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Showing papers in "AAPG Bulletin in 1998"



Journal ArticleDOI
TL;DR: In this article, a transition from an early, sand-prone basin-fill succession (ponded facies assemblage) to a later shale-prone, slope-bypass succession (bypass facies) is described.
Abstract: Seismic facies in Gulf of Mexico intraslope basins reflect the interplay of a variety of deep-water depositional processes and the evolution of accommodation space on the slope. This interplay of processes results in a transition from an early, sand-prone ponded basin-fill succession (ponded facies assemblage) to a later shale-prone, slope-bypass succession (bypass facies assemblage). Convergent-baselapping facies in combination with localized chaotic and draping facies dominate the ponded facies assemblage. Stratigraphic relationships among these three units illustrate how fill-and-spill depositional processes occur within ponded-basin accommodation space. Convergent-thinning facies with widespread chaotic and draping facies dominate the bypass facies assemblage. These units represent filling of different types of slope accommodation space. The transition from ponded to bypass facies assemblages can be sharp or gradational over hundreds of meters. Transitions occured across the central Gulf of Mexico during the late Pliocene between 2.0 and 1.8 Ma, and in the early Pleistocene between 1.2 and 1.0 Ma. Nearly synchronous transitions throughout basins in the upper to middle slope suggest that increased sediment supply, resulting from a second-order sea level fall, and capture of large drainage areas by the Mississippi River during the Pleistocene are the primary controls on development of this large-scale stratigraphic architecture.

391 citations


Journal ArticleDOI
TL;DR: In this article, the fourfold rift basin infill classification scheme was proposed for predicting the distribution and geometry of synrift reservoir and source rock types, despite the inherent variability of the marine synrift infills.
Abstract: Marine rift basins represent a continuum ranging from mixed nonmarine/marine through shallow marine to deep marine, or from partly emergent through partly submergent to completely submergent basin types. These rift basin types have strongly variable synrift sedimentary architectures because of temporal changes in relative sea level, accommodation creation, and sediment supply throughout the rift cycle. Accommodation changes are controlled mainly by local basin-floor rotation, basinwide background subsidence, and, to a lesser degree, by eustatic changes. Sediment supply determines how much of the accommodation is filled and in what manner, and is controlled by the distance to the main hinterland areas, and the size and sediment- yield potential of any local fault-block source area. Marine siliciclastic synrift successions, whether dominantly shallow or deep marine in nature, are classified in terms of sediment supply as overfilled, balanced, underfilled, and starved. Sediment-overfilled and sediment-balanced infill types are characterized by a threefold sandstone-mudstone- sandstone synrift sediment-infill motif; the sediment-underfilled type is represented by a two-fold conglomerate-sandstone-mudstone motif; and the sediment-starved type commonly is represented by a one-fold mudstone motif. The sequential development, linked depositional systems, and stratigraphic signatures of the early synrift, the rift climax, and the late synrift to early postrift stages vary significantly between these rift basin infill types, as do the tectonic significance (timing of initiation and duration) of stratal surfaces, such as footwall unconformities, nondepositional hiatuses, and marine condensed sections. The construction of the fourfold rift basin infill classification scheme provides a first basis and a strong tool for predicting the distribution and geometry of synrift reservoir and source rock types, despite the inherent variability of the marine synrift infills.

304 citations


Journal ArticleDOI
TL;DR: A newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the Cretaceous-Tertiary boundary and provides an independent test of sequence stratigraphic-based eustatic curves.
Abstract: A newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the Cretaceous-Tertiary boundary and provides an independent test of sequence stratigraphic-based eustatic curves. The isotope record shows several eustatic episodes that are consistent with the geological record of ice-sheet evolution. The first evidence for the existence of an ice sheet in East Antarctica occurs near the lower-middle Eocene boundary (base of the Lutetian stage). There is no evidence for a large ice sheet on Antarctica prior to this time; however, strata of this age are lacking over most of the continent. The isotope curve also indicates that the ice sheet experienced phases of growth during the late Eocene and middle Oligocene, followed by a decrease in volume in the early Miocene. The Ross Sea stratigraphic record indicates initial evolution of the West Antarctica ice sheet during the early Miocene. By the middle Miocene, the ice sheet spread across the Ross Sea, Weddell Sea, and Antarctic Peninsula continental shelves. The Pliocene-Pleistocene record of glaciation in Antarctica includes numerous glacial erosion surfaces on the continental shelf, indicating repeated advance and retreat of both East and West Antarctica ice sheets. These volume changes in the Antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting Northern Hemisphere ice sheets. There is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle Eocene. This correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle Eocene.

256 citations


Journal ArticleDOI
TL;DR: In this article, a method of digital image analysis can quantify pore parameters over more than three orders of magnitude, from a submicron to a millimeter scale, based on digital analyses of images from thin sections at variable magnifications taken under an optical microscope (OM) and under an environmental scanning electron microscope (ESEM).
Abstract: A new method of digital image analysis can quantify pore parameters over more than three orders of magnitude, from a submicron to a millimeter scale. This porosity characterization does not require knowledge of lithology, age, burial depth, or diagenesis of the sample. The method is based on digital analyses of images from thin sections at variable magnifications taken under an optical microscope (OM) and under an environmental scanning electron microscope (ESEM). The results help explain variations in permeability for carbonate samples with a variety of complex pore structures. The analyses, however, can be done on any thin sections of other rock types. The OM images provide macroporosity information, whereas the ESEM images yield information on microporosity. The boundary between macroporosity and microporosity is defined at a pore area of 500 µm2, which translates to a pore length of approximately 20 µm, which is roughly the thickness of a thin section and thus the resolution of the OM. The digitized thin-section images are binarized into a macropore and a matrix phase (OM) or a micropore and a solid phase (ESEM). A standard digital image analysis program is used to detect all individual pores and to measure pore area and pore perimeter. Based on these analyses, one can calculate for each sample the amount of macroporosity, the amount of microporosity within the matrix (intrinsic microporosity), the shapes of the macropores (perimeter over area), and the pore size distribution. Comparison of total porosity determined from plugs indicates that macroporosity and microporosity values based on this methodology match the plug data, confirming the validity of the method. The combination of macroporosity and microporosity data yields pore size distribution and pore shape information that can explain the distribution of physical properties, in particular permeability. In parameter sensitivity analyses using neural networks, permeability appears to be mainly controlled by the macropore shape in high-permeability samples, and by the amount of intrinsic microporosity in the low-permeability samples.

250 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that the transition from rifting to drifting was diachronous and that the deformation of the passive margin of eastern North America between the Carolina Trough and the Scotian Basin was considerably more complex than the classic two-stage, rift-drift model.
Abstract: Integration of new data with existing information indicates that the tectonic development of the passive margin of eastern North America between the Carolina Trough and Scotian Basin was considerably more complex than the classic two-stage, rift-drift model. First, the transition from rifting to drifting was diachronous. In the southeastern United States, the rift-drift transition occurred after the Late Triassic synrift deposition and before eastern North America magmatism in the earliest Jurassic (~200 Ma). In maritime Canada, the rift-drift transition occurred after eastern North America magmatic activity and synrift deposition in the Early Jurassic and before postrift deposition in the early Middle Jurassic (~185 Ma). Second, the deformational regime changed substantially after rifting on both the southern and northern segments of the margin. Generally, northwest-southeast postrift shortening replaced northwest-southeast synrift extension. Northeast-striking reverse faults formed, and many of the rift-basin boundary faults had reverse displacements. In the southeastern United States, the change in the deformational regime occurred in the Late Triassic-Early Jurassic during the rift-drift transition. Simultaneously, diabase sills and dikes, many striking nearly perpendicular to the trend of the rift basins, intruded the continental crust; and a massive wedge of volcanic or volcaniclastic rocks developed near the continent-ocean boundary. In maritime Canada, the change in the deformational regime occurred during or after the Early Jurassic and before or during the Early Cretaceous; that is, during the rift-drift transition or early stages of sea-floor spreading.

241 citations


Journal ArticleDOI
TL;DR: The facies architecture of allochthonous slope systems is determined jointly by the sediment texture and pattern of supply to the shelf margin this article, which is a primary control on channel and lobe morphologies and on the scale and importance of slump and debris flow deposits.
Abstract: Subaqueous slope and base-of-slope depositional systems are a major component of most marine and many lacustrine basin fills, and constitute primary targets for hydrocarbon exploration and development. Seven basic facies building blocks comprise slope systems: (1) turbidite channel fills, (2) turbidite lobes, (3) sheet turbidites, (4) slide, slump, and debris-flow sheets, lobes, and tongues, (5) fine-grained turbidite fills and sheets, (6) contourite drifts, and (7) hemipelagic drapes and fills. The grain size of supplied sediment is a primary control on channel and lobe morphologies and on the scale and importance of slump and debris-flow deposits. Two general families of siliciclastic slope systems occur. Constructional (allochthonous) systems, including fans, aprons, and basin-floor channels, are built of sediment supplied from superjacent delta, shore-zone, shelf, or glacial systems. The facies architecture of allochthonous systems is determined jointly by the sediment texture and pattern of supply to the shelf margin. Point sources of supply create fans; line sources create strike-elongate prisms of slope sediment called slope aprons. Shelf-margin deltas provide a particularly common intermediate source geometry, forming offlapping delta-fed aprons. Autochthonous systems, including retrogressive aprons, canyon fills, and megaslump complexes, record slope reworking and resedimentation.

209 citations


Journal ArticleDOI
TL;DR: In this paper, a normal velocity-depth trend for the Upper Cretaceous-Danian Chalk Group is determined by identifying interval-velocity data that represent maximum burial in areas unaffected by overpressuring; these data are derived from 845 wells throughout the North Sea Basin.
Abstract: A normal velocity-depth trend for the Upper Cretaceous-Danian Chalk Group is determined by identifying interval-velocity data that represent maximum burial in areas unaffected by overpressuring; these data are derived from 845 wells throughout the North Sea Basin. Data from pelagic carbonate deposits on a stable plateau constrain the trend for shallow depths. Positive velocity anomalies relative to the trend are mapped along the western and eastern margins of the North Sea Basin, and reflect regional Neogene uplift and erosion of up to 1 km along the present-day limit of the Chalk. A hiatus at the base of the Quaternary increases in magnitude away from the basin center, where a complete Cenozoic succession is found. This hiatus is consistent in size with the missing section estimated from Chalk velocities when allowance is made for the Quaternary reburial of the Chalk. Negative velocity anomalies in the central and southern parts of the basin outline an area within which overpressures in the Chalk exceed 10 MPa, equivalent to a burial anomaly greater than 1 km relative to the normal trend. The Chalk pressure system is primarily dependent on overburden properties because retention of overpressure generated by the load of the upper overburden depends on the thickness and sealing quality of the lower overburden; therefore, the Chalk is considered to represent a regional aquitard, and the hydrodynamic model of long-distance migration within the Chalk is rejected. The Neogene uplift and erosion of the margins of the North Sea Basin and the rapid, late Cenozoic subsidence of its center fit into a pattern of late Cenozoic vertical movements around the North Atlantic.

204 citations


Journal ArticleDOI
TL;DR: In this article, the variation of porosity in quartzose sandstones is calculated as a function of depth, temperature gradient, burial rate, stylolite frequency, and hydrocarbon saturation.
Abstract: The variation of porosity in quartzose sandstones is calculated as a function of depth, temperature gradient, burial rate, stylolite frequency, and hydrocarbon saturation. Calculations were performed by considering the effects of both mechanical compaction and chemical compaction/cementation. This latter process dominates at temperatures greater than approximately 90°C and is due to quartz redistribution within the sandstone. Quartz redistribution stems from clay-induced quartz dissolution at stylolite interfaces, coupled with diffusional transport of aqueous silica into the interstylolite sandstone and precipitation on quartz surfaces as cement. Many model parameters are obtained from theoretical calculations or laboratory measurements, and few basin-dependent parameters are required to make porosity predictions. A set of porosity predictions is presented in porosity/depth figures. Close correspondence between computed results and measured porosities in cores from a variety of sedimentary basins demonstrates the accuracy of the predictions.

190 citations


Journal ArticleDOI
TL;DR: The Salin subbasin of Myanmar (part of the larger Central basin) is a fore-arc/back-arc basin couplet situated between an oblique subduction zone to the west and a major right-lateral strike-slip fault to the east as discussed by the authors.
Abstract: The Salin subbasin of Myanmar (part of the larger Central basin) is a fore-arc/back-arc basin couplet situated between an oblique subduction zone to the west and a major right-lateral strike-slip fault to the east. Surface and subsurface expressions of folds and faults suggest that the basin experienced north-northwest-directed extensional deformation in the Miocene followed by east-northeast-directed Pliocene-Pleistocene transpressional deformation, resulting in a variety of structural styles, including thrust faults, oblique-reverse faults, strike-slip faults, and normal faults. Fault-propagation folds cored by west-dipping thrust faults in the basin center are located above steps in the top-of-basement surface (most likely fault controlled). Unconformities at the base of and within the Pliocene-Pleistocene synorogenic section indicate that the thrust faults were active during the Pliocene-Pleistocene. The southeastern region contains broad, north-northwest- trending uplifts and east-northeast-striking normal faults associated with thickened Miocene synorogenic deposits. Pliocene-Pleistocene sedimentary rocks lie unconformably above the Miocene section and are folded above the uplifts, reflecting Pliocene-Pleistocene compression. In the southern part of the basin, Miocene sedimentary rocks thicken dramatically over the 20°N uplift and the Yedwet uplift, suggesting that the north-northwest-striking faults that bound them represent Pliocene- Pleistocene inversion of Miocene normal faults. During the Miocene, the Burma plate acted as a fore-arc sliver coupled with the India plate, subducting obliquely underneath it, and moved northward relative to Asia along the Sagaing fault. Normal faulting and local basin formation took place at this time. When the northern part of the Burma plate collided with eastern Asia in the Pliocene, transpressional deformation predominated, creating thrust and reverse faults, positive flower structures, and inverted basins.

131 citations


Journal ArticleDOI
TL;DR: Basement-involved structures commonly occur as long, irregular chains of uplifts in foreland basins as discussed by the authors, with most major fields located on the broad crests of these structures.
Abstract: Basement-involved structures commonly occur as long, irregular chains of uplifts in foreland basins. These structures commonly contain significant hydrocarbon accumulations, with most major fields located on the broad crests of these structures. The search for complex traps in deeper targets and in subthrust structures requires an improved understanding of the geometry and evolution of these structures. Characteristic features of basement structures include deformation zones within the sedimentary cover that dissipate significant fault slip, and gently dipping frontlimbs and backlimbs. Fault slip in the basement is usually accommodated in the cover by a triangular, widening-upward deformation zone on the forelimb, with the nature of deformation controlled primarily by the mechanical stratigraphy. If the cover contains interlayered competent and incompetent units, the incompetent units are characterized by significant penetrative deformation, whereas the competent units are faulted after a relatively small amount of penetrative deformation. Depending on the competency contrast between the basement and cover, the nature of basement, and the physical conditions of deformation, the deformation zone may also propagate downward into the basement. Gently dipping backlimb and frontlimb panels are related to movement of the hanging wall over synclinal and anticlinal bends in the major fault, respectively. Many basement faults are characterized by a number of synclinal fault bends within the basement, which result in long and gently dipping backlimbs. Forelimb panels are related to anticlinal bends that typically occur at the basement-cover interface, as well as at one or more locations in the sedimentary cover. Case studies of well-constrained examples of structures from the Bighorn and Uinta basins and the Central Basin platform, demonstrate the development of these characteristic features and their strong dependence on the mechanical stratigraphy. These models and case studies will be useful in interpreting foreland basement structures in areas with poor or limited data.

Journal ArticleDOI
TL;DR: Saller and Henderson as discussed by the authors investigated porosity and permeability variations in two west Texas oil fields (North Riley and South Cowden fields) and found that porosity tends to increase in a basinward direction.
Abstract: Saller and Henderson (1998) presented an article concerning porosity and permeability variations in two west Texas oil fields (North Riley and South Cowden fields). These fields occur within dolomitized Permian platform carbonates near the basinward shelf edge of the Central Basin platform, a paleogeographic element that influenced Permian deposition in west Texas. Their carefully documented study outlines several anomalous aspects concerning porosity distribution. They noted, in particular, that porosity distribution is not strictly facies dependent but that porosity tends to increase in a basinward direction. They suggested that porosity developed largely during dolomitization by the action of hypersaline evaporative fluids that flowed downdip in a basinward direction during the Permian. These brines were generated in restricted shelf interior lagoons and moved downdip parallel with bedding in a shallow reflux type of hydrologic system driven by subsurface fluid density differences in the Permian Clear Fork and Grayburg formations, as shown here in Figure 1 (see figure 18 in Saller and Henderson [1998]). Figure 1 Part A shows the scenario proposed by Saller and Henderson (1998) for porosity creation, dolomitization, and dolomite cementation of the Permian Clear Fork and Grayburg formations of west Texas. They suggested that macrodissolution of calcium carbonate occurred contemporaneously with dolomitization and dolomite cementation. This process of brine backreaction, however, would cause a net increase of porosity in the shelf interior, the opposite of what is observed. Part B shows a two-stage scenario proposed here to circumvent the problem of limestone macrodissolution by shelf interior brines that must have been initially in approximate bulk equilibrium with calcium carbonate. The first stage records dolomitization by replacement of limestone with little macrodissolution. In stage two, evaporative shelf interior brines may have evolved in equilibrium with dolomite only and became undersaturated with calcite and aragonite. Reflux migration of these brines downdip may …

Journal ArticleDOI
TL;DR: In this paper, structural and sequence stratigraphic interpretations of two-dimensional seismic and well data from northern Green Canyon and Ewing Bank were integrated to evaluate how salt deformation influenced the distribution of Pliocene-Pleistocene facies in time and space.
Abstract: Structural and sequence stratigraphic interpretations of two-dimensional seismic and well data from northern Green Canyon and Ewing Bank were integrated to evaluate how salt deformation influenced the distribution of Pliocene-Pleistocene facies in time and space. Two techniques were employed. First, twelve palinspastic maps of near-surface structure were constructed. These were combined with maps of interpreted depositional environments to show how shallow salt diapirism created bathymetric relief that influenced the configuration of sediment transport systems and depocenters through time. Second, tectonostratigraphic packages comprising multiple sequences were defined based on external geometry. Different stacking patterns of these packages characterize four types of minibasins, each with a distinct history of salt evacuation from underlying salt stocks and sheets. Interpreted seismic facies were analyzed within this minibasin framework to evaluate how deep-salt withdrawal influenced the distribution of depositional systems. The results show that both structural and sedimentological variables influenced lithofacies development. External factors dictated the volume and type of systemwide clastic input. Regional factors, such as nearby salt structures and the position of deltas, controlled the dispersal of clastics. Local factors, such as the thickness of underlying salt, influenced minibasin-specific evolution. These factors interacted at three scales: (1) a broad transition from sand-rich ponded settings to shale-dominated bypass settings during the Pliocene-Pleistocene, (2) fluctuations over periods of several sequences that created highly variable stratigraphic stacking patterns, and (3) a progression from ponded to bypass facies within individual sea level cycles. Analysis of these various factors can improve the prediction of reservoir distribution within slope minibasins, and thereby reduce the risk in subsalt and deep-water exploration.

Journal ArticleDOI
TL;DR: In this article, the facies associations and stratigraphic architecture, together with outcrop observations of cementation and faulting, are summarized in terms of four idealized reservoir models: fluvial, delta plain, proximal delta front, and distal delta front.
Abstract: The Neogene sediments of eastern Azerbaijan and western Turkmenistan contain significant hydrocarbon reserves in deltaic reservoirs. Sedimentary logging of these reservoirs at outcrop in Azerbaijan has outlined four facies associations that encompass a range of paleoenvironments, from alluvial braided river sandstones and conglomerates to delta-front siltstones and mudstones. The facies associations suggest a river-dominated braid delta and are arranged into an architecture controlled by base-level changes: parasequences, parasequence sets, and sequence boundaries are key elements. The facies associations and stratigraphic architecture, together with outcrop observations of cementation and faulting, are summarized in terms of four idealized reservoir models: fluvial, delta plain, proximal delta front, and distal delta front. Each reservoir model has distinctive grain-size and shale distributions. Comparison of nearby oil fields with the studied outcrops suggests that the outcrops form good analogs from which to model reservoir architecture, barriers and baffles to fluid flow, reservoir heterogeneity, and reservoir quality variations.

Journal ArticleDOI
José Sebastián Galeazzi1
TL;DR: The Malvinas Basin is one of the few basins on the Argentine continental shelf that contains a proven petroleum system; however, uneconomical oil discoveries keep the basin at a frontier exploration status as mentioned in this paper.
Abstract: The Malvinas Basin is one of the few basins on the Argentine continental shelf that contains a proven petroleum system; however, uneconomical oil discoveries keep the basin at a frontier exploration status. The Malvinas Basin evolved through three main tectonic phases: rift, sag, and foredeep. The sedimentary fill of the basin is closely related to its tectonic history. Middle Jurassic rifting resulted in north-northwest-oriented grabens that filled with volcanic and pyroclastic continental rocks. Diminished faulting and generalized subsidence during the Late Jurassic-Neocomian early sag phase were accompanied by deposition of a basal transgressive marine wedge. The Aptian-Maastrichtian interval was characterized by tectonic quiescence and deposition of offshore mud-prone sediments. Southerly localized early Paleogene transtensional tectonism accompanied the early development of a foredeep trough. Outer shelf glauconite-rich sandstones, basinal claystones, and localized carbonate buildups partially filled the basin. By the middle Eocene-Oligocene, a strong deepening event marked the initiation of the foredeep sensu stricto phase. This phase resulted in the full development of the Malvinas foredeep and the formation of compressional structures in the foreland. The foredeep basin was replenished by a westerly derived offlapping siliciclastic wedge of Oligocene-Miocene age. Noncommercial hydrocarbon discoveries in 5 of the 17 wells drilled in the basin suggest the presence of an undercharged Lower Inoceramus-Springhill petroleum system.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss the northern Tarim basin's structural features, which include three main tectonic units: the Kalpin uplift, the Kuqa depression, and the North Tarim uplift along the northern margin of the basin.
Abstract: The rhombus-shaped Tarim basin in northwestern China is controlled mainly by two left-lateral strike-slip systems: the northeast-trending Altun fault zone along its southeastern side and the northeast-trending Aheqi fault zone along its northwestern side. In this paper, we discuss the northern Tarim basin's structural features, which include three main tectonic units: the Kalpin uplift, the Kuqa depression, and the North Tarim uplift along the northern margin of the Tarim basin. Structural mapping in the Kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike-slip faulting. The amount of strike-slip displacement is estimated to be 148 km by restoration of strike-slip structures in the uplift. The Kuqa depression is a Mesozoic-Cenozoic foredeep depression with well-developed flat-ramp structures and fault-related folds. The Baicheng basin, a Quaternary pull-apart basin, developed at the center of the Kuqa depression. Subsurface structures in the North Tarim uplift can be divided into the Mesozoic-Cenozoic and the Paleozoic lithotectonic sequences in seismic profiles. The Paleozoic litho-tectonic sequence exhibits the interference of earlier left-lateral and later right-lateral strike-slip structures. Many normal faults in the Mesozoic-Cenozoic litho-tectonic sequence form the negative flower structures in the North Tarim uplift; these structures commonly directly overlie the positive flower structures in the Paleozoic litho-tectonic sequence. The interference regions of the northwest-trending and northeast-trending folds in the Paleozoic tectonic sequence have been identified to have the best trap structures. Our structural analysis indicates that the Tarim basin is a transpressional foreland basin rejuvenated during the Cenozoic.

Journal ArticleDOI
TL;DR: In this paper, a multidisciplinary study involving both geologic field data and borehole geophysical data, on the Monterey Formation reveals a critical relationship in which brittle fault zones provide permeable conduits for hydrocarbon transport and production.
Abstract: Field studies of low-permeability siliceous shale units of the Monterey Formation in the southern San Joaquin Valley and coastal California show evidence for fault control on hydrocarbon transport important for both migration and production. Shearing along preexisting discontinuities, such as bedding planes and joints, locally increases permeability in the sheared zone and surrounding fractured rock. As the rock is subjected to shear, it begins to systematically fragment and subsequently to brecciate, thereby creating interconnected voids for hydrocarbon transport. Petroleum-filled breccia zones are exposed in the Antelope Shale at Chico Martinez Creek on the northeastern flank of the Temblor Range near McKittrick, California. Breccia zones are found predominantly parallel to bedding in porcelanite units (4-10 cm thick) and are bounded above and below by siliceous shale beds (2-20 cm thick). Spacing between breccia zones is a function of lithology and diagenesis. This section of the Antelope Shale exposure originated as alternating layers of pure and terrigenous-rich diatomaceous sediment, in which these compositional variations influence the postdiagenetic material properties. Terrigenous-rich diatomite diagenetically alters to an incompetent siliceous shale (opal CT), whereas the cleaner sediments alter to a more brittle porcelanite (opal CT). Secondary fractures, or splay cracks, localize in the more brittle porcelanite in response to shearing along both bed-parallel lithologic discontinuities and bed-parallel fractures. With increased shearing, the fractured porcelanite subsequently evolves into brecciated fault zones. In the Chico Martinez Creek outcrop, individual breccia zones combine to make a petroleum-filled compound breccia zone approximately 10 m thick in which the original zones are partially obliterated by subsequent deformation. This outcrop-based conceptual model for the development of hydrocarbon pathways in the Monterey Formation is applied to the subsurface using formation microscanner (FMS) data and core. Bed-parallel breccia zones are identified in the Antelope Shale at Buena Vista Hills oil field. In the borehole image, the brecciated fault zone appears as unorganized patches of high and low resistivity with hints of bedding. At least one breccia zone identified in the borehole image correlates directly to hydrocarbon production as indicated by spinner flow-meter data. Although core recovery from fractured or brecciated zones is typically poor, there appears to be an association between fractures related to shearing processes and hydrocarbon occurrence in cores examined for this study. Oil-stained and brecciated fracture zones associated End page 1551---------------- with slip exist in Buena Vista Hills and other nearby fields producing from the Antelope Shale. Our multidisciplinary study, involving both geologic field data and borehole geophysical data, on the Monterey Formation reveals a critical relationship in which brittle fault zones provide permeable conduits for hydrocarbon transport and production.

Journal ArticleDOI
TL;DR: Aatite fission-track, vitrinite reflectance, and heat-flow data were used to constrain regional aspects of the burial history of the Anadarko basin this article.
Abstract: New heat-flow values for seven sites in the Anadarko basin, Oklahoma, were determined using high-precision temperature logs and thermal conductivity measurements from nearly 300 core plugs. Three of the sites are on the northern shelf, three sites are in the deep basin, and one site is in the frontal fault zone of the northern Wichita Mountains. The heat flow decreased from 55 to 64 mW/m2 in the north, and from 39 to 54 mW/m2 in the south, due to a decrease in heat generation in the underlying basement rock toward the south. Lateral lithologic changes in the basin, combined with the change in heat flow across the basin, resulted in an unusual pattern of thermal maturity. The vitrinite reflectance values of the Upper Devonian- Lower Mississippian Woodford formation are highest 30-40 km north-northwest of the deepest part of the basin. The offset in highest reflectance values is due to the contrast in thermal conductivity between the Pennsylvanian "granite wash" section adjacent to the Wichita uplift and the Pennsylvanian shale section to the north. The geothermal gradient in the low-conductivity shale section is elevated relative to the geothermal gradient in the high-conductivity "granite wash" section, thus displacing the highest temperatures to the north of the deepest part of the basin. Apatite fission-track, vitrinite reflectance, and heat-flow data were used to constrain regional aspects of the burial history of the Anadarko basin. By combining these data sets, we infer that at least 1.5 km of denudation has occurred at two sites in the deep Anadarko basin since the early to middle Cenozoic (40 ±10 m.y.). The timing of the onset of denudation in the southern Anadarko basin coincides with the period of late Eocene erosion observed in the southern Rocky Mountains and in the northern Great Plains. Burial history models for two wells from the deep Anadarko basin predict that shales of the Woodford formation passed through the hydrocarbon maturity window by the end of the Permian. The Late Pennsylvanian-Early Permian section in the deep basin moved into the hydrocarbon maturity window during Mesozoic burial of the region. Presently, the depth interval of the main zone of oil maturation (% Ro = 0.7-0.9) is approximately 2800-3800 m in the eastern deep basin and 2200-3000 m in the western deep basin. The greater depth to the top of the oil maturity zone and larger depth range of the zone in the eastern part of the deep basin are due to the lower heat flow associated with more mafic basement toward the east. The burial history model for the northern shelf indicates that the Woodford formation has been in the early oil maturity zone since the Early Permian.

Journal ArticleDOI
TL;DR: In this article, the authors investigated deformation above subsiding tabular salt, salt walls, and salt stocks by creating 15 physical models, and they suggested that salt dissolution forms similar structures to those physically modeled for salt withdrawal.
Abstract: By creating 15 physical models, we investigated deformation above subsiding tabular salt, salt walls, and salt stocks. Dry quartz sand simulated a brittle sedimentary roof above viscous silicone representing salt. The modeled diapiric walls had linear planforms and rectangular, semicircular, triangular, or leaning cross sectional shapes; the stock was cylindrical. In models where the source layer (or allochthonous salt sheet) was initially tabular, a gentle, flat-bottomed syncline bounded by monoclinal flexures formed above a linear zone where the silicone was locally removed. Above all subsiding diapirs, the deformed roof was bounded by an inner zone of steep, convex-upward reverse faults and an outer zone of normal faults. Above subsiding diapiric walls, extensional and contractional zones were balanced. Above the subsiding salt stock, conical, concentric fault zones comprised inner reverse faults and outer normal faults. Sediments were added both before (prekinematic) and during (synkinematic) salt withdrawal. In entirely prekinematic roofs, reverse fault zones and normal fault zones both widened with time. Reverse faults propagated upward from the corners of the withdrawing diapirs. New reverse faults formed in the footwalls of reverse faults, each nearer the center of the deepening roof trough. Conversely, new normal faults formed successively outward from the sagging trough. Synkinematic deposition retarded faulting, but the pattern of inner reverse and outer normal faults was repeated; however, reverse faults formed successively outward, whereas normal faults formed inward. New conceptual models suggest that salt dissolution forms similar structures to those physically modeled for salt withdrawal. The appropriate physical models resemble natural dissolution structures above tabular salt. Extension alone above diapirs is not caused merely by salt withdrawal or dissolution, but by regional extension or active diapirism.

Journal ArticleDOI
TL;DR: In this article, the authors focus on the northern Green Canyon and central Ewing Bank protraction (lease) areas, where the Pliocene-Pleistocene turbidite systems were mapped using an integrated exploration database.
Abstract: Neogene turbidite systems are major reservoirs in the northern deep Gulf of Mexico. Few publications have described the stratigraphic variations or the three-dimensional geometries of these turbidite systems in detail; hence, an understanding of the stratigraphic characteristics of the producing sands is important for deep-water exploration in the Gulf of Mexico and similar basins worldwide. This study focuses on the northern Green Canyon and central Ewing Bank protraction (lease) areas, where the Pliocene-Pleistocene turbidite systems were mapped using an integrated exploration database. Interpretation of 10,000 km of two-dimensional seismic, 185 well logs, and biostratigraphy from 180 wells allowed us to define the regional sequence stratigraphic framework for this area and potential areas for future exploration. A complex Pliocene-Pleistocene geologic evolution of the area is indicated by the seismic and geologic facies, depositional rates, nature of turbidite systems, and sand content. Significant sand deposits (basin-floor fans) were deposited in most sequences and directly overlie sequence boundaries. Salt tectonics and faulting greatly influenced the loci of these fans’ deposition. Large, thick fans fill entire salt-withdrawal minibasins at the base of the Pliocene sequences. In the Pleistocene sequences, where the rate of salt withdrawal was less, smaller and thinner fans were deposited downdip of faults and adjacent to shallow salt bodies. Channel systems, interbedded with overbank shales, constitute most of the sediments in the sequences. The older sequences contain more channels and sandier channel fills than the younger sequences. Analysis of all sequences indicates a complex depositional history where significant sands were deposited where abrupt decreases in bathymetric gradient are associated with salt tectonics or faulting.

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TL;DR: Seismic images of the continental margin in the western Great Australian Bight reveal the internal anatomy of a long-lived Cenozoic cool-water carbonate shelf as discussed by the authors.
Abstract: Seismic images of the continental margin in the western Great Australian Bight reveal the internal anatomy of a long-lived Cenozoic cool-water carbonate shelf. The Cenozoic succession is divisible into seven seismic sequences that reflect four depositional phases. Phase A (Paleocene-middle Eocene) is a progradational siliciclastic wedge deposited in a depositional sag, and represents lowstand and transgressive sedimentation. Phase B (middle Eocene- earliest middle Miocene) contains cool-water ramp carbonates with biogenic mounds (Eocene- Oligocene), overlain by a warm-water, flat-topped platform rimmed by the early middle Miocene(?) Little Barrier Reef. Coeval deep-water carbonate deposition formed a multi-lobed sediment apron. This phase was terminated by gentle uplift and tilting throughout southern Australia in the late middle Miocene. Phase C (late Miocene-early Pliocene) represents cool-water lowstand wedge and ramp deposition, and contains numerous biogenic mounds in the youngest sequence. This phase is terminated by an unconformity attributed to marine erosion. Phase D (Pliocene-Quaternary) is a thick succession of cool-water carbonates with spectacular clinoform ramp geometry that forms most of the modern outer shelf, and contains large deep-water biogenic mounds. This platform, the first large cool-water carbonate shelf imaged by high-quality seismic reflection data, demonstrates the interaction between regional tectonic and local and global paleo-oceanographic processes. As Australia drifted northward during the Cenozoic, the Great Australian Bight moved from high to middle latitudes, and the regional oceanographic regime remained cool water largely because of coeval development of the Antarctic Circumpolar Current in the evolving Southern Ocean. Short episodes of warm-water deposition probably reflect incursions of a proto-Leeuwin current from the Indian Ocean, whereas growth of the Miocene coral-algal "Little Barrier Reef" resulted from a short-term global increase in sea-surface temperatures. This platform, dominated by stacked carbonate ramps, is most similar to the West Florida Shelf, but contains many more biogenic mounds. The western Great Australian Bight carbonate platform is an excellent modern analog for the mesoscale structure of cool-water platforms in the older geologic record.

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TL;DR: In this article, organic matter reflectance, illite crystallinity, and fluid-inclusion techniques have been used to evaluate burial metamorphic conditions for the lithostratigraphic successions that accumulated during the Cretaceous in the southern Benue trough and Anambra basin of southern Nigeria.
Abstract: Organic matter reflectance, illite crystallinity, and fluid-inclusion techniques have been used to evaluate burial metamorphic conditions for the lithostratigraphic successions that accumulated during the Cretaceous in the southern Benue trough and Anambra basin of southern Nigeria. These successions were invaded by intrusives, volcanic rocks, and vein-type lead-zinc minerals, especially in the Albian-Cenomanian section of the Abakaliki anticline. The sequence includes lower Maastrichtian subbituminous coals in the Anambra basin. In exposed Cretaceous deposits on a northwest-southeast section from Enugu to Abakaliki, mean random vitrinite reflectance (Rom) in oil ranges from 0.55 to 0.67% in the lower Maastrichtian coals and shales, approximately 0.91% in the Coniacian shales, 0.97% in the Turonian shales, and up to 4.31% in the Albian shales. A corresponding increase in the illite content of the illite-smectite mixed-layer clay fractions is reflected in the low values of illite crystallinity indices coupled with a decrease from 32 to 0% in the percentage of smectite from the northwest-southeast Maastrichtian-Albian section. Fluid-inclusion pressure-corrected temperatures from vein quartz in the Albian shales range from 170 to 250°C. The results of this work show that thermal maturation in the Cretaceous successions increases from the post-Santonian (Campanian-Maastrichtian) Anambra basin into the older Benue trough where strong diagenetic to "anchimetamorphic" (i.e., very low grade metamorphism) conditions were reached. The data suggest that these sediments at the present outcrop levels originally were buried at higher maturity levels. Maximum erosion appears to have taken place on the axis of the Abakaliki anticline. The presence of bitumen in fractures and pores of the exposed Maastrichtian units in the Anambra basin suggests that the matured sediments generated some unknown quantity of petroleum. This finding, coupled with reported gas finds and some oil in previous exploration wells of the Anambra basin, enhances the possibilities of Cretaceous targets in the downdip regions.

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TL;DR: In this paper, the authors proposed a method to determine petroleum migration pathways and zones of concentration by integrating predictions of potential source rocks, structural restorations, thermal maturation modeling, regional salt maps, and petroleum systems logic.
Abstract: The northern Green Canyon/Ewing Bank region, northern Gulf of Mexico basin, contains the Oxfordian-Neogene (.), Tithonian-Neogene (.), Albian-Neogene (.), Turonian-Neogene (.), and Eocene-Neogene (.) petroleum systems. The systems encompass 42 fields or discoveries in the study area and include four subsalt discoveries. Essential elements of the systems include source shales of Oxfordian, Tithonian, Albian, Turonian, and Eocene age; Neogene siliciclastic turbidite reservoirs; allochthonous salt; and overburden strata ranging in age from Jurassic to Quaternary. The petroleum systems of the area are significantly affected by the evolution of allochthonous salt. The high thermal conductivity of salt retards the thermal maturation of subsalt petroleum source rocks and causes late generation and migration from them. Most traps were formed during the Pliocene-Pleistocene, and the generation-migration-accumulation of petroleum ranges from early Miocene to the Holocene. The critical moment of peak oil generation for each source varies spatially and temporally as a function of the overlying sediments and allochthonous salt evolution. The impermeability of salt prevents vertical petroleum migration and causes migration pathways to be deflected laterally up the dip of base salt. Where salt welds form, petroleum migration is unimpeded and continues vertically. By integrating predictions of potential source rocks, structural restorations, thermal maturation modeling, regional salt maps, and petroleum systems logic, we can determine petroleum migration pathways and zones of concentration. All 42 fields or discoveries within the study area are associated with predicted zones of paleosubsalt petroleum concentration. Present-day salt geometries do not delineate many of these zones because of salt weld formation during the Pleistocene. This generation, migration, and accumulation technique enables geoscientists to focus their exploration efforts toward areas with a greater probability of success.


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TL;DR: In this article, an interpretation of more than 10,000 km (6200 mi) of multifold seismic data, and sequential restoration of eleven profiles, were used to determine the geometry and evolution of allochthonous salt structures within Ewing Bank and northern Green Canyon protraction areas.
Abstract: The discovery that major episodes of subhorizontal, allochthonous salt flow have occurred in the Gulf of Mexico Basin requires a means of quantifying the evolution of allochthonous salt and associated structures to conduct both basin and petroleum systems analyses. Sequential structural restorations of allochthonous salt systems provide an evolving structural framework for integrating stratigraphic, geophysical, and geochemical data sets. In this study, interpretation of more than 10,000 km (6200 mi) of multifold seismic data, and sequential restoration of eleven profiles, were used to determine the geometry and evolution of allochthonous salt structures within Ewing Bank and northern Green Canyon protraction areas. The results illustrate the complex geometry of the multilevel salt system and the types of interactions between counterregional and salt-stock canopy models of allochthonous salt system evolution. Sedimentary loading is accommodated by salt sheet extrusion, gravity spreading, gravity gliding, extension, salt evacuation, and contraction. Salt geometry commonly changes dramatically through time because it provides much of the accommodation for sediments and absorbs much of the extension and contraction within its overburden. The positioning and kinematics of extensional and contractional structures are controlled by salt body geometries, salt system interactions, and, most importantly, the topography of the base salt or equivalent salt weld. The structural restorations also constrain the timing of salt sheet and salt weld formation and document the positive correlation among sedimentation rates, salt flow, and structural deformation. Cross-sectional salt area generally decreases through time in areas of salt evacuation and minibasin formation, but increases in sections crossing growing salt bodies. Three-dimensional restoration is required to determine the three-dimensional kinematics and balance of allochthonous salt tectonics.

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TL;DR: The concept of reserve or resource estimates by current or projected annual consumption is circular in reasoning and can lead to highly erroneous conclusions as discussed by the authors, which leads to the following conclusions: 1) Resource estimates of resources and reserves are inventories of the amounts of a fossil fuel perceived to be available over some future period of time, as those resources/reserves are depleted over time, additional amounts of fossil fuels are inventoried.
Abstract: Over the last 25 yr, considerable debate has continued about the future supply of fossil fuel. On one side are those who believe we are rapidly depleting resources and that the resulting shortages will have a profound impact on society. On the other side are those who see no impending crisis because long-term trends are for cheaper prices despite rising production. The concepts of resources and reserves have historically created considerable misunderstanding in the minds of many nongeologists. Hubbert-type predictions of energy production assume that there is a finite supply of energy that is measurable; however, estimates of resources and reserves are inventories of the amounts of a fossil fuel perceived to be available over some future period of time. As those resources/reserves are depleted over time, additional amounts of fossil fuels are inventoried. Throughout most of this century, for example, crude oil reserves in the United States have represented a 10-14-yr supply. For the last 50 yr, resource crude oil estimates have represented about a 60-70-yr supply for the United States. Division of reserve or resource estimates by current or projected annual consumption therefore is circular in reasoning and can lead to highly erroneous conclusions. Production histories of fossil fuels are driven more by demand than by the geologic abundance of the resource. Examination of some energy resources with well-documented histories leads to two conceptual models that relate production to price. The closed-market model assumes that there is only one source of energy available. Although the price initially may fall because of economies of scale long term, prices rise as the energy source is depleted and it becomes progressively more expensive to extract. By contrast, the open-market model assumes that there is a variety of available energy sources and that competition among them leads to long-term stable or falling prices. At the moment, the United States and the world approximate the open-market model, but in the long run the supply of fossil fuel is finite, and prices inevitably will rise unless alternate energy sources substitute for fossil energy supplies; however, there appears little reason to suspect that long-term price trends will rise significantly over the next few decades.

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TL;DR: Archean sedimentary rocks from the Pilbara Craton, Australia, contain evidence for petroleum generation and migration in the form of bitumen nodules produced by radiogenic immobilization of fluid hydrocarbons around detrital uraninite, thorite, and monazite grains.
Abstract: Archean sedimentary rocks from the Pilbara Craton, Australia, contain evidence for petroleum generation and migration in the form of bitumen nodules produced by radiogenic immobilization of fluid hydrocarbons around detrital uraninite, thorite, and monazite grains. The nodules are preserved in sandstones at several stratigraphic levels in the Fortescue Group (~2.75 Ga) and Lalla Rookh Formation (~3.0 Ga), both nonmarine successions, and in deltaic sediments of the Mosquito Creek Formation (~3.25 Ga). The most ancient evidence comes from the Warrawoona Group (>3.46 Ga), where hydrocarbon droplets were apparently formed in situ from kerogenous sediments by flash maturation during early hydrothermal silicification. Bituminous relics of petroleum are also commonly preserved in shallow-marine sandstones of the Black Reef Formation (~2.59 Ga) and the Witwatersrand Supergroup (~2.85 Ga) from the Kaapvaal Craton, South Africa, along with subeconomic methane accumulations. In all cases, the petroleum was apparently sourced from Archean shales, generated during the Archean, and migrated before the late Archean or early Early Proterozoic metamorphism occluded fluid pathways. Given this widespread and abundant evidence for hydrocarbon generation and migration in Archean depositional basins, it seems that primordial bacterial biomass, producing labile type I kerogen, was often buried in sufficient quantities to successfully generate and expel petroleum. Depositional basins on ancient cratons clearly contained permeable rocks amenable to the migration, and probably to the accumulation, of petroleum. Thus, the main factors precluding the discovery of economically exploitable hydrocarbon accumulations in Archean basins are the subsequent destructive effects of deformation and metamorphism, which causes trap breaching, imperfect sealing, or thermal obliteration. However, there are ancient stable cratons where such disruption may not have occurred, and so petroleum explorers may wish to reassess the possibility of finding valuable hydrocarbon resources in Archean rocks.

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TL;DR: In this paper, an early diagenetic origin of the cements is also suggested by the fact that the majority of sandstone samples have lost more porosity due to cementation than through compaction.
Abstract: Reservoir quality of Rotliegende sandstones (Lower Permian) in the northern Netherlands was significantly affected by early diagenetic processes that are related to sedimentary facies in marginal desert/playa lake environments. In the past, burial-related products and processes have received more attention than early diagenetic processes, neglecting the effects that early diagenesis can have on reservoir quality and well productivity of Rotliegende sandstones. Shallow groundwater-related diagenesis is a major factor affecting Rotliegende reservoir sandstones. The precipitation of the main porosity-occluding cements (dolomite, anhydrite, and quartz) occurred early in the diagenetic history. Oxygen isotopes of dolomite (d18O = 18.4 to 23.4‰ SMOW) suggest that meteoric water has played a major role throughout the diagenetic history, and that precipitation of these cements occurred at low temperatures (<80°C). The strontium isotopes of dolomite cements (87Sr/86Sr = 0.70935-0.71387) and the sulfur isotopes of anhydrite cements (d34S = 6.7 to 9.7‰ CDT) rule out Permian or younger seawater as a source for these cements, and are consistent with formation from meteoric water within a continental basin. An early diagenetic origin of the cements is also suggested by the fact that the majority of sandstone samples have lost more porosity due to cementation than through compaction. Most samples with high (<20%) amounts of porosity loss via cementation were affected by early dolomite and anhydrite. The relative abundance of dolomite and anhydrite cements can be correlated with depositional environments. Wet depositional environments (e.g., interdune and fluvial sandstones) with water tables close to the surface show the highest amount of dolomite and anhydrite cements, whereas dry environments with relatively deep water tables (e.g., dune sandstones) are characterized by low amounts of cements. The precipitation of early diagenetic cements has strongly influenced the present-day porosity patterns, with depositional environments interpreted as "drier" showing less cements and significantly altering the porosity patterns formed during early diagenesis. Knowledge of the influence of sedimentology and paleogeography on the diagenetic patterns is a key element for improved understanding and prediction of reservoir quality in the Rotliegende sandstones of the northern Netherlands.

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TL;DR: In this article, chemical and isotopic analyses of these waters indicate mixing of brines of quite different origins in the deep subsurface of the Permian basin, and the results of these analyses indicate that meteoric waters can migrate large distances and displace saline waters deep in a basin that has numerous oil reservoirs that have solution-gas drive.
Abstract: Formation waters from producing reservoirs in Paleozoic carbonates have been studied to determine the origin of brines on the eastern Central Basin platform in west Texas. Chemical and isotopic analyses of these waters indicate mixing of brines of quite different origins in the deep subsurface of the Permian basin. Formation waters from the middle Permian San Andres Formation at 1430 m (4700 ft) and from Devonian limestones at 3200 m (10,500 ft) have salinities of 26-59 g/L and dD-d18O values in the same range as modern precipitation and groundwater in the near-surface Ogallala aquifer. Na-Cl-Br concentrations and molar ratios show that the salinity of these waters was largely acquired through halite dissolution. Formation waters from Pennsylvanian and Lower Permian shelf limestones at 2600-3000 m (8500-9800 ft) are more saline (70-215 g/L) and apparently represent a mixture of two different fluids. One end member was highly saline, derived from seawater evaporated well beyond halite saturation, and the other end member was a moderately saline meteoric water similar to the San Andres and Devonian formation waters. Halite beds occur only in Upper Permian (upper Guadalupian and Ochoan) strata in this area; hence, extremely saline evaporated seawater apparently descended into the Paleozoic carbonates during halite deposition in the Late Permian, mixing with and displacing marine formation waters by buoyancy-driven convective flow. These modified evaporitic brines were the dominant fluids in the Paleozoic carbonates until the late Tertiary, when meteoric water began to flow into deeper Paleozoic strata from outcrops and near-surface aquifers in southeastern New Mexico in association with tectonic uplift that began at 5-10 Ma. The meteoric water dissolved halite and anhydrite from Permian evaporites near the basin margin and moved eastward along the regional hydraulic gradient, mixing with and displacing the modified evaporitic brine in deeper hydrogeologic systems. These late Cenozoic meteoric fluids probably are responsible for widespread biodegradation of oil in the San Andres/Grayburg interval. The results of this study indicate that meteoric waters can migrate large distances and displace saline waters deep in a basin that has numerous oil reservoirs that have solution-gas drive. Understanding the history of formation waters can assist in exploration and production through improved (1) interpretation of reservoir-rock diagenesis, (2) prediction of oil biodegradation and displacement, (3) understanding of subsurface water pressures, and (4) interpretation of hydrocarbon saturations from resistivity logs.

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TL;DR: In this article, a grid of commercial multichannel seismic data offshore New Jersey, extending more than 70 km along strike and approximately 50 km downdip, reveal the three-dimensional morphology and evolution of four buried surfaces correlated with middle-upper Miocene sequence boundaries calibrated by drilling on the adjacent continental slope.
Abstract: Documentation of along-strike variations in the morphologies of continental-margin clinoforms is essential for understanding mechanisms of progradation, one of the fundamental relationships between depositional processes and preserved stratigraphy. Maps based on a grid of commercial multichannel seismic data offshore New Jersey, extending more than 70 km along strike and approximately 50 km downdip, reveal the three-dimensional morphology and evolution of four buried surfaces correlated with middle-upper Miocene sequence boundaries calibrated by drilling on the adjacent continental slope. Miocene clinoform breakpoints are not depositional analogs of the modern shelf edge. They are linear to gently arcuate; breakpoint and slope trends indicate a systematic southward displacement of depocenters over about 5.6 m.y. Progradation responded to point (fluvial) sediment sources, but efficient along-strike sediment dispersal muted their influence. Canyons are absent on three of four clinoform slopes; the fourth slope has one v-shaped canyon and a broad erosional area (possible slope failure?). Planar-floored canyons also occur, albeit rarely, seaward of clinoform toes. Apparently, v-shaped and planar-floored canyons, previously ascribed to downslope erosion vs. slope failure/headward erosion, respectively, can coexist. The accretionary northern slope of Little Bahama Bank is a possible morphologic analog. By analogy with Pleistocene shelf/slope geometries, an absence of canyons breaching clinoform breakpoints suggests that rivers did not discharge at paleoshelf edges, indicating that sea level lowstands postulated for the middle-upper Miocene did not expose breakpoints. Reconstruction of breakpoint paleoelevations supports this conclusion for three of the four mapped surfaces, suggesting that elevations of some Miocene lowstands on the global sea level curve are too high by up to 60 m.