Deep-marine Depositional Systems Research Articles

Peak Cenozoic warmth enabled deep-sea sand deposition

The early Eocene (~ 56–48 million years ago) was marked by peak Cenozoic warmth and sea levels, high CO2, and largely ice-free conditions. This time has been described as a period of increased continental erosion and silicate weathering. However, these conclusions are based largely on geochemical investigation of marine mudstones and carbonates or study of intermontane Laramide basin settings. Here, we evaluate the marine coarse siliciclastic response to early Paleogene hothouse climatic and oceanographic conditions. We compile an inventory of documented sand-rich (turbidite) deep-marine depositional systems, recording 59 instances of early Eocene turbidite systems along nearly all continental margins despite globally-elevated sea levels. Sand-rich systems were widespread on active margins (42 instances), but also on passive margins (17 instances). Along passive margins, 13 of 17 early Eocene systems are associated with known Eocene-age fluvial systems, consistent with a fluvial clastic response to Paleogene warming. We suggest that deep-marine sedimentary basins preserve clastic records of early Eocene climatic extremes. We also suggest that in addition to control by eustasy and tectonism, climate-driven increases in sediment supply (e.g., drainage integration, global rainfall, denudation) may significantly contribute to the global distribution and volume of coarse-grained deep-marine deposition despite high sea level.

GeoReservoir: An ontology for deep-marine depositional system geometry description

An ontology is a logical theory that accounts for a domain vocabulary’s intended meaning, allowing us to develop a computational artifact that explicitly and formally represents the community’s conceptualization related to a vocabulary. This paper presents the GeoReservoir ontology — the result of the ontological analysis of the terminology adopted by geologists in sedimentological studies about deep-marine depositional systems, which is one of the most relevant types of oil and gas reservoirs around the world. Despite the variety of studies describing the patterns of productive reservoirs, this domain demanded new approaches in conceptual modeling methodologies because the available terminology presents issues such as ambiguity and contamination of different interpretations in the terms’ definitions. Previous work has dealt with these issues in geology, resulting in the GeoCore, an ontology that explicitly defines the most generic entities in geology. However, the domain in focus still demanded a specialized ontology containing the particular terms found in reports about deep-marine deposits. GeoReservoir is an extension of GeoCore, which, in its turn, extends the Basic Formal Ontology (BFO), a foundational ontology for scientific domains. GeoReservoir takes advantage of both BFO and GeoCore’s foundations, allowing us to focus our effort on defining the domain-specific entities. A team of professional reservoir geologists supported the knowledge acquisition process. We developed the ontology in iterative steps from an initial prototype to a complete artifact containing the taxonomy of entities and the relations between the entities, being increasingly refined by the experts. We further present a case study demonstrating how one could describe a depositional system in GeoReservoir terms. Moreover, we validated the ontology against defined competency questions (CQs). This work’s final result is offering a sound, consistent and unambiguous terminology to support the integration of data and knowledge about deep-marine depositional system geometry and lithology.

Chlorite coating patterns and reservoir quality in deep marine depositional systems – Example from the Cretaceous Agat Formation, Northern North Sea, Norway

AbstractSediment gravity flows transport large volumes of sand and clay minerals into submarine systems, which store some of the world's major reserves of oil and gas. However, knowledge about grain‐coating clay mineral formation and its role in preserving reservoir quality in deep marine settings is poorly documented. Here we present a case study on the Agat Formation, a deep marine deposit interpreted as a series of turbidites, using a multimethod approach including petrographical, petrophysical and sedimentological data. This study investigates the occurrence and origin of chlorite coating and demonstrates how extensive chlorite coating substantially affects reservoir quality. The presence of green marine clay pellets suggests an initial shallow marine origin and sedimentological evidence reveals that the sediments were later remobilized by gravity flows and deposited at their present location. We suggest that the precursor clay coating was emplaced prior to sediment remobilization because of the presence of clay coating on grain contacts and all detrital components, the continuous nature of coating and the lack of clay bridges between the grains. Therefore, the origin of chlorite coating in deep marine environments may be recognized using the characteristic properties of inherited precursor clay coating. Chlorite coating thickness varies between an upper and lower sand unit, with an average of ca. 4.5 µm and ca. 24 µm, respectively. Permeability is significantly reduced in the interval with exceedingly thick chlorite coating but shows only a subtle decrease in helium porosity. This study enlightens the importance of crucially evaluating porosity in sandstones with thick chlorite coating using a multimethod approach. The results from this study can be useful in future exploration endeavours in the area and in other deep marine systems with a similar setting worldwide.

Dispersion, Accumulation, and the Ultimate Fate of Microplastics in Deep-Marine Environments: A Review and Future Directions

An estimated 8.3 billion tonnes of non-biodegradable plastic has been produced over the last 65 years. Much of this is not recycled or disposed of ‘properly’, has a long environmental residence time and accumulates in sedimentary systems worldwide, posing a threat to important ecosystems and potentially human health. We synthesise existing knowledge of seafloor microplastic distribution, and integrate this with process-based sedimentological models of particle transport, to provide new insights, and critically, to identify future research challenges. Compilation of published data shows that microplastics pervade the global seafloor, from abyssal plains to submarine canyons and deep-sea trenches. However, few studies relate microplastic accumulation to sediment transport and deposition. Microplastics may enter directly into the sea as marine litter from shipping and fishing, or indirectly via fluvial and aeolian systems from terrestrial environments. The nature of the entry-point is critical to how terrestrially-sourced microplastics are transferred to offshore sedimentary systems. We present models for physiographic shelf connection types related to the tectono-sedimentary regime of the margin. Beyond the shelf, the principal agents for microplastic transport are: i) gravity-driven transport in sediment-laden flows; ii) settling, or conveyance through biological processes, of material that was formerly floating on the surface or suspended in the water column; iii) transport by thermohaline currents, either during settling or by reworking of deposited microplastics. We compare microplastic settling velocities to natural sediments to understand how appropriate existing sediment transport models are for explaining microplastic dispersal. Based on this analysis, and the relatively well-known behaviour or deep-marine flow types, we explore the expected distribution of microplastic particles, both in individual sedimentary event deposits and within deep-marine depositional systems. Residence time within certain deposit types and depositional environments is anticipated to be variable, which has implications for the likelihood of ingestion and incorporation into the food chain, further transport, or deeper burial. We conclude that integration of process-based sedimentological and stratigraphic knowledge with insights from modern sedimentary systems, and biological activity within them, will provide essential constraints on the transfer of microplastics to deep-marine environments, their distribution and ultimate fate, and the implications that these have for benthic ecosystems.

Detrital-Zircon Mixing and Partitioning In Fluvial To Deep Marine Systems, Central California, U.S.A.

The increasing use of detailed detrital-zircon provenance data calls for an understanding of the controls that sedimentary processes exert on changing detrital-zircon provenance signatures in time and space in addition to the well-established influence of tectonics. Our U-Pb detrital-zircon data from seventeen samples taken across a series of modern second-order rivers to deep-marine depositional systems in central California show that marine mixing processes and sediment pathway partitioning exert important controls on detrital-zircon provenance signatures. The second-order rivers that input sediment into this system produce differentiable detrital-zircon provenance signatures as a function of the unique geology of their drainage areas. The mixing of sediment through the marine realm can be traced through the evolution of distinct detrital-zircon signatures as sediment is transported from rivers down system through longshore drift into submarine canyons. Sediment input from second-order streams is mixed in the littoral and upper submarine-canyon environments, yielding provenance signatures that are not thoroughly mixed until the lower reaches of submarine canyons. Sediment partitioning in these dispersal systems results in distinct detrital-zircon provenance signatures for different dispersal systems over short length scales (< 50 km). These data suggest that sediment mixing in the marine realm is likely an important control on detrital-zircon provenance signatures in any system in which sediment is transported through longshore drift and sediment pathways are distinctly partitioned. Changes in the way sediment pathways are partitioned through time has the potential to create heterogeneous detrital-zircon provenance signatures in stratigraphic successions through time and between closely spaced deposits of the same age. When seen in an ancient system, this heterogeneity may be mistakenly attributed to tectonic controls without the recognition of the influence of sedimentary process.

Palynofacies classification of the depositional elements of confined turbidite systems: Examples from the Gres d'Annot, SE France

Turbidites deposited in confined mini-basins may demonstrate extremely complex stratigraphic architectures. We hypothesize that particulate organic matter preserved in turbidites will not be randomly distributed and may be used to assist the identification of architectural elements. An integrated sedimentological and palynological study was conducted on confined turbidites in the Peïra Cava sub-basin of the Eocene to Oligocene Grès d'Annot system, SE France; this provides a natural laboratory, where certainty in the stratigraphy allows confidence in sampling of sub-environments. Elements reflect deposits from high and low density flows including: thin-beds that onlap the basin margin and heterolithics spread across the basin; base of slope megabeds; and thick-beds that have a proximal to distal expression from south to north across the basin. One hundred samples were collected from logged sections across the basin, with 10 g of mudstone per sample being processed for a count of three hundred pieces of organic matter. Both allochthonous terrestrial and relatively autochthonous marine matter were recovered, with results showing a progressive fining of material from proximal to distal areas. Base of slope megabeds and proximal ponded thick-beds are dominated by dense humic matter, medial areas become dominated by light plant material, and distal samples are dominated by amorphous matter, interpreted as a result of density sorting of organic matter in turbidity currents. Exploratory ordination analysis and fuzzy cluster analysis were used to examine these results. Based on this study, we provide evidence of density fractionation of organics in turbidity currents, which is implied to be a major control on the distribution of particles in deep-marine depositional systems. This allows a palynofacies classification scheme to be developed to recognise architectural elements, which may be applied to sub-surface samples to assist the characterization of deep-water mini-basin architecture, understanding of which is crucial for hydrocarbon exploration and development.

Sedimentological evolution of Sele Formation deep-marine depositional systems of the Central North Sea

Abstract The Paleocene–Eocene-aged Sele Formation is developed across the basinal region of the Central North Sea. The section comprises a number of deep-marine fan systems that expanded and contracted across the basin floor in response to relative sea-level changes on the basin margin and fluctuating sediment yield off the Scottish landmass modulated by climate and hinterland uplift. Persistent sediment entry points to the basin resulted in the development of discrete axial and transverse fan fairways with a geometry dictated by an irregular bathymetry sculpted by differential compaction across Mesozoic faults, halokinesis and antecedent fan systems. A high-resolution biostratigraphic framework has allowed the evolution of fan-dispersal systems in response to these effects to be tracked across the basin within four genetic sequences. The proximal parts of the fans comprised channel complexes of low sinuosity, high lateral offset, and low aggradation. The development of these systems in a bathymetrically confined corridor of the Central Graben ( c. 65 km wide), combined with high sediment supply, resulted in the eventual burial of any underlying relief. The behaviour of sand-rich reservoirs in this region is dominated by the permeability contrast between high-quality channel fairways and more heterolithic overbank regions, with the potential for early water breakthrough and aquifer coning in the channel fairways, and unswept volumes in overbank locations. Compartmentalization of compensationally stacked channel bodies occurs locally, with stratigraphic trapping caused by lateral channel pinch-outs, channel-base debrites, mud-rich drapes and abandonment fines. Towards the southern part of Quadrant 22, approximately 150 km down-palaeoflow, the systems became less confined and in this region are dominated by channel–lobe complexes, which continued to interact with an irregular bathymetry controlled by antecedent fans, mass-transport complexes and halokinesis in the form of rising salt diapirs. Reservoirs in this region are inherently stratigraphically compartmentalized by their heterolithic lithology and compensational stacking of lobes, and further complicated by structuration and instability induced by the diapiric or basement structures needed to generate a trapping structure in these settings.

Deep-water Circulation: Processes &amp; Products (16–18 June 2010, Baiona): introduction and future challenges

Deep-water circulation is a critical part of the global conveyor belt that regulates Earth’s climate. The bottom (contour)-current component of this circulation is of key significance in shaping the deep seafloor through erosion, transport, and deposition. As a result, there exists a high variety of large-scale erosional and depositional features (drifts) that together form more complex contourite depositional systems on continental slopes and rises as well as in ocean basins, generated by different water masses flowing at different depths and at different speeds either in the same or in opposite directions. Yet, the nature of these deep-water processes and the deposited contourites is still poorly understood in detail. Their ultimate decoding will undoubtedly yield information of fundamental importance to the earth and ocean sciences. The international congress Deep-water Circulation: Processes & Products was held from 16–18 June 2010 in Baiona, Spain, hosted by the University of Vigo. Volume 31(5/6) of Geo-Marine Letters is a special double issue containing 17 selected contributions from the congress, guest edited by F.J. Hernandez-Molina, D.A.V. Stow, E. Llave, M. Rebesco, G. Ercilla, D. Van Rooij, A. Mena, J.-T. Vazquez and A.H.L. Voelker. The papers and discussions at the congress and the articles in this special issue provide a truly multidisciplinary perspective of interest to both academic and industrial participants, contributing to the advancement of knowledge on deep-water bottom circulation and related processes, as well as contourite sedimentation. The multidisciplinary contributions (including geomorphology, tectonics, stratigraphy, sedimentology, paleoceanography, physical oceanography, and deep-water ecology) have demonstrated that advances in paleoceanographic reconstructions and our understanding of the ocean’s role in the global climate system depend largely on the feedbacks among disciplines. New insights into the link between the biota of deep-water ecosystems and bottom currents confirm the need for this field to be investigated and mapped in detail. Likewise, it is confirmed that deep-water contourites are not only of academic interest but also potential resources of economic value. Cumulatively, both the congress and the present volume serve to demonstrate that the role of bottom currents in shaping the seafloor has to date been generally underestimated, and that our understanding of such systems is still in its infancy. Future research on contourites, using new and more advanced techniques, should focus on a more detailed visualization of water-mass circulation and its variability, in order to decipher the physical processes involved and the associations between drifts and other common bedforms. Moreover, contourite facies models should be better established, including their associations with other deep-water sedimentary environments both in modern and ancient submarine domains. The rapid increase in deep-water exploration and the new deep-water technologies available to the oil industry and academic institutions will undoubtedly lead to spectacular advances in contourite research in terms of processes, morphology, sediment stacking patterns, facies, and their relationships with other deep-marine depositional systems.

Impact of eustatic amplitude variations on shelf morphology, sediment dispersal, and sequence stratigraphic interpretation: Icehouse versus greenhouse systems: COMMENT

[Somme et al. (2009)][1] present an important contribution in the ongoing development of ideas regarding clinoform geometries and the timing and volume of sediment supply to deep-marine depositional systems. Much progress has been made since the original overly simplistic lowstand models (e.g., [

Evolution and strike variability of early post-rift deep-marine depositional systems: Lower to Mid-Cretaceous, North Viking Graben, Norwegian North Sea

The controls and development of early-post-rift, deep-water depositional systems are poorly understood due to their commonly deeply-buried nature. As a consequence, in the subsurface there is usually a lack of well penetrations and/or weak seismic imaging. At outcrop, early post-rift strata have commonly been deformed beyond reasonable recognition by later inversion tectonics. In contrast to these systems, the North Viking Graben shows a well-imaged Cretaceous early post-rift package with good well control and little effect from inversion. Therefore, this paper examines the early post-rift, deep-water depositional systems of the North Viking Graben to determine the controls on their stratigraphic position, geometry and evolution, and thus provide an analogue for comparable systems. Greater understanding of such systems will allow for the enhanced prediction of reservoir units in the subsurface and development of new play models since post-rift intervals are generally under-explored. The basin configuration inherited by the Cretaceous early post-rift in the northern North Sea was set up by Permo-Triassic and Late Jurassic rifting. In the North Viking Graben this established considerable along-strike variability, resulting in a northern basin segment surrounded by steep slopes and faulted-bounded structural highs and a southern basin segment margined by slopes with noticeably gentler gradients. Associated with the Cretaceous post-rift is an overall transgressional trend, which drowned local source areas, resulting in prevalent carbonate and hemipelagic mudstone deposition in the basins. In the North Viking Graben, the uplifted Oseberg fault-block provided the sub-aerial clastic source area until it was submerged in the early Upper Cretaceous. The early post-rift infill of the North Viking Graben was divided into four key seismic stratigraphic units (K1, K2, K3 and K4) using an integration of seismic and well data. Inside this stratigraphic framework, the depositional systems within each K-unit were resolved from characteristic seismic facies, amplitude anomalies, relationship with adjacent reflections, and geomorphologies. In the northern basin segment, the early post-rift stratigraphy contains basin-floor fans, a channel complex and a shoreline-like geometry, whereas the southern basin segment is solely characterised by hemipelagic and carbonate deposition. This spatial variability indicates that one of the dominant controls on the development of the early post-rift depositional systems in the North Viking Graben was the inherited syn-rift fault-controlled topography. The steep slopes bounding the northern basin segment aided the delivery of sediment from the sub-aerial Oseberg source area to the graben whereas the submerged, gentle slopes in the southern basin segment were relatively sediment-starved. Long- and short-term changes in relative sea-level also heavily influenced the evolution of the early post-rift basin stratigraphy. Short-term relative sea-level fall allowed basin-floor fan emplacement whereas short-term relative sea-level stand-still favoured deposition of a channel complex. Deposition of the shoreface-like geometry is associated with a short-term relative sea-level rise. This temporal difference in the style and scale of the depositional systems is also interpreted to reflect the gradual denudation and drowning of the Oseberg source area. Regional short-term trangressive and anoxic events in the northern North Sea further influenced the early post-rift strata, resulting in the deposition of stratigraphic units that can be correlated across the North Sea.

Silurian–Devonian active-margin deep-marine systems and palaeogeography, Alai Range, Southern Tien Shan, Central Asia

Analysis of Mid-Palaeozoic successions in the northern part of the Alai Range (Kyrgyzstan and bordering Uzbekistan), Southern Tien Shan, Central Asia, has identified a Silurian–Devonian deep-marine depositional system of basin-slope facies-associations. Here, we document the stratigraphy and sedimentology of a region in Central Asia that, through conflict, has become inaccessible for geological research. The turbidite-dominated Pul'gon Formation (Silurian) accumulated in sea-floor depressions and within the inferred basin axis. The large-scale, coarse clastic lenses of the Dzhidala Formation (mostly Devonian) represent the fills of submarine channels, canyons or gullies of the palaeoslope; other slope apron processes include sediment slides, debris flows and olistoliths. The partly time-equivalent condensed sequences of the Mid- to Late Silurian Kursala Formation and Early Devonian Tamasha Formation represent graptolitic mudstone and chert accumulation, respectively, together with thin dolomitic limestones, that accumulated over c . 10–15 Ma, probably on seamounts in the Turkestan (Fergana) Ocean between the continental margin of Kazakhstania and the Alai microcontinent. The graptolitic shale-rich Chakush Formation (early Silurian) is geographically and petrographically different from the Pul'gon and Dzhidala formations and suggests a different provenance (opposing continental margin or seamount talus).

Deep-marine sedimentary facies in the Belaga Formation (Cretaceous-Eocene), Sarawak: Observations from new outcrops in the Sibu and Tatau areas

Deep-marine rocks of the Belaga Formation (Cretaceous-Eocene) in the Sibu-Tatau area, Sarawak, show a variety of facies types, which are characterized by grain fabric, bed thickness, and sedimentary structures. The main facies types are (A) thick-bedded sandstone, (B) thinly-bedded heterolithic sandstone-mudstone interbeds, and (C) mudstone facies. These facies may be interpreted in relation to a submarine fan model, in which facies A represents a proximal position (near to source area) while facies B and C represent deposition in the middle to distal parts of the system, respectively. Within this general fan model, a detailed characterization of the facies can be made to understand the depositional processes operating in the deep-marine environment. Facies A, for instance, comprises massive and graded sand beds that appear to be linked genetically; the massive bed, often with floating mudclasts at the top, probably represent a debris flow deposit laid down over a pre-cursor turbidity flow deposit, which is commonly preserved as a thin graded bed at the base of the sandbody. Such linked debrite-turbidite facies association seems to be a common feature in the Belaga Formation, similar to many other deep-marine depositional systems, including the West Crocker in Sabah.

Seismic stratigraphic and geomorphic analysis of deep-marine deposition along the West African continental margin

Abstract The West African continental margin evolution is preserved in a small source-distant setting (20 x 30 km area) by changes in lobe-channel-levee seismic geomorphological elements within a threefold seismic stratigraphic hierarchy. The C . 32 Ma depositional record of rift, drift and depositional outbuilding of the margin by gravity-driven adjustment, deformation and deposition produced a hierarchy of second- through fourth-order stratigraphic cycles bounded by laterally continuous fine-grained drapes inferred to record prolonged periods of sediment starvation. The margin outbuilding phase, the focus of this contribution, consists of three second-order adjustment bounded cycles (ABCs) that record major adjustment and/or modification of the deep-marine depositional system. Seven third-order cycles also show changes in depositional trend and seismic facies architecture. Ten fourth-order cycles, best resolved within the upper part of the succession, consist of multiple, wedge-shaped and compensating, lobe-channel-levee complexes up to 20 km wide. These complexes show an upward increase in channel-levee and decrease in lobe proportion. They also show an upward change from lobes incised by sinuous channels to channels deflected to lobe flanks. Outcrop and shallow core-calibrated analogues from the Permian Brushy Canyon Formation, and modern Amazon and Zaire Fans help constrain these patterns. Changes in the sediment composition and volume of subaqueous flows at their point of origin, and subsequent gravitational deformation, syn-sedimentary mass-wasting and large-scale fan avulsion punctuating deep-marine sedimentation, adjust deep-marine depositional pattern during basin margin outbuilding. Lobe-channel-levee distributions in this sediment source-distant setting record a progressive increase in local topographic relief and gradient related to the basinward migration of deformation during depositional outbuilding of the continental margin. Two important conclusions derived from this record include (1) the importance of local seabed topography and gradient on producing changes in depositional pattern, and (2) that repeated and cyclic changes in these patterns reflect adjustment/deformation within, and probably restricted to, the deep-marine record. Integrated seismic stratigraphic and geomorphic analysis delineates multiple scales of these adjustment-bounded cycles. The evolving map patterns record adjustment by shifts in geomorphic pattern and orientation. These local geomorphic changes can be used to predict longer-term and larger-scale changes in the depositional record of the continental margin evolution. This analytical approach should have general utility along high shelf-to-basin relief margins with similar gravity-driven deformation.

Screening for deep-marine reservoirs in frontier basins: Part 1—Examples from offshore mid-Norway

This article illustrates a successful methodology used to screen a series of deep-marine depositional systems in the gigantic (180,000-km2; 69,500-mi2) Vring and Mre basins, offshore mid-Norway. Seismic and well data have been integrated with architectural information from selected outcrop analogs from the Delaware basin in United States and the Ainsa basin in Spain to describe the three-dimensional depositional geometries of the deep-water sedimentary systems.The examples presented document the large variability in geometry and size by illustrating seismic facies and sequences of deep-marine fan systems in the Vring and Mre basins. The main architectural elements are (1) basin-floor deposits characterized by constructional processes such as sheet sands and lobe forms; (2) canyons and channels with several phases of infill; and (3) slope accommodation deposits governed by the topography with a variety of infilling stratigraphic architectures.Offshore mid-Norway, the distance to sediment provenance area varies between tens and hundreds of kilometers for the deep-marine systems, and the basin-floor deposits cover up to several thousands of square kilometers. However, insight into the lithofacies distribution and architectural features of different scales seen in outcrop and subsurface data suggest that common depositional processes may be involved regardless of scale differences across a deep-water profile. In frontier basins, sand prediction will be regional in scale, and the applied methodology is a very useful screening tool to predict what part of the deep-water basin is most likely to be sand prone and also the ultimate reservoir quality.

High resolution geochemical and petrographical correlation of deep marine Palaeocene sandstones from the Foinaven Field, West of Shetland

Cores from three wells in the Upper Palaeocene deep-marine reservoir interval of the Foinaven Field, West of Shetland have been analysed using trace element geochemistry and petrography. The 60 m thick turbidite-dominated succession is restricted to the T34 biozone and comprises a series of seismically defined channel and overbank deposits. Petrographic and trace element geochemical data indicate that wells 204/24a-3 and 204/25b-5 have strong similarities and that strata in the remaining well (204/24a-7) have distinctly different signatures. Of the two related wells, 204/25b-5 is dominated by a thick amalgamated sandstone succession, 204/24a-3 by more thinly bedded and finer grained sandstones considered to represent channel and associated overbank deposits respectively. Similarities in geochemical and petrographic data allow division of the biozone in the two related wells into four principal correlation zones with two additional sub-zones. The study has established a high resolution correlation scheme and constrained correlation lengths for reservoir and non-reservoir facies in a deep marine depositional system.

Abstract: Deep marine depositional systems

Abstract: Deep marine depositional systems

Upper Miocene Stevens Sandstone, San Joaquin Basin, California: Reinterpretation of a Petroliferous, Sand-Rich, Deep-Sea Depositional System

Deep-marine sands of the upper Miocene Stevens sandstone, one of the most important hydrocarbon-producing units in the United States, were deposited by sediment-gravity flows in the Bakersfield arch area of the southern San Joaquin basin. The Stevens sandstone historically has been considered to be a thick turbidite succession shed off the southern Sierra Nevada as four fans in a long-lived submarine fan system fed in large part by several large submarine canyons. Access to previously unavailable proprietary two-dimensional and three-dimensional seismic data sets, carefully calibrated by well-log and core data, permits a more complete understanding of the depositional architecture of this highly petroliferous, deep-marine depositional system. We conclude that these units were deposited in a structurally controlled, sand-rich deep-sea system, which was fed by a delta system that lacked major submarine canyons. The uppermost sand unit, the upper Stevens sandstone, developed as a deep-sea braid plain in the area of the present Bakersfield arch. Within the braid plain, curvilinear features detected on horizon slices through a three-dimensional seismic data cube are interpreted as braided channel-form deposits. Hydrocarbon production established along these linear trends may reflect improved reservoir quality localized by channel sedimentary processes.

A Delta Submarine Ramp Alternative to the Canyon-Fed Depositional Model of the Stevens Submarine Fan System, Southeastern San Joaquin Basin, Kern County, California: ABSTRACT

Deep-marine sands of the Upper Miocene Stevens Sandstone, one of the most important hydrocarbon-producing units in the United States, were deposited by sediment-gravity flows in the Bakersfield Arch area of the southern San Joaquin basin. The Stevens Sandstone has historically been considered to be a thick turbidite succession shed off the southern Sierra Nevada as four fans in a long-lived submarine fan system fed by several large submarine canyons. Access to previously unavailable proprietary 2-D and 3-D seismic data sets, carefully calibrated by well-log and core data, permits a more complete understanding of the depositional architecture of this highly petroliferous, deep-marine depositional system. This study concludes that these units were deposited in a delta-fed, line- sourced deep-sea system, whose distribution was structurally-controlled. Seismic lines examined in this study show evidence for a large fault-controlled slump feature in the area that has been referred to as [open quotes]Rosedale Canyon,[close quotes] and no evidence supports the existence of submarine canyons feeding the system. The highly progradational Stevens interval consists of thick siliciclastic units separated by thin, intervening biosiliceous shales. Seismically, the upper bounding surfaces of these biosiliceous shales represent major downlap surfaces. As sands were deposited by high-density turbidity currents, the areamore » of the present Bakersfield Arch developed into a deep-sea braid plain. Smaller-scale linear features detected on horizon slices through the 3-D seismic data cube have been interpreted in this study as braided channelform features deposited on the deep-sea braid plain. Hydrocarbon production along these linear trends may be associated with porosity and permeability variations resulting from channelized versus non-channelized sedimentation.« less

Sediment dispersal patterns in a deep marine back-arc basin: evidence from heavy mineral provenance studies

Abstract Heavy mineral provenance studies can aid reservoir description in deep marine depositional systems by providing a clearer understanding of the lateral extent of discrete sediment bodies. In this study the lower Gustav Group (Lagrelius Point, Kotick Point and Whisky Bay formations) of James Ross Island, Antarctica, which was deposited in a deep marine slope-apron-submarine fan complex has been investigated. The Kotick Point and Whisky Bay formations crop out in two separate areas on the west coast of James Ross Island. The provenance of the group has been studied by both standard sandstone petrography and electron microprobe analysis of the heavy minerals’ garnet, pyroxene and Fe-Ti oxides. The sandstones are lithic to arkosic arenites derived from the adjacent Antarctic Peninsula magmatic arc. Although the general source area can be recognized, individual stratigraphical or depositional units cannot be distinguished on the basis of sandstone petrography. However, electron microprobe analyses of the detrital heavy minerals allows a more detailed discrimination of sediment provenance. In particular, analyses of the detrital Fe-Ti oxide minerals show that in the Whisky Bay Formation, the southern outcrop area, contains ilmenite, whilst the northern outcrop area contains titanomagnetite. In conjunction with the available biostratigraphical and palaeocurrent evidence, this can be interpreted in two ways. Firstly, if the two outcrop areas are direct age equivalents then they were derived from separate point sources, and deposited as discrete sediment lobes. Alternatively, if they are not directly time-equivalent, the depositional system may have switched laterally with time, with sediment derived from source rocks of varying composition. Either interpretation has implications for the understanding of the deep marine depositional system. Detrital opaque minerals are commonly source specific and should not be ignored during provenance studies.

Depositional Architecture and Provenance of the Petroliferous Upper Stevens Sand Deep-Marine Depositional System, Southern San Joaquin Basin, California: ABSTRACT

Deep-marine sandstones of the upper Miocene Stevens Sandstone, derived from both easterly sierra Nevada and westerly Gabilan Range sources, were deposited by sediment gravity flows in the Bakersfield arch area of the southern San Joaquin basin. Access to previously unavailable proprietary 2-D and 3-D seismic data sets, calibrated by well-log and core data, permits a more complete understanding of the depositional architecture of this highly petroliferous, deep-marine depositional system. The Stevens interval consists of packages of thick siliciclastic units separated by thin, intervening biosiliceous shales. Seismically, the upper bounding surfaces of these shales represent major downlap surfaces. The structurally controlled Upper Stevens Sandstone is generally considered to be one of succession of high-density turbidity current deposits shed off the southern sierra Nevada. The Upper Stevens in the Bakersfield Arch area lacks a typical deep-sea fan morphology and cores do not display classic Bouma sequences. Slumping and debris flows appear to have significance as depositional processes. Furthermore, stratigraphic architecture suggests that a significant proportion of Upper Stevens coarse clastic sediment in the Bakersfield arch area may have been derived from the west side of the basin.