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The Geological Society of America Field Guide 29 2012

Overview of the stratigraphic and structural evolution of the Talladega slate belt, Alabama Appalachians

James F. Tull* Department of Earth, Ocean, and Atmospheric Science, Florida State University

Clinton I. Barineau* Department of Earth and Space Sciences, Columbus State University

ABSTRACT

The allochthonous Talladega belt of eastern-northeastern Alabama and north- western Georgia is a northeast striking, fault bounded block of lower greenschist facies metasedimentary and metaigneous rocks that formed along the margin of Lau- rentia at or outboard of the seaward edge of the Alabama promontory. Bounded by metamorphic rocks of the higher grade Neoproterozoic(?) to Carboniferous eastern Blue Ridge on the southeast and unmetamorphosed to anchimetamorphic Paleozoic rocks of the Appalachian foreland on the northwest, the Talladega belt includes shelf facies rocks of the latest Neoproterozoic/earliest Cambrian Kahatchee Mountain Group, Cambrian-Ordovician Sylacauga Marble Group, and the latest Silurian(?) to uppermost Devonian/earliest Mississippian Talladega Group. Along the southeast- ern fl ank of these metasedimentary sequences, a Middle Ordovician back-arc terrane (Hillabee Greenstone) was tectonically emplaced along a cryptic pre-metamorphic thrust fault (Hillabee thrust) and subsequently dismembered with units of the upper Talladega Group along the post-metamorphic Hollins Line fault system. Importantly, strata within the Talladega belt are critical for understanding the tectonic evolution of the southern Appalachian orogen when coupled with the geologic history of adjacent terranes. Rocks of the lower Talladega Group, the Lay Dam Formation, suggest latest Silurian-earliest Devonian tectonism that is only now being recognized in other areas of the southern Appalachians. Additionally, correlation between the Middle Ordovi- cian Hillabee Greenstone and similar bimodal metavolcanic suites in the Alabama eastern Blue Ridge and equivalent Dahlonega Gold belt of Georgia and North Caro- lina suggests the presence of an extensive back-arc volcanic system on the Laurentian plate just outboard of the continental margin during the Ordovician and has signifi - cant implications for models of southern Appalachian Taconic orogenesis.

*[email protected]: [email protected].

Tull, J.F., and Barineau, C.I., 2012, Overview of the stratigraphic and structural evolution of the Talladega slate belt, Alabama Appalachians, in Eppes, M.C., and Bartholomew, M.J., eds., From the Blue Ridge to the Coastal Plain: Field Excursions in the Southeastern United States: Geological Society of America Field Guide 29, p. 1–40, doi:10.1130/2012.0029(xx). For permission to copy, contact [email protected]. © 2012 The Geological Society of America. All rights reserved.

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INTRODUCTION to anchimetamorphic rocks of the Appalachian foreland fold and thrust belt, and on the southeast by a major thrust duplex system Our purpose for this year’s fi eld trip is to present an overview below the amphibolite-facies eastern Blue Ridge allochthon. Unfor- of the stratigraphy and structure of the Talladega slate belt, a far- tunately, a number of different workers have presented contradic- traveled lower greenschist facies allochthon, ~100,000 km2 in area, tory views regarding the age of key stratigraphic units (e.g., Lay at the southwestern extremity of the exposed Appalachian orogen Dam Formation) and the nature of stratigraphic contacts (fault (Figs. 1 and 2). Studies of the geology of the Talladega belt have pro- versus unconformity; e.g., basal Lay Dam contact, upper Talladega vided invaluable insight into understanding the tectonic evolution of Group strata, basal Hillabee contact) within the geologic literature the southernmost Appalachians because of its unique stratigraphy (Carrington, 1973; Gastaldo and Cook, 1982; Mies, 1991, 1992; and structural setting and the fact that it represents the most com- Higgins and Crawford, 2008; Hatcher, 2008; Hatcher et al., 2007), pletely preserved and most distal (outboard) fragment of Paleozoic clouding the geologic literature with confl icting interpretations. We Laurentian cover rocks in the orogen, thus providing stratigraphic hope that this guidebook will present a comprehensive overview of information not preserved in similar age rocks of the Appalachian these varying viewpoints and help to resolve many of these confl ict- foreland to the northwest. For nearly a century, the Talladega belt ing interpretations. has also been recognized as containing some of the youngest units in the metamorphic Appalachians (Butts, 1926). The belt extends STRATIGRAPHY from beneath the Gulf Coastal Plain Cretaceous unconformity in Alabama, to Cartersville, Georgia, where its stratigraphy continues Introduction into the Murphy belt of the western Blue Ridge (Tull and Holm, 2005) (Fig. 1). It is bounded on the northwest by the frontal Blue The Talladega belt is divisible into four major lithologic Ridge thrust system, beneath which are found unmetamorphosed units: the earliest Cambrian Kahatchee Mountain Group,

Figure 1. Regional overview map of the southern Appalachians showing the locations of the Talladega belt and Figure 2 (red dashed box). fl d029-08 1st pgs page 3

Talladega slate belt, Alabama Appalachians 3 ion of Figure 8 is outlined. Figure 2. Geologic map of the Talladega belt in Alabama and Georgia. See Figure 1 for location. (From Tull et al., 2010.) Locat Tull See Figure 1 for location. (From Alabama and Georgia. belt in Talladega Figure 2. Geologic map of the fl d029-08 1st pgs page 4

4 Tull and Barineau

Cambrian-Ordovician Sylacauga Marble Group, Silurian- taposing the Lay Dam Formation with the underlying Kahatchee Mississippian Talladega Group, and Middle Ordovician Hilla- Mountain Group (Shaw, 1970; Tull and Telle, 1989). The Lay bee Greenstone (Fig. 2). Fossils, an internal unconformity, and Dam Formation is overlain by the Lower Devonian Butting Ram abundant primary structures indicate that the fi rst three groups Quartzite and its northeastern equivalent, the Cheaha Quartzite, a are upright (Tull, 1982, 1998, 2002). However, the fourth group thick, shallow-water metasandstone-metaconglomerate unit. The (Hillabee Greenstone) lies structurally above the stratigraphically Butting Ram–Cheaha Quartzite grades upward into the upper- younger Talladega Group along the cryptic pre- metamorphic Hil- most Devonian–lowermost Mississippian Jemison Chert–Erin labee thrust. The northwestern, structurally lower, part of the belt Slate. Overlying the Jemison Chert–Erin Slate is a tectonically contains a distinctive sequence of rocks (Kahatchee Mountain emplaced >2-km-thick bimodal volcanic sequence, the Hillabee Group) that were deposited during passive continental separa- Greenstone (Tull et al., 2007; McClellan et al., 2007). tion and formation of the Iapetus ocean following Neoprotero- zoic breakup of the Rodinian supercontinent. This sequence Kahatchee Mountain Group was deposited across the Alabama Promontory, above an upper plate (proximal) rifted margin (Thomas, 1993). In the southern The Kahatchee Mountain Group, the oldest unit in the belt, Appalachians, several lines of geologic and isotopic evidence occurs discontinuously along the northwest fl ank of the Talla- suggest that continental separation and the rift to drift transition dega allochthon (Fig. 2) (Tull, 1982, 1985). Although lacking that established Iapetus sea fl oor occurred in earliest Cambrian fossiliferous strata, this sequence is gradationally and conform- time (Rankin et al., 1993), near the base of the Chilhowee Group ably overlain by shallow water dolomitic marbles of the Jumbo (Simpson and Eriksson, 1989). The Chilhowee and younger Dolomite at the base of the Sylacauga Marble Group, which con- rocks thus constitute part of a craton-wide transgressive post-rift tain late Placentian (Early Cambrian–base of Stage 2, Series 1 of passive-margin sequence (Sauk sequence of Sloss, 1963) which Babcock and Peng, 2007) archaeocyathids, oncoids, echinoderm locally steps across the Blue Ridge rift-fi ll facies onto crystalline plates, and trilobite fragments (Bearce and McKinney, 1977; basement rocks. This sequence is interpreted to be the result of Tull et al., 1988; Johnson and Tull, 2002), making the Kahatchee drift-related thermal subsidence (Bond et al., 1984) and accom- Mountain Group early Cambrian or older. It is a thick (minimum panying eustatic sea level rise (Vail et al., 1977), and overlies a of 4.7 km above the tectonic base—Talladega-Cartersville fault), regional disconformity, or “breakup unconformity.” mostly thinly bedded metaclastic sequence (Tull, 1982; Tull et In the Talladega belt, Chilhowee-equivalent rocks are rep- al., 2010) (Fig. 3). Cross beds from several intervals consistently resented by the Kahatchee Mountain Group (Tull et al., 2010), indicate that the Kahatchee Mountain Group is upright, except and the overlying carbonate bank facies by the Sylacauga Marble where it is repeated with the overlying Lay Dam Formation in Group (Johnson and Tull, 2002), a thick (>3 km) shallow water an isoclinal anticline near the state’s eastern border (Allison et carbonate sequence equivalent to the Lower Cambrian–Lower al., 2008) (Fig. 2). The most complete section and type local- Ordovician Shady-Knox sequence in the foreland to the north- ity (Butts, 1926) occurs in the southwest, but it is locally absent west (Fig. 2). No rift-facies rocks are known from this south- where the basal thrust rises into younger rocks to the northeast ernmost segment of the orogen. Higgins and Crawford (2008, (Fig. 2). Butts (1940) divided the sequence into the following p. 24) argue that the Kahatchee Mountain Group and Sylacauga three mappable units, in ascending order: the Waxahatchee Slate, Marble Group, traditionally included as part of the lower green- the Brewer Phyllite, and the Wash Creek Slate (Fig. 3). schist facies Talladega belt (Tull et al., 1988; Johnson and Tull, Waxahatchee Slate. The Waxahatchee Slate (Butts, 1940) 2002), are actually part of the “Valley and Ridge rocks that share is the lowest exposed unit of the group, occurring in the extreme anchizone metamorphism, slaty cleavage, and other characteris- southwestern Talladega belt, and in the northeastern part of the tics with accepted Valley and Ridge rocks adjacent to them on belt in along the Alabama-Georgia border, where it cores an the north.” However, they fail to note that both the Kahatchee allochthonous, northwest-vergent, isoclinal anticline (Allison et Mountain Group and Sylacauga Marble Group rocks included in al., 2008) (Fig. 2). In the southwest, where the unit is >2 km their Valley and Ridge stratigraphy east of Interstate 65 contain thick (Figs. 2 and 3), it is dominated by distinctive, thinly (<1 cm) a well-documented lower greenschist facies mineral assemblage parallel bedded, dark metamudstone, interbedded with buff col- (chlorite-actinolite-epidote), well above that of the anchizone ored metasiltstone and very fi ne-grained metasandstone. Approx- Valley and Ridge rocks. This makes lumping the Kahatchee imately 4% to 5% of these metamudstones are interlayered with Mountain and Sylacauaga Marble Groups with the lower grade bodies (<15 m thick) of massive, coarse-grained to granule- Valley and Ridge rocks an untenable hypothesis (see below). bearing metasandstone (quartz arenite), locally tracable for sev- The drift-facies rocks are overlain by a successor basin eral kilometers. Near the center of the unit are beds of calcareous sequence, the Talladega Group, along a regional low-angle slate and thinly bedded calcarenite (Butts, 1940). Both lenticular unconformity. At the base of the group is a thick (up to 2.5 km) and asymmetric current ripple bedding and small scale scour and Silurian (?) to Lower Devonian clastic wedge constituting the fi ll structures occur locally. Lay Dam Formation. The sub–Lay Dam Formation unconformity In southwestern exposures, the <30-m-thick Sawyer Lime- regionally truncates the entire carbonate bank facies, locally jux- stone Member (Butts, 1940) (Fig. 3) forms a unique lithofacies fl d029-08 1st pgs page 5

Talladega slate belt, Alabama Appalachians 5 at the top of the formation. It is a medium to thick bedded (0.15– beds of massive, layered, and thinly bedded purple, maroon, and 1.5 m), impure, locally silicifi ed, dolomitic marble, locally con- green metamudstone and metasiltstone containing large chlorite taining öolites nucleated on quartz grains (Warren, 1969); and porphyroblasts and detrital muscovite fl akes. In the absence of stromatolites (Butts, 1926). Both upper and lower contacts are the Brewer, it would be diffi cult to differentiate the Kahatchee conformable and gradational. Mountain Group into subunits because the underlying Waxa- Brewer Phyllite. The Sawyer grades into the overlying, hatchee and overlying Wash Creek Slates represent assemblages ~300–400-m-thick Brewer Phyllite through a zone of calcare- of very similar lithologies (fi ne-grained, thin and evenly bedded, ous phyllite. The Brewer consists predominantly of alternating commonly carbonaceous rocks). Interlayered with the Brewer phyllites are quartzite intervals <15 m thick containing medium- to-coarse grained, thick bedded, locally cross bedded, moder- ately to well-rounded sand grains. Wash Creek Slate. The Brewer is gradationally overlain by the Wash Creek Slate (Butts, 1940), an ~2300–2400-m-thick sequence dominated by thinly bedded, locally highly carbo- naceous dark phyllite (metasiltstone), commonly interbedded with thin beds of very fi ne-grained metasandstone. Because the basal thrust rises in stratigraphic level northeastward, except for the salient in the Talladega belt along the Alabama-Georgia bor- der, only the upper Wash Creek or stratigraphically higher units are present along most of the belt (Fig. 2). Metasandstone beds <30 m thick make up <10% of the unit, but some are traceable for >10 km. More common near the top of the formation, they are commonly massive, coarse-grained quartzites, interlayered locally with granule metaconglomerates, and hold up the moun- tains along the west fl ank of the Talladega belt (Fig. 2). They are commonly cross-bedded and locally contain channels. Dis- rupted bedding, vertical and horizontal burrow-like structures, and feeding trail-like features on bedding planes in several zones, especially near the top of the unit, suggest bioturbation (Guth- rie, 1994). Thin sandstones locally display oscillation and current ripple bedding, scour and fi ll structures, and liquefaction features (Guthrie, 1994). The upper, locally highly carbonaceous strata, grades through an ~11-m-thick interlayered zone of thinly bedded black metasiltstone and dark silty dolostone into the Jumbo Dolo- mite, the basal unit of the Sylacauga Marble Group (Tull, 1985). Discussion. Parasequences in the Waxahatchee and Wash Creek Formations are represented by thinly bedded metapelitic sequences overlain by coarse metasandstone intervals. The upper Waxahatchee contains zones of soft sediment deformation features (Guthrie, 1994), suggesting periodic adjustments of mostly stabi- lized faults beneath or within the compacting sedimentary prism, and/or earthquakes. The Waxahatchee represents the initial trans- gressive systems tract in the Kahatchee Mountain Group, similar to that in the upper Unicoi through upper Erwin formations of the Chilhowee Group. Above the Waxahatchee, several unique depo- sitional facies suggest a period of regression along the Alabama promontory, beginning with deposition of the Sawyer Limestone, which contains shallow water features (öolites, stromatolites, and possible eolian quartz sand). Although the fi rst fully successful carbonate bank assemblage along the ancient continental margin is represented by the younger Shady-Jumbo Dolomite, the Sawyer Figure 3. Composite stratigraphic column of the Kahatchee was an isolated earlier carbonate buildup, and is the only marine Mountain Group in the southwestern Talladega belt. (From Tull carbonate unit within any Chilhowee Group–equivalent sequence. et al., 2010.) It indicates that immediately following Waxahatchee deposition, fl d029-08 1st pgs page 6

6 Tull and Barineau

water depths were very shallow. The Sawyer is succeeded by red northwest, indicating that it formed during an interval spanning beds of the Brewer Phyllite. The Brewer contains metaconglomer- ~80 Ma of Iapetus spreading. In this region, this sequence occu- ates, which are commonly channeled and grade into trough cross pies a broad valley up to 7 km wide, tapering to a feather edge to beds, as well as fi ne-to-medium grained metasandstone, and prob- the southwest, and is bounded to the northwest by the mountain- ably represents fl uvial braided plain deposits (Reineck and Singh, ous Kahatchee Mountain Group and on the southeast by the rug- 1980; Nystuen, 1982; Guthrie, 1985). Brewer carbonate inter- ged topography held up by the Lay Dam Formation. South and vals may represent either tidal fl at or lacustrine deposits (Nickel, west of Sylacauga, this sequence reaches its maximum thickness 1985; Guthrie, 1994). The unit may represent the only unit of the of >2.5 km, as the sub–Lay Dam unconformity rises to its highest Kahatchee Mountain Group which is not completely marine in stratigraphic level. Fossils are currently known from only three nature. Along with the Sawyer Limestone, the Brewer probably localities in the Sylacauga Marble Group, but a rather detailed records the maximum fl ooding surface/condensed section and is lithostratigraphy has been established (Tull, 1985; Johnson, likely equivalent to that seen in the lower Nichols (Hampton) For- 1999; Johnson and Tull, 2002). The Sylacauga Marble Group has mation of the Chilhowee Group. been divided into fi ve formations: the Jumbo Dolomite, the Fay- Marine conditions similar to those that formed the Waxa- etteville Phyllite, the Shelvin Rock Church Formation, the Gooch hatchee were reinstated following Brewer deposition. The typi- Branch Chert, and the Gantts Quarry Formation. cal dark, thinly bedded, fi ne-grained metasiltstone and sandstone Jumbo Dolomite. The Jumbo Dolomite (Butts, 1926), the beds of the Wash Creek Slate locally contain both asymmetric and lowest unit of the Sylacauga Marble Group, conformably over- symmetric ripples, and fl aser laminations. This facies is interbed- lies and is interbedded on a decimeter scale with uppermost ded with coarse-grained sandstones containing cross beds and carbonaceous calcareous phyllites of the Wash Creek Slate. The local trough-shaped channels, and fi ne-grained metasandstone top of the Jumbo is interbedded with the overlying Fayetteville that contains oscillation and current rippled bedding, as well as Phyllite. The unit averages ~300 m in thickness but ranges to small-scale scour and fi ll structures. Cross beds occur in all for- over 600 m. The basal section (~50 m) consists of thin lamina- mations of the Kahatchee Mountain Group, but are most com- tions (0.2–1.0 mm thick) of light to dark gray, fi nely crystalline mon near the top of the Wash Creek, and collectively indicate marble, separated by thin phyllite layers (0.02–0.25 mm thick). predominately a southeast paleocurrent direction, with possible Overlying the thinly laminated carbonates at the base is ~120 m longshore current infl uences. All of these features indicate rela- of massively bedded, gray to light gray dolostone. The overly- tively shallow water, tidal or other current-infl uenced deposition, ing upper Jumbo section (100–200 m thick) is massively bedded, and are characteristic of transitional to shallow shelf environ- and contains ubiquitous oncoids, pellets, algal/cryptalgal-coated ments (Reineck and Singh, 1980). Like those in the Weisner, grains, grains composed of coated-grain calcarenite, micrite, pel- quartzites in the upper Wash Creek contain bioturbation features. letal micrite, echinoderm plates, and possible trilobite fragments, The coarse-grained, aerially extensive Wash Creek metasand- as well as archaeocyathids (Tull et al., 1988). Massive metachert stone layers, like those in the Waxahatchee, probably represent ridges within the Jumbo locally crop out above the fl oor of the subtidal sand bodies similar to offshore bars associated with bar- marble valley. The most defi nitive primary features in the Jumbo, rier systems in a marine shelf environment (Reineck and Singh, including possible algal “clumps” or nodular evaporites, desic- 1980). The Wash Creek Slate thus forms a second shallowing- cation cracks or gas escape structures, tepee structures, fenes- upward high-stand systems tract in the Kahatchee Mountain trae, oncoids, and archaeocyathids, indicate a peritidal (shallow- Group, equivalent to the Wilson Ridge and Weisner formations marine to supratidal) origin for most of the unit (Johnson and in the Chilhowee Group. Like the second transgressional systems Tull, 2002). tract in the Chilhowee, the Wash Creek transitions into overlying The age of the Jumbo Dolomite has been established as early carbonate bank, sea-level highstand deposits (Jumbo Dolomite). Cambrian on the basis of the presence of archaeocyathids near the top of the unit near Fayetteville (Tull et al., 1988). The most Sylacauga Marble Group abundant forms belong to Class Irregulares, Order Archaeocy- athida. Others belong to the Superfamily Tumulocyathacea, At localities where the sub–Lay Dam Formation uncon- Class Regulares, Order Ajaicicyathida. The age assignment of formity has not cut into the Kahatchee Mountain Group, and these fossils is based on their exclusive occurrence in lower Cam- where the Talladega-Cartersville fault has not risen to a strati- brian rocks in North America. The fossils also limit the age of the graphic level above the sub–Lay Dam Formation unconfor- underlying unfossiliferous Kahatchee Mountain Group as noted mity, a sequence of metacarbonate rocks, referred to as the Syl- above. At a locality south of Winteroboro (Fig. 2), the uppermost acauga Marble Group, occurs between the unconformity and Jumbo–lowermost Fayetteville Phyllite yield phosphatic frag- the Kahatchee Mountain Group. This is the case from ~20 km ments of probable brachiopod shards. northeast of Sylacauga, to ~40 km southwest of Sylacauga (Fig. There is compelling evidence that the Lower Cambrian 2). Rare paleontologic discoveries and detailed lithostratigraphy Shady Dolomite and Jumbo Dolomite are correlative. Early (Figs. 4 and 5) link this sequence to the lower Cambrian to Lower Cambrian archaeocyathids from the Jumbo Dolomite link it to Ordovician carbonate sequence of the adjacent foreland to the the Shady Dolomite temporally and environmentally (Bearce and fl d029-08 1st pgs page 7

Talladega slate belt, Alabama Appalachians 7

AB C

Figure 4: Stratigraphic column of the Sylacauga Marble Group: A) Jumbo Dolomite and Fayetteville Phyllite;B) Shelvin Rock Church Formation; C) Gooch Branch Chert and Gantts Quarry Formation. (From Johnson and Tull, 2002) Figure 4. Composite stratigraphic column of the Sylacauga Marble Group. (From Johnson and Tull, 2002.)

McKinney, 1977; Palmer and Rozanov, 1976; Pfeil and Read, breccia containing ~70% angular lithic clasts (0.1–7 mm in long 1980; Tull et al., 1988). Both units are dominantly dolostone, dimension) interlayered with dark, charcoal-gray, mm-scale, and contain zones of massive chert. Like the Jumbo, the Shady laminated phyllite. The lithic clasts are of three types: (a) dark contains a signifi cant amount of quartz silt and sand within lami- brown metashale (mud) fragments very similar to the matrix, nated and massive dolostone layers near the base (Bearce, 1985). (b) light beige metashale clasts, and (c) metasiltstone clasts. The Similar quartz-rich Shady dolostones have been described in Vir- high clast-to-matrix ratio suggests that the rock was originally ginia by Pfeil and Read (1980). Many of the quartz silt and sand- clast supported. rich layers are interbedded with thin algal laminations. Arkosic metasandstone within the Fayetteville is thinly bed- As a result of drift-related thermal subsidence (Bond et al., ded (2–20 cm scale) and fi nely laminated (mm scale), locally 1984) and accompanying eustatic sea level rise (Vail et al., 1977), cross laminated (sets ~15 cm thick), and contains both wave the Jumbo (Shady) was deposited during a major change in depo- current (oscillation) ripple and current ripple marks. Individual sitional setting, following the initiation of seafl oor spreading of metasandstone beds are laterally continuous and are commonly Iapetus, when the southeastern margin of Laurentia was no longer separated by thin phyllite partings. A continuous interval, 20– receiving large volumes of siliciclastic material, and a carbonate 30 m thick, of well sorted, fi ne-to very fi ne-grained metaar- bank could form. This vast carbonate bank, which was initiated kose (quartz—49.3%, K-feldspar—41.6%, plagioclase—2.3%, at the base of the Jumbo, lasted for another 100 million years. calcite—4.6%, mica—0.6%, and opaque minerals—1.3%, plus Fayetteville Phyllite. The Fayetteville Phyllite conformably trace zircon and tourmaline) is found within the Fayetteville near overlies sandy argillaceous marbles at the top of the Jumbo Dolo- Winterboro (Fig. 2; see also Stop 8, Tull, 1985). Dip-corrected mite. The Fayetteville is predominantly a maroon to charcoal- cross laminations indicate paleocurrent directions between S 39° E purple, strongly foliated and lineated phyllite, 80 m to 290 m and S 54° E, whereas wave current ripples indicate a current thick. Interlayered with the fi ne-grained pelitic rocks are tan meta- direction of S 20° W. siltstone, and yellowish-brown to ochre, thinly bedded, very-fi ne The transition from the carbonate-dominated Jumbo Dolo- to fi ne-grained, micaceous arkosic metasandstone. A distinctive mite to the siliciclastic-dominated Fayetteville Phyllite represents lithology within the phyllite facies is a clast- dominated micro- an extensive, platform-wide change in sediment composition and fl d029-08 1st pgs page 8

8 Tull and Barineau 2.) Figure 5. Stratigraphic column of the Sylacauga Marble Group and correlative units of the foreland. (From Johnson and Tull, 200 Tull, units of the foreland. (From Johnson and Figure 5. Stratigraphic column of the Sylacauga Marble Group and correlative fl d029-08 1st pgs page 9

Talladega slate belt, Alabama Appalachians 9 depositional environment. In the Appalachian foreland, the pas- cross stratifi cation, suggest a tidal-fl at environment for much of sive margin transgressive carbonate facies of the Shady Dolomite the Fayetteville. In this context, the thicker units of fi ne-grained was abruptly interrupted by an infl ux of craton-derived clastic meta-arkose likely represent subtidal sand shoals or bars. The sediments forming the Rome Formation of Early Cambrian age. localized, poorly sorted metagraywacke facies may represent a Thomas et al. (2000) suggest that this clastic infl ux was geneti- slump feature or debris fl ow within a low spot, such as a tidal cally associated with a small component of crustal extension and channel, which cut into the tidal-fl at facies. uplift in the present Appalachian foreland during the initiation Shelvin Rock Church Formation. The lowest marble strati- of the Ouachita rift, which began propagating eastward along a graphically above the Fayetteville Phyllite marks the base of the transform fault (Alabama-Oklahoma transform) at the southern Shelvin Rock Church Formation. This unit conformably and margin of the Alabama continental promontory at this time. The gradationally overlies the Fayetteville. Ranging between 600 m Rome consists of a heterogeneous sequence of variably colored and 1000 m in thickness, it is the thickest unit of the Sylacauga mudstones, siltstones, and rare very fi ne-grained sandstones con- Marble Group and contains the most diverse lithologies. It is taining interbedded limestone and dolostone. In the subsurface, separated into a lower and upper sequence, each containing a dif- the unit contains anhydrite and other features of evaporite deposi- ferentiated member (Fig. 4). tion (Thomas et al., 2000). The Fayetteville Phyllite, which con- The lower Shelvin Rock Church Formation is a lens-shaped tains many similar lithologies and shares a similar depositional mixed carbonate-siliciclastic unit extending 10.5 km along setting with the Rome Formation, also marks a period of regres- strike. It consists of a series of variably thick (a few centime- sion during which siliciclastic sediments (shale and arkose) were ters to one meter) marble layers cyclically interbedded with dark deposited in a shallow-marine environment which prograded out charcoal to maroon phyllite (generally a few centimeters thick, onto the carbonate platform. Other than a difference in degree but ranging from <1 mm to 0.5 m thick). The subunit reaches a of metamorphism, the maroon and charcoal-purple phyllites of maximum thickness of ~700 m, 5 km west of Sylacauga, pro- the Fayetteville are essentially identical to typical shales of the gressively thinning toward the northeast and southwest (Johnson Rome in Alabama. Fayetteville microbreccias, interpreted to and Tull. 2002). The lateral transition from the lower subunit to have formed in a shallow-water/intertidal zone, with the brec- lithologies of the upper subunit (see below) is not well exposed cia fragments either derived as storm-generated rip-up clasts or but appears to involve intertonguing of lithologies representative desiccation-generated cracks, also have similar analogues in the of both subunits. Typical marble layers within the lower Shelvin Rome. Although no fossils have been recovered from the Fay- Rock Church Formation range from white, pink, to dark gray; etteville, it can be bracketed between early and Middle Cambrian are medium to coarsely crystalline; and are commonly dolomitic. by archaeocyathids from the underlying Jumbo Dolomite and tri- They commonly contain fi ner-scale beds and laminations (a lobites from the overlying Shelvin Rock Church Formation (see few mm thick), and locally contain minor disseminated (<1%) below), within the depositional age range of the Rome Forma- quartz sand/silt. Many of the thinner marble beds are lenticular in tion. Correlation of the Rome and Fayetteville (Fig. 5) indicates form. Both upper and lower contacts of marble layers are sharp. that the infl ux of craton-derived clastic sediments prograded out On average, phyllite constitutes 20% to 30% of this part of the across the platform at least as far as the palinspastic position of formation. Reasonable values of differential compaction (80%) the Talladega belt and that a signifi cant component of these sedi- suggest that the mudstone protoliths of the phyllites may have ments was arkosic sands. originally constituted from 36% to 54% of this lower interval. In Probable lateral facies transitions into carbonate rocks addition to phyllite, non-marble layers include metasiltstone, and within the Fayetteville suggest, however, that carbonate sedimen- locally, thin, fi ne-grained, feldspathic meta-sandstone. Because tation along the platform may not have completely ceased dur- the phyllites are more resistant to erosion than the surrounding ing deposition of the unit. Such an infl ux of siliciclastic sediment carbonates, the lower Shelvin Rock Church Formation com- from a terrestrial source, like the craton, must prograde out onto monly forms low ridges throughout its extent. the carbonate platform, and be great enough to choke-out most The Cedar Creek Marble Member (Johnson, 1999) is a carbonate deposition and fi rmly establish siliciclastic deposition. 30-m-thick calcite and dolomite marble near the base of the lower This could be achieved by uplift of siliciclastic-source rocks and/ Shelvin Rock Church Formation. It is characterized by marble or progradation of fi ne siliciclastic sediments out onto the car- containing internal thin wavy, crinkly and undulate micritic lam- bonate platform as a result of sea-level fall. inations, typically 1–5 mm thick, but ranging to 1 cm. Unlike The fi ne-grained meta-arkose facies, containing small- other parts of the lower Shelvin Rock Church Formation above scale, mud-coated cross laminations and both symmetrical and and below, the Cedar Creek has very few (<0.5%), thin (<5 mm) asymmetrical ripple marks, provides additional evidence for phyllite interbeds. Fine quartz silt and muscovite “fi lms,” 0.05– shallow-water deposition of the unit. Both primary features are 0.1 mm thick, separate the micritic laminations, and are com- indicative of shallow-water, current-driven environments. Taken monly no thicker than the dimensions of a single silt grain. together, the potential desiccation-produced microbreccia in oth- The upper Shelvin Rock Church Formation (Fig. 4) is found erwise laminated meta-mud and siltstones, with the combina- above and at the lateral extents of the lower part of the forma- tion of mud-coated symmetrical and asymmetrical ripples and tion, and consists predominantly of coarsely crystalline, thinly fl d029-08 1st pgs page 10

10 Tull and Barineau

laminated (0.5 mm to 1 cm thick) and banded (1 m thick), dove be identifi ed, but many are likely trilobite fragments. One prev- gray and white, calcitic/dolomitic marble containing dissemi- alent unidentifi ed non-trilobite fossil has an irregularly shaped nated coarse to very coarse-grained, rounded quartz sand grains. honeycomb-like structure 1–3 cm across. Locally, the quartz sand is concentrated into tabular calcareous Metamorphic recrystallization of the interbedded marbles sandstone beds 1–4 cm thick. The unit also contains minor (1% and phyllites has obscured any original primary features other to 3%) quartz silt and muscovite in very thin, discontinuous lami- than bedding in the lower Shelvin Rock Church Formation. The nae, similar to the Cedar Creek Marble. Beyond the northeast and outcrop distribution of this part of the unit suggests that deposi- southwest extents of the lower Shelvin Rock Church sequence, tion of the mixed carbonate-siliciclastic facies was restricted to the upper Shelvin Rock Church Formation rests directly upon a specifi c area of the carbonate platform. The Cedar Creek Mar- the Fayetteville Phyllite. The vertical transition from the phyl- ble Member and the upper Shelvin Rock Church Formation are lite/marble interbedded facies into the overlying thinly laminated phyllite-free, and thus represent a different depositional setting. marbles is abrupt. The thickness variations in the lower Shelvin Rock Church The Averett Branch Meta-arkose Member (Fig. 4) is a thick Formation are interpreted to be the result of an intrashelf depocen- metasandstone lens within the thinly laminated marbles of the ter, or basin, which underwent periodic differential subsidence upper Shelvin Rock Church Formation. It is a well sutured, well relative to the basin fl anks. In comparison to the laterally adja- sorted, fi ne-grained (0.5 mm), tan to pink, arkosic to sub-arkosic cent shallow-marine carbonates of the upper Shelvin Rock, the meta-arenite containing quartz (66.3%–78.9%), K-feldspar phyllite interbeds, deposited as siliciclastic mudstones, siltstones, (19.1%–31.5%), and trace amounts of detrital muscovite, biotite, and locally, very fi ne-grained sandstones, probably represent a zircon, and tourmaline, with little or no matrix. It extends along relatively deeper-water facies. This localized deposition of rela- strike for ~2.4 km, reaching a maximum thickness of ~86 m. tively deeper marine siliciclastic sediments adjacent to shallow- The porous nature of the rock suggests that it may have con- marine carbonates is best explained by the presence of an intra- tained a carbonate cement, a likely scenario considering that it shelf depocenter, the location of which was possibly controlled is stratigraphically surrounded by carbonate rocks. The sand- by syndepositional faults. Such a setting also accounts for why stone contains thin, delicate laminations (<1 mm to 5 cm thick), extensive siliciclastic mud (phyllite) deposition was not basin- indicating that the unit was not signifi cantly bioturbated. It also wide, but was restricted to a specifi c area. Carbonate layers inter- contains upright cross-beds. The Averett Branch contains poorly bedded with the phyllites may have been composed dominantly preserved trilobite cranidia as casts and molds along bedding of ribbon grainstones that formed in somewhat deeper water than planes (Johnson and Tull, 2002). Because the grains creating the the adjacent phyllite-free carbonates. A mechanism for deposi- casts and molds are sand-sized, many of the fi ner details of the tion of the lower Shelvin Rock must be invoked which would original fossils are lost, and most do not have enough detail to be restrict siliciclastic mud and silt sedimentation to only part of identifi ed at the species level. However, the casts and molds do the basin, leaving the rest mud-free. One such mechanism could preserve some recognizable forms, as well as different sizes and have involved an extrabasinal distribution system which chan- shapes that represent different genera and maturity stages of trilo- neled fi ne siliciclastic sediments across the platform into tectoni- bites. Two species, on the basis of shape and structure of cranidial cally driven topographic depressions, to areas now represented casts, have tentatively been identifi ed as Solenopleurella? sp. and by the intrashelf depocenter. Astini et al. (2000) suggested that Elrathia cf. E. antiquata (David R. Schwimmer, written and oral a similar (and probably correlative) mixed carbonate-siliciclastic communication, 1998). Solenopleurella? sp. is Middle Cambrian facies in the Conasauga Formation in Alabama may have resulted in age, whereas Elrathia cf. E. antiquata ranges from Middle from either: (a) productivity cycles, (b) high-frequency sea-level to Late Cambrian and is not as useful for biostratigraphic work oscillations involving clastic input and carbonate retreat, or as Solenopleurella? sp. (David R. Schwimmer, written and oral (c) event cycles. The relatively regular cyclicity of the carbonate/ communication, 1998). Solenopleurella? sp. is a very common siliciclastic interval in the Shelvin Rock Church suggests a com- species throughout the Consauga Formation of the Appalachian bination of the fi rst two mechanisms. Beyond the rim (ramp?) of foreland (Schwimmer, 1989). The fact that cranidial morpholo- the intrashelf depocenter elevations were likely high enough not gies resembling Solenopleurella? sp. and Elrathia cf. E. anti- to be affected by either of these possible fl uctuations, and thus quata were found together in the same unit strengthens the likeli- would have maintained more constant shallow-marine carbon- hood that both identifi cations are correct (David R. Schwimmer, ate deposition. Unfortunately, the lateral transition between the written and oral communication, 1998). There are also numerous upper and lower parts of the formation is very poorly exposed, trilobite species in the Averett Branch Meta-arkose that cannot be but probably represents a carbonate ramp between the peritidal identifi ed. Schwimmer (written and oral communication, 1998) platform and intrashelf basin. Except for a short period of stabil- believes that several very small cranidia (~3–4 mm across) are ity during which the Cedar Creek Marble was deposited across from a type of planktonic trilobite called Agnostida. Unfortu- the basin, differential subsidence, probably in combination with nately, these trilobites require exceptional preservation for spe- fourth and fi fth order sea-level oscillation cycles, apparently cies identifi cation, a necessity for biostratigraphic work. There kept the basin deep enough to form the cyclically interbed- are other fossils within the Averett Branch member that cannot ded phyllite/ carbonate facies. Eventually, however, subsidence fl d029-08 1st pgs page 11

Talladega slate belt, Alabama Appalachians 11

ceased, probably as a result of cessation of fault movements, and coarse-grained rounded quartz sand grains, locally concentrated the depositional environment was maintained as shallow-marine. into tabular calcareous sandstone beds suggests that it may have At this point, thinly laminated marbles of the upper Shelvin Rock originally consisted of grainstone and/or packstone layers. Thin, Church were deposited continually across the basin. mm-scale laminations, interlayered with thicker, cm-scale layers Intrashelf depocenters similar to that proposed here for the of fi ne grainstone or packstone, like those found in this part of the lower Shelvin Rock Church Formation have been recognized in formation, are often associated with peritidal carbonate deposits the Conasauga Group of the Appalachian foreland (Markello and (Tucker and Wright, 1990). Read, 1982; Hasson and Haase, 1988). These intrashelf depocen- The mechanism for depositing enigmatic sand bodies like ters, however, are much broader and the deposits are thinner and the Averett Branch Meta-arkose Member within carbonate units more shale-dominated. Nevertheless, they do display carbonate/ like the upper Shelvin Rock Church Formation is unclear. The shale interbeds similar to the lower Shelvin Rock Church. feldspar and trace minerals (zircon, tourmaline) indicate a gra- Because the latter formation is homoclinally dipping, however, nitic source rock, probably basement. The thinly laminated it is possible that this basin represents one edge of a larger basin, nature of the protolith probably indicates that relatively calm most of which is not exposed. water lacking high turbidity, but moderate energy, including pos- The Cedar Creek Marble apparently represents a short hia- sibly mild wave and/or tidal action, was required for currents to tus in differential subsidence of the intrashelf basin, because it is move the sand body out onto the shelf and to produce the cross overlain by the main sequence of cyclically bedded siliciclastic/ laminations. Although the trilobite fossils are marine, their eury- carbonate rocks of the lower Shelvin Rock Church Formation. The topic nature sheds little light on the depositional environment of fi ne laminations of the Cedar Creek consistently exhibit a wavy or the unit. It grades laterally into thinly laminated marbles and its crinkled appearance suggestive of algal or stromatolitic lamina- position within these upper Shelvin Rock Church marbles indi- tions (Scholle et al., 1983), and the unit is therefore interpreted cates that it was probably deposited landward of the carbonate to contain cryptalgal laminite or stromatolites. The small surface platform rim or ramp. Thus, it must have been a sand lens depos- relief features are believed to have been caused by microbial mats ited on the carbonate platform in roughly the same overall set- which occurred on, and below, the sediment surface. Such features ting as the thinly laminated micrite, and a shallow-marine origin can allow for distinction between microbially colonized tidal fl at is therefore likely. Such sandstone bodies, found in association surfaces and purely sedimentary laminated sediments (Tucker and with carbonate sequences with little or no associated shale, were Wright, 1990). The depositional setting of the Cedar Creek was common within the extensive carbonate platforms of the middle therefore probably one where thin micrite laminations formed to late Precambrian and early Paleozoic (Pettijohn et al., 1987). under relatively quiet, peritidal (supratidal?) conditions in which Because of the lack of interbedded shale and carbonate, most are carbonate mud was bound to the substrate by algal mats (Tucker classifi ed as shallow-marine deposits. The Averett Branch Meta- and Wright, 1990). The fi ne quartz silt and muscovite “fi lms” sep- arkose appears analogous to these deposits in terms of lithology arating the micritic laminations occur in regular, thin laminae and and carbonate association. Similar carbonate-associated sand- are not mixed in with the micrite. Because the siliciclastic “fi lms” stones are rare in modern carbonate settings, presumably because are distinct from the micritic laminae, it is likely that some deposi- the platforms are not as extensive as those formed during the Pre- tional process in addition to the background carbonate sedimenta- cambrian and Paleozoic (Pettijohn et al., 1987). tion is responsible for their occurrence. If algae had bound these The Shelvin Rock Church and Conasauga Formations (the sediments along with carbonate mud from the water column, a Conasauga has “formation” status in Alabama and “group” status mixing of the sediments would be expected. The regularity and in Tennessee) are lithologically similar and contain a common close spacing of the laminations indicates that the change in depo- Middle Cambrian fauna. The Shelvin Rock Church Formation sition occurred systematically and frequently. Fine-grained silici- ranges between ~350 m and ~1000 m in thickness. The thickest clastic sediments such as these are typically deposited in greater interval of the Conasauga Formation in Alabama is comparable amounts if they are transported by terrestrial water currents. The at ~930 m, but the thickness range is also highly variable, and silt and fi ner siliciclastic grains within the Cedar Creek are in such at some localities the interval is only ~100 m thick (Osborne et delicate thin laminations, however, that it seems unlikely that al., 2000). The Conasauga ranges from Middle to Late Cambrian they were deposited by a current with a regular siliciclastic sedi- in age, and represents the transition from the regressive Rome ment load. The fact that the predominant component of the sedi- clastic succession to the more massive carbonate facies of the ments is carbonate supports this assumption. A reasonable inter- Upper Cambrian to Lower Ordovician Knox Group. Osborne pretation is that the quartz silt and clay “fi lms” are wind-blown et al. (2000) describe the unit in Alabama as a complex interval deposits, suggesting that these stratiform cryptalgal sheets were relative to thickness, lithofacies, diagenesis, and nomenclature. exposed during low tide. The upper Shelvin Rock Church For- The highly variable mix of lithologies consists predominantly mation, represented predominantly by a homogeneous lithofacies of limestone, dolostone, and shale in varying proportions, with of laminated and banded marble, was deposited under relatively minor sandstone. Variable degrees of dolomitization and silicifi - uniform conditions. The fact that much of this coarsely crystal- cation have complicated correlation and nomenclature. In addi- line marble sequence also contains disseminated coarse to very tion, the unit commonly changes character signifi cantly from one fl d029-08 1st pgs page 12

12 Tull and Barineau thrust sheet to another within the Appalachian foreland (Osborne of a primary carbonate (dolomitic) protolith. Locally exposed et al., 2000). The interbedded marbles and phyllites (limestones within the upper part of the chert interval is a dull gray-white and shales) within the lower Shelvin Rock Church Formation are massive dolomitic marble as much as 70 m thick. Near the a common characteristic of the lower Conasauga interval in many top, this marble contains abundant (>90%) spherical to sub- parts of the foreland in Alabama (Thomas et al., 2000) as well spherical coated grains best classifi ed as oöids/pisoids forming as Tennessee and Virginia (Hasson and Haase, 1988; Markello a packstone or pisolite in beds 2–3 cm thick, vaguely sorted by and Read, 1982). One feature common to the Conasauga but not diameter. Some of the oöids/pisoids are oblong and irregularly recognized in the Shelvin Rock Church is the presence of oölitic shaped, in part because of irregularly shaped cores, but mostly intervals. Additionally, dolomitic intervals in the Conasauga are as a result of fl attening. Above and below the 20 m thick oöid/ commonly chertifi ed, but metachert does not appear in the Shel- pisoid zone is medium-to coarse-grained crystalline dolomitic/ vin Rock Church. calcitic marble with <1% disseminated fi ne-to medium-grained Thomas et al. (2000) suggest that the irregular distribution of quartz sand like that forming the nuclei of many of the oöids/ Conasauga carbonate and coeval fi ne siliciclastic rocks resulted pisoids. The oöids/pisoids range from 1 to 5 mm in diameter, and from signifi cant variations in depositional setting and sediment have nuclei 0.5–3 mm in diameter (majority 0.7–0.8 mm). The source due to syndepositional faulting. They attribute this faulting nucleus of each is surrounded by cortex of diagenetically and/or to crustal instability associated with continued (through Middle metamorphically recrystallized medium-grained, twinned, rhom- Cambrian time) migration of the Ouachita rift along the transform bic calcite/ dolomite crystals formed in faint spherical concentric bounding the southern margin of the Alabama continental prom- laminations (0.25–1 mm thick) about the nucleus. Uncoated sand ontory. The Conasauga intrashelf depocenters may thus represent grains and dark micritic balls (peloids?) can also be found fl oat- regions of the platform which underwent more signifi cant subsid- ing independently between the oöids/pisoids. Very fi ne calcite/ ence as a result of syndepositional fault motion. Differential sub- dolomite crystals, probably representing a recrystallized primary sidence of fault blocks beneath the platform would account for micritic matrix, occur between the oöid/pisoid grains. The pres- the abrupt thickening and thinning and the complex assemblage ence of primary matrix between the oöids/pisoids, the fact that of sedimentary facies within the Conasauga interval. Apparently, the oöids/pisoids appear to be sorted by size into different layers many of these fault blocks were tilted, because signifi cant varia- and contain a variety of nuclei types, and the presence of concen- tions in Conasauga thickness occur within the same foreland tric laminations within many of the oöids/pisoids, suggest that thrust sheet (Thomas et al., 2000). The same is true of the Shelvin these features are primary. None of the distinctive characteris- Rock Church Formation in the Talladega belt. The depositional tics of vadose pisoids have been observed, and thus the pisoids setting of the lower Shelvin Rock Church Formation conforms are interpreted as coated grains which originated at the seafl oor well to an intrashelf depocenter model of Conasauga deposition surface and apparently accumulated as a packstone. Recrystal- and suggests that syndepositional basement faults may have been lization has apparently precluded preservation of microstructures disbursed at least as far outboard on the southeast trailing mar- within the cortex, thus preventing recognition of internal fabrics gin of the Alabama promontory as the region now represented other than the faint concentric laminations. by the Talladega belt, i.e., very near the shelf edge. The presence Overlying the pisoid and oöid (?)/intraclast-bearing dolo- of a cyclic siliciclastic/carbonate intrashelf depocenter in the stone is a 20–30-m-thick, dull, earthy tan to maroon phyllite Talladega belt indicates that the siliciclastic dispersal system(s) that marks the boundary between the Gooch Branch Chert and extended to the outermost parts of the platform. Proposed intra- overlying Gantts Quarry Formation throughout most of the study shelf depocenters in the Conasauga are, however, much larger area. The highly porous nature of the phyllite suggests that it was than that within the lower Shelvin Rock Church Formation (sev- calcareous before weathering, and thus the protolith is believed eral tens of kilometers across versus ~10 km across) (Markello to have been a calcareous mudstone or marl. and Read, 1982). The intrashelf depocenter represented by the Although little can be inferred about the depositional envi- lower Shelvin Rock Church Formation may appear deceptively ronment of the protolith of the metachert, the other lithologies small in areal extent because only a two-dimensional (map) view within the Gooch Branch Chert provide some basis for inter- can be obtained. Alternatively, the size of the proposed Shelvin pretation. Pisoids and oöids form in a variety of environments Rock Church intrashelf depocenter may be the result of a smaller but are common components of shelf-margin sands (Tucker region of subsidence due to block faulting along outer parts of and Wright, 1990). The bedded and sorted nature of the oölitic/ the platform. pisolitic packstone suggests that the rock may have accumu- Gooch Branch Chert. The Gooch Branch Chert (Fig. 4) lated as a near-shoreline carbonate body in a setting such as an is characterized by large blocks and narrow ridges of metach- oöitic/pisolitic shoal complex or offshore bar. A shallow-marine ert cropping out above the relatively fl at fl oor of the Sylacauga (inner, shallow ramp?) origin is also supported by the presence valley. Metachert within the 250 m to 600 m thick unit is white of intraclasts within these rocks. Peloids, which dominate the to cream in color and forms massive, moderately foliated oöid/pisoid nuclei, in addition to the skeletal fragment nucleii, lenses. Unfortunately, other lithologies within the unit are gen- could have been derived from nearby algal mats on the adjacent erally not well exposed. The metachert is likely a replacement platform interior, as algae were important producers of peloids fl d029-08 1st pgs page 13

Talladega slate belt, Alabama Appalachians 13 in the early to middle Paleozoic (Tucker and Wright, 1990). Pel- on a dry hypersaline carbonate shoreline (Sternbach, 1984). oids commonly make up an important constituent of the sand Sternbach (1984) interpreted parts of the unit to have formed as fraction of low energy shallow marine carbonate sediments. The arid sabka fl ats. The Gooch Branch likely represents a more dis- other nuclei (sand, silt, and lithic fragments) could have been tal portion of the lower Knox Group, with the upper part of the easily transported from subaerial exposures on the platform by unit possibly representing facies associated with an upper (shal- wind, particularly in an arid setting. No crossbeds, ripples, or low) carbonate ramp. The generally poor exposure of both units, channels have been observed in association with the oölitic/ however, prevents a signifi cantly detailed comparison. pisolitic packstone. Gantts Quarry Formation. Capping the Gooch Branch Chert The intraclastic dolostone resembles a series of storm depos- is the uppermost unit of the Sylacauga Marble Group, the Gantts its. The alternation of the intraclastic layers with the fi ne-grained Quarry Formation, which is exposed in the core of the pre-Lay micritic/oölitic layers is indicative of episodic storms, in which Dam Formation syncline (Sylacauga syncline) (Tull, 1998). The the thicker intraclast beds probably represent rapidly formed, tur- Gantts Quarry Formation, composed of a relatively pure, fi ne-to bulent storm deposits. The thinner interbedded fi ne-grained beds medium-grained, calcitic marble, is the most intensely quarried probably represent longer, quiet periods of deposition when the marble in the Sylacauga Marble Group, being prized for dimen- shallow-marine waters were calm (Scholle, et al., 1983). Many sion and decorative stone, fi ller, and other industrial uses. Essen- of the intraclasts are of biologic origin, and include possible tially all exposures of the unit are within marble quarries. The oncoids derived from algal mats that grew on the tidal-fl at. Low top of the unit is defi ned by the sub–Lay Dam Formation uncon- tide stands would have exposed these mats to desiccation. Once formity. The marble is dominantly white, but localized layers of desiccated, the mats could easily be ripped up by storms to form off-white, light gray, dark gray, and pink marble can be found. intraclasts. The intraclasts that do not have an obvious biologic Thin dark gray phyllite laminations (<1 cm thick) composing less origin may have been supplied from the supratidal zone. A cal- than 5% of the rock, are present in all exposures of the unit. The cite matrix surrounds many of the dolomitic intraclasts. It is thus unit also contains intervals a few meters to several meters thick of possible that dolomitization of these intraclasts is primary and dark gray, dolomitic marble layers that were mechanically more that they originated as dolomitic crusts in the supratidal zone. competent than the calcite marble during synmetamorphic defor- If the climate were arid, then a sabkha-type facies could gener- mation, and these beds are commonly highly boudinaged. ate dolomitic crusts. A supratidal dolomitic crust would desiccate The high calcite content of the unit results in the fact that and eventually break up to produce numerous intraclasts during synmetamorphic ductile deformation is much more strongly storm events (Tucker and Wright, 1990). The laterally extensive partitioned into the Gantts Quarry Formation than other (mostly calcareous phyllite overlying the pisoid/oöid/intraclast dolo- dolomitic) units of the Sylacauga Marble Group. Outcrop-scale stone is distinctive because it originally contained an appreciable isoclinal and sheath folds are common. Extensive deformation amount of siliciclastic mud. This unit may represent a deeper- and metamorphic recrystallization have obliterated essentially water outer ramp marlstone facies. all primary features other than bedding. However, three con- Paleontological evidence from the underlying Shelvin Rock odont species, Scolopodus gacilis, Gloptoconus quadraplica- Church Formation (Middle Cambrian) and the overlying Gantts tus, and Eucharodus parallelus, were recovered from quarries Quarry Formation (Lower Ordovician) allows a possible Late and outcrops near Carara from within an interval 60–70 m from Cambrian age for the Gooch Branch Chert, compatible with that the base of the unit (Tull et al., 1988). These are of latest Early of the Copper Ridge Dolomite. Like the Gooch Branch Chert, Ordovician age (Arenig) (North American Midcontinent Faunas the Lower Knox Group (Copper Ridge/Chepultepec Dolomite) D-E) and are representative of warm, shallow-water biofacies commonly forms ridges of white or light gray, dense chert (Tull et al., 1988). Although there are almost no primary fea- (Brockman, 1978). Although silicifi ed Cryptozoans occur in the tures that allow for speculation about the depositional environ- Copper Ridge Dolomite, primary features have not been found ment, the homogeneous, fi ne-grained nature and high purity of in the chert facies of the Gooch Branch Chert. A rarity of car- the dominantly “cream” white marble, suggest that the protolith bonate outcrops is a common attribute to both units, but where was a micrite, and the included conodonts indicate a shallow, carbonate rocks are exposed, they are dominantly dolomitic. The tropical environment. Gooch Branch Chert consists of light colored calcitic to dolo- The upper Knox Group is distinguished from units below it mitic marble and very dark, charcoal gray dolomitic marble with by the relative rarity of both chert and dolostone layers. Beds of white calcite banding and/or cement. Similar lithologies have Newala Limestone are commonly massive and consist of high- also been recognized in the Copper Ridge Dolomite in Alabama calcium, pearly white to light gray micritic limestone with some (Sternbach, 1984). The lighter calcitic/dolomitic marble in the dolomite (Gore and Whitfi eld, 1974), analogous to the “cream” Gooch Branch Chert contains oölitic/pisolitic beds near the top calcite marbles of the Gantts Quarry Formation. Within the of the unit. Oölitic lenses are also common in the Copper Ridge Newala are thick beds of fossiliferous, fi ne-grained packstone, Dolomite (Sternbach, 1984). The lower Knox Group in Alabama wackestone, and mudstone. The Gantts Quarry Formation, how- likely formed in an intertidal to supratidal environment marked ever, is essentially devoid of primary features. Importantly how- by widespread syngenetic desiccation and mudcrack formation ever, the unit has yielded the same uppermost Early Ordovician fl d029-08 1st pgs page 14

14 Tull and Barineau

(Arenigian) conodont species as those found in the Newala, indi- rapid uplift and erosion. The olistostromal facies and other inter- cating a warm, shallow-marine environment and equivalency in calated lithofacies are indicative of extremely rapid sedimenta- age (Tull et al., 1988). tion rates, suggesting that the entire sequence represents unusu- ally fast deposition. Thus, post-Ordovician conodonts near the Talladega Group top of the formation may indicate that the entire sequence is Silurian (?) to Early Devonian in age, and if so, any stratigraphic The >2.5-km-thick Silurian (?)-lowest Mississippian (?) Tal- evidence of the Ordovician Taconic orogeny is missing in this ladega Group, lies above a regional unconformity that cuts both thrust sheet. This sequence may therefore be in part equivalent in underlying groups described above (Fig. 2). No unconformities age and lithofacies to the New England fl ysch deposits that are have been recognized within this group. The relatively deep-water interpreted as precursors to the Acadian orogeny in that region Lay Dam Formation, a thick sequence of metaturbidic rocks, lies (Osberg et al., 1989). directly above the regional unconformity at the base of the Tal- Sub–Lay Dam Formation Unconformity. The base of the ladega Group, and is interpreted to have formed in an extensional Lay Dam Formation has been variously interpreted as either a setting as a clastic wedge (Tull and Telle, 1989; Tull, 1998). The fault (Prouty, 1916; Butts, 1926; Carrington, 1973; Guthrie, underlying Lower Cambrian–Lower Ordovician shallow-water 1989; Higgins and Crawford, 2008; Hatcher, 2008), an uncon- shelf sequence (described above) beneath the unconformity formity (Shaw, 1970; Tull, 1982, 1998; Tull and Telle, 1989), underwent open folding and signifi cant uplift and erosion, fol- or a faulted unconformity (Guthrie, 1989). Because of several lowed by rapid subsidence. The Lay Dam Formation is overlain excellent exposures of the contact southwest of the Coosa River by the Butting Ram Quartzite and its northeastern equivalent, most authors (Shaw, 1970; Carrington, 1973; Tull, 1985; Tull and the Cheaha Quartzite, a thick, shallow-water metasandstone and Telle, 1988; Pendexter, 1982, 1985; Guthrie, 1989) agree that the metaconglomerate. All of these units were derived from erosion Lay Dam Formation lies unconformably above the basal Jumbo of the underlying lower Paleozoic shelf clastic and carbonate Dolomite and upper Wash Creek Slate in this area. This contact rocks, as well as underlying Grenville (ca. 1.1 Ga) basement. The will be examined at Stop 6 of Day 1 so that the participants can Butting Ram–Cheaha Quartzite transitions into the Erin Slate– draw their own conclusions about its nature. Higgins and Craw- Jemison Chert at the stratigraphic top of the Talladega Group. ford (2008) and Hatcher (2008), however, argued for the pres- Lay Dam Formation. The Lay Dam Formation comprises ence of a signifi cant thrust fault with a “minimum of 10s of kilo- a >2-km-thick clastic wedge containing metaturbidite, arkosic meters” of displacement along the sub–Lay Dam contact. These conglomerate, and thick olistostromal beds derived from uplifts authors, following Guthrie (1989), referred to the basal Lay Dam to the south and southeast (Shaw, 1970; Carrington, 1973; Tull contact as the “Talladega-Cartersville fault,” whereas most other and Telle, 1989; Lim, 1998; Tull, 1998). The olistostromes authors place this fault beneath the Kahatchee Mountain Group contain sand-to-boulder-size fragments of (1) carbonate rock, (see below) to the northwest. Although Guthrie (1989) mapped (2) metachert, and (3) metasandstone and metasiltstone, all typi- this contact as a thrust east of the Coosa River, he mapped it as an cal of the underlying Sylacauga Marble and Kahatchee Moun- unconformity to the west of the river. tain Groups. The most abundant clasts, however, are granite and Tull (1998) cited fi ve lines of evidence that the basal Lay granitic gneiss that U/Pb zircon dating indicates were derived Dam contact is an unconformity which accommodates local from Grenville (ca. 1.1 Ga) basement that underlay southeastern shearing: (1) The Lay Dam is younger than underlying units Laurentia (Telle et al., 1979). No exposures of this basement ter- based upon paleontologic evidence (Tull et al., 1998). The Gantts rane are preserved in the Talladega belt today. The olistostromal Quarry Formation contains uppermost Lower Ordovician con- units probably represent a proximal submarine fan facies (Tull odonts, while the Lay Dam contains post-Ordovician conodonts. and Telle, 1989). Below the Butting Ram Quartzite, near Jemison This is supported by primary facing data from above and below (Fig. 2), the Lay Dam is ~1250 m thick. Northeastward, the unit the contact. (2) An abrupt and signifi cant change in depositional thickens to ~2400 m and is a more distal turbiditic facies (Tull setting occurs at the contact, with shallow-water carbonate rocks and Telle, 1989; Lim, 1998). The age of the Lay Dam Formation of the Sylacauga Marble Group below, and deep-water siliciclas- is constrained by the following: (A) youngest underlying rocks tic rocks of the Lay Dam Formation above. (3) The Lay Dam of the Sylacauga Marble Group contain youngest Early Ordo- includes olistrostromal and conglomeratic facies that contain vician conodonts (Tull et al., 1988); (B) the overlying Butting detrital material clearly derived from underlying units. The olis- Ram Quartzite and Jemison Chert contain an Early to Middle trostromal facies contains sand- to boulder-sized rock fragments Devonian fauna (see below); (C) metasiltstones in the upper Lay of a variety of carbonate rock types, including laminated cal- Dam Formation contain conodonts with an age range of Silu- cite marble and massive dolomite marble, some of which con- rian to Pennsylvanian (Tull et al., 1988). Thus, the upper Lay tain oncolites, pellets, and algal and/or cryptalgal coated grains Dam Formation must be Silurian and/or Devonian. Olistostromes identical to primary features observed in the underlying marble are found at both the base and top of the Lay Dam Formation units. (4) Lithologic units in the Lay Dam parallel the unit’s basal and locally make up as much as 50% of the unit (Tull and Telle, contact, but both features are discordant to underlying units. 1989). The immature lithic clast population suggests steep and (5) Local relief of 1–8 m over a lateral distance of a few 10s of fl d029-08 1st pgs page 15

Talladega slate belt, Alabama Appalachians 15 meters has been observed along the contact at several localities (2008) to be a major displacement fault, and by Guthrie (1989, (Shaw, 1970; Tull, 1985). These features are atypical of thrust p. 52) to be “one of the most prominent structures in the south- trajectories and appear to be the result of erosional relief. ern Appalachians of Alabama and Georgia.” All of the geomet- In 2011, R.D. Hatcher Jr. visited the basal Lay Dam con- rical relationships can be better and more simply explained by tact at environs near Jumbo (Fig. 2 and Stop 6, Day 1) with the the presence of a well-established regional unconformity (Tull, senior author, and agreed that, in this area, the contact is indeed 1998). Adding a fault explanation seems entirely unnecessary. an unconformity (R.D. Hatcher Jr., oral communication, 2011). It does not follow from our interpretation, however, that the The presence of the sub–Lay Dam unconformity west of the Sylacauga Marble Group–Lay Dam Formation contact is not Coosa River brings up the following important geometric con- locally a surface of concentrated shear strain. In fact, ductility straints on any fault displacement which may occur along this contrasts across this contact would be expected during the ambi- contact to the northeast: (A) As it is traced northeast of the river, ent conditions of deformation. Localized concentrations of shear a fault at this boundary must climb up section in the footwall strain have been observed by the current authors and (Hatcher, from the lower Jumbo Dolomite (position of the unconformity 2008) along the contact northeast of the Coosa River between the at Jumbo) obliquely through the Jumbo and the rest of the Syl- underlying carbonate rocks and the overlying pelitic rocks. At acauga Marble Group. Although it must ramp laterally upward in localities where the olistostromal facies is in direct contact with the footwall, units in the Lay Dam Formation are not truncated, underlying carbonate rocks, however, pebbles and cobbles of both but remain parallel to the basal Lay Dam contact, and the same carbonate and crystalline rocks in the olistostromes immediately lithofacies (olistostromes) of the Lay Dam lies directly above the above the contact show evidence of only very minor distortion basal contact, even though east of the river the contact has been (Woodall and Barineau, 2010), precluding a faulted boundary. If interpreted as a major fault (see above). In fact, the Lay Dam the contact is pinned along an unfaulted unconformity southwest maintains essentially the same thickness from the Coosa River, of the river (Stop 6, Day 1), then tens of kilometers of northwest northeastward at least into southern Cleburne County, a distance thrust displacement along this contact northeast of the Coosa of >100 km. These observations imply that the trajectory of any River, as proposed by Guthrie (1989) and Hatcher (2008), should proposed fault must remain exactly at the stratigraphic level of produce a major cross-strike structure in the Lay Dam and over- the sub–Lay Dam Formation unconformity in the hangingwall. lying units along the zone between the unconformity and where (B) In order for units stratigraphically above the Jumbo in the the contact becomes the proposed major thrust. However, such a Sylacauga Marble Group to exist, as they do northeast of the cross-strike structure is not found. Units above the Lay Dam, like river, the unconformity must have risen progressively northeast- the Butting Ram–Cheaha Quartzite, continue northeastward and ward in that group’s stratigraphy at a regional angle of >8° (Tull undefl ected by any such structure required by the proposed major and Telle, 1988). For the “Talladega-Cartersville fault” of Guth- displacement thrust (Fig. 2). rie (1989), Higgins and Crawford (2008), and Hatcher (2008) Butting Ram–Cheaha Quartzites (Early Devonian restabi- to exist however, it must coincidently also cut up section in the lization of the shelf margin). Overlying the Lay Dam Forma- Sylacauga Marble Group northeastward, but always at an angle tion and gradationally below the Jemison Chert is the Butting equal to that of the unconformity, in order to keep the Sylacauga Ram Quartzite (Figs. 6 and 7). To the northeast, the Butting Ram Marble Group and the Lay Dam Formation separated by the can be traced into the Cheaha Quartzite (Fig. 7) and both units proposed fault, because nowhere does the Lay Dam exist in the are considered stratigraphic equivalents. This metasandstone footwall of this proposed fault, and nowhere does the Sylacauga sequence represents reestablishment of a stable basin margin, a Marble Group exist in the hangingwall. (C) Northeast of the river, decrease in sediment supply, a shallowing-upward sequence, and the proposed thrust fault must everywhere place younger rocks extensive reworking of sediments in a shallow coastal environ- over older rocks. This geometry is unusual for thrusts, requir- ment. These rocks are thin to massively bedded, locally conglom- ing out-of-sequence thrusting. No explanation was given by the eratic, medium to coarse grained, and range from metasubarkose above authors as to how or why such an out-of-sequence thrust near the base, to overlying metaquartz sublitharenites and meta- might exist in this area. Because the Lay Dam is never found in arenites. The metasandstones contain minor sericite and chlorite, the thrust’s footwall and the Sylacauga Marble is never found trace amounts of detrital muscovite, tourmaline, and zircon, as in the hangingwall of the proposed fault, the other thing that is well as rare metamorphosed sandstone, chert, granite, and pelitic clear from the proposed thrust’s geometry is that it must occur rock fragments. Sand grains are subrounded to rounded, but com- everywhere at exactly the same stratigraphic position as a major monly are highly sutured. The Butting Ram is ~370 m thick near unconformity (sub–Lay Dam Formation unconformity). For all Jemison (Figs. 2 and 3), thinning to ~200 m to the east-southeast. of the above reasons, the fact that the proposed thrust would Northeastward, the equivalent Cheaha Quartzite ranges between have to place younger rocks over older rocks, and the fact that 290 m and 380 m thick (Carter, 1985) in the vicinity of Bulls the proposed fault is constrained to occur at essentially the same Gap and Cheaha Mountain, but thins signifi cantly (as thin as position as a regional unconformity, we believe that the proposed 10 m) in other areas of the belt and suggests signifi cant variation “Talladega-Cartersville fault” does not exist, in spite of the fact in original stratigraphic thickness. Carrington (1973) reported that it is considered by Higgins and Crawford (2008) and Hatcher the presence of Early Devonian fenestrate and ramose bryozoa, fl d029-08 1st pgs page 16

16 Tull and Barineau

Figure 6. Stratigraphic column of the type area of the Jemison Chert. Trian- gle pattern represents metachert. (From Tull, 2002.)

gastropods, horn corals, and several genera of brachipods from trace of the Jemison Chert, near Jemison, ~14 km to the northwest the uppermost Butting Ram, and brachipods were found near the relative the rest of the ~N 58 E-trending Talladega belt containing base of the unit by these authors. The mature quartz arenites, low- the Erin (Fig. 2). A cross section projection parallel to the axial angle planar crossbeds, and shallow-marine fauna suggest that surface of these folds demonstrates that the palinspastic position the Butting Ram/Cheaha Quartzite represents a regionally exten- of the Jemison type section was ~12 km northwest of the more sive, near shoreface to shallow, open-marine deposit, involving basinal facies of the Erin Slate (Tull, 2002). signifi cant sediment reworking above the immature lithologies Jemison Chert. The type section of the Jemison Chert, near of the Lay Dam Formation. Detrital zircons from the Butting Jemison (Figs. 2 and 6), contains the thickest (~400 m) and least Ram yield U/Pb ages of 920–1320 Ma, but Paleozoic zircons are deformed part of the unit, consisting dominantly of macrofauna- absent (Tull et al., 2007). bearing metachert, and subordinate siliceous argillite, phyllite, Jemison Chert–Erin Slate (“starved” basin sequence). and metasandstone (Fig. 6). Metachert comprises ~80% of the Deposition of the Jemison Chert above the Butting Ram signifi es Jemison in its type area, grading into siliceous argillite and phyl- a major decrease in clastic sediment supply to the shelf. Like simi- lite in the “phyllite zone” near the middle of the unit (Fig. 6). lar age chert sequences (ex. Armuchee, Huntersville, Shriver) that Sandy metachert and metasandstone occur sporadically through- rim the southeast margin of Laurentia, this metachert unit implies out the unit, most commonly within 30 m of the basal grada- a period of tectonic stability when the continental margin was tional contact with the Butting Ram Quartzite. Subangular to starved of signifi cant terrigenous detritus, as well as a time when rounded, fi ne-to medium-grained metamorphosed sand grains the shelf was subjected to high regional silica levels. Northeast (locally 50% of the rock) composed of quartz, minor chert, and of the Jemison Chert, the Erin Slate, primarily a carbonaceous trace zircon, tourmaline, and detrital mica, is enclosed in a very metapelite, was deposited gradationally above the Cheaha Quartz- fi ne-grained micaceous metachert matrix. Fine-grained, sandy ite under dominantly anaerobic conditions in deeper parts of the chert (15%–25% sand) is common within the phyllite zone, and basin. The Kelly Mountain antiform and Jemison- Columbiana fi ne-grained sandstone layers with detrital quartz (94%) and chert synform are regional fl exural slip folds that offset the outcrop (3.5%), and trace muscovite, zircon, and tourmaline, are found fl d029-08 1st pgs page 17

Talladega slate belt, Alabama Appalachians 17

A B

CD

Figure 7. Geologic maps of the Talladega belt and northwestern part of the eastern.

~60 m above the phyllite zone. The thickest metasandstone unit the lower Jemison interval to being most likely mid-Emsian (late (Posey Sandstone Member of Sutley, 1977) is near the top of the Early Devonian) or older, but no younger than Frasnian (early Jemison in the hinge of the Jemison-Columbiana synform (Fig. Late Devonian) (R. Lindemann, written communication, 1998). 2). Northeast of the type area, similar sandy quartzite is locally Other than sponge spicules, fossils are known only within the found near the top of the Jemison and correlative Erin Slate. lower 200 m of the Jemison (Fig. 6); no age constraints exist for Chert and argillite rock fragments in the sandstones were likely the upper half of the unit, although chert similar to that lower in derived from local erosion of underlying parts of the Jemison. the section occurs near the top. Detrital zircon and tourmaline within both Jemison metasand- Sponge spicules (mostly monoaxons with a few tetraxons; stone and metachert indicate a basement source for the detrital length = 0.1–0.9 mm; diameter = 0.02–0.05 mm), found in 53% component, similar to that of the underlying Lay Dam and Butt- of the chert samples, are abundant throughout much of the unit ing Ram–Cheaha Quartzites. The metasandstone lenses and the (Fig. 6), but are generally poorly preserved due to extensive coarse sand fraction of the sandy cherts were probably deposited recrystallization. Locally, the rock is a spiculite. Chalcedony- principally as bed load sediment. fi lled ovals and spherules (<0.9 mm in diameter) surrounded by The lower half of the Jemison Chert in its type area contains a wall of fi ne-grained chalcedony, are found in many chert speci- a marine invertebrate fauna (Fig. 6) dominated by brachipods mens. Some may be partially resorbed radiolaria but no internal (Butts, 1926; Carrington, 1973; Sutley, 1977; J.T. Dutro Jr. and or external ornamentation is preserved. Others may be concentri- E.L. Yochelson, written commun. to M. Higgins, 1982, 1983), cally fi lled chalcedony oncolites. but also including bryozoans, corals, pelmatozoans, sponge spic- Protolith studies of the metachert facies are inhibited ules, tentaculitids, and rare trilobites. These faunal elements are because of pervasive metamorphic recrystallization and variable typical of the Lower Devonian Oriskany Group and its equiv- strain. The local silica source apparently was abundant siliceous alents in the Appalachian foreland. The most restricted to this biogenic detritus related to subtidal accumulations of sponge interval are A. murchisoni and Tentaculites. Tentaculites restricts spicule muds and radiolarian-like spheres which accumulated fl d029-08 1st pgs page 18

18 Tull and Barineau along the shelf margin below storm wave base. Complete silici- posed by previous authors. Some rocks mapped as mylonites by fi cation of the originally shallow-water carbonate fauna indi- Higgins and Crawford (2008) actually contain weakly deformed cates considerable mobilization of silica prior to metamorphism, sponge spicules, brachiopod fragments, and detrital silt grains. probably resulting from the dissolution and recrystallization of Metasandstone and metaconglomerate grains east of the interstate primary biogenic opal during diagenesis. The presence of abun- are well sutured but do not show large distortions and none of dant and apparently locally derived chert sand grains within the these rocks have the petrographic characteristics of mylonites. In metasandstone beds of the Jemison also suggests early (diage- a detailed study of chert crystallinity in this particular area, King netic?) chertifi cation of the unit. The ultimate silica source, how- and Keller (1992) collected more than 300 samples of the Jemi- ever, was likely non-biogenic, as suggested for similar regionally son Chert from 33 separate outcrop on both sides of Interstate 65 distributed Devonian–lower Mississippian siliceous units along and the proposed north-trending “fault.” King and Keller (1992) Laurentia’s southern and eastern margin (Lowe, 1975). These note that all samples from the Jemison Chert (both east and west deposits were clearly formed when the continental margin was of Interstate 65) had a “distinct metamorphic crystal texture” and tectonically stable and cut off from signifi cant terrigenous detri- that none of the samples showed “anhedral, cryptocrystalline tus, and when the shelf was subjected to high regional silica lev- texture indicative of non-metamorphic or sedimentary chert.” els (Lowe, 1975). Paleomagnetic data indicate that this region The crystal size increase to the northeast is accompanied by a was at low southern paleolatitudes during the Devonian (Kent, progressive increase in slaty cleavage seen in scanning electron 1985; Ettensohn et al., 1988). Lowe (1975) suggested two pos- microscopy (SEM) and thin section in rocks both west and east of sible silica sources for these middle Paleozoic siliceous deposits: I-65. King and Keller (1992) also note that, where bulk strain has (1) volcanism associated with orogenesis fl anking southern Lau- resulted in coarser granoblastic textures, the Jemison Chert could rentia may have provided much of the primary silica by increas- be texturally described as a quartzite. However, they use the term ing the overall dissolved-silica level in equatorial surface cur- “metachert” for the entire unit, regardless of the degree of quartz rents; and (2) silica-rich waters may also have originated from recrystallization. Using SEM images to analyze quartz crystal- dynamic upwelling along the west coasts of middle Paleozoic linity, King and Keller (1992) concluded that bulk strain and Laurentia and Gondwana, and been channeled eastward into the metamorphic grade increased from west to east in the study area, ocean separating those continents along the Ouachita embay- consistent with interpretations of increasing metamorphic grade ment, where middle Paleozoic chert deposits are extensive, and from the southwestern to the northeastern end of the Talladega still farther east onto the Alabama continental promontory. belt, where the Barrovian chlorite zone gives way to rocks within Hatcher et al. (2007) and Higgins and Crawford (2008) have the biotite zone near the Alabama-Georgia state line (Tull and proposed that the Jemison Chert and Butting Ram Quartzite are Holm, 2005). As the metachert is traced eastward from its type not constituents of the Talladega slate belt, but terminate east- section, the mean apparent crystal diameters progressively and ward along an unmapped north-south fault beneath U.S. Inter- gradationally increase from 0.8 μm on the southwest, to 29.9 μm state 65, ~6 km east of Jemison (Fig. 2), questioning the exis- east of the Coosa River (King and Keller, 1992) (Fig. 2). The tence of post-Cambrian rocks in the Talladega belt. These authors crystal size increase is accompanied by a progressive increase in assert that the rocks previously mapped by Butts (1926), Tull et slaty cleavage, suggesting that higher deviatoric stresses toward al. (1988), Tull and Telle (1989), Tull (1998, 2002), and King and the east resulted in greater syntectonic strain-driven recrystalliza- Keller (1992) as Jemison Chert and Butting Ram Quartzite to the tion (King and Keller, 1992). The largely monomineralic rocks east and northeast of the interstate are instead an unrelated belt with larger crystal sizes and strongly foliated fabrics, and occu- of “Permian-Ordovician” mylonites which occur adjacent to and pying the same stratigraphic interval as the Jemison type section, directly along strike of the Jemison and Butting Ram (Higgins appear as slaty quartzite with no obvious detrital grains. This and Crawford, 2008), or “belong to the Neoproterozoic to early foliated quartzite, referred to as metachert by King and Keller Paleozoic rifted margin succession, and not to the mid-Paleozoic (1992), is thus presumed to have had a chert protolith, and can be sequence” (Hatcher et al., 2007, p. 616). These interpretations traced continuously for ~45 km, from the Coastal Plain, north- are odd for several reasons. First, the actual type section of the eastward into southwestern Clay County (Fig. 2). The lower part Butting Ram Quartzite as defi ned by Butts (1926) is 15 km east of the Erin Slate farther northeast contains discontinuous zones of its proposed termination by the “interstate fault,” occurring of similar fi ne-grained slaty quartzite and in east Alabama and in the region presumably composed of “Permian-Ordovician” west Georgia, Bearce (1973) and Heuler (1993) mapped simi- mylonites and/or “the Neoproterozoic to early Paleozoic rifted lar quartzites as the Chulafi nnee Schist and the Tally Mountain margin succession.” Also, a number of the following relationships Quartzite. Thus, the fi ne-grained quartzite, or metachert, extends indicate that rocks mapped as “siliceous mylonites” of the “Hil- in a similar stratigraphic position, at least discontinuously, labee fault zone” by Higgins and Crawford (2008), are in fact, throughout much of the extent of the Talladega belt. metachert and metsasandstone or metaconglomerate with stable Erin Slate. Northeast of the Jemison Chert type area, the greenschist facies metamorphic microstructures, and that the Cheaha Quartzite in Clay County (Fig. 2) is gradationally over- Jemison Chert and Butting Ram do continue to the northeast of lain by a thick sequence of thinly laminated carbonaceous ser- I-65 as constituent units of the Talladega belt for ~175 km as pro- icite phyllite and slate, interlayered with metasandstone, slaty fl d029-08 1st pgs page 19

Talladega slate belt, Alabama Appalachians 19

quartzite, and rare, very thinly laminated sandy marble, collec- signifi cantly older than the Tournaisian age typically assigned to tively referred to as the Erin Slate (Erin Shale of Butts, 1926). this fossil. Complicating the issue, in southwestern Kentucky, The stratigraphic position of the Erin, above the Cheaha Quartz- where Beck (1978) collected his samples, the Falling Run bed ite, is equivalent to that of the Jemison Chert. The thickness of the (from which Beck assumed his phosphate nodules came) has Erin is estimated to be locally as great as 950 m (Carter, 1985). been removed by erosion (Ettensohn et al. 1988), leaving open Erin metasandstone bodies range to several tens of meters thick, the question from which strata Beck’s samples originated. Inter- and are composed of poorly sorted, fi ne to coarse quartz sand estingly, to the south of Beck’s sample localities, in central Ten- (85%–95%), sericite + chlorite (5%–12%), and minor detrital nessee, where the Falling Run Bed reappears, this phosphatic plagioclase, muscovite, tourmaline, and zircon. nodule-bearing lag zone contains conodonts of both latest Devo- For over a century, controversy has centered on the age and nian and Early Mississippian age (Ettensohn et al., 1988). Thus, stratigraphic position of the Erin. It was among the fi rst units in it is not inconceivable that Periastron (found in only two other the metamorphic Appalachians to be assigned a paleontologi- localities outside of North America) could range from latest cally determined age. Smith (1903) reported a specimen (sent to Devonian to Early Mississippian in age. From the Erin Perias- him by a local Erin resident) of a lycophyte strobilli, most likely tron locality, Tull et al. (1989) reported Veryhachium, a marine of Late Carboniferous age. This age assignment was widely acritarch characteristic of Devonian and older rocks in eastern accepted (Prouty, 1923; Butts, 1926; Griffi n, 1951; Gastaldo North America but extremely rare worldwide in Carboniferous and Cook, 1982), and led early workers (Jonas, 1932; Park, rocks. Because Periastron has been found only in Tournaisian 1935) to place the Erin within a window through the metamor- strata, Gastaldo (1995) reasonably argued that at least the upper- phic sequence. Later studies showed that the Erin is a conform- most Erin is lowest Mississippian in age. However, the factors able unit at the top of the Talladega Group (Tull, 2002), but the cited above suggest the possibility that the unit may, in fact, be earlier idea has been followed recently by other workers who no younger than Middle Devonian, an age compatible with the wanted to exclude post-Cambrian rocks from the Talladega belt. Jemison Chert fauna. The minimum age of the Erin is critical to For example Hatcher et al. (2007, p. 616) stated that “the Erin establishing the time of metamorphism and deformation in the Slate probably unconformably overlies (or is faulted against)” region (see below). older rocks, and Higgins and Crawford (2008, p. 6) state that Higgins and Crawford (2008) argue that the Erin Slate and the Erin is in an “area of very low metamorphic grade nearly Jemison Chert cannot be correlated, in part, because “the Jemi- undeformed…surrounded by slightly higher grade unfossilifer- son is Lower and Middle Devonian” and “the Erin is lower Mis- ous phyllites.” Our studies have shown, however, that there is sissippian,” based on the presence of Periastron. They fail to no fault or unconformity at the base of the Erin. It grades down note, however, that the well documented fossil assemblage of the through an interval 10s of meters thick into the Cheaha Quartz- Jemison Chert is constrained to the lower 200 m of the strati- ite. The unit is strongly deformed (see Stop 8) and is the same graphic package, whereas the uppermost strata of the Jemison grade as surrounding units. Importantly, vitrinite refl ectance and do not, to date, have a well delineated age (Tull, 2002). Regard- fl uorescence studies (Tull et al., 1989) demonstrates that the less of the age of Periastron, because rocks of the Jemison Chert original strobilar fragment (reported as Lepidostrobus hobbsii of can be mapped to the northeast into rocks of the Erin Slate, they White in Adams, 1926) is much less thermally mature than the are interpreted as facies equivalents, thus making it reasonable to in situ Erin, and is exotic to the unit. assume that this stratigraphic interval ranges in age from Early Gastaldo (1995) reported a specimen from the uppermost to Middle Devonian at its base to latest Devonian or Early Mis- Erin Slate that he assigned to Periastron reticulatum, a very sissippian near its stratigraphic top. If the nearly 1000 m of Erin rare and unusual aquatic or semi-aquatic plant genus of uncer- Slate now exposed in the Talladega belt (Tull, 2002) spanned an tain taxonomic affi nity. Established by Unger (1856) from the interval of this nature (~50–60 m.y.), deposition rates would fall Russchiefer shales in Thuringia, Germany, Periastron was sub- in the 1.5–2 cm per k.y. range, well within sedimentation rates for sequently identifi ed from the New Albany Shale in Indiana and black shales forming in starved basins. Thus, the age constraints Kentucky and the Lydiennes formation in southern France (Scott placed upon the Erin-Jemison interval, do not preclude the two and Jeffrey, 1914; Read, 1936). The permineralized axes of Peri- units from representing facies equivalents. astron exhibit bilateral symmetry of lacunae across a central Regional facies relationships. As the Jemison Chert is row of vascular bundles (Beck, 1978) and researchers generally traced southeastward across regional strike from Jemison into the have agreed that Periastron represents the petiole of a large leaf, hinge of the Kelley Mountain antiform, it thins from ~400 m to possibly from a fern or fern-like seed plant (Unger, 1856; Scott ~200 m and is composed of fi ne-grained slaty quartzite, highly and Jeffrey, 1914; Beck, 1978; Gastaldo, 1995), although taxo- graphitic near the top East of the Coosa River, the distinctive fi ne- nomic affi nity has yet to be conclusively established. In the most grained slaty quartzite in the lower half of the section, grades comprehensive work to date on Periastron, Beck (1978) was the upward into locally highly graphitic, chlorite/sericite phyllite fi rst researcher to suggest, although with much caution, a pos- interlayered with minor fi ne-grained quartzite, lithologically sible taxonomic affi nity, noting that Periastron might represent similar to the Erin Slate. Farther northeast, the section thickens the petiole of a Middle Devonian plant, Psygmophyllum gilkineti, signifi cantly, and graphitic phyllite-strongly foliated quartzites of fl d029-08 1st pgs page 20

20 Tull and Barineau the Erin Slate dominate the interval above the Cheaha Quartz- Calc-alkaline metadacites and metarhyodacites are found ite. Still farther northeast, the equivalent sequence can be traced throughout the Hillabee. Locally making up as much as 25% of into western Georgia (Heuler, 1993). Thus, the interval contain- the Hillabee, many of these units can be traced for >20 km along ing the Jemison and Erin can be traced for 175 km from inliers strike and parallel internal greenstone stratigraphy (e.g., massive within the Coastal Plain, northeastward into Georgia. Through- sulfi des). Ranging from 50 to >150 m in thickness, individual out most of this distance, the unit is represented by graphitic and metadacite layers are interpreted as laterally extensive felsic ash nongraphitic phyllite, with layers of fi ne-grained slaty quartzite, falls and welded ash fl ow crystal tuffs, in some cases covering metasandstone, and rare, thinly laminated sandy marble. The >300 km2 and representing >50 km3 of eruptive material (Tull thickening of the unit northeastward from Jemison to Erin mir- and Stow, 1980; Tull et al., 1998, 2007). Metadacites commonly rors a similar thickness increase of the underlying Lay Dam contain large hornblende, plagioclase, and/or quartz crystals in a Formation (Tull and Telle, 1989), suggesting that the Talladega fi ner grained matrix of quartz, sericite, epidote and actinolite and Group basin was hinged on the southwest, with greater subsid- are interpreted as relict phenocrystic components. Major, trace, ence toward the northeast. and rare earth element analyses indicate that metavolcanic rocks The Jemison Chert lithofacies and fauna suggest deposi- of the bimodal Hillabee Greenstone formed in a suprasubduction tion under shallow-water, open-marine conditions. The northeast setting, most likely in the back-arc region of a continental mar- transition into the Erin Slate black shale basinal facies suggests a gin arc (Tull et al., 1978; Tull and Stow, 1979, 1980; Durham et slope grading into a quiet, anoxic, possibly deeper marine basin, al., 1990; Tull et al., 1998; Barineau et al., 2006; Holm-Denoma, and the possibility of a shelf-slope-basin plain transition toward 2006; Tull et al., 2007). the northeast, oblique to present structural strike. A number of geologists (Neathery, 1973; Neathery and Footwall imbrication beneath the Hollins Line roof thrust Reynolds; Tull et al., 1978; Tull, 1979; Tull and Stow, 1980) repeats the Butting Ram/Cheaha and Jemison/Erin intervals, and have argued that the Hillabee post-dated underlying units based the overlying Hillabee Greenstone in a series of thrust horses on structural and metamorphic observations, interpreting it as (Fig. 2). These thrust imbricates were derived from down-dip a mid to late Paleozoic volcanic suite in stratigraphic contact (southeastern) parts of the basin relative to the parautochthon with the underlying Talladega Group. In contrast, analyses of containing the type Jemison/Erin sections, and thus contain the zircon from a Hillabee metadacite unit (Russell, 1978; Russell most outboard exposed parts of the Devonian–Early Mississip- et al., 1984) provided 207Pb/206Pb ages ranging from 444 Ma to pian (?) basin. Within these horses, the lower part of the Jemison/ 462 Ma, indicating that the Hillabee must be in fault contact with Erin interval contains non-graphitic phyllite and fi ne-grained the structurally underlying Talladega Group. Subsequent ion quartzite, whereas graphitic metapelite, capped by fi ne-grained microprobe U/Pb analyses of HG metadacite zircons confi rmed micaceous quartzite, is confi ned mainly to the upper half. this Middle to early Late Ordovician age of crystallization for the Hillabee and, therefore, its tectonic position above rocks of Hillabee Greenstone the Paleozoic Laurentian trailing margin (McClellan and Miller, 2000; McClellan et al., 2005, Tull et al., 2007; McClellan et al., Structurally above the Talladega Group lies the Hillabee 2007). Metadacite units of the Hillabee were erupted during the Greenstone, a bimodal metavolcanic sequence. Compositionally, same time frame as Early and Middle Ordovician bimodal vol- the Hillabee consists dominantly of mafi c phyllites-greenstones canic suites in the Dahlonega Gold belt (Thomas, 2001; Bream, and subordinate quartz metadacites. Mafi c lithologies within 2003; Holm-Denoma and Das, 2010) and Ordovician (Whiter- the Hillabee range from well foliated chlorite, albite, epidote- ockian) volcanism and K-bentonites of the Appalachian foreland clinozoisite-zoisite, actinolite phyllites to mineralogically and basins (Kolata et al., 1996) and have been proposed to be part of chemically similar non-foliated massive greenstones. Igneous an Ordovician continental margin arc system along the Alabama features, including rare relict plagioclase and clinopyroxene promontory (Barineau et al., 2006; Tull et al., 2007; Barineau, grains, in addition to more common ophiitic and porphyritic tex- 2009, 2010). tures, support interpretations of the Hillabee as having an igneous protolith (Tull and Stow, 1980). Ellipsoidal masses of greenstone BOUNDING THRUST SYSTEMS recognized within mafi c phyllite are sometimes found concen- trated at similar stratigraphic levels and may represent volcanic Talladega-Cartersville Fault ejecta (Tull and Stow, 1980). Mafi c phyllites and greenstones are interpreted as low potassium tholeiites and basaltic andesites Geologists since McCalley (1897) have mapped a thrust based on major and trace element studies, and represent extensive fault along the northwest fl ank (base) of the Talladega belt, basaltic lavas and basaltic ash deposits (Tull et al., 1978; Tull and between it and rocks of the unmetamorphosed to anchimetamor- Stow, 1980; Stow, 1982). In the central portion of the Talladega phosed foreland fold and thrust belt. This is a major displace- belt, at Pyriton, Alabama, massive strata-bound sulfi de zones ment, post-metamorphic thrust (minimum horizontal component have been mapped near the tectonic base of the Hillabee (Stow of net slip >23 km) with a large stratigraphic throw of 5–7 km. and Tull, 1979; Tull and Stow, 1982). (Lower Cambrian Chilhowee Group locally above Mississippian fl d029-08 1st pgs page 21

Talladega slate belt, Alabama Appalachians 21

Floyd Shale), marked by an abrupt change in metamorphic grade. concordancy of the Hillabee Greenstone with stratigraphy of the Over much of the region, the fault zone, which generally dips less Talladega Group within both horses of the Hollins Line footwall than 10°, contains a well-developed shear band cleavage in hang- duplex and the parautochthon. As such, metavolcanics of the Hil- ing wall rocks, with a top-to-the-northwest shear sense (Lim, labee Greenstone were interpreted as Devonian or younger based 1998). In the footwall, at several localities, it cuts the Mississip- on this apparent concordant contact and lack of a metamorphic or pian Floyd Shale in Alabama and Georgia, but is most likely a fabric break between the Devonian–Lowermost Mississippian(?) Permian thrust system (Tull, 1978). It is considered to be a south- Erin Slate-Jemison Chert and the Hillabee Greenstone (Tull et al., west extension of the Great Smoky fault system at the base of 2007). Isotopic dating of metadacites within the Hillabee Green- the western Blue Ridge allochthon (Tull and Holm, 2005). For stone metavolcanic complex (Russell, 1978; Russell et al., 1984; historical reasons (Talladega fault of McCalley, 1897; Carters- McClellan and Miller, 2000; McClellan et al., 2005, Tull et al., ville fault of Crickmay, 1936), we refer to this thrust system as 2007; McClellan et al., 2007), however, has shown conclusively the Talladega-Cartersville fault, but other authors have used other that the Ordovician Hillabee must be in fault contact with the names. Thomas and Neathery (1980) referred to it as the “Tal- underlying younger Talladega Group metasediments. Because ladega front fault,” while various segments of the fault have been Laurentian shelf rocks of the Talladega belt share the same meta- referred to by McCalley (1897) as the “Kathachee Mountain morphic and deformational characteristics as the structurally fault”, by Crawford and Cressler (1982) as the “Emerson fault,” overlying, fault-emplaced Hillabee Greenstone, this fault must and by Guthrie (1994) as the “Mardisville fault.” be either pre- or syn-metamorphic in nature (Barineau and Tull, Regional, three-dimensional views of the fault are made pos- 2001; Barineau et al., 2006; Tull et al., 2007; McClellan et al., sible because the thrust system has been folded by post-faulting, 2007). The Hillabee Greenstone can be mapped along strike for large regional cross folds, producing half-windows and major more than 230 km, from outliers in the Gulf Coastal Plain south- recesses along the thrust’s trace. Because the fault post-dates sig- west of Jemison, Alabama, to south of Tallapoosa, Georgia (Heu- nifi cant deformation in both hanging and footwalls, its trajectory ler and Tull, 1988; Heuler, 1993). The tectonic base of the Hil- is not that typical of foreland thrusts. The fault trace is marked by labee is in contact with only the uppermost unit of the Talladega truncation of both hanging and footwall mesoscopic fabrics, stra- Group stratigraphy over this entire length—the upper Devonian tigraphy, and map-scale folds (Tull and Hilton, 2008). Along its to lowermost Mississippian(?) Erin Slate–Jemison Chert (Tull et trace southwestward from Georgia, the thrust cuts through under- al., 2007). This relationship holds true in both horses of the Hol- lying foreland stratigraphy and structure, excising the major fore- lins Line footwall duplex and in parautochthonous rocks of the land thrust sheet above the eastern Coosa–Pell City thrust and Hollins Line fl oor thrust, Talladega belt footwall. Additionally, cutting down into that thrust sheet’s footwall. internal stratigraphy of the Hillabee (extensive metadacites and Above the thrust, Talladega belt stratigraphy is also discor- massive sulfi de zones) is not only internally concordant, but is dant to the thrust surface. Just north of the Coastal Plain uncon- also parallel to internal stratigraphy of the Erin-Jemison in both formity, the thrust is at the lowest stratigraphic level, exposing the parautochthon and the footwall duplex along the entire length >4.7 km of the Lower Cambrian Kahatchee Mountain Group. of the Talladega belt. Finally, the fault separating the Hillabee To the northeast of Sylacauga (Fig. 2), it cuts up section, such from the underlying Erin-Jemison remains essentially parallel that the stratigraphic level of the thrust is in the Cambrian–Lower to stratigraphy of the Cheaha Quartzite–Butting Ram Sandstone Ordovician Sylacauga Marble Group. Still farther northeast, the beneath the Erin-Jemison in both horses of the footwall duplex thrust cuts farther up section into the Lay Dam Formation before and the parautochthon (Tull et al., 2007). This remarkable con- cutting down section and decapitating a map-scale isoclinal anti- cordancy suggests that the fault along which the Hillabee was cline near the Alabama-Georgia border. Farther northeast toward emplaced paralleled stratigraphy of both the hanging and foot- Cartersville, Georgia, the thrust stays near the stratigraphic wall, resulting in a fl at-on-fl at geometry of considerable length level of the sub–Lay Dam unconformity, locally retaining the and areal extent (Barineau and Tull, 2001; Tull et al., 2007). Kahatchee Mountain Group in the hanging wall. Some segments Radiometric ages of Hillabee metadacite crystallization of the northwest fl ank of the Talladega allochthon, such as north- and Talladega belt metamorphism, the geometric relationships east of Sylacauga (Whiting, 2009) and near the Alabama-Georgia between the Hillabee and underlying Talladega Group, and geo- border (Bearce, 1985, 1991), have been imbricated into an imbri- chemical interpretations of the tectonic origin of the Hillabee cate fan, repeating the structurally lower part of the Talladega suggest the following characteristics for the Hillabee thrust sepa- stratigraphy (Fig. 2). Parts of these imbricate sheets have been rating the Hillabee Greenstone and underlying Talladega Group isolated as klippen (e.g., Sleeping Giants, Bearce, 1977). shelf metasediments: (1) Because the Talladega belt can be palinspastically Hillabee Thrust Fault restored to at least the present location of the Pine Mountain belt, rocks of the Talladega Group must have formed at or beyond Geologic mapping within the Talladega belt by a number of the Paleozoic Laurentian shelf edge (Ferrill and Thomas, 1988; workers (Neathery, 1973; Neathery and Reynolds, 1973; Tull et Thomas, 2004). Because there are no plutonic or effusive volca- al., 1978; Tull, 1979; Tull and Stow, 1980) indicates remarkable nic rocks of coeval age in either the Talladega belt or foreland fold fl d029-08 1st pgs page 22

22 Tull and Barineau

and thrust belt to the northwest, and because rocks of the Hilla- labee must have remained, essentially, tectonically undisturbed bee metavolcanic suite are fault emplaced, they must be exotic to following eruption of the mafi c-felsic volcanic suite in a conti- the Laurentian shelf at the palinspastic location of the Talladega nental margin back-arc and their emplacement atop rocks of the Group. Additionally rocks of the Silurian(?)–Lower Devonian Laurentian shelf (from ca. 470 Ma to a period between 375 and Lay Dam Formation within the Talladega Group, which formed 320 Ma, i.e., 95–150 million years). unconformably atop strata of the underlying Sylacauga Marble and Kahatchee Mountain Groups, cannibalized both Cambrian- Hollins Line Fault System Ordovician carbonate and clastic rocks of the underlying strata, as well as Grenville basement, but show no evidence of entrain- The Hollins Line fault represents the fundamental bound- ing debris from an Ordovician volcanic terrane. Thus, the Hil- ary between rocks of the Talladega belt (footwall) and Ashland- labee Greenstone (Hillabee terrane) cannot be native to the Tal- Wedowee-Emuckfaw belt (hanging wall) of Alabama-Georgia. ladega belt Laurentian shelf and must have formed outboard of As such, the Hollins Line is the eastern Blue Ridge–western Blue the Laurentian shelf edge and continental hinge zone (Barineau Ridge boundary in this segment of the Appalachian orogenic and Tull, 2006; Tull et al., 2007; Barineau, 2009). belt. The fault-bounded western Blue Ridge terrane is interpreted (2) Because the youngest metasedimentary rocks of the Tal- as the most internal segment of the Appalachians that has defi ni- ladega Group (Erin-Jemison) are at least uppermost Devonian tive links to ancient North America and collectively includes rift, and possibly as young as lowermost Mississippian, emplacement drift, and cover sequences of the trailing Laurentian margin fol- of the Hillabee and active movement along the Hillabee thrust lowing Neoproterozoic breakup of Rodinia. Rocks of the central can be no older than 375–359 Ma (Butts, 1926; Gastaldo, 1995; and eastern Blue Ridge have been historically viewed as suspect Tull, 2002; Tull et al., 2007). or exotic terranes, and were generally subjected to higher grades (3) Because of the extensive fl at-on-fl at geometry of the Hil- of metamorphism and deformation, and are more internal to the labee thrust and the remarkable concordance between strata in Appalachian orogenic belt. In recent years, detrital zircon data the Talladega Group and Hillabee Greenstone, the Hillabee thrust from central and eastern Blue Ridge rocks (Bream et al., 2004; must be a thin-skinned thrust that transported rocks of the Hillabee Barineau et al., 2012) in Alabama, Georgia, North Carolina, and back-arc from their palinspastic location outboard of the Lauren- Tennessee have suggested a Laurentian affi nity for many of these tian shelf onto cover sequences of the Laurentian shelf (Talladega fault bounded terranes, indicating that the central/eastern Blue Group) without signifi cantly deforming the hanging or footwall Ridge should probably be viewed as a composite terrane with stratigraphy (Tull et al., 2007). Three scenarios have the potential varying tectonic origins and histories. to explain this lack of fault-related (Hillabee thrust) deformation. The eastern Blue Ridge–central/western Blue Ridge bound- First, this might suggest that transport of the Hillabee terrane did ary consists of different generations of faults with unclear rela- not involve translation over signifi cant thrust ramps as the fault tionships (Fig. 1). To the northeast, in North Carolina and Geor- cut up section from the level of the Hillabee back-arc to the level gia, the Hayesville fault separates rocks of the western Blue Ridge of the Laurentian shelf margin (Talladega Group). Alternatively, and rocks of the central Blue Ridge (Hatcher, 1978; Settles, 2002; if the Hillabee thrust did involve translation of the Hillabee ter- Hatcher et al., 2005, 2007). Relationships between the Hayesville rane over signifi cant thrust ramps, then evidence for deformation fault to the northeast and Allatoona fault to the southwest at the of hanging wall rocks (Hillabee Greenstone) has been removed structural base of the Dahlonega Gold belt and southern terminus by post-metamorphic Hollins Line thrusting. Finally, it is pos- of the Hayesville–Soque River thrust sheet in northern Georgia sible that Hillabee thrust-related deformation is evident, but has are complex (Settles, 2002). Unlike the complexly deformed not yet been recognized in the Talladega belt Hayesville fault, the relatively straight trace of the Allatoona (4) Because the Talladega belt was metamorphosed between fault suggests late stage, post-metamorphic displacement along 370 and 366 Ma (approximate metamorphic age of the adjacent its length (Tull and Holm, 2005; Holm-Denoma, 2006; Tull et eastern Blue Ridge allochthon) and 334–320 Ma (40Ar/39Ar age al., 2007), although some workers have suggested pre- to syn- for Talladega belt white mica—see Tull et al., 2007 for discus- metamorphic movement along the Allatoona fault followed by sion), the Hillabee thrust must have ceased to be active prior to late Paleozoic reactivation (Settles, 2002; Eckert and Hatcher, the youngest possible metamorphic age. This, coupled with point 2003). To the southwest, the Allatoona fault truncates the post- #2 above, indicates that the Hillabee was emplaced between 375 metamorphic Hollins Line fault system in Alabama immedi- and 320 Ma in the most liberal interpretation (Barineau and Tull, ately west of the Alabama-Georgia state line, evidenced by the 2001; Tull et al., 2007; McClellan et al., 2007). post-metamorphic cross-folds affecting the Hollins Line but not (5) Because the Hillabee and metasediments of the Talla- affecting the Allatoona fault Georgia. dega belt share a common metamorphic and deformational his- Marking a signifi cant topographic, structural, stratigraphic, tory, with no evidence for earlier thermal or deformational events and metamorphic discontinuity in eastern Alabama, the Hollins in either body of rock, and because isotopic ages of Hillabee Line fault system has been described and studied by a number of metadacites indicate crystallization of the Hillabee during the workers (Prouty, 1923; Adams, 1926; Neathery and Reynolds, lower Middle Ordovician (ca. 468–472 Ma), rocks of the Hil- 1973; Tull, 1975, 1977, 1978, 1982; Mies, 1991, 1992; Tull et al., fl d029-08 1st pgs page 23

Talladega slate belt, Alabama Appalachians 23

2007; Barineau, 2009). To the northwest of the Hollins Line fault tion annually) typically limits exposure of Hillabee Greenstone system, the lower greenschist facies Talladega belt footwall rep- and Poe Bridge Mountain/Higgins Ferry amphibolites to select resents the leading metamorphic allochthon in this portion of the roadside exposures and some stream cuts, the Hollins Line is Appalachian orogen. Southeast of the Hollins Line, the middle not generally visible as a distinct feature in outcrop, but can to upper amphibolite facies Ashland-Wedowee-Emuckfaw belt be commonly delineated to within an area of a few meters to makes up rocks of the hanging wall. Stratigraphy of the upper- few hundred meters dependent on surrounding outcrop. Mica most Talladega Group and Hillabee Greenstone in the Talladega schists of the hanging wall Ashland-Wedowee-Emuckfaw belt belt footwall, as well as the penetrative metamorphic fabric, is sometimes exhibit “button” textures (S-C mylonites) associated truncated by the Hollins Line, a feature similarly observed in the with rare outcrops in which the Hollins Line can be observed, stratigraphic and structural cutoffs of the hanging wall Ashland- but as with the footwall Talladega belt rocks, weathering com- Wedowee-Emuckfaw belt. monly obscures fault-related shear fabrics. The Hollins Line consists of a roof thrust, fl oor thrust, and The Hollins Line fl oor and splay thrusts imbricate rock units connecting splay thrusts. Because splay thrusts from the main in the Talladega belt footwall and delineate a number of parau- roof thrust imbricate rocks of the footwall Talladega belt (Moore tochthonous fault bounded “horses” (Boyer and Elliott, 1982). et al., 1983; Tull, 1994; Tull et al., 2007), the Hollins Line can be Horses of the fault duplex are typically stacked in an en-echelon classifi ed as a footwall duplex thrust system after the terminology right sense (Fig. 6) and vary in length from 2 to 100 km (Tull of Boyer and Elliott (1982). et al., 2007). Unlike the roof thrust, the Hollins Line fl oor and The ~200 km trace of the Hollins Line roof thrust marks splay thrusts are not associated with a metamorphic discontinu- a signifi cant topographic, structural, stratigraphic, and meta- ity, although Talladega belt stratigraphy and structures are com- morphic break between the lower greenschist facies, amalgam- monly truncated by these faults. Footwall splays commonly sole ated Hillabee Greenstone–Laurentian shelf drift/cover strata of in and are parallel to stratigraphy of the Erin-Jemison and Hil- the Talladega belt and the middle to upper amphibolite facies labee strata, although rocks of the Cheaha-Butting Ram locally Laurentian attenuated margin rift-drift(?) and Ordovician mark the structural base of duplex horses. Thus, while the Hil- extensional basin strata of the Ashland-Wedowee-Emuckfaw labee Greenstone exerted the dominant mechanical control on belt (Tull, 1978; Barineau et al., 2012). Stratigraphy of both the position of the Hollins Line roof thrust, splay thrusts most the Talladega and Ashland-Wedowee-Emuckfaw belts, as commonly cut structurally through the Hillabee Greenstone well as stratigraphically controlled topography in the vicin- stratigraphy and sole in the metapelites of the Erin-Jemison ity of the Hollins Line, is commonly truncated across the roof (>56% of the trace of the fl oor thrust). Less commonly, splay thrust. Whereas rocks of the hanging wall Ashland-Wedowee- thrusts cut completely through the Hillabee and Erin-Jemison Emuckfaw-Emuckfaw belt exhibit little mechanical control strata and sole in quartzites of the underlying Cheaha–Butting on the stratigraphic level of the Hollins Line roof thrust, the Ram (~18% of the trace of the fl oor thrust) which are generally mechanically weak Hillabee Greenstone exhibited signifi cant more mechanically competent than the micaceous lithologies of mechanical control over the stratigraphic level of the roof thrust the Erin-Jemison. in the Talladega belt footwall. As such, >82% of the trace of the Although evidence for a thrusting along the Hollins line Hollins Line roof thrust abuts rocks of the Hillabee Greenstone system is unequivocal, lack of cohesive exposures in proximity in the footwall, with rocks of the Erin-Jemison making up the to the Hollins Line constituent faults limits outcrop availability remaining ~18% of the structural top of the Talladega belt. In for kinematic analysis and, additionally, kinematic indicators general, the Hollins Line roof thrust dips, on average, 15–20° do not provide a consistent direction of displacement. However, and juxtaposes mica schists, quartzites, and amphibolites of the fault decapitation of dextral, map scale folds (half wavelength Ashland-Wedowee-Emuckfaw belt in the hanging wall against >1.5 km) in the footwall duplex and fl oor thrust footwall (par- chlorite phyllites (greenstones) of the Hillabee Greenstone autochthon) during emplacement of the eastern Blue Ridge (Tull, 1995). Because of the differences in relative resistivity allochthon along the Hollins Line, coupled with en-echelon between the easily weathered mafi c rocks (greenstones and right stacking of horses within the Hollins Line footwall duplex mafi c phyllites) of the Talladega belt and more resistant mica suggest dextral transpressional movement along the fault sys- schists and quartzites of the Ashland-Wedowee-Emuckfaw tem (Tull, 1994, 1995a, 1995b; Tull et al., 2007). Detailed study belt, the fault is commonly marked by a distinct topographic of a single outcrop within ~40 m of the Hollins Line roof thrust escarpment. However, where amphibolites of the Poe Bridge (Lay Dam, 7.5′ quadrangle), however, did provide a single Mountain–Higgins Ferry Group are juxtaposed against rocks unequivocal S-C fabric within rocks of the footwall Talladega of the Hillabee Greenstone in the footwall, the Hollins Line Group (Erin-Jemison) with a calculated top to the west along roof thrust is not generally marked by a change in topography a bearing of 25° N90E, consistent with interpretations of the and is typically diffi cult to locate barring excellent exposure, Hollins Line as accommodating dextral transpressional motion. as the highly weathered greenstone/mafi c phyllite is usually Additionally, asymmetrical extensional shear bands in this same indistinguishable from highly weathered amphibolite. Because outcrop, which typically develop at angles of 15° to 25° to the intense weathering in the study area (>59 inches of precipita- plane of bulk fl ow within a shear zone (Hanmer and Passchier, fl d029-08 1st pgs page 24

24 Tull and Barineau

1991) suggest top to the west-northwest displacement along the (Microtel Inn and Suites) in Bremen, Georgia, prior to 11:00 Hollins Line. p.m., local time (EST).

Tectonic Signifi cance Day 2. (Figure 8)

Geology of the Talladega belt records events from earliest All participants should be ready to depart from the hotel no Cambrian to Carboniferous—or younger—at the southernmost later than 7:30 a.m., local time (EST). A complimentary break- end of the Appalachian orogeny along the Alabama promon- fast is available at the hotel. Alternatively, a number of restau- tory. First, metasedimentary rocks of the Kahatchee Mountain rants (e.g., McDonalds, Waffl e House, Cracker Barrel) are within and Sylacauga Marble Groups suggest that the Talladega belt walking distance of the hotel. must have been part of the drifting Laurentian margin which • From the hotel parking lot, turn right (east) on Price formed following late Neoproterozoic breakout of Laurentian Creek Road. from the Rodinian supercontinent. Slight warping of these units • After ~0.1 miles, at the intersection of Price Creek Road prior to deposition of the Lay Dam Formation suggests that and U.S. Hwy 27, turn right (south) toward Interstate 20. pre-Silurian–Early Devonian deformation of these units must • After ~0.1 miles, make a right turn (west) on the I-20 West have been mild. Coupled with Mississippian white mica cool- on-ramp toward Birmingham, Alabama. ing ages for Talladega belt rocks, this suggests that any effects • After ~40 miles on I-20 West, take exit 185 in Oxford/ of the Ordovician Taconic orogeny must have been mild—at Anniston, Alabama (AL Hwy 21 South). At the end of best—and that any Taconic allochthons must have remained far the off-ramp, turn left on AL Hwy 21S (Jacksonville State outboard of the Talladega belt Laurentian shelf margin. Talla- University Highway) toward Winterboro, Alabama. dega belt rocks do, however, suggest the presence of an Early- • After ~30 miles on AL Hwy 21S, in Winterboro, Alabama, Middle Ordovician back-arc terrane (Hillabee Greenstone) turn right on AL Hwy 76 West (DeSoto Caverns Parkway) proximal and outboard of the Talladega belt which must have toward Childersburg, Alabama. remained outboard of the Alabama promontory until the lat- • After 1 mile, turn left on Risers Mill Road (County est Devonican-earliest Mississippian. The inferred palinspastic Road 139). position of this back-arc terrane, coupled with metamorphic • Stop 1 is a large outcrop on the right side (north) of Risers ages and lack of signifi cant deformation in pre-Taconic rocks Mill Road, ~0.75 miles from its intersection with AL Hwy of the Laurentian Talladega belt shelf indicates that the Lau- 76. We should arrive at this stop between 8:00 a.m. and rentian margin along the Alabama promontory could not have 8:30 a.m., local time (Central Standard Time). been subducted beneath an exotic or peri-Laurentian Taconic arc, as proposed for the northern and central Appalachians. Stop 1 (~1 hour; Figure 9): Uppermost Wash Creek Slate We propose, in fact, that the geologic history of the Talladega (Chilhowee-Equivalent) and Lowermost Jumbo (Shady) belt and adjacent eastern Blue Ridge composite terrane sug- Dolomite (Lower Cambrian) gests the presence of an Early-Middle Ordovician continental This stop (Fig. 9) in the Winterboro area is in the upper- margin back-arc above westward subducting Iapetus oceanic most Wash Creek Slate of the Kahatchee Mountain Group (Chil- lithosphere (Tull et al., 2007; Holm-Denoma and Das, 2010; howee Group equivalent) immediately below the Jumbo Dolo- Barineau et al., 2012). mite (Shady Dolomite). This area contains part of a preserved Rocks of the Talladega Group (Lay Dam, Butting Ram- imbricate fan exposing a series of imbricate slices at the base of Cheaha Quartzite, Jemison-Erin) suggest formation of a late the Talladega belt allochthon. The large Sleeping Giants klippe Silurian-earliest Devonian successor basin, most likely associ- (Bearce, 1985. 1991) (Fig. 2) to the north is an isolated part of ated with extensional tectonics, in the southernmost Appala- this imbricate fan. These thrust slices are at the same metamor- chians. To date, Silurian–Early Devonian sedimentary basins, phic grade as the overlying Talladega belt proper, and repeat the metamorphism, and igneous activity has been largely unrecog- uppermost Wash Creek Slate and Jumbo Dolomite. The Jumbo nized in the southern Appalachians west of the Cat Square ter- (Shady equivalent) Dolomite at this locality contains lens-shaped rane (Hatcher et al., 2007). bodies of talc (Blount and Vassiliou, 1980) that was mined in open pits (now a pond) immediately east of this stop from 1953 ROAD LOG STOPS to 1976, and from 1988 to 1992. These are the only known large deposits of talc in Alabama. The talc bodies are oriented along Day 1. Charlotte, North Carolina to Bremen, Georgia fractures in the dolomite, highly oblique (N 65°W–43° NE) to bedding in the bedrock. Textural and fi eld evidence and the We will leave from the southwestern side of the Charlotte character and distribution of insoluble residues in the dolomite Convention Center no later than 5:00 p.m., local time (East- suggest that hydrothermal solutions and metasomatic processes ern Standard Time) and will make a dinner stop (~7:00 p.m.) replaced the dolomite with Talc and illite with chlorite along frac- near Greenville, South Carolina. We should arrive at our hotel tures in the dolomite (Blount and Vassiliou, 1980). fl d029-08 1st pgs page 25

Talladega slate belt, Alabama Appalachians 25 ed from Tull et al., 2010.) Tull ed from Figure 8. Geologic map showing the locations for Stops 1–6, Day 1. (Modifi Figure 8. Geologic map showing fl d029-08 1st pgs page 26

26 Tull and Barineau

On the northwest side of the road are exposures of typical ilarities (distinctive, thinly interbedded [1–3 mm to 2 cm thick] lithofacies found in the Wash Creek Slate, which is dominated by schistose, gray to tan, fi ne-grained feldspathic metasandstone, thin bedded, locally highly carbonaceous dark phyllite (metasilt- and dark gray to black, graphitic metasiltstone) with exposures stone), often interbedded with thin beds of very fi ne-grained sand- at this stop. Continuous sandstone beds <30 m thick (<10% of stone. Tull et al. (2010) correlate the Kahatchee Mountain Group the unit) somewhat lower in the section, hold up the ridges to our with the Nantahala and Brasstown Formations in the Murphy belt immediate west (Riser Mountain) and east. These are commonly of the Blue Ridge to the northeast in Georgia and North Carolina, massive, coarse-grained quartz arenites, interlayered locally and those familiar with these units will note strong lithologic sim- with granule conglomerates. They are commonly cross-bedded

A

Stop 1

B

Figure 9. (A, B) Geologic (from Whit- ing, 2009) and topographic maps of the region of Stop 1. fl d029-08 1st pgs page 27

Talladega slate belt, Alabama Appalachians 27 and locally contain channels. The upper, locally highly carbo- to erosion than the surrounding carbonates, the lower Shelvin naceous part of this unit, grades through an interlayered zone Rock Church Formation commonly forms low ridges throughout ~11 m thick of thinly bedded black meta-siltstone and dark silty its extent (Fig. 10). dolostone up into the Jumbo Dolomite, the basal unit of the Syl- Turn around on CR-34/Old Fayetteville Hwy (south) and acauga Marble Group (Tull, 1985). This contact crosses the road travel ~1 mile to CR-2/Sylacauga Fayetteville Hwy. Turn right obliquely and if one continues southwest along the road, deep (west) on CR-2/Sylacauga Fayetteville Hwy toward Fayette- maroon saprolite of the Jumbo Dolomite will be encountered. On ville, Alabama. the southeast side of the road across the fence are large blocks of • After ~4.6 miles, turn left (south) on CR-9/East Marble Jumbo Dolomite which were cleared from the old Talc mines in Valley Road. the valley to the east. • After 0.3 miles, make a slight left into Alabama Marble • From Stop 1, continue south on CR-139/Risers Mill/ Company’s quarry. Continue along the Alabama Marble Tallasahatchee Road. Co. driveway to the parking lot between the active quarry • After ~8 miles, turn left on Odena Road South/CR-24. and processing buildings (~0.4 miles). Hard hats are not • After 0.1 miles, turn right (south) on AL Hwy 21S/Talladega required for this stop. We should arrive at this stop at Hwy toward Sylacauga, Alabama. ~11:00 a.m. CST. • After ~3.1 miles, in downtown Sylacauga, Alabama, turn right (west) on Ft. Williams St/CR-511. Stop 3 (Figure 11): Alabama Marble Company Quarry in • After ~1.5 miles, Ft. Williams St. crosses U.S. Hwy 231/280 Gantts Quarry Formation (Uppermost Lower Ordovician) and becomes CR-2/Sylacauga Fayetteville Hwy. Continue This stop is in an active dimension stone marble quarry of west on Sylacauga Fayetteville Hwy/CR-2 toward Fay- the Alabama Marble Co. and can only be visited by permission etteville, Alabama. of the owners (see below). The quarry (as are most quarries in • After ~2.3 miles, turn right (north) on CR-34/Old Fayette- the Sylacauga area) is opened into the uppermost Lower Ordovi- ville Road. cian Gantts Quarry Formation. Early Ordovician conodonts are • Stop 2 is on the right side (north) of CR-34/Old Fay- reported from this unit northeast of Sylacauga (Tull et al., 1988), etteville Road ~1 mile from its intersection with CR-2/ and they are the same warm, shallow water species found in the Sylacauga Fayetteville Hwy. We should arrive at this stop Lower Ordovician Newalla Limestone in the adjacent foreland to at ~10:00 a.m. CST. the northwest. This formation has been heavily quarried because of the purity (high calcite content) of the marbles it contains. Stop 2: Exposures of the Lower Shelvin Rock Church Essentially all exposures of the unit are within marble quarries. Formation (Conasauga Formation) (Middle Cambrian) The marble is applied to a wide variety of uses, such as decora- Exposed in the road cut (Fig. 10) are typical lithologies of tive and dimension stone (this quarry), agricultural applications, the Lower Shelvin Rock Church Formation, here located along and fi ller in carpet and plastics, among others. Marble in this unit the crest of a map-scale anticline (Oak Grove Church anticline of is dominantly pure calcite with thin layers of pelitic rock (mus- Johnson, 1999). These exposures are part of a large lens-shaped covite and chlorite-rich). Dolomitic marble occurs in layers up to body (in map-view), consisting of a series of variably thick mar- ~1 m thick. Because of their high ductility at the ambient condi- ble layers interbedded with gray sericite phyllite, which is inter- tions of peak metamorphism (~350–400 °C) the calcite marbles preted to be the result of an intrashelf basin. The unit reaches a experienced the highest strain of any units in the Talladega belt, maximum thickness of ~700 m, but pinches out along strike in due to strain partitioning. For this reason, mesoscopic isoclinal both directions, and thus does not extend the entire length of the folds and some sheath folds can commonly be observed in quarry formation. In this unit, typical marble layers are a few centime- exposures, as can be seen here and in random quarry blocks. ters to one meter thick and range from white, pink, to dark gray The creek just outside the quarry entrance gate exposes dolo- in color, and are medium to coarsely crystalline and commonly mite marble within the Gooch Branch Chert that contains abun- dolomitic. They often contain thin beds and laminations (a few dant oölites/pisolites forming a packstone. Because of their dolo- mm thick). Some marble layers contain minor (<1%) quartz sand/ mitic composition, these rocks have experienced only mild strain silt. Interbedded phyllite beds are typically much thinner than the as contrasted with the adjacent calcite marbles in the quarry. carbonate beds, <1 mm thick in some instances, but most com- We would like to thank Stephen Musolino Sr. (owner) and monly up to a few centimeters, and rarely 0.5 m thick. On aver- Tony Musolino (quarry manager) for allowing us access to this age, phyllites constitute 20% to 30% of the lower Shelvin Rock site. Alabama Marble Co. has graciously hosted numerous geol- Church Formation. Here they may be slightly more than that. ogy fi eld trips from Florida State University, Valdosta State Uni- Some of the non-marble layers are meta-siltstone, and locally, versity, and Columbus State University over the past decade. thin, fi ne-grained, feldspathic meta-sandstone occurs within the They are willing to schedule group tours of the facilities and can interval. Pelitic layers exhibit a well-developed, steeply dipping be contacted at (256)245-9868 (Tony Musolino). crenulation cleavage, with subhorizontal axes parallel to the Oak Upon completion of this stop (~12:00 p.m. CST) we will Grove Church anticline. Because the phyllites are more resistant return to Sylacauga, Alabama, for lunch. fl d029-08 1st pgs page 28

28 Tull and Barineau

From the Alabama Marble Co. quarry parking lot, return to CR-9/East Marble Valley Road and turn right (east) toward Syl- acauga, Alabama. Continue ~8 miles (across U.S. Hwy 231/280) into downtown Sylacauga on Ft. Williams St. near its intersection with Old Birmingham Hwy. A number of restaurants (e.g., Arby’s, McDonalds, Sonic, Peking Garden, Pizza Hut) are within walking distance of one another. We will spend ~1 hour in Sylacauga and should depart by 1:30 p.m. CST. From restaurant locations in downtown Sylcauga, Ala- bama, drive west on Ft. Williams St. toward U.S. Hwy 231/280. Cross over U.S. Hwy 231/280 (where Ft. Williams St. becomes CR-2/Sylacauga Fayetteville Hwy) and continue west on CR-2/ Sylacauga Fayetteville Hwy toward Fayetteville, Alabama. After ~8.1 miles, in downtown Fayetteville, Alabama, turn left (south) on Marble Valley Road. Stop 4 will be on the right side of Marble Valley Road near the Coosa-Talladega county line, ~3 miles south of its intersec- tion with CR-2/Sylacauga Fayetteville Hwy. We should arrive at this location no later than 2:00 p.m. CST.

Stop 4 (15 minutes; Figure 12): Lower Cambrian Fayetteville Phylite (Rome Formation) The Fayetteville Phyllite is a fi ne-grained clastic unit that forms low ridges rising 15–45 m above the valley fl oor. The unit is dominated by a fi nely laminated maroon metapelite (as seen here in this small driveway exposure), but also contains calcareous Figure 10. Geologic map of the region of Stop 2. tan and gray phyllite, and distinctive very fi ne- to fi ne-grained, laminated, locally crossbedded meta-subarkose to arkosic meta- sandstone up to 20 m thick. Crossbeds yield bimodal paleocur- rent directions of northwest to southeast (Whiting, 2009), and asymmetrical ripples yield a paleo-current direction of S 20° W (Johnson, 1999). Because of its position above the fossiliferous Lower Cambrian Jumbo Dolomite (Shady equivalent) and below the fossiliferous Middle Cambrian Shelvin Rock Church Forma- tion, and its distinctive lithofacies, the Fayetteville Phyllite is cor- related with the Lower Cambrian Rome Formation. • From the Coosa-Talladega county line on Marble Valley Road, drive south toward Unity, Alabama. Marble Valley Road will become Coosa CR-5. • After ~4.7 miles, turn left (east) on CR-56. • After ~6.8 miles, turn right (south) on CR-55/Lay Dam Road toward Lay Dam. • Stop 5 is a road cut on CR-55/Lay Dam Road, ~12.5 miles west of its intersection with CR-56. This extensive out- crop is immediately west of the CR-55 bridge over the Coosa River (just below Lay Dam, which is visible just upstream of the CR-55 bridge). We should arrive at Stop 5 at ~2:45 p.m.

Stop 5 (45 minutes; Figure 13A): Meta-Diamictite Facies of the Lay Dam Formation The Silurian (?)–Lower Devonian Lay Dam Formation is the Figure 11. Geologic map of the region of Stop 3. thickest (locally > 2 km thick) unit in the Talladega Group and fl d029-08 1st pgs page 29

Talladega slate belt, Alabama Appalachians 29

Figure 12. Geologic map of the region of Stop 4.

marks a time interval of a major tectonic event in which the outer • After ~2.5 miles, turn right (east) on CR-8 (dirt road). Laurentian Cambrian-Ordovician shelf sequence was uplifted and • Stop 6 is on the right side (south) of CR-8, ~1 mile from its eroded and the submerged and buried by a thick ensialic succes- intersection with CR-61 near Jumbo, Alabama. We should sor basin. The most spectacular and distinctive lithofacies in the arrive at Stop 6 at ~4:00 p.m. CST. Lay Dam Formation consists of unsorted, unbedded, ungraded boulder-bearing diamictites (olistostromes) up to several 100 m Stop 6 (~1 hour): Abandoned Quarry West of Jumbo, thick. In the section here along the Coosa River these units make Alabama; Sub-Lay Dam Unconformity (Late Silurian– up >50% of the Lay Dam section. These rocks are interpreted as Earliest Devonian) resedimented deposits formed in relatively deep water by grav- At this stop, we will examine the contact between diamic- ity-fl ow mechanisms, such as debris fl ow and turbidity currents tites at the base of the Lay Dam Formation and carbonates of in a submarine fan-like environment (Tull and Telle, 1989). This the Sylacauga Marble Group, which was alternatively inter- site represents one of the most spectacular olistostromal deposits. preted as an unconformity (Shaw, 1970; Tull, 1982, 1998; It contains sand to boulder- sized (up to 2 m in diameter) clasts Tull and Telle, 1989), fault, or faulted unconformity (Prouty, of metastable lithologies (e.g., granite, granitic gneiss, calcite and 1916; Butts, 1926; Carrington, 1973; Guthrie, 1989; Higgins dolomite marble) suspended in a fi ne-grained, muddy matrix. and Crawford, 2010; Hatcher, 2008). We will examine evidence The diamictite facies is interlayered with other deep-water turbi- here that supports the presence of an unconformity between the dite facies, including: rhythmically laminated and non- laminated two stratigraphic units. phyllite (distal turbidites), and feldspathic meta-sandstone, On the south side of CR-8, a prominent ridge north of Yel- conglomerate, and metagreywacke (fan channel deposits). The low Leaf Creek contains relatively impure marbles of the Syl- diamictite at this stop has been penetratively deformed and the acauga Marble Group—Jumbo Dolomite—structurally below matrix contains a pervasive slaty cleavage. Clasts are variably coarse meta-clastic units of the Lay Dam Formation. Large deformed as a function of their rheology under the conditions blocks of marble can be found along the lower slopes of the north of peak greenschist facies metamorphism, with granitoid clasts side of the ridge and are remnants of a former quarrying opera- the least deformed and calcite marble clasts the most strongly tion. In place, carbonate strata can be found half to three-quarters deformed. A more in depth description and discussion of this stop of the way up the north slope face. Near the top of the ridge, is presented in Tull and Telle (1986). exposures of coarse meta-clastic units consist of sand to boulder • From Stop 5 on CR-55 west of the Coosa River at Lay sized gneiss, marble, and quartzofeldspathic lithic fragments in a Dam, continue west on CR-55. fi ne grained matrix of chlorite-actinolite and fi ne grained quartz • After ~2.9 miles on CR-55, turn left to stay on CR-55. and feldspar grains. These units closely resemble the meta- • After ~1.8 miles, turn right (north) on CR-61 (dirt road). diamictites observed at Stop 5 and have been assigned to the fl d029-08 1st pgs page 30

30 Tull and Barineau

A

B Area where samples for Rf/ Stop 6 analysis were collected.

Figure 13 (continued on following page). Geologic map of the region of Stops 5 and 6. (From Tull and Telle, 1986) fl d029-08 1st pgs page 31

Talladega slate belt, Alabama Appalachians 31

C

Kahatchee Mountain Group

Stop 6 Jumbo Dolomite

Lay Dam Formation

LnR vs. Phi LnR vs. Phi f f D Lay Dam Formation, Sample 4, immediately above the basal contact Lay Dam Formation, Sample 1, 6 feet above basal contact -90 -90

-70 -70

-50 -50

-30 -30

-10 -10 Phi 10Phi 10

30 30

50 50

70 70

90 90 0 0.5 1 1.5LnR 2 2.5 3 3.5 0 0.5 1 1.5LnRf 2 2.5 3 3.5 f

LnRf vs. Phi LnRf vs. Phi Lay Dam Formation, Sample 2, 25 feet above contact Lay Dam Formation, Sample 3, 67 feet above contact -90 -90

-70 -70

-50 -50

-30 -30

-10 -10

10Phi 10Phi

30 30

50 50

70 70

90 90 0 0.5 1 1.5LnRf 2 2.5 3 3.5 0 0.5 1 1.5LnRf 2 2.5 3 3.5

Figure 13 (continued). fl d029-08 1st pgs page 32

32 Tull and Barineau lower Lay Dam Formation. At this location, the basal contact of We anticipate this will take ~3 hours, which includes a dinner the Lay Dam Formation largely places meta-diamictites structur- stop in Alexander City, Alabama. We should arrive at the hotel ally atop phyllites, slates, and metagraywackes of the Kahatchee between 8 p.m. and 8:30 p.m. CST. Mountain Group (exposed in the road here at Stop 6) and all but the lowest portions of the Sylacauga Marble Group are missing Day 3 along this contact. This missing stratigraphy has been alternately attributed to erosion along an angular unconformity and tectonic All participants should be prepared to depart the hotel by removal of this stratigraphic unit by a thrust fault. In an attempt 8:30 a.m. CST. The restaurant across from the hotel opens for to resolve these competing hypotheses, a strain study was car- breakfast at 7:30 a.m. CST and on clear mornings offers a scenic ried out on the metadiamictites exposed in the hillside. Oriented view of the Talladega belt northwest of the Talladega Mountains. samples at the basal Lay Dam contact and at repeated intervals Weather permitting, we will gather at 8:30 a.m. on the back porch (6, 25, and 67 feet) above the basal contact to the top of the ridge of the restaurant and discuss the overall geology of the region as were collected and used to conduct Rf/Φ analysis (Woodall and seen from that vantage point. At 9:00 a.m. CST, we will depart Barineau, 2010). In thin section and hand sample, porphyroclasts from the state park for Stop 1. are largely fl attened and no easily observed stretching lineation • From the hotel-restaurant parking lot, drive downhill is observed. Due to lack of observable stretching lineations in (south) ~0.1 miles (through the automatic gate) toward the outcrops of the meta-diamictites, Rf/Φ analyses on cut hand sam- main entrance and turn left (east) on AL Hwy 281. ples collected at the contact was conducted in order to determine • After ~3.4 miles, turn right (south) on AL Hwy 49 toward if clasts were preferentially elongated in a more subtle manner. Lineville, Alabama. Samples were cut parallel to dip (perpendicular to foliation) and • After ~6 miles turn right (west) on CR-31. then at 10° intervals away from the dip direction over a 60° inter- • After ~4.3 miles, turn right (west) on CR-12/Clairmont val. Rf/Φ analysis of these surfaces suggests slight elongation in Springs Road. the dip direction. • After ~1.6 miles, turn right onto High Falls Road. Subsequently, four samples at increasing distance from • Stop 7 begins in the parking lot at the trail head to the High the contact were cut parallel to dip direction (perpendicular to Falls area, ~0.3 miles north of CR-12/Clairmont Springs foliation) and thin-sectioned for further analysis. Rf/Φ analysis Road. We should arrive at this stop by 9:30 a.m. CST. suggests that no strain gradient exists within ~70 feet of the basal contact. Fluctuation ranged from 150° to 180° in the four Stop 7 (~1 hour; Figure 14): Cheaha Quartzite at High Falls samples, suggesting minimal rotation of grain axes, and bulk Branch (Early Devonian) strain for all four samples are very similar (Fig. 13D—a, b, c, South of Cheaha Mountain (highest point in Alabama), the and d). If the basal Lay Dam contact were a fault, as proposed ridge defi ning the Talladega Mountains bifurcates around a large by some researchers (Prouty, 1916; Butts, 1926; Carrington, south-plunging syncline cored by the Erin Slate. The ridge form- 1973; Guthrie, 1989; Higgins and Crawford, 2010; Hatcher, ing strata—Butting Ram–Cheaha Quartzite—continues to the 2008), the relatively low temperature conditions under which southwest of the bifurcation for more than 100 km. The southern it formed (below lower greenschist facies) should have resulted spur of the ridge, however, is <5 km in length, terminating just in more intense strain at the basal Lay Dam contact. The lack northwest of Pyriton, Alabama, at the High Falls along High Falls of a strain gradient approaching the contact, coupled with the Branch as a result of thrust faulting along the Hollins Line fault signifi cant local relief on the contact in this area and the nature system. Erosion by High Falls Branch has exposed a spectacu- of the clasts in the diamictites (derived from underlying strati- lar asymmetric anticline in the tan-blue quartzites and metacon- graphic units: see discussion on Lay Dam Formation), indicate glomerates of the Cheaha Quartzite. that the contact between the Sylacauga Marble and Lay Dam As we walk up the trail from the parking lot to the lowest fall Formation is an unconformity. (~1000 feet), bedding within the quartzites (easily recognized by The presence of brittle shear fabrics along the sub-Lay metaconglomeratic layers in a sequence dominated by metasand- Dam unconformity near Sylacauga, Alabama, (Hatcher, 2008) stones) at the southern end of the structure is nearly vertical on the to the northeast of Stop 5, however, suggests the contact may short limb of the fold. An abandoned quarry ~700 feet up the trail be a locally faulted unconformity. If so, this suggests displace- from the parking lot provides excellent exposure of the quartzite, ment along the contact increases from southwest to north- including heavy mineral laminations, and shows signifi cant shal- east. However, the contact cannot have accommodated the lowing (of dip?) of bedding planes as we approach the core of 10’s of kilometers of displacement argued for at that location the structure. Excellent joint ornamentation, including hackles, (Hatcher, 2008) if it is “pinned” at this location (Woodall and plumose structures, and slickensides can also be observed along Barineau, 2010). the quarry walls. Additionally, at the top of the quarry wall, a This concludes Day 1 geology activities. The van(s) will sigmoidally deformed en echelon quartz vein—most likely asso- now travel to Cheaha State Park, south of Oxford, Alabama, ciated with thrusting along the Hollins Line—suggests top to the where we will stay in the hotel at the top of Cheaha Mountain. north-northwest displacement. fl d029-08 1st pgs page 33

Talladega slate belt, Alabama Appalachians 33 A CCheahaheaha State PParka rk

SStoptopo 7 Figure 14. Geologic map of the region of Stop 7.

0 km 2

B

LoLLowerower FallsFaF alls QQuarryuarrrry

SStoptop 7 fl d029-08 1st pgs page 34

34 Tull and Barineau

A

Stop 8

B

Erin Slate Lay Dam Formation

Poe Bridge Mountain Eastern Blue Ridge

Figure 15. Geologic map of the region of Stop 8.

Figure 16. Geologic map of the region of Stop 9. fl d029-08 1st pgs page 35

Talladega slate belt, Alabama Appalachians 35

Farther along the trail in the core of the fold, large cross- Stop 9 (30 minutes; Figure 16): Meta-basalt (Greenstone) of beds can be observed immediately north of the quarry in a north- the Hillabee Greenstone (Early/Middle Ordovician) facing vertical cliff face. Continuing up the trail parallel to the The Hillabee Greenstone (Tull and Stow, 1980; Tull et al., stream, dips on quartzite bedding gradually change orienta- 1998) is the thickest (locally > 2 km) and most laterally extensive tion as the long limb of the structure is exposed. At the lower meta-igneous unit in the western Blue Ridge. It is dominantly falls, bedding planes dip moderately to the east (compare to the mafi c (meta-basalt) as seen at this exposure, but a signifi cant por- steep west-dipping beds close to the parking lot). Additionally, a tion (15%–25%) of the exposed sequence is felsic rock (meta- prominent layer of cross-beds ~1 m thick is exposed around the dacite) (see Stop 10). Mafi c rocks range from poorly foliated steep quartzite walls eroded by the stream. Facing data on these to nonfoliated massive greenstone (seen here) to mafi c phyllite. cross-beds and others in the area consistently indicate an overall These lithologies are chemically and mineralogically equivalent, upright sequence for the Cheaha Quartzite. fi ne grained (0.1–1 mm), and, throughout most of the region, • From the parking lot below High Falls Branch, return to contain the mineral assemblage actinolite (25%–70%), epidote- CR-12/Clairmont Springs Road (~0.3 miles) and turn clinozoisite-zoisite (10%–60%), albite (20%–30%), and chlorite right (west). (1%–10%), a typical mineral assemblage of the lower greenschist • After ~4.8 miles, turn left (south) on Hanging Rock Road. facies of metamorphism (Tull et al., 1978; Stow, 1982). Relict • After 0.9 miles, park near the railroad tracks where they igneous textures (porphyritic, diabasic, and ophitic) are common cross Hanging Rock Road. Stop 8 is an outcrop on the in the greenstones, which are interpreted to have originated as north side of the railway ~800 feet east of its intersection basalt fl ows, and mafi c phyllites are interpreted to represent both with Hanging Rock Road. This is an active rail line and more highly deformed greenstone protoliths and basaltic tuff. passing freight trains are not uncommon. Please keep Both lithologies have the chemistry of low-potassium tholeiitic this in mind as we hike down the rail road track to Stop basalts. The mafi c phyllites commonly preserve delicate compo- 8. If a train approaches, please move as far away from sitional layering on a millimeter and centimeter scale defi ned by the track as possible. We should arrive at this stop by alterations of plagioclase-rich and mafi c mineral-rich laminae. 11:30 a.m. CST. • From Stop 9, continue west on AL Hwy 148 toward Syl- acauga, Alabama. Stop 8 (~1 hour; Figure 15): Erin Slate Southwest of Erin, • After ~2.3 miles, turn right (north) on Cann Road. Alabama (Late Devonian–Earliest Mississippian?) • After ~2 miles, park on the shoulder of Cann Road. Stop Along the north side of the railroad cut, the Erin Slate is 10 is located on a small stream which fl ows in from the exposed over a signifi cant distance. These railroad cuts are con- right (east) side of Cann Road into Mill Creek on the sidered to be the type locality of the Erin Slate, and is the local- west side of Cann Road. We should arrive at this stop by ity that yielded the Periastron reticulatum (Gastaldo, 1995), and ~3:00 p.m. CST. Veryhachium (Tull et al., 1989) fossils, among the youngest in the metamorphic Appalachians. For a description of the Erin Slate Stop 10 (45 minutes; Figure 17): Meta-dacite of the Hillabee refer to the guidebook text. Greenstone (Early/Middle Ordovician) At the conclusion of this stop (~12:30 p.m. CST), we will The Hillabee Greenstone is composed of bimodal tholeiitic travel to Ashland, Alabama, for lunch. metabasalts and interstratifi ed calc-alkaline felsic metavolca- • From the intersection of Hanging Rock Road and the CSX nic rocks (15%–25%) (Tull and Stow, 1980). We will examine Rail Transportation line, travel south toward Ashland, Ala- the felsic metavolcanic rocks at this locality. They are chemi- bama. After ~2.6 miles, turn right on CR-146/Mountain cally similar to meta-dacites and meta-rhyolites, occur as thick, View Road. chemically and mineralogically homogeneous, tabular sheets • After ~0.7 miles, turn left on Idaho Road. that display very large area-to-thickness ratios. Contacts of the • After ~3 miles, turn left on AL Hwy 77 toward Ashland, felsic sheets are planar, concordant with surrounding strati- Alabama, which is ~3.5 miles east of its intersection with graphic contacts, and parallel for distances of many kilometers, Idaho Road. Ashland has a number of restaurants in the extending over many hundreds of km2, and exhibit petrographic downtown square. and geochemical evidence for crystal fractionation and accumu- At the conclusion of lunch (~1:45 p.m. CST), we will drive lation of plagioclase and hornblende. Their regional geometry, to Stop 9, west of Millerville, Alabama. primary textural features, and chemical homogeneity indicate • From downtown Ashland, Alabama, take AL Hwy 9 South that these units originated as large-volume ash-fl ow crystal tuffs toward Millerville, Alabama. (ignimbrites). Each sheet is of relatively uniform thickness and • After ~8.2 miles, turn right on AL Hwy 148 toward Syl- has large lateral dimensions. Six major felsic sheets mapped in acauga, Alabama. the central portion of the Hillabee Greenstone range from ~50 m • Stop 9 is on the right side (south) of AL Hwy 148, ~2.6 miles to 165 m thick (Tull et al., 1998) (Fig. 7). Boundaries with mafi c from its intersection with AL Hwy 9 in Millerville. We meta-volcanic rocks are planar and sharp, and lack evidence of should arrive at Stop 9 by 2:15 p.m. CST. localized high shear strain, and are thus interpreted to represent fl d029-08 1st pgs page 36

36 Tull and Barineau

A

B Stop 10

Figure 17. Geologic map of the region of Stop 10. fl d029-08 1st pgs page 37

Talladega slate belt, Alabama Appalachians 37 un-faulted, pre-metamorphic volcanic contacts. Here, we exam- either expressed or implied, of the U.S. government. Reviews ine the lowest major felsic unit (~165 m thick) which occurs by Ed Osborne (Alabama Geological Survey) and Chris Holm- ~250 m above the structural base (Hillabee thrust fault) of the Denoma (USGS) were both helpful and appreciated. Hillabee Greenstone. This felsic sheet maintains a relatively con- stant thickness over a minimum distance of 16 km across strike REFERENCES CITED (NW-SE), and for 30 km along-strike (SW-NE). A minimal origi- nal areal extent of ~300 km2 and volume of ~50 km of the lower Adams, G.I., 1926, Geology of Alabama; the crystalline rocks: Alabama Geo- logical Survey: Special Report, v. 14, p. 25–40. sheet can be estimated by assuming that it initially occupied at Allison, D.T., Sandy, D., Barclay, E., and Tull, J.F., 2008, A new interpretation least the roughly triangular region of its outcrop trace before of the northern Talladega belt internal structure: a megascopic overturned folding (Fig. 7). isoclinal anticline: Geological Society of America Abstracts with Pro- grams, v. 40, no. 4, p. 14. The felsic rocks are light-gray phyllite in which slaty Astini, R.A., Thomas, W.A., and Osborne, W.E., 2000, Sedimentology of the Cona- cleavage is variably developed. Less foliated rocks appear sauga Formation and equivalent units, Appalachian thrust belt in Alabama: gneissic. A very fi ne-grained (0.01–0.1 mm) matrix surrounds Alabama Geological Society 37th Annual Field Trip Guidebook, p. 41–71. Babcock, L.E., and Peng, S., 2007, Cambrian chronostratigraphy: current state much larger (0.5–10.0 mm) porphyroclasts of albitic plagio- and future plans: Palaeogeography, Palaeoclimatology, Palaeoecology, clase, amphibole (edenitic hornblende/actinolite), quartz, and v. 254, p. 62B66. laminated quartz-mica fragments. Approximately 80 vol% Barineau, C.I., 2009, Superposed fault systems of the southernmost Appala- chian Talladega belt: implications for Paleozoic orogenesis in the south- of most of the felsic rocks consists of matrix quartz+ ern Appalachians [Ph.D. dissertation]: Tallahassee, Florida, Florida State albite+muscovite+ actinolite, ± minor chlorite and epidote, University, 136 p. and trace zircon, apatite and titanite. The matrix commonly Barineau, C.I., 2010, Paleotectonic reconstructions, back-arc evolution, and the southern Appalachian Taconic orogeny: Geological Society of America displays thin (0.1–3 mm), discontinuous and anastomosing Abstracts with Programs, v. 42, no. 5, p. 678. layers of muscovite and chlorite that alternate with quartz- Barineau, C.I., and Tull, J.F., 2001, Nature and timing of multiple(?) terrane plagioclase layers, probably refl ecting metamorphic differen- accretion along the eastern/western Blue Ridge (Talladega belt) bound- ary, Alabama: Geological Society of America Abstracts with Programs, tiation. The regional strain appears to have been partitioned v. 33, no. 2, p. A-74. more strongly into the felsic as opposed to the mafi c rocks of Barineau, C.I., and Tull, J.F., 2006, Did subduction initiate along the Cambrian the Hillabee Greenstone, so that the felsic rocks commonly Alabama promontory?: Geological Society of America Abstracts with Programs, v. 38, no. 7, p. 213. exhibit a mylonitic matrix fabric around the more rigid original Barineau, C.I., Tull, J.F., and Mueller, P.A., 2006, Accretion of a volcanic igneous porphyroclasts of hornblende and plagioclase. complex along the Paleozoic Laurentian margin; potential links between the Hillabee Greenstone, eastern Blue Ridge of Alabama, and Paleozoic events in the foreland: Geological Society of America Abstracts with Pro- Field Trip Discussion and Return Travel to grams, v. 38, no. 3, p. 6. Atlanta, Georgia Barineau, C.I., Holm-Denoma, C.S., and Tull. J.F., 2012, Growing evidence for the presence of Laurentian margin Ordovician back-arc basin(s) in the southern Appalachians: Geological Society of America Abstracts with Following Stop 10 (fi nal stop of the trip), we will have a brief Programs, v. 44, no. 4, p. 64. discussion of the overall tectonic signifi cance of Talladega belt Beck, C.B., 1978, Periastron Retculatum Unger and Aerocortex Kentuckiensis, rocks for the Paleozoic history of the southern Appalachians. At N. Gen. et Sp., from the New Albany Shale of Kentucky: American Jour- nal of Botany, v. 65, p. 221–235, doi:10.2307/2442456. the conclusion of this discussion (~3:45 p.m. CST), we will begin Bearce, D.N., 1973, Geology of the Talladega Metamorphic Belt in Cleburne travel back toward Atlanta, Georgia, where the fi eld trip will end. and Calhoun counties, Alabama; Symposium; Geology of the Blue Ridge- Participants can be dropped off at the Hartsfi eld- Jackson Inter- Ashland-Wedowee belt in the Piedmont: American Journal of Science, v. 273, p. 742–754. national Airport (anticipated arrival of 7:30 p.m. EST) or at local Bearce, D.N., 1977, Stratigraphic problems in the eastern Coosa Valley, in Bearce, hotels if needed. D.N., ed., Cambrian and Devonian stratigraphic problems of eastern Alabama: Guidebook, 19th Annual Field Trip, Alabama Geological Society, p. 10–21. Bearce, D.N., 1985, Early Cambrian nappes bordering Talladega belt in eastern ACKNOWLEDGMENTS Alabama, in Tull, J.F., Bearce, D.N., and Guthrie, G.M., eds., Early evolu- tion of the Appalachian Miogeocline: upper Precambrian-lower Paleozoic Research related to this study has been supported by the Stratigraphy of the Talladega Slate Belt: Alabama Geological Society 22nd Annual Field Trip Guidebook, p. 37–49. National Science Foundation (EAR-611 0309284, EAR- Bearce, D.N., 1991, Nappes of Lower Cambrian strata in eastern Alabama: Tal- 8109056, EAR-0309284), and the U.S. Geological Survey, ladega slate belt-foreland boundary redefi ned: American Journal of Sci- National Cooperative Geologic Mapping Program (assistance ence, v. 291, p. 711–735, doi:10.2475/ajs.291.7.711. Bearce, D.N., and McKinney, F.K., 1977, Archaeocyathids in eastern Alabama: Sig- award nos. 01-HQAG0160, 02-HQAG0100, O3-HQAG0100, nifi cance to geological interpretation of Coosa deformed belt: Geology, v. 5, O4-HQAG093613 O5-HQAG0107, O7-HQAG0139, p. 467–470, doi:10.1130/0091-7613(1977)5<467:AIEAST>2.0.CO;2. 08-HQAG0076, and 09-7904-2078) to J.F. Tull. This manu- Blount, A.M., and Vassiliou, A.H., 1980, The mineralogy and origin of the talc deposits near Winterboro, Alabama: Economic Geology and the Bulletin script is submitted for publication with the understanding that of the Society of Economic Geologists, v. 75, p. 107–116, doi:10.2113/ the U.S. government is authorized to reproduce and distribute gsecongeo.75.1.107. reprints for governmental use. The views and conclusions con- Bond, G.C., Nickeson, P.A., and Kominz, M.A., 1984, Breakup of a supercon- tinent between 625 Ma and 555 Ma: New evidence and implications for tained in this document are those of the authors and should not continental histories: Earth and Planetary Science Letters, v. 70, p. 325– be interpreted as necessarily representing the offi cial policies, 345, doi:10.1016/0012-821X(84)90017-7. fl d029-08 1st pgs page 38

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Boyer, S.E., and Elliott, D., 1982, Thrust systems: AAPG Bulletin, v. 66, p. 1196– Guthrie, G.M., 1989, Geology and marble resources of the Sylacauga Marble 1230, doi:10.1306/03B5A77D-16D1-11D7-8645000102C1865D. District: Geological Survey of Alabama Bulletin 131, 81 p. Bream, B.R., 2003, Tectonic implications of para- and orthogneiss geochro- Guthrie, G.M., 1994, Geology of the Columbiana area, Chilton, Coosa, and nology and geochemistry from the Southern Appalachian crystalline core Shelby Counties, Alabama: Geological Survey of Alabama Bulletin 151, [Ph.D. dissertation]: Knoxville, Tennessee, University of Tennessee at 80 p. Knoxville, 310 p. 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McClellan, E.A., and Miller, C.F., 2000, Ordovician age confi rmed for the Hil- Reineck, M.E., and Singh, I.B., 1980, Depositional Sedimentary Environments: labee Greenstone, Talladega belt, southernmost Appalachians: Geological Springer-Verlag, New York, 519 p. Society of America Abstracts with Programs, v. 32, no. 2, p. 61. Russell, G.S., 1978, U-Pb, Rb-Sr, and K-Ar isotopic studies bearing on the McClellan, E.A., Steltenpohl, M.G., Thomas, C., Miller, C.F., and Hanley, T.B., tectonic development of the southernmost Appalachian Orogen, Alabama: 2005, Isotopic age constraints and metamorphic history of the Talladega [Ph.D. thesis]: Tallahassee, Florida, Florida State University, 197 p. 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F-2, p. 179–232. mation), Appalachian fold belt, Alabama [M.S. thesis]: Troy, New York, Osborne, W.E., Thomas, W.A., Astini, R.A., and Irvin, G.D., 2000, Stratigraphy Rensselaer Polytechnic Institute, 165. of the Conasauga Formation and equivalent units, Appalachian thrust belt Stow, S.H. 1982, Igneous petrology of the Hillabee Greenstone, northern Ala- in Alabama: Alabama Geological Society 37th Annual Field Trip Guide- bama Piedmont, in Bearce, D.N., et al., eds., Tectonic studies in the Tal- book, p. 19–40. ladega and Carolina slate belts, southern Appalachian orogen: Geological Palmer, A.R., and Rozanov, A.Y., 1976, Archaeocytha from New Jersey: evi- Society of America Special Paper 191, p. 79–92. dence for and intra-Cambrian unconformity in the north-central Appala- Stow, S.H., and Tull, J.F., 1979, Sulfi de mineralization; The Hillabee metavol- chians: Geology, v. 4, p. 773–774, doi:10.1130/0091-7613(1976)4<773: canic complex and associated rock sequences: Guidebook for the Annual AFNJEF>2.0.CO;2. 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Pendexter, W.S., 1985, Structural and stratigraphic relationships of the low Thomas, C.W., 2001, Origins of mafi c-ultramafi c complexes of the Eastern grade metamorphic rocks in the Marble Valley area, Coosa and Chilton Blue Ridge province, southern Appalachians: Geochronological and geo- Counties [master’s thesis]: Tuscaloosa, University of Alabama, 83 p. chemical constraints [Ph.D. dissertation]: Nashville, Tennessee, Vander- Pettijohn, F.J., Potter, P.E., and Siever, R., 1987, Sand and Sandstone: New bilt University, 154 p. York, New York, Springer-Verlag, p. 152–389. Thomas, W.A., 1993, Low-angle geometry of the late Precambrian-Cambrian Pfeil, R.W., and Read, J.F., 1980, Cambrian carbonate platform facies, Shady Appalachian-Ouachita rifted margin of southeastern North America: Geol- Dolomite, southwestern Virginia, U.S.A: Journal of Sedimentary Petrol- ogy, v. 21, p. 921–924, doi:10.1130/0091-7613(1993)021<0921:LADGOT ogy, v. 50, p. 91–116. >2.3.CO;2. 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Thomas, W.A., and Neathery, T.L., 1980, Tectonic framework of the Appala- Rankin, D.W., et al., 1993, Proterozoic rocks east and southeast of the Gren- chian orogen in Alabama, in Frey, R.W., ed., Excursions in southeast- ville front, in Reed, J.C., Jr., et al., eds., Precambrian: Conterminous U.S.: ern geology, VII: Geological Society of America fi eld trip guidebook, Boulder, Colorado, Geological Society of America, The Geology of North p. 465–526. America, v. C-2, p. 335–338. Thomas, W.A., Astini, R.A., and Osborne, W.E., 2000, Tectonic framework Read, C.B., 1936, A Devonian Flora from Kentucky: Journal of Paleontology, of deposition of the Conasauga Formation: Alabama Geological Society v. 10, no. 3, p. 215–227. 37th Annual Field Trip Guidebook, p. 19–40. fl d029-08 1st pgs page 40

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Tucker, M.E., and Wright, V.P., 1990, Carbonate Sedimentology: Oxford, cal Society of America Bulletin, v. 91, p. 27–36, doi:10.1130/0016 Blackwells, 482 p. -7606(1980)91<27:THGAMV>2.0.CO;2. Tull, J.F., 1975, Structural and Metamorphic Aspects of the Northern Alabama Tull, J.F., and Stow, S.H., 1982, Geologic Setting of the Hillabee Metavolcanic Piedmont, in Neathery, T.L., and Tull, J.F., eds., Geologic Profi les of the Complex and Associated Strata-bound Sulfi de Deposits in the Appala- Northern Alabama Piedmont: Alabama Geological Society Guidebook, chian Piedmont of Alabama: Economic Geology, v. 77, p. 318–327. 13th Annual Field Trip, p. 63–86. Tull, J.F., and Telle, W.R., 1986, Olistostromal unit of the Silurian-Lower Devo- Tull, J.F., 1977, Structural Development of the Alabama Piedmont Northwest nian Lay Dam Formation, Talladega slate belt, Chilton County, Alabama, of the Brevard Zone: American Journal of Science, v. 278, p. 422–460. in Neathery, T.L., ed., Geological Society of America Centennial Field Tull, J.F., 1978, Structural development of the Alabama Piedmont northwest Guide, Southeastern Section, v. 6, p. 305–308. of the Brevard Zone: American Journal of Science, v. 278, p. 442–460, Tull, J.F., and Telle, W.R., 1989, Tectonic setting of olistostromal units and doi:10.2475/ajs.278.4.442. associated rocks in the Talladega slate belt, Alabama Appalachians, in Tull, J.F., 1979, Overview of the Sequence and Timing of Deformational Events Horton, J.W., and Rast, N., eds., Mélanges and olistostromes of the Appa- in the Southern Appalachians: Evidence from the Crystalline Rocks, lachians: Geological Society of America Special Paper 228, p. 247–269. North Carolina to Alabama: IGCP project Caledonide Orogen, Abstracts Tull, J.F., Stow, S.H., Long. A.L., and Hayes-Davis, B., 1978, The Hillabee with Programs, p. A10. Greenstone: stratigraphy, petrology, structure, geochemistry, and miner- Tull, J.F., 1982, Stratigraphic framework of the Talladega slate belt, Alabama alization: University of Alabama, Mineral Resources Institute Research Appalachians, in Bearce, D.N., Black, W.W., Kish, S.A., and Tull, J.F., Report, No. 1, 100 p. eds., Tectonic studies in the Talladega and Carolina slate belts, southern Tull, J.F., Harris, A.G., Repetzki, J.E., McKinney, F.K., Garrett, C.B., and Appalachian orogen: Geological Society of America Special Paper 191, Bearce, D.N., 1988, New paleontologic evidence constraining the age p. 3–18. and paleotectonic setting of the Talladega slate belt, southern Appala- Tull, J.F., 1985, Stratigraphy of the Sylacauga Marble Group, in Tull, J.F., chians: Geological Society of America Bulletin, v. 100, p. 1291–1299, Bearce, D.N., and Guthrie, G.M., eds., Early evolution of the Appalachian doi:10.1130/0016-7606(1988)100<1291:NPECTA>2.3.CO;2. Miogeocline: upper Precambrian-lower Paleozoic Stratigraphy of the Tal- Tull, J.F., Jacobson, S.R., Stanton, R.W., Harris, A.G., Repetski, J.E., and ladega Slate Belt: Alabama Geological Society 22nd Annual Field Trip Bostick, N.H., 1989, The Erin Slate, Talladega Group, Alabama Appala- Guidebook, p. 21–26. chians, is Devonian (?), not Carboniferous: Geological Society of Amer- Tull, J.F., 1994, Map-scale dextral folds in the footwall of a far-traveled crystal- ica Abstracts with Programs, v. 21, no. 6, p. A342. line thrust sheet, Alabama-Georgia Appalachians: Geological Society of Tull, J.F., Ragland, P.C., and Durham, R.B., 1998, Geologic, geochemical, and America Abstracts with Programs, v. 26, no. 4, p. 66. tectonic setting of felsic metavolcanic rocks along the Alabama recess, Tull, J.F., 1995a, Hollins Line transpressional duplex: eastern-western Blue southern Appalachian Blue Ridge: Southeastern Geology, v. 38, p. 39–64. Ridge terrane boundary: Geological Society of America Abstracts with Tull, J.F., Barineau, C.I., Mueller, P.M., and Wooden, J.L., 2007, Volcanic Programs, v. 27, no. 2, p. 93. arc emplacement onto the southernmost Appalachian Laurentian shelf: Tull, J.F., 1995b, Southern Appalachian Terrane boundary is a transpressional characteristics and constraints: Geological Society of America Bulletin, duplex: Geological Society of America Abstracts with Programs, v. 27, v. 119, no. 3/4, p. 261–274, doi:10.1130/B25998.1. no. 6, p. 223. Tull, J.F., Allison, D.T., and Whiting, S.E., John, 2010, Southern Appalachian Tull, J.F., 1998, Analysis of a regional middle Paleozoic unconformity along outer Laurentian margin initial drift-facies (Chilhowee Group- equivalent) the distal southeastern Laurentian margin, southernmost Appalachians: sequences: implications for margin evolution, in Tollo, R.P., Bar- implications for tectonic evolution: Geological Society of America Bul- tholomew, M.J., Hibbard, J.P., and Karabinos, P.M., eds., From Rodinia letin, v. 110, p. 1149–1162, doi:10.1130/0016-7606(1998)110<1149: to Pangea: Geological Society of America Memoir 206, p. 935–956. doi: AOARMP>2.3.CO;2. 10.1130/2010.1206(36). Tull, J.F., 2002, Southeast margin of the middle Paleozoic shelf, southwest- Unger, F. 1856, Zweiter Theil, Schiefer und Sandsteinfl ora, in Richter, R., and ernmost Appalachians: regional stability bracketed by Acadian and Unger, F., eds., Beitrag zur Paläontologie des Thüringer Waldes: Denk- Alleghanian tectonism: Geological Society of America Bulletin, v. 114, schrift Kaiser Akademie Wissenschaft Wien, v. 11, p. 139–186. no. 6, p. 643–655, doi:10.1130/0016-7606(2002)114<0643:SMOTMP Vail, P.R., Mitchum, R.M., Jr., and Thompson, S., III, 1977, Seismic stratig- >2.0.CO;2. raphy and global changes of sea level, Part 4: Global cycles of relative Tull, J.F., and Hilton, D.C., 2008, Studies of the structure and stratigraphy of changes of sea level: American Association of Petroleum Geologists the Rockmart area, Georgia Appalachians: Tectonic implications: Georgia Memoir 26, p. 83–97. Geological Society Guidebook, v. 28, p. 1–24. Warren, R. N., 1969, Geology of a portion of the Stumps Hills in southern Tull, J.F., and Holm, C.S., 2005, Structural evolution of a major Appalachian Shelby County and northern Chilton County, Alabama [M.S. thesis]: New salient-recess junction: consequences of oblique collisional convergence Orleans, Louisiana, Tulane University, 120 p. across a continental margin transform fault: Geological Society of Amer- Whiting, S.E., 2009, Geology of the Talladega slate belt and the foreland fold- ica Bulletin, v. 117, no. 3/4, p. 482–499, doi:10.1130/B25578.1. and-thrust belt, Talladega County, Alabama: [master’s thesis]: Tallahas- Tull, J.F., and Stow, S.H., 1979, Regional Tectonic Setting of the Hillabee see, Florida, Florida State University, 200 p. Greenstone, in Tull, J.F., and Stow, S.H., eds., The Hillabee Metavolcanic Woodall, J., and Barineau, C.I., 2010, Strain Analysis along the Basal Contact Complex and Associated Rock Sequences: Alabama Geological Society of the Lay Dam Formation, Talladega Belt, Alabama: Geological Society Guidebook, 17th Annual Field Trip, p. 30–32. of America Abstracts with Programs, v. 42, no. 1, p. 93. Tull, J.F., and Stow, S.H., 1980, The Hillabee Greenstone: A mafi c vol- canic complex in the Appalachian Piedmont of Alabama: Geologi- MANUSCRIPT ACCEPTED BY THE SOCIETY 19 JULY 2012

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