Lithology-Based Sequence-Stratigraphic Framework of a Mixed Carbonate-Siliciclastic Succession, Lower Cretaceous, Atlantic Coastal Plain
In:
Submitted By zhy921125 Words 14261 Pages 58
Lithology-based sequence-stratigraphic framework of a mixed carbonate-siliciclastic succession, Lower Cretaceous, Atlantic coastal plain
Brian P. Coffey and Richard F. Sunde
AUTHORS
Brian P. Coffey ∼ Earth Sciences, Simon Fraser University, Burnaby, British Columbia, Canada, present address: Apache Corporation, Houston, 2000 Post Oak Boulevard, Texas 77056; bpcoffey@ gmail.com Brian Coffey received his B.Sc. degree in geology from the University of North Carolina at Chapel Hill in 1995 and his Ph.D. in geology at Virginia Polytechnic Institute and State University in 1999. He has worked at ExxonMobil, Simon Fraser University, and Maersk Oil and has been a private consultant specializing in carbonate reservoir characterization. He currently works as a carbonate specialist at Apache Corporation in Houston. Richard F. Sunde ∼ EnCana, 500 Centre Street, Calgary, Alberta, Canada T2G1A6; richard.sunde@encana.com Richard Sunde earned a D.E.C. degree (Diplôme dietudes Collégiales) at Dawson College, Montreal, in 2000 and a B.Sc. degree in geology at McGill University, Montreal, in 2004. He then completed an M.Sc. degree at Simon Fraser University, British Columbia, in 2008; his thesis research focused on the content presented in this article. Richard currently is employed as a Geoscientist at Encana Corporation in Calgary.
ACKNOWLEDGEMENTS
ABSTRACT This study presents a lithology-based sequence-stratigraphic framework and depositional model for Lower Cretaceous, mixed siliciclastic-carbonate sediments of the Mid-Atlantic coastal plain (eastern United States). Lithologic data from cores and cuttings were integrated with wireline logs and twodimensional seismic data to document lithofacies variability and stacking patterns across the Albemarle Basin of eastern North Carolina. Ten facies associations are defined, which are variably present within siliciclastic- and carbonate-dominated depositional profiles interpreted to extend from onshore lowland coastal plain to deep-shelf depositional environments. Three depositional sequences (0, 1, 2) were identified, each with component upward-shoaling parasequences. Seismic reflectors typically coincided with key sequence-stratigraphic surfaces, which guided correlations between wells. Parasequences are grouped into parasequence sets with progressive progradational or retrogradational (highstand and transgressive systems tracts, respectively) stacking patterns. Transgressive parasequences are thinner, uniform in thickness, and tend to be more dominated by molluskan carbonate facies. Highstand parasequences have more variable thickness, are siliciclastic dominated, and tend to be progradational on seismic data. Late highstand deposits of sequence 1 are dominated by restricted carbonate facies that likely reflect increased aridity. Lowstand deposits were not recognized from onshore well and seismic data.
The authors thank the North Carolina and the Delaware Geological Surveys for access to well data repositories. Financial support for this study was provided by the American Chemical Society (Petroleum Research Fund Grant 42033-AC8 to B. Coffey), the Natural Sciences and Engineering Research Council (graduate fellowship to R. Sunde), Society for Sedimentary Geology (SEPM), and the Society of Petrophysicists and Well Log Analysts. Tim Bralower attempted to provide assistance with calcareous nannofossil biostratigraphy. Geomark performed gas chromatography–mass spectrometry on selected cuttings to confirm the presence and approximate age of hydrocarbons.
AAPG Bulletin, v. 98, no. 8 (August 2014), pp. 1599–1630
1599
AAPG Bulletin reviewers Gregg Brooks, W. Burleigh Harris, Don McNeill, and Peter Warwick provided many helpful comments that significantly improved the content and clarity of this manuscript. The AAPG Editor thanks the following reviewers for their work on this paper: Gregg Brooks, W. Burleigh Harris, Don McNeill, and Peter D. Warwick.
EDITOR’S NOTE
Color version of Figure 4 can be seen in the online version of this paper.
The sequence-stratigraphic framework developed documents the complex spatial and temporal facies relationships within a wave-dominated, mixed carbonate-siliciclastic passive-margin succession. The strata studied document the complex interplay of lithofacies within a transition zone between near-shore carbonate-dominated strata to the south (Southeast Georgia Embayment) and siliciclastic-dominated marginal-marine successions to the north (Baltimore Canyon Trough). It also provides a useful stratigraphic calibration set for coeval offshore sediments that have been identified as potential areas for hydrocarbon exploration.
INTRODUCTION The Lower Cretaceous series is a well-documented example of global greenhouse climatic conditions. However, much of the published literature has focused on either carbonate ramps or siliciclastic-dominated provinces. Facies relationships and sequence-stratigraphic relationships are less understood from mixed carbonate-siliciclastic successions, particularly in tropical settings. The purpose of this article is to document the facies, stacking patterns, and regional depositional sequences of an extensively mixed siliciclastic-carbonate succession of Lower Cretaceous (upper Aptian–Albian) sediments from the Atlantic coastal plain of eastern North America. The eastern North Carolina study area was selected because it contains sufficient subsurface data to document regional depositional trends and facies variations across a relatively thick (500 m [1650 ft]) Lower Cretaceous succession beneath the onshore Atlantic coastal plain. The study area contains a mixed carbonate-siliciclastic section that has not been deformed by salt migration or tectonism. It also lies within the region of transition between the dominantly siliciclastic strata to the north and carbonate-dominated successions to the south. Limited research has focused on these Lower Cretaceous strata because of the paucity of easily workable data sets. Strata are confined to the subsurface and have been discontinuously cored in only one well. However, well cuttings and wire-line logs from approximately 40 vintage oil test wells provide valuable lithologic information for this mixed carbonate-siliciclastic succession (Figure 1). Limited two-dimensional (2-D) seismic data provide further stratal control between onshore wells. This study offers a higher degree of lithologic resolution through the use of detailed petrographic study of thin-sectioned well cuttings, which were integrated with seismic and biostratigraphic data.
1600 Mixed Carbonate-Siliciclastic Sequence Stratigraphy, Cretaceous, Atlantic Coastal Plain
Figure 1. Study area, mid-Atlantic, United States. Wells with detailed cuttings analysis are labeled, as is line of cross section (AA′, Figure 8). Dashed lines indicate seismic lines (G-1 to G-5) used to tie wells and document lateral stratigraphic relationships (Figure 7). Isopach is thickness of Aptian–Albian deposits (in meters) based mostly on biostratigraphic control from Brown et al. (1972) and Zarra (1989). Current-day water bathymetry is shown in gray-dashed contours. Inset figure shows location of offshore wells and cores from adjacent basins that were used to validate stacking patterns observed in well cuttings.
This study provides a much needed link between the more heavily studied coeval units from the Gulf Coast and Baltimore Canyon Trough regions; it also provides further insight into depositional and diagenetic processes in emerging exploration areas along the western Atlantic margin. No exploration wells have tested coeval units offshore North Carolina, but these strata are prospective hydrocarbon exploration targets. Hence, documentation of onshore stratigraphy is highly advantageous to future offshore exploration ventures. The study also documents the complex vertical and lateral facies relationships of mixed carbonate-siliciclastic settings within a sequence-stratigraphic framework. GEOLOGIC BACKGROUND The North Carolina part of the Atlantic coastal plain contains a thick onshore accumulation of Mesozoic
passive-margin sediments (greater than 2 km [1.2 mi]). The Albemarle Basin is one of a series of embayments along the northwest Atlantic margin that developed in response to Late Triassic to Middle Jurassic rifting associated with the opening of the Atlantic Ocean (Manspeizer, 1985; Owens and Gohn, 1985). The Albemarle Basin is bordered to the south by the Cape Fear arch and to the north by the Norfolk arch (Figure 1) (Bonini and Woollard, 1960; Harris, 1975). Lower Cretaceous plate reconstructions interpret a relatively narrow Atlantic Ocean that was connected to the Tethys Sea and larger Panthalassa (ancient Pacific Ocean) to the east and west, respectively (Gradstein and Sheridan, 1983; Scotese and McKerrow, 1990; Francis and Frakes, 1993; Scotese, 1997). This connectivity resulted in a westward-flowing circumequatorial current driven by equatorial wind patterns (Gradstein and Sheridan,
COFFEY AND SUNDE 1601
Figure 2. Chronostratigraphic framework for the Lower Cretaceous study interval, plus coeval nomenclature from basins along trend.
1983; Haq, 1984; Francis and Frakes, 1993). The southeastern margin of North America, however, may have been swept by an eastward-flowing protoGulf Stream, the existence of which is hypothesized by Harris and Self-Trail (2006). Lower Cretaceous strata were selected for study because of the extensive thickness of the succession (up to 500 m [1650 ft]) and mixed carbonatesiliciclastic character. Previous work in the basin by Brown et al. (1972) and Zarra (1989) provided a coarse biostratigraphic and sequence-stratigraphic framework (Figure 2). However, limited efforts have been made to relate these units to depositional environments or regional lithology-based stratigraphic frameworks. Although some of the key stratigraphic surfaces identified in this study coincide with key surfaces in previous studies, this study recognizes an additional sequence and attempts to correlate high-frequency sequence-stratigraphic surfaces across the study area within a lithologic context. Attempts were made to improve the biostratigraphic control on the timing of these sequences, but most samples analyzed for microfossils were barren. Hence, identified sequences have been arbitrarily
1602
assigned numbers (0, 1, and 2) until improved age resolutions are available. The extent and significance of mixed carbonatesiliciclastic sediments have been the topic of increased research efforts (e.g., Brooks et al., 2003b; Coffey and Read, 2004, 2007; Halfar et al., 2004; McNeill et al., 2004; LaGesse and Read, 2006; Best et al., 2007; Francis et al., 2007; Harilal et al., 2008). Common depositional controls affecting mixed carbonate-siliciclastic systems include distance from siliciclastic sources, relative sea level change, and climate. METHODS More than 400 wells have been drilled in the North Carolina coastal plain. However, less than 40 of these wells penetrate the subsurface Lower Cretaceous interval; only one well was discontinuously cored (Esso 1 Hatteras Light well, drilled in 1946; Figure 1). Approximately 1500 well-cutting intervals (representing about 4.5 km [2.8 mi] of vertical section) were studied with binocular microscopy from 12 of these wells to determine the
relative abundance of the various lithologies present (Appendix 1). A subset of four wells was selected from the thick, downdip part of the basin for detailed petrographic analysis of cuttings. From this subset, 600 cuttings sample intervals were washed, dried, plastic impregnated, and thin-sectioned for detailed petrographic study. Thin sections were stained with Dickson’s solution (Dickson, 1965) to more accurately identify carbonate grain types, diagenetic history, and lithologies. Dunham’s (1962) carbonate classification scheme is used to characterize the carbonate lithologies. Sandstones are
classified according to the nomenclature of Pettijohn et al. (1987). The percent abundance of lithofacies types was determined for each cuttings interval. The graphical method used to illustrate the cuttings data involved plotting the percent abundance of the lithofacies (left to right in an order approximating the interpreted progressive basinward position of deposition of the lithofacies; Coffey and Read, 2002). Cuttings intervals were plotted along the vertical axis scaled at the same ratio as the geophysical well logs (Figure 3). This method allows easy identification of vertical
Figure 3. Example of cuttings-based lithologic and wireline data used to interpret lithofacies associations and stacking patterns in wells (selected interval from Mobil 2, DR-OT-2-65 well shown here). Middle column shows the percent abundance of cuttings lithologies, grouped by interpreted lithofacies. Arrows indicate the repetitive shoaling-upward successions observed regionally. The right column shows the resulting interpreted lithologic column, with the flooding surfaces indicated (correlatable to neighboring wells; labeled at right). The lithofacies column was interpreted in a top-down manner to identify first appearances and/or increases of specific lithologies in the cuttings data, whereas tying the cuttings lithofacies to wireline responses. The lithofacies legend shown is consistent with all subsequent diagrams. COFFEY AND SUNDE 1603
1604 Constituents Coal; pyrite dessiminated in parrallel, discontinuous bands Plant type not identified Small quatitites in updip wells. Associated with quartz sandstone, siltstone, and shales. Dominantly in the northern parts of the basin, particularly in cuttings intervals lacking carbonate material. Biota Occurrence Core Expression Individual grains of quartzose sand None identified Dominantly fine- to mediumgrained, calcite-cemented, quartzose sandstone. Rare glaucony may be present. None identified Present throughout basin; but more common updip and in northern areas. Dominantly fine- to mediumgrained, calcite-cemented, skeletal quartzose sandstone. Rare glaucony or ooids may be present. Disarticulated, abraded bivalves. Rare echinoderms Present throughout basin. Consists of silt-sized quartz and argellaceous material. Rare feldspar, biotite, muscovite, or glaucony. None identified Present throughout basin. Strong association with nonfossiliferous shale. May have preserved laminae. Coal bed underlying ostracodbearing shale in COST B-2; occurs as carbonaceous fragments in Shell 93–1 and COST B-3 cores. DR-OT-1-46: medium- to coarse-grained, bioturbated, poorly cemented, quartzose sandstone. COST B-3: cemented coarse-grained quartz sandstone at the top of a siliciclastic coarseningupward succession. Possesses root traces and sparse oyster fragments. Cored in all studied basins. Intensively bioturbated, with preserved oscillatory ripples and rare planar laminae. Found near the top of siliciclastic coarsening-upward successions. Cored in the Albemarle embayment, offshore Balitmore Canyon Trough and Southeast Georgia embayment. Intensively bioturbated; densely calcite cemented. DR-OT-1-46 and COST-B-3: bioturbated, fissile, shaley siltstone coarsens upward into quartz sandstone.
Consists of silt-sized quartz and argellaceous material. Rare feldspar, biotite, muscovite, or glaucony. Consists of argellaceous shale with rare silt-sized quartz. None identified
Diatomaceous shale
Light brown in thin section
Primarily diatoms and argillaceous shale. Rare siltsized quartz and glaucony.
DR-OT-1-46 and COST-B-3: Bioturbated, fissile, shaley siltstone coarsens upward into quartz sandstone. DR-OT-1-46 and COST-B-3, bioturbated, fissile quartzose silty shale coarsens upward into quartz sandstone. Not observed in core.
Glauconitic sandstone
Dark green
Fine- to medium-grained sandsized glaucony. Phosophate commonly associated; rare quartz and skeletal fragments.
Present throughout basin. Strong association with nonfossiliferous shale. May have preserved laminae. Present throughout basin. Strong association with siltstone. May have preserved laminae. Rarely present, only found in downdip and northern wells. Associated with marl and planktonic foraminiferabearing siltstone Rarely present and only in small quantities. Typically associated with phosphate in cuttings samples.
Chert Rare planktonic foraminifera and mollusks
Colorless in thin section
Not observed in core. However, fine-grained glaucony is present as a minor constituent in quartzose sandy, skeletalbearing lag deposits of the COST B-3 and GE-1 wells. Not observed in core.
Evaporites
White to colorless
Chert fragments are variably associated with skeletal grains, silt-sized quartz, glaucony, and opaque minerals. Anhydrite and/or gypsum. Rare, admixed quartz sand. None identified
Found at the base of study section in small quantities. Associated with glaucony, phosphate, and algal laminites. Rare, generally found in southern and downdip areas. Found in association with algal laminite, lime mudstone, quartzose sandy miliolid packstones, and ooid grainstones.
COFFEY AND SUNDE
COST GE-1: (A) cement in ooidskeletal grainstone; (B) centimeter-size nodules in lime mudstone or skeletal grainstone; (C) massive chicken-wire anhydrite in variably dolomitized lime mudstone or miliolid wackestone; and (D) layered evaporites. (continued )
1605
1606 Constituents Preserved as discontinuous and undulatory laminae, with rare very fine-grained quartz sand or chert. Algel laminites Not observed in core. Dominantly miliolid skeletal tests, encased in lime mud. Rare very fine grained quartzose sand or skeletal fragments are present. Dominantly miliolid benthic foraminifera, rare bivalves, ostracods, or gastropods. Biota Occurrence Core Expression COST GE-1: Variably dolomitized, miliolid packstone and wackestone beds found closely associated with evaporites, overlying skeletal-ooid grainstones. Very fine grained quartzose sandy lime mudstone. Dolomitized (ferroan) in lower parts of the study interval. Unfossiliferous; sponge spicules present in lower study interval. Small quantities present in most carbonate-dominated cuttings samples. More common in southern and downdip wells. Locally present in small quantities within carbonatedominated intervals. Most common in southern and downdip wells. Associated with evaporites, lime mudstone, and ooid grainstone. Rarely present, this lithofacies is more abundant in the deeper portions of the study interval. Well-rounded and well-sorted ooids and coated grains, cemented by sparry ferroan calcite. Mollusk fragments, peloids, and fine-grained quartzose sand commonly associated. Coated mollusks and rare echinoderms are commonly associated. Present in small quantities of samples containing abundant carbonates, primarily in the southern and downdip regions. Associated with molluskan packstone. COST GE-1: Quartzose sandy lime mudstones are assocaited with miliolidbearing lithofacies and evaporties. This lithofacies typically overlies skeletal-ooid grainstones. COST GE-1: Common skeletal ooid-grainstone beds that are planar and symmetric ripple laminated, as well as trough cross-bedded. Abundant admixed quartzose sand and skeletal material present. Shell 586–1: ooid-rich beds encased in skeletal packstone.
Quartzose sandy packstone and grainstone Most commonly bivalves, rare echinoderms, and brachiopods. Present in small quantities in most cuttings samples throughout the basin. Typically associated with mollusk-bearing packstones.
White
Defined as cuttings fragments that contain about 50:50 siliciclastic and carbonate material. Typically possesses interstitial micrite mud. Typically cemented by calcite. Dominantly bivalves (oysters, rudists, and inoceramids); rare corals and gastropods. Rare, micrite-rimmed bivalves Locally present in small quantities within carbonatedominated wells. Abundant in most cuttings intervals throughout the basin.
Mollusk packstone and grainstone
Light gray to white
Peloid packstone
Light-gray to white carbonate mud with dark-gray peloids
Pelletal packstone
Light gray
Mollusk bivalve packstone and grainstone. Other allochems include rare skeletal fragments and peloids. Finegrained, admixed quartzose sand commonly present. Fine-grained, well-rounded, subspherical peloids possessing interstitial lime mudstone. Fine-grained ooids, quartzose sand, and micrite-rimmed mollusk fragments locally present. Lower very fine grained sized, grain-supported peloids possessing interstitial micrite. None identified
Not specifically observed in core, although a highly variable range of skeletal sandstones to quartzose sandy packstones and grainstones are present in core of all studied regions. Several cored intervals. Most notably, in the COST GE-1 well, where it underlies ooidrich units. Abraison of bivalves is variable. Overlies shale-rich beds in this well. Not specifically observed in core. However, skeletal packstone beds from the COST GE-1 well contain peloids. Oncoid-rich beds of the Shell 586–1 well contain peloids as well. Not observed in core.
Skeletal packstone
Colorless in thin section
Bryozoan and brachiopods dominate. Rare large benthic foraminifera, bivalves, and echinoderms. Planktonic and benthic foraminifera, and thin-walled bivalves are most common.
Locally present in very small quantities of cuttings sample intervals that contain abundant carbonate lithologies Present in small quantities throughout the basin.
Not observed in core.
COFFEY AND SUNDE
Fine-grained skeletal wackestone
Colorless to light gray in thin section
Grain-supported skeletal material possessing interstitial lime mudstone. Allochems show little evidence of abrasion, and rare desseminated quartzose sand is present. Fine-grained skeletal fragments supported in a lime mudstone matrix. Rare admixed very fine grained quartzose sand.
Locally present in small quantities within carbonatedominated cuttings samples.
Not observed in core.
1607
(continued )
1608 Constituents Well-sorted, thin-walled, very fine grained to silt-sized planktonic foraminiferal tests dominate. Rare glaucony and quartzose sand are present. Planktonic foraminifera dominate. Planktonic formanifera in shallower portions of study interval. Locally present in small quantities within carbonaterich cuttings samples. Most commonly found in downdip wells and is associated with marl and lime mudstone. Present in small to moderate quantities of carbonatedominated cuttings intervals in downdip and southern wells, where it is associated with lime mudstone. Not observed in core. Biota Occurrence Core Expression Not observed in core. Fossiliferous in shallower parts of study interval. Argellaceous lime mudstone (+ minor dolomite) in lower parts of study interval. Variable glauconnitic and silt-size quartzose grains are present. Lime mudstone. Dolomitzed (ferroan) near base of study section. Very fine grained glaucony rarely present. Rare sponge spicules at base of study interval. Variably fossiliferous. Typically associated with glaucony, and rare very fine grained quartzose sand. Planktonic and benthic foraminifera, and mollusks are locally present. Present in small quantities, in sample intervals containing abundant carbonate material; primarily in the southern and downdip areas. Locally present in very small quantities. It is primarily located in downdip areas and is generally associated with glaucony and marl. Not observed in core. Not observed in core.
changes in the abundance of cuttings lithofacies types, and easy comparison to the geophysical logs to correct depths for downhole mixing of cuttings and to calibrate petrophysical responses to lithologies. Cuttings data were integrated with geophysical logs to create an interpreted stratigraphic column for each well (Figure 3). Cores were studied from eight offshore exploration wells in the Baltimore Canyon Trough and Southeast Georgia Embayment, in addition to the single cored well from within the onshore part of the Albemarle Basin (Appendix 2). Not all cores studies were age-equivalent to the main study interval, but Lower Cretaceous strata were used to better understand detailed stacking patterns and heterogeneity within lithofacies similar to those observed in cuttings; this effort also helped to constrain lithofacies expression on wireline logs. In addition, comparison of the cuttings data with well logs and core helped to identify intervals prone to downhole mixing of well cuttings. Well data were integrated with available 2-D multichannel onshore seismic reflection data (collected over the North Carolina waterways by the Geophysical Services Inc. in 1972). Synthetic seismograms (generated by Chevron and the authors) constrained well to seismic data ties. Eight seismic lines (about 225 km [140 mi] line length) were used to guide correlations between studied wells and confirm sequence-stratigraphic interpretations using seismic facies descriptions (cf. Mitchum et al., 1977). Well data, cuttings, cores, and article copies of the 2-D seismic data are stored and maintained at the North Carolina Geological Survey; data from the offshore wells are stored at the Delaware Geological Survey.
Coal The coal-bearing lithofacies is dominantly composed of coal, but also may contain minor interbeds of quartz sandstone, siltstone, and shale. The coal beds commonly contain minor amounts of pyrite. This lithofacies is locally present in wells that lie in updip positions and has an average thickness of 1.8 m (5.9 ft). This facies association is interpreted to have been deposited in a backbarrier, delta-plain or coastal-plain setting; environments of deposition include peat swamps and tidal or coastal marshes. The associated pyrite in the coal indicates high sulfur contents, which suggests possible deposition near marine basins (Ingram, 1987; Galloway and Hobday, 1996). However, no sulfur analyses were performed in the scope of this study. The Snuggedy Swamp of South Carolina provides a modern example of backbarrier peat accumulation, occurring behind an abandoned barrier complex (Staub and Cohen, 1979). These peats likely would be preserved as thin, high-sulfur coals and carbonaceous black shales, with the thickest peats flanking the barrier sands (Renton and Cecil, 1979). Cores from the Baltimore Canyon Trough support the presence of coal overlying quartzose sandstones of marginalmarine affinity. Quartzose and Skeletal Quartzose Sandstone Coarse-grained quartz and calcite-cemented very fine-grained quartz sandstone are present throughout the basin, but it is typically slightly thicker in the northern and updip parts of the basin (4 to 7 m [13 to 23 ft]). Skeletal quartz sandstone is present throughout the basin and consists of fine-grained quartz sandstone with admixed, well-rounded mollusk fragments (Figure 4A). Abraded echinoderm fragments, ooids, and glauconite grains are locally present. Cutting fragments are typically white in color, and the sandstones are dominantly classified as subarkosic arenites, following the classification of Pettijohn et al. (1987). In cores of comparable offshore facies from the Baltimore Canyon Trough area, coarsening-upward packages were observed, and sandstones were commonly intensively bioturbated
COFFEY AND SUNDE 1609
LITHOFACIES SUMMARY Ten major interpreted lithofacies are identified in the studied Lower Cretaceous section of the Albemarle embayment (Table 1) (Figure 4). The descriptive summaries and environments of deposition described below are simplified from Sunde (2008). The interpreted environments of deposition range from supratidal to deep-shelf settings (Figure 5).
Figure 4. Examples of selected lithofacies in thin section. Fields of view are indicated on each photomicrograph. (A) Very fine feldspathic sandstone with ferroan calcite cement. Planepolarized light. Well: Mobil 2, DR-OT-2-65; 5260–5270 ft (1603– 1607 m). (B) Phosphatized (P) hardground fragment with glauconitic sand (G). Planepolarized light. Well: Mobil 2, DR-OT-2-65; 6500–6510 ft (1981– 1984 m). (C) Gray siltstone with admixed planktonic foraminifera (F). Plane-polarized light. COST B-3 well, 11,041 ft (3365 m). (D) Ooid (O)-coated grain (CG) grainstone with extensive ferroan calcite cement. Cross-polarized light. Well: Blair 3 Marshall Collins, DR-OT-3-65; 4800–4810 ft (1463–1466 m). (E) Miliolid foram (M) wackestone with admixed very fine silty quartz and local anhydrite (A). Cross-polarized light. Well: COST GE-1, 7072.4 ft (2155.7 m). (F) Quartz sandy to silty mollusk packstone. Bivalve (B) fragments loosely cemented with ferroan carbonate. Plane-polarized light. Well: Blair 3 Marshall Collins, DR-OT-3-65; 4730–4740 ft (1442–1445 m).
Figure 5. Generalized facies association profiles of the Lower Cretaceous sediments in the Albemarle embayment of North Carolina. Siliciclastic-dominated sedimentation (profile A) is most common. Carbonates (profile B) accumulated primarily during periods of low siliciclastic input to the shelf, mostly during the sea level lowstand to early transgressions. Interpreted shelf bathymetric profile is indicated at the top of the diagram. Heavy lines represent the region of most likely accumulation of facies types; light lines represent the zone of less likely accumulation. FWB and SWB = fair-weather- and storm-wave bases, respectively. The facies association legend can be found in Figure 3.
(BI 4–5 of Taylor and Goldring, 1993; Planolities, Palaeophycus, Asterosoma, and Ophiomorphia are most common). Oscillatory ripples and flaser bedding also were rarely observed in these cores. The quartzose sandstone facies association likely was deposited in a range of settings that include fluvial, proximal delta, and shoreface to shallow-shelf regimes (Galloway and Hobday, 1996; Collinson, 2005; Johnson and Baldwin, 2005; Reading and Collinson, 2005). Offshore core analogs from the Baltimore Canyon Trough and Georgia Embayment display stacked coarsening-upward siliciclastic cycles (each about 10 m [33 ft] thick) interpreted to be deposited in highenergy shoreface environments. The presence of
marine fossils in skeletal quartzose sandstones indicates that this sandstone was deposited in marine or marginal-marine settings, such as deltas, shorefaces, and shallow-shelf settings (Galloway and Hobday, 1996; Johnson and Baldwin, 2005). Similar Holocene examples associated with the present highstand sea level position are found on the western Florida shelf and southern United States Atlantic shelf (Milliman et al., 1968; Ginsburg and James, 1974; Doyle and Sparks, 1980; Brooks et al., 2003a, b). These well-sorted quartzose sands were deposited in shorefaces, and barrier island systems developed landward of mollusk-bearing skeletal-quartz sand and grade seaward into fully carbonate molluskan facies of
COFFEY AND SUNDE 1611
the shallow, open-marine inner shelf (Figure 5). Coffey and Read (2007) provide a Paleogene example from the Albemarle embayment, interpreting a similar skeletal-quartz sandstone facies association to have been deposited in a shoreface to shallow inner-shelf setting.
Shale and Siltstone This lithofacies consists of shale and siltstone that are gray to black in color. Generally lacking fossil material, this association is present throughout the basin in great abundance and is commonly associated with skeletal quartz sandstones and sandy mollusk packstones. Shales were rarely cored, although when collected, they gradually coarsen upward to finegrained quartz sandstones. This lithofacies is interpreted to have been deposited in a low-energy setting, lying below or protected from wave energy. Thin, coarser grained beds may represent distal tempestites or remnants of material winnowed during high-energy events. Deposition of shale and silt is widespread in the low-energy settings of siliciclastic-dominated shorelines and continental shelves (cf., Johnson and Baldwin, 2005; Reading and Collinson, 2005). Ludwick (1964) described silt- and clay-size sediments settling in basins behind and offshore of the segmented, sandy barrier islands in the modern northeastern United States Gulf Coast region, interbedded with patches of shell-rich sand and sand layering up to several centimeters thick. Diatomaceous Shale and Marl This association consists of two end members: silica rich and carbonate rich; both are interpreted to represent similar environments of deposition. The silica-rich end member includes diatomaceous shale and planktonic foraminiferal bearing siltstones (Figure 4B). The carbonate-rich end member includes marls, fine-grained skeletal packstones, and planktonic foraminiferal packstones and wackestones. These associations are more common and thicker in the basinal parts of the basin (mean thickness of 4.5 m [15 ft]). Local glauconite grains are identified in thin-sectioned cuttings of this facies. The open-marine fossil assemblage and finegrained character supports a deep-shelf depositional environment for both end members. The silica-rich end member, likely accumulated distal to siliciclastic sediment sources, whereas the carbonate-rich end member likely accumulated in regions removed from siliciclastic sediment sources (Figure 5).
Quartzose Sandy Molluskan Grainstone and Packstone This facies association is dominated by oyster skeletal fragments with variable amounts of admixed quartz sand (Figure 4E). Inoceramid and rudist bivalves also are common skeletal fragments, whereas coral and gastropod fragments are variably present. This association is present throughout the basin, with the greater abundances and thicknesses (mean = 3.5 m [11.5 ft], locally exceeding 9 m [30 ft]) in the southern and downdip parts of the basin. The presence of quartz-rich sandstone and abundant bivalves in this facies suggests an open-marine depositional environment, likely reflecting the shallow shelf (inner middle ramp). Variable mollusk fragment abrasion suggests deposition above stormweather wave base. This association was deposited outboard of near-shore quartzose sand-dominated shorefaces and barrier islands, particularly in regions of low siliciclastic input (Figure 5). The quartzose sandy molluskan packstone and grainstone lithofacies also developed across broad areas of the shelf as transgressive lags during the early stages of transgression. Lithologic differences between these two depositional scenarios are minor, and so they can only be distinguished on the basis of associated rock types and vertical stacking patterns. Surficial sediments on the modern southern United States Atlantic shelf and western Florida shelf are composed of abundant mollusk shell-bearing facies that grade landward to skeletal quartz sands (Milliman et al., 1968; Ginsburg and James, 1974; Brooks et al., 2003a, b). Wilson (1975) describes a Cretaceous example from central Mexico, where rudist bivalve buildups formed basinward of ooid-skeletal sand banks, supporting the observed ooid-rich grainstone stacking pattern in the Albemarle embayment.
1612
Diatomaceous shales are pelagic deposits, resulting from productive surface waters that may have been associated with marine upwelling; nutrient supply directly from continental runoff also may have been important in diatom proliferation (Maliva et al., 1989). Along the modern western Florida shelf and southern United States Atlantic margin, planktonic foraminifera, lime mud, and clay minerals are presently being deposited in deep shelf to upper slope settings; these would be preserved as a marl or chalk deposits (Ludwick, 1964; Milliman et al., 1968; Ginsburg and James, 1974; Doyle and Sparks, 1980). Holdgate and Gallagher (1997) provide a Neogene example from the Gippsland Basin of Australia, whereby planktonic foraminiferal marls were deposited during transgressive systems tracts (TST) in water depths deeper than 100 m (330 ft). Evaporites, Algal Laminites, and Miliolid Wackestone
are commonly found in the restricted upper intertidal regions because of their ability to withstand the stressful hypersaline environmental conditions and frequent subaerial exposure (Wilson, 1975; Kendall and Harwood, 2005). Lime mud resulting from the breakdown of calcareous green algae commonly accumulates in low-energy settings of tidal flats and shallow lagoons (Wilson, 1975). Miliolid benthic foraminifera inhabit a variety of environments, but where they constitute the prevailing allochem type in mud-rich units, stressed, hypersaline conditions commonly prevail (Poag 1981; Brooks et al., 2003b; Wright and Burchette, 2005). Abundant miliolids can be observed in the modern hypersaline lagoons of Shark Bay of Western Australia (Logan and Cebulski, 1970; James et al., 1999). Further, Wilson (1975) describes a Cretaceous example from the El Abra Limestone of central Mexico, where abundant miliolids were deposited in the saline, inner-bank environments.
Ooid Grainstone and Mud-Lean Packstone This association consists of several lithologies that represent similar environments of deposition. It is locally found in southern parts of the basin. Bedded evaporites (gypsum or anhydrite) approximately 2 m (6.6 ft) thick are the most distinctive lithology, whereas algal laminites and quartz sandy lime mudstones are the most abundant of this association (averaging 4.5 m [14.7 ft] thick). Quartzose sandy miliolid packstones and wackestones, admixed with quartz sand-bearing lime mudstones, are commonly found (Figure 4C). Offshore coeval strata cored by the COST GE-1 well from offshore Georgia shows abundant miliolids interbedded with evaporites, lime-mudstones, and thin quartz-rich laminations; planar laminations and oscillatory ripples were observed. The associated lithologies indicate a depositional environment characterized by restricted marine circulation with shallow subtidal to supratidal water depths (0 to 3 m [0 to 10 ft]; Figure 5). The presence of bedded evaporites is diagnostic of hypersaline conditions because of restricted circulation coupled with high rates of evaporation, and frequent, prolonged, subaerial exposure; typical of sabkhas, tidal flats, and restricted lagoons (Wilson, 1975). Cryptalgal mats Ooid-rich carbonates are uncommon in the Albemarle embayment, typically being preserved in the southern and downdip parts of the basin. White in color, ooid grainstones are commonly quartz sandy, and beds have a mean thickness of 3 m (10 ft). Packstones locally comprise peloids, coated skeletal grains, mollusks, or echinoderm skeletal material (Figure 4D). Quartzskeletal-ooid grainstones are found underlying evaporitic facies in the COST GE-1 well, whereas ooid-rich units are sharply overlain and underlain by skeletal packstones in the core from Shell 586-1 well (offshore Baltimore Canyon Trough, United States East Coast). This lithofacies is interpreted to have formed as skeletal-ooid sand sheets and shoals deposited in a high-energy, shallow subtidal to intertidal, innerramp setting (Figure 5). Modern ooids from the Bahamas Bank and Texas Gulf Coast form in subtropical to tropical, wave-agitated, high-energy settings subject to active carbonate deposition (Newell et al., 1960; Rusnak, 1960). Commonly, elevated salinity is a contributing factor to ooid formation, as precipitation of calcite directly from seawater may occur (Rusnak, 1960).
COFFEY AND SUNDE 1613
Peloidal and Pelletal Packstone Peloid packstones consist of dark-gray peloids encased in a carbonate mud matrix. Small, micriterimmed bivalves, very fine grained quartz, and ooids are locally present. This association is uncommon; it was found only in the southern and downdip parts of the basin, rarely exceeding 5 m (16.5 ft) in thickness. The peloidal packstone lithofacies was likely deposited in a mid- to deep-ramp setting, downdip of shallower molluskan-rich buildups and ooid shoals. Boreen et al. (1993) noted the presence of similar pelletal-skeletal muds accumulating in the deep shelf to upper slope setting of the modern Otway continental margin of southern Australia. Wilson (1975) indicates that mud-rich pellet, peloid, and coated grain sediments associated with bioclastic wackestone are commonly found in open-marine, deep-shelf settings, as well as shallow, protected, subtidal settings. Skeletal Packstone Dominated by bryozoan and brachiopod skeletal packstones with little evidence of reworking, this rare association is found in the southern (downdip) parts of the basin. Mud-rich packstones containing pellets, mollusks, and echinoderm fragments also form minor components of this association. This association ranges in thickness from 1 to 5 m (3.3 to 16.5 ft). The skeletal packstone lithofacies is interpreted to have been deposited in a low-energy deep-ramp to outer-shelf setting, near or immediately below storm-wave base. The deep shelf to upper slope (130 to 350 m [427 to 1148 ft] water depth) of the Otway continental margin contains a diverse assemblage of aphotic bryozoans, sponges, and azooxanthellate corals that are accumulating with pelleted muds in the nutrient-rich, upwelling waters (Boreen et al., 1993). This may be a modern analog to the biologically diverse Albemarle embayment assemblage. Within the basin, a similar bryozoan-brachiopod-echinoderm facies accumulated during the Paleogene and Neogene under mesotrophic to possibly eutrophic conditions in the middle to deep (30 to 100 m [98 to 330 ft] interpreted water depth) inner-shelf setting (Coffey and Read, 2004, 2007).
1614
Hardground Characterized by phosphatic and glauconitic sandstones and associated chert nodules (Figure 4B), this association is present throughout the basin in small quantities in well cuttings (chert is most abundant at the base of the study interval). Hardgrounds were not observed directly in core, but sands consisting of glauconite grains and associated phosphatic rim coatings were observed in cuttings fragments. This lithofacies association is interpreted to form as thin surficial coatings less than 1 m (3.3 ft) thick. The hardground lithofacies records episodes of condensed sedimentation, likely related to transgressive drowning of the shelf. Deposition of phosphate, glauconite, and chert is favored in marine waters with elevated nutrient levels coupled with low rates of sedimentation (Cloud, 1955; Harder, 1980; Odin and Letolle, 1980; Glenn and Arthur, 1988; Maliva et al., 1989; Gates et al., 2004). Phosphate deposition occurred during the Paleogene and Neogene along the southeastern North American margin during sea level transgressions, in mid- to deep-shelf, sedimentstarved, current-swept settings (Riggs, 1984; Coffey and Read, 2004, 2007). Harris and Self-Trail (2006) noted the presence of abundant phosphate and glauconite in the vicinity of transgressive flooding surfaces from an Upper Cretaceous core drilled in the North Carolina coastal plain. Glauconite most commonly forms in water depths of 60 to 350 m (197 to 1148 ft) (Odin and Letolle, 1980). Thus, a deep-shelf, open-marine setting with high nutrient levels (more likely to occur during transgressive events) coupled with low sedimentation rates is favored as the interpreted environment of deposition for phosphate, glauconite, and chert accumulations in the Lower Cretaceous sediments of the Albemarle embayment (cf., Savrda et al., 2001).
STACKING PATTERNS The lithofacies data collected from cuttings descriptions were integrated with available geophysical logs and available core to create stratigraphic columns for each well (Figure 3). These data indicate two dominant vertical stacking patterns with a thickness
Figure 6. Examples of representative carbonate (A) and siliciclastic (B) stacking patterns based on well cuttings; interpreted lithofacies columns are shown to the right of the raw cuttings data. Black and white arrows indicate general trends in relative abundance of lithofacies associations, which suggest thin basal flooding events, followed by upward-shoaling trends. Solid black horizontal lines denote interpreted parasequence boundaries.
of 50 to 70 ft (15 to 20 m), bounded by interpreted flooding surfaces (Figure 6). The prevailing pattern in the Albemarle Basin is a siliciclastic-dominated succession that is characteristic of high-energy siliciclastic continental shelves. The less common assemblage is a carbonate-dominated succession that is more characteristic of grain-rich carbonate
continental shelves. These stacking patterns comprise end members; some degree of facies mixing occurs throughout the study area. The siliciclastic-dominated succession (Figure 6A) is found throughout the study area, but is better developed in the northern and updip areas of the basin. The basal part of the interval studied consists
COFFEY AND SUNDE 1615
of molluskan-dominated carbonates that locally are admixed with phosphate and glauconite (likely representing hardground development near the top of the mollusk-rich unit). The molluskan carbonate interval is overlain by deeper water units representing pelagic sedimentation in basinal parts of the basin, whereas shale and siltstone are more prominent in updip positions. Diatomaceous shales and marls grade upward into shales and siltstone. The shale is overlain by a quartzose sand-bearing molluskan carbonate in regions distal to abundant siliciclastic sedimentation. More commonly, the shale and siltstone are overlain by skeletal quartz sandstones that grade and coarsen upward to quartz sandstones. The thick quartz sandstones are locally overlain by a coal-rich unit in the updip areas of the basin. The quartz sandstone or coal is typically overlain by a molluskan carbonate unit of the succeeding parasequence; this stacking pattern is interpreted to mark a flooding surface. This interpretation is further substantiated when the stacking pattern is correlatable in neighboring wells. The carbonate-dominated stacking succession (Figure 6B) is less common and is mostly confined to the southern and downdip parts of the study area. This succession similarly starts with a basal molluskan carbonate locally containing phosphatic and glauconitic hardground surfaces. The molluskan carbonate is overlain by deeper water associations representing pelagic sedimentation in basinal parts of the basin. In rare cases, the marly units are overlain by thin skeletal packstones, which subsequently grade upward to molluskan peloidal packstone. Shale beds can be common, likely signifying proximity to a siliciclastic sediment source. These units grade into quartzose sand-bearing molluskan packstones and grainstones, which then pass upward into quartz sand-bearing ooid-skeletal grainstone. The ooid grainstone is locally capped by algal laminites that are interbedded with rare bedded evaporites and miliolid foram packstones, which suggest deposition in restricted lagoons and tidal flats. Overlying the succession, the ooid grainstone or restricted tidal-flat associations are capped by the molluskan carbonate unit of the succeeding parasequence. Hence, these boundaries mark flooding events.
1616
By applying Waltherian concepts (1894), the described vertical stacking patterns of facies associations can be placed into depositional context. Given the relatively coarse conditioning data sets (cuttings and wireline logs with limited core) and the variability within each package, only broad depositional profiles could be constructed with confidence. Facies association contacts were assumed to be conformable, except in the instances where an association representing a deeper water depositional environment abruptly overlies a shallower water facies association, and the abrupt contact could be correlated in neighboring wells or seismic data. The regionally correlative abrupt contacts were interpreted as flooding surfaces. Regionally mappable shoaling-upward successions were interpreted as parasequences.
DEPOSITIONAL PROFILES Available data sets were integrated to construct idealized depositional models for the siliciclasticand carbonate-dominated systems (Figure 5), each profile representing end members of a continuum. The model represents deposition on a broad, gently sloping continental shelf. Adopted shelf terminology is modified from Wright (1995), Galloway and Hobday (1996), and Boggs (2001). The carbonate sediments are interpreted to have accumulated on a ramp. The carbonate ramp model (Ahr, 1973; Burchette and Wright, 1992) resembles high-energy siliciclastic shelves in terms of hydrodynamics and morphologies. This depositional architecture is supported by the subparallel, regionally extensive reflectors derived from the seismic data and the lack of framework-constructing carbonate organisms. Note that the range of facies associations observed in this study area includes attributes of both siliciclastic-dominated assemblages to the north and carbonate-dominated assemblages to the south. This transition zone in facies associations is long-lived within the Albemarle Basin; similar transitions are present in the overlying Paleogene succession (Coffey and Read, 2007).
SILICICLASTIC- VERSUS CARBONATEDOMINATED PROFILES The siliciclastic-dominated system (Figure 5) consists of marginal-marine environments (lagoons, fluvial, and delta plain) that grade seaward through shoreface, shallow-shelf, and deep-shelf settings. Biostromes, consisting mainly of mollusk bivalve fragments, likely existed in areas of the shallow shelf basinward of the quartzose sand-dominated, high-energy shoreface. This molluskan biostrome is best developed distally from siliciclastic point sources. Proximal to fluvial sediment influx areas, the abundance of siliciclastic material likely limited or diluted carbonate biota, resulting in accumulations dominated by siliciclastic sands, silts, and clays. The deep shelf and slope is characterized by pelagic sedimentation. The siliciclastic-dominated system is similar to the Neogene depositional model of the Gippsland Basin (cf. Holdgate and Gallagher, 1997). The carbonate-dominated system (Figure 5) consisted of restricted tidal flats and lagoons that graded basinward into high-energy, quartzose sandy shoal complexes. Basinward, these graded into a molluskrich shallow shelf. As water depths increased, the amount of admixed carbonate mud also increased. Reworking of mud-rich sediment by benthic feeder organisms resulted in the development of molluskan peloidal packstones. In low-energy areas with limited siliciclastic input, bryozoan and brachiopod skeletal packstones were deposited, possibly facilitated by increased nutrient levels to develop banks or mounds. The deep shelf was characterized by pelagic sedimentation. This carbonate-dominated system is less common than the siliciclastic-dominated system. It also received siliciclastic material during deposition, likely transported to the area via longshore drift in shallow-shelf settings or other bottom-water currents in deeper shelf positions. Burchette and Wright (1992) noted that the outer-ramp zones of many carbonate ramps have admixed, suspension-derived terrigenous mud. The carbonate-dominated system is consistent with the Cretaceous depositional model of central Mexico (cf. Wilson, 1975) but lacks clearly defined rudist bivalve-dominated buildups or banks. The Lower Cretaceous Mural Limestone of Mexico
also possesses similar lithofacies to the Albemarle embayment (Lawton et al., 2004). During relative sea level rises, much of the siliciclastic material is trapped and deposited in estuaries (Galloway and Hobday, 1996). A relative sea level rise therefore favors smaller quantities of siliciclastic material reaching the open shelf, facilitating biogenic carbonate production in these settings (Milliman et al., 1968; Ginsburg and James, 1974). Sea level transgressions during the Early Cretaceous of the Albemarle embayment are likely to have resulted in the widespread deposition of thin molluskan carbonates on the open shelf, similar to the modern molluskan accumulations on the southeastern North American and western Florida shelves (Milliman et al., 1968, Ginsburg and James, 1974). In shelf settings subject to limited sedimentation or to nutrientrich bottom-water currents, hardground surfaces may have developed (e.g., Savrda et al., 2001), resembling those found in younger strata within this basin during similar major transgressions (Riggs, 1984; Coffey and Read, 2004, 2007).
SEISMIC DATA AND INTERPRETATION Seismic data collected landward of the North Carolina outer banks are limited to vintage 2-D multichannel lines (Zarra, 1989, 1990); however, numerous 2-D lines have been collected offshore of the Albemarle embayment (Figure 1). Eight seismic lines that connect the studied wells were integrated into this study (∼225 km [∼140 mi] line length). Reflector geometry guided correlations between the studied wells and provided insights into regional stratal geometries across the basin. Synthetic seismograms were used to tie seismic responses to lithologic descriptions generated from well cuttings and wireline logs. Seismic reflectors observed throughout most of the study interval are subparallel. However, some areas have subtle, shingled, clinoform geometries. Few reflector terminations are observed in the study interval, but those observed include downlap and toplap within the shingled intervals (Figure 7A, 7B). Seismic stratigraphic interpretations are based on reflector configurations and termination types, as
COFFEY AND SUNDE 1617
Figure 7. Seismic expression of mixed carbonate-siliciclastic packages on vintage 2-D reflection data. (A) Raw 2-D data (study interval noted on the margins of the profile); (B) line drawing from raw data to highlight reflector strata geometries; (C) interpreted seismic stratigraphic relationships in the study interval. Note that the local onlap confirms the interpreted sequence boundaries (SB, annotated on diagram margins) from well data, progradational clinoform geometries in the interpreted highstands, and the general absence of seismic expression of the transgressive systems tracts (thin, subtuning). Interpreted maximum flooding surfaces also are annotated on the diagram margins.
described by Mitchum et al. (1977). Subparallel configurations are regarded to have resulted from uniform rates of deposition over a uniformly subsiding shelf or stable basin platform, whereas the observed unfaulted, shingled geometries within seismic intervals are interpreted to reflect progradation with unit thicknesses that lie just within seismic resolution (Figure 7C). The seismic geometries indicate that Lower Cretaceous sediments were deposited on a broad, low-angle shelf that dipped gently toward the southeast. No shelf break is apparent in the seismic data; it presumably lies farther offshore to the east. Relating the seismic reflections to well data was integral to the interpretation of the seismic data. This iterative process produced an integrated sequencestratigraphic framework for the study interval by providing a lithology-based ground truth to better interpret depositional and stratigraphic variations across the basin.
SEQUENCE-STRATIGRAPHIC FRAMEWORK Integration of well cuttings data, 2-D seismic data, core analogs from wells with slightly older strata in adjacent offshore basins, wireline logs, and published literature allowed a sequence-stratigraphic framework to be developed for Lower Cretaceous sediments of the Albemarle Basin. This framework incorporates the facies association-based stratigraphic columns and available biostratigraphic data (Brown et al., 1972; Zarra, 1989). Facies association stratigraphic columns were correlated between wells using seismic reflectors. Seismic data integration ensured that stratigraphic correlations honored the large-scale stratigraphic geometries that defined sediment packages across the basin, particularly the third-order sequence-scale systems tracts (Reading and Levell, 2005). Many of the seismic reflectors were generated from acoustic impedance contrasts at surfaces demarcating changes in third-order systems tracts because of the significant changes in prevailing lithologies associated with these events (Figure 7B, 7C). Sequence-stratigraphic surfaces and systems tracts were assigned in a manner similar to that
COFFEY AND SUNDE 1619
Figure 8. Interpreted lithofacies cross sections constrained by seismic, well, and biostratigraphic data. Note the generally uniform thickness of upward-shoaling, molluskan carbonate-rich transgressive parasequences versus more progradational, siliciclastic-dominated parasequences from highstand systems tracts. (A) Sequence 2 (younger) and (B) sequence 1 (older). Both sequences are flattened on the upper sequence boundary in an attempt to better demonstrate asymmetric progradational fill during sequence highstands within the central part of the basin. Note that late-stage hightstand parasequences are only observed in basin-center wells (middle of diagram). High-frequency component parasequences are noted on the margins of the diagram. TS = transgressive parasequence boundaries; HS = highstand parasequence boundaries. MFS = maximum flooding surface; SB = sequence boundary. All depths are reported in feet (measured depth).
employed by Coffey and Read (2004) using the terminology of Van Wagoner et al. (1988). Flooding surfaces were defined at the top of each shoalingupward succession that could be correlated in wells across the basin; these packages are interpreted as parasequences. Groups of parasequences that demonstrate progressive changes in stacking patterns were grouped as parasequence sets. Sequence boundaries were picked at the tops of major regional shoaling-upward trends; these typically coincided with seismic reflectors (Figure 8). Lowstand systems tract sediments were not recognized in the study area (criteria used were thick, basinal accumulations of shallow-water facies associations in cuttings, coupled with wedgelike onlapping geometries in the seismic profiles). Instead, transgressive parasequence sets are developed as thin, regionally extensive packages that cannot be differentiated as discrete reflectors on the available low-frequency seismic profiles. The TSTs consist of an upward increase in deep-water facies associations, which combine to form overall retrogradational parasequence sets (Figure 8). Maximum flooding surfaces were picked to coincide with the bases of regionally extensive, deep-water facies associations, where they typically coincided with seismic reflectors (Figure 8). Flooding surfaces interpreted from well data also showed evidence of downlapping relationships onto underlying seismic reflectors. Highstand systems tract (HST) sediments consist of upwardshoaling facies associations, which combine to form overall progradational parasequence sets. The HST sediments occasionally show shingled geometries that downlapped onto the interpreted maximum flooding surface on seismic data (Figure 7), indicating progradational sedimentation at the limit of seismic resolution (Mitchum et al., 1977). The three large-scale transgressive-regressive packages identified in the study interval (Figure 8) are interpreted as third-order sequences, each with multiple-component higher order parasequences. Attempts to better constrain the duration of sequences with biostratigraphic analyses failed because of pervasive recrystallization of micritic carbonate matrix during burial diagenesis. The HSTs are thicker than the TSTs, and they have a more pronounced basinward progradation of facies.
COFFEY AND SUNDE 1621
TRANSGRESSIVE VS. HIGHSTAND SEDIMENTATION Transgressive systems tracts are generally thinner and approximately equally distributed across the basin. Internally, they consist of several parasequences that developed as a series of upward-thinning, retrogradational packages (Figure 8). The most abundant component lithofacies is molluskan packstone containing grains of admixed quartz, glauconite, and phosphate. Fine-grained quartz-skeletal sandstones also are locally present. The abundance of carbonate material and fine-grained pelagic and hemipelagic sediments (marls and diatomaceous shales) increases upward, and the maximum abundance of these deep-shelf sediments indicate the approximate position of the maximum flooding surface. The relatively reduced abundance of siliciclastic material relative to carbonate material is likely the result of siliciclastics being trapped and deposited in updip estuaries, thus favoring biogenic carbonate production and accumulation on the shelf. This, coupled with the wave-dominated passivemargin setting, likely resulted in facies belts that were elongated parallel to the paleoshoreline trend (Figure 9). Given the limited input of siliciclastic material during transgressive times, much of the sediment was subjected to wave reworking under conditions of relatively condensed sedimentation rates. The absence of phototrophic organisms capable of constructional carbonate fabrics, such as rudist bivalves, suggests that the oceanographic conditions may have favored oligotrophs; this may be caused by increased nutrient levels along the shelf. Highstand systems tract sedimentation shows a greater abundance of shale and siltstone and quartzose sandstone lithofacies, with limited coal deposited in updip positions (Figure 10). Molluskan carbonates with admixed quartz sand are present. However, their decreased abundance is likely caused by terrigenous sediment hampering the growth of biogenic carbonate material by adding turbidity to the water column, clogging feeding structures, and providing an unsuitable substrate for growth (Ginsburg and James, 1974). Although there appears to be increased siliciclastic sediment input into the basin,
1622
the wave-dominated shelf likely limited the construction of delta systems. Instead, the shoreface likely varied along strike from areas with more sand and less carbonate near- and downcurrent from point sources (Figure 10, inset DD′) to areas with greater amounts of reworked molluskan carbonate in areas removed from quartzose sands (Figure 10, inset CC′). More distal environments appear to transition from diatomaceous shales basinward into marls with planktonic foraminifera. Internal parasequences are developed in an overall progradational or shoaling pattern (Figure 8). In contrast to the siliciclastic-rich late highstands of sequences 0 and 2, the late HST of sequence 1 is carbonate dominated. This package consists of mollusk-rich packstones and grainstones plus miliolid-peloid packstones (Figure 8). Quartzose ooid grainstones, algal laminites, and evaporites are locally present. Increased aridity suggested by these carbonate facies likely limited the amount of fluvial output in this system during this time. Hence, siliciclastic material entering the basin likely was localized to isolated point sources or areas where previously deposited sediments were cannibalized. Coeval strata examined in core from the COST GE-1 well from the adjacent Southeast Georgia Embayment to the south are dominated by oolitic carbonates that are interspersed with bedded anhydrite and red mudstones. Although more extensively developed in this core than observed in the Albemarle Basin, these facies further substantiate the regional development of arid climates. However, the more paleoequatorial location of the COST GE-1 well (and presumably further removed from nearby siliciclastic sources) likely accounts for the predominance of arid peritidal carbonate and evaporite facies. Coeval strata from the northeastern United States Gulf Coast include the Ferry Lake Anhydrite, which further reinforces episodes of widespread evaporate deposition to the south. Climate has long been recognized to be a significant factor in the deposition of carbonate material. One commonly recognized trend is the association of aridity with late highstand and lowstand times because of expansion of the emergent land surface (cf. Riggs, 1984; Read, 1995). This potentially enhances
Figure 9. Paleogeographic model for carbonate-dominated depositional systems. Note inboard development of arid peritidal facies belts suggestive of sabkha conditions that transition basinward to thin wave-dominated coated-grain shoals and beaches. Molluskskeletal carbonates prevail in the wave-swept shallow shelf, which likely transitions to hemipelagic marls and wackestones below the influence of wave sweeping (as demonstrated in the inset shelf profile BB′ at top left). Note siliciclastic material is present, but mostly isolated in the vicinity of fluvial point sources. This material likely is heavily reworked and admixed with mollusk-dominated shelf facies away from the point sources. FWB = fairweather-wave base; SWB = storm-wave base.
evaporation and reduces the potential of siliciclastic sediment transport via fluvial processes to the shelf. During deposition of the late highstand sediments of sequence 1, relative sea level fall may have resulted in a more arid climate (as indicated by abundant carbonates, evaporites, and ooids). In addition, fluvial sources may have avulsed or migrated to more distal
positions along the shoreline relative to the study area, thus decreasing the input of siliciclastic material during the late highstand of sequence 1. Observations of the Pleistocene surficial shelf sediments of the southeastern United States provide an analog to the Lower Cretaceous of North Carolina. The spatial distribution and production
COFFEY AND SUNDE 1623
Figure 10. Paleogeographic model for siliciclastic-dominated depositional systems. Note more widespread sand-prone facies belts that likely initiated at fluvial point sources, but were subjected to extensive wave reworking and longshore transport to develop as shore-parallel features. Also note the presence of coastal-plain facies (mudstones with associated coals) in proximal settings, suggestive of more humid climates. Inset depositional profiles CC′ and DD′ depict more abrupt shelf profiles (1) with increased detrital carbonate material in areas removed from siliciclastic point sources and more flattened, argillaceous shelf profiles (2) in proximity of terrigenous point sources. FWB and SWB, approximate fairweather- and storm-wave bases, respectively.
rates of carbonates are likely very different in the Pleistocene relative to the Cretaceous because of the predominantly ice-house Neogene conditions. During lowstand times when the climate was drier (and presumably windier), ooid and mollusk-rich carbonates formed along the southeastern United
1624
States and western Florida shelves (Milliman et al., 1968; Ginsburg and James, 1974; Ingram, 1987; Brooks et al., 2003a, b). During the present sea level highstand, carbonate sedimentation is locally reduced because of the effects of increased siliciclastic sedimentation (Milliman et al., 1968;
Ginsburg and James, 1974; Brooks et al., 2003a, b). Evidence of a dry-to-wet climate transition during the Holocene sea level rise also is recorded along the northeastern and southeastern margins of Australia (Ferland and Roy, 1997; Francis et al., 2007).
facies development and distribution in the Albemarle Basin.
IMPLICATIONS FOR HYDROCARBON EXPLORATION No wells have tested coeval offshore North Carolina units, but Lower Cretaceous strata have been recognized as prospective hydrocarbon exploration targets in the Carolina Trough area (Vigil, 1998). Hence, this documentation of facies, stacking patterns, and regional depositional sequences may aid in future downdip exploration ventures. Some facies within the onshore succession resemble gas-bearing units on the Scotian Shelf and Baltimore Canyon Trough areas to the north (Mattick and LibbyFrench, 1988; Sawyer, 1988). The best porosity observed in the Albemarle Basin study interval was in dolomitized highstand carbonates. Hydrocarbon staining observed in similar Jurassic oolitic grainstones from the most downdip well studied (Esso 1 Hatteras Light, Figure 1) confirms the presence of mature source rocks within the Albemarle Basin. Unpublished geochemical evaluation of these samples suggests a Jurassic marine source rock in the early stages of maturity that is capable of localized oil generation. Gas and condensate shows are better documented from the offshore Wilmington and Baltimore Canyon Troughs to the north (Amato and Simonis, 1979; Edson, 1987; Vigil, 1998). However, these shows are from older Jurassic prograding marginal-marine siliciclastic successions.
OCEANOGRAPHIC CONTROLS Nutrient levels are considered to have been high in the Albemarle Basin during the Early Cretaceous. This is supported by the presence of phosphate and glauconite-rich hardground fragments and abundance of heterozoan skeletal carbonate assemblages (cf. James, 1997). Similar hardground surfaces were extensively developed in the Albemarle Basin during the Cenozoic (Riggs, 1984; Coffey and Read, 2004, 2007). They most commonly developed in association with major transgressive events on the middle to deep shelf in sediment-starved, current-swept settings. Early Cretaceous relative sea level rises likely also resulted in the formation of hardground surfaces in similar settings. Heterozoan carbonate assemblages are favored in regions with elevated nutrient levels mostly because of the inability of photozoan communities to survive under these conditions. The observation that oligotrophic communities and phosphate- or glauconite-bearing facies associations are developed in the Lower Cretaceous of the Albemarle Basin compare favorably with similar facies relationships observed in the Paleogene and Neogene from the same basin (Coffey and Read, 2007; Riggs, 1984). The apparent longevity of nutrientenriched waters in this area suggests that basin configurations responsible for nutrient enrichment in the Cenozoic, namely, shelf promontories presumably set up by basement highs along the passive margin, likely were present as bathymetric features capable of influencing boundary currents similar to the modern Gulf Stream in the Early Cretaceous. Although greatly subdued relative to modern flow rates by the prevailing greenhouse climates and more sluggish ocean circulation, the presence of an ancestral Gulf Stream system in the Early Cretaceous may have been a factor in carbonate
CONCLUSIONS This study documents the lithofacies associations and regional stacking patterns of Lower Cretaceous strata from the onshore Atlantic coastal plain of eastern North Carolina. The high degree of mixing between siliciclastic and carbonate components within the observed facies resulted from the combined effects of a wave-swept shelf geometry, variable (both temporal and spatial) input of siliciclastic material, and also perhaps the transition zone from
COFFEY AND SUNDE 1625
carbonate-dominated to siliciclastic-dominated depositional systems. The siliciclastic lithofacies associations observed are dominated by near-shore, relatively high-energy shelf assemblages that contain admixed detrital carbonate skeletal grains. Carbonate-dominated assemblages commonly incorporate siliciclastic sand as the nuclei for coated grains. Elsewhere, they appear to develop in areas that are removed from primary siliciclastic point sources, either spatially or temporally. Both assemblages appear to transition basinward into marl-prone facies. Three upper Aptian to Albian sequences were identified in cuttings and log data; they can be correlated across the Albemarle Basin with vintage 2-D seismic data. Sequences are characterized by transgressive parasequences that have stacked, upward-shoaling packages of relatively uniform
thickness and overall retrogradational stacking patterns. Highstand parasequences have progradational geometries that progressively thicken basinward. Sequence lowstands were not identified in the relatively updip part of the basin studied. Differentiation of carbonate- and siliciclastic-prone facies is most pronounced in late highstand sediments, possibly because of greater paleogeographic (shelf morphology) influence on facies distributions. This study provides lithologic and sequencestratigraphic calibration to aid in future hydrocarbon exploration in the adjacent offshore Central Atlantic margin of the eastern United States. It also demonstrates a cost-effective manner for lithologic calibration of geophysical data sets to provide a more holistic sequence-stratigraphic framework in areas with limited core control.
APPENDIX 1: LOCATION AND KELLY BUSHING INFORMATION FROM WELLS INCLUDED IN THIS STUDY
Well Location and Kelly Bushing Elevations for Wells from the Offshore United States Mentioned in this Study Planning Area Mid-Atlantic Mid-Atlantic Mid-Atlantic Mid-Atlantic Mid-Atlantic Mid-Atlantic Mid-Atlantic South Atlantic NCGS Code** CK-OT-1-65 CK-OT-1-69 DR-OT-1-46 DR-OT-1-47 DR-OT-1-65 DR-OT-2-65 DR-OT-2-71 DR-OT-2-74 DR-OT-3-65 HY-OT-1-65 HY-OT-2-65 Well Name* Shell 93-1 Shell 372-1 Shell 586-1 Shell 587-1 Tenneco 495-1 COST B-2 COST B-3 COST GE-1 Well Name Twiford 1 Kellog 1 Esso 1 Hatteras Light Esso 2 Mobil 1 Mobil 2 Westvaco A 2 First Colony Farms 2 Marshall Collins 1 Mobil 3 Octavius Ballance 1 Latitude (N) 37°53′35″ 38°36′01″ 38°24′19″ 38°22′52″ 38°27′59″ 39°22′32″ 38°55′01″ 30°37′08″ Latitude (N) 36°18′10″ 36°07′02″ 35°15′00″ 35°42′12″ 35°59′55″ 35°26′20″ 35°51′48″ 35°56′38″ 35°53′00″ 35°18′25″ 35°27′25″ Longitude (W) 73°44′09″ 72°56′13″ 73°13′03″ 73°09′52″ 73°22′39″ 72°44′04″ 72°46′22″ 80°17′59″ Longitude (W) 75°55′30″ 75°51′10″ 75°31′45″ 75°35′54″ 75°52′00″ 75°34′35″ 75°51′04″ 75°52′20″ 75°40′15″ 75°49′45″ 76°01′50″ Kelly Bushing ft (m) 48 (14.6) 48 (14.6) 48 (14.6) 48 (14.6) 88 (26.8) 90 (27.4) 42 (12.8) 99 (30.2) Kelly Bushing ft (m) 12 (3.7) 17 (5.2) 24 (7.3) 21 (6.4) 24 (7.3) 24 (7.3) 23 (7.0) 11 (3.4) 14 (4.3) 24 (7.3) 10 (3.0)
*The first name of the well refers to the well operator; the following three digits refer to the block lease number, and the final digit is the well number. For Continental Offshore Stratigraphic Test (COST) wells, the letters and numbers refer to the depositional basin (B denotes Baltimore Canyon Trough and GE denotes Southeast Georgia Embayment) and well number, respectively. **The first two letters of the North Carolina Geological Survey (NCGS) well code indicate the county where drilled (CK = Currituck; DR = Dare; HY = Hyde); the following two letters indicate the type of well; in this case, all are oil test (OT); the following digit indicates the well number drilled that year; and the final two digits indicate the year drilled.
APPENDIX 2: SUMMARY OF CORE ANALOG DATA INTEGRATED INTO THE STUDY
Core Analog Data*
Well DR-OT-1-46 Reference Self-Trail (2006, personal communication) Self-Trail (2006, personal communication) Amato and Simonis (1979) Scholle (1977) Scholle (1977) Scholle (1977) Amato and Bebout (1978) Edson (1986) Amato (1986) Amato (1986) Edson (1987) Material core fragments Depth (feet MD) 6309–7133 Age late Albian–early Cenomanian (CC9B) early Valanginian–early Hauterivian (CC4-3) Hauterivian–Valanginian late Albian Aptian Berriasian Albian–Early Cretaceous Albian Hauterivian Berriasian(?) Albian–Hauterivian Dominant Lithofacies Quartzose and skeletal quartzose sandstone Quartzose and skeletal quartzose sandstone Ooid-skeletal grainstones and packstones Quartzose and skeletal quartzose sandstone Quartzose and skeletal quartzose sandstone Quartzose and skeletal quartzose sandstone Ooid grainstone and anhydrite Ooid-skeletal grainstones and packstones Lithic and skeletal quartzose sandstone Siltstone and silty sandstone Skeletal packstones and floatstones
*Wells identified in bold text have biostratigraphic evidence of Albian Age (roughly coeval to the study interval).
REFERENCES CITED
Ahr, W. M., 1973, The carbonate ramp: An alternative to the shelf model: Gulf Coast Association of Geological Societies Transactions, v. 23, p. 221–225. Amato, R. V., ed., 1986, Shell Baltimore Rise 93–1 well geological and operational summary: Outer continental shelf Report Minerals Management Service 86–0128, 55 p. Amato, R. V., and J. W. Bebout, eds., 1978, Geological and operational summary COST No. GE-1 well, Southeast Georgia Embayment area, South Atlantic: OCS Open File Report 78–668, Reston, U.S. Department of Interior, U.S. Geological Survey, 122 p. Amato, R. V., and E. K. Simonis, 1979, Geological and operational summary, COST no. B-3 well, Baltimore Canyon Trough area, Mid-Atlantic: OCS U.S. Geological Survey Open-File Report 79–1159, 118 p. Best, M. M., T. C. W. Ku, S. M. Kidwell, and L. M. Walter, 2007, Carbonate preservation in shallow marine environments; unexpected role of tropical siliciclastics: Journal of Geology, v. 115, no. 4, p. 437–456, doi: 10 .1086/518051. Boggs, S., 2001, Principles of sedimentology and stratigraphy, 3d ed.: Upper Saddle River, Prentice Hall, 726 p. Bonini, W. E., and G. P. Woollard, 1960, Subsurface geology of North Carolina–South Carolina coastal plain from seismic data: AAPG Bulletin, v. 44, no. 3, p. 298–315.
Boreen, T. N., J. C. Wilson, and D. Heggie, 1993, Surficial coolwater carbonate sediments on the Otway continental margin, southeastern Australia: Marine Geology, v. 112, p. 35–56, doi: 10.1016/0025-3227(93)90160-W. Brooks, G. R., L. J. Doyle, R. A. Davis, N. T. DeWitt, and B. C. Suthard, 2003a, Patterns and controls of surface sediment distribution: West-central Florida inner shelf: Marine Geology, v. 200, p. 307–324, doi: 10.1016/S0025-3227(03)00189-0. Brooks, G. R., L. J. Doyle, B. C. Suthard, S. D. Locker, and A. C. Hine, 2003b, Facies architecture of the mixed carbonate /siliciclastic inner continental shelf of west-central Florida: Implications for Holocene barrier development: Marine Geology, v. 200, p. 325–349, doi: 10.1016/S0025-3227 (03)00190-7. Brown, P. M., J. A. Miller, and F. M. Swain, 1972, Structural and stratigraphic framework, and spatial distribution of permeability of the Atlantic coastal plain, North Carolina to New York, Washington: U.S. Geological Survey Professional Paper 796, 79 p. Burchette, T. P., and V. P. Wright, 1992, Carbonate ramp depositional systems: Sedimentary Geology, v. 79, p. 3–57, doi: 10 .1016/0037-0738(92)90003-A. Cloud, P. E., 1955, Physical limits of glauconite formation: AAPG Bulletin, v. 39, no. 4, p. 484–492. Coffey, B. P., and J. F. Read, 2002, High-resolution sequence stratigraphy in Tertiary carbonate-rich sections by thin-sectioned well cuttings: AAPG Bulletin, v. 86, no. 8, p. 1407–1415.
COFFEY AND SUNDE
1627
Coffey, B. P., and J. F. Read, 2004, Mixed carbonate-siliciclastic sequence stratigraphy of a Palaeogene transition zone continental shelf, southeastern U.S.A.: Sedimentary Geology, v. 166, p. 21–57, doi: 10.1016/j.sedgeo.2003.11.018. Coffey, B. P., and J. F. Read, 2007, Subtropical to temperate facies from a transition zone, mixed carbonate-siliciclastic system, Palaeogene, North Carolina, U.S.A.: Sedimentology, v. 54, no. 2, p. 339–365, doi: 10.1111/j.1365-3091.2006 .00839.x. Collinson, J. D., 2005, Alluvial sediments, in H. G. Reading, ed., Sedimentary environments: Processes, facies and stratigraphy, 3d ed.: Malden, Blackwell Publishing, p. 37–81. Dickson, J. A. D., 1965, A modified staining technique for carbonates in thin section: Nature, v. 205, 587 p., doi: 10 .1038/205587a0. Doyle, L. J., and T. N. Sparks, 1980, Sediments of the Mississippi, Alabama, and Florida (MAFLA) continental shelf: Journal of Sedimentary Petrology, v. 50, no. 3, p. 905–916. Dunham, R. J., 1962, Classification of carbonate rocks according to their depositional texture, in W. E. Ham, ed., Classification of carbonate rocks—A symposium: AAPG Memoir 1, p. 108–121. Edson, G., ed., 1986, Shell Wilmington Canyon 586–1 Geological and operational summary: OCS Report MMS 86–0099, 46 p. Edson, G., ed., 1987, Shell Wilmington Canyon 372–1 Geological and operational summary: OCS Report MMS 87–0118, 49 p. Eluik, L. S., 1978, The Abenaki Formation, Nova Scotia Shelf, Canada—A depositional and diagenetic model for a Mesozoic carbonate platform: Bulletin of Canadian Petroleum Geology, v. 26, no. 4, p. 424–514. Ferland, M. A., and P. S. Roy, 1997, Southeastern Australia: A sea-level dependent, cool-water carbonate margin, in N. P. James and J. A. D. Clarke, eds., Cool-water carbonates: SEPM Special Publication 56, p. 37–52. Francis, J. E., and L. A. Frakes, 1993, Cretaceous climates, in P. Wright, ed., Sedimentology review: Boston, Blackwell Scientific Publications, p. 17–30. Francis, J. M., G. B. Dunbar, G. R. Dickens, I. A. Sutherland, and A. W. Droxler, 2007, Siliciclastic sediment across the north Queensland margin (Australia): A Holocene perspective on reciprocal versus coeval deposition in tropical mixed siliciclastic-carbonate systems: Journal of Sedimentary Research, v. 77, p. 572–586, doi: 10.2110/jsr.2007.057. Galloway, W. E., and D. K. Hobday, 1996, Terrigenous clastic depositional systems, applications to fossil fuel and groundwater resources, 2d ed.: New York, Springer, 489 p. Gates, L. M., N. P. James, and B. Beauchamp, 2004, A glass ramp: Shallow-water Permian spiculitic chert sedimentation, Sverdrup Basin, Arctic Canada: Sedimentary Geology, v. 168, p. 125–147, doi: 10.1016/j.sedgeo.2004.03.008. Ginsburg, R. N., and N. P. James, 1974, Holocene carbonate sediments of continental shelves, in C. A. Burk and C. L. Drake, eds., The geology of continental margins: New York, Springer-Verlag, p. 137–155. Glenn, C. R., and M. A. Arthur, 1988, Petrology and major element geochemistry of Peru margin phosphorites and associated diagenetic minerals: Authigenesis in modern organic-rich sediments: Marine Geology, v. 80, p. 231–267, doi: 10.1016/0025-3227(88)90092-8.
Gradstein, F. M., and R. E. Sheridan, 1983, On the Jurassic Atlantic Ocean and a synthesis of results of DSDP Project Leg 76: Initial Reports of the Deep Sea Drilling Project, v. 76, p. 913–943. Halfar, J., J. C. Ingle, and L. Godinez-Orta, 2004, Modern nontropical mixed carbonate-siliciclastic sediments and environments of the southwestern Gulf of California, Mexico: Sedimentary Geology, v. 165, no. 1–2, p. 93–115, doi: 10 .1016/j.sedgeo.2003.11.005. Haq, B. U., 1984, Paleoceanography: A synoptic overview of 200 million years of ocean history, in B. U. Haq and J. D. Milliman, eds., Maine geology and oceanography of Arabian Sea and coastal Pakistan: New York, Van Nostrand Reinhold Company, p. 201–231. Haq, B. U., J. Hardenbol, and P. R. Vail, 1987, Chronology of fluctuating sea levels since the Triassic: Science, v. 235, p. 1156–1167, doi: 10.1126/science.235.4793.1156. Hardenbol, J., J. Thierry, M. B. Farley, Th. Jacquin, P.-C. De Graciansky, and P. R. Vail, 1998, Mesozoic and Cenozoic sequence chronostratigraphic framework of European basins, in P.-C. De Graciansky, J. Hardenbol, Th. Jacquin, and P. R. Vail, eds., Mesozoic and Cenozoic sequence stratigraphy of European basins: SEPM Special Publication 60, p. 3–13, charts 1–8, CD-ROM. Harder, H., 1980, Syntheses of glauconite at surface temperatures: Clays and Clay Minerals, v. 28, no. 3, p. 217–222, doi: 10.1346/CCMN.1980.0280308. Harilal, S., K. Biswal, A. Sood, and V. Rangachari, 2008, Identification of reservoir facies within a carbonate and mixed carbonate-siliciclastic sequence: Application of seismic stratigraphy, seismic attributes, and 3D visualization: The Leading Edge, v. 27, 18 p. Harris, W. B., 1975, Stratigraphy, petrology, and radiometric age (Upper Cretaceous) of the Rocky Point Member, Peedee Formation, North Carolina: Ph.D. dissertation, Chapel Hill, North Carolina, University of North Carolina, 189 p. Harris, W. B., and J. M. Self-Trail, 2006, Late Cretaceous base level lowering in Campanian and Maastrichtian depositional sequences, Kure Beach, North Carolina: Stratigraphy, v. 3, no. 3, p. 195–216. Holdgate, G., and S. Gallagher, 1997, Microfossil paleoenvironments and sequence stratigraphy of Tertiary cool-water carbonates, onshore Gippsland Basin, southeastern Australia, in N. P. James and J. A. D. Clarke, eds., Cool-water carbonates: SEPM Special Publication 56, p. 205–220. Ingram, R. L., 1987, Peat deposits of North Carolina: Raleigh, Department of Natural Resources and Community Development, Division of Land Resources: Geological Survey Section, Bulletin 88, 84 p. James, N. P., 1997, The cool-water carbonate depositional realm, in N. P. James and J. A. D. Clarke, eds., Cool-water carbonates: SEPM Special Publication 56, p. 1–20. James, N. P., L. B. Collins, Y. Bone, and P. Hallock, 1999, Subtropical carbonates in a temperate realm: Modern sediments on the southwest Australian Shelf: Journal of Sedimentary Research, v. 69, no. 6, p. 1297–1321, doi: 10 .2110/jsr.69.1297.
Johnson, H. D., and C. T. Baldwin, 2005, Shallow clastic seas, in H. G. Reading, ed., Sedimentary environments: Processes, facies and stratigraphy, 3d ed.: Malden, Blackwell Publishing, p. 232–277. Kendall, A. C., and G. M. Harwood, 2005, Marine evaporites: Arid shorelines and basins, in H. G. Reading, ed., Sedimentary environments: Processes, facies and stratigraphy, 3d ed.: Malden, Blackwell Publishing, p. 281–325. Lagesse, J., and J. F. Read, 2006, Up-dip sequence development on a wave- and current-dominated, mixed carbonatesiliciclastic continental shelf; Paleogene, North Carolina, eastern U.S.A.: Sedimentary Geology, v. 184, no. 1–2, p. 155–182, doi: 10.1016/j.sedgeo.2005.10.004. Lawton, T. F., C. M. Gonzalez-Leon, S. G. Lucas, and R. W. Scott, 2004, Stratigraphy and sedimentology of the upper Aptian–upper Albian Mural Limestone (Bisbee Group) in northern Sonora, Mexico: Cretaceous Research, v. 25, p. 43–60, doi: 10.1016/j.cretres.2003.09.003. Logan, B. W., and D. E. Cebulski, 1970, Sedimentary environments of Shark Bay, Western Australia, in B. W. Logan, G. R. Davies, J. F. Read, and D. E. Cebulski, Carbonate sedimentation and environments, Shark Bay, Western Australia: AAPG Memoir 13, p. 1–37. Ludwick, J. C., 1964, Sediments in northeastern Gulf of Mexico, in R. L. Miller, ed., Papers in marine geology, Shepard Commemorative Volume: New York, Macmillan Company, p. 204–238. Maliva, R. G., A. H. Knoll, and R. Siever, 1989, Secular change in chert distribution: A reflection of evolving biological participation in the silica cycle: Palaios, v. 4, p. 519–532, doi: 10.2307/3514743. Mancini, E. A., and T. M. Puckett, 2005, Jurassic and Cretaceous transgressive-regressive (T-R) cycles, northern Gulf of Mexico, U.S.A.: Stratigraphy, v. 2, no. 1, p. 31–48. Manspeizer, W., 1985, Early Mesozoic history of the Atlantic passive margin, in C. W. Poag, ed., Geologic evolution of the United States Atlantic margin: New York, Van Norstrand Reinhold Company, p. 1–23. Mattick, R. E., and J. Libby-French, 1988, Petroleum geology of the United States Atlantic continental margin, in R. E. Sheridan and J. A. Grow, eds., The Atlantic continental margin, U.S., The Geology of North America, Boulder, Geological Society of America, v. I-2, p. 445–462. McNeill, D. F., K. J. Cunningham, L. A. Guertin, and F. S. Anselmetti, 2004, Depositional themes of mixed carbonate-siliciclastics in the South Florida Neogene; application to ancient deposits, in G. M. Grammer, P. M. Harris, and G. P. Eberli, eds., Integration of outcrop and modern analogs in reservoir modeling: AAPG Memoir 80, p. 23–43. Milliman, J. D., O. H. Pilkey, and B. W. Blackwelder, 1968, Carbonate sediments on the continental shelf, Cape Hatteras to Cape Romain: Southeastern Geology, v. 9, p. 245–267. Mitchum, R. M., Jr., P. R. Vail, and J. B. Sangree, 1977, Seismic stratigraphy and global changes of sea level: Part 6. Stratigraphic interpretation of seismic reflection patterns in depositional sequences, in C. E. Payton, ed., Seismic stratigraphy—Applications to hydrocarbon exploration: AAPG Memoir 26, p. 117–133.
Newell, N. D., E. G. Purdy, and J. Imbrie, 1960, Bahamian oölitic sand: Journal of Geology, v. 68, no. 5, p. 481–497, doi: 10 .1086/626683. Odin, G. S., and R. Letolle, 1980, Glauconitization and phosphatization environments: A tentative comparison, in Y. K. Bentor, ed., Marine phosphorites—Geochemistry, occurrence, genesis: SEPM Special Publication 29, p. 227–237. Owens, J. P., and G. S. Gohn, 1985, Depositional history of the Cretaceous series in the U.S. Atlantic coastal plain: Stratigraphy, paleoenvironments, and tectonic controls of sedimentation, in C. W. Poag, ed., Geologic evolution of the United States Atlantic margin: New York, Van Norstrand Reinhold Company, p. 25–86. Pettijohn, F. J., P. E. Potter, and R. Seiver, 1987, Sand and sandstone: New York, Springer-Verlag, 553 p. Poag, C. W., 1981, Ecological atlas of benthic foraminifera of the Gulf of Mexico: Woods Hole, Hutchinson Ross Publishing Company, 175 p. Prather, B. E., 1991, Petroleum geology of the Upper Jurassic and Lower Cretaceous, Baltimore Canyon Trough, western North Atlantic Ocean: AAPG Bulletin, v. 75, no. 2, p. 258–277. Read, J. F., 1995, Overview of carbonate platform sequences, cycle stratigraphy and reservoirs in greenhouse and ice-house worlds, in J. F. Read, C. Kerans, L. J. Weber, J. F. Sarg, and F. M. Wright, eds., Milankovitch sea-level changes, cycles, and reservoirs on carbonate platforms in greenhouse and ice-house worlds: SEPM Short Course 35, p. 1–102. Reading, H. G., and J. D. Collinson, 2005, Clastic coasts, in H. G. Reading, ed., Sedimentary environments: Processes, facies and stratigraphy, 3d ed.: Malden, Blackwell Publishing, p. 154–228. Reading, H. G., and B. K. Levell, 2005, Controls on the sedimentary rock record, in H. G. Reading, ed., Sedimentary environments, 3d ed.: Processes, facies and stratigraphy: Malden, Blackwell Publishing, p. 5–36. Renton, J. J., and C. B. Cecil, 1979, The origin of mineral matter in coal, in A. C. Donaldson, M. W. Presley, and J. J. Renton, eds., Carboniferous coal guidebook: West Virginia Geological and Economic Survey, v. 1, p. 206–223. Riggs, S. R., 1984, Paleoceanographic model of Neogene phosphorite deposition, U.S. Atlantic continental margin: Science, v. 223, no. 4632, p. 123–131, doi: 10.1126 /science.223.4632.123. Rusnak, G. A., 1960, Some observations of recent oolites: Journal of Sedimentary Petrology, v. 30, no. 3, p. 471–480. Savrda, C. E., J. V. Browning, H. Krawinkel, and S. P. Hesselbo, 2001, Firmground ichnofabrics in deep-water sequence stratigraphy, Tertiary clinoform-toe deposits, New Jersey slope: Palaios, v. 16, p. 294–305, doi: 10.1669/0883-1351(2001) 0162.0.CO;2. Sawyer, D. S., 1988, Thermal evolution, in R. E. Sheridan and J. A. Grow, eds., The Atlantic continental margin, U.S.: The Geology of North America: Boulder, Geological Society of America, v. I-2, p. 417–428. Scholle, P. A., 1977, Geological studies on the COST B-2 well, U.S. mid-Atlantic outer continental shelf area, Geological Survey Circular 750: U.S. Geological Survey, 79 p.
COFFEY AND SUNDE
1629
Scotese, C. R., 1997, Continental drift flip book, 7th ed.: Arlington, Texas, 80 p., accessed September 11, 2013, http://www.scotese.com/scotesepubs.htm. Scotese, C. R., and W. S. McKerrow, 1990, Revised world maps and introduction, in C. R. Scotese and W. S. McKerrow, eds., Palaeozoic palaeogeography and biogeography: London Geological Society Memoir 12, p. 1–21. Staub, J. R., and A. D. Cohen, 1979, The Snuggedy Swamp of South Carolina—A back-barrier estuarine coal-forming environment: Journal of Sedimentary Petrology, v. 49, p. 133–144. Sunde, R. F., 2008, Sequence stratigraphy of the mixed clasticcarbonate Lower Cretaceous Albemarle embayment: M. Sc. Thesis, Simon Fraser University, North Carolina, 163 p. Taylor, A. N., and R. Goldring, 1993, Description and analysis of bioturbation and ichnofabric: Journal of the Geological Society, v. 150, no. 1, p. 141–148, doi: 10.1144/gsjgs.150 .1.0141. Van Wagoner, J. C., H. W. Posamentier, R. M. Mitchum, P. R. Vail, J. F. Sarg, T. S. Loutit, and J. Hardenbol, 1988, An overview of the fundamentals of sequence stratigraphy and key definitions, in C. K. Wilgus, B. S. Hastings, C. G. St. C. Kendall, H. W. Posamentier, C. A. Ross, and J. C. Van Wagoner, eds., Sea-level changes: An integrated approach: SEPM Special Publication 42, p. 39–45.
Vigil, D. L., 1998, North Carolina/Minerals Management Service Technical Workshop on Manteo Unit Exploration: February 4–5, 1998, OCS Study MMS 98–0024, U.S. Department of Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, 168 p. Walther, J., 1894, Einleitung in die geologia als historische wissenschaft, Bd. 3, Lithogenesis der Gegenwart: Jena, Fischer Verlag, p. 535–1055. Wilson, J. L., 1975, Carbonate facies in geologic history: New York, Springer-Verlag, 471 p. Wright, L. D., 1995, Morphodynamics of inner continental shelves: Ann Arbor, CRC Press, 241 p. Wright, V. P., and T. P. Burchette, 2005, Shallow-water carbonate environments, in H. G. Reading, ed., Sedimentary environments: Processes, facies and stratigraphy, 3d ed.: Malden, Blackwell Publishing, p. 325–394. Zarra, L., 1989, Sequence stratigraphy and foraminiferal biostratigraphy for selected wells in the Albemarle embayment, North Carolina: North Carolina Geological Survey OpenFile Report 89-5, 48 p. Zarra, L., 1990, Review of seismic reflection data from the North Carolina coastal plain and adjacent continental shelf: Raleigh, U.S. Geological Survey Section, Division of Land Resources, Department of Environment, Health, and Natural Resources, 16 p.
