Abstract Characterization of 15 stratigraphic sections of the Pennsylvanian Jackfork Group deepwater (turbidite) deposits of Arkansas have provided a set of criteria to distinguish an updip slope facies tract from a downdip basinal facies tract . The updip facies tract is characterized by lenticular sandstone packages with internal thick-bedded, lenticular to sheet sandstones, associated muddy debrites, and other ‘disturbed’ strata. Characteristic features at a smaller scale include (a) irregular upper and lower slumped/scoured surfaces of beds, (b) stretched, distorted, and contorted shales, (c) a wide variety of lithofacies, including muddy debrites and pseudo-conglomerates or breccias, (d) common shale rip-up clasts in sandstones, (e) non-systematic vertical stacking of diverse facies, and (f) overall fining- and thinning-upward stratification pattern. Lenticular, channel-fill sandstones generally comprise >50% of the sandstone strata. By contrast, the downdip basinal facies tract is characterized by evenly-bedded sheet sandstones, as well as thinner channel-fill sandstones in variable proportions. Characteristic features at a smaller scale include (a) flat-based, thick amalgamated and layered sheet sandstones with fewer erosional bases and slumped/scoured tops, (b) relatively good lateral continuity, (c) compensation style deposition, (d) relatively fewer muddy debrites, (e) laminated shales and mudstones, and (f) relatively ordered vertical stacking of strata. Sandstone packages within the downdip basinal facies tract thin at rates on the order of 0.40%. Individual sandstone beds thin at appreciably lower rates of < 0.1%. Thus, sheet sandstone beds can be continuous for thousands of feet and packages of beds can be continuous for miles. Many of the sedimentologic and stratigraphic criteria for distinguishing these updip and downdip facies tracts can be identified in core or borehole-image logs from subsurface reservoirs, in order to better understand reservoir characteristics and architecture. The architectural differences between updip and downdip facies tracts indicate that in analog reservoirs, different development and management scenarios should be employed to maximize production. Owing to lateral and vertical discontinuities and internal complexities in the updip facies tract, wells should be more closely spaced in order to maximize primary or secondary recovery. In the more continuous downdip facies tract, wells can be drilled at larger, more economical spacing and hydrocarbons can be produced more easily in both primary and secondary recovery modes.

Abstract Fine-grained, mud-rich turbidite systems primarily occur in basins with a large fluvial input. Depositional models derived from sand-rich turbidite systems are not appropriate because the large volume of mud in fine-grained turbidite systems produces different sediment distribution patterns, geomor-phic features, and internal architecture at bed-to-sequence scales. Many of the chapters in this volume demonstrate that understanding fine-grained turbidite systems requires a number of steps and degrees of resolution, very similar to the range of data utilized in the oil industry. Industrial examples include 2-D and 3-D seismic, cores, and well logs. To refine the understanding of a turbidite field, the earth scientist must integrate the most applicable models with subsurface data, outcrop analyses, modern analogs, and experimental results.

Abstract Several models of submarine fans/turbidite systems have been published, based on tectonic setting, basin characteristics, grain size, types of gravity flows, relative sea-level fluctuations, and so on. Among the various general and specific models are two siliciclastic end members that are important guides for many turbidite studies: fine-grained, mud-rich, and coarse-grained, sand-rich turbidite systems. Fine-grained, mud-rich complexes are typical for passive margin settings, with long fluvial transport, fed by deltas, wide shelf, efficient basin transport, resulting in a bypassing system. A high sand-to-shale ratio occurs at the base-of-slope, changes to an overall low ratio on the middle fan and to a high ratio on the outer fan. Coarse-grained, sand-rich complexes are typical for regions in active margin setting, characterized by a short continental transport distance, narrow shelf, and a canyon-sourced, nonefficient basin transport system that results in a prograding type of fan. The high sand-to-shale ratio slowly decreases away from channels and in the fan fringe region.

Abstract The Paleozoic stratigraphic succession of the Ouachita Basin is dominated by deepwater siliciclastics, carbonates, and chert. Within the Carboniferous, the Stanley fan complex is a thick shale interval, with upper and lower sandstone sections, that was deposited during an overall sea level highstand. The overlying Jackfork Formation is predominantly a sandstone section, with no shelf equivalent. The Johns Valley Formation, a unit of turbidite sandstone, shales, and unusual boulder beds, overlies the Jackfork. The 6100-m-thick Atoka Formation succeeds the Johns Valley. This thick sandstone and shale interval is divisible into a central basin (or axial) fan complex, a series of slope (or intraslope basin) fans, and thick shelf margin deltaic complex.

Abstract The recently compiled multibeam and digitized seismic data detail the complex bathymetry of the continental slope of the northern Gulf of Mexico slope and deepwater areas. Detailed bathymetry data, together with a watershed basin analysis model, generate landlike drainage paths in the submarine environment. Four drainage systems were identified and coincide with the major sediment sources in the west (Rio Grande River system), the northwest (Brazos and Colorado river systems), and the north (Mississippi River system). The carbonate-dominated platforms in the eastern and southern Gulf of Mexico show few drainage paths. On a regional scale, these drainage paths were the primary conduits for density currents during periods of low sea stand, which may help our understanding of the distribution of turbidite-derived sediments in the Gulf of Mexico.

Abstract The Permian Tanqua and Laingsburg subbasins in the southwestern Karoo Basin, South Africa, had near-contemporaneous formation and filling. Five submarine fan systems are in the broad, shallow Tanqua subbasin and four in the more typical foredeep-style Laingsburg subbasin. Petrologic and micro-probe analysis of the sandstones indicates a distant source area. Tectonic events led to varying sea-floor topography that directed sediment transport to the subbasins. Tectonic activity was low to nonexistent during deposition of any one or more of the submarine fans and indicates that the depositional cycle is much shorter than a tectonic cycle. The tectonic style of a basin may not always define the sedimentary characteristics of turbidite systems deposited in that basin.

Abstract Debris flows tend to conserve their density, whereas turbidity currents constantly change theirs through erosion, deposition, and entrainment. Numerical models illustrate how this distinction leads to fundamental differences in the behaviors of debris flows and turbidity currents and the deposits they produce. The models predict that when begun on a slope that extends onto a basin floor, a debris flow will form a deposit that begins near its point of origin and gradually thickens basinward, ending abruptly at its head. By contrast, deposition from an ignitive turbidity current (i.e., one that causes significant erosion) will largely be restricted to the basin floor and will be separated from its origin on the slope by a zone of erosion. Furthermore, the turbidite will be thickest just beyond the slope base and thin basinward. These contrasting styles of deposition are accentuated when debris flows and turbidites are stacked.

Abstract Medium- to high-sinuosity, aggradational submarine channels have frequently been considered analogous to subaerial channels. However, planform evolution and resulting architecture in these submarine channels are characterized by absence of downstream migration, eventual cessation of movement, and ribbon geometries. In contrast, alluvial rivers undergo continuous downstream and lateral movement to form tabular, sheetlike bodies. A simple process model of flow structure and evolution is described for these submarine channels. Flows are predicted to be highly stratified, have significant supra-levee thicknesses, and form broad over-bank wedges of low-concentration fluid. The model, for the first time, provides a coherent set of process explanations for the primary observations of submarine channels.

Abstract A significant portion of the geologic community’s understanding of tur-bidite systems is derived from the interpretation of 2-D and 3-D seismic data. The images generated from 3-D seismic data, in particular, have caused the re-examination and reinterpretation of deep-water sedimentary processes. In the future, the integration of 3-D seismic data with other data sets and technologies will continue to increase our understanding these systems, and specifically for improved reservoir management in turbidite reservoirs. Some of the new areas of investigation will include: increased study of modern fans and intraslope turbidite systems by integrating multiple data sets (deep cores, sidscan images) with 3-D data; the use of 4-D seismic and reservoir monitoring; repeat 3-D seismic surveys integrated with reservoir simulation; time lapse, multicomponent (4-D, 3-D); artificial intelligence, viz, neutral networks for more accurate lithologic prediction; and the use of large-scale visualization rooms in enhancing interpretation.

Abstract In the study area of the eastern Gulf of Guinea continental margin slope, offshore Nigeria, turbidite depositional systems are confined to slope-valley and slope-basin bathymetric lows bounded by densely faulted, structurally complex zones. Each depositional system consists of three architectural segments (in order): (1) upper slope, small-scale channel elements converging downslope, (2) single channel and nested channel elements with linear to sinuous map patterns, grading further downslope (3) slope-basin lobe and sheet elements. Incised channels and constructional levees indicate transport by turbulent flow. Comparison of the mapped seismic amplitude patterns of different sequences suggests switching of the inferred sand-prone turbidite systems from one slope valley to another through time. This is interpreted to reflect both the lateral shifting of the fluvial sediment supply on the shelf, and the local tectonic modification of slope-valley geometry.

Abstract Seismic facies mapping and seismic stratigraphic analysis in the northeastern Gulf of Mexico indicate the presence of a middle Miocene fan complex, here termed the M4. This fan complex is interpreted to comprise at least two fourth-order sequences deposited during lowstand by the Mississippi River. Each depositional sequence is well organized in sets of laterally continuous and discontinuous/hummocky seismic reflectors that are interpreted to be sheet-sand lobe, nonleveed channel and distributary channel facies. Sea-floor compensation is shown by east–west migration of the M4 sequences. The average depositional rate across the fan complex was about 0.5 m/1000 yr.

Abstract Economical production of hydrocarbons from submarine fan reservoirs requires a clear understanding of reservoir architecture and fluid flow properties. Seismic profiling has been used to delineate the extent of hydrocarbon-bearing reservoir architecture and associated flow heterogeneities. Outcrop study constrains the architectural interpretation options in field development plans. Seismic modeling of an outcrop of a submarine fan channel complex was undertaken to illustrate the acquisition and processing requirements and interpretation limits for a generic exploration seismic program. Unless appropriately designed, conventional, exploration-grade seismic data will not have the frequency content and resolution capability to image clearly submarine channel complexity of a detail commonly observed in outcrop.

Abstract Lithology and fluid information can be extracted from seismic data of deepwater clastics if their relative contribution to the signal is understood. Brushy Canyon Formation outcrop seismic models are constructed for the Western Escarpment of the Guadalupe Mountains using properties from outcrop, normal, and overpressured Gulf of Mexico and North Sea basins to test seismic sensitivity to lithology, fluid, and pressure. Large, clean, gas-saturated, and overpressured sandstones have the best resolution. Hydrocarbon saturation does not necessarily enhance seismic response. Lithology and fluid effects can reduce impedance contrast, resulting in low amplitudes (dim spots). Elevated geopressures preserve porosity producing low velocities and high amplitudes (bright spots). Even in low-impedance contrast intervals, offset-dependent amplitudes increase resolution and indicate hydrocarbons.

Abstract Late Miocene Mount Messenger Formation exposures in north Taranaki, New Zealand, demonstrate contrasting styles of deepwater basin-floor fan and slope fan development. Some of these attributes may have analogs in subsurface thin-bedded, deepwater reservoirs. Basin-floor fan settings are characterized by thick-bedded sandstone litho-facies (central lobe) and thin-bedded sandstone/siltstone lithofacies (lobe fringe). The thick- and thin-bedded sandstones were deposited by high-density mass flows. Stratigraphically higher slope fan units are invariably thin bedded. They display scouring at various scales and well-developed sedimentary structures that are indicative of deposition by turbidity flows. The slope fan depositional settings include individual and nested channels, and vertically stacked and shingled levee complexes.

Abstract The Permian Tanqua fan complex, SW Karoo Basin, South Africa, is unde-formed and well exposed, allowing 3-D viewing of outcrops that are laterally continuous over tens of kilometers. The complex consists of six sand-rich tur-bidite systems, separated by basin shales. The first five form an incrementally prograding, laterally compensating set, whereas the sixth fan, located to the south, downlaps onto Fan 5. Although deposited in a basin flanked by an oro-genic belt, the Tanqua fan complex has depositional characteristics similar to fans deposited in passive margin settings. It is a fine-grained, mud-rich bypass system deposited within an unconfined basinal setting. The deposits show architectural and reservoir character changes as they occur from the base-of-slope to their distal termination.

Abstract The Late Permian Ecca Group (1300 m thick) in the Tanqua Karoo consists of a basin floor fan complex (400 m thick), overlain by river-dominated deltaic deposits and associated updip fluvial deposits. This succession is subdivided into two “third-order” depositional sequences with several superimposed high-frequency, “fourth-order” depositional sequences. The Tanqua submarine fan complex contains six regionally distinct fan systems (24 to 60 m thick), five of which form a progradational stack, as revealed by their spatial distribution and regional facies variation. The sixth fan is situated to the south and downlaps onto the fifth fan. This long-term (third-order) progradational pattern records a combination of reduced accommodation space and/or increased sediment supply. Each fan system is assigned to the lowstand systems tract of each high-frequency, fourth-order sequence, and the particular attributes of each fan system are a consequence of their respective positions within the lower-frequency third-order sequence.

Abstract Superb sections of submarine fan deposits within the Late Permian Ecca Group are exposed within the Tanqua Karoo basin. Five discrete fan systems are capped by shales and deltaic deposits of the Kookfontein and equivalent Koedoesberg formations. Progradation of the deltaic deposits across the basin was in response to a decrease in accommodation space created by relatively high rates of sedimentation within the foreland basin setting. Evidence for the transition from submarine fans to deltaic deposition has been enigmatic, with limited evidence of sediments representative of slope deposition. The sedimentology and sequence stratigraphy of the Hangklip Fan represents a slope fan and channel complex that shallows up into deltaic deposits, coincident with decresing accomodation space. Erosional slump scars, cutting into laminated shale with chaotic infill of sand intraclasts, point toward slope depositional processes that are not in evidence in the underlying submarine fan deposits. Wave ripples and the trace fossil Gyrochorte suggest substantially shallower depositional conditions than either the submarine fan or slope fan deposits, which are devoid of such features.

Abstract Building geologic models of turbidite reservoirs for simulation and development planning using only subsurface data suffers from either discontinuous information or information that is displayed at too large a scale of resolution to detect variations in significant geologic properties. Large, continuous outcrops help constrain characterization of reservoirs by providing quantitative lateral and vertical attributes of strata and their bounding surfaces. Besides the traditional tools for examining outcrops, newer techniques include photo imaging, behind-outcrop logging/coring/seismic, gamma-ray/velocity logging, permeability profiling, and ground-penetrating radar. When used in combination, reliable, quantitative characterizations of tur-bidite outcrops can be developed. Future research should focus on full 3-D quantification of outcrops.

Abstract Detailed geologic mapping of the Pennsylvanian Jackfork Group turbidites in the DeGray Lake area of Arkansas has provided a 3-D geologic model of a mile-long, steeply dipping turbidite succession that is separated into east and west fault blocks by a zone of strike-slip faults. By scaling-up the stratigraphy into four reservoir zones and by choosing two topographic ground surface elevations to represent an unconformity top-seal and an oil-water contact, this outcrop can be considered a pseudoturbidite “reservoir,” amenable to production simulation. “Reservoir” performance simulation was conducted in 3-D, three-phase black oil mode, using vertical- and horizontal-well drilling scenarios for both water drive and depletion drive cases. The results demonstrate the ability to perform simulation on an outcrop to visualize, directly examine, and, hence, better understand the geologic controls on the performance of analog oil and gas reservoirs.