Lithofacies and Paleogeography of the Conasauga Group, (Middle and Late Cambrian) in the Valley and Ridge Province of East Tennessee

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Lithofacies and paleogeography of the Conasauga Group, (Middle and Late Cambrian) in the Valley and Ridge province of east Tennessee

KENNETH O. HASSON Department of Geography/Geology, East Tennessee State University, Johnson City, Tennessee 37614, and Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 C. STEPHEN HAASE Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831

ABSTRACT A sub-basin within the regional intrashelf basin has been identified. The axis of this sub-basin is oriented northwest, perpendicular to A comprehensive data base for the Conasauga Group (Middle the regional trend of the shelf and Appalachian structure. Approxi- and Late Cambrian) throughout the Valley and Ridge province in east mately 2,900 ft (883 m) of Conasauga strata accumulated in the sub- Tennessee was compiled from published and unpublished sources. basin, which first appeared during Pumpkin Valley Shale deposition Lithofacies and isopach maps and stratigraphic cross sections were and persisted through Maynardville Limestone deposition. We inter- constructed from this data base on both present-day and palinspastic pret the abrupt thickening at the margin of this basin to result from bases to define regional depositional patterns of the Conasauga basement faulting, which produced a graben that subsided intermit- Group. tently during basin filling. This structure may have economic signifi- Isopach and lithofacies trends recognized on present-day base cance in that there is an apparent correlation between the margin of maps are generally consistent with those previously recognized. Litho- this second-order basin and zinc mineralization in overlying carbon- facies data are consistent with a shelf-intrashelf-basin-carbonate- ates of the Knox Group. ramp model proposed by other investigators for the Nolichucky Shale. Our study suggests that the southern edge of an intrashelf basin rec- INTRODUCTION ognized within the Conasauga Group in southwest Virginia was 20 to 50 km southwest of present-day Knoxville. Strata of the Conasauga Group were deposited marginally to and Palinspastic-base lithofacies and isopach patterns for the Cona- within an intrashelf basin bounded on the east by a high-relief carbonate sauga Group in east Tennessee suggest (1) the existence of a generally shelf and on the west by the craton (Rodgers, 1968; Palmer, 1971; Mar- elliptical intrashelf basin that closes to the southwest and the north- kello and Read, 1982). The depositional environments and lithofacies east; (2) that the eastern margin of the intrashelf basin consists of shaly limestone and dolostone, the dolostone being dominant eastward; (3) that basin sediments are limestone, shale, and shaly limestone (40%-80% limestone); and (4) that the western basin margin sediments are mostly calcareous shale and siltstone (20%-60% limestone) that become terrigenous west of the basin.

Figure 1. Location map of study area, illustrating Conasauga Group outcrop belts (Hardeman and others, 1966). References for data points are summarized in Table A.

Additional material for this article (tables) may be obtained free of charge by requesting Supplementary Data 8801 from the GSA Documents Secretary.

Geological Society of America Bulletin, v. 100, p. 234-246, 13 figs., February 1988.

234

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Figure 2. Palinspastic base map of study area, illustrating pre-Appalachian orogeny positions, major thrust faults, and displacement on faults. Faults are labeled within area of displacement. Palinspastic base taken from Roeder and Witherspoon (1978). Letters refer to towns mentioned in text and are as follows: K = Knoxville, JC = Johnson City, S = Sneedville, C = Cleveland, M = Morristown, R = Rogersville, E = Elizabethton, G = Greenville, B = Blountville.

recorded in Conasauga Group strata include (1) shallow water, shale- data is from localities northeast of Knoxville (K)2; southwest of Knoxville, dominated peritidal settings on the cratonward northwestern margin of the there are few data. To facilitate interpretation, data are plotted on a Valley and Ridge, (2) mixed carbonate/shale intrashelf basin, and (3) shelf palinspastic map of east Tennessee (Roeder and Witherspoon, 1978) margin carbonate-dominated shoal and peritidal complex. which removes effects of Alleghanian orogeny foreshortening on facies The purpose of this paper is to summarize, using isopachous and and isopach patterns (Fig. 2). lithofacies maps and stratigraphic cross sections, regional depositional patterns of the Conasauga Group (Middle and Late Cambrian) in the GENERAL SETTING Valley and Ridge province of east Tennessee. We present a regional pic- ture of the stratigraphy and lithofacies patterns for a major unit of the In east Tennessee, Conasauga Group sediments crop out in northeast- Appalachian Valley and Ridge province. Our synthesis combines data southwest-trending belts (Fig. 1). Northwest of the Pulaski fault, Cona- from adjacent southwest Virginia (Markello and Read, 1981, 1982) and sauga Group exposures are on hanging walls of thrust faults. Between the Tennessee and summarizes the lithostratigraphy of the Conasauga Group Pulaski and Holston Mountain faults, Conasauga strata occur in a series of throughout a major portion of the southeastern Overthrust Belt. With the narrow, anticlinal folds commonly faulted on the northwest (Hardeman current interest in energy resource exploration within this region, such a and others, 1966). summary is useful for geological interpretation of seismic data and for the Conasauga Group rocks were deposited during the major Middle and understanding and identification of regional trends in sedimentation pat- Late Cambrian marine transgression over a subsiding, aggraded, and terns and paleogeography. rimmed shelf. This rimmed carbonate shelf has been documented by Locations of data sources are shown in Figure 1. References to data Rodgers (1968), Palmer (1971), Samman (1975), and Markello and Read points are given in Table A, which is available from the GSA Data (1981,1982). The Shady Dolomite comprises the pre-Conasauga Group Repository.1 Thickness data for the various Conasauga Group units at carbonate shelf rim sequence, which thins westward in east Tennessee and each of the data localities illustrated in Figure 1 are summarized in Table interfingers with the Rome Formation. The Shady Dolomite consists of B, which is also available from the GSA Data Repository.1 The bulk of the supratidal dolostones with abundant intercalated red shale and siltstone

'To obtain Tables A and B free of charge, request Supplementary Data 8801 2Letters and numbers within parentheses refer to cities and data localities, from the GSA Documents Secretary. respectively. Data localities are shown in Figure 1.

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NW SE 1 2 3 Maynardville Limestone Maynardville Limestone Maynardville Limestone Nolichucky Shale Nolichucky Shale

Bradley Creek Mbr. Bradley Creek Mbr. Figure 3. Régional stratigraph- Maryville Limestone ie nomenclature of the Conasauga Group in east Tennessee. Conasauga Shale Rogersville Shale Undivided Honaker Dolomite Craig Mbr

Rutledge Limestone Pumpkin Valley Shale

2,900 ft (885 m). Thickness trends change abruptly at the basin margin 1. Northwest of Wallen Valley Fault (Fig. 4); offset of isopach lines on opposite sides of the basin suggests that 2. Between Wallen Valley Fault and Pulaski Fault the Luttrell sub-basin is a fault-bounded graben, perhaps similar to the Rome trough but of smaller scale. The Luttrell sub-basin, prior to Appala- 3. Southeast of Pulaski Fault chian foreshortening, is — 70 mi (112 km) long and 20 mi (32 km) wide. Downward movement in the Luttrell sub-basin did not affect all formations of the Conasauga Group, and subsidence was insufficient at any time (Byrd, 1973). The Rome Formation underlies the Conasauga Group to influence major lithofacies trends. throughout eastern Tennessee. To the west, closer to the craton, the Rome Lithofacies trends parallel present-day structural strike. The Cona- Formation consists of red and green sandstone, mudstone, and shale; oo- sauga Group becomes more calcareous from northwest to southeast, and litic limestone is present locally and glauconitic intervals are common, as the southeastern border of the basin is predominantly dolostone. Data are are halite casts and mudcracks (Samman, 1975; Spigai, 1963). Southeast- insufficient to allow mapping of a limestone-dolostone transition. On a ward, toward the shelf margin, the Rome Formation is principally shale palinspastic base (Fig. 5), lithofacies trends remain generally parallel to and dolomite and lacks sandstone (Rodgers, 1953). structural strike on the northwestern margin of the study area. The iso- Throughout the study area, the Conasauga Group is conformably pachs on the southeast side of the basin, however, are initially east-west overlain by the Knox Group. Northwest of the Pulaski fault, the basal and then swing to a northeast-southwest orientation. On the southeastern Knox formation is the Copper Ridge Dolomite. The base of this formation side of the study area, lithofacies trends (Fig. 5) generally follow isopachs, is defined as the lowest bed of dark, asphaltic, chert-bearing dolomite and a broad transitional area between the southeastern dolostones and the above the Maynardville Limestone (Rodgers and Kent, 1948). Southeast limestone and shale of the central area can be inferred. of the Pulaski fault, the top of the Conasauga Group is placed at the first Data are few for the area occupied by the Conasauga Shale (Fig. 3) sandstone at the base of the Conococheague Limestone (Pugh, 1966; and come from Master of Science theses (Mann, 1963; Hajosy, 1960; Little, 1969; Wilson, 1979). Cryptozoan chert occurs locally with the Jones, 1962) and published geologic quadrangle maps (Finlayson, 1964b; sandstone near the base of the Conococheague (Laws and Taylor, 1986). Swingle, 1964; McMaster, 1963). In this area, only Maynardville Lime- Conasauga Group strata are predominantly shale northwest of the stone is differentiated, and rocks between it and the Rome Formation are Wallen Valley fault, alternating shale and limestone between the Wallen mapped as a single unit, the Conasauga Shale. Valley and Pulaski faults, and mostly carbonate southeast of the Pulaski Red, green, maroon, and purple thin-bedded shale and siltstone at the fault (Rodgers, 1953; Hardeman and others, 1966). Nomenclature for the base of the section are assigned by us to the Pumpkin Valley Shale. Conasauga Group is summarized in Figure 3. Limestones with edgewise conglomerate in the higher portions of the section may represent the feather edge of the Maryville Limestone or CONASAUGA GROUP STRATIGRAPHY limestones in the Nolichucky Shale. The stratigraphic position of the limestones cannot be determined from the data. Total thickness of Conasauga Conasauga Group Undifferentiated Shale is between 1,125 ft (343 m) and 1,300 ft (396 m) (Hajosy, 1960; Jones, 1962). The Conasauga Group occupies a northeast-southwest-trending in- The Maynardville Limestone consists of fine- to coarse-grained, trashelf basin, closed to the southwest; isopachs and lithofacies boundaries medium- to thick-bedded, ribbon-banded limestone with some shale in- generally parallel present-day structural strike (Fig. 4). There is a steep terbeds. The upper third of the formation is dolostone; thickness varies thickness gradient on the northwestern margin of the basin. This gradient between 250 and 510 ft (76-155 m). marks the break between shelf and basin. Thickness of the Conasauga Group typically ranges between 1,000 and 2,000 ft (305-610 m), with a Pumpkin Valley Shale maximum of 2,900 ft (885 m). A localized thickening occurs in a sub-basin that trends northwest- In the type section (42),3 the Pumpkin Valley Shale is 360 ft (110 m) southeast, perpendicular to structural strike (Fig. 4). Thickness of the thick and consists of red and green shales and siltstones with minor lime- Conasauga Group in this sub-basin, herein designated the "Luttrell sub- basin" because of its maximum development in the Luttrell quadrangle, is 3See footnote 2.

Figure 4. Isopach and lithofacies trends for the complete Cona- sauga Group within east Tennessee, plotted on a present-day base map (see Fig. 1). Alternate shaded and unshaded bands are lithofacies zones which are identified by large numbers that refer to regions within the compositional triangle. Isopach contour interval is irregular, and the contour values are given in feet (100 ft = 30.48 m) Data localities indicated by dots. The same label- ing conventions are used in Figures 5 and 8 through 13.

LIMESTONE D0L0ST0NE

stone (Rodgers and Kent, 1948). Where recognized, the base of the The Pumpkin Valley Shale thickens cratonward and thins eastward formation is placed at the top of the uppermost massive sandstone in the to extinction. The formation is most likely present, but not mapped, in Rome Formation. The top of the Pumpkin Valley Shale is placed at the areas where the Conasauga Group is undivided. Maroon, red, and green base of medium-bedded, ribboned Rutledge Limestone. Thickness data are shale typical of the Pumpkin Valley Shale occurs near the base of the untrustworthy, owing to internal deformation and faulting common to Conasauga Group on the Wallen Ridge fault sheet [Mann, 1963 (29); Pumpkin Valley Shale. Only general thickness trends can be suggested, Hajosy, 1960 (34); Jones, 1962 (33)]. At its southeastern limit, the Pump- and available data do not allow reliable lithofacies patterns to be kin Valley Shale is ~ 100 ft (30 m) thick and has interbedded limestones determined. (Neuman, 1960; Cattermole, 1962). It appears that the Pumpkin Valley

Figure 5. Isopach and lithofacies trends for the complete Conasauga Group within east Tennessee, plotted on a palinspastic base map taken from Roeder and Witherspoon (1978).

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Chances Branch Dolomite Member

ilomet

Figure 6. Stratigaphic cross section of the Conasauga Group along the Saltville fault block within east Tennessee and southwest Virginia. Data for Virginia localities (V2, V3, V4, Vll, V13, and V17) from Markello and Read (1981,1982).

Shale is replaced by equivalent carbonate rocks southeastward. Abnormal shale in the basal part of the Conasauga Group described by Swingle thicknesses of Pumpkin Valley Shale occur in Knox County (65, 66, 50, (1959) in the Cleveland area (45) to be Pumpkin Valley Shale equivalent, 51) (Cattermole, 1958,1960,1966a, 1966b; Milici, 1973). Such localized on the basis of its lithology and stratigraphic position. The formation thickening suggests that the onset of faulting which produced the Luttrell pinches out and is replaced by carbonates between the Saltville and sub-basin occurred either before or, at the latest, in Pumpkin Valley time. Pulaski thrust sheets (Fig. 8). Westward, the formation merges into the The Pumpkin Valley Shale maintains an apparent uniform thickness main mass of Conasauga Shale (Harris, 1964). for the length of the Copper Creek thrust sheet (Fig. 6), but lithologic variations cannot be determined. On the Saltville thrust sheet (Fig. 7), the Rutledge Limestone formation either pinches out northeastward or passes laterally into the basal part of the Honaker Dolomite immediately north of the Tennessee- The Rutledge Limestone thickens gradually from -100 ft (30 m) Virginia border. Mapping in northeastern Tennessee (Helton, 1967) shows thick at its western limit to -500 ft (152 m) thick at its eastern limit that the upper part of the formation is replaced by Rutledge Limestone as (Fig. 9). It is thickest on the Saltville and Dumplin Valley thrust sheets. the shale thins. The Pumpkin Valley Shale is mappable southwest of There are a few localities where the formation is anomalously thin (Cat- Knoxville (Rodgers, 1952), and we consider the olive, red, and purple termole, 1955, 166a, 1966b; Neuman, 1960).

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Figure 7. Stratigraphie cross section of the Conasauga Group in east Tennessee, illustrating stratigraphie relationships among formations of central and southeastern phases. Diagram plotted on a palinspastic base taken from Roeder and Witherspoon (1978).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/100/2/234/3379924/i0016-7606-100-2-234.pdf by guest on 28 September 2021 Figure 8. Isopach and lithofacies trends for the Pumpkin Valley Shale within east Tennessee. Data plotted on palinspastic base map taken from Roeder and Witherspoon (1978).

Figure 9. Isopach and lithofacies trends of the Rutledge Limestone within east Tennessee. Data plotted on palinspastic base map taken from Roeder and Witherspoon (1978).

In the central outcrop areas, the Rutledge Limestone is composed Near the Virginia-Tennessee border on the Saltville thrust sheet predominantly of limestone but becomes increasingly dolomitic southeast (17-19), the Rogersville Shale is very dolomitic and dark greenish gray to and northeast (Fig. 9). The upper dolomitic part is apparently a grayish black with thin, interbedded dolomite; it is 45 ft (14 m) thick basinward-extending tongue of the Honaker Dolomite (Figs. 6 and 7) (Helton, 1967) but thins rapidly eastward to 10 ft (3 m) on the Carter which reaches at least to the Copper Creek thrust sheet. Valley thrust sheet (7) and then to extinction (Helton, 1967). Northwest of the Copper Creek thrust sheet and southwest of Knox- Craig Limestone Member. The Craig Limestone Member (see ville, the Rutledge Limestone becomes shaly and is generally mapped Fig. 10) is a persistent limestone bed in the Rogersville Shale (Rodgers and together with the overlying Rogersville Shale (Rodgers, 1952; Cattermole, Kent, 1948). It is a ribbon limestone, locally stromatolitic, similar to the 1958, 1960, 1966a, 1966b; Swingle, 1959; Swingle and others, 1967a, overlying Mary ville Limestone. The thickness of the member varies from 1967b; Finlayson and others, 1964a, 1964b). Rutledge Limestone extends 86 ft (26 m), at its type section, to 11 ft (3.3 m). In the Knoxville area (K), at least as far west as the White Oak Mountain thrust sheet (Haase, 1987). it is interbedded shale and limestone. Limestone in the Rogersville Shale The Rutledge Limestone (Fig. 9) is typically a dolostone-ribboned farther west on the Hunter Valley thrust sheet (Fig. 2) may or may not limestone similar to other limestones in the Conasauga Group. The upper represent the Craig Member; because the stratigraphic position is not Rutledge Limestone in the northeastern part of the Saltville fault block is certain, we exclude these limestones from the Craig. The areal extent of the dolostone; this dolostone is a westward extension of the lower Honaker Craig Member is shown in Figure 10. Dolomite. The eastern limit of the Rutledge Limestone is placed at the The Rogersville Shale is an extension of the main mass of Conasauga southeast margin of the Saltville thrust sheet where the limestones become Shale that pinches out eastward and northeastward. Where the Rogersville dolostones (Fig. 9). Shale disappears (Figs. 7 and 8), the Craig Member merges with the lower part of the overlying Maryville Limestone (Helton, 1967). The Rogersville Shale Craig Member is a basinward, southwestward-thinning extension of the Maryville Limestone and Honaker Dolomite lithosome. The eastern limit The Rogersville Shale is a fissile gray shale which weathers to various of the Rogersville Shale is placed at the southeast margin of the Saltville shades of green. It is 400 ft (122 m) thick on the Hunter Valley thrust sheet thrust sheet. on the northwest and thins to 200 ft (61 m) on the Dumplin Valley sheet; it pinches out to the southeast (Fig. 10). Maryville Limestone The isopachs crudely outline a northwest-southeast-trending basin near Knoxville (50, 51), where the formation is >300 ft (91 m) thick The Maryville Limestone is thickest on the Saltville and Dumplin (Cattermole, 1966a, 1966b). This pattern suggests renewed subsidence in Valley thrust sheets in a basin centered on these thrust sheets and open to the Luttrell sub-basin. the northeast (Fig. 11). Maximum thickness of the formation on the Salt-

O 20 40 KILOMETERS LIMESTONE DOLOSTONE

Figure 10. Isopach and lithofacies trends of the Rogersville Shale within east Tennessee. Data plotted on palinspastic base map taken from Roeder and Witherspoon (1978). Area enclosed by hachures marks the areal extent of the Craig Limestone Member.

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ville thrust sheet is 900 ft (274 m) (Smith, 1968); it is thinnest (350 ft, Tennessee-Virginia border, the dolomitic part of the Maryville Limestone 107 m) in the Knoxville area (Cattermole, 1966a). Its maximum thickness merges with the Rutledge Limestone to form the Honaker Dolomite on the Dumplin Valley fault is 950 ft (259 m) (Neuman, 1960). Thickness (Fig. 6). The upper limestone part continues farther northeastward into of the Maryville Limestone decreases northwestward between the Copper Virginia as a distinct formation until it merges into the Honaker Dolomite Creek and Hunter Valley faults (Fig. 11), and it is not mapped separately (Markello and Read, 1982). on the Wallen Ridge fault block. On the Saltville thrust sheet, the Maryville Limestone consists of Nolichucky Shale medium to dark gray, thinly to massively bedded, finely to coarsely crystalline to aphanitic ribbon limestone; oolites and interbeds of limestone peb- Thickness and lithofacies trends of the Nolichucky Shale (Fig. 12) ble conglomerate are common. On the northeastern part of the Saltville show a pronounced east-west swing of both isopach and lithofacies thrust sheet, the Maryville Limestone is more dolomitic (Figs. 6,7, and 11) boundaries superimposed on the generally northeast-southwest trend of (Smith, 1968; Haney, 1966; Helton, 1967). the basin axis. The Nolichucky Shale thins eastward and the zero isopach On the Dumplin Valley thrust sheet, the Maryville Limestone is dark is placed east of locality 2 (King and Ferguson, 1960; Derby, 1965) near to medium gray, fine- to medium-grained, medium- to thick-bedded lime- Elizabethton (E); this is the easternmost section that contains a trace of stone with a persistent dolostone bed 3 to 100 ft (1.0-30 m) thick. The shale. Here, the calcareous lowermost shale rests on the Honaker dolostone bed is believed to be a basinward projection of the Honaker Dolomite. Dolomite (Hatcher, 1965; Smith, 1968; Haney, 1966). Renewed subsidence in the Luttrell sub-basin during Nolichucky On the Copper Creek thrust sheet, the Maryville Limestone is princi- deposition is evident. The greatest thickness (1,400 ft, 427 m) of Noli- pally calcarenite; on the Hunter Valley sheet, the formation is approxi- chucky Shale is in Knox County (Cattermole, 1958). From limited data, mately half calcareous siltstone and shale and half medium dark gray Milici (1973) correctly surmised that depositional strike differed from limestone. The limestone is an oolitic calcarenite with common intrafor- structural strike in Knox County. This conclusion is supported by our mational conglomerates (Harris, 1965; Mixon and Harris, 1971; Harris studies and the inferred existence of the Luttrell sub-basin. and Mixon, 1970). Maryville Limestone is not recognized or mapped in Outside of the Luttrell sub-basin, the Nolichucky Shale averages the next northwest fault, the Wallen Ridge thrust sheet. between 500 and 600 ft (152-183 m) thick. It thins eastward to 228 ft In the Knoxville quadrangle (65) (Cattermole, 1958), the Maryville (69 m) near Elizabethton (2) in a section described by King and Ferguson Limestone is a mappable unit that pinches out to the southwest (Figs. 6 (I960), Derby (1965), and Gentry (1983) and reinterpreted by us. Here, and 7). Limestone lenses in the undifferentiated Conasauga Shale (Fig. 6) the Nolichucky Shale consists of two thin shale beds in an otherwise may represent the Maryville Limestone, but correlation is uncertain carbonate sequence. The shales pinch out, and the carbonates merge (Swingle, 1959; Rodgers, 1952). The Maryville Limestone becomes dolo- northeastward into the Elbrook Dolomite. stone northeastward. Where the Rogersville Shale pinches out near the Southwest in the Cleveland area (45, 46), Swingle (1959) assigned

Figure 11. Isopach and lithofacies trends of the Maryville Limestone within east Tennessee. Data plotted on palinspastic base map taken from Roeder and Witherspoon (1978).

some 900 ft (274 m) of strata to the Nolichucky Shale. This thickness is the Nolichucky Shale by Helton (1967). He has also described a type somewhat excessive, on the basis of regional trends. If a lower limestone section for the member along Bradley Creek (approximately locality 9 of member, which may correspond to the Maryville Limestone, is removed this study). The areal extent of the Bradley Creek Member is shown in from the Nolichucky Shale, however, the thickness is -700 ft (213 m), Figure 12. Because the middle limestone is easily recognizable and is so which agrees with regional trends suggested in Figures 6, 7, and 12. widespread, we recommend formalizing the name. The Nolichucky Shale is typically a thinly laminated, calcareous clay In the type section, the Bradley Creek Member is 164 ft (50 m) thick shale with numerous interbedded oolitic limestones and limestone-pebble and is characteristically sublithographic, with some coarsely crystalline conglomerates. The shales vary in color from yellowish green to olive oolitic or pelletal limestone. Bedding is typically massive, with some beds green or gray. >20 ft (6 m) thick. There are algal mounds, outlined faintly by silty Regional lithofacies trends shown in Figure 12 indicate increasing stringers, in the lower part of the section. Throughout its outcrop area, the carbonate content eastward, with limestone dominating on the eastern Bradley Creek Member varies widely in thickness and lithology (Milici, margin and shale dominating to the west and transitional areas between 1973; Hatcher, 1965; Oder and Milici, 1965; Wilson, 1979; Little, 1969; them. Recognition of the Nolichucky Shale in easternmost outcrops is Neuman and Wilson, 1960; Neuman, 1960; Cattermole, 1955, 1962). difficult because of the preponderance of limestones, and perhaps the name Regional Trends. Stratigraphic relationships within the Nolichucky should not be used east of the Holston Mountain fault. To the northwest, Shale are shown in Figures 6 and 7. On the Copper Creek thrust sheet, the the Nolichucky Shale merges into the undifferentiated Conasauga Group. Nolichucky is predominantly shale. The Bradley Creek Member between In much of its outcrop area, the Nolichucky Shale can be divided into localities 27 and 59 is interbedded shale and limestone and is not recog- three parts, a lower shale; a middle, frequently stromatolitic, limestone nized as a distinct unit. (Bradley Creek Member); and an upper shale. On the Saltville thrust sheet (Fig. 6), the Nolichucky Shale is thickest Lower and Upper Shale Parts. The lower shale part of the Noli- in the Knoxville area (65), where it is a heterogeneous limestone and shale chucky Shale is slightly calcific, silty gray to olive-gray-green shale with unit; it is undifferentiated to the southwest (Rodgers, 1952). Swingle locally interbedded limestones. The thickness of the lower shale varies (1959) used the term "Nolichucky Shale" for limestones and shales be- widely, from between 300 and 400 ft (92-122 m) (Helton, 1967; Smith, tween the Pumpkin Valley Shale and Maynardville Limestone in the 1968) to 570 ft (174 m) (Haney, 1966) southeast of the Saltville fault to Cleveland area (45,46). Because the correlation can be only partly correct, 200 ft (61 m) southeast of the Dumplin Valley block (21, 22) (Oder and we consider this interval as Conasauga Shale, undivided. Milici, 1965). The upper shale part is lithologically similar to the lower The Nolichucky Shale thins northeastward; the basal shale is replaced shale part. by limestones of the upper Maryville Limestone. The middle limestone The Bradley Creek Limestone Member. The name "Bradley Creek member of the Nolichucky Shale in Virginia (Markello and Read, 1982) is Limestone Member" was proposed informally for the middle limestone of the northeastward extension of the Bradley Creek Member of Tennessee.

5¡E eL A/ \ . i—n r—r O 20 40 60 KILOMETERS LIMESTONE OOLOSTONE

Figure 12. Isopach and lithofacies trends of the Nolichucky Shale within east Tennessee. Data plotted on palinspastic base map taken from Roeder and Witherspoon (1978). Area enclosed within the hachures represents the inferred extent of the Bradley Creek Limestone Member in east Tennessee.

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In Virginia, we apply the term "Bradley Creek" only to where the lower northwestward approximately perpendicular to strike, which suggests re- shale pinches out and it becomes a basal limestone (Fig. 6). Southwest- newed subsidence in the Luttrell sub-basin; this movement, however, was ward, in the Russellville quadrangle (20), the Bradley Creek Member not sufficient to offset lithofacies trends. becomes a series of disconnected limestone lenses and is no longer a The Maynardville Limestone consists of a lower limestone and an distinct member. upper dolostone. In the extreme eastern occurrence near Elizabethton The threefold subdivision of the Nolichucky Shale is maintained on (2), King and Ferguson (1960) included ribbon limestone above the the Pulaski thrust sheet, but farther eastward on the Holston Valley sheet, olive-colored shales of the Nolichucky Shale as a member of that forma- both shales disappear and the middle limestone member (Bradley Creek) tion. We consider this limestone to be Maynardville Limestone (Fig. 7). merges into the Elbrook Dolomite. In the Greenville area (G), the Bradley Formal stratigraphie names for the major lithologie divisions of the May- Creek Member is a basinward extension of the basal Maynardville Lime- nardville Limestone have been used by the U.S. Geological Survey in stone (Elton, 1974). The Bradley Creek Member and the Low Hollow maps of the Howard Quarter and Tazewell quadrangles (39, 37, 38) Member of the Maynardville Limestone merge northeastward and become (Harris and Mixon, 1970; Harris, 1965). These are a lower Low Hollow part of the Elbrook Dolomite. In the Johnson City area (JC), the Bradley Limestone Member and an upper Chances Branch Dolomite Member Creek is a westward-extending tongue of the Elbrook Dolomite (Fig. 7). (Figs. 6 and 7). The lower limestone is typically ribboned, fine grained, and massive, Maynardville Limestone and the upper dolostone is fine grained to aphanitic (Pugh, 1966; Wilson, 1979; Little, 1969; Harris, 1965; Harris and Mixon, 1970). The limestones The Maynardville Limestone, transitional between the Nolichucky may contain algal mounds, oolites, pisolites, and pyritic intraformational Shale and overlying Knox Group, was considered to be the upper member conglomerate (Bridge and Hatcher, 1973; Oder and Bumgarner, 1961; of the Nolichucky Shale by Bridge (cited in Rodgers and Kent, 1948). Tarkoy, 1967). Chert nodules and a bed of black chert near the middle of Later, Rodgers (1953) elevated the Maynardville to formational status, the formation in the Maryville quadrangle (56) (Cattermole, 1962) may be the classification followed by recent workers. The formation ranges in correlative with similar zones recognized by Rodgers and Kent (1948) and thickness from 139 ft (42 m) (VanArsdall, 1974) to 510 ft (155 m) traced by McConnell (1967) in the Copper Creek fault block. Pétro- (Jones, 1962). graphie details of the Maynardville Limestone on the Copper Creek and In general, the isopachs show a symmetrical northeast-trending belt Hunter Valley fault blocks are given by McConnell (1967) and Tarkoy in which the formation ranges between 180 and 250 ft (33-76 m) thick (1967). (see Fig. 13). This belt is transected by a thicker sequence trending The Maynardville Limestone maintains a remarkable lithologie con-

Figure 13. Isopach and lithofacies trends of the Maynardville Limestone within east Tennessee. Data plotted on palinspastic base map taken from Roeder and Witherspoon (1978).

sistency throughout the length of section. There are minor thickness varia- Details of the east-to-west stratigraphic relationships among Cona- tions, but both the Low Hollow and Chances Branch Members persist sauga Group strata in the central and southeastern phases are complex throughout. The Chances Branch Member is a westward-spreading tongue (Fig. 3). These relationships are summarized in the cross section in Figure of Elbrook Dolomite, although dolostone is absent at localities 2 and 5. 7. Depositional environments represented in the Conasauga Group strata The boundary between the Maynardville Limestone and the Copper of east Tennessee range from clastic subtidal on the northwestern margin Ridge Dolomite or the Conococheague Limestone is variable. On the of the basin to carbonate peritidal on the southeast margin, with gradations Copper Creek thrust sheet, it is placed at the first appearance of chert. between them. Facies are similar to the model given by Markello and Southeast of the Copper Creek fault, a thin quartz sandstone marks the Read (1982). Maynardville-Copper Ridge contact (Finlayson and others, 1965a; Oder and Milici, 1965). On the Dumplin Valley thrust sheet, the sandstone The Luttrell Sub-Basin contains white oolitic chert (Bridge and Hatcher, 1973; Hatcher, 1973). On the Pulaski and Dunham Ridge thrust sheets, the Maynardville- The Luttrell sub-basin is a structure that trends northwest-southeast Conococheague boundary is placed at the base of a quartz sandstone (perpendicular to regional strike) in the approximate center of the intra- (Pugh, 1966; Little, 1969; Wilson, 1979). This sandstone is locally cherty shelf basin. The shape of the structure suggests a graben. A basement and contains halite casts (Laws and Taylor, 1986). graben trending parallel to strike and affecting Cambrian and possibly Precambrian sediments has been recognized from seismic and surface data Honaker Dolomite in Alabama. This structure is as much as 25 mi (40 km) wide, with an offset on the northwest side of 10,000 ft (3,048 m) and on the southeast The Honaker Dolomite is the equivalent of the merged Rutledge and side of 5,000 ft (1,524 m) (Kaygi and others, 1983). Although the trend of Maryville Limestones and crops out on the Pulaski, Dunham Ridge, and the Luttrell sub-basin is different from that of the Alabama graben, the Holston Mountain thrust sheets. Thickness of the formation is unknown possibility of a similar structure is evident. because of structural complications and poor exposures. Estimates of min- Geophysical data (Watkins, 1964) indicate a high-angle basement imum thickness of the Honaker Dolomite for the belts between the Pulaski fault coincident with the southern margin of the Luttrell sub-basin. Pohn and Holston Mountain faults, however, are 1,300 ft (396 m) by Rodgers (1985) and Black (1985) have suggested control of Appalachian structures (1953), 1,400 ft (427 m) by Wilson (1979), 1,100+ ft (334+ m) by Pugh by a system of Precambrian basement faults. Black (1985) recognized the (1966), and 800 to 1,100 ft (244-335 m) by Little (1969). On the Holston Knoxville lineament, a basement fault which extends from Kentucky into Mountain fault block, the Honaker Dolomite is 2,200 to 2,500 ft Tennessee; the Knoxville lineament coincides with the southern bounding (671-762 m) thick (King and Ferguson, 1960). fault of the Luttrell sub-basin. Movement on the faults bounding the Measured sections of the Honaker Dolomite are given by Pugh Luttrell sub-basin was intermittent and apparently not of sufficient magni- (1966) and Little (1969). Little recognized three informal members, a tude to affect major lithofacies trends. Isopachs, however, are offset in a lower limestone and dolostone member, a middle limestone member, and manner suggestive of faulting (Figs. 4 and 5). an upper dolostone member. Pugh (1966) did not divide the Honaker The Luttrell sub-basin may have significant economic interest with Dolomite but did recognize 329 ft (100 m) of limestone between predom- respect to zinc mineralization in east Tennessee. The basin margins coin- inantly dolostone units in the Blountville area (3). This limestone appears cide approximately with several major Mississippi Valley-type zinc dis- to correspond to the middle limestone member described by Little (1969). tricts in east Tennessee. The zinc mineralization is concentrated in the overlying dolostones of the Knox Group, and available petrogenetic data DISCUSSION from the zinc deposits are consistent with the possibility that fluids origi- nating during dewatering of shales in the Luttrell sub-basin could have Conasauga Group Stratigraphy been the source of at least some of the mineralizing fluids (Haase and Hasson, 1986). Stratigraphic relationships among the formations of the Conasauga Group are illustrated in Figures 6 and 7. The localities that are included SUMMARY extend from the cratonward western edge of the intrashelf basin to the eastern edge adjacent to the carbonate shelf. The lithostratigraphy of the Conasauga Group has been summarized Conasauga Group stratigraphy on the Saltville thrust sheet is shown in a series of isopachous and lithofacies maps and stratigraphic cross in Figure 6. This cross section extends from near the southern border of sections. The group is predominantly terrigenous clastic rocks to the Tennessee to Newport, Virginia. The Virginia data were obtained by en- northwest and carbonate to the southeast. These extremes are separated by larging Figure 4 of Markello and Read (1982) to the same scale as in our an intrashelf basin which is the southwestern extension of the intrashelf compilation and simplifying the figure.Th e agreement of their compilation basin in Virginia described by Markello and Read (1981, 1982). Our with ours is excellent. The cross section shows regional facies changes in study shows a basin closed to the southwest, in which Conasauga Group the Conasauga Group oblique to depositional strike from the central part strata average 2,000 to 2,200 ft (610-670 m) thick. In the central part of of the intrashelf basin northeastward onto the eastern carbonate bank. In this basin, shale and carbonate lithosomes alternate to form six mappable southwestern outcrops, the Conasauga Group is predominantly shale; the formations (Rodgers, 1953). These lithosomes, except for the Maynard- limestone formations characteristic of the central phase (Rodgers, 1953; ville Limestone, are not mappable southwest of Knoxville. see also Fig. 3) are broken up into discontinuous lenses or beds. Poor The eastern limits of the Pumpkin Valley Shale, Rutledge Limestone, exposures preclude detailed stratigraphic study and correlation of such Rogersville Shale, and Maryville Limestone are on the eastern margin of units. The northeastern merger of carbonate formations into the Honaker the Saltville thrust sheet. On the Pulaski fault, the Rutledge and Maryville Dolomite as shale units pinch out is evident. The great thickness increase limestones are merged into the Honaker Dolomite. The Honaker, Noli- in the Knoxville area (65) is associated with the subsidence and infilling of chucky, and Maynardville formations merge farther northeastward into the Luttrell sub-basin. the Elbrook Dolomite.

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Hatcher, R. D., Jr., 1965, Structure of the northern portion of the Dumplin Valley fault zone in east Tennessee [Ph.D. The intrashelf basin is cut by a northwest-trending graben, the Lut- dissert.]: Knoxville, Tennessee, University of Tennessee. trell sub-basin. Subsidence in the sub-basin was intermittent but sufficient 1973, Geologic map and mineral resources summary of the Jefferson City quadrangle, Tennessee: Tennessee Division of Geology Geologic Map GM-163-SW. to offset isopach lines; major lithofacies trends were not, however, appreci- Helton, W. L., 1967, Lithostratigraphy of the Conasauga Group between Rogersville and Kingsport, Tennessee [Ph.D. ably affected. The boundaries of the sub-basin are generally coincident dissert.]: Knoxville, Tennessee, University of Tennessee. Jones, C., 1962, The geology of the New Royston area, Union and Anderson Counties, Tennessee [M.S. thesis]: Knoxville, with structures interpreted as major basement faults. The boundaries of the Tennessee, University of Tennessee. Kaygi, P. B., Cameron, T. F., and Raeuchle, S. K., 1983, Regional cross section and palinspastic reconstruction of the sub-basin also coincide with Mississippi Valley-type zinc and barite min- Alabama fold and thrust belt: Geological Society of America Abstracts with Programs, v. 15, no. 2, p. 95. eralization in Tennessee. We believe that dewatering of shales within the King, P. B., and Ferguson, H. W., I960, Geology of northeastern-most Tennessee: U.S. Geological Survey Professional Paper 311. Conasauga Group and fluid movement along boundary faults of the sub- Laws, J., and Taylor, D., 1986, Depositional environment and stratigraphy of the Maynardville Formation on the Pulaski fault block, Washington and Sullivan Counties, Tennessee [B.S. thesis]: Johnson City, Tennessee, East Tennessee basin were contributing factors to the localization of the mineral deposits. State University. Little, R. L., 1969, Lithostratigraphy and structural geology of a portion of the Dunham Ridge thrust block, Greene and Washington Counties, Tennessee [Ph.D. dissert.]: Knoxville, Tennessee, University of Tennessee. ACKNOWLEDGMENTS Luther, E. T., Wilson, R. L., Milici, R. C., Sitterly, P. D., Avel, A. P., and Hartman, G. S., 1978, Geology of Hamilton County, Tennessee: Tennessee Division of Geology Bulletin 79. Mann, C. F., 1963, The geology of the Oliver Springs area, Roane and Anderson Counties, Tennessee [M.S. thesis]: Knoxville, Tennessee, University of Tennessee. The authors thank J. F. Read for discussions and encouragement Markello, J. R., and Read, J. F., 1981, Carbonate ramp-to-deeper shale shelf transitions of an Upper Cambrian intrashelf throughout the course of the study. J. F. Read, J. R. Markello, R. 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D., 1964, Fades relations of exposed Rome Formation and Conasauga Group of northeastern Tennessee with equivalent rocks in the subsurface of Kentucky and Virginia: U.S. Geological Survey Professional Paper 501-B, p. B25-B29. 1965, Geologic map of the Tazewell quadrangle, Claiborne County, Tennessee: U.S. Geological Survey Geological Quadrangle Map GQ-465. Harris, L. D., and Mixon, R. B., 1970, Geologic map of the Howard Quarter quadrangle, northeastern Tennessee: U.S. MANUSCRIPT RECEIVED BY THE SOCIETY APRIL 19,1985 Geological Survey Geological Quadrangle Map GQ-842. REVISED MANUSCRIPT RECEIVED JANUARY 22,1987 Harris, L. D., Stephens, J. G., and Miller, R. L., 1962, Geologic map of the Coleman Gap quadrangle, Tennessee and MANUSCRIPT ACCEPTED APRIL 6,1987 Virginia: U.S. Geological Survey Geological Quadrangle Map GQ-188. ENVIRONMENTAL SCIENCES DIVISION, OAK RIDGE NATIONAL LABORATORY. PUBLICATION NO. 2795

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