SEDIMENTOLOGY AND DEPOSITIONAL ENVIRONMENT OF THE WADESBORO SUB- BASIN, EASTERN PIEDMONT, NORTH CAROLINA. Seth Brazell

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1 SEDIMENTOLOGY AND DEPOSITIONAL ENVIRONMENT OF THE WADESBORO SUB- BASIN, EASTERN PIEDMONT, NORTH CAROLINA Seth Brazell

2 I. INTRODUCTION Background Rift basins form under extensional tectonic regimes and contain valuable repositories of sediment that record signioicant episodes of geologic history (LeTourneau and Olsen 2003; Schlische 1993). The timing and rates of rifting can be constrained by documenting the age, thickness, and stratigraphy of rift basin sequences (Randazzo et al. 1970, Tiercelin 1990). The Mesozoic rift basins of eastern North America provide valuable sedimentary records for the breakup of Pangea in Triassic and Jurassic times. In addition, these rift basins are known to contain valuable economic resources including oil, coal, natural gas, uranium, and materials used for brick- making (Schlische 1993; Olsen et al. 1996, Olsen et al. 1991). Further study is needed to constrain the geometries of extensional basins so that accurate Oilling models of the basins can be developed (Schlische and Olsen 1990). The following proposed research project focuses on a Mesozoic rift basin located in the Piedmont physiographic province of North Carolina. Rift basins located in North Carolina include the Dan River Basin, the Deep River Group (Durham, Sanford, and Wadesboro sub- basins) and small outliers, the Davie County Basin and the Ellerbe basin. This study focuses on the southernmost exposed sub- basin of the Deep River Group, the Wadesboro basin, which covers portions of Union, Anson, Richmond, and Montgomery Counties and a portion crosses into South Carolina (Figure 1).

3 Figure 1: Location map of research project 9ield site highlighting the Wadesboro- sub- basin and clay pit in Anson County. (Modi9ied from Olsen et. al, 1996 and Randazzo, 1970) Few studies have examined the geologic history of the Wadesboro sub- basin, however, extensive studies have been conducted in the adjacent Sanford and Durham sub- basins of the Deep River Group (Olsen et. al 1996, Reid and Milici 2008) and detailed geologic maps of the northern two members of the Deep River Group have been produced. Recent work in the Sanford and Durham sub- basins have identioied the presence of natural gas which has spurred the need for a comprehensive study of the Deep River and Dan River Groups for their economic resources by differentiating the bedrock geology and identifying the depositional history of the sub- basin.

4 In order to reconstruct the geologic history of the Wadesboro sub- basin and assess its economic potential, a detailed study, including petrographic, stratigraphic, and structural analyses, is proposed here. Previous studies of the Wadesboro sub- basin have been limited in extent by comparison to other basins within the Newark Supergroup (Clark et al. 2001). Since 1970 there have been few studies of the Wadesboro sub- basin; furthermore, detailed geologic mapping for the Wadesboro sub- basin is absent, and stratigraphic units are only generally deoined (Randazzo et al. 1970). This study proposes to document the geometry, sedimentology, depositional environments and economic potential of the central portion of the Wadesboro sub- basin. Central to this study is the detailed study of the sedimentology, stratigraphy and provenance of 87 meters of exposure in a clay pit that is located in the geographic center of the Wadesboro sub- basin. The facies and stratigraphy identioied from detailed work at the clay pit will be extended to a map area comprising the southern- central portion of the Wadesboro sub- basin, which is typioied by limited and poor surface exposures. This project aims to Oill a gap in knowledge concerning the geologic history of the Wadesboro sub- basin. This will be accomplished by a combination of detailed sedimentologic logging, facies analysis, petrographic analysis, and geologic mapping. Literature Review Pangea began to break up during the Mesozoic period approximately 200Ma. Extensional forces produced by this rifting event created a series of segmented faults along the eastern margin of the North American continent that paralleled

5 Paleozoic contractional structures and faults that were activated during the Appalachian orogen and where extensional forces were at a high angle to the preexisting structures (Schlische 1993). These segmented faults produced numerous northeast- southwest trending half- graben basins known as the Newark Supergroup that are present, exposed or buried, from Nova- Scotia to Florida. The highest displacement along the border fault systems occur in the center of the basins with decreasing displacement toward the ends of the basins. As the border fault systems grew during extension the basins likely widened and linked to other once isolated basins. Most of the exposed Mesozoic basins experienced an incipient period of Oluvial sedimentation that was replaced by lacustrine sedimentation (Schlische 1993). Most extensional basin Oilling models have focused on tectonics (differential subsidence) and climate Oluctuations as the mechanisms controlling depositional environments. Other models have attributed transitions from Oluvial to lacustrine environments to increases or decreases in sediment supply (Lambiase and Bosworth, 1995), however, Schlische and Olsen have proposed a simple model that assumes constant subsidence and inputs of sediment and water, a model that yields results consistent with previous theoretical models and observed basin Oilling (Schlische and Olsen 1990, Tiercelin 1990). The Schlische and Olsen model prediction suggests Oluvial and alluvial deposition during initial subsidence, processes indicative of open- basin conditions, followed by a transition to lacustrine deposition as the basin grows. During lacustrine deposition the basin continues to grow and transitions from an open to a closed- basin environment, which results in

6 deep lacustrine deposition followed by a further subsidence, a wider and shallower basin, and a decrease in lacustrine deposition with a Oinal return to Oluvial deposition (Schlische and Olsen, 1990). The Oilling model proposed by Schlische and Olsen makes simple assumptions that do not reolect the obvious complexities of many extensional basins and, furthermore, this model assumes full- graben basin architecture though evidence is available to suggest a correlation of the Oilling model for half- graben basins. Quantitatively analyzing basin sediments for changing provenance is another aspect of this project. Provenance analysis is never straight forward, however, advances have been made in the last few decades. Large concentrations of zircon, tourmaline, and rutile and Zr/Sc ratios have been used to suggest sediment recycling and may be used to suggest interbasin sediment transport (Huert, 1962 and McLennan et al., 1993). SEM, CL, and ICP- MS have also been used as microscopic- morphological techniques to constrain protolith characteristics (Weltje and von Eynatten, 2004) Of the 9 major basins the Deep River basin is the southern most exposed basin in North America. The Deep River Basin is sub divided into three basins, the Durham sub- basin, Sanford sub- basin, and the Wadesboro sub- basin from north to south, respectively. The three basins are structurally separated by cross structures with the Durham and Sanford sub- basins separated by the Colon cross structure and the Sanford and Wadesboro sub- basins separated by the Pekin cross- structure. The Durham and Sanford sub- basins are differentiated by the presence of dark, organic rich strata that is not present or is unexposed in the Wadesboro sub- basin. Of the

7 three sub- basins, the Wadesboro sub- basin is the least studied and much of the strata remain undifferentiated. Studies that have been conducted in the Wadesboro sub- basin (Reinemund 1955, Zablocki 1959, Randazzo et al. 1970, Clark et. al 2001, and Reid and Milici 2008,) lack fundamental context to cohesively address important economic questions of today. The development of a geologic framework including a detailed bedrock map, and understanding of basin depositional history and the identioication of formations is needed to assess the economic potential of the Wadesboro sub- basin. II. PROBLEM STATEMENT Few studies of the Wadesboro sub- basin exist that examine the extent of lithologies present in the basin and their depositional environments. Coal and other economic deposits have been identioied in adjacent basins within the Deep River Group (Sanford and Durham sub- basins), however no such deposits have been identioied in the Wadesboro sub- basin. III. HYPOTHESES The hypotheses to be tested include: 1) whether depositional environments such as alluvial fans, axial Oluvial rivers, and lakes can be recognized in the Wadesboro sub- basin; 2) are the depositional environments tectonically controlled; 3) did

8 sedimentary provenance change over time; and 4) did conditions exist for natural gas production? This study will document the sedimentology and depositional environments of the Wadesboro sub- basin. This information will be used to constrain the tectonic controls on basin evolution and to assess natural gas potential of the Wadesboro sub- basin. IV. METHODS This project aims to Oill a gap in knowledge concerning the geologic history of the Wadesboro sub- basin. This will be accomplished by a combination of detailed sedimentologic logging, facies analysis, petrography, and geologic mapping. Each of the hypotheses can be tested by this approach. Hypothesis 1: Sedimentologic logging and facies analysis should provide a detailed record of sedimentary environments that existed during rifting of the basin. Interpretation of the various depositional environments will depend on comparison of sedimentologic logs from the Wadesboro sub- basin with established facies models (e.g. Cant and Walker 1978) and well- documented sections from other Triassic rift basins (e.g. Olsen et al. 1996). To address this problem, a detailed study of a brick quarry in Anson County, NC, has been initiated. The facies established in the clay pit will be used to extend a geologic map to those portions of the basin that lack good exposures. Hypothesis 2: Geologic mapping of the central portion of the Wadesboro sub- basin (an area equivalent to a standard USGS 7.5 quadrangle) will provide

9 information about thicknesses, attitude and distribution of stratigraphic units. This map will identify faults, joints, and possibly folds within the sub- basin. Progressive changes in dip could provide information about the amount and timing of fault motion on the margins of the rift basin. The distribution of Oluvial channel deposits could provide information about the fault control on the basin (e.g. Alexander and Leeder 1987). Hypothesis 3: Petrographic analysis of sandstones could provide information about provenance and tectonic setting (e.g. Dickinson 1985). Petrographic analysis of major constituents could be supplemented by heavy mineral analyses using both heavy liquids and magnetic separation to segregate the heavy mineral assemblages. Mineralogy of the mudstones will be analyzed using X- ray diffraction. Hypothesis 4: The facies analysis and geologic mapping could provide information about the thickness and lateral extent of organic- rich lacustrine facies. Combined with estimates of total organic content (TOC) and depth of burial derived from vitrinite reolectance data, it may be possible to establish whether suitable sediments have entered the hydrocarbon window. Natural gas and other hydrocarbon resources have been identioied in the adjacent Sanford sub- basin of the Deep River group (Reid and Milici 2008). This study proposes to document the geometry, sedimentology, depositional environments and economic potential of the Wadesboro sub- basin. Central to this study is the detailed study of the sedimentology, stratigraphy and provenance of 87 meters of exposure in a brick quarry that is located in the geographic center of the Wadesboro sub- basin. The facies and stratigraphy developed from the detailed

10 work at that quarry will be extended to a map area comprising the southern half of the Wadesboro sub- basin which is generally characterized by limited and poor exposures. V. PRELIMINARY RESULTS Fieldwork in a clay pit in Anson County, N.C. has been conducted in which 87 meters of continuous exposure was sedimentologically described, sampled, and logged (Appendix A). This stratigraphic work has identioied 7 distinct lithofacies: 1) a cyclic Oining upward facies m; 2) an interbedded sand and siltstone facies m; 3) a channelized deposit m; 4) a massive mudstone facies m; 5) an interbedded mudstone, siltstone, and sandstone facies m; 6) an interbedded mudstone and siltstone with alternating gray and red beds m; and 7) an organic rich gray shale in the lowest exposed section of the pit located at 1.7-0m with a base not seen. Facies 1 contains 7 cyclic Oining upward sequences, possibly climactically inoluenced, that grade from Oine sandstone to siltstone and is interpreted as a proximal Olood plain facies as crevasse splays were accreted onto a Olood plain dominated by silt and clay. Facies 2 is not obviously cyclic but does display similar Oining upward sequences as identioied in facies 1. Facies 2 contains coarser grained sandstones that generally Oine upward, interbedded with siltstones and is interpreted as a proximal Olood plain facies when the channel was closer than facies 1. Facies 3 is interpreted as a channelized Oluvial deposit reaching 7m at its thickest extent and spanning ~50m laterally that has eroded into facies 4 and contains very coarse grained to granular sandstones that Oine upward to medium sandstone.

11 Trough cross stratioication is visible in the deposit and a paleo- Olow direction of azimuth 190 was measured suggesting axial basin Olow. Facies 4 is a massive, red, silty- mudstone with numerous crosscutting veins of calcite.5-2cm thick with very few thin beds of siltstone and very Oine sandstone 5-10cm thick. This facies is interpreted as a distal Oloodplain facies as the dominant grain size is silt and clay and thin beds of siltstone and sandstone that may have been deposited during large Olood events. The bright red color and mottled texture of this facies suggests an oxidizing environment and a vegetated surface, however, the presence of paleosols was not observed in the Oield. Facies 5 contains siltstone beds 1-2m thick interbedded with Oine to medium sandstones and small- scale coarsening upward sequence with cross trough laminations and is interpreted as a Oluvial- dominated delta. Facies 6 represents a departure from Oluvial dominated depositional environments and a transition to shallow lacustrine facies. This facies is comprised of siltstone and silty- mudstones that alternate color from gray to red. This cyclic color change is interpreted as a function of oxidizing and reducing environment as a lacustrine transgression and regression. Desiccation cracks at the tops of gray siltstone beds evidence periods of aridity and variable lake levels, which allowed the subsequently deposited sediments to be oxidized. Facies 7 is partially exposed in the clay pit and is comprised of gray shale and is interpreted as lacustrine in origin. This bed is of interest for its potential to produce natural gas, however, initial Total Organic Carbon (TOC) analysis does not support this view. There is anecdotal evidence of numerous vertebrate fossils in facies 7, however, none were found during preliminary Oield work.

12 Additional measured section of an outcrop on the CSX rail line near Russellville at Bogan Cut Road was logged. The Bogan Cut outcrop is composed of channelized deposits of gray, coarse to medium grain lithic arenite sandstone with lenses of dark gray, Oine grained low- Olow deposits and alternating beds of red, very Oine sandstone overbank deposits. This outcrop was Oirst described by Russell 1892 and is described as a normal fault dominated environment, however, this interpretation is rejected in place of a Oluvial dominated environment with evidence of only 1 normal fault with a throw of ~1.5m. The measured section for Bogan Cut can be found in Appendix B. Preliminary petrographic analysis of selected sandstones within the clay pit has been conducted by examining thin sections of sandstone units within the pit and by preforming XRD analysis of those thin sections. Dominant mineralogies include quartz, feldspar, and calcite (a likely precipitating cement). Data from this analysis can be found in Appendix C. Additional Oieldwork has been conducted in the basin surrounding the clay pit by examining roadside outcrops and those along rail lines. This preliminary Oieldwork will contribute to a detailed bedrock geologic map of the basin with the clay pit at the center point. Outcrop lithologies, bed attitude (where available), and location have been digitally mapped (Appendix D). Sandstone samples from basin outcrops, as well as samples from within the clay pit, have been processed using the Frantz magnetic barrier separator to determine weight percentages of magnetic mineral facies (Table 1), which will be used to infer changes in sediment provenance.

13 Magnetic Mineral Facies Facies 1 Non- Magnetic Facies 2 Flux 0.40 Amp Facies 3 Flux 0.80 Amp Facies 4 Flux 1.50 Amp Mineralogy Quarts, Feldspar, Calcite, Zircon, Rutile, Apatite, Corundum, Fluorite, Sillimanite Garnet, Ilmenite, Chromite, Chloritoid, Olivine Biotite, Hornblende, Hypersthene, Augite, Actinolite, Staurolite, Epidote, Chlorite Muscovite, Spinel, Enstatite, Tourmaline, Clinozosite, Diopside, Tremolite Table 1. Magnetic mineral facies assemblages, from Rosenblum, 1958) Magnetic separation data has been arranged perpendicular to basin strike (NW to SE) in order to capture changes in mineralogy over time that may indicate changes in sediment provenance (Figure 2). Figure 2. Cross sectional magnetic mineral facies distribution within Wadesboro sub- basin, perpendicular to basin strike by wt.%. The data shows three areas in the basin with a higher percentage of magnetic minerals. Little correlation can be discerned from the current, small data set, furthermore, additional analysis will be conducted to measure the effects of weathering on the magnetic susceptibility of minerals within a lithology. The magnetic data collected from the clay pit samples sandstones over the extent of the exposure includes the interpreted lacustrine and Oluvial facies and are identioied in Appendix A (Figure 3).

14 Figure 3. Magnetic mineral facies distribution up section in a clay pit in Anson County, N.C. Location of samples noted in Appendix A. The clap pit samples contained anomalously higher weight percentages of magnetic minerals than were identioied in samples from the surrounding basin. This may be a result of FexOx coating mineral grains freshly exposed in the pit than may be leached with continued surface exposure. VI. TIMELINE Conducting Research (Summer 2012, by week) Contact Land Owners X X X Complete Field Work X X X X X X Lab Analysis X X X X X X Conducting Research (Fall 2012, by week) Conduct Research for Study X X X X X X X X X X X X X X X X X Lab Analysis X X X X X X X X X X X X X X X X X Analyze data from research X X X X X Writing and Defending Dissertation (Spring 2013, by week) Outline Dissertation X Update Proposal Chapters For Dissertation X X X X X Write Results Chapter X X X X X X X Write Summary and

15 Conclusions Chapter X X X X X X X Polish Writing X X X X Defend Dissertation X X X Minor Revisions X X Graduate X

16 VII. REFERENCES Clark, T.W., Gore, P.J., and Watson, M.E., 2001, Depositional and structural framework of the Deep River Triassic basin, North Carolina, in Hoffman, C.W., ed. Field Trip Guidebook for the 50th Annual Meeting of the Southeastern Section, Geological Society of America, Raleigh, North Carolina, p Dickinson, W.D., 1985, Interpreting provenance relations from detrital modes of sandstone, in Zuffa, G.G., editor, Provenance of Arenites: Dordrecht, Holland, Reidel p Hubert, J.F., A zircon-tourmaline-rutile maturity index and the interdependence of the composition of heavy mineral assemblages with the gross composition and texture of sandstones. Journal of Sediment and Petrology, v.32, p Lambiase, J. J., and Bosworth, W., 1995, Structural controls on sedimentation in continental rifts, in Lambiase, J.J., ed., Hydrocarbon habitat in rift basins: Geological Society Special Publication 80, p Letourneau, P.M., and Olsen, P.E. (Eds.), 2003, The Great Rift Valleys of Pangea in Eastern North America, Volume 1: Tectonics, Structure, and Volcanism: Columbia University Press. McLennan, S.M., Hemming, S., McDaniel, D.K., Hanson, G.N., 1993, Geochemical approaches to sedimentation, provenance, and tectonics. In: Johnsson, M.J., Basu, A. (Eds.), Processes Controlling the Composition of Clastic Sediments. Special Paper, Geologic Society of America, v. 284, p Olsen, P.E., Froelich, A.J., Daniels, D.L., Smoot, J.P., and Gore, P.W., 1991, The Geology of the Carolinas: North,, p Olsen, P.E., Kent, D.V., Cornet, B., Witte, W.K., and Schlische, R.W., 1996, High-resolution stratigraphy of the Newark rift basin (early Mesozoic, eastern North America): Geological Society of America Bulletin, v. 108, no. 1, p , doi: / (1996)108<0040:HRSOTN>2.3.CO;2. Randazzo, A.F., Swe, W., and Wheeler, W.H., 1970, A study of tectonic influence on triassic sedimentation - the Wadesboro Basin, Central Piedmont: Journal of Sedimentary Petrology, v. 40, no. 3, p Reid, B.J.C., Milici, R.C., and Survey, U.S.G., 2008, Hydrocarbon Source Rocks in the Deep River and Dan River Triassic Basins, North Carolina: North,. Reinemund, J.A., 1955, Geology of the Deep River coal field, North Carolina: U.S. Geological Survey Professional Paper 246, 159 p. Schlische, R.W., 1993, TRIASSIC-JURASSIC CONTINENTAL RIFT SYSTEM, EASTERN NORTH AMERICA: America, v. 12, no. 4, p Schlische, R.W., and Olsen, P.E., 1990, Quantitative filling model for continental extensional basins with applications to Early Mesozoic rifts of Eastern North America: The Journal of Geology, v. 98, no. 2, p Tiercelin, J.J., 1990, Rift-basin sedimentation : responses to climate, tectonism and volcanism. Examples of the East African Rift: Journal of African Earth Sciences, v. 10, no. 1, p Weltje, G.J. & von Eynatten, H. 2004, Quantitative provenance analysis of sediments: review and outlook.- Sedimentary Geology, v.171, p. 1-11

17 Zablocki, F.S., 1959, A gravity study of the Deep River-Wadesboro Triassic basin of North Carolina: (Unpubl. MS Thesis) University of North Carolina at Chapel Hill, North Carolina, 44 p.

18 VIII. APPENDIX A Anson County Clay Pit Stratigraphic Column

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23 IX. APPENDIX B Bogan Cut Stratigraphic Column

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27 X. APPENDIX C Anson County Clay Pit XRD Analysis TBQ00-02 Tbq 00-2 Phase Mineral Figure of Merit Major Quartz 1.9 Major Albite- high 6 Minor Quartz 3.3 Minor Albite- high 6 Trace Quartz 10.2 TBQ01-05 Tbq Phase Mineral Figure of Merit Major Quartz 1.4 Major Calcite 4.3 Major Albite- high 9.4 Minor Albite- low 5.7 Minor Calcite 5.9 Minor Quartz 6.6 Minor Cuprite 7 Minor Cristolobite 7.4 Minor Wurtzite 8.3 Minor Corundum 9.4 Trace Albite- high 4.6 Trace Calcite 6.3 Trace Corundum 6.7 Trace Wurtzite 7.4 Trace Cobalite 9.8 TBQ Tbq Phase Mineral Figure of Merit Major Quartz 2.8 Major Albite- low 6 Major Cristobolite(low) 6.1 Major Topaz 8.2

28 Major Calcite 9.4 Minor Calcite 5.4 Minor Quartz 6.1 Minor Corundum 7.1 Minor Chalcopyrite 7.5 Minor Cristobolite(low) 7.7 Minor Albite- low 7.9 Trace Calcite 7.4 Trace Quartz 8.4 Trace Albite- low 9.6 Trace Cristobolite(low) 9.7 TBQ Tbq Phase Mineral Figure of Merit Major Quartz 1 Major Albite- high 6 Major Analcime 8.6 Major Calcite 9.5 Minor Quartz 3.9 Minor Cuprite 6.4 Minor Albite 7.4 Minor Analcime 10 Trace N/a <10.0 TBQ Tbq Phase Mineral Figure of Merit Major Quartz 1.9 Major Analcime 8.3 Major Cristobolite(low) 9.2 Minor Quartz 3.7 Minor Albite- low 5.7 Minor Calcite 8.1 Minor Cuprite 9.1 Trace Lime 6.1 Trace Beryll 7.7 Trace Silicon 9.4

29 TBQ Tbq Phase Mineral Figure of Merit Major Quartz 1.8 Major Albite- low 7.3 Major Calcite 9.8 Minor Calcite 6 Minor Quartz 1.8 Minor Cristobolite(low) 7.3 Minor Albite- low 3.6 Trace Calcite 2.9 Trace Lime 6 Trace Albite- low 2.7 Trace Halite 8.8 XI. APPENDIX D Outcrop map of southern- central portion of Wadesboro sub- basin

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