

0.6

107.7

0.5

1 OR.2

0.5

108.7

1.0

109.7

1.4

111.1

2.8

113.9

0.1

114.0

0.1

114.1

0.8

114.9

0.2

115.1

0.6

115.7

0.2

115.9

0.5

116.4

0.2

116.6

0.2

116.8

0.1

116.9

0.1

117.0

Suwannee chert Suwannee chert Suwannee chert Suwannee chert Upper part of Twiggs Clay with glauconitic horizons present. Little Creek. Twiggs Clay on right. Suwannee chert. Dooley-Macon County line. Twiggs Clay in ditch on left. Intersection of Ga. 329 and Ga. 26. Turn left on Ga. 26. Hogcrawl Creek. Claibornian (?) sands on left. Spring Creek. Beaver Dam on right. Creek flows along the top of the Gravel Creek Member of the Nanafalia. Claibornian sands in dirt road on left. City limits of Montezuma, Georgia. Seaboard Coast Line Railroad overpass. Stop light. Junction of Ga. 90 and Ga. 26 . Continue on Ga. 26. Cementary on left. Yield sign. Turn right. Beaver Creek. Railroad crossing. City of Montezuma. Railroad crossing, junction of Ga. 26, Ga. 90, and Ga. 49. Proceed north on Ga. 49. Police Dept. on left. First Baptist Church on left.
2-30

2.3 0.2 0.6 STOP 7.

119.3

Large Pecan Grove on right.

119.5

Paved road on left. Turn left.

120.1

Stop 7.

Section exposed along the road consists of Providence Sand, Clayton Formation, Port.ers Creek Clay, Gravel Creek Member of the Nanafalia Formation, and surficial red sands. The Flint River is at the base of the hill.

2-31

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LOWER PALEOCENE

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DEEPLY WEATHERED SURFICIAL DEPOSITS
?

MEDUSA CEMENT COMPANY WEST QUARRY CLINCHFIELD, HOUSTON COUNTY, GEORGIA

DESCRIPTION

THICKNESS

Holocene-Miocene (Undifferentiated) (30.75 feet)

22. Sand, coarse-medium, argillaceous; cherty, boulders and cobbles of fossiliferous chert in the upper 10 feet; most boulders contain Chickasawhayan fossils, one boulder contains an apparent Vicksburgian fossil suite; sand deeply weathered; moderate reddish brown (10 R 4/6).
21. Sand, very cherty sand-sandy chert, deeply weathered; moderate yellowish orange (10 YR 7/6).
Upper Eocene (Twiggs Clay) (100.75 feet)

30' 0.75'

20. Sand, manganiferous; unconsolidated; black (N1).
19. Clay, sandy, cherty, glauconitic to sandy, clayey, cherty glauconite; poorly mixed combination of coarse sand, leached sticky clay, coarse pelletal glauconite, and abundant chert concretions.
18. Clay; nonclacareous, leached; sticky and plastic when wet; yellowish gray (5 Y 8/1); one-foot bed of unconsolidated sand 3 feet below top.
17. Glauconitite, sandy, slightly argillaceous; calcareous; partially indurated; may have 6" bed of calcilutite limestone at base.
16. Clay; calcareous toward base, noncalcareous toward top; blocky to very conchoidal fracture, moderately well bedded; base of weathering in the present quarry wall, some lenses of blue clay remaining; weathered grayish-yellow (5 Y 8/1).
15. Clay, sandy; very glauconitic, noncalcareous; contains angular clay fragments, very finely bedded; may have fine grained, almost lithographic, calcilutite limestone overlying and underlying glauconite bed, limestone beds pinch out by becoming concretionary and discontinuous.
14. Clay, silty; calcareous; finely bedded, almost massive when fresh, breaks into blocky chunks when exposed for a very short time; greenish gray (5 GY 6/1- 5 G 6/1).
Covered

1' 2' 9' 2' 13'
4'
11.5' 4.5'

13. Sand to sandstone, very calcareous, glauconitic, some sandy marly lime-

9.5'

stone; sand medium to coarse grained; indurated beds 2 feet thick or

less, some intervals or beds of poorly mixed sand and fine textured,

indurated limestone and claystone; some horizons abundantly macro-

fossiliferous, almost a coquina of molluscan molds; top one foot of bed

consists of a poorly mixed, fossiliferous, glauconitic, marly sand and

clay; greenish gray (5 GY 5/1) when fresh, grayish-orange to dark

yellowish orange when weathered (10 YR 7/4- 10 YR 6/6).

2-33

12. Clay, calcareous; fine to very fine sand, mica, glauconite, and fine, sandsize pyrite, distributed in laminae or thin beds; most clay is blocky and hackly; some almost pure clay with conchoidal fracture; sandy and limey beds and laminae very characteristic of this interval, thin, 6 inch beds of dense, fin -grained limestone characteristi of the upper part of the interval; I ss clearly defined sandy, calcareous, micaceous, glauconitic, slightly pyritic b ds and lamina mor characteristic of the lower part. These beds app ar less continuous and may hav indurated 1 nses within them. Sediment within them is poorly mixed, often marbled, disturbed and apparently bioturbated; color of clay is greenish gray (5 GY 6/1 to 5 GY 8/1 to 5 G 6/1); sandy layers and limestone layers are light gray (N7).
Covered
11. Clay to marl, very slightly sandy; glauconitic, very calcareous, bryozoanrich clay to a very clayey, bryozoan-rich glauconitic, sandy marl; greenish gray (5 GY 6/1 - 5 G 5/1 ).
10. Limestone; glauconitic; hard, dense, re-crystallized; massive bedded; uneven texture; yellowish-gray (5 Y 8/1 ).
9. Clay, silty, calcareous; very slightly micaceous, some fine sand size pyrite grains; blocky; dark greenish gray (5 GY 5/1).
8. Marl, sand and clay, poorly mixed; fossiliferous, clayey, sandy marl; argillaceous marly-textured fine sand; marly-textured clay; calcareous; slightly micaceous and macrofossiliferous; characteristically more marly-textured and calcareous in lower part, more sandy and less calcareous in upper part; three beds of limestone, either continuous or discontinuous; silty, unfossiliferous.
TIVOLA LIMESTONE (42.5 feet)
7. Limestone, slightly glauconitic; abundantly fossiliferous, coarse, uneven textured, rubbly, uneven bedded, bioclastic; indurated, hard beds up to 2' thick interspersed with thin, soft, marly-textured, uneven beds; Lepidocyclina, Periarchus pileussinensis, Pecten spillmani, and molds of molluscs often in a matrix of clastic bryozoan debris; very pale orange to pale yellowish orange (10 YR 8/2- 10 YR 8/6).
6. Limestone, strongly bimodal; plastic, lutite matrix with clastic, often chalky, skeletal debris, mainly bryozoans with some Pecten spillmani and Periarchus pileussinensis; very pale orange (10 YR 8/2) to almost white when slightly weathered.
5. Limestone, very slightly glauconitic, some fine pyrite grains present; very massive bedded, soft, nonindurated but very tough and brittle; medium to coarse textured, uneven grained due to abundance of bioclastic debris, esp. bryozoans; more coarsely bioclastic, more apparent bedding, and sandy with frosted quartz granules toward base; some apparently discontinuous, indurated, thin limestone beds in lower part; very pale orange to pale grayish orange to yellowish gray (10 YR 8/210 YR 9/4- 5 Y 8/1).

29'
3. 5' 1.5' 1.5'
.75' 8'
10' 1'
31.5'

2-34

CLINCHFIELD SAND (4. 75+ feet)
4. Sandstone, medium to coarse, poorly sorted, some angular quartz granules; rubbly, massive bedded, glauconitic, calcareous; very shelly with molds and casts of rather large molluscs; Ostrea cf. gigantissima, Periarchus lyelli, large bryozoans, bones, and sharks' teeth common and characteristic.
3. Sandstone, poorly sorted; calcareous; extremely hard, dense slightly fossiliferous; 2-4" of calcareous clay to claystone on top of bed; grayish orange to grayish orange pink (10 YR 7/4- 5 YR 7/2).
2. Sand, calcareous; coarse grained; soft, unconsolidated; abundant chalky, aragonitic shells with well preserved calcitic shells; grayish orange (10 YR 7/4).
1. Sand, medium, very slightly argillaceous; calcareous; soft, unconsolidated, extensively and intricately burrowed; grayish orange (10 YR 7/4).

1'
.75' 1' 2'+

2-35

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STRUCTURE MAP

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GEOLOGIC MAP
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Plate 1-B

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STRUCTURE MAP

FROLONA

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GEOLOGIC MAP

.

Explanation: see Plate 1-E
Plate 1-C

BREVARD FAULT ZONE
Western Georgia Eastern Alabama

Auste ll - Fro lona

Centra lhatchee

Anticlinorium

Synclino rium

Axis

Axis

I

I

Chattahoochee

I I I

Fau lt
I

A

Long
lsl 'and Faul t
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Zone of
Intense
Cotoclo~is

Sea level

Austell - Fro lana

Centralhatc hee

Antic linorium

Synclinorium

Axis I I
I I
I

Axis

Chattahoochee! Fault I long Island

\ Zone :
l lnt~~se I

Fault
I

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level

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Axis

Chattahoochee

Axis

fault
I
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I

' ' I

long Islant!

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: c~::7s-

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eo level

EXPLANATION

Muscovite -Biotite-QuartzFeldspar Gneiss
Graphitic Schist, Quartzite, And Mica-Quartz Schist, lnterlayered
Garnet-Micaschist, Biotite Gneiss, And Hornblende Gneiss; lnterlaye red

..

Hornblende Gneiss Garnet-Mica Schist

Biotite-Muscovite -Quartz Schist And Hornblende Gneiss; lnterlaye red

Porphyroblastic Granitic Gneiss

Schist, Metagraywacke, Phyllite; lnterlayered
Graphitic Schist, Quartzite; lnterlayered

FOLDS
Anticline, upright; with plunge direction
Anticline, overturned with plunge direction
Syncline, overturned with plunge direction

-------- FAULTS
Fault, aP>proximately

. . located




Shear zone

!Illlll]J
Brevard shear zone

SCALE b48,000

y,

0

2

3

5

Miles

Geology by Thomas J. Crawford and Jack H. Medlin NSF Grant GA-15917

Plate 1-E