Annot Sandstone in the Peïra Cava basin: An example of an asymmetric facies distribution in a confined turbidite system (SE France)

High-resolution physical stratigraphy and detailed facies analysis have been carried out in the foredeep turbidites of Annot Sandstone in the Peïra Cava basin (French Maritime Alps) in order to characterize the relationship between facies and basin morphology. Detailed correlation patterns are evidence of a distinction between a southern bypass-dominated region, coincident with a channel-lobe transition and a north-eastern depositional zone, represented by sheet-like basin plain. These depositional elements are characterized by three main groups of beds related to the downcurrent evolution of bipartite flows. These facies groups are: 1) pebbly coarse-grained massive sandstones with rip-up mudstone clasts and impact mudstone breccias (Type I and II beds) deposited by basal dense flows, 2) coarse-grained massive sandstone overlain by tractive structures (Type III and IV beds) indicating the bypass of overlying turbulent flows and 3) massive medium-grained and fine-grained laminated sandstones related to the deposition of high and low density turbidity currents (Type V and VI beds). Ponding and reflection processes, affecting the upper turbulent flows, can characterize all type beds, but especially the beds of the third group. As described in other confined basins of the northern Apennines (Italy), the lateral and vertical distribution of these type of beds, together with other important sedimentary characteristics, - such as the sandstone/mudstone ratio, bed thicknesses, amalgamation surfaces and paleocurrents - reveal that the deposition of the Annot Sandstone in the Peïra Cava basin was controlled by an asymmetric basin with a steep western margin. This margin favored, on the one hand, basal dense flow decelerations and impacts, as well as bypass and deflection of the upper turbulent flows towards the north east.     

辽东湾南部下第三系地震地层学研究

本文依据地震地层学原理,结合层速度和砂岩百分比的研究,描述了辽东湾南部下第三系地震相和沉积相类型及特征,确定出近岸水下扇沉积体系、三角洲—滑塌浊积扇沉积体系、滨浅湖—滩坝沉积体系和深湖—深水浊积扇沉积体系,指出这些沉积体系的平面分布具有不对称性,垂向演化具有继承性和新生性的特点。最后预测了有利勘探地区。     

Depositional processes and stratigraphic architecture within a coarse-grained rift-margin turbidite system: The Wollaston Forland Group,east Greenland

The Wollaston Forland Basin, NE Greenland, is a half-graben with a Middle Jurassic to Lower Cretaceous basin-fill. In this outcrop study we investigate the facies, architectural elements, depositional environments and sediment delivery systems of the deep marine syn-rift succession. Coarse-grained sand and gravel, as well as large boulders, were emplaced by rock-falls, debris flows and turbulent flows sourced from the immediate footwall. The bulk of these sediments were point-sourced and accumulated in a system of coalescing fans that formed a clastic wedge along the boundary fault system. In addition, this clastic wedge was supplied by a sand-rich turbidite system that is interpreted to have entered the basin axially, possibly via a prominent relay ramp within the main fault system. The proximal part of the clastic wedge consists of a steeply dipping, conformable succession of thick-bedded deposits from gravity flows that transformed down-slope from laminar to turbulent flow behaviour. Pervasive scour-and-fill features are observed at the base of the depositional slope of the clastic wedge, c. 5 km into the basin. These scour-fills are interpreted to have formed from high-density turbulent flows that were forced to decelerate and likely became subject to a hydraulic jump, forming plunge pools at the base of slope. The distal part of the wedge represents a basin plain environment and is characterised by a series of crude fining upward successions that are interpreted to reflect changes in the rate of accommodation generation and sediment supply, following from periodic increases in fault activity. This study demonstrates how rift basin physiography directly influences the behaviour of gravity flows. Conceptual models for the stratigraphic response to periodic fault activity, and the transformation and deposition of coarse-grained gravity flows in a deep water basin with strong contrasts in slope gradients, are presented and discussed.     

Prerift and synrift sedimentation during early fault segmentation of a Tertiary carbonate platform, Indonesia

Eocene carbonate deposits of the Barru area, Sulawesi, Indonesia, provide a rare insight into sedimentation prior to and during propagation of normal faults to the surface. Three main successions; late prerift, latest prerift/earliest synrift and synrift, are characterised by distinctive facies associations and sequence development. Shallow water foraminiferal shoals and intervening lower energy depositional environments occurred during the late prerift in areas which latter formed footwall highs and hangingwall depocentres, respectively. During the latest prerift/earliest synrift, shallow water shelves deepened laterally into slope environments in developing hangingwall depocentres. In both these sequences, sections in developing hangingwall areas are thickest, deepen up-section and thin laterally towards growing footwall highs. Active faulting resulted in rapid drowning of hangingwall depocentres and massive reworking of material derived from collapse of the platform margin and adjacent shallow water/emergent footwall highs.Differential subsidence, controlling water depths and accommodation space, types of carbonate producers and active faulting were the main factors affecting depositional environments and facies distributions. Carbonate producers are extremely sensitive indicators of depositional water depth and energy, hence rapid lateral and vertical facies variations in the Barru area provide quantifiable insight into environmental changes prior to and during active faulting.     

Synsedimentary structural control on foredeep turbidites: An example from Miocene Marnoso-arenacea Formation, Northern Apennines, Italy

This work discusses the synsedimentary structural control affecting the turbidites of the Marnoso-arenacea Formation (MAF) deposited in an elongate, NW-stretched foredeep basin formed in front of the growing Northern Apennines orogenic wedge. The stratigraphic succession of the MAF (about 4000 m thick) records the progressive closure of the Apennine foredeep basin due to the NE propagation of thrust fronts. In this setting, Langhian to Serravallian turbidites are overlain by Tortonian mixed turbidite deposits, i.e. sandstone-rich low-efficiency turbidites. The high-resolution stratigraphic framework of basin-plain turbidites has made it possible to identify five informal stratigraphic units (I, II, III, IV, V) mainly on the basis of the structural control highlighted by: 1) the presence of topographic highs and relative depocentres detected through a progressive flattening approach, and 2) the presence of thrust-related mass-transport complexes and the progressive appearance and disappearance of five bed types (Types 1, 2, 3, 4, 5) considered important to understand the interaction between flow efficiency and basin morphology. By contrast, the upper part of the MAF succession (Tortonian in age) is formed by more sandstone-rich systems characterized by beds whose origin is likely to depend, at least in part, upon flow decelerations related to topographic confinement due to the progressive closure of the foredeep. The vertical and lateral distribution of these types of beds is, therefore, useful for the reconstruction of the morphological evolution of structurally controlled basins; in the MAF example, this is mainly due to the progressive narrowing of the foredeep caused by the propagation of the main thrust fronts toward the foreland.     

Turbidites and foreland basins: an Apenninic perspective

Do the Apennines represent a vantage point for studying turbidites? How did research develop in this area? These questions are discussed briefly in the following pages from a historical and autobiographical perspective. Some items are emphasized: the shifting of depocentres, the presence of megabeds (basinwide events), the definition of ‘classical’ turbidites, the facies approach, the recognition and distinction of hyperpycnal flows     

3-D internal architecture of methane hydrate-bearing turbidite channels in the eastern Nankai Trough, Japan

The reservoir architecture of methane hydrate (MH) bearing turbidite channels in the eastern Nankai Trough, offshore Japan is evaluated using a combination of 3-D seismic and well data. On the 3-D seismic section, the MH-bearing turbidite channels correspond to complex patterns of strong seismic reflectors, which show the 3-D internal architecture of the channel complex. A seismic-sequence stratigraphic analysis reveals that the channel complex can be roughly classified into three different stages of depositional sequence (upper, middle, and lower). Each depositional sequence results in a different depositional system that primarily controls the reservoir architecture of the turbidite channels. To construct a 3-D facies model, the stacking patterns of the turbidite channels are interpreted, and the reservoir heterogeneities of MH-bearing sediments are discussed. The identified channels at the upper sequence around the β1 well exhibit low-sinuosity channels consisting of various channel widths that range from tens to several hundreds of meters. Paleo-current flow directions of the turbidite channels are typically oriented along the north-northeast-to-south-southwest direction. High-amplitude patterns were identified above the channels along the north-to-south and north-northeast-to-south-southeast directions. These roughly coincide with the paleo-current flow of the turbidite channels. An interval velocity using high-density velocity analysis shows that velocity anomalies (>2000 m/s) are found on the northeastern side of the turbidite channels. The depositional stage of the northeastern side of the turbidite channels exhibits slightly older sediment stages than the depositional stages of the remaining channels. Hence, the velocity anomalies of the northeastern side of the channels are related to the different stages of sediment supply, and this may lead to the different reservoir architectures of the turbidite channels.     

Sequence stratigraphy of the Miocene section,southern Gulf of Mexico

This study focuses on the interpretation of stratigraphic sequences through the integration of biostratigraphic, well log and 3D seismic data. Sequence analysis is used to identify significant surfaces, systems tracts, and sequences for the Miocene succession.The depositional systems in this area are dominantly represented by submarine fans deposited on the slope and the basin floor. The main depositional elements that characterize these depositional settings are channel systems (channel-fills, channel-levee systems), frontal splays, frontal splay complexes, lobes of debrites and mass-transport complexes.Five genetic sequences were identified and eleven stratigraphic surfaces interpreted and correlated through the study area. The Oligocene-lower Miocene, lower Miocene and middle Miocene sequences were deposited in bathyal water depths, whereas the upper Miocene sequences (Tortonian and Messinian) were deposited in bathyal and outer neritic water depths. The bulk of the Miocene succession, from the older to younger deposits consists of mass-transport deposits (Oligocene-lower Miocene); mass transport deposits and turbidite deposits (lower Miocene); debrite deposits and turbidite deposits (middle Miocene); and debrite deposits, turbidite deposits and pelagic and hemipelagic sediments (upper Miocene). Cycles of sedimentation are delineated by regionally extensive maximum flooding surfaces within condensed sections of hemipelagic mudstone which represent starved basin floors. These condensed sections are markers for regional correlation, and the maximum flooding surfaces, which they include, are the key surfaces for the construction of the Miocene stratigraphic framework. The falling-stage system tract forms the bulk of the Miocene sequences. Individual sequence geometry and thickness were controlled largely by salt evacuation and large-scale sedimentation patterns. For the upper Miocene, the older sequence (Tortonian) includes sandy deposits, whereas the overlying younger sequence (Messinian) includes sandy facies at the base and muddy facies at the top; this trend reflects the change from slope to shelf settings.     

Stratigraphic evolution of Eocene clinoforms from northern Santos Basin,offshore Brazil: Evaluating controlling factors on shelf-margin growth and deep-water sedimentation

In order to assess the controlling factors on the evolution of a shelf margin and the timing of sediment transfer to deep waters, a seismic stratigraphic investigation was carried out in the Eocene interval of northern Santos Basin, offshore Brazil. The studied succession configures a complex of prograding slope clinoforms formed in a passive margin and encompasses five seismic facies and their respective depositional settings: shelf-margin deltas/shorefaces, oblique slope clinoforms, sigmoidal slope clinoforms, continental to shelfal deposits and mass-transport deposits. These are stratigraphically arranged as seven depositional sequences recording a total shelf-edge progradation of about 35 km and a progradation rate of 1,75 km/My. Two main types of sequences can be recognized, the first one (type A) being dominated by oblique slope clinoforms and shelf-margin deltas/shorefaces in which shelf-edge trajectories were essentially flat to descending and extensive sandy turbidites were deposited on the foreset to bottomset zones. Sequences of this type are dominated by forced-regressive units deposited during extensive periods of relative sea-level fall. Type B comprises an upper part represented by aggradational shelfal deposits and a lower part composed of mass-transport deposits and high-relief sigmoidal clinoforms with descending shelf-edge trajectory. Steep slump scars deeply cut the shelfal strata and constitutes the boundary between the two intervals observed in type B sequences. Sandy turbidites occur at the same frequency in both forced- and normal-regressive units but are more voluminous within forced-regressive clinoforms associated with shelf-margin deltas/shorefaces. Major slope failures and mass-transport deposits, by the other hand, occurred exclusively in type B sequences during the onset of sea-level fall and their volume are directly related to the thickness of the shelfal sediments formed during the pre-failure normal regressions.     

Geometry and architectural associations of co-genetic debrite–turbidite beds in basin-margin strata, Carboniferous Ross Sandstone (Ireland): Applications to reservoirs located on the margins of structurally confined submarine fans

Co-genetic debrite–turbidite beds are most commonly found in distal basin-plain settings and basin margins. This study documents the geometry, architectural association and paleogeographic occurrence of co-genetic debrite–turbidite beds in the Carboniferous Ross Sandstone with the goal of reducing uncertainty in the interpretation of subsurface data in similarly shaped basins where oil and gas is produced.The Ross Sandstone of western Ireland was deposited in a structurally confined submarine basin. Two outcrops contain co-genetic debrite–turbidite beds: Ballybunnion and Inishcorker. Both of the exposures contain strata deposited on the margin of the basin. An integrated dataset was used to characterize the stratigraphy of the Ballybunnion exposure. The exposure is divided into lower, middle, and upper units. The lower unit contains laminated shale with phosphate nodules, structureless siltstone, convolute bedding/slumps, locally contorted shale, and siltstone turbidites. The middle unit contains co-genetic debrite–turbidite beds, siltstone turbidites, and structureless siltstone. Each co-genetic debrite–turbidite bed contains evidence that fluid turbulence and matrix strength operated alternately and possibly simultaneously during deposition by a single sediment-gravity-flow event. The upper unit contains thin-bedded sandy turbidites, amalgamated sandy turbidites, siltstone turbidites, structureless siltstone, and laminated shale. A similar vertical facies pattern is found at Inishcorker.Co-genetic debrite–turbidite beds are only found at the basin-margin. We interpret these distinct beds to have originated as sand-rich, fully turbulent flows that eroded muddy strata on the slope as well as interbedded sandstone and mudstone in axial positions of the basin floor forming channels and associated megaflute erosional surfaces. This erosion caused the axially dispersing flows to laterally evolve to silt- and clay-rich flows suspended by both fluid turbulence and matrix strength due to a relative increase in clay proportions and associated turbulence suppression. The flows were efficient enough to bypass the basin center/floor, physically disconnecting their deposits from coeval lobes, resulting in deposition of co-genetic debrite–turbidite beds on the basin margin. The record of these bypassing flows in axial positions of the basin is erosional surfaces draped by thin siltstone beds with organic debris.A detailed cross-section through the Ross Sandstone reveals a wedge of low net-to-gross, poor reservoir-quality strata that physically separates sandy, basin-floor strata from the basin margin. The wedge of strata is referred to as the transition zone. The transition zone is composed of co-genetic debrite–turbidite beds, structureless siltstone, slumps, locally contorted shale, and laminated shale. Using data from the Ross Sandstone, two equations are defined that predict the size and shape of the transition zone. The equations use three variables (thickness of basin-margin strata, thickness of coeval strata on the basin floor, and angle of the basin margin) to solve for width (w) and trajectory of the basinward side of the low net-to-gross wedge (β). Beta is not a time line, but a facies boundary that separates sandy basin floor strata from silty basin-margin strata. The transition zone is interpreted to exist on lateral and distal margins of the structurally confined basin.Seismic examples from Gulf of Mexico minibasins reveal a wedge of low continuity, low amplitude seismic facies adjacent to the basin margin. Strata in this wedge are interpreted as transition-zone sediments, similar to those in the Ross Sandstone. Besides defining the size and shape of the transition zone, the variables “w” and “β” define two important drilling parameters. The variable “w” corresponds to the minimum distance a well bore should be positioned from the lateral basin margin to intersect sandy strata, and “β” corresponds to the deviation (from horizontal) of the well bore to follow the interface between sandy and low net-to-gross strata. Calculations reveal that “w” and “β” are related to the relative amount of draping, condensed strata on the margin and the angle of the basin margin. Basins with shallowly dipping margins and relatively high proportions of draping, clay-rich strata have wider transition zones compared to basins with steeply dipping margins with little draping strata. These concepts can reduce uncertainty when interpreting subsurface data in other structurally confined basins including those in Gulf of Mexico, offshore West Africa, and Brunei.     

Filling the gap: A 60 ky record of mixed carbonate-siliciclastic turbidite deposition from the Great Barrier Reef

Late Pleistocene to Holocene margin sedimentation on the Great Barrier Reef, a mixed carbonate-siliciclastic margin, has been explained by a transgressive shedding model. This model has challenged widely accepted sequence stratigraphic models in terms of the timing and type of sediment (i.e. carbonate vs. siliciclastic) deposited during sea-level oscillations. However, this model documents only hemipelagic sedimentation and the contribution of coarse-grained turbidite deposition, and the role of submarine canyons in this process, remain elusive on this archetypal margin. Here we present a new model of turbidite deposition for the last 60 ky in the north-eastern Australia margin. Using high-resolution bathymetry, 58 new and existing radiometric ages, and the composition of 81 turbidites from 15 piston cores, we found that the spatial and temporal variation of turbidites is controlled by the relationship between sea-level change and the variable physiography along the margin. Siliciclastic and mixed carbonate-siliciclastic turbidites were linked to canyons indenting the shelf-break and the well-developed shelf-edge reef barriers that stored sediment behind them. Turbidite deposition was sustained while the sea-level position allowed the connection and sediment bypassing through the inter-reef passages and canyons. Carbonate turbidites dominated in regions with more open conditions at the outer-shelf and where slope-confined canyons dominated or where canyons are generally less abundant. The turn-on and maintenance of carbonate production during sea-level fluctuations also influenced the timing of carbonate turbidite deposition. We show that a fundamental understanding of the variable physiography inherent to mixed carbonate-siliciclastic margins is essential to accurately interpret deep-water, coarse-grained deposition within a sequence stratigraphic context.     

Deltaic,mixed and turbidite sedimentation of ancient foreland basins

The marine fill of ancient foreland basins is primarily recorded by depositional systems consisting of facies and facies associations deposited by a variety of sediment gravity flows in shallow-marine, slope and basinal settings. Tectonism and climate were apparently the main factors controlling the sediment supply, accommodation and depositional style of these systems. In marginal deltaic systems, sedimentation is dominated by flood-generated hyperpycnal flows that build up impressive accumulations of graded sandstone beds in front of relatively small high-gradient fan-deltas and river deltas. During periods of tectonically forced lowstands of sealevel, these systems may commonly shift basinward to shelfal and slope regions. Instability along the edges of these lowstand deltas and sand-laden hyperpycnal flows generate immature and coarse-grained turbidite systems commonly confined within structural depressions and generally encased in distal delta-front and prodeltaic deposits. Because of the close vertical and lateral stratigraphic relations between deltaic and turbidite-like facies, these marginal systems are herein termed ‘mixed depositional systems’. They are very common in the fill of foreland basins and represent the natural link between deltaic and basinal turbidite sedimentation.Basinal turbidite systems form in deeper water elongate highly subsiding troughs (foredeeps) that developed in front of advancing thrust systems. The impressive volumes of sheet-sandstones that form the fill of these troughs suggest that basinal turbidite systems are likely to form following periods of dramatic tectonic uplift of adjacent orogenic wedges and related high-amplitude tectonically-forced sealevel lowstands. In such deep basinal settings, sediment flux to the sea is dramatically increased by newly formed sediment in fluvial drainage basins and the subaerial and submarine erosion of falling-sealevel deltaic deposits generated during the uplift. Turbidity currents are very likely to be mainly triggered by floods, via hyperpycnal flows and related sediment failures, but can fully develop only in large-scale erosional conduits after a phase of catastrophic acceleration and ensuing bulking produced by bed erosion. This process leads to deepening and widening of the conduits and the formation of large-volume highly efficient bipartite currents whose energy dissipation is substantially reduced by the narrow and elongate basin geometry. These currents can thus carry their sediment load over considerable distances down the basin axis.     

珠江口盆地白云凹陷陆坡区10.5 Ma以来的沉积体系

通过对珠江口盆地白云凹陷陆坡区10.5Ma以来的地震相分析,共识别出席状平行亚平行地震相、透镜状前积地震相、深切河谷地震相、帚状地震相和杂乱地震相,不同的地震相分别代表不同的沉积体系类型。综合所识别的地震相类型,分析了陆架边缘下切谷、浊积扇和陆架边缘三角洲3种主要的沉积体系及其配置关系。物源供给是影响陆坡区沉积体系发育的最重要因素,是沉积体系发育的物质基础,海平面变化和构造运动为沉积体系发育提供了可容纳空间,3种影响因素共同影响了陆坡区沉积体系的发育。     

Tectono-sequence stratigraphic analysis on Paleogene Shahejie Formation in the Banqiao sub-basin,Eastern China

Tectonics is extremely important to the depositional record preserved in continental sedimentary basins, affecting both the formation of sequence boundaries and the filling characters of these sequences. This comprehensive analysis of Paleogene depositional patterns and the sequence compositional types in the Banqiao sub-basin of the Bohai Basin, Eastern China, shows that episodic rifting and differential activity on major faults have resulted in the formation of various types of transfer zones and structural slope-break zones, both of which played significant roles in the formation and distribution of sequence types and depositional systems. Transfer zones controlled the positions of sediment source areas, entry points for sediment into the basin and, as a result, the development of depositional systems. Structural slope-break zones are paleotopographic features where there is a sharp basinward increase in depositional slope that is controlled by fault geometry. The location of structural slope-break zones influenced the distribution of depositional systems and sand bodies. Areas where the structural slope-break zone overlapped with transfer zones were sites for major drainage systems and the preferred positions of delta fans and turbidite fans. The areas controlled by the transfer zone and the structural slope-break zone with the distribution of sand bodies are the favorable place for the prospecting of subtle stratigraphic traps in the Banqiao sub-basin.     

Heterogeneity of fill within an incised channel: The Oligocene Grès du Champsaur,SE France

Submarine channel deposits are recognised as the primary heterogeneity within the turbidite systems that host them, with channel fill heterogeneities being considered secondary. An investigation of channel fill heterogeneities was conducted on Oligocene turbidites of the Grès du Champsaur, Hautes Alpes, SE France, which was deposited in a sub-basin within the Alpine peripheral foreland basin. Here, a series of erosional channels are exposed in mountainous terrain. Maximum channel widths are in the order of 1000 m, and depths of the order of 100 m. The channels can be traced along axis for at least 6 km. Mapping of channel facies revealed three orientations of fill heterogeneity expressed as: (1) upward variations in the character of vertically stacked fill sequences, (2) lateral variability, and (3) the occurrence of downstream dipping and stacking units forming the uppermost parts of channel fill. Vertically expressed heterogeneities are thought to have developed via the gradual reduction in the efficiency of channelised flow, leading to a progressive reduction in scour and the deposition of overall thinning and fining upwards sequences. Lateral heterogeneity is related to the development of downstream-oriented elongated scour and fill facies. Downstream-dipping heterogeneity is represented by a series of several metre-scale downstream-dipping low-angle clinoforms thought to be related to final infill of the negative channel bathymetry by a migrating front of sand that would have formed part of a downstream-migrating sheet to channel transition in plan view. Both first and second orders of channel heterogeneity may control the reservoir performance of channel prone turbidite sequences. Preferred-orientation channel facies heterogeneities are thought to affect potential hydrocarbon recovery through their impact on permeability anisotropy within the confines of the channel.     

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.     

Structural styles and depositional architecture in the Triassic of the Ninian and Alwyn North fields: Implications for basin development and prospectivity in the Northern North Sea

Interpretation of well-calibrated three-dimensional seismic volumes, sedimentological analysis and electrical well-log correlations from the Ninian and Alwyn North fields challenge the long-held view that Mid-Late Jurassic extensional faults in the East Shetland Basin represent a simple reactivation of older (Triassic) fault systems. Restoration for the effects of the younger, predominantly eastward-dipping, Mid-Late Jurassic structures clearly demonstrates that Triassic precursors had a steep, westerly dip. In contrast to the eastern flank of the Viking Graben (e.g. Troll and Oseberg areas), where the west-dipping Triassic structures are reutilised in the Mid-Late Jurassic, those of the East Shetland Basin have largely been dissected and rotated during the later event. Those west-dipping faults that did see later movement appear to have simply acted as minor antithetic structures to the throughgoing east-dipping ones.The Triassic normal fault patterns actively controlled sediment thicknesses and facies distribution within the Lunde and Teist Formations in the basin. Use of seismic stratigraphic surfaces, calibrated by biostratigraphy and chemostratigraphic markers, provides strong evidence that the Triassic depocentres are spatially offset from their Mid-Late Jurassic counterparts. The combination of structural, stratigraphic and sedimentary effects reveal the existence of an emergent deeper Triassic play opportunity in footwall locations to the Mid-Late Jurassic normal faults, which has the potential to extend the life of what is otherwise mature acreage.     

花东盆地晚中新世以来沉积演化特征

利用近年来在台湾东部海域采集的多道地震和多波速测深资料,对该海域花东海盆区晚中新世以来的沉积充填演化特征进行描述和分析。通过对花东海盆区域地形特征描述、层序地层格架的建立和地震剖面的解译,在本区晚中新世以来的沉积充填中刻画出6种典型地震相类型,并分析其对应的沉积相类型,包括浊积扇、浊积水道充填、块体流、沉积物波、海底峡谷－伴生沉积物滑塌变形－充填、深水扇沉积。结合地震相平面分布及垂向沉积相叠置关系,将晚中新世－第四纪沉积充填演化划分为3个阶段:晚中新世晚期开始受到块体流冲蚀阶段,到海底峡谷冲刷－沉积物失稳－峡谷充填－再侵蚀阶段,到峡谷输送的大量沉积物在上新世以来主要堆积发育了沉积物波、浊积扇、深水扇等沉积体系阶段。     

西菲律宾海15万年以来的浊流沉积及其成因

MD06-3052孔取自西菲律宾海吕宋岛岸外上陆坡,通过AMS14 C测年、沉积物粒度和浮游有孔虫氧同位素记录,揭示了15万年以来5个浊流沉积层的特征和浊积事件的发生时间。浊流沉积物粒度明显较上下层的粗,主要组分为砂质和粉砂质沉积。通过AMS14 C测年和氧同位素年代标尺,计算了5个浊流沉积层发生的时间分别为13.3、20.4、34.3、41.7和121.8kaBP,其中上部4次浊积事件发生于末次冰期,特别是MIS 3晚期和MIS 2期的低海平面时期,仅底部一次出现于末次间冰期MIS 5e中期相对低海平面时期,因而推测研究区浊流沉积事件的主要诱因是低海平面时期的海平面波动造成临近陆架上的沉积物不稳定,同时较陡的陆坡为浊流沉积提供了有利地形,因而造成了向陆坡方向的浊流搬运。