~-
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field Excursion
Ocoee .M, ~tasediments
North Central Georgia-
Southeast Tennessee
VERNON J. HURST and JOHN S. SCHLEE
ANNUAL MEETING
Sottthenstern Section
The Geological Society
of A rtlerica
APRIL 14, 19b2
GUIDEBOOK NUMBER 3
Department of.Mines. A\ining and
Geology
GARLAND DEYTON, DIPECTOR Atlantn, Geor-9ia
COVER
X-bedding, scours, and penecontemporaneous deformation structures, 7 times natural size, in fine-grained Ocoee rocks. Drawings from an outcrop at Stop 40 in Ocoee gorge.
TABLE OF CONTENTS
INTRODUCTION_ __________
Page - - - - - - - - - - - - - - - -- - - -- - - 5
LITHOLOGY OF OCOEE GORGE, PARKSVILLE TO DUCKTOWN, TENN.
General Character and Stratigraphic Succession_ _______
---------
7
Description of Rocks between Parksville Dam and the Sylco Creek Fault. ----------------------------------------- 8 Quartzites______--------------------------------____....------------------------___________..........-------------------...._____.__________________________ 8
Shales and phyllites.
8
Limestone_______ ----------- ------------------- - - -- - - - - - -- - - - - - 8 Description of rocks between Sylco Creek Fault and Ducktown________________ ---------------------------------------------------- 11
Phyllite_________________-------------..____------------------------___......._________________________----____---------------------____....______________ 11
Quartzite z.one
11
Dark pyritic slate......-----------------------------------------
_________
__ 11
Great Smoky group --------------______________....------------------------______________--.. _______________-----.-----------------_________________ 13
STRUCTURE
Primary Structures Bedding_______________---------------___________________________________---------------------------- ___.---___--------------------_______________.....__ 15
Graded bedding----------------------------------.___-------------------------------------..._______--------------------------_________________________ 15
Cross-bedding _______ _ _
--------
--------------------- 15
Scour channels _______--------___------------------..._______--------------------------------- _....._________---------...----------------...______ 15 Penecontemporaneous structures .____________--------------------...._________________________________---------------______________--------- 17 Nodules______________________________________________________________________________________________._______________________________________________________ 17
Secondary Structures
Folds_ _ ________________________
19
Faults_ _ __
19
Cleavage____________________--------_____----------------...___________--------------__________________----------------------_______________________ 19
Flowage_____________
__ _ _ 19
METAMORPHISM__________________________________________ _ ___ 19
CONCLUSIONS - - - - - -ACKNOWLEDGEMENTS..___________ _ _______ __ R E F E R E N C E S_ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ APPENDIX (Road log)____________
3
21 _ ___ 22
- 22 23
LIST OF FIGURES
Page
Figure 1-X-ray diffraction patterns of phyllites along Ocoee gorge _ __
9
Figure 2-Laminated to thinly bedded phyllite near Stop 19 - - - - - -- - - - - - - - - ----- 12
Figure 3-Laminated to thinly bedded phyllite near Stop 25 -------------------------------- 12
Figure 4-Zone of quartzite and calcareous quartzite at Stop 32 - - - - - - - ---- - -- - - - - -
14
Figure 5-Quartzite beds transversely cut by quartz-calcite-chlorjte veinlets, Stop 32___ _ _ - - - 14 Figure 6-Dark laminated slate with coarse pyrite crystals scattered along bedding planes, Stop 30.................... 16
Figure 7-Graded bedding and scour channels in quartzite zone at Stop 32_____ __
16
Figure 8-Cross-bedding, scours, penecontemporaneous deformation structures in Ocoee rocks at Stop 40______ 18
Figure 9-Penecontemporaneous deformation structures in laminated limestone at Stop 6.----- --------------------- 18
Figure 10--Shear folds in laminated phyllite near Stop 20--- --- - - -- ----- - -- -- - -- -- 20
Figure 11-Convoluted quartzite at Stop 22.
20
Figure 12-Sketch of roadcut on northeast side of highway at Stop 6
- 25
LIST OF TABLES Table !-Stratigraphic units of Ocoee Series of Great Smoky Mountains------------------------------------------------------------ 7 Table 2-Correlations of Ocoee rocks in the southern Appalachians.------------------------------ --------------------- 17
LIST OF MAPS Map No. !-Distribution of Ocoee rocks in north-central Georgia and southeast Tennessee______________________________ 10 Map No. 2-Cross-sections along Ocoee gorge in southeast Tennessee____________________________________Tipped in
4
OCOEE ROCKS IN NORTH CENTRAL GEORGIA AND SOUTHEAST TENNESSEE
INTRODUCTION
The rocks along Ocoee Gorge (Map No. 1) were first described by Safford (1856) who applied the name "Ocoee conglomerate and slate" to the older main body of rocks and the name "Chilhowee sandstone" to the overlying younger unil Subsequently Keith mapped several quadrangles to the northeast containing these rocks but did not continue the use of Safford's terms. Keith's formational names and boundaries were adopted by LaForge and Phalen in the Ellijay quadrangle ( 1913). More recently Stose and Stose ( 1944; 1949) defined the Ocoee series, after large scale reconnaissance in the southern Appalachians. Their work was not sufficiently detailed, however, for accurate stratigraphic division or correlation.
Between 1946 and 1955 geologists of the U. S. Geological Survey mapped a 1300 square mile area, largely Ocoee rocks, in the Great Smoky mountains of Tennessee and North Carolina. A sununary of the stratigraphy evolved by their work and that of earlier geologists is reproduced in Table 1 (King, Hadley, Neuman, and Hamilton, 1958).
Outcrop mapping in the Mineral Bluff quadrangle (Hurst, 1955) delineated four formations within the unit previously called "Great Smoky formation" by LaForge and Phalen. These new formations (Dean, Hothouse, Hughes Gap, and Copperhill) were termed the Great Smoky group, a designation accepted by King, Hadley, Neuman and Hamilton as part of the Ocoee series. The Mineral Bluff mapping verified the Murphy syncline (Stose & Stose, 1949; Furcron, 1953), the axis of which passes through Mineral Bluff and Blue Ridge, and gave a clearcut stratigraphic sequence on the syncline's west limb.
Subsequent mapping in the Epworth quadrangle which adjoins the Mineral Bluff quadrangle on the west (Hurst, 1955; unpublished) revealed a large anticlinorium that crosses the Ducktown basin and plunges to the southwest in Georgia. Along the axis of the anticlinorium, one mile west of Copperhill, a fifth formation below the Copperhill formation and within the Great Smoky group is exposed. The delineation of staurolite, garnet, and biotite isograds in the Epworth quadrangle showed how the grade of regional metamorphism drops off on the west limb of the Ducktown anticlinorum. The change in metamorphic grade accounts for the mineralogical differences between rocks on the east limb of the anticlinorurn and those on the west limb. When equivalent mineral assemblages appropriate to the metamorphic zones are taken into account, along with thickness and sequence of beds, the similarity of formations on the limbs of the anticlinorum is apparent.
The investigation of the northwest corner of the Cohutta Mountain quadrangle (Salisbury, 1961) clarified the stratigraphy of the westernmost Ocoee rocks in Georgia and their relation to known Paleozoic rocks farther west. Only one unmapped quadrangle separated the area investigated by Salisbury from the quadrangles mapped by Hurst, but because of this gap and the change in appearance due to westward drop in metamorphic grade, the Great Smoky rocks of the two areas could not be correlated.
To bridge the gap, the section along the gorge of the Ocoee River, 7 miles to the north, has been studied. The gorge was chosen because it affords an almost continuous exposure from Parksville to Ducktown, Tennessee, crosscutting the Ocoee rocks.
This guide presents a brief description of the Ocoee Gorge section and a summary of what is known about the stratigraphy of Ocoee rocks in north central Georgia and southeast Tennessee.
5
LITHOLOGY OF OCOEE GORGE~ PARKSVILLE TO DUCKTOWN, TENNESSEE
General Character and Stratigraphic Succession
The rocks fall naturally into two groups: ( 1) those between Parksville Dam and the Sylco Creek fault; (2) those between the Sylco Creek fault and Ducktown (see Map No. 1).
The rocks ~f the first group are quartzite, arkosic quartzite, siltstone, shale or phyllite, and limestone. Rodgers' Geologic Map of Eastern Tennessee (1953) shows the westernmost quartzites as the Nebo quartzite and the other rocks as Sandsuck shale. New road cuts reveal considerably more quartzite than was previously exposed; much of it arkosic and deeply weathered. The Nebo quartzite (Stops 1 and 2) is intensely faulted: Intense faulting at other places, particularly between Stops 8-13, renders the sequence of rocks in this section uncertain. Still, none of the faults except those of the Great Smoky fault zone appear to have caused any great displacement, and the rocks are right-side up over most of the distance, as shown by common top-bottom criteria. Possibly the disruption of the sequence is more apparent than real.
The youngest formation of the second group consists of gray-green, laminated phyllites with a total thickness of at least 1500 feet. Jn the phyllite formation is a zone of thin quartzites and calcareous quartzites. Underlying the phyllite unit and conformable with it is a formation about 600 feet thick of dark pyritic phyllite or slate. Underneath and conformable with the black slate is the Great Smoky group composed of metagraywacke, metaconglom eratc, and mica schist.
AGE
NORTti 01" ANO BELOW Glll!ENBJ<'LI!R FAVLT
SOVT"' OF AND ABOVE GREENBRieR FAV~T
CAMBRIAN ANI> PRCAM8RIANW
tATE/? PRECAMBRIAN
Af/LicR PI>ECAMfJRIAN
C>i/LHOW OROcJP
Cochran ft>rmlJ//ot'J ar~d hightr emits
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OIS<:ONF"ORMITY l
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FAUlT CONTACT, SEQUENCE UNC(R'TA,N -
WE.S1'RN 9AqT OJ'" AREA
VN(".tASS
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1'01>MATIONS
Csdes 38nd3tor~e- ::t
I EAS'1'ER"t.a P/>ltT 0 11 A~A.
~ocks of W6bl> Rch
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Plgeot1 .siflstont: .;,
* #osrmg ForX Jona.slone '* t.on9t1r'm qv8~'t~ile
Wading 8r8nr-h /Dtmalif>n
VtJc;Or-IYOft"'iiT"f'-
{jrtJf)ific and gne,ssic rocks
1/0CJ<.$ ~ MUIIJ!IIIY
MAP$'& 81-7
N.t,f.tl?al,. .sial(!$ 6/'ld hl9hU unit$ (P/l~CAM8fi/AN I!) AND AA'Y PAL.OZQIC tl)J
t.TioiOLOGIC B~fAK. ~UT P~8A!.LY COHf:ORMA&Le:-
~
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Elkmont $4nd~!OIHJ 'A'
* RQaring F~rk $()1"'ulsfmt '* l.on.qerrn gvartzite '* W~dihg IJr$r>Ch rorntsticn
l.tNCQN FOR M J'T'f
'"'" t;r"'t1itic
gi"Jeissit; rc~s
Table I.-Stratigraphic Units of Ocoee Series of Great Smoky Mountains (From King et al., 1958) 7
Description of Rocks Between Parksville Dam and the Sylco Creek Fault
QUARTZITES
The quartzites along the Great Smoky fault are interbedded with thin phyllites or shales. They vary from thin to massive, the massive beds up to 30 feet thick. Feldspar is generally a minor constituent. Intense deformation and silicification have obscured original textures, but original grain shapes, conglomeratic texture, and cross-bedding are still recognizable at places. Conglomeratic layers are visible at Stop 2. Scolithus tubes have been found in a bed directly opposite the dam, about J0 feet east of the contact with the Athens shale at Stop 1.
The quartzites at Stops 4 and 5 contain rounded to subangular grains of feldspar and quartzite in addition to grains of quartz, all cemented by fine granular calcite.
The quartzites at Stops 8-13 are commonly arkosic but are too weathered for their original mineralogy to be examined in detail.
The quartzites of this section are closely similar to those described by Salisbury in the Cohutta Mountain quadrangle to the south ( 1961, p. 22-30) and in the Chilhowee group to the northeast.
SHALES AND PHYLLITES
Shales or phyllites comprise more than half the section.
X-ray powder patterns of samples collected at random across the section are reproduced in Fig. 1. The principal minerals are 2M sericite or illite, chlorite, and quartz. A variable amount of calcite is present, generally less than 5 per cent. Fresh specimens contain a minor amount of feldspar; deeply weathered specimens contain kaolin instead, probably formed by weathering of feldspar. The x-ray patterns show a gradual transition from poorly crystallized 2M sericite or illite and chlorite in the shales along and on both sides of the Great Smoky fault to better crystallized micas in the phyllite near Sylco Creek. The better crystallinity of the micas toward the east reflects the rising metamorphic grade in that direction. No sharp break in crystallinity exists at the Great Smoky fault. This contrasts with the sharp break several miles to the southwest in the vicinity of Chatsworth, and at other places farther to the southwest along the fault. Stratigraphic displacement along the fault at Parksville is not as great as at other places to the southwest in Georgia.
LIMESTONE
The limestone is dark colored, laminated and cut by calcite veinlets. Thin sections show fine granular carbonate with very fine pigmenting matter. The silty layers contain fine subangular quartz and other clay-size minerals. Some of the limestone is dolomitic.
Salisbury reported limestone at the same stratigraphic position in the Cohutta Mountain quadrangle ( 1961, p. 30-32) .
8
Fig. 1-X-ray diffraction patterns of phyllites along
Ocoee gorge. The numbers are the stops (Map 2) where
0
the samples were collected. The letter A marks the 14A
0
0
+chlorite peak, B the 1OA sericite peak, C the 7A kaolin chlorite peak, D the (1.00) quartz peak and E the
0
3.04A calcite peak. X is the position of the Sylco Creek
fault.
I
UllJJ1 1 'i: I I ! 33
9
J TENN . ~- /''I~- .CAROLI NA
I ""<r_- __
___-;T
ROCKS (
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-MA
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I:XP\.A....,110tl
~ Do,_ PJritk. - ,..
d' 0... fC.tl!ttllotl
~ Topot~1 SmOkJO~
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GREAT S N 0'-"1'
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MAP NO.1-DISTRIBUTION OF OCOEE ROCKS IN NORTH -CENTRAL GEORGIA AND SOUTHEAST TENNESSEE
The location of the Great Smoky Fault in the Parksville quadrangle is from Rodgers (1953). The NW comer of the Cohutta Mtn. quadrangle is from Salisbury (1961). The contacts along the Ocoee Gorge ore from Hurst & Schlee. The Epworth and Mineral Bluff quadrangle and the metamorphic isograds are from Hurst.
Description of Rocks Between the Sylco Creek Fault and Ducktown
PHYLLITE
The youngest rocks in this section are gray-green laminated to thin bedded phyllites. A stratigraphic thickness of at least 1500 feet is exposed. The top is cut off by the Sylco Creek fault. The bottom is transitional by interbedding to a thick, dark, carbonaceous, pyritic slate. About 900 feet, stratigraphically, from the bottom of the phyllite is a horizon of thin interbedded quartzites and calcareous quartzites.
The layers of phyllite are generally 1h-2 inches thick, occasionally as much as 6 inches thick. Fine-grained carbonate*-rich beds are interlayered with finer-grained, less competent mica-rich or quartz-mica-rich beds. The carbonate-rich layers have been disrupted by differential movement along cleavage planes so that they are now generally visible as trains of irregularly shaped lenses or clots (Fig. 2). Where weathered, the carbonate-rich portions are usually some shade of brown; where long exposed to weathering, they have been leached away leaving small surficial voids along the bedding planes (Fig. 3).
Thin sections of the phyllites show fine-grained sericite, quartz, chlorite and minor feldspar. Minute grains of carbonate are generally present. Where they constitute several percent of the rock they are often coarser, and may appear as sand-size porphyroblasts.
QUARTZITE ZONE
The quartzite-rich zone (Fig. 4) is 30-50 feet thick. The individual beds are generally 1 to 4 inches thick. A few have a thickness exceeding 1 foot. The quartzite beds constitute Y.'l to \h. of the zone, the other part being interbedded phyllite similar to that above and below the zone. Genera1ly the quartzhc layers are somewhat thicker and more numerous near the bottom of the zone. The quartzite unit thickens a little to the east. At the same time the beds within the unit thicken.
Although the quartzites just east of Sylco Creek arc fine-grained, they sometimes show graded bedding. Farther east where beds are thicker and fine conglomerates are found, cross bedding and scours are common as well as graded bedding. Good examples can be seen at Stop 32.
The quartzites are generally fractured and cut by veins of quartz-calcite-chlorite (Fig. 5). The convolutions of the beds suggest that considerable deformation might have taken place prior to consolidation and fracturing (see Fig. 11).
The quartzites are generally calcareous and commonly feldspathic. The fine conglomerates are feldspathic.
DARK PYRITIC SLATE
Beneath the gray-green phyllite and conformable with it is a band of dark, laminated, pyritic phyllite or slate which is about 600 feet thick, except where thinned by faulting. The best exposure is at Stop 30.
The layers are mostly less than % inches thick and are commonly marked by concentrations of pyrite cubes, many of them up to 1 inch across (Fig. 6). The pyrite crystals are more common in the coarser-grained layers.
*The carbonate in the phyllite varies compositionally from sample to sample. Generally it is neither calcite nor dolomite (from x-ray diffraction patterns). Much of it appears to be ankerite.
11
Fig. 2-Laminated to thinly bedded phyllite near Stop 19. Bedding is almost vertical. Flow cleavage dips 50 to the right (southeast). The more competent layers have been displaced, even segmented, by differential movements along the cleavage planes.
Fig. 3-Laminated to thinly bedded phyllite near Stop 25. The carbonaterich layers have dissolved near the surface (right side of photograph) leaving trains of voids. Pronounced flow cleavage and shear folds in left half of photograph.
12
GREAT SMOKY GROUP The top of the Great Smoky group is exposed at three places: Stops 23, 24, and 34. The best exposure is at
Stop 34. The Great Smoky group is conformable to the overlying carbonaceous slate. The top of the group is a zone of
thin quartzites and calcareous quartzites, some of which show current structures, interbedded with thin greenish phyllites. Beneath this zone are thick metaconglomerates interbedded with metagraywacke and phyllite or mica schist. These rocks closely resembled those of the Dean formation, which is the top of the Great Smoky group in the Mineral Bluff quadrangle.
The rocks from Stop 34 through Stop 40 constitute the uppermost formation in the Great Smoky group. Far~ ther east is a monotonous sequence of metagraywacke and mica schist resembling the Hothouse formation in the Mineral Bluff and Epworth quadrangles.
From Stop 42 to Ducktown, exposures are not good enough to permit exact formational divisions from the mapping of a single narrow strip. Beds similar to those in the Hughes Gap formation cross the road in the vicinity of Stop 43. Between Stop 43 and Ducktown is a sequence of metagraywacke and mica schist belonging to the Copperhill formation. Metaconglomerate layers are found in this formation, particularly in its lower half. One such layer crosses the road at Stop 44.
The biotite isograd runs NE~SW between Stops 42 and 43.
Metaconglomerate The mctaconglomerates in the Great Smoky group characteristically contain subangular to rounded pebbles of
quartz and feldspar and slabs of dark slate. Other rock fragments are found at places. At Stop 35 there are pebbles of limestone and chert (?). A pebble of a medium-grained igneous rock of dioritic composition has been found at Stop 36. Fragments of dark slate are common in outcrops between Stops 35 and 36.
Metagraywacke West of the biotite isograd (which is between Stops 42 and 43) the metagraywacke consists mainly of quartz,
feldspar, sericite and chlorite. East of the isograd the mineralogy is the same except for the substitution of biotite for chlorite. Chlorite is still sometimes present east of the biotite isograd as a secondary alteration product.
13
Fig. 4-Zone of quartzite and calcareous quartzite thinly interbedded with phyllite at Stop 32.
Fig. 5-Quart;zite beds transversely cut by quartz-calcite-chlorite veinlets, Stop 32.
14
STRUCTURE
BEDDING
Primary Structures
At most outcrops bedding is clearly visible, due to planar changes in composition, color, fabric and grain size. The ease with which bedding can be recognized is due partly to original sedimentation differences and partly to deformation and weathering. Deformation has exaggerated competency differences. Bedding planes that were hard to see prior ~o deformation between fine-grained quartzite and phyllite are now plainly visible as alternating strongly foliated and poorly foliated layers. Weathering has "retouched" some of the beds with new color and has etched some of the layers because of differences in the rate at which they decompose. In the laminated phyllites, the dissolution of carbonate-rich layers has left surficial voids which cause the bedding planes to stand out in relief. Even where axial plane cleavage is strongly developed and bedding laminae most disrupted by cleavage movements the bedding is still marked by segments of the disrupted layers (see Fig. 2).
GRADED BEDDING
This structure is common in quartzites within the gray-green phyllite and in the metasediments of tlte Great Smoky group. It is strikingly developed in some of the conglomeratic zones of the latter. Best exposures are at Stops 29 and 35.
Many of the fine-grained calcareous quartzites show a sharp boundary at the bottom of the layer and a gradual transition upward to a fissile, more micaceous layer; this fissile layer is again sharply separated from the next finegrained quartzite overlying it (Fig. 7). Because of the fine grain of both layers, this grading probably was not visible in the unmetamorphosed sediment. Regional deformation and metamorphism have accentuated the grading by developing rock cleavage in the finer upper portion better than in the lower, slightly coarser or more siliceous portion.
CROSS-BEDDING
Poorly preserved cross-bedding is visible in the quartzite at Stop 1. At numerous other places cross-bedding is well preserved, but usually in thin beds and not visible at a distance. The cross-bedded layers generaJly show scour features. Good exposures are at Stops 29 and 40 (Fig. 8).
SCOUR CHANNELS
Small scale scour features usually marked by the truncation of several laminae, but also sometimes by pockets of coarser fill, are preserved commonly in the quartzite of the gray-green phyllite and in the coarser metasediments of the Great Smoky group. They are best observed at Stops 29 and 40. Large scale scours can be seen between Stops 35 and 37, best at Stop 36.
15
Fig. 6-Dark laminated slate with c:oarse pyrite crystals (light gray) scattered along bedding planes. Flow cleavage dips about 45" to the right. Stop 30.
Fig.7-Graded bedding and scour channels, some of them marked by arrows, in zone of quartzites at Stop 32. Scale given by pencil.
16
PENECONTEMPORANEOUS STRUCTURES
Penecontemporaneous slump is strikingly developed in laminated limestone at Stop 6 (Fig. 9) .
Other penecontemporaneous features are in some of the quartzites and especially in two zones of laminated rocks within the Great Smoky group.
Penecontemporaneous structures due to the tearing off or picking up of fragments from the bottom and the incorporation of these fragments in the overlying deposit are found in the Dean fonnation between Stops 35 and 36. More striking penecontemporaneous features involving the deformation of lamellae, probably the result of unequal loading, compaction, or sliding are well exposed at Stop 40 and in the bed of the Ocoee River near Stop 39. Similar features in the Great Smoky group have been described by Mellen (1956, p. 46-61).
NODULES
Occasional ellipsoidal nodules up to a foot or more thick weather out of the Great Smoky beds. They are very fine-grained, generally dark, and calcareous. They have been found in place in both schist and massive metagraywacke. The composition of the nodules is such that they can recrystallize as pseudodiorite when metamorphosed to the staurolite grade. Some of the pscudodiorite nodules in high-grade metamorphic areas to the east might have originated this way, though many of them originated by boudinage.
Table 2. Correlations of Southern Appalachian Formations.
.... KinQ Jovr~ Sti 1949
No11~e11 1/o.
d~\1114 a Hnr"'"
f'eny UIJ! ;:.l
Not1 heoaJern Tenn
(.kill"'''' ~or UIIICOI COVAIIeSl
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Tom,rown <Jol"mlh:
Anlla i11m Clnllllnl
$111td'{d~~
1
Sli
-
M(
-
(I
~~ ---
tnscouolltdt
(f:Jollll (ltrfl(l'lll1
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Vnitol rv-nolivn
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CG1DCIII\ '1!1..1\Mt~
s..u. 1<1\ ~
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M I . A191rl
O:OUIII
S.,tford Geology of TtM 1869
Chlih.tWtt I .Udtil..ll
C!t.,.
10
~M:I.VI~Ie Fo41o 189~
Ketlh
A'llvtllt f'olio 1904
NotiOlloiG F'ouo 1907
l-lt.w son4t.tono !.liii i U) ' t i i : J j t ~:"lllli.l lll'..-: f(!.c!KII!I thOle
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C 'H.Jlf' Oft. ~llq iGIII Hif~-
C:~I)GIIIII <Ofl9 lu.mr~
""~ llllt
lhy lll,rhoud c:tftg)Mualt
CIIChl); C;t191
G:uull S'110k/
ae~~l ,
C lllu <9'19\omtrflll
rtotitll q ..,..,,.,, Andfnn. uhnt t l<clf t i i ! V P '' - b t t
Vnll ay i~ I'm
8vUht~'lf(hill TV'0'"'t 11110111110
tllllfi"'IIttJ.ati&Jt
G11tt Smeky CO(IoO in..tHITI
f>19tlll! tJul l Wfl hUt d nll
Htfii..II.Ufl a.tabl
Hhrnut tlo te
loforge 8 Plloten Ellijoy rquo 1913
tcvnl MJnetol 81" H
1954
*'r.'nCJ ol ~ 19$&
Hurd 8 SCIIIca OC<~t Otgt Section
1962
Notlaly ouOIItlla Al'ldrt t t"ht
14tnaroJ l.!luU lm
111o11a1v ho~o~
A~d!'1Wf llfl
IAVfOIIV lllotDII
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fm
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lm
lfiCOIIICrlllllt- --~;. ,;~
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GI01"0 lom)nO.Itd ~tll)'1111t (Slope 14, 1t!, 25, ttc 1
ro.,tieh. h' lii!Si:O:J''IJ
OtiJif fo,,.n!!GII (Stop J.4, 3-S, 4())
"'101 Sm011y OIWII
l'l.oJnouu l m 'SI ~pt 41,42 )
l-luonn Oup '"' (StOll 431
r.o~ptrpul lm (Stop 441
!iifiOWIIItd
91'1111~
"-'nnornelll t01mol!CA - ..,; , lllf'...ll) - -
._\II\COI IW111il;'-
>-
pl'r ~
Alltrt.d tOtll,
9 DIIIU 8
rnlen ' ""'
SollpUuet, 11\llllhi f' Uft!OAitnt
SH II \ 1.,_, IIYfJ.. 8 Uf'p ltflllfl6
Coroll!'lft
9"' '"
S-10
" '" '1, 19541 H"rst & ')chlu,1~5Z
17
Fig. 8-X-bedding, scours, penecontemporaneous deformation structures in fine- to medium-grained Ocoee rocks at Stop 40. Scale given by pencil at upper left.
Fig. 9-Penecontemporaneous deformation structures in laminated limestone at Stop 6. The contorted layer is about 6 inches thick.
18
SECONDARY STRUCTURES
FOLDS
The principal fold in the section between Parksville and the Sylco Creek fault is an anticline whose axis runs NE-SW between Stops 4 and 5. Numerous smaller folds are exposed. A small overturned syncline is visible in a new road cut 800 feet east of Stop 4, opposite the boat harbor.
The section between the Sylco Creek fault and Ducktown is on the west limb of a NE-SW trending anticlinorium. The overturned syncline between Stops 32-34 and the overturned anticline between Stops 23 and 24 are second order folds on this large structure. Several third order folds are in the vicinity of Stop 38 and between Stops 42 and 43.
Numerous small shear folds are in the gray-green phyllite, especially between Stops 18 and 23 (Fig. 10).
FAULTS
Great Smoky Fault (Cartersville Fault) At Parksville the Great Smoky fault zone strikes N40E and dips 80 to the Soutl1east. It juxtaposes the Athens
shale and the Sandsuck shale (Rodgers, I953) and contains slivers of the Nebo quartzite and other Chilhowee rocks. The fault is well exposed. The probable displacement at this point has already been discussed on page 5.
Sylco Creek Fault A second fault has been mapped along the course of Sylco Creek. It connects with the Alaculsey Valley fault
described by Salisbury ( 1961, p. 50-52). The rocks to the west of the fault are low-grade quartzite, arkose and phyllite; those to the east are low-grade phyllite. No sharp break in the crystallinity of the micas could be detected across the fault (see Fig. 1) and it is possible that the total displacement along it is not great.
Other Faults Small scale faults are exposed at Stops 1, 2, east of 4, 6, 8, 9, 10, 11, 12, 13, 20, 22, 23, and east of 25.
CLEAVAGE
Flow cleavage is well developed in the less competent layers of the Great Smoky group and strikingly developed in the overlying phyllites between Stops 34 and 18. It is best developed between Stops 20 and 18. West of the Sylco Creek fault axial plane cleavage is well developed between Stops 7 and 8 and at Stop 4, though not to the extent as in the phyllites to the east.
FLOWAGE
Although most of the quartzites within the gray-green phyllite are now highly fractured, they show thickness changes and intricate convolutions which can only be attributed to some earlier deformation involving flowage (Fig. 11 ).
MET AMORPHISM
The grade of metamorphism drops off gradually from the staurolite zone just east of Ducktown to slightly metamorphosed sediments at Parksville (see Map No. 1). The biotite isograd crosses the Ocoee Gorge section between Stops 42 and 43. All the rocks in the section west of this isograd are in the chlorite zone.
19
Fig. 10--Shear folds in laminated phyllite near Stop 20. Flow cleavage dips about 65 to the right.
Fig. 11-Convoluted quartzite at Stop 22. 20
CONCLUSIONS
That the grade of regional metamorphism drops off on the west side of the Piedmont has long been known, but the metamorphic isograds have not been traced previously. Metamorphism drops off gradually from Ducktown to Parksville and extends into the Paleozoic rock on the west side of the Great Smoky fault.
The above conclusion stems not only from the work represented by Map 1 but also from a study in 1956 of the mineralogy of Cambrian shales in Georgia (Hurst, unpublished). X-ray diffractograms of shale samples collected along and to the west of the Cartersville fault (Great Smoky fault) for distances up to 6 miles show that the crystallinity of the micas generally drops off from cast to west as in Fig. 1; but the Cartersville fault is not found at the same point with respect to crystallinity of the micas, from one traverse to another. At places (as a few miles north of Chatsworth) there is a sharp drop in crystallinity at the Cartersville fault. At other places (as on the west side of Georgia) no hiatus in crystallinity is apparent. In the Ranger-Fairmount area, high crystallinity of micas extends several miles into the Paleozoic rocks; locally there are chlorite porphyroblasts.
From the Cambrian shale study and from work reported here it is evident that at least part of the movement along the Great Smoky-Cartersville fault postdates regional metamorphism. Not only does the fault truncate stratigraphic units, it also disrupts the pattem of metamorphic grade. Delineation of metamorphic isograds south of the Map I area (Hurst, unpublished) shows that they continue to approach the fault as far down as Fairmount, where the biotite isograd almost reaches the fault, and diverge from the fault farther south. At least two periods of metamorphism have been recognized, though their effects have not been clearly separated. Whether the present distribution of isograds is mainly a consequence of one metamorphic event or the net effect of at least two is yet to be worked out. Anyway, considerable deformation involving the Cartersville fault and some of the flexures in the Murphy syncline took place after the imprint of regional metamorphism.
The formations of the Great Smoky group previously defined in the Mineral Bluff quadrangle {Hurst, 1955) are repeated by folding to the west. One additional formation beneath the Copperhill formation (the lowest exposed in the Mineral Bluff quadrangle) crops out in the northern part of the Epworth quadrangle. The base of the Great Smoky group is not exposed in the area of Map I.
Table 2 shows various correlations of southern Appalachian formations. In column 11 are suggested correlations for the Ocoee Gorge. The upper formation of Ocoee rocks in the gorge is strikingly similar to the Dean formation at the top of the Great Smoky group in the Mineral Bluff quadrangle, except for differences to be expected from the drop in metamorphic grade. The equivalence of the dark pyritic slate at the gorge and the Nantahala slate is indicated by lithologic similarities and by stratigraphic position.
The section in the gorge from the Sylco Creek fault to the biotite isograd is unusually well exposed and top~ bottom criteria are abundant. The lithologic units are the same as those described by Salisbury in the northwest quarter of the Cohutta Mountain quadrangle, but the sequence is different. Salisbury concludes that the Great Smoky group (which he calls the coarse-grained part of the Ocoee series) overlies the slate and phyllite sequence (which he called the fine-grained part of the Ocoee series). His conclusion is based on top-of-bed indications at six exposures (including one reversal) along an eight mile stretch of the contact. The rocks along the contact are strongly deformed and faulted, especially along the western two-thirds of the contact where it swings from southwest to west to northwest before being truncated by the Great Smoky fault. Of the 15 top-bottom directions east of the Alaculsey Valley fault on Salisbury's map, only three more indicate top of beds to the east than top to the west. The poor exposures, the small number of outcrops showing top-bottom features and th~ common reversals, coupled with strong faulting and folding along the contact, do not permit a reliable statement of the sequence to be made for this area.
In the Ocoee Gorge where exposures are excellent and top-bottom features prevalent, the dark pyritic slate and the gray-green phyllite clearly overlie the Great Smoky group and are not a part of it.
21
ACKNOWlEDGMENTS
Field expenses were defrayed by the Georgia Department of Mines, Mining, and Geology, Captain Garland Peyton, Director.
The drawings for the cover were made by Miss Myra Sides of the Art Department, University of Georgia. Table 2 was prepared by Professor James A. Barnes, Geography Department, University of Georgia, who also assisted with the preparation of the maps. Special effort in the typing and editing of the manuscript by Mrs. Audrey Miller is acknowledged.
REFERENCES
Furcron, A. S. (1953) Comments of the Geology of the Ellijay Quadrangle-Georgia, North Carolina, Tennessee. Ga. Geol. Surv. Bull. 60, p. 32-40.
Hurst, Vernon J. (1955) Stratigraphy, Structure, and Mineral Resources of the Mineral Bluff Quadrangle, Georgia. Ga. GeoL Surv. BulJ. 63.
King, Philip B.; Hadley, Jarvis B.; Neuman, Robert B.; Hamilton, Warren (1958) Stratigraphy of Ocoee Series, Great Smoky Mountains, Tennessee and North Carolina. Geol. Soc. Am., Bull. 69, p. 947-966.
LaForge, Laurence and Phalen, W. C. (1913} Ellijay Folio No. 187, U. S. Geol. Surv. Mellen, James (1956) Pre-Cambrian Sedimentation in the Northeast Part of Cohutta Mountain Quadrangle, Georgia.
Ga. Mini. Newsletter, Vol. 9, p. 46-61. Rodgers, John (1953) Geologic Map of East Tennessee. Tennessee Dept. Conserv., Div. Geol. Bull. 58. Safford, J. M. (1956) A Geological Reconnaissance of the State of Tennessee. Nashville, lst Bienn. Rpt. State Geologist. Salisbury, J. W. (1961) Geology and Mineral Resources of the Northwest Quarter of the Cohutta Mountain Quadrangle.
Ga. Geol. Surv. Bull. 71. Stose, G. W. and Stose, A. J. (1944) The Chilhowee Group and Ocoee Series of the Southern Appalachians.
Am. Joum. Sci. Vol. 242, p. 367-390, 401416. -- - (1949) Ocoee Series of the &>uthern Appalachians.
Geol. Soc. Am., Bull. Vol. 60, p. 267-320.
22
Miles from Ocoee Dam No. 1 (Parksville, Tenn.)
0.0
STOP 1
0.07
STOP 2
APPENDIX
Road Log
Great Smoky fault zone.
The Great Smoky fault (a northward extension of the Cartersville fault) juxtaposes the Sandsuck formation (later preCambrian-King et al, I 958, Table 1) and the Athens shale (Ordovician-Rodgers 1953, plate 13). Slivers of the Chilhowee group (Ncbo sandstone and Nichols shale - Rodgers 1953, plate 13) are included in the main part of the fault zone. Exposures of the fault begin at the overlook by the Ocoee No. 1 Dam and continue for several hundred feet along the highway to the northeast. Several faults comprise the zone. They are revealed by sharp changes in attitude of the rocks and by zones of gouge and brecciation. One fault is along the west edge of the quartzite; it strikes N40E and dips about 80SE. The trace of this fault is visible near the base of the hill across the Ocoee River to the south, just west of Ocoee Dam No. I. Other faults to the east of the first one range in strike from N45E to N70E, with the exception of a few minor cross faults, all dip to the southeast. Mullion structure is on some of the fault planes.
Scolithus tubes have been found near the middle of the quartzite directly north of the dam. Around the corner, just west of stop 2, the quartzite is conglomeratic. Poor, cross bedding is visible in places. Secondary green chlorite and calcite coat some fractures.
The rocks west of the fault zone arc light brown ( 5 YR 5I 6) massive, poorly
compacted claystone and shale. The upper part of the unit contains discontinuous
beds of shaley, yellowish gray (5 YR 7/2) finely crystalline to saccharoidal lime-
stone. No fossils were seen. The unit becomes foliated, intensely folded, and brecciated near the fault. Foliation strikes N20W and dips 40-60 northeast. Within the fault zone the sequence consists of thick quartzites interbedded with phyllites and shale. The quartzite is fine- to coarse-grained, yellowish gray (5 YR 7/2), thick- to thin-bedded, and well indurated. Adjacent to the faults it is highly fractured; away from faults, bedding is discernible and some faint cross-bedding can be seen. Sedimentation units are up to two feet thick and tend to be discontinuous and Lenticular. Some lenticularity may be due to structural modification of the original stratification during folding and faulting. In coarser-grained units, interpenetration of grains is evident. Quartzite units strike N5E dip east at 50-60 and are as much as 270 feet thick. The interbedded shales and phyllites are fissile, mottled dark yellowish orange ( 10 YR 6/6) to dusky brown (5 YR 2/2) laminated and massive clayey and silty, and well compacted. The shales and phyllites are crumpled and show slickensided surfaces. East of the fault zone, the phyllites in the Sandsuck formation strike N50E and dip 34NW; they terminate abruptly against southeast dipping quartzite in the fault zone.
Dark greenish gray, phyllites thinly interbedded with quartzites. Numerous fracture surfaces stained red brown. An x-ray powder pattern of a composite sample of the phyllite shows that it is composed of fine-grained 2M sericite, about 18% quartz, minor feldspar and chlorite; kaolinite also shows in the deeply weathered samples.
23
0.4
STOP 3
0.9
STOP 4
1.4
STOP 5
1.5
STOP 6
2.8
STOP 7
3.4
STOP 8
3.5
STOP 9
Phyllites with quartzite to the west. (See Fig. 1 for the mineralogy of the phyllites.)
Fine conglomerate and coarse sandstone interbedded with shale or phyllite. A thin section shows well-rounded, subangular to rounded grains of quartz, feldspar and quartzite in a matrix of fine granular calcite. Top of beds to northwest by grading and small scours.
These beds are on the west limb of a small anticlinorium and are equivalent to the beds at Stop 5.
Fine conglomerate, coarse sandstone and shale or phyllite equivalent to the beds at Stop 4. Axial plane cleavage has developed here in the least competent layers.
A small asymmetric syncline cut by a high-angle reverse fault. (See Fig. 12) . Excellent examples of penecontemporaneous slump structures in limestone.
The syncline trends N45E and plunges to the northeast at a low angle. The
fault strikes N25E dips 45 southeast and has an apparent offset of between 15-20
feet. The fold is on the southeast flank of a northeast-southwest trending anticlinorium. To the southeast the strata assume a gentler dip.
The strata are divisible into three units. The lowest consists of interbedded non-laminated silty fissile light olive gray (5 YR 611) shale, and fine-grained wavey laminated light gray (N7) to light brownish gray (5 YR 611) sandstone. Six feet .below the top of the unit is a persistent conglomerate three inches thick and composed of rounded to subangular pebbles of quartz and feldspar with a mode in the 2-4 mm. size grade, and set in a matrix of sand and silt. The second unit is approximately ten feet thick and is a massive, moderate yellowish brown
( 10 YR 514) to grayish orange ( 10 YR 7I 4) impure fine-grained limestone.
The upper two feet of the unit is a persistent dark gray (N3) to light olive gray (5 YR 611) claystone with a subconchoidal fracture. The limestone is silty, limonitic, and fractured; crystalline calcite coats the fracture planes. The uppermost unit is thick bedded to laminated (sedimentation units up to 18 inches thick) medium dark gray (N4) to light olive gray (5 YR 611) limestone interbedded with laminated calcareous silty shale. The limestone contains wisps of carbon as well as silt and clay; tiny cubes of pyrite are associated with the carbon. The most striking features in the lower part of the unit arc angular fragments of the delicately laminated silty limestone incorporated within the massive thick bedded limestone layers. Other layers of laminated limestone are contorted and the bent laminae are truncated by the overlying layers. (See Fig. 9). To the east are nearly horizontal carbonates.
Complexly folded and faulted sequence of silty shale and weathered siltstone.
Tightly folded overturned syncline of sericitic phyllite.
Possible angular unconformity between calcareous phyllites below and channeling quartzose sandstones above.
24
rood
0 !5 10 1!5fttt
Fig. 12-Sketch of roadcut on northeast side of highway at Stop 6.
25
4.0
STOP 10
4.2
STOP 11
5.2
STOP 12
5.3
STOP 13
5.7
STOP 14
5.74
STOP 15
5.8
STOP 16
5.9
STOP 17
6.1
STOP 18
6.3
STOP 19
6.7
STOP 20
Medium-grained kaolinitic quartzite with thin green claystones (weathered phyllite or shale). An x-ray powder pattern shows well crystallized 2M sericite,
kaolinite, and quartz; the kaolinite is a result of weathering of feldspar that was in
the fresh rock.
Broad open anticline exposing quartz sandstone and purplish silty shale.
Outcrops of vertically dipping and overturned arkosic sandstone and shale, west of Sylco Creek fault.
Weathered quartzite and phyllite. An x-ray powder pattern of the phyllite shows well crystallized 2M sericite and quartz plus minor chlorite and kaolin. Again the kaolin is a secondary product due to weathering of feldspar in the fresh rock.
Much faulting to the east in the direction of Sylco Creek fault. (See Stop 18) .
Deeply weathered phyllite mineralogically equivalent to the gray-green phyllite at Stop 18. Cleavage well developed.
Deeply weathered phyllite with well developed cleavage equivalent mineralogically to phyllite at Stop 18.
Deeply weathered phyllite with well developed cleavage equivalent mineralogically to phyllite at Stop 18.
Deeply weathered phyllite with well developed cleavage equivalent mineralogically to phyllite at Stop 18.
Moderately weathered gray-green phyllite contorted by shear folding, and displaying well developed axial plane cleavage. Excellent cleavage-bedding relations. The phyllite is thinly bedded to laminated and is composed of quartz, 2M sericite, chlorite, minor fine-grained felspar, and a variable amount of fine granular calcite. Many of the layers are principally calcite. The laminae have been disrupted by the cleavage into small lenses, streaks, and irregularly shaped clots. On weathered surfaces, the calcite has been leached out, leaving pockety layers. (See Fig. 3).
Thin-bedded to laminated gray-green phyllite with thin carbonate-rich layers.
Zone of quartzite and calcareous quartzite interbedded with gray-green phyllite. This zone, where completely exposed and not thinned by faulting, is about 30 feet thick.
Thin sections of the quartzites show fine quartz and a minor amount of feldspar, sericite, chlorite, and calcite. The calcareous quartzites have more calcite and less mica. In the phyllites micas predominate.
26
7.3
7.6 7.9
8.4 8.9
9.4 9.5 9.8 10.0 10.6
11.1 1!.4 11.7 12.0
STOP 21 STOP 22 STOP 23
STOP 24 STOP 25
STOP 26
STOP 27 STOP 28 STOP 29 STOP 30 STOP 31 ST OP 32 STOP 33 STOP 34
Same horizon of thin quartzites and calcerous quartzites interbedded with phyllites as at Stop 20. Repetition due to folding.
Same horizon as Stops 20 and 21. Grading in the quartzite layers indicates top of beds to the west. Quartzites highly contorted.
To the west is about 150 feet of laminated carbonaceous slate. To the east is thick Ocoee-type metaconglomerate. Fractured and faulted. Grading shows top of beds to west. The conglomerate belongs to the top of the Great Smoky group. The black carbonaceous slates are probably the Nantahala. This is the west limb of an anticline.
Same rocks as Stop 23. Thickness of the overlying black slate reduced by fa ulting.
Greenish laminated phyllite to west. Zone of thin quartzites and calcareous quartzites interlayered with phyllites to the east. The quartzites are up to about 4 inches thick and comprise about 50% of the zone. The quartzite layers are thinner and more sparing toward the top of the zone.
Same quartzite-rich horizon as Stop 25. Top of beds to west by grading.
A repetition of the quartzite-rich horizon at Stop 26. Quartzites commonly fractured and veined.
Top of dark laminated carbonaceous phyllite or slate. Dark slate to the south containing abundant pyrite cubes up to ~ inches across scattered mainly along bedding planes. Gray green phyllite to the north. Top of beds to the west.
Quartzites up to 6 inches thick with good cross bedding and scour features.
Excellent exposure of the dark slate. Bedding planes dip gently to the northwest; cleavage dip 45 to the southeast. Abundant large pyrite crystals scattered along the bedding planes.
Top of dark slate. Gray-green phyllite to the east. Graded bedding indicates beds right-side up.
Quartzite-rich horizon in the gray-green phyllite. Many of the quartzites show grading and some of them show scour features.
O ld quarry in the gray-green phyllite.
T hin, dense fine-grained quartzites interbedded with phyllite. This is the top
ot the Great Smoky formation . Between 34 and 35 are coarse metaconglomc rates at
least 75 feet thick.
27
12.2 13.3
13.6 13.8 14.3 14.6 15.1 15.4 16.4 22.4
STOP 35 STOP 36
STOP 37 STOP 38 STOP 39 STOP 40 STOP 41 STOP 42 STOP 43
Metaconglomerates containing pebbles of limestone, chert (?), and black slate.
Thick metaconglomerate and metagraywacke. Beds to the northwest showing coarse scour structures and grading. The strike of the beds is parallel to the road. The dip plane approximates the slope of the outcrop northwest of the road. Beds overturned.
Laminated phyllite or schist interbedded with thin quartzites. Metagraywacke and conglomerate to the north. Beds overturned.
Same rock type as Stop 37. Excellent cross bedding. Beds overturned.
Metagraywacke and mica schist. Thin layers in the bed of the Ocoee River southeast of the dam show good penecontemporaneous deformation features.
Excellent current structures in the road cut.
Massive metagraywacke right~side up.
Interbedded metagraywacke and mica schist and a zone about 100 feet thick of fine-grained laminated dark schist. Beds overturned.
Current structures common here and to the northwest, though not well exposed. This might be equivalent to the Hughes Gap formation.
Intersection of U.S. 64 and Tenn. 68 at Ducktown, Tenn.
28