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GEOLOGY OF THE SOUTHEAST DURHAM AND SOUTHWEST DURHAM 7.5-MINUTE QUADRANGLES, NORTH CAROLINA By N.C. DOCUMENTS Charles W. Hoffman and Patricia E. Gallagher CLEARINGHOUSE BULLETIN 92 MAR 23 1990 N.C, STATE LIBRARY RALEIGH •n«** >$j»v NORTH CAROLINA GEOLOGICAL SURVEY DIVISION OF LAND RESOURCES DEPARTMENT OF NATURAL RESOURCES AND COMMUNITY DEVELOPMENT GEOLOGICAL SURVEY SECTION The Geological Survey Section examines, surveys, and maps the geology, mineral resources, and topography ofthe state to encourage the wise conservation and use ofthese resources by industry, commerce, agriculture, and government agencies for the general welfare of the citizens of North Carolina. The Section conducts basic and applied research projects in environmental geology, mineral resource exploration, and systematic geologic mapping. Services include identifying rock and mineral samples submitted by citizens and providing consulting services and specially prepared reports to agencies that need geological information. The Geological Survey Section publishes Bulletins, Economic Papers, Information Circu-lars, Educational Series, Geologic Maps and Special Publications. For a list of publications or more information about the Section please contact the Geological Survey Section at P.O. Box 27687, Raleigh, North Carolina 2761 1-7687, or call (919) 733-2423. Jeffrey C. Reid Chief Geologist GEOLOGY OF THE SOUTHEAST DURHAM AND SOUTHWEST DURHAM 7.5-MINUTE QUADRANGLES, NORTH CAROLINA By Charles W. Hoffman and Patricia E. Gallagher BULLETIN 92 NORTH CAROLINA GEOLOGICAL SURVEY DIVISION OF LAND RESOURCES RALEIGH 1989 STATE OF NORTH CAROLINA DEPARTMENT OF NATURAL RESOURCES AND TAA/nrcr mad™ rnvi?DMnp COMMUNITY DEVELOPMENT JAMES G. MARTIN, GOVERNOR WILLIAM W. COBEY, JR., SECRETARY CONTENTS Page Abstract 1 Introduction 1 Location 1 Objectives, Scope, and Methods 1 Conventions 3 Geologic Setting 3 Previous Work 4 Geology 6 Igneous and Metamorphic Rocks 6 Carolina Slate Belt Rocks 6 Diabase 6 Sedimentary rocks 8 Lithofacies Association I 8 Trcs/sij - Sandstone With Inter-bedded Siltstone 8 Description 8 Localities 10 Interpretation 10 Lithofacies Association II 10 Trcs/si 2 - Sandstone With Inter-bedded Siltstone 13 Description 13 Localities 13 Interpretation 13 Trcsi/s -Siltstone With Interbed-ded Sandstone 14 Description 14 Localities 16 Interpretation 16 Lithofacies Association III 16 Page Trcs - Sandstone 17 Description 17 Localities 17 Interpretation 18 Trcsc - Pebbly Sandstone 18 Description 18 Localities 19 Interpretation 19 Trcs/c - Sandstone With Interbed-ded Conglomerate 19 Description 19 Localities 19 Interpretation 21 Tree - Conglomerate 21 Description 21 Localities 21 Interpretation 21 Structure 24 Discussion 24 Depositional model 24 Paleoclimate 26 Conclusions 26 Acknowledgements 27 References Cited 27 Appendices A. Mineralogical Composition of Sandstones 30 B. Locality Register 31 C. Geochemical Data For Diabase 34 ILLUSTRATIONS Plates (in pocket) 1. Geologic map of Southeast Durham 7.5-minute Quadrangle 2. Geologic map of Southwest Durham 7.5-minute Quadrangle Figure Page 1. Location map 2 2. Newark rift system basins of eastern North America 4 3. Weight percent Ti02 versus Mafic Index (Fe 2 3 */(Fe 2 3 *+MgO)) for representative diabase samples 7 ILLUSTRATIONS (continued) Figure Page 4. Generalized distribution of lithofacies and major diabase bodies 9 5. Outcrop of Trcs/sij fades exposed at Locality 1 11 6. Outcrop of Trcs/sij facies exposed at Locality 2 12 7. Section of Trcs/si 2 facies exposed at Locality 7 14 8. Composite section of Trcs/si 2 facies ex-posed in Borden Brick and Tile Hoover Road Quarry (Locality 8).... 15 9. Ternary plot of sandstone composition 16 10. Tics facies exposed in excavation east of Page Road (SR 1973) at 1-40 (Locality 14) 17 11. Excavated block of bioturbated Trcs sandstone at Locality 15, Southern Parkway west of U.S. 70 17 Figure Page 12. Section of Trcs facies exposed at Locality 16, west side of Miami Boulevard (SR 1959) north of 1-40 18 13. Outcrop of Trcsc facies on Kemp Road (SR 1902) east of junction with Virgil Road(SR 1903) (Locality 20) 20 14. Interbedded sandstone and conglom-erate of Trcs/c facies at Raleigh- Durham International Airport 21 15. Jonesboro fault at Locality 26 in Leesville Industrial Park 22 16. Ditch excavation on north side of Trusswood lot, Leesville Industrial Park (Locality 27) 23 17. Sketch diagrams of proposed depositional models 25 u GEOLOGY OF THE SOUTHEAST DURHAM AND SOUTHWEST DURHAM 7.5-MINUTE QUADRANGLES, NORTH CAROLINA Bulletin 92 By Charles W. Hoffman and Patricia E. Gallagher ABSTRACT INTRODUCTION The Southeast Durham and Southwest Durham 7.5- minute Quadrangles include a 26 kilometer transect of the Durham Triassic basin from the Jonesboro fault on the south-eastern side of this half-graben structure to a bounding un-conformity on the northwestern side. The basin is filled with non-marine, primarily fluvial, clastic deposits of the Late Triassic Chatham Group. The Chatham Group rocks are intruded by Early Jurassic diabase as dikes and sheets. Bordering rocks are pre-Mesozoic intrusive, metavolcanic and metasedimentary rocks of the Carolina slate belt. Within the Triassic sedimentary rocks, three litho-facies associations comprised of seven distinct lithofacies form three belts that generally conform to the trend of the basin. The western association is comprised of a single lithofacies consisting ofsandstone with interbedded siltstone. The central association is comprised of two lithofacies, sand-stone with interbedded siltstone and siltstone with interbed-ded sandstone. The eastern association is comprised of four lithofacies; sandstone, pebbly sandstone, sandstone with interbedded conglomerate, and conglomerate. The western lithofacies association consists of mud-clast-rich, trough crossbedded, arkosic sandstone interspersed with locally thick siltstone beds. The unit is interpreted to represent sandy braided streams flowing within fine-grained interstream areas. The central lithofacies association consists ofarkosic, fining-upward, meandering stream deposits in the northern part of its area. To the south, in the upper part of its section, this lithofacies association grades to a muddy system dominated by fine-grained overbank fluvial and lacustrine deposits with intercalated sandstone. The eastern lithofacies association consists of conglomerates along the border fault and grades basinward through interbedded sandstone and conglomerate to pebbly sandstone and then to muddy sandstone. Adjacent facies exhibit both intertonguing and gradational relation-ships. This set oflithofacies is interpreted to represent basin-margin alluvial fan deposits that prograded from a southeast-ern highland. LOCATION The Southeast Durham and Southwest Durham 7.5-minute Quadrangles encompass an area of approximately 300 square kilometers. The quadrangles include a large part ofthe Durham Tri-assic basin and small areas of the adjacent Pied-mont region (figure 1). A significant amount of the study area is urban and suburban. Large portions of Durham, Research Triangle Park, and Raleigh- Durham International Airport are located within the study area as are developing sections ofRaleigh and Chapel Hill. OBJECTIVES, SCOPE, AND METHODS Adequate land use planning and resource management require, among many other things, sound baseline information on a variety of proper-ties that are directly related to geology. Such information includes soil types and their ability to bear weight, maintain a slope, or transmit fluid; groundwater quality and quantity; mineral resource potential (especially aggregates for highway and building construction); and potential geologic hazards such as landslides or radon gas. In the rapidly urbanizing Research Triangle area, where proper planning is basic to maintaining a desirable quality of life, the need for accurate geologic maps at a suitable scale is vital. This study was undertaken to meet these — 36° "<y / Sanf v ' Wadesboro I Durham basin ord basin >asin > 80° 1 Durham J* STUDY AREA Raleigh ^ 78° 1 76° 1 lOOmi -34° 100km Figure 1. Map of North Carolina showing location of study area within the Durham Triassic basin. needs. The specific objective was to provide de-tailed surface geologic mapping of the study area. Toward this end, lithofacies within the Triassic sedimentary rocks of the two quadrangles were identified and mapped. The lithofacies are defined chiefly by field criteria including mineralogical composition and sedimentary textures and struc-tures. Binocular and petrographic examination of selected samples was conducted to support and refine the field descriptions. Thin-section point count data are tabulated in Appendix A. Additionally, Jurassic diabase bodies and the contact between Triassic sedimentary rocks and pre-Mesozoic crystalline rocks were mapped. The distribution of pre-Mesozoic crystalline rock lithologies was compiled from existing sources (Parker, 1979; Wilson and Carpenter, 1981; North Carolina Geological Survey, 1985). Other than to delineate the contact between these rocks and the Triassic sedimentary rocks, the crystalline rocks were not investigated. The distribution ofalluvium was interpreted from topographic and soils maps. The quadrangle maps included in this re-port (Plates 1 and 2, in pocket) have been reduced in scale for publication. Full size ( 1 :24,000 scale) diazo prints of the quadrangle maps (with topogra-phy) are available separately as North Carolina Geological Survey Open-File Reports 89- 1 (South-east Durham Quadrangle) and 89-2 (Southwest Durham Quadrangle). Outcrop within the two quadrangles is limited and generally poor because of deep weath-ering and extensive soil development. Total out-crop area is estimated to be less than two percent. Except in the upper reaches of tributary streams, alluvium masks outcrop within most portions of the drainage system. These streambed outcrops usually provide little vertical exposure but do yield representative samples for grain size and textural observations. Roadside ditches and road cuts also expose some bedrock, however primary deposi-tional features such as bedding orientation and sedimentary structures are obscured by weathering in most of these outcrops. Three quarries operated by Borden Brick and Tile Company (a division of Cherokee Sanford Group) are within the study area and provided some of the better sections during the study. Key exposures examined for the project are listed in the Locality Register (Appendix B). Additionally, information was provided by temporary exposures created by construction ac-tivity. Construction in progress during this project included excavation for the Southern Parkway (no Wake County Secondary Route (SR) number as-signed to date) from Alexander Drive (SR 2028) at Miami Boulevard (SR 1959) to U.S. 70, major expansion of Burroughs-Wellcome and Glaxo pharmaceutical companies in Research Triangle Park, excavation for a sewer line along Stirrup Iron Creek from Chin Page Road (SR 1969) to Page Road (SR 1973), initial development ofACC park north of U.S. 70 between Mt. Herman Road (SR 1646) and Sycamore Creek, and numerous smaller scale activities. Excavation for the 10,000 foot runway (5R - 23L) at Raleigh-Durham Interna-tional Airport and for Interstate 40 from the Dur-ham Freeway (N.C. 147) to U.S. 15-501 pre-dated this project but engineering data and interviews with personnel associated with those activities were utilized. CONVENTIONS Several conventions used in this report may not be familiar or evident to some readers. One is the terminology and symbols used to identify the sedimentary lithofacies. These are based on a system used by the U.S. Geological Survey for Newark Supergroup rocks of the eastern United States early Mesozoic basins (Smoot, Froelich, and Luttrell, 1988). The standardized symbols and terms facilitate interbasin and intrabasinal com-parisons ofdepositional units. In this report the age (Tr = Triassic) and group (c = Chatham Group) are common to all of the Triassic lithofacies. Trc is followed by a symbol for the major or characteris-tic lithology (c = conglomerate, sc = pebbly sand-stone, s = sandstone, and si = siltstone) to further designate the lithofacies. Subscript numerals dif-ferentiate similar lithologies of different facies and interbedded lithologies are separated by a slash (/) with the dominant lithology being given first. For example, "s/si" denotes sandstone with interbed-ded siltstone. This report does not apply formal nomen-clature below group rank. Until additional detailed facies mapping is completed over a wider area and until subsurface relationships are better under-stood, it is inappropriate to apply formal nomencla-ture below group rank to rocks of the Durham basin. Many of the rock descriptions, mainly in the figured geologic sections, include standard color names based on the Rock-Color Chart pre-pared by The Rock Color Chart Committee (1948) and distributed by the Geological Society ofAmer-ica. Both English and metric units are used. Distances that are likely to be measured with a motor vehicle's odometer are given as miles; oth-erwise metric units are used. Another convention is in the identification of streets, roads, and highways. Generally, the street or road name is given first and followed in parentheses by the state route number. This is because much of this area is urban or becoming urban and signs and local recognition are generally based on street or road names rather than route numbers (although the quadrangle maps generally show only the route numbers). In some cases, streets within private developments are not state maintained and Secondary Route (SR) numbers do not apply. GEOLOGIC SETTING The Durham basin is part of a series of extensional basins in eastern North America that developed during rifting in the early Mesozoic. This rifting event resulted in the separation of the North American and African plates. Approxi-mately 20 "synrift" basins, collectively identified as the Newark rift system, are exposed along the North American continental margin from South Carolina to Nova Scotia (figure 2). Many other, presumably coeval, basins have been interpreted to lie beneath the late Mesozoic and Cenozoic sedi-ments of the Atlantic Coastal Plain and adjacent continental shelf (for example Benson, 1984). Newark rift system basins contain Late Triassic and Early Jurassic non-marine clastic 100 100 -h- 200 200 300 MILES I 300 400 KILOMETERS EXPLANATION 1. Wadesboro(N.C.-S.C) 2. Sanford (N.C.) 3. Durham (N.C.) 4. Davie County (N.C.) 5. Dan River and Danville (N.C. -Va.) 6. Scottsburg (Va.) 7. Basins north of Scottsburg (Va.) 8. Farmville (Va.) 9. Richmond (Va.) 10. Taylorsville (Va.) 11. Scottsville (Va.) 12. Barboursville (Va.) 13. Culpeper(Va.-Md.) 14. Gettysburg (Md. - Pa.) 15. Newark (N.J.- Pa. -N.Y.) 16. Pomperaug (Conn.) 17. Hartford (Conn. - Mass.) 18. Deerfield (Mass.) 19. Fundy or Minas (Nova Scotia -Canada) 20. Chedabucto (Nova Scotia -Canada) <igure 2. Newark rift system basins of eastern North America (from Froelich and Olsen, 1984). deposits of fluvial and lacustrine origin with inter-bedded evaporites and basaltic flows. These rocks form the Newark Supergroup (Froelich and Olsen, 1984). Interbedded basalt flows belonging to the Newark Supergroup are limited to basins from Virginia northward. A second Early Jurassic epi-sode of intrusion by diabase dikes, sheets, and sills occurred. These intrusions are concentrated mainly in the Carolinas and are sparse to absent in the more northern basins (ManspeizerandCousminer, 1988). Due to their cross-cutting relationships and post-depositional emplacement, these rocks are not included in the Newark Supergroup. The Durham basin, and the Sanford and Wadesboro basins to the south, form a 240-kilome-ter- long by up to 26-kilometer-wide structureknown as the Deep River basin (figure 1). The individual basins are separated by cross-trending structural highs named the Colon cross structure (between Durham and Sanford basins) and the Pekin cross structure (between Sanford and Wadesboro ba-sins). Sedimentary rocks of the Deep River basin of Chatham County were named the Chatham series by Emmons (1857). Subsequently, the term Chatham Group has been used to include all the Late Triassic (Carnian) rocks of the Deep River basin (Froelich and Olsen, 1984; North Carolina Geological Survey, 1985). The Durham basin is a half-graben struc-ture within crystalline rocks of the Piedmont re-gion. It is down-faulted on the southeastern margin and bounded on the west mainly by an uncon-formity. Locally, the western border is formed by minor southeast dipping high-angle normal faults . The eastern border fault was named the Jonesboro fault (Campbell and Kimball, 1923) for an expo-sure in Lee County . It dips northwestward at a high angle. PREVIOUS WORK Very little detailed geologic work has been published on the Durham basin. Harrington (1951) mapped the basin's western border at a scale of approximately 1:125,000. The 1977 Carolina Geological Society Field Trip Guidebook (Bain and Harvey, 1977) contains a reconnaissance geo-logic map of the Durham basin at a scale of 1:250,000 which has been extensively referenced by subsequent investigators. Bain and Harvey's map was used in the compilation of the Geologic Map ofNorth Carolina (North Carolina Geological Survey, 1985). Wheeler and Textoris (1978) described several occurrences of chert and limestone within the Durham basin. They concluded that the chert and limestone were precipitated under semi-arid to arid conditions in and along the margins of playa lakes that formed during wet climatic periods and evaporated during subsequent dry periods. Their study constitutes the only published detailed petro-graphic analysis of Durham basin chert and car-bonate. In his reporton the geology ofWake County, Parker (1979) mapped a portion of the Durham basin along with the crystalline rocks ofthe county. He recognized three belts or facies within the Triassic sedimentary rocks: a fanglomerate belt adjacent to the eastern border fault, a sandstone-mudstone belt basinward of the fanglomerate, and a limestone-chert belt basinward of the sandstone-mudstone. Heregarded these belts as lateral equiva-lents that persisted vertically through the sedimen-tary section. The metavolcanic and metasedimen-tary rocks immediately adjacent to the Durham basin on its southeast side was termed the Cary se-quence. Bain and Brown (1980) characterized the structure and sedimentation of the "Durham Trias-sic basin" (Deep River basin of current usage) using a variety of geophysical tools including seis-mic reflection and refraction, gravity, resistivity, and aeromagnetic surveys. Their study is the most extensive work on the structural aspects of the Deep River basin. Most of their work specific to the Durham basin, however, was conducted south of the Southeast and Southwest Durham Quad-rangles. One key finding was that the basin's eastern border is a step-faulted zone several kilo-meters wide. From this observation Bain and Brown (1980) inferred that, contrary to conven-tional thinking, some of the border conglomerates may be older than more basinward strata. They also inferred that the basin was faulted longitudi-nally and transversely to create individual horsts and grabens as small as 1 kilometer wide by 3 kilo-meters long and that most of these are rotated east to southeast by post-depositional faulting. Dis-placement of at least 300 to 600 meters was in-ferred along the largest inrrabasin fault, the Bonsal- Morrisville fault, which trends northeast- south-west and terminates at approximately the Durham- Chatham County line about 2 miles south of Nel-son. Wilson and Carpenter (1981) compiled the work ofHarrington (1951) and Parker ( 1 979) along with unpublished mapping of the Durham basin as part of a five-county report. In their report, the name Sanford Formation was applied to all Trias-sic strata of the Durham basin. Bain and Harvey (1977) had previously argued that the stratigraphic nomenclature of the Sanford basin (Sanford, Cumnock, and Pekin Formations) proposed by Reinemund (1955) was not applicable to the rocks of the Durham basin. The bulk of Wilson and Carpenter's (1981) report dealt with crystalline rocks of the Piedmont that surround the Durham basin. Diabase of the eastern United States early Mesozoic basins has been the object of many studies on many scales (see summary in Froelich and Gottfried, 1985). Investigations by Ragland and others (1968) andWeigand and Ragland( 1970) contain data on the petrography and geochemistry of some Durham basin diabase dikes. Several of the dikes examined in those reports are located in the project area. Gore (1986) compiled a field trip guide-book for the Durham and Sanford basins which includes contributions by several other authors. That publication reviews much of the previous work and presents new data as well. GEOLOGY IGNEOUS AND METAMORPHIC ROCKS Carolina Slate Belt Rocks The Durham basin is bordered on both sides by metavolcanic and metasedimentary rocks of the Carolina slate belt (North Carolina Geologi-cal Survey, 1985). Parker (1979) described crys-talline rocks of a 1.5- to 3.0-kilometer-wide belt adjacent to the Jonesboro fault as "dacitic and an-desitic metatuffs and flows with phyllite, meta-siltstone, pebbly arkose, and ilmenite-magnetite quartzite." Several small adamellite bodies are interspersed within the mixed lithology unit. The term "Cary sequence" was used by Parker (1979) for these rocks. To the west of the Durham basin, within the northwest corner of the study area, Wilson and Carpenter (1981) mapped two units. They named one " felsic igneous complex" and the other "felsic crystal tuffs and felsic tuffs." Diabase Early Jurassic diabase dikes and sheets intrude the Triassic strata of the Durham basin. The diabase is dark gray to black, fine to medium crystalline, and composed mainly of an interlock-ing mosaic of equigranular plagioclase feldspar, clinopyroxene (commonly augite), and olivine (Froelich, written communication, 1988). Aphanitic "chill margins" were observed in a few outcrops. Coarse crystalline textures occur in some of the thicker diabase bodies. A distinctive "knobby" weathering texture caused by very large (1 to 2 centimeters) clinopyroxene oikocrysts is notice-able in some outcrops of a large diabase body in the Oak Grove area. Diabase commonly weathers into spheroidal boulders with a dark-yellowish orange (10YR 6/6) surface stain and yields a characteris-tic yellow-orange soil. Weigand and Ragland (1970) classified Mesozoic dolerite dikes of eastern North America. They recognized both quartz-normative and oli-vine- normative bodies and subdivided the quartz-normative type into high-Ti0 2, low-TiO z, and high Fe^*1 sub-types. They observed that quartz-nor-mative dikes are the dominant variety from Nova Scotia to Maryland, olivine-normative dikes are dominant in the Carolinas, and both types occur in approximately equal proportions in Virginia and Georgia. Figure 3 shows weight percent Ti0 2 versus mafic index (Fe 2 3 */(Fe 2 3*+MgO)) for representative eastern North American diabase dikes reported elsewhere (Ragland and others, 1968 ; Weigand and Ragland, 1970) along with new val-ues for two diabase bodies from the Southeast and Southwest Durham Quadrangles. Two of the plot-ted values, DDH- 1 and DDH-2, are from drill core from the Oak Grove diabase sheet. These fall within the typical compositional range for olivine-normative dikes (samples provided by Nello Teer Company; analyses performed by J. D. Arthur, Florida State University, and provided by A. J. Froelich). Another plotted value, JY(2), is from the large north-south trending dike in the south-central portion of the Southwest Durham Quad-rangle. This dike plots as a high-Ti0 2 quartz-nor-mative type (samples collected as part ofthis study; analyses performed by J. Taggart, A. Bartel, and D. Siems, U.S. Geological Survey, and provided by A. J. Froelich). Contact metamorphic aureoles of hornfels or "baked" sedimentary rocks occur in strata in-truded by diabase. These blackened and hardened zones are commonly about half as wide as the dike and typically exhibit closely spaced parallel frac-tures. Such fracture patterns locally continue straight across the sedimentary-igneous contact without interruption and are interpreted as cooling features. Where diabase intruded lithologies of varying porosity, for example a unit of interbedded sandstone and mudstone, the thickness and inten-sity of alteration within the contact aureole is highly irregular. Coarse-grained arkose is espe-cially distinctive where thermally metamorphosed. Superficially, the baked arkose resembles granite. 1 Fe 2 3 * = Fe 2 3 + FeO o OX) + a* fa fa a» a 76 — 72 — *? 68 — 64 — 60 — 56 — u 48 — 44 0.2 high Fe.O * quartz-nomiative low TiO.quartz-noimative high Ti02 quartz-normative olivine-normative i— i 1— r 0.4 0.6 1—i—i—i— r 0.8 1.0 1.2 1.4 Weight Percent Ti0 2 Figure 3. Plot of weight percent TiO versus Mafic Index (weight percent Fe,0 */(Fe2 '2~3* + MgO)) for representative diabase dikes reported by Weigand and Ragland (1970) and Ragland and others (1968) (•) and for newly analyzed samples (). Four major diabase chemical types are shown. See Appendix C for table of analyses and key to samples. Diabase dikes occur throughout the two quadrangles. The dikes are generally linear; how-ever, detailed mapping shows that some are sinu-ous. Thickness is highly variable, both within indi-vidual dikes and from one dike to another. Ob-served dikes were as thin as 5 centimeters and as thick as over 100 meters. Dikes are usually steeply dipping to vertical. The Durham and Sanford basins contain the southernmost known occurrences of sheet- like diabase bodies within the eastern U.S. early Meso-zoic basins (Froelich and Gottfried, 1985). Fro-elich and Gottfried (1985) define the term "sheet" (as applied to Newark Supergroup diabase bodies) to "embrace all ofa great variety offorms displayed by the intrusive diabase other than vertical or steeply inclined dikes ...." The term "sill" has been used by some workers (Wilson and Carpenter, 1981; North Carolina Geological Survey, 1985) to describe the larger diabase bodies of the Durham basin. Structural observations and drill data, however, indicate that these bodies are discordant to the sedimentary strata. For example, the Oak Grove diabase sheet dips northward at a moderate angle of 25°-40° (Nello Teer Company, unpub-lished data). Thus, the term "sheet" is more appro-priate. Our mapping in the Southwest Durham Quadrangle has significantly enlarged the mapped outcrop area of the BP dike of Ragland and others (1968). They studied the body in the vicinity of its outcrop inthelargeroadcutonU.S. 15-501 Bypass just south of the Cornwallis Road interchange. This body lies along the trend of a prominent aero-magnetic anomaly (U.S. Geological Survey, 1974) that continues eastward and aligns with the Oak Grove diabase sheet. The aeromagnetic anomaly passes through urban area; therefore, it is difficult to confirm the continuity of diabase outcrop. It seems reasonable to infer diabase as the underlying cause of this anomaly, but some sort of structure or lithologic variation within basement rocks can not be ruled out. Soil maps were of limited use for delineat-ing the occurrence and extent of diabase. Iredell and Mecklenburg soil types are generally recog-nized as indicating mafic parent material. Map-ping for this project, however, found significantly more diabase than is suggested by the distribution of Iredell and Mecklenburg soils on the Durham and Wake County soils maps (U. S. Department of Agriculture, 1976; U.S. Department of Agricul-ture, 1970. SEDIMENTARY ROCKS Mapping of Triassic sedimentary rocks delineated seven lithofacies that are grouped into three lithofacies associations (figure 4). The three associations form three belts that generally con-form to the trend of the basin. The western associa-tion (Lithofacies Association I) is comprised of a single lithofacies consisting of sandstone with in-terbedded siltstone (Trcs/sij). The central associa-tion (Lithofacies Association II) is comprised of two lithofacies, sandstone with interbedded siltstone (Trcs/si 2 ) and siltstone with interbedded sandstone (Trcsi/s). The eastern association (Lithofacies As-sociation III) is comprised of four lithofacies, sandstone (Trcs), pebbly sandstone (Trcsc), sand-stone with interbedded conglomerate (Trcs/c), and conglomerate (Tree). Floodplain alluvium (Qal) is also shown on the geologic maps although specific investigation of this material was beyond the project's scope. The mapped distribution of alluvium is largely interpretive and is based on a combination of topo-graphic and soils information. Relatively flat, locally broad, surfaces are evident along most streams and tributary drainages of the study area. These areas approximately coincide with the Chew-acla- Wehadkee-Congaree or the Altavista soil associations (U. S. Department of Agriculture, 1976). With modification, alluvium is mapped where both the topography and soils maps suggest alluvial deposits. Lithofacies Association I Trcs/si, - Sandstone With Interbedded Siltstone Description. Lithofacies Association I consists of a single facies identified as the Trcs/sij facies. This unit consists of fine- to medium-grained, pinkish-gray (5YR 8/1) to light-olive-gray (5Y 6/1), feld-spathic sandstone and reddish-brown bioturbated siltstone and mudstone. Fine- to very fine-grained biotite is a common accessory that helps to distin-guish the sandstones of this facies from sandstones of the other lithofacies. Muscovite is also com-mon, though it is not distinctive to this lithofacies. Widespread red clayey soils, abundant and large mud clasts in sandstone channel deposits, and some exposures which contain thick siltstone beds indicate that siltstone is, volumetrically, a signifi-cant component of this facies. Sandstone preferentially outcrops and thus is the dominant lithology exposed through the area underlain by this facies. Overall, outcrops of this facies are less abundant but usually larger than those of the other lithofacies associations. The outcrops of Lithofacies Association I also exhibit more large-scale sedimentary structures than out-crops of the other lithofacies associations. In aggregate, sandstone sequences are usually thick (5 meters or more) and are composed of individual depositional units that are character-ized by rapid vertical and lateral changes. The smaller scale sequences are typically 1 .5 to 2.0 me-ters thick and exhibit poorly defined, fining-up-ward trends from erosional or channel-form basal contacts. Sandstone immediately overlying the basal scours is very coarse grained to pebbly and contains abundant mudstone clasts. Mudstone clasts range up to 50 centimeters in diameter and are commonly scattered along scour surfaces. The 8 rrrr, _J >o <^ _ Xo l-c a, o 00 s J*oo .s 1=1 c3 U o W3 N .SJ o o t/3 w 1) <*2 o s s p J £a 00 "3b 3 C/5 s3O CO 1Q a3 t> J3 3 O CO co <</> 00 'a o J3 oco 3 53 T3 N c o B3 upper portions of fining-upward sequences, where they are not truncated or removed by another de-positional sequence, consist ofbioturbated siltstone and mudstone. Trough crossbedding is abundant in the sandstones of this facies. Individual sets decrease in thickness from between 30 and 40 centimeters near the base of a sequence to between 10 and 15 centimeters in the upper portions. Tabular foresets are less abundant, but individual sets up to 1.5 meters thick occur near the tops of fining-upward sequences in a few outcrops. Paleocurrent determination by trough cross-bed orientations from a limited number of locali-ties show a broad scatter with a strong southerly component. Within a single outcrop the trough crossbeds generally show little variability in direc-tion. Tabular foresets, where preserved, have ori-entations that vary considerably (up to 90 degrees) from the trough crossbed orientation of the same outcrop. Bioturbation is extensive in the finer grained portions and within the thinner sandy beds of this facies. Both root structures and burrows (Scoyenia) were observed. Rooted zones usually exhibit light-green to whitish reduction haloes along root traces. Locally, thin zones of nodular carbonate also occur in the muddy to silty beds of the Trcs/sij facies. Voids within the basal portions of some sandstones are interpreted as weathered-out carbonate and/or mud clasts that were reworked from underlying mudstone. Localities. Representative outcrops of the Trcs/sij facies occur at Localities 1 and 2 on the Southwest Durham Quadrangle. Locality 1 (figure 5) is a construction and road cut at the j unction of Pearson Drive (SR 1221) and Mimosa Drive approximately 0.3 miles west of Fayetteville Road (SR 1118). Locality 2 (figure 6), a cut along the abandoned Norfolk Southern Railroad right-of-way at the Fayetteville Road overpass about 1.4 miles south of Interstate 40, was described by Textoris and Holden (1986). This outcrop is one of the localities within this facies in which nodular carbonate hori-zons occur. Supplemental localities for the Trcs/si 1 facies are numbers 3, 4, and 5. Interpretation. Sandstone sequences within this facies resemble those of sandy braided rivers de-scribed by Cant (1978) in that 1) large scale, poorly defined mud-clast-rich trough crossbeds grade vertically to smaller scale trough crossbeds, 2) fining-upward sequences are poorly developed, 3) intercalated sets of tabular crossbeds have pale-ocurrent directions at high angles to the directions indicated by the trough crossbeds, and 4) ripple cross-laminated, fine-grained sandstone and siltstone beds are thin to absent at the tops offining-upward sequences. By this model the tabular foresets represent mid-channel sand sheets and bars deposited in waning flow conditions over the trough crossbeds formed by dunes during high flow stages. Unlike Cant's model, however, the Trcs/sij facies sandstones are surrounded by apparently thick sequences of heavily bioturbated siltstone and mudstone. The sparse but well-developed character of sandstone outcrops suggests that onset and termination of braid channel sedimentation happened suddenly and not by lateral migration. This might be explained by channel avulsion on a muddy floodplain in a manner similar to that de-scribed by Smith and Smith (1980) for anastomos-ing streams. Lithofacies Association n Lithofacies Association II is comprised of twolithofacies, a dominantly sandstone facies (Trcs/ si 2 ) and a dominantly mudstone facies (Trcsi/s). The Trcs/si 2 facies is the more widespread facies. In the south-central portion of the map area, the Trcs/si 2 facies grades upward into the Trcsi/s fa-cies. The contact between Lithofacies Associa-tion I and Lithofacies Association II appears to be gradational. This change occurs through a zone wherein the lithologic and sedimentary character- 10 SOIL mud-clast-rich mud-clast conglomerate trough crossbeds Figure 5. Outcrop of Trcs/sij facies exposed at Locality 1 . Paleoflow is into the page and toward the left. 11 31 oP a\ cl • p era a p3 Cl °1§" £ & 00 n CL 5? Z ^ ° o S" s- s « Sis, o *o v> O <"> SS £•8. 1- ? s § era B^ .-*. p S <*' §•£ | & ^< Z ^ o o 3 3 3 tra 2 p m a* *i p P3 . CL 3 _• n> CL o & 3* 00 O o era £ 3T s" c«" ^ P m •a B2. 2. g 3 o-p a. « era ^? oH-» O>/> 3 * l-l P * Tl hfl P p *< 2o m~ ca < o tt 3 rT CL o s 3 3 3 COVERED ^\ AV =» s5s2;.T 2. =• w o 12 istics of both associations occur. Some outcrops or individual beds within this zone are more distinctly like one facies or the other, but there is no apparent systematic vertical change. Trcs/si 2 - Sandstone With Interbedded Siltstone Description. The dominantly sandstone facies (Trcs/si 2) consists of medium- to coarse-grained, typically grayish-pink (5R 8/2) to pale-red (10R 6/ 2), very feldspathic sandstone that grades upward through finer-grained sandstone into reddish-brown, bioturbated siltstone and mudstone. Mus-covite mica is a very common accessory mineral. Sandstones ofthis facies are distinguished from the Trcs/sij sandstones by their generally coarser grain size, noticeably abundant pink potassium feldspar which gives these sandstones a slighdy different hue (more red), and relatively less biotite. A better developed and more consistent rhythmic character of fining-upward sequences also helps distinguish the Trcs/si 2 facies from the Trcs/sij and other facies of the study area. Depositional sequences in this facies are typically 2 to 5 meters thick. Coarse- to very coarse-grained pebbly sandstone with very coarse-grained muscovite generally marks the base of cycles. Both flattened and rounded mud clasts commonly overlie scour surfaces. Typically, these clasts are only 1 to 2 centimeters in diameter as compared to the much larger clasts of the Trcs/sij sandstones. Sequences normally fine upward through medium- and fine-grained sandstone into siltstone or mudstone. Sedimentary structures are commonly absent or difficult to see due to weathering. Where crossbedding is obvious, it grades upward from trough to planar form and decreases in size. Fine-grained sandstone and siltstone with ripple cross-lamination and bioturbation gradationally overlie crossbedded sandstone within fining-upward se-quences. The few exposures where trough cross-beds provide paleocurrent data indicate a south-west flow direction. Bioturbation is very common within the muddier beds of this facies and in the thinner sandy zones between muddier beds. Root structures and burrows are both present. Thin, discontinuous lenses of laminated to thin-bedded shale contain-ing the fossil branchiopod conchostracan (Cyzicus) occur locally within the Trcs/si 2 unit. In many outcrops ofthis facies, nodular and "bedded" limestone zones occur in the thicker mudstone and siltstone horizons. Limestone nod-ules are commonly associated with root structures. The "bedded" limestone occurs as discontinuous stringers up to several centimeters thick, is usually dense, and has a laminated structure. Although these stringers appear to be primary features within massive mudstone, they rarely yield a strike and dip conformable with those obtained for enclosing sedimentary strata. It would thus seem that they are possibly diagenetic features. Chert occurs locally within the Trcs/si 2 facies. This is as a replacement of nodular lime-stone; as float in soil; and, rarely, as pebbles in channel lag deposits. Localities. Two key outcrops for this facies are Locality 7, a roadcut on the west side of Van Road (SR 2052) approximately 0.3 miles north of its intersection with Holden Road (SR 1911) (figure 7); and Locality 8, the abandoned Hoover Road quarry ofBorden Brick and Tile Company which is reached via an unnamed dirt road that runs west from East End Avenue opposite Rowena Avenue (figure 8). Supplementary localities are numbers 9, 10, and 11. Locality 1 1 is the Borden Brick and Tile Company (a division of Cherokee Sanford Group) Stone Road Quarry. A significant amount of stratigraphic section (over 100 meters) was exposed in the various parts of this quarry. Part of this section was described by Gore (1986). Interpretation. Within the Trcs/si 2 facies, well de-veloped, cyclical, fining-upward sequences con-sist of pebbly, trough crossbedded bases which grade upward through finer- grained, ripple- to parallel-laminated sands into rooted and burrowed, 13 t—m— r M VFSFS MSCS Covered Pale-reddish-brown (10R 5/4), coarse-grained, micaceous, feldspathic sandstone grading upward through medium- to fine-grained sandstone to dark-reddish- brown (10R 3/4) siltstone. Pale-reddish-brown (10R 5/4), coarse-grained, feldspathic sandstone fining upward to medium-grained sandstone. Pebble lag at base; lenses of coarse- to very coarse-grained sandstone occur near top of interval. Pale-red (5R 6/2), coarse- to very coarse-grained, micaceous, feldspathic sandstone. Pebbles, granules, and siltstone rip-up clasts at base. Largest clast is a 4 cm pebble of felsic intrusive rock. Lower 1 m is crossbedded and biorurbated. Dark-reddish-brown (10R 3/4), medium-grained, micaceous, feldspathic sandstone fining upward to siltstone. Lower half of interval contains lenses of coarse - to very coarse-grained sandstone with pebbles. Pale-reddish-brown (10R 5/4), coarse- to very coarse-grained, micaceous, feldspathic sandstone fining upward to dark-reddish-brown (10R 3/4), fine-grained sandstone. Base of interval consists of a 10 cm muddy zone (weathered rip-up clasts?) overlain by pebbles and granules. Pale-reddish-brown (10R 5/4), coarse- to very coarse-grained, micaceous, feldspathic sandstone grading upward to dark-reddish-brown (10R 3/4), fine-grained sandstone. Upper sandstone coarsens laterally. Sand-filled vertical and horizontal burrows occur at top of interval. Figure 7. Section of Trcs/si facies exposed along Van Road (SR 2052) (Locality 7). sometimes calcareous, siltstone and mudstone. These characteristics are consistent with lateral point bar aggradation within a meandering fluvial system surrounded by a vegetated floodplain (Cant, 1982; Walker and Cant, 1984). The carbon-ates appear to be pedogenic and are partially re-placed by chert. The abundant potassium feldspar and mica, along with the coarse to very coarse grain size of the Trcs/si 2 facies, especially in the more northern portion of this facies, suggests a granitic source area. Trcsi/s - Siltstone With Interbedded Sandstone Description. The upper part of the Trcs/s^ facies grades southward into the Trcsi/s facies that gener-ally underlies the Research Triangle Park area. Temporary exposures made during construction of the Southern Parkway from Miami Boulevard (SR 1959) east to about Page Road (SR 1973) and subsurface data obtained from the North Carolina Department of Human Resources (Soil and Mate-rial Engineers, 1987) were important supplements to the otherwise sparse outcrop data for this facies. Siltstone is the dominant lithology of the Trcsi/s facies. It is typically reddish brown with light-green to whitish-gray mottling along both fossil and modern root structures (similar mottling is also developed along fractures within the soil zone). Bedding is usually massive; however, this may be due to either weathering or intense biotur-bation which has destroyed primary structures. Scoyenia burrows are very abundant. Laminated to thin-bedded reddish-brown shale containing con-chostracans and ostracods occurs at several locali-ties. Sandstones within this facies are fine- to medium grained and are usually less than a meter thick. Sandstone composition is difficult to dis-cern in the field because of the relatively fine grain 14 t— m M VFS FS CS VCS Grayish-orange-pink (10R 8/2), coarse- to fine-grained, micaceous, feldspathic sandstone. Individual beds are separated by thin shaly partings. Lower sandstone contains trough crossbeds up to 30 cm high; smaller planar crossbeds occur higher in sandstone. Grayish-orange-pink (10R 8/2), medium-grained, micaceous, feldspathic sand-stone. Bed pinches out laterally. Grayish-orange-pink (5YR 7/2), coarse-grained, micaceous, feldspathic sand-stone grading upward to crossbedded fine- to medium-grained sandstone. Contains large vertical burrows. Mottled light-bluish-gray (5B 7/1) to grayish-red (10R 4/2) to brownish-gray (5 YR 6/1), bioturbated, micaceous, very fine-grained feldspathic sandstone with calcareous nodules. Thin lens of fine-grained calcareous sandstone near top of interval. Sand-filled burrows occur at upper contact. Mottled grayish-red (10R 4/2) to light-gray (N7), medium- to fine-grained, micaceous, feldspathic sandstone. Granule conglomerate with siltstone rip-up clasts occurs at base and abruptly grades upward to bioturbated fine-grained sandstone with faint planar crossbeds. Moderate-brown (5YR 3/4), micaceous siltstone. Intensely burrowed with horizontal burrows and large vertical burrows; contains calcareous nodules. Moderate-brown (5YR 3/4), fine-grained, micaceous, bioturbated, feldspathic sandstone with small planar crossbeds. Moderate-brown (5YR 3/4), silty, micaceous, fine-grained, feldspathic sandstone with horizontal burrows. Figure 8. Composite section of Trcs/si 2 facies exposed in abandoned Hoover Road Quarry of Borden Brick and Tile Company (Locality 8). size. In coarser lenses, sandstones are clearly feldspathic. Two sandstone samples from this facies that were examined petrographically are arkose (figure 9). In a few exposures the sandstones exhibit small-scale planar crossbedding and ripple cross lamination. Otherwise, flow structures were not observed. Fining or coarsening trends within indi-vidual sandstone beds are usually very subtle or absent. Subsurface data and surface exposures suggest that many of the sandstone beds are len-ticular in cross-section. However, in several in-stances beds persist laterally within a given out-crop (for example Locality 12) for tens of meters. This persistence of such thin beds suggests a sheet-like geometry. Nodular and "bedded" carbonate horizons as described above for the Trcs/si 2 facies are exten-sive within the Trcsi/s facies. Most outcrops con-tain some carbonate either in this form or as cement within siltstone beds. Chert, also more abundant in this facies than others, is most often found as float; however, a number of outcrops contain in-place chert stringers or nodular-like "bedded" masses. These are nearly always associated with carbonate. The major difference between the Trcsi/s and Trcs/ si 2 facies with respect to carbonate and chert is the relative abundance rather than any characteristic related to depositional setting. Wheeler and Tex-toris (1978) hypothesized that chert and limestone of the Research Triangle Park area (Trcsi/s facies of this report) were deposited in and along the margins of playa lakes. The fact that chert and limestone lithologies occur across several facies of the basin and that these facies are clearly the result of sustained fluvial deposition argues against this hypothesis. Subsurface data (Soil and Material Engi-neers, 1987) from the main IBM facility located 15 Quartz ^V_— Quartzarenite Subarkose \ Sublitharenite r ° /" T\ /d n/ • \ \ / / \ \ / / Lithic / Arkose / Arkose Feldspalhic \ \ Litharenite \ Litharenite \ Feldspar Rock Fragments O Trcs/si i Trcsi/s Trcsc n Trcs/si2 Trcs • Trcs/c, Tree Figure 9. Ternary plot of sandstone composition from point-count data. Classification after Folk (1974). west of Miami Boulevard (SR 1959) and south of Alexander Drive (SR 2028) is consistent, at least in a qualitative sense, with what is indicated for this facies by outcrop. Drill cuttings and core descrip-tions document a section that is predominantly mudstone with interbedded, reddish-brown to tan, pink, or pinkish-brown, fine- to medium-grained sandstone. Numerous thin carbonate horizons were reported. Localities. Representative outcrops of the Trcsi/s facies are found at Locality 1 2, along N.C. 55 south ofits intersection with Alexander Drive (SR 2028), and Locality 13, ditch and roadcut exposures in the vicinity of the intersection of N.C. 54 and Davis Drive (SR 1999). Interpretation. Laminated shale beds in theTrcsi/s facies indicate deposition in quiet standing water. In a sewer excavation (now filled) along Stirrup Iron Creek, northeast of the Miami Boulevard (SR 1959) - Interstate 40 interchange, a few fish scales were found with conchostracans and ostracods. These fossils were deposited in a brownish-gray laminated shale overlying a coarsening-upward sandstone sequence containing climbing ripples. This is interpreted as a lake margin deposit. Olsen ( 1977) observed a 1 -meter-thick laminated siltstone bed south of this study area which contains abun-dant fossils, including fish scales and bones. That bed was interpreted as being oflacustrine origin set within an overall fluvial sequence (Olsen, 1977; Renwick, 1987). The Trcsi/s facies is interpreted as repre-senting mostly fluvial overbank deposits with lo-cally developed, areally limited, ephemeral, shal-low, freshwater lakes. Abundant root structures and carbonate nodules suggest that exposed sur-faces were vegetated and that soils developed on them. The Trcsi/s facies may represent a local lowland away from the main fluvial belt of the Trcs/si 2 facies or it could represent a change to muddier conditions in the later part ofdeposition of Lithofacies Association II. The change could be due to basin filling or an increased input of fine-grained sediment from another source area (possi-bly the east). Another consideration is that the drainage system of this lithofacies association may have flowed into a large lake to the south. A relative rise of that lake's level would tend to decrease stream gradients within its feeder fluvial system. Lithofacies Association III Lithofacies Association III is comprised of four lithofacies that are texturally and mineralogi-cally distinct from the sedimentary rocks of the first two lithofacies associations. Namely, musco-vite, which is very common in the rocks of Litho-facies Associations I and n, is absent from these rocks. Also, lithic fragments are more common. Matrix is a more significant component and ma-trix- supported textures are common. The facies of this association progress from massive, boulder-dominated deposits (Tree) adj acent to the Jonesboro fault through gradually finer grained cobble, pebble, and sandstone deposits (Trcs/c and Trcsc) to muddy sandstone (Trcs) toward the central portion of the basin. 16 Trcs - Sandstone Description. A dominantly sandstone fades (Trcs) comprises the most distal and finest grained facies of Lithofacies Association in. This facies gener-ally consists of reddish-brown, poorly- to moder-ately sorted, fine- to medium-grained sandstone and muddy sandstone. Matrix-supported granules and coarse sand grains are common. Locally, some beds and lenses are moderately well sorted and relatively low in mud content, but siltstone and mudstone are typically minor constituents. Com-position, like texture, is highly variable. Quartz is the dominant constituent. Lithic fragments are generally present and in places are abundant. Noticeably absent from this facies is muscovite. This property serves to distinguish Trcs sandstones from sometimes otherwise very similar Trcs/si 2 sandstones. The two samples of this facies that were examined petrographically plotted as arkose and lithic arkose (figure 9). Beds are typically 1 to 2 meters thick and are commonly tabular bodies that display good lateral continuity (figure 10). Relatively thin (5 to 20 centimeters), sometimes burrowed, muddy sandstone zones usually cap the beds of this facies. Gradation from cleaner sandstone to these fine-grained zones is usually abrupt. A lack of internal stratification appears to be due to intense bioturba-tion. The section exposed by the excavation shown in figure 10 contains a 25-centimeter-thick, heav-ily burrowed mudstone bed. Another example of bioturbation within the Trcs unit is illustrated in figure 11 (Locality 15). Root mottling similar to that observed in the other lithofacies associations is common within this facies. Localities. A representative section for the Trcs facies is exposed at Locality 16, a road cut on the west side ofMiami Boulevard (SR 1959) about 300 meters north of Interstate 40 (figure 12). Supple-mental localities are numbers 17 and 18. Figure 10. Exposure of Trcs facies in sewer exca-vation east of Page Road (SR 1973) at Inter-state 40 (Locality 14). Figure 11. Excavated block of bioturbated sand-stone from Trcs facies along Southern Park-way (locality 15). Rock hammer in lower right for scale. 17 4 —.'•;''.' '.'••'.'.' *:.'• •'•*.'* '.'• '.'.'• •":.•j 3 — 2 — '. j •• ° J ? (?*;<" <> 6 .o <t:oy 1 — \ * * J o L •/.•©•;: ••.'••.•"*:. .•"•.•"••i Moderate-reddish-brown (10R 4/6), very fine- to fine-grained, moderately sorted, feldspathic sandstone with scattered light colored reduction spots. Lacks coarser grains seen in lower beds. Overall grain size slightly finer than underlying beds. Dark-reddish-brown (10R 3/4), muddy, fine-grained, feldspathic sandstone with abundant horizontal burrows. Moderate-reddish-brown (10R 4/6), very fine- to fine-grained, moderately sorted, feldspathic sandstone with scattered coarse to very coarse grains. Reduction spots scattered through bed and concentrated in a narrow zone near the base. _^ Zone of reduction spots. Dark-reddish-brown (10R 3/4), muddy, fine-grained, feldspathic sandstone with horizontal burrows. Zone of reduction spots. Moderate-reddish-brown (10R 4/6), fine-grained, moderately sorted, feldspathic sandstone with scattered coarse- to granule-sized grains. Reduction spots scattered through bed and concentrated in a narrow zone. Figure 12. Section of Trcs facies exposed at Locality 16 along west side of Miami Boulevard ( SR 1959) about 300 meters north of Interstate 40. Interpretation. The Trcs facies is somewhat en-igmatic. It has physical characteristics, namely li-thology, color, and texture, that place it in Lithofa-cies Association III; yet the unit's fluvial charac-teristics suggests a close relationship with Lithofa-cies Association II deposits. An intertonguing relationship between Lithofacies Association II and Lithofacies Association III is indicated by interbedding ofmicaceous, arkosic sandstones and mudstones of the Trcs/si 2 facies with muddy, ma-trix- supported, poorly sorted, sandstons of the Trcs facies. This relation is exhibited at Locality 17, the Borden Brick and Tile Highway 70 quarry, along the road into the quarry, and in the northeast-trending drainage east of the quarry. Locally, the two lithofacies associations also exhibit a mixing of lithologic and sedimentologic characteristics. The Trcs facies appears to reflect deposi-tion in broad shallow channels incised into muddy flats. The eradication of internal stratification by bioturbation indicates relatively thin depositional units or relatively long periods of non-deposition between sedimentation events or both. Muddy, matrix-supported sandstones may also represent distal debris flow deposits or hyperconcentrated stream flow deposits (Nilsen, 1982; Pierson and Scott, 1985) Trcsc - Pebbly Sandstone Description. Sandstone of the Trcs facies grades upsection and southeastward to pebbly sandstone of the Trcsc facies. The Trcsc facies consists of reddish-brown, poorly sorted sandstone with at least 5 percent gravel (chiefly granules with subor-dinate amounts of pebbles and cobbles). Coarse clasts are generally matrix supported and scattered throughout sandstone beds. Siltstone and mudstone are minor components in this facies. Two of the three point-counted samples from this facies are feldspathic litharenites; the third is a lithic arkose (figure 9). Bedding on the order of 1 to 3 meters thick is defined by concentrations ofpebbles and cobbles 18 along basal contacts. These contacts are usually scour surfaces with conglomeratic zones that range up to 50 centimeters thick. The conglomeratic por-tions grade rapidly upward into poorly sorted sand-stone. Such beds are laterally continuous for only a few meters. Internal stratification is limited to rare occurrences of pebble and cobble trains, commonly only one or two clast diameters thick, which define flat to slightly inclined lenses within sandstones. Root mottling is common in this facies. Localities. A representative section of the Trcsc facies is exposed at Locality 20, a roadcut on the north side of Kemp Road (SRI902) j ust east of its junction with Virgil Road (SR 1903) (figure 13). Supplementary outcrops are at Localities 19, 21, and 22. This facies is very poorly exposed through the southern half of its mapped extent. Here, a few scattered outcrops and the relative abundance and size of gravel float were used to infer the distribu-tion of the unit. Interpretation. The Trcsc facies appears to have been deposited in broad, shallow channels. The poor sorting and general lack of stratification within the sandstones may indicate deposition by streams with high sediment concentrations (hyperconcen-trated flow) or it could be due to bioturbation disrupting previously better stratified deposits. Some of the deposits may also have been formed by low-viscosity debris flows (Nilsen, 1982). The coarser grain size and paucity of muddy interbeds suggest higher energy flow conditions for this facies versus for the Trcs facies. Trcs/c - Sandstone With Interbedded Conglomer-ate Description. Pebbly sandstone of the Trcsc facies grades upsection and southeastward toward the basin margin into a coarser grained facies consist-ing of sandstone with interbedded conglomerate (Trcs/c). The presence of well-defined conglomer-ate beds, as opposed to basal conglomeratic lags, distinguishes this facies from the Trcsc facies. An arbitrary cut-offof less than 50 percent conglomer-ate was used to distinguish the Trcs/c facies from the overlying conglomerate facies (Tree). Most outcrops of Trcs/c facies exhibit considerably less conglomerate than this 50 percent limit. Rock fragments are a noticeable compo-nent of the pebbly sandstone facies. Two samples that were point counted plot as arkose and lithic arkose (figure 9). Sorting is poor and matrix-supported granule and larger size clasts are very abundant in the sandstone beds. Within the con-glomerate beds, both matrix- and clast-supported textures occur. Conglomerate clasts, generally coarser than in the Trcsc facies, are mostly cobble size. The average clast size tends to be larger in the area north of Leesville Road (SR 1906) where the width of the outcrop belt decreases. Also to the north, bedding is more regular with distinctly inter-bedded sandstone and conglomerate. Clasts in the northern area are chiefly coarse-grained intermedi-ate to felsic intrusive rock. South of Leesville Road, clasts primarily reflect metavolcanic and metasedimentary source materials. Outcrops of this facies are relatively sparse and small. Therefore the relative abundance of cobble- to boulder- size float was used in some areas to delineate the unit. Outcrop observations in the adjacent Cary and Bayleaf Quadrangles were useful in projecting contacts through areas of lim-ited access or exposure. Localities. At Locality 23, the Trcs/c facies is ex-posed along the sides and bottom of Rocky Branch for a distance of several hundred meters. Here the facies consists of alternating tabular sandstone and conglomerate beds that are approximately equal in thickness (usually 1 to 2 meters). A second refer-ence locality is number 24, the east bank of Little Brier Creek approximately 500 meters north of Globe Road (SR 1644), and a supplemental local-ity is number 25. At these two outcrops, the con-glomerates are channel shaped and define scour surfaces on underlying pebbly sandstone beds. These gravels fine upward into pebbly sandstone. Figure 14 illustrates an outcrop (now covered) of the Trcs/c facies located about 300 meters south of 19 I—»• crq b oc o3 a H o Po CB VJ P, O* 3 Crq n> 3 oP JO *o o p f—t-o BW mWBsm r METERS ,»" . .i a — i c3 OI— f o" 3 3- < crq OP i— » VO O p o 5-8. 8 EL iS 5-3 en # O 5 Is <S §* ll 1' s •— ' 8 w> ' -^ V tfl 71 « O e e c s, 3 3 CO o- a. e a. K ST (TO '-I § § ££ C (1 B (« c — <* CL " £§? rt w <; B" a o Saps -a eL^v a" o O r» <* ON 0(jq >-- *< C O o # w si a 8. a? Hi 5 < — go ° B I S 3 as- 7 rt O S p -. 8.8.5- O p <&> O 3 &. gag I s" 8. 3i I3t 5i (tip ' » ^ Gg.8 O m H 3 - g a. ^ g. H M (B £§| 2 o £, o •3? r~ O o go rp-o 1-0 (TO ST "SI 5* 32 5' oc i B. 20 Figure 14. Interbedded sandstone and conglomer-ate of Trcs/c facies at Raleigh-Durham Inter-national Airport (now covered). Rock ham-mer in lower left of photo for scale. the Southeast Durham Quadrangle on Raleigh- Durham International Airport property. Interpretation. The Trcs/c facies appears to have been deposited in broad, relatively shallow chan-nels by streams with high sediment concentrations or as debris flows or both. Streams that deposited this facies were apparently larger and deeper than those that deposited the Trcsc facies. Tree - Conglomerate Description. The Trcs/c facies grades upsection and southeastward toward the border fault into a dominantly conglomerate facies (Tree). The Tree facies is composed mainly of cobble- to boulder-size clasts that occur in thick to massive beds with a subordinate amount of very coarse-grained to gravelly sandstone as matrix, beds, and lenses. Both clast-supported and matrix-supported tex-tures are found within the conglomerates of this facies. Clasts are generally rounded and their size and composition are highly variable. Localities. The coarsest-grained deposit observed is at Locality 26 where massive Triassic conglom-erate is in fault contact with deeply weathered, foliated crystalline rocks of the pre-Mesozoic Carolina slate belt (figure 15). Bedding is not apparent within the conglomerate adjacent to the fault. Clast orientation is chaotic with material ranging from boulder to coarse sand size being thoroughly intermixed. The largest boulders at this locality (many are over a meter in diameter) are metamorphosed felsic volcanic rock. Specular hematite clasts (ranging up to boulder size), quartz-ite, and foliated metamorphic clasts are common. About 300 meters southwest of this first locality is another Tree outcrop (Locality 27) in which the conglomerate adjacent to the border fault is again exposed. Here, several crudely de-fined beds of granule to pebbly sandstone and conglomerate are exposed in an excavated ditch behind the Trusswood manufacturing facility load-ing yard off Running Oak Road (figure 16). Maximum clast size is about 50 centimeters with average clast size about 10 centimeters. Clasts are chiefly foliated metamorphic rocks, metavolcan-ics, and quartz. The Tree facies exhibits systematic com-positional and textural changes along strike. North of the Leesville road area, felsic intrusive (granitic to dioritic) clasts predominate. Sandstone inter-beds, averaging about 0.5 meters thick, are more distinct in the northern area. Sorting within the conglomerate beds, which are generally 1 to 2 meters thick, is somewhat better toward the north. Average clast size in the northern conglomerates is about 10 to 12 centimeters and these clasts are usu-ally more spherical than the clasts of the southern area. A representative outcrop (Locality 28) of the northern conglomerate occurs in the bank ofRocky Branch east of Virgil Road (SR 1903) where a small power line crosses the drainage. Interpretation. The Tree facies, with its poor sorting and matrix-supported character, is inter- 21 •>>>>>>>,Weathered #&/&:, Tree .-.'.' Figure 15. Jonesboro fault exposed at Locality 26 in Leesville Industrial Park off Westgate Road (SR 1837). Breccia zone is about 1.5 meters wide. View is northeast along trend offault. Gullying along fault creates illusion of a southeast dip in this photo. preted as primarily representing debris flow depos-its. Lenses of grain-supported conglomerate are interpreted as deposits of small channels. These channels either were incised into debris flows or flowed around them. To the north, channel depos-its are more dominant in this facies. The Trcsc, Trcs/c, and Tree facies are inter-preted as the deposits that developed adjacent to the eastern border fault as alluvial fans extending northwestward into the basin. Several paleocur-rent measurements based on imbricated pebble orientations indicate northwestward flow. This information, together with the consistent eastern source or provenance, the gradational fining of the facies away from the eastern border fault, the basinward transition from debris-flow-dominated to fluvial-dominated deposition, and the basin-ward transition from thicker channel conglomer-ates to thinner, sheet-like sandstones are all consis- 22 .n't <-\ <o m •J" u m Ad fiP-0 fr-?. :W -t-> \» rX) S3 18) <-\ SJ019UI Z < — 3 | So T3 O <D &•« X <- •g S CO *'"H W) ^ G 00 & o 11 • S3 « 3 5 s .§ 13 £ J <L> & g 13 «* fi-9 *§£ |-H o <u g ^3 O •> -g I—1 I—, -t—» • O T3 ^ G -rt <u O +-> o 2 •a ,2 e 13 "3 S 00 G S <U D ° n c O *Z N J? C/3 <3 > <U l-i <U c3 J3 o <l> 8 C 23 tent with an alluvial fan model (Nilsen, 1982). The systematic lithologic change of the conglomerate deposits along strike suggests that there were multiple feeder systems operating along the border fault to produce a complex deposit. Variable width of outcrop for the respec-tive fan facies may be attributed to at least two causes. First, variable original thicknesses, either depositional or erosional, may have developed within the individual fan facies. Second, post-depositional reactivation of normal faults of the border fault zone would alter the outcrop width of the various facies. The rounded nature of the conglomerate clasts, especially of very large clasts adjacent to the border fault, suggests reworking and supports the latter consideration. Both options are viable and they are not mutually exclusive. STRUCTURE Strike and dip measurements were difficult to obtain from the generally poor and highly weath-ered exposures. Those strike and dip measure-ments shown on Plates 1 and 2 include several which are only approximate. The most reliable measurements—where bedding orientation was unequivocal—tended to be measurements that most consistently agreed with regional strike of about N40°-50°E with a 7- 10° southeast dip. Intrabasinal block faults which have been demonstrated else-where in the basin (Bain and Brown, 1980) can not reasonably be interpreted from our structural data; but neither can their likelihood be excluded. Only minor (outcrop scale) faults such as the fault that occurs at Locality 2 or the one reported by Gore (1986) for Locality 1 1 were observed. These are generally high-angle normal faults with displace-ments on the order of 1 to 1 meters. None of these are mappable at 1:24,000 scale. The western border of the basin is not ex-posed in the study area. A roadside ditch on the northeast side of Cornwallis Road (SR 1308) about 0.1 miles northwest of the intersection with Erwin Road (SR 1306) contains outcropping felsic intru-sive rocks in close proximity (less than 2 meters) to typical arkosic sandstone of the Trcs/sij facies but their contact relationship is not evident. Angular quartz cobbles, suggestive of conglomeratic de-posits, are common as float in sandy soil devel-oped on Trias sic sedimentary rocks in the area northwest of Erwin Road and east of the Orange- Durham County Line. An exposure at Nello Teer Company's Durham Quarry, located about 4.5 to 5.0 kilometers from the area described above, provides some indication as to the nature of the basin's western border. In the quarry, up to 10 meters of arkosic sandstone with interspersed beds of conglomerate unconformably overlie felsic volcanic rocks of the Carolina slate belt. The unconformity dips southeastward. Neither the quarry exposure nor outcrops in the Durham South-west Quadrangle provide evidence of a western border fault along this segment of the Durham basin. Using a 7°-10° southeast dip, a 26 kilome-ter width of the basin, and a 65° dip for the eastern border fault, the projected maximum thickness for the rocks of the Durham basin is 3.0 to 4.2 kilome-ters. Given that the eastern border is step-faulted (Bain and Brown, 1980), the maximum thickness could be considerably less than this value. Bain and Brown (1980), on the basis of gravity and aeromagnetic modeling, estimated the maximum thickness of the Durham basin to be about 2 kilo-meters. This is not inconsistent with the observa-tions of this study. DISCUSSION DEPOSITIONAL MODEL The three lithofacies associations define three belts of different provenance and deposi-tional style: a western belt of arkosic anastomosing braided stream deposits, a central belt of arkosic meandering stream deposits, and an eastern belt of conglomeratic alluvial fan deposits. The pale-ogeographic reconstruction of this portion of the Durham basin can be interpreted several ways depending upon how the stratigraphic relation-ships of these belts are viewed. Figure 17 illus- 24 NW |_—^-| siltstone sandstone \'.*%?j\ conglomerate & pebbly sandstone p>— <<l| swamp/wetlands NW ^L'ihof,", ^oracies |~—~^-| siltstone U- .•'-.[ sandstone f*.»;.y^ conglomerate & pebbly sandstone [>— CI swamp/wetlands "mm trend of time lines Figure 17. Sketch diagrams of possible depositional models. Upper sketch represents lateral facies model wherein the three lithofacies associations are deposited throughout the depositional history of basin. Lower sketch shows Lithofacies Association I as an early stage depositional unit underlying Lithofacies Association II. Both models presume persistent alluvial fan deposition (Lithofacies Asssociation III) along southeastern basin margin. 25 trates the two principle interpretations. In one sketch, each of the belts represent laterally equiva-lent facies. By this model the central belt fluvial deposits intertongue with alluvial fan deposits draining from an eastern highland and with fluvial deposits draining from a lower relief western high-land. Small lakes formed in the central lowland in interchannel areas. Textoris and Holden (1986), and Traverse (1986). The first two of these papers concluded that there were alternating wet and dry climatic cycles during deposition of these rocks. On the other hand, Traverse (1986), citing palynological evidence, interprets a "drying-upwards" trend from four Sanford basin samples which span from early to late Carnian. Alternatively, as shown in the other sketch, the western and central belts may each represent a period ofdeposition in the basin. By this model, the western belt was deposited during an early stage of basin development and the central belt was depos-ited subsequently. In this scenario, the western belt rocks would extend southeastward beneath the central belt rocks and intertongue with early stage alluvial fan deposits. The western belt rocks would also represent, at least in part, an axial fluvial system in this model. Resolving between these two models is difficult with the data presently available. The map pattern of the lithofacies belts, the gradational nature of the contact between the western and central belts, and the intertonguing nature of the contact between the central and eastern belts are consistent with both models. The available pale-ocurrent data are insufficient to constrain either model. One consideration is that the lateral facies model requires that the fluvial drainage systems persist during accumulation of several kilometers of section within a technically active basin. This is unlikely, and significant lateral shifts in the facies would be expected. The degree to which these shifts would occur is unpredictable. The impact of such shifts on the model would be to alter the amplitude and frequency of the intertonguing between the two facies. In the final analysis, any model, based solely on outcrop study, will proba-bly not apply to the full history of the basin. PALEOCLIMATE The paleoclimate of the Durham basin sedimentary rocks has been discussed in several papers including Wheeler and Textoris (1978), One striking aspect of the Durham basin sedimentary rocks is the abundance of primary sedimentary structures indicative of generally wet conditions. Mainly these are root casts and bur-rowing. Virtually every facies except the con-glomerate is extensively bioturbated. Smoot and Olsen (1985) classified massive mudstones of the Newark Supergroup into mudcracked, sand-patch, root-disrupted, and burrowed types. The first two types were considered indicative of dry paleocli-matic conditions while the latter two were consid-ered indicative of wet conditions. Durham basin mudstones are almost exclusively the burrowed and root-disrupted types. The interpretation of nodular limestone as caliche is one of the major points cited by propo-nents an arid or semi-arid paleoclimate (Textoris and Holden, 1986). Smoot and Olsen (1985) described small spherical nodules of micritic cal-cite concentrated in root tubes and surrounding matrix of their root-disrupted massive mudstones (wet conditions). The possibility that nodular limestone may be formed in a humid setting pre-cludes the need to interpret a dry paleoclimate on the basis of nodular limestone. In summary, the evidence pertinent to inter-pretation of the paleoclimate remains equivocal, but the field observations of this study appear to favor the interpretation that the sedimentary rocks exposed in the Durham basin were deposited under dominantly wet conditions. CONCLUSIONS Trias sic sedimentary rocks exposed in the 26 Southeast Durham and Southwest Durham 7.5- minute Quadrangles comprise seven distinct litho-facies that may be grouped into three lithofacies associations with distinctive lithological and sedi-mentological characteristics. Adjacent facies are gradational and intertonguing. These rocks were intruded during the Early Jurassic by dikes and sheets of diabase. Either of two main depositional models may account for the field relationships seen in outcrop. This mapping of the sedimentary and igneous rocks of a portion of the Durham basin is a considerable revision and refinement ofprevious reconnaissance work. Much additional work and data are required to reliably characterize the geo-logic history of this basin. ACKNOWLEDGEMENTS This project was proposed and conducted under the Cooperative Geologic Mapping Program (COGEOMAP) between the United States Geo-logical Survey and the North Carolina Geological Survey (Agreement Number 14-08-0001-A0433). Work began in February, 1987, and had a duration of 12 months. A report was submitted by the North Carolina Geological Survey to the U. S. Geological Survey in February, 1988, as part of the contract between the two agencies. This report is a revision of that contractual report with limited additional field and laboratory work. Joe Smoot and Al Froelich of the U.S. Geological Survey were cooperating investigators who provided field consultation during the map-ping and supplied unpublished manuscripts, field notes and sketches, and geophysical data to aid in preparation of the contractual report. Vic Cavaroc of North Carolina State University, as well as Smoot and Froelich, reviewed the contractual re-port. Their efforts were significant and greatly improved this report. North Carolina Geological Survey col-leagues Al Carpenter, Jeff Reid, Leonard Wiener, and Carl Merschat provided helpful review of this report. REFERENCES CITED Bain, G. L., and Brown, C. E., 1980, Evaluation of the Durham Triassic basin of North Carolina and techniques used to characterize its waste-storage potential: U.S. Geological Survey Open-File Report 80-1295, 133 p. Bain, G. L., and Harvey, B. W., 1977, Field guide to the geology of the Durham Triassicbasin: Carolina Geological Society, Fortieth Annual Meeting, October 7-9, 1977, Geology and Mineral Resources Section, Raleigh, 84 p. Benson, R. N., 1984, Structure contour map ofpre- Mesozoic basement, landward margin ofBali-more Canyon trough: Delaware Geological Survey Miscellaneous Map Series, n. 2, 1 sheet, scale 1:500,000. Campbell, M. R., and Kimball, K. W., 1923, The Deep River coal field ofNorth Carolina : North Carolina Geological and Economic Survey Bulletin 33, 95 p. Cant, D. J., 1978, Fluvial processes and facies sequences in the sandy, braided South Sas-katchewan River, Canada: Sedimentology, v. 25, p. 625-648. Cant, D. J., 1982, Fluvial facies models and their applications, in Scholle, P. A., and Spearing, D. R., editors, Sandstone depositional envi-ronments: American Association of Petro-leum Geologists Memoir 31, p. 1 15-137. Emmons, E. E., 1857, American geology, part iv, v, vi: Albany, New York, p. 19. Folk, R. L., 1974, Petrology of sedimentary rocks: Hemphill Publishing Company, Austin, Texas, 182 p. Froelich, A. J., and Gottfried, David, 1985, Early Jurassic diabase sheets of the Eastern United States - a preliminary overview, in Robinson, G. R., Jr., and Froelich, A. J., editors, Pro- 27 ceedings of the Second U.S. Geological Sur-vey Workshop on the early Mesozoic basins of the eastern United States: U.S. Geological Survey Circular 946, p. 79-86. Froelich, A. J., and Olsen, P. E., 1984, Newark Supergroup, a revision of the Newark Group in eastern North America: U.S. Geological Survey Bulletin 1537-A, p. A55-A58. Gore, P. J. W., 1986, Depositional framework of a Trias sic rift basin: the Durham and Sanford sub-basins of the Deep River Basin, North Carolina, in Textoris, D. A., editor, Society of Economic Paleontologists and Mineralogists Field Guidebook, Third Annual MidyearMeet-ing, Raleigh, North Carolina, p. 53-115. Hoffman, C. W., and Gallagher, P.E., 1989, Geo-logic map of the Southeast Durham 7.5-min-ute Quadrangle: North Carolina Geological Survey Open-File Report 89-1, 1 sheet, scale 1:24,000. Hoffman, C. W., and Gallagher, P.E., 1989, Geo-logic map of the Southwest Durham 7.5-min-ute Quadrangle: North Carolina Geological Survey Open-File Report 89-2, 1 sheet, scale 1:24,000. Harrington, J. W., 1951, Structural analysis of the west border of the Durham Triassic Basin: Geological Society of America Bulletin, v. 62, p. 149-158. Manspeizer,W., andCousminer,H. L., 1988, Late Triassic-Early Jurassic synrift basins of the U.S. Atlantic margin, in Sheridan, R. E., and Grow, J. A., editors, The Geology of North America, Volume 1-2, The Atlantic Continen-tal Margin, U.S.: Geological Society of America, p. 197-216. Nilsen, T. H. , 1 982, Alluvial fan deposits, in Scholle, P. A., and Spearing, D. R., editors, Sandstone depositional environments: American Asso-ciation of Petroleum Geologists Memoir 31, p. 49-86. North Carolina Geological Survey, 1985, Geo-logic map of North Carolina: North Carolina Department of Natural Resources and Com-munity Development, Raleigh, North Caro-lina, 1 sheet, colored geologic map, scale 1:500,000. Olsen, P. E., 1977, Stop 1 1 - Triangle brick quarry, in Bain, G. L., and Harvey, B. W., 1977, Field guide to the geology of the Durham Triassic basin: Carolina Geological Society, Fortieth Annual Meeting, October 7-9, 1977, Geology and Mineral Resources Section, Raleigh, p. 59-60. Pierson, T. C. and Scott, K. M., 1985, Downstream dilution of a lahar: transition from debris flow to hyperconcentrated streamflow: Water Resources Research, v. 21, p. 1511-1524. Parker, J. M., HI, 1979, Geology and mineral resources of Wake County: North Carolina Geological Survey Bulletin 86, 122 p. Ragland, P. C, Rodgers, J. J. W., and Justus, P. S., 1968, Origin and differentiation of Triassic doleritic magmas, North Carolina, USA: Con-tributions to Mineralogy and Petrology, v. 20, p. 57-80. Reinemund, J. A., 1955, Geology of the Deep River coal field, North Carolina: U.S. Geo-logical Survey Professional Paper 246, 159 p. Renwick, P. L., 1987, Paleoecology of afloodplain lake in the Durham sub-basin of the Deep River basin (Late Triassic), North Carolina [M.S. thesis]: Atlanta, Emory University, 324 P-Smoot, J. P., Froelich, A. J., and Luttrell, G. W., 1988, Uniform symbols for the Newark Su-pergroup, in Froelich, A. J., and Robinson, G. R., Jr., editors, Studies of the early Mesozoic basins of the eastern United States: U.S. 28 Geological Survey Bulletin 1776, p. 1-6. Smoot, J. P., and Olsen, P. E., 1985, Massive mudstones in basin analysis and paleoclimate interpretation of the Newark Supergroup, in Robinson, G. R., Jr., and Froelich, A. J., edi-tors, Proceedings of the Second U.S. Geologi-cal Survey Workshop on the early Mesozoic basins of the eastern United States: U.S. Geological Survey Circular 946, p. 29-33. Soil and Material Engineers, 1987, Appendix C — Geologic Well Records, Post Closure Permit Application, prepared by International Busi-ness Machines and Soil and Material Engi-neers, Cary, North Carolina. Smith, D. G., and Smith, N. D., 1980, Sedimenta-tion in anastomosed river systems: examples from alluvial valleys near Banff, Alberta: Journal of Sedimentary Petrology, v. 50, p. 157-164. Textoris, D. A., and Holden, C. J., 1986, Paleocli-mate change within a stratigraphic section, in Gore, P. J. W., Depositional framework of a Triassic rift basin: the Durham and Sanford sub-basins of the Deep River Basin, North Carolina, in Textoris, D. A., editor, Society of Economic Paleontologists and Mineralogists Field Guidebook, Third Annual Midyear Meeting, Raleigh, North Carolina, p. 101- 102. The Rock-Color Chart Committee, 1948, Rock-color chart: Geological Society of America, 5 pi. Traverse, Alfred, 1986, Palynology of the Deep River Basin, North Carolina, in Gore, P. J. W., Depositional frameworkofaTriassicrift basin: the Durham and Sanford sub-basins of the Deep River Basin, North Carolina, in Texto-ris, D. A., editor, Society ofEconomic Paleon-tologists and Mineralogists Field Guidebook, Third Annual Midyear Meeting, Raleigh, North Carolina, p. 66-71 U.S. Department ofAgriculture, 1970, Soil Survey of Wake County, North Carolina: U.S. De-partment of Agriculture, Soil Conservation Service, 118 p., 104 pi. U.S. Department of Agriculture, 1976, Soil Survey of Durham County, North Carolina: U.S. De-partment of Agriculture, Soil Conservation Service, 74 p., 42 pi. U.S. Geological Survey, 1974, Aeromagnetic map of parts of the Greensboro and Raleigh l°x2° Quadrangles: U.S. Geological Survey Open- File report 74-29, 16 pi., scale 1:62,500. Walker, R. G., and Cant, D. J., 1984, Sandy fluvial systems, in Walker, R. G., editor, Facies Models: Geological Association of Canada, Geoscience Canada Reprint Series 1, p. 71- 89. Weigand, P. W., and Ragland, P. C, 1970, Geo-chemistry of Mesozoic dolerite dikes from eastern North America: Contributions to Min-eralogy and Petrology, v. 29, p. 195-214. Wheeler, W.H., and Textoris, D. A., 1978, Triassic limestone and chert of playa origin in North Carolina: Journal of Sedimentary Petrology, v. 48, p. 765-776. Wilson, W. F., and Carpenter, P. A., 1981, Region J geology: a guide for North Carolina mineral resource development and land use planning: North Carolina Geological Survey Section Regional Geology Series 1, 45 p. 29 in H Z oH QZ< OZO C0 o Sou uI— < o < as wz XQ Zw Pu On <3 E 9 < 00 2& ^© ^\© ^<S gg#gggfg^^^#^ r^ o in o <-H ON <N m en 00(NO(S O ^H Tj-* O -H _] < !oo\qpvqcnr^«Nvooo<rjvo»ocn»np»n ^ i *' ^" t^ d ol vd h m' vd ri d od ci d pi ci r^cxstxsr^^r^r^vnpco^inr^copro od ">* r^ od on o>I ai •n- c4 cn in i-J >n" »n od <n OoOoOoOoOoOoQoQoOoOoQoQoOoOoOoOo 22^f>'ONNO(Nl!o2oO<OmoO 22m h ©^^ i« <»22ooooo <N O O O ^J-r- H^^rg.—i^T+mi—i CN en ° "^ ~ ° ^ Ocn—iOOO^OOO^hOOO<N-h cniT)\0 id^OOhcoO^hOcON nin^m^cnm^^tt ooomNOHoMoc^n^w-O ^*ovor^ CO NOONcnrf^tn.Ot'H'OVON'Hro '-iNro^O'HiO n.^.O oo O tJ- ^h o <r> en co cs 00 CN m m n i/i P p p O o O o J-* 00 00 00 OO 00 00 P p o o c> C) S-i r»1 r^H J-l rV-i rt-i '55 [m ; y £ 00 .00 00 HHHHHHHHHHHHH 00 OO 30 APPENDIX A - LOCALITY REGISTER LOC NO MAP UNIT LOCALITY DESCRIPTION LATITUDE LONGITUDE 355610 785506 355319 785636 355810 785710 355250 785606 355709 785359 355811 784725 1 Trcs/sij S side of Pearson Rd (SR 1221) at Coral Dr about 0.2 mi Wof FayettevilleRd(SR1118) 2 Trcs/sij Cut along abandoned Norfolk Southern RR at Fayetteville Rd (SR 1 1 1 8) 3 Trcs/si Exposure behind Uzzle Cadillac on S side of U.S. 15-501 - 0.5 mi W of N.C. 751 4 Trcs/sij Cut along abandoned Norfolk Southern RR 700m N of Scott King Rd (SR 1 103) 5 Trcs/sij Cut behind houses along Ancroft Rd N of Riddle Rd (SR 1 171) NE of Keene 6 Trcs/si 2 Small SW trending drainage within an aborted subdivision - SE of int. of un-maintained Rondelay Dr and Flanders St 7 Trcs/si 2 W side of Van Rd(SR 2052) just N of Hutson Rd - about 0.3 mi N of HoldenRd(SR1911) 8 Trcs/si 2 Borden Brick and Tile Company Hoover Road Pit - N of East End Ave along dirt road opposite Rowena Ave 9 Trcs/si 2 Bluff on S bank of Little Lick Creek about 500m upstream from Durham City sewage treatment plant 10 Trcs/si 2 NE side of Ellis Rd (SR 1954) N of So-Hi Dr (SR 1951) - just N and across from Southern High School 11 Trcs/si 2 Borden Brick and Tile Company Stone Road Pit - N of Stone Rd (SR 1956) and E of Wrenn Rd (SR 1955) 12 Trcsi/s Roadcut on east side of N.C. 55 0.2 mi S of Alexander Dr (SR 2028) 355816 355834 355907 355638 355701 355237 784828 785135 784826 785200 785127 785329 31 APPENDIX B - LOCALITY REGISTER (continued) LOC NO MAP UNIT LOCALITY DESCRIPTION LATITUDE LONGITUDE 13 Trcsi/s Exposures at intersection of 355328 785146 N.C. 54 and Davis Dr (SR 1999) 355502 784747 355337 785054 355642 784837 14 Trcs Excavation for sewer pump station in 355257 785003 Stirrup Iron Creek E of Page Rd (SR 1973) and 1-40 (back-filled) 15 Trcs Cut on S side of Southern Parkway (SR # not available) 0.4 mi W of U.S. 70 16 Trcs W side of Miami Blvd (SR 1959) just N of 1-40 interchange 17 Trcs Borden Brick and Tile Company High-way 70 Pit - N of U.S. 70 at end of dirt road 0.3 mi W of Leesville Rd (SR 1906) 18 Trcs Bluff at sharp bend in unnamed 355715 784723 tributary to Lick Creek E of Doc Nichols Rd (1908) - about 700m N of AT&T cable 19 Trcsc N side of Kemp Rd (SR 1902) 0.15 mi 355753 784552 W of Virgil Rd(SR 1903) 20 Trcsc N side of Kemp Rd(SR 1902) just E 355753 784542 of Virgil Rd(SR 1903) 21 Trcsc Upper reach of Martin Branch E of 355627 784607 Olive Branch Rd (SR 1905) downstream of AT&T cable 22 Trcsc Bluff on E side of uppermost part 355616 784631 of Martin Branch on W side of Olive Branch Rd (SR 1905) 23 Trcs/c Approx. 300m of streambed in Rocky 355659 784523 Branch - above NE-SW power line SE of substation 24 Trcs/c E side of Little Briar Creek about 355320 784742 500m N of Globe Rd (SR 1644) - behind Sheriffs Dept. pistol range 32 APPENDIX B - LOCALITY REGISTER (continued) LOC NO MAP UNIT LOCALITY DESCRIPTION LATITUDE LONGITUDE 25 Trcs/c Bank of Little Brier Creek about 100m 355405 784720 NofLumleyRd(SR1645) 26 Trcc High-Tech Fabricators - Midway-West Dr - construction cut at E corner of building 27 Trcc Trusswood plant - Running Oak Dr off Westgate Rd (SR 1837) - ditch excavation on N side of wood lot 28 Trcc E bank of Rocky Branch - domestic utility line crosses stream and Virgil Rd (SR 1903) about 0.75 mi N of Carpenter Pond Rd (1901) 355429 355422 355621 784526 784535 784520 33 APPENDIX C - GEOCHEMICAL DATA FOR DIABASE Sample sio2 52.20 A12 3 14.05 Fe 2 3 * 11.55 MgO 7.47 CaO 10.80 Na2 1.94 K2 0.53 Ti02 1.18 MnO 0.17 Total 1 JY(2) 99.88 2 DDH-1(4) 48.48 13.78 12.37 12.22 11.10 1.75 0.16 0.42 0.20 100.48 3 DDH-2(8) 48.47 13.82 12.03 12.44 11.09 1.55 0.18 0.40 0.19 100.16 4 JY(5) 52.50 14.56 10.60 7.63 10.02 2.04 0.58 1.20 0.19 99.32 5 BP(20) 48.36 16.34 11.00 10.16 9.97 2.10 0.27 0.68 0.19 99.07 6 DU-6(4) 47.83 15.93 10.57 11.69 9.67 2.05 0.13 0.60 0.21 98.66 7 D5(4) 48.08 16.55 11.94 9.67 10.09 2.09 0.18 0.69 0.19 99.46 8 W&R,#9 48.20 15.40 11.50 9.95 10.57 2.21 0.39 0.45 0.17 100.16 9 W&R, #12 47.20 15.70 11.90 9.85 11.30 1.87 0.20 0.69 0.19 100.16 10 W&R, #6 52.50 14.10 11.50 7.54 10.59 2.11 0.74 1.07 0.18 98.20 11 W&R, #8 52.60 14.90 11.60 7.27 10.76 2.22 0.53 0.75 0.20 98.20 12 W&R, #7 51.10 15.00 12.00 7.69 10.85 2.25 0.43 0.77 0.22 98.20 13 W&R, #2 51.60 15.10 13.50 5.62 10.42 2.54 0.68 1.27 0.20 98.20 14 W&R, #3 53.10 14.00 14.20 5.59 9.69 2.54 0.68 1.09 0.22 98.20 15 W&R, #4 53.00 13.70 13.70 5.33 9.60 2.42 0.51 1.08 0.22 98.20 Number in parentheses represents number of analyses averaged for value. 1. Durham basin, N.C., this study, JY dike, SW Durham Quad 2. Durham basin, N.C., this study , Oak Grove sheet, SE durham Quad 3. Durham basin, N.C., this study , Oak Grove sheet, SE Durham Quad 4. Durham basin, N.C., Ragland and others (1968, Table 3) 5. Durham basin, N.C., Ragland and others (1968, Table 3) 6. Durham basin, N.C., Ragland and others (1968, Table 3) 7. Sanford basin, N.C. Ragland and others (1968, Table 3) 8. Pennsylvania, Weigand and Ragland (1970, Table 1, sample 9) 9. Georgia-Alabama, Weigand and Ragland (1970, Table 1, sample 12) 10. Virginia, Weigand and Ragland (1970, Table 1, sample 6) 11. Georgia-Alabama, Weigand and Ragland (1970, Table 1, sample 8) 12. Connecticut-Pennsylvania, Weigand and Ragland (1970, Table 1, sample 7) 13. Connecticut, Weigand and Ragland (1970, Table 1, sample 2) 14. Virginia, Weigand and Ragland (1970, Table 1, sample 3) 15. North Carolina, Weigand and Ragland (1970, Table 1, sample 4) 34
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|Geology of the Southeast Durham and Southwest Durham 7.5-minute quadrangles, North Carolina
Hoffman, Charles W.
Gallagher, Patricia E.
North Carolina. Geological Survey Section.
Geology--North Carolina--Durham.
Durham (N.C.)
Durham County, North Carolina, United States
|Time Period
|(1945-1989) Post War/Cold War period
|2 folded maps in pocket;Includes bibliographical references (p. 27-29).
|Geological Survey, Division of Land Resources, Dept. of Natural Resources and Community Development
North Carolina Department of Environmental Quality
|State Document see http://digital.ncdcr.gov/u?/p249901coll22,63754
|Physical Characteristics
|ii, 34 p. : ill. ; 28 cm.
|North Carolina State Documents Collection. State Library of North Carolina
|Digital Characteristics-A
|5442 KB; 37 p.
|Bulletin (North Carolina. Geological Survey Section) ; 92.
|Serial Title
|North Carolina Geological Survey bulletin
|Digital Collection
|North Carolina Digital State Documents Collection
|Digital Format
|Pres File Name-M
|Pres Local File Path-M
|Full Text
Charles W. Hoffman and Patricia E. Gallagher CLEARINGHOUSE
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The Geological Survey Section examines, surveys, and maps the geology, mineral resources,
and topography ofthe state to encourage the wise conservation and use ofthese resources by industry,
commerce, agriculture, and government agencies for the general welfare of the citizens of North
The Section conducts basic and applied research projects in environmental geology, mineral
resource exploration, and systematic geologic mapping. Services include identifying rock and
mineral samples submitted by citizens and providing consulting services and specially prepared
reports to agencies that need geological information.
The Geological Survey Section publishes Bulletins, Economic Papers, Information Circu-lars,
Educational Series, Geologic Maps and Special Publications. For a list of publications or more
information about the Section please contact the Geological Survey Section at P.O. Box 27687,
Raleigh, North Carolina 2761 1-7687, or call (919) 733-2423.
Jeffrey C. Reid
Chief Geologist
Charles W. Hoffman and Patricia E. Gallagher
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Abstract 1
Introduction 1
Location 1
Objectives, Scope, and Methods 1
Conventions 3
Geologic Setting 3
Previous Work 4
Geology 6
Igneous and Metamorphic Rocks 6
Carolina Slate Belt Rocks 6
Diabase 6
Sedimentary rocks 8
Lithofacies Association I 8
Trcs/sij - Sandstone With Inter-bedded
Siltstone 8
Description 8
Localities 10
Interpretation 10
Lithofacies Association II 10
- Sandstone With Inter-bedded
Siltstone 13
Description 13
Localities 13
Interpretation 13
Trcsi/s -Siltstone With Interbed-ded
Sandstone 14
Description 14
Localities 16
Interpretation 16
Lithofacies Association III 16
Trcs - Sandstone 17
Description 17
Localities 17
Interpretation 18
Trcsc - Pebbly Sandstone 18
Description 18
Localities 19
Interpretation 19
Trcs/c - Sandstone With Interbed-ded
Conglomerate 19
Description 19
Localities 19
Interpretation 21
Tree - Conglomerate 21
Description 21
Localities 21
Interpretation 21
Structure 24
Discussion 24
Depositional model 24
Paleoclimate 26
Conclusions 26
Acknowledgements 27
References Cited 27
A. Mineralogical Composition of
Sandstones 30
B. Locality Register 31
C. Geochemical Data For Diabase 34
Plates (in pocket)
1. Geologic map of Southeast Durham
7.5-minute Quadrangle
2. Geologic map of Southwest Durham
7.5-minute Quadrangle
Figure Page
1. Location map 2
2. Newark rift system basins of eastern
North America 4
3. Weight percent Ti02
versus Mafic
Index (Fe
2 3
2 3
*+MgO)) for
representative diabase samples 7
ILLUSTRATIONS (continued)
Figure Page
4. Generalized distribution of lithofacies
and major diabase bodies 9
5. Outcrop of Trcs/sij fades exposed at
Locality 1 11
6. Outcrop of Trcs/sij facies exposed at
Locality 2 12
7. Section of Trcs/si
facies exposed at
Locality 7 14
8. Composite section of Trcs/si
facies ex-posed
in Borden Brick and Tile
Hoover Road Quarry (Locality 8).... 15
9. Ternary plot of sandstone
composition 16
10. Tics facies exposed in excavation
east of Page Road (SR 1973) at 1-40
(Locality 14) 17
11. Excavated block of bioturbated Trcs
sandstone at Locality 15, Southern
Parkway west of U.S. 70 17
Figure Page
12. Section of Trcs facies exposed at
Locality 16, west side of Miami
Boulevard (SR 1959) north of
1-40 18
13. Outcrop of Trcsc facies on Kemp
Road (SR 1902) east of junction
with Virgil Road(SR 1903)
(Locality 20) 20
14. Interbedded sandstone and conglom-erate
of Trcs/c facies at Raleigh-
Durham International Airport 21
15. Jonesboro fault at Locality 26 in
Leesville Industrial Park 22
16. Ditch excavation on north side of
Trusswood lot, Leesville Industrial
Park (Locality 27) 23
17. Sketch diagrams of proposed
depositional models 25
Bulletin 92
By Charles W. Hoffman and Patricia E. Gallagher
The Southeast Durham and Southwest Durham 7.5-
minute Quadrangles include a 26 kilometer transect of the
Durham Triassic basin from the Jonesboro fault on the south-eastern
side of this half-graben structure to a bounding un-conformity
on the northwestern side. The basin is filled with
non-marine, primarily fluvial, clastic deposits of the Late
Triassic Chatham Group. The Chatham Group rocks are
intruded by Early Jurassic diabase as dikes and sheets.
Bordering rocks are pre-Mesozoic intrusive, metavolcanic
and metasedimentary rocks of the Carolina slate belt.
Within the Triassic sedimentary rocks, three litho-facies
associations comprised of seven distinct lithofacies
form three belts that generally conform to the trend of the
basin. The western association is comprised of a single
lithofacies consisting ofsandstone with interbedded siltstone.
The central association is comprised of two lithofacies, sand-stone
with interbedded siltstone and siltstone with interbed-ded
sandstone. The eastern association is comprised of four
lithofacies; sandstone, pebbly sandstone, sandstone with
interbedded conglomerate, and conglomerate. The western
lithofacies association consists of mud-clast-rich, trough
crossbedded, arkosic sandstone interspersed with locally
thick siltstone beds. The unit is interpreted to represent sandy
braided streams flowing within fine-grained interstream areas.
The central lithofacies association consists ofarkosic, fining-upward,
meandering stream deposits in the northern part of
its area. To the south, in the upper part of its section, this
lithofacies association grades to a muddy system dominated
by fine-grained overbank fluvial and lacustrine deposits with
intercalated sandstone. The eastern lithofacies association
consists of conglomerates along the border fault and grades
basinward through interbedded sandstone and conglomerate
to pebbly sandstone and then to muddy sandstone. Adjacent
facies exhibit both intertonguing and gradational relation-ships.
This set oflithofacies is interpreted to represent basin-margin
alluvial fan deposits that prograded from a southeast-ern
The Southeast Durham and Southwest
Durham 7.5-minute Quadrangles encompass an
area of approximately 300 square kilometers. The
quadrangles include a large part ofthe Durham Tri-assic
basin and small areas of the adjacent Pied-mont
region (figure 1). A significant amount of the
study area is urban and suburban. Large portions of
Durham, Research Triangle Park, and Raleigh-
Durham International Airport are located within
the study area as are developing sections ofRaleigh
and Chapel Hill.
Adequate land use planning and resource
management require, among many other things,
sound baseline information on a variety of proper-ties
that are directly related to geology. Such
information includes soil types and their ability to
bear weight, maintain a slope, or transmit fluid;
groundwater quality and quantity; mineral resource
potential (especially aggregates for highway and
building construction); and potential geologic
hazards such as landslides or radon gas. In the
rapidly urbanizing Research Triangle area, where
proper planning is basic to maintaining a desirable
quality of life, the need for accurate geologic maps
at a suitable scale is vital.
This study was undertaken to meet these
— 36°
|OCLC Number-Original
|21353508; 23977217
|OCLC number
|21353508; 23977217


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