Sand-rich Deposits Research Articles

El Paso Formation: A key unit for the correlation of the Carboniferous glaciation in the Calingasta-Uspallata basin of western Argentina

The Late Paleozoic successions exposed along the western flank of the Precordillera at the latitude of Barreal in western Argentina are characterized by mid-Carboniferous glacial marine and glacially-influenced sediments (San Eduardo Group sensu Mésigos, 1953), followed by shallow marine, sand-rich deposits (Barreal Group).The El Paso Formation, exposed in the homonymous brachyanticline, is here subdivided into six facies associations (FAs), in ascending stratigraphic order: Boulder Conglomerate Complex FA, Sandstone Complex FA, Mudstones with Gastropods FA, Diamictite Complex FA, and Mudstones and Fine Sandstones FA. This analysis focuses on climatically sensitive facies related to the late Paleozoic Ice Age (LPIA), evidence of which is recorded in the adjacent Hoyada Verde Formation. The Boulder Conglomerate Complex FA includes boulders with striations on polished surfaces, indicative of glacially derived material. It grades up to sandstones with tangential cross-bedding and wave ripples, indicative of deposition as delta-scale sand-prone subaqueous clinoforms along a slope. The Diamictite Complex FA includes ice-rafted detritus (IRD) in two of its facies (dropstone mudstones and thin-bedded diamictites). The postglacial flooding, identified in various basins of western Argentina, is also present in the uppermost interval of the El Paso Formation (Mudstones and Fine Sandstones FA). It includes mudstones and rippled sandstones with abundant invertebrate fauna mainly brachiopods, bivalves, and gastropods, accompanied by conulariids, nautiloids, ostracods and corals, associated with palynomorphs. This study demonstrates through several lines of evidence that the upper interval of the El Paso and the Hoyada Verde Formations are time equivalent and represent key localities for the mid-Carboniferous (Serpukhovian-Early Bashkirian) event of the LPIA in the Calingasta Uspallata basin. Furthermore, unlike in the Hoyada Verde Formation, where the Carboniferous/pre-Carboniferous ("Pre-Tillítico") unconformity contact is concealed, the El Paso basal coarse fill rests on basement. The lower interval of the El Paso Formation exhibits similar facies characteristics and fining-upwards stacking pattern to the lower interval of the Majaditas Formation exposed further south.

Behaviors of redox-sensitive tungsten and molybdenum in the northern South China Sea: From the Pearl River to the continental slope

To increase the proxy toolbox for the reconstruction of redox conditions, the transition metal tungsten (W) has been increasingly suggested as a promising new candidate during the last few years. However, compared to other trace metals such as molybdenum (Mo), studies on the redox behavior of W in the brackish/marine environment are relatively rare and mainly limited to euxinic settings. To contribute to our understanding of the behavior of W in modern aquatic ecosystems, we here present a water column W and Mo dataset that follows the salinity gradient of the Pearl River Estuary towards the adjacent coastal and offshore waters of the northern South China Sea (water depths range from 36 m to 3735 m) with the latter also including mostly anoxic porewater and rather oxic sediment surface data. Except for deviations of W in the low-salinity reaches of the Pearl River Estuary, both metals are conservatively introduced to the coastal ocean. The contribution of dissolved W via the Pearl River plume was identified in surface waters along the coastline. In line with previous open ocean studies, the conservative behavior of W proceeds towards the remote parts of the study area with surface waters that are possibly also affected by the South China Sea Warm Current. Within the short core porewater profiles, W concentrations increased with sediment depth and reached the highest levels at the more distal sites. These trends are not linked to the formation of more soluble thiotungstate species as indicated by generally non-sulfidic porewaters. Along with porewater gradients of W, the W concentrations in near-bottom waters suggest effective trapping of W at the sediment/water interface by Mn oxides especially at greater water depths and limited contribution to the open water column W inventory. In contrast to W, Mo concentrations show little variation in the reducing porewaters and remain close to or slightly above the ocean level. Enrichments of W and Mo in the surface sediments from the upper and lower continental slope reflect the known affinity of both trace metals to Mn oxides. Positive correlations of W with the heavy mineral-associated metals titanium (Ti) and zirconium (Zr) in sand-rich deposits of the outer continental shelf subjected to stronger near-bottom currents, further indicate a relation of sedimentary W abundances to the depositional environment.

Substrate Entrainment, Depositional Relief, and Sediment Capture: Impact of a Submarine Landslide on Flow Process and Sediment Supply

Submarine landslides can generate complicated patterns of seafloor relief that influence subsequent flow behaviour and sediment dispersal patterns. In subsurface studies, the term mass transport deposits (MTDs) is commonly used and covers a range of processes and resultant deposits. While the large-scale morphology of submarine landslide deposits can be resolved in seismic reflection data, the nature of their upper surface and its impact on both facies distributions and stratal architecture of overlying deposits is rarely resolvable. However, field-based studies often allow a more detailed characterisation of the deposit. The early post-rift Middle Jurassic deep-water succession of the Los Molles Formation is exceptionally well-exposed along a dip-orientated WSW-ENE outcrop belt in the Chacay Melehue depocentre, Neuquén Basin, Argentina. We correlate 27 sedimentary logs constrained by marker beds to document the sedimentology and architecture of a >47 m thick and at least 9.6 km long debrite, which contains two different types of megaclasts. The debrite overlies ramps and steps, indicating erosion and substrate entrainment. Two distinct sandstone-dominated units overlie the debrite. The lower sandstone unit is characterised by: 1) abrupt thickness changes, wedging and progressive rotation of laminae in sandstone beds associated with growth strata; and 2) detached sandstone load balls within the underlying debrite. The combination of these features suggests syn-sedimentary foundering processes due to density instabilities at the top of the fluid-saturated mud-rich debrite. The debrite relief controlled the spatial distribution of foundered sandstones. The upper sandstone unit is characterised by thin-bedded deposits, locally overlain by medium-to thick-bedded lobe axis/off-axis deposits. The thin-beds show local thinning and onlapping onto the debrite, where it develops its highest relief. Facies distributions and stacking patterns record the progradation of submarine lobes and their complex interaction with long-lived debrite-related topography. The emplacement of a kilometre-scale debrite in an otherwise mud-rich basinal setting and accumulation of overlying sand-rich deposits suggests a genetic link between the mass-wasting event and transient coarse clastic sediment supply to an otherwise sand-starved part of the basin. Therefore, submarine landslides demonstrably impact the routing and behaviour of subsequent sediment gravity flows, which must be considered when predicting facies distributions and palaeoenvironments above MTDs in subsurface datasets.

Submarine-fan development revealed by integrated high-resolution datasets from La Jolla Fan, offshore California, U.S.A.

ABSTRACT New high-resolution datasets across La Jolla submarine fan, offshore California, illuminate low-relief, down-dip widening conduits emanating from a deep-sea channel that deposited a combination of laterally extensive sand strata seemingly crisscrossed by distributary patterns. Extensive coverage of this sector of the seafloor shows submarine-fan architecture and morphologies essentially different than distributary channelized patterns characteristic of subaerial systems and previous conceptual models of submarine fans. The main La Jolla channel, connected to La Jolla Canyon, loses confinement by widening, decreasing in relief, and developing scoured margins across kilometers-long down-slope and lateral distances. Two scales of distributary patterns are associated with sand-rich deposits down-system from, and outside of, fully formed channels. A larger-scale distributary pattern is identified in backscatter and bathymetry from trains of preferential erosion associated with laterally continuous repetitive steps that extend for kilometers outside channel confinement and may represent net erosional upper-flow-regime transitional bedforms. Smaller-scale distributary backscatter patterns in unconfined sand-rich deposits originate from the wide, low-relief channel. We suggest that the newly imaged La Jolla seascape displays sedimentary features that may be common on deep-sea fans but missed in previous lower resolution studies of submarine fans. Thus, La Jolla provides the basis for integrating previously enigmatic and (or) incomplete images of submarine fans. High-resolution seafloor, subsurface, and sample datasets highlight the importance of channel widening, headward erosion, and unconfined flows in La Jolla submarine-fan development, and may be relevant to other sandy submarine fan systems.

Quaternary coastal plains as reservoir analogs: Wave-dominated sand-body heterogeneity from outcrop and ground-penetrating radar, central Santos Basin, southeast Brazil

Sub-seismic sand-body characterization depends largely on understanding the heterogeneities observed in outcrops of equivalent depositional settings to subsurface reservoirs (reservoir analogs). Outcrop information, however, rarely covers the whole depositional system. Ground-penetrating radar (GPR), on the other hand, is a powerful tool for the high-resolution visualization of sand-rich deposits in the shallow subsurface, allowing for the description of their internal architecture, relationships with depositional systems, and its larger scale stratigraphic evolution. The internal character of radar patterns can be interpreted with respect to facies seen in exposures, leading to the prediction of heterogeneities below radar resolution. In this paper we use GPR and outcrops to describe the heterogeneity of Quaternary coastal-plain deposits from central Santos Basin (Paraná state, southern Brazil) where Pleistocene and Holocene, wave-dominated regressive barriers and transgressive lagoons and estuaries were formed under the influence of Quaternary sea level and climatic changes. Sedimentary facies reveal the predominance of sand deposited under the influence of tidal processes, fair-weather and storm wave processes. Radarfacies indicate a tendency of progradation of beach-face reflectors over subtidal radarfacies within two regressive successions separated by a regional unconformity. Interpretation of GPR resulted in the definition of 13 radarfacies arranged in three associations reflecting major depositional systems: (1) strandplains formed by prograding beach/dune-ridge sets over subtidal deposits, (2) spit-inlets, with progradation of beach faces over subtidal deposits and longshore accretion of spits, and (3) paleolagoons/paleoestuaries. Sedimentary facies indicate that strandplains and spit-inlets are predominantly sandy, while a muddy composition is expected in paleolagoons/paleoestuaries. The distribution and evolution of these systems were controlled by base-level oscillations and/or sediment supply that resulted in the formation of two regressive barriers separated by a wave ravinement surface configuring two parasequences with a wide variety of inter- and intra-sand body heterogeneities. This arrangement imprints a relatively high degree of compartmentalization within deposits that are traditionally considered continuous and homogeneous. Therefore, the Quaternary coastal plain of Paraná can be used as an analog for compartmentalized coastal reservoirs.

Optical dating of K-feldspar grains from Middle Pleistocene lacustrine sediment at Marathousa 1 (Greece)

Post-infrared infrared stimulated luminescence (pIRIR) measurements are reported for multiple aliquots of potassium-rich feldspar grains from sedimentary deposits at Marathousa 1 and Choremi Mine in the Megalopolis Basin in southern Greece. Ages were obtained for 9 samples from the deposits that over- and underlie as well as include the archaeological and palaeontological deposits at Marathousa 1. These sediments are sandwiched between lignite seams II and III and thought to represent sediment deposition during a single glacial period. A single age was obtained for a sample from Choremi mine. The equivalent dose estimates are based on a newly developed method presented elsewhere, and environmental dose rate determinations followed standard procedures. A specific focus of this paper is the determination of a representative estimate of time-averaged palaeo-water content of the organic and sand-rich deposits and the impact of porosity and compaction on these estimates. Ages are presented using two water content scenarios. These final ages have relatively large uncertainties, making it difficult to accurately assign deposition to a single oxygen isotope stage (OIS). Taking uncertainty into account, sediment deposition at Marathousa 1 occur sometime during OIS 12 and 11 and at Choremi mine during MIS 8. When combined with other proxy information, these results support the interpretation that the peat deposits (represented by lignite seams II and III) were deposited during warm interglacial periods, and that the intervening clastic materials were deposited during glacial periods. In this case, the ages are best interpreted as supporting deposition of sediments during MIS12. This is consistent with one of the proposed age models, but younger than the other.

Tectono-sedimentary evolution and hydrocarbon reservoirs in the Early Cretaceous Tanan Depression, Tamtsag Basin, Mongolia

Abstract The responses of depositional patterns to extensional faulting during the rift cycle are discussed in this article, based on an integrated analysis of 3D seismic reflections, wire logs and cores from the Early Cretaceous Tanan Depression in the Tamtsag Basin, Mongolia. The synrift succession comprises four third-order sequences (SQ1-4). A four-stage fault evolution is defined, including early synrift SQ1 (initial isolate faults), early synrift SQ2 (rapid fault propagation), climax synrift SQ3 (maximum fault relief) and late synrift SQ4 (minor fault activity) stages. The initial isolated fault stage is defined by separated and small-sized half-grabens associated with short-dispersal alluvium. In contrast, the rapid fault propagation stage is characterised by much longer dispersal systems of fan-delta deposits. As rifting progressed, a considerable increase in the basin subsidence occurred and the maximum fault displacement led to a dustpan basin geometry, the coalescence of depocentres and extensive deep-water deposits. The observed both sediment starvation and balanced-filled patterns in SQ3 indicate that caution must be exercised when attempting to correlate reservoirs and source rocks since variations in basin-filled patterns would be enhanced by the displacement localisation on several major faults during the significant basin formation. During the early period of the climax synrift stage, footwall-sourced systems were prominent, but drainages in prior relay zone sites were mostly decayed or submerged. In response to the subsequent degradation of the footwall sources, axial-sourced braided deltaic systems became more important during the later period. An abrupt decrease of faulting at the end of the rift cycle gave a rise to an increased sediment supply and long-dispersal axially-sourced systems in the Tanan Depression. Petroleum exploration shows that fan-delta front sandstones in SQ2 are the most prospective hydrocarbon reservoirs, whereas the nearshore and offshore sub-lacustrine fan deposits in SQ3 have proved to be secondary potential oil-bearing reservoirs. This study indicates that sediment dispersal patterns would be significantly re-organised by the differential faulting displacement patterns and varied sediment potentials during the different synrift stages. The rapid fault propagation allowed the fault arrays to reach their nearly maximum length during the early period of the basin evolution, while the displacement remained almost constant. This fault growth pattern tends to establish large-scale topographic lows including overlapped transfer zones and hanging dip-slope. Hence, major drainage catchments and long-dispersal depositional systems of sand-rich deposits are facilitated during this early fault propagation stage, which may be a key aspect for the tectono-sedimentary evolution in rift basins. In addition, the fault and sedimentary relationships defined here may be used as a model when studying less data-rich rift basins elsewhere.

A geostatistical approach to the simulation of stacked channels

Turbiditic channels evolve continuously in relation to erosion-deposition events. They are often gathered into complexes and display various stacking patterns. These patterns have a direct impact on the connectivity of sand-rich deposits. Being able to reproduce them in stochastic simulations is thus of significant importance. We propose a geometrical and descriptive approach to stochastically control the channel stacking patterns. This approach relies on the simulation of an initial channel using a Lindenmayer system. This system migrates proportionally to a migration factor through either a forward or a backward migration process. The migration factor is simulated using a sequential Gaussian simulation or a multiple-point simulation. Avulsions are performed using a Lindenmayer system, similarly to the initial channel simulation. This method makes it possible to control the connectivity between the channels by adjusting the geometry of the migrating areas. It furnishes encouraging results with both forward and backward migration processes, even if some aspects such as data conditioning still need to be explored.

Application of Ground Penetrating Radar for Identification of Washover Deposits and Other Stratigraphic Features: Assateague Island, MD

A combination of ground penetrating radar (GPR) data, core data, and aerial photographs were analyzed to better understand the evolution of two portions of Assateague Island, Maryland. The focus of the study was to investigate the applicability of using GPR data to image washover deposits in the stratigraphic record. High amplitude reflections observed in two shore-perpendicular GPR profiles were correlated to shallow (<1 m) lithologic contacts observed in sediment cores. At these contacts, deposits consisting primarily of quartz sand overlie sediments with organic matter that include degraded plant root or stem material. The underlying organic matter likely represents the vegetated portion of the barrier island that was buried by washover fans deposited during hurricanes Irene (2011) and Sandy (2012), as indicated in high-resolution aerial photographs. The GPR data were able to delineate the washover deposits from the underlying stratigraphic unit; however, the radar data did not resolve finer structures necessary to definitively differentiate washover facies from other sand-rich deposits (e.g., flood-tide deltas and dunes). Other GPR profiles contain reflections that likely correlate to geomorphic features like tidal channels and vegetated zones observed in historical aerial imagery. Burial of these features by overwash fluxes were observed in the aerial imagery and thus the resulting radar sequence is largely interpreted as washover deposits. Deeper, channel-like features that have been infilled were also observed in shore-parallel profiles and these features coincide with scour channels observed in the 1966 aerial photography. Additional sedimentological data are required to determine what role overwash played in the in-filling of these features.

Interplay of fan-fringe reservoir deterioration and hydrodynamic aquifer: understanding the margins of gas development in the Ormen Lange Field

Abstract The Ormen Lange Field is a gas reservoir offshore mid-Norway, developed in a combined structural–stratigraphic–hydrodynamic trap. The lobe-dominated turbidite deposits are mostly of excellent quality, but show a significant deterioration trend towards the fan fringe at its northern margin. Axial parts of the fan contain amalgamated sand-rich deposits, which pass laterally into layered sequences characterized by intercalation of low-permeability heterolithic drapes. Along its 40 km length, the field contains in excess of 400 linked polygonal faults attributed to de-watering of underlying shales. Despite pervasive faulting, reservoir connectivity on a geological timescale is proved by a common pressure gradient in pre-production wells and depletion seen in all later development wells. Recent appraisal drilling of the fan fringe, occupying the crest of the field, encountered only residual gas saturations, despite being located in an area delineated by a seismic direct hydrocarbon indicator. A hydrodynamic aquifer concept is the most plausible explanation for the fluid distribution, in which the gas from the crest of the structure is displaced, leaving behind a northward-thickening prism of residual gas. Dynamic simulation of the fluid-fill evolution over geological time showed the hydrodynamically tilted contact depends on rate of water flow across the aquifer, stratigraphic baffling and faulting, and reservoir quality, i.e. clean sand fraction and effective permeability. Optimal development of this deep-water reservoir depends on understanding the relationship between reservoir quality, connectivity, and the position of the free water level (FWL) in the field. A range of FWL in the north of the field, only weakly constrained by the wells, was empirically established from the hydrodynamically initialized models. This allowed a robust test of the production wells planned to drain the margin of the field. Modelled predictions of reservoir quality and pressures were confirmed by subsequent drilling.

Seismic Sedimentology Research on Sublacustrine Fan of the Oligocene Dongying Formation, Liaozhong Depression, Bohai Bay Basin, Northeast China

In Liaozhong Depression, five types of sublacustrine fans are developed in the relative lowstand systems tracts of the fourth-order sequence in Dongying Formation. In drilling cores, typical turbidites characteristics exist including bedding structures such as slump deformation structure, parallel bedding, grading laminations and multi-stage scoured basal surfaces. They also can be recognized in well logs with distinctive low gamma-ray and high-resistivity stacking patterns. Logging curves usually display serrated bell shape, cylinder shape and funnel shape respectively. On seismic reflection profiles, sublacustrine fan typically shows lateral downlap on its external geometry and continuous or discontinuous “vermicular” reflection characteristics in its inner seismic reflection texture. According to the calibration results of drilling data, continuous seismic reflection profiles are interpreted to be mud-rich deposits with cohesive, soft sediment-deformation. Discontinuous seismic reflections with lateral migration and apparent incised valleys are interpreted to be sand-rich deposits which probably host the most potential litho-stratigraphic traps.

Detailed mapping of Miocene sand-rich deposits in Denmark with high-resolution 2D land streamer vibroseis

T. Vangkilde-Pedersen, E.S. Rasmussen and M. Kristensen present large-scale use of onshore high-resolution 2D seismic in regional groundwater mapping adopting a multi-disciplinary approach, including sedimentology and biostratigraphy in a sequence-stratigraphic framework.

Postavulsion channel evolution: Niger Delta continental slope

Channel avulsion is fundamental in defining submarine fan morphology yet, as a process, is poorly understood. The postavulsion evolution of five channel-levee systems, documented from both the shallow subsurface and the sea floor, is marked in the early stages by relatively wide axial channel belts containing sinuous channel elements. The axial channel belt in each system narrowed through time in association with levee aggradation, which resulted in increased channel confinement. Of the five systems studied, four avulsed from a radial avulsion node at the mouth of the basin feeder-channel complex, which is the entry point to the basin. Only one avulsion occurred at an avulsion node downflow of the mouth of the feeder-channel complex. The degree of channel instability in three of the four systems before an avulsion event was increased by channel-floor aggradation caused by the backfilling of channel-confined turbidity current deposits. Channel-floor aggradation reduced the confinement relief of the systems, thereby increasing the probability of avulsion during an outsized flow event. The backfilled deposits in the channel belts display relatively high seismic-reflection amplitudes inferred to be coarser grained (more sand rich) than their surroundings, that is, out-of-channel deposits. Overbank cyclic steps are exceptionally well preserved on subsurface levees, and their potential function in promoting an avulsion event is discussed. The actual process of avulsion is caused by the flow itself instead of a reduction in confinement relief, and although outsized flows are the likely trigger, depending on the degree of this relief in the channel, multiple small flows could also be responsible for levee breaching, resulting in avulsion. The process of channel-system evolution resulting in avulsion can be applied to other subsurface data where compensating high-amplitude channel belts are recognized. In the context of hydrocarbon exploration, investigating up depositional dip to identify avulsion nodes increases the chance of locating sand-rich deposits, especially where multiple channels converge on one point.

Sedimentary environments and depositional characteristics of the Middle to Upper Eocene whale-bearing succession in the Fayum Depression, Egypt

The discovery of whale fossils from Eocene strata in the Fayum Depression has provoked interest in the life and lifestyle of early whales. Excellent outcrop exposure also affords the dataset to develop sedimentological and stratigraphic models within the Eocene strata. Previous work generally asserts that the thick, sand-rich deposits of the Fayum Depression represent shoreface and barrier island successions with fine-grained lagoonal and fluvial associations capping progradational successions. However, a complete absence of wave-generated sedimentary structures, a preponderance of thoroughly bioturbated strata and increasingly proximal sedimentary successions upwards are contrary to accepted models of the local sedimentological and stratigraphic development. This study considers data collected from two Middle to Upper Eocene successions exposed in outcrop in the Wadi El-Hitan and Qasr El-Sagha areas of the Fayum Depression to determine the depositional affinities of Fayum strata. Based on sedimentological and ichnological data, five facies associations (Facies Association 1 to Facies Association 5) are identified. The biological and sedimentological characteristics of the reported facies associations indicate that the whale-bearing sandstones (Facies Association 1) record distal positions in a large, open, quiescent marine bay that is abruptly succeeded by a bay-margin environment (Facies Association 2). Upwards, marginal-marine lagoonal and shallow-bay parasequences (Facies Association 3) are overlain by thick deltaic distributary channel deposits (Facies Association 4). The capping unit (Facies Association 5) represents a transgressive estuarine depositional environment. The general stratigraphic evolution resulted from a regional, tectonically controlled second-order cycle, associated with northward regression of the Tethys. Subordinate cycles (i.e. third-order and fourth-order cycles) are evidenced by several Glossifungites-ichnofacies demarcated discontinuities, which were emplaced at the base of flooding surfaces. The proposed depositional models recognize the importance of identifying and linking ichnological data with physical–sedimentological observations. As such – with the exception of wave-generated ravinement surfaces – earlier assertions of wave-dominated sedimentation can be discarded. Moreover, this study provides important data for the recognition of (rarely reported) completely bioturbated sand-dominated offshore to nearshore sediments (Facies Association 1) and affords excellent characterization of bioturbated inclined heterolithic stratification of deltaic deposits. Another outcome of the study is the recognition that the whales of the Fayum Depression are restricted to the highstand systems tracts, and lived under conditions of low depositional energy, low to moderate sedimentation rates, and (not surprisingly) in fully marine waters characterized by a high biomass.

Structures and hydrocarbon prospectivity in the northern Davis Strait area, offshore West Greenland

In the northern Davis Strait to southernmost Baffin Bay area, offshore West Greenland, deep basins with Mesozoic and Cenozoic sedimentary successions occur and a number of large structures and closures at likely reservoir levels have been found. Mid-Cretaceous, Upper Cretaceous and Paleocene sand-rich deposits are well known onshore east of the study area and in offshore wells, and equivalent deposits may also be present in the structures. Some of the potential structural leads have thick seals of late Cretaceous–Cenozoic deposits and short distances to deep possible kitchens with mid-Cretaceous and Paleocene source rocks, which mainly came into the oil window during the Neogene. Onshore oil seeps and gas shows, together with amplitude anomalies from seismic data, such as possible bright spots, support a live petroleum system in the region. During Early to mid-Cretaceous time a number of large structures and basins formed as a result of extensional faulting, including the Kangerluk Structure, the Aasiaat Structural Trend, structures in the Aasiaat and Sisimiut basins, and in the Nagssugtôq Sub-basin. A period with less tectonic activity followed in the Late Cretaceous, with deposition of thick, basinal mudstone-dominated successions. In the Late Cretaceous to Early Paleocene renewed tectonic activity caused uplift and faulting of large structures, such as the Davis Strait High and partly the Kangerluk Structure. Late Paleocene to Early Eocene strike-slip movements created thrust faults and compressional structures, mainly in the Ikermiut Fault Zone, associated with formation of the Ikermiut Basin. During the Paleocene and mainly the Early Eocene the >200 km long Ilulissat Graben developed. Paleocene and Eocene basalts occur west of Disko and Nuussuaq and narrow in distribution further south. The basalt cover offshore may be more limited than believed earlier. The area was offered for licensing in two periods from 2006 to early 2008.

Prediction of reservoir sand in Miocene deltaic deposits in Denmark based on high-resolution seismic data

Intense investigations of deep aquifers in Jylland, western Denmark, during the last seven years have resulted in detailed mapping of Miocene sand-rich deposits laid down in fluvial channels, delta lobes, shoreface and spit complexes (Fig. 1; Rasmussen 2004). Detailed sedimentological and palynological studies of outcrops and cores, and interpretation of high-resolution seismic data, have resulted in a well-founded sequence-stratigraphic and lithostratigraphic scheme (Fig. 1) suitable for prediction of the distribution of sand. The Miocene succession onshore Denmark is divided into three sand-rich deltaic units: the Ribe and Bastrup sands and the Odderup Formation (Fig. 2). Prodeltaic clayey deposits of the Vejle Fjord and Arnum Formations interfinger with the sand-rich deposits. Most of the middle and upper Miocene in Denmark is composed of clayey sediments referred to the Hodde and Gram Formations (Fig. 2). This paper presents examples of seismic reflection patterns that have proved to correlate with sand-rich deposits from lower Miocene deltaic deposits and that could be applied in future exploration for aquifers and as analogues for oil- and gas-bearing sands in wave-dominated deltas.

Facies, Architecture, and Origin of a Reservoir-Scale Sand-Rich Succession Within Submarine Canyon Fill: Insights from Wagon Caves Rock (Paleocene), Santa Lucia Range, California, U.S.A.

Abstract Large submarine canyons incise most continental margins, but outcrops of comparably sized ancient examples are relatively rare. A preserved cross section of a filled Cretaceous–Paleocene submarine canyon, tens of kilometers wide by hundreds of meters deep and cut into granitic basement of the Salinian block, is exposed in the Santa Lucia Range of central coastal California. The exposure allows an opportunity for the detailed analysis of associated sand-rich deposits analogous to one type of petroleum reservoir. A succession of coarse-grained high-density turbidity current deposits present at Wagon Caves Rock (WCR), a 0.5 km2 mesa in the Indians Ranch area, is part of a lenticular sandstone body up to 75 m thick and several kilometers wide that accumulated within the confines of the submarine canyon. The facies architecture of the outcrop records canyon axial channel deposition in the middle reaches of the submarine canyon system. The uppermost beds at WCR record the catastrophic failure of the submarine-canyon wall, which was associated with the termination of coarse clastic deposition in the area. The modern Monterey submarine canyon, which incises Salinian block basement identical to that cut by the ancient canyon, provides a close analog for the depositional setting of the canyon deposits of the Indians Ranch area. The architectural analysis provides insight into facies and stratal architecture within a part of the deep-water slope environment that is relatively poorly known due to limited rock data from canyon successions and the inherent difficulty of recognizing large-scale submarine-canyon deposits in outcrop.

The Grès d’Annot as an analogue for Brazilian Cretaceous sandstone reservoirs: comparing convergent to passive-margin confined turbidites

Abstract The Eocene deep-water sand-rich deposits of the Grès d’Annot of southern France have been used as outcrop analogues for offshore Cretaceous reservoirs of Campos Basin, southeastern Brazil. The analogy is chiefly based on the sand-rich, confined nature of the two systems. Such application can be questioned as the contrasting geological settings, i.e. convergent versus passive margin, could produce rather different depositional scenarios. Detailed comparison between the two systems permits, however, recognizing additional similarities, and also some differences, whose recognition is important to ensure the correct application of the Grès d’Annot as an analogue for this and other passive-margin reservoirs. Comparative analysis of channel dimensions, facies continuity, and three-dimensional expression suggests that confined sand-rich systems show many similarities in terms of critical reservoir heterogeneity, providing that palaeotopographic control was similar, regardless of the tectonic environment in which they were formed. In addition, contrasts found among sequences in the same tectonic setting suggest that other factors (such as, for example, sand/shale ratio of the sediment input) play an important role in defining reservoir architecture. These observations further suggest that, once similarities and differences are correctly understood, analogue data, even from quite different tectonic settings, may provide a powerful tool for improving subsurface reservoir models.

The interplay between true eustatic sea-level changes, tectonics, and climatic changes: what is the dominating factor in sequence formation of the Upper Oligocene–Miocene succession in the eastern North Sea Basin, Denmark?

The Upper Oligocene–Miocene succession of the eastern North Sea is subdivided into six sequences on the basis of an integrated study of outcrops, boreholes, and seismic data. All available data and methodologies/criteria for the definition of sequences have been used. Datings of the sequences are based on palynology, micropalaeontology, and macropalaeontolgy, which give them a high confidence. The six sequences defined in this study do not correlate to the eight marked changes in true eustatic sea-level variation as indicated from oxygen isotope curves nor to the nine glacial maxima that have been recognised within the Miocene. The development of the individual sequences and the stacking pattern of the sequences is dependent both on true eustatic sea-level changes, relative sea-level changes (tectonics), and sediment supply. For example, a true eustatic sea-level fall as well as uplift may result in major progradation of a siliciclastic wedge. In the Miocene succession studied here, a distinct progradation in the lower Aquitanian was the result of a true eustatic sea-level fall. This resulted in deposition of a clean and widespread sand-rich clastic wedge. Marked progradation associated with an uplift of the hinterland in the Langhian resulted in sand-rich deposits alternating with coals. The interbedded coal seams were the result of a rising ground water table within the basin due partly to stable or even rising sea level and partly to local subsidence around faults. Similarly, a major transgression may be a result of a true sea-level rise or accelerated subsidence of a basin. In the case of the eastern North Sea Basin, accelerated subsidence was responsible for the major transgression in the Serravallian and Tortonian times, which is a period with a general climatic cooling. The frequency of true eustatic sea-level changes and relative sea-level changes (tectonic pulses) in the Miocene is of the order of 2.9–2.0 to 4 m.y., respectively. Both these intervals are within the time range of the studied sequences, which span 2–4 m.y. Consequently, but not surprisingly, neither of the two processes responsible for changes in relative sea level can be solely attributed to glaciations nor to tectonics. The climatic changes during the Late Oligocene–Miocene, which changed from cool temperate to subtropical with several reversals, did not influence the sediment yield.

Paleo-bathymetric controls on the stratigraphic architecture and reservoir development of confined fans in the Auger Basin: central Gulf of Mexico slope

With abundant well penetrations in proximal and distal settings and 3D seismic coverage, the Auger Basin is an ideal location to study the influence of basin setting and accommodation on the stratigraphic architecture of ancient turbidite systems. Pliocene-age turbidites at Macaroni Field were deposited in ponded accommodation in the distal portion of a salt-bounded intraslope basin, immediately inboard of a sediment spill point to the linked outboard basin. Deposits at Auger Field are contained within point-sourced submarine fans deposited in healed slope accommodation in the more proximal portion of the basin on the flank of a paleo-bathymetric ridge, immediately down depositional dip of a sediment spill point from an inboard basin. Both areas of the basin are distinct in terms of sediment dispersal patterns, rate of sediment fill, and preservation potential of reservoir/seal pairs, and while both fields contain sand-rich deposits and record vertical evolution from older sheet dominated- to younger channel dominated deposits over the Late Pliocene section, there are key differences in the nature in which the fill occurs. The ponded stratigraphic section at Macaroni Field records (1) an early mud-rich phase in which incoming flows are completely captured by confining topography, (2) a brief phase of diminished relief when high frequency fill/spill cycles occur, and ultimately (3) a phase of incision of the former basin sill and large-scale bypass to the outboard basin. Over the same period, the healed-slope section at Auger Field records a fill pattern consisting of alternating episodes of initial sand-rich sheet/lobe deposition followed by intervals of channelization. We acknowledge extra-basinal controls (eustacy, climate) on the timing, rate, and nature of sediment supply to the basin, but there is considerable evidence for paleo-bathymetric control on cyclical fill patterns observed at fourth and higher-order scales.