River-dominated and tide-influenced shelf-edge delta systems: Coarse-grained deltas straddling the Early–Middle Jurassic shelf–slope break and transforming downslope,Lajas–Los Molles formations,Neuquén Basin,Argentina

The three-dimensional facies and architecture variability of shelf-edge deltaic units cropping out at the transition between the Lower–Middle Jurassic Lajas and Los Molles formations of southern Neuquén Basin, Argentina, is presented here, as well as their stratigraphic relationship to uppermost deep-water slope channel systems. Deep-water, slope mudstones with thin turbidite beds merge upward with prodelta mudstones and thin sandstones, which are truncated by delta-front to mouth-bar sandstones. The latter sandstones are then downcut by large-scale, trough cross-stratified coarse-grained sandstones and conglomerates of distributary channel systems and along-strike, amalgamated with cross-bedded sandy units showing evidence of tidal reworking. Proximal–distal facies and architecture variability within a shelf-edge deltaic succession demonstrates that distributary channel-complexes become wider and deeper basinward, forming channelized river-dominated distributary fairways separated by tidally reworked inter-distributary sand belts at the shelf edge. Evidence from depositional-dip oriented outcrops shows a lack of collapsed and slumped strata at the shelf edge, and that the coarse shelf-edge distributary channel fills continue far down the deepwater slope, and conglomerates transform to become high-density turbidites to mainly thick-bedded, sand-matrix-supported debrites. The interplay between flood tides and river currents is interpreted to have primarily modulated the focusing of river drainages, and consequently coarse-grained sediment transport, along preferential routes on the outer-shelf to shelf-edge and down onto the slope. This contribution documents a unique example of coarse-grained (mostly conglomeratic) shelf-edge delta systems, tying bed-scale facies and architecture data to a seismic-scale shelf-margin morphology, thus providing outcrop analogue data for the characterization of shelf-edge delta systems in the subsurface.     

贺兰奥拉槽早古生代深水重力流体系的沉积特征和充填样式

位于鄂尔多斯西缘的贺兰构造带为一中元古代一古生代的奥拉槽。在区内的中寒武和中奥陶统中识别了一套巨厚的深水重力流沉积,其中包括下斜坡滑塌泥石流复合体、浊积扇以及碳酸盐岩斜坡扇裙等沉积类型。主要的相单元包括充填沟道或进入扇面形成的泥石流钙质角砾岩和砾岩、充填辫状水道的多层叠置的砂岩和砂砾岩、上叠扇的砂、泥岩互层以及浊积砂屑或含砾砂屑灰岩等。在中奥陶世该奥拉槽发展成一深水一半深水海槽,沿盆地西侧发育有浊积扇,而东侧仅有碳酸盐岩滑塌扇裙。它们可能是沿深水盆地两侧深大断裂产生的陡坡或水下断崖分布的,代表了早古生代贺兰奥拉槽在强烈沉陷期特定的深水盆地充填。     

Architecture of a coarse‐grained channel–levée system: the Rosario Formation,Baja California,Mexico

Seafloor images of coarse‐grained submarine channel–levée systems commonly reveal complex braid‐plain patterns of low‐amplitude bedforms and zones of apparent bypass; however, mechanisms of channel evolution and the resultant channel‐fill architecture are poorly understood. At Playa Esqueleto the lateral relationships between various elements of a deep‐marine slope channel system are well‐exposed. Specifically, the transition from gravel‐dominated axial thalwegs to laterally persistent marginal sandstones and isolated gravel‐filled scours is revealed. Marginal sandstones pass into a monotonous thin‐bedded succession which built to form relatively low‐relief levées bounding the channel belt; in turn, the levées onlap the canyon walls. Three orders of confinement were important during the evolution of the channel system: (i) first‐order confinement was provided by the erosional canyon which confined the entire system; (ii) confined levées built of turbidite sandstones and mudstones formed the second‐order confinement, and it is demonstrated that these built from overspill at thalweg margins; and (iii) third‐order confinement describes the erosional confinement of coarse‐grained thalwegs and scours. Finer‐grained sediment was transported in suspension and largely was unaffected by topography at the scale of individual thalwegs. Facies and clast analyses of conglomerate overlying channel‐marginal scours reveal that they were deposited by composite gravity flows, which were non‐cohesive, grain‐dominant debris flows with more fluidal cores. These flows were capable of basal erosion but were strongly depositional; frictional freezing at flow margins built gravel levées, while the core maintained a more fluidal transport regime. The resultant architecture consists of matrix‐rich, poorly sorted levées bounding better‐sorted, traction‐dominated cores. The planform geometry is interpreted to have consisted of a low‐sinuosity gravel braid‐plain built by accretion around mid‐channel and bank‐attached bars. This part of the system may be analogous to fluvial systems; however, the finer‐grained sediment load formed thick suspension clouds, probably several orders of magnitude thicker than the relief of braid‐plain topography and therefore controlled by the levées and canyon wall confinement.     

鄂尔多斯盆地晚二叠世湖相沉积

鄂尔多斯盆地晚二叠世湖相沉积主要由灰棕色砂砾岩和红至灰色泥岩组成,厚500-600米。从该套沉积中已识别出五个主要相组合,即水下扇、湖岸冲积平原、湖成三角洲、边缘湖和滨外湖相组合。水下扇相发育于研究区西南缘,冲积平原相发育于研究区北部,湖成三角洲相发育于研究区北部和东部,边缘湖相发育于研究区中部,滨外湖相发育于研究区南部。     

The Cambro-Ordovician Cap Enragé Formation, Queébec, Canada: conglomeratic deposits of a braided submarine channel with terraces

The Cambro-Ordovician Cap Enragé Formation is interpreted as a deep submarine channel complex of conglomerates, pebbly sandstones and massive sandstones. The formation is up to 270 m thick, and crops out in a coastal belt 50 km long. In general terms, it has previously been interpreted as a deep sea channel deposit, with the channel about 300 m deep, at least 10 km wide and trending south-westward, parallel to the coastal outcrops. Eight facies have been defined in this study and they have been grouped into three major facies associations. In the Coarse Channelled Association, conglomerates with carbonate boulders up to about 4 m are associated with graded-stratified finer grained conglomerates. Facies of this association make up about 25% of all the beds in the formation. The association is also characterized by abundant major channels 1–10 m deep and up to 250 m wide. Excellent outcrop allows the reconstruction of topographic highs (bars) within the channels and the association is interpreted as a braided channel and bar system. The second association, Multiple-Scoured Coarse Sandstones, contains some graded-stratified fine conglomerates, along with massive to structureless coarse and pebbly sandstones, and rare cross-bedded pebbly sandstones. Deep channels are absent, but multiple channelling on the scale of 0.5–1 m is characteristic. In the absence of the very coarse conglomerates and deeper channelling, this association is interpreted as being deposited on topographically higher terrace areas adjacent to the main braid plain. The third facies association, Unchannelled Sandstones, is characterized by massive sandstones with abundant fluid-escape structures, classical turbidites and thin shales. In the absence of any scouring deeper than a few tens of centimetres, this association is interpreted as being deposited on an even higher and smoother terrace, farther from the braid plain. Palaeoflow directions for conglomerate facies indicate fairly consistent south-westward transport, apparently parallel to the base of the Cambro-Ordovician continental slope. Flow directions in the finer-grained facies are rather variable, suggesting complex bar development and overbank spills. Thinning-and fining-upward sequences are present on two scales. The smaller, 1–10 m sequence, is related to channel filling and abandonment. Thicker sequences (10–100 m), with facies of the Multiple Scoured, and Unchannelled Sandstone Associations, may indicate switching of a main channel away from the area and its subsequent burial by marginal terrace and higher terrace deposits.     

Turbidites in the Upper Carboniferous Ross Formation, western Ireland: reconstruction of a channel and spillover system

ABSTRACT The Upper Carboniferous deep‐water rocks of the Shannon Group were deposited in the extensional Shannon Basin of County Clare in western Ireland and are superbly exposed in sea cliffs along the Shannon estuary. Carboniferous limestone floors the basin, and the basin‐fill succession begins with the deep‐water Clare Shales. These shales are overlain by various turbidite facies of the Ross Formation (460 m thick). The type of turbidite system, scale of turbidite sandstone bodies and the overall character of the stratigraphic succession make the Ross Formation well suited as an analogue for sand‐rich turbidite plays in passive margin basins around the world. The lower 170 m of the Ross Formation contains tabular turbidites with no channels, with an overall tendency to become sandier upwards, although there are no small‐scale thickening‐ or thinning‐upward successions. The upper 290 m of the Ross Formation consists of turbidites, commonly arranged in thickening‐upward packages, and amalgamated turbidites that form channel fills that are individually up to 10 m thick. A few of the upper Ross channels have an initial lateral accretion phase with interbedded sandstone and mudstone deposits and a subsequent vertical aggradation phase with thick‐bedded amalgamated turbidites. This paper proposes that, as the channels filled, more and more turbidites spilled further and further overbank. Superb outcrops show that thickening‐upward packages developed when channels initially spilled muds and thin‐bedded turbidites up to 1 km overbank, followed by thick‐bedded amalgamated turbidites that spilled close to the channel margins. The palaeocurrent directions associated with the amalgamated channel fills suggest a low channel sinuosity. Stacks of channels and spillover packages 25–40 m thick may show significant palaeocurrent variability at the same stratigraphic interval but at different locations. This suggests that individual channels and spillover packages were stacked into channel‐spillover belts, and that the belts also followed a sinuous pattern. Reservoir elements of the Ross system include tabular turbidites, channel‐fill deposits, thickening‐upward packages that formed as spillover lobes and, on a larger scale, sinuous channel belts 2·5–5 km wide. The edges of the belts can be roughly defined where well‐packaged spillover deposits pass laterally into muddier, poorly packaged tabular turbidites. The low‐sinuosity channel belts are interpreted to pass downstream into unchannellized tabular turbidites, equivalent to lower Ross Formation facies.     

Depositional history and stratigraphical evolution of the Sakamena group (Middle Karoo Supergroup) in the southern Morondava Basin, Madagascar

The Karoo Supergroup in Madagascar is subdivided into three lithostratigraphical units: the Late Carboniferous-Early Permian Sakoa Group; the Late Permian-Middle Triassic Sakamena Group; and the Triassic-Early Jurassic Isalo Group. The Sakamena Group is fairly well exposed in the southern Morondava Basin, where it is approximately 4000 m thick. The Sakamena Group is separated from the Sakoa Group by an angular unconformity. The Lower Sakamena Formation is characterised by two major facies associations: (1) interbedded muddy conglomerates and coarse sandstones; and (2) interbedded sandstones and mudstones, which were deposited in a rejuvenated rift setting by coarse-grained fluvial systems and debris flows on the rift margins. In the Vatambe area, facies represent fandelta deposition in a saline lake or tongue of the ocean. The Middle Sakamena Formation comprises three major facies: (1) laminated mudstones and sandstones; (2) sandstones; and (3) mudstones. The Middle Sakamena facies were deposited by low gradient meandering streams and in shallow lakes. The Upper Sakamena Formation was deposited in similar environments, except that it is comprised predominantly of red beds. The Isalo Group consists predominantly of coarse-grained sandstones (up to 6000 m thick). These sandstones were deposited by braided streams with the coarse detritus derived from a structural uplift in the east.     

辽河盆地大凌河油层湖底扇沉积特征

辽河盆地位于辽宁省南部,渤海湾盆地东北角,是继中生代发育起来的第三纪断陷盆地。分东部凹陷,西部凹陷和大民屯凹陷等二级构造单元(图1)。     

Stratigraphic organization and predictability of mixed coarse‐grained and fine‐grained successions in an upper slope Pleistocene turbidite system of the Peri‐Adriatic basin

The early Pleistocene clastic succession of the Peri‐Adriatic basin, eastern central Italy, records the filling of a series of piggyback sub‐basins that formed in response to the development of the eastward‐verging Apennine fold‐thrust belt. During the Gelasian (2·588 to 1·806 Ma), large volumes of Apennine‐derived sediments were routed to these basins through a number of slope turbidite systems. Using a comprehensive outcrop‐based dataset, the current study documents the depositional processes, stratigraphic organization, foraminiferal age and palaeodepth, and stratigraphic evolution of one of these systems exposed in the surroundings of the Castignano village. Analysis of foraminiferal assemblages consistently indicates Gelasian deposition in upper bathyal water depths. Sediments exposed in the study area can be broken into seven main lithofacies, reflecting specific gravity‐induced depositional elements and slope background deposition: (i) clast‐supported conglomerates (conglomerate channel‐fill); (ii) amalgamated sandstones (late stage sandstone channel‐fill); (iii) medium to thick‐bedded tabular sandstones (frontal splay sandstones); (iv) thin to thick‐bedded channelized sandstones (sandy channel‐fill); (v) medium to very thin‐bedded sandstones and mudstones (levée‐overbank deposits); (vi) pebbly mudstones and chaotic beds (mudstone‐rich mass‐transport deposits); and (vii) massive mudstones (hemipelagic deposits). Individual lithofacies combine vertically and laterally to form decametre‐scale, disconformably bounded, fining‐upward lithofacies successions that, in turn, stack to form slope valley fills bounded by deeply incised erosion surfaces. A hierarchical approach to the physical stratigraphy of the slope system indicates that it has evolved through multiple cycles of waxing then waning flow energy at multiple scales and that its packaging can be described in terms of a six‐fold hierarchy of architectural elements and bounding surfaces. In this scheme, the whole system (sixth‐order element) is comprised of three distinct fifth‐order stratigraphic cycles (valley fills), which define sixth‐order initiation, growth and retreat phases of slope deposition, respectively; they are separated by discrete periods of entrenchment that generated erosional valleys interpreted to record fifth‐order initiation phases. Backfilling of individual valleys progressed through deposition of two vertically stacked lithofacies successions (fourth‐order elements), which record fifth‐order growth and retreat phases. Fourth‐order initiation phases are represented by erosional surfaces bounding lithofacies successions. The component lithofacies (third‐order element) record fourth‐order growth and retreat phases. Map trends of erosional valleys and palaeocurrent indicators converge to indicate that the sea floor bathymetric expression of a developing thrust‐related anticline markedly influenced the downslope transport direction of gravity currents and was sufficient to cause a major diversion of the turbidite system around the growing structure. This field‐based study permits the development of a sedimentological model that predicts the evolutionary style of mixed coarse‐grained and fine‐grained turbidite slope systems, the internal distribution of reservoir and non‐reservoir lithofacies within them, and has the potential to serve as an analogue for seismic or outcrop‐based studies of slope valley fills developed in actively deforming structural settings and under severe icehouse regimes.     

Facies architecture of a submarine fan channel–levee complex: the Juniper Ridge Conglomerate, Coalinga, California

The Upper Cretaceous Juniper Ridge Conglomerate (JRC) near Coalinga, California, provides a rare, high-quality exposure of a submarine channel to overbank transition. The facies architecture of the JRC comprises a thick, predominantly mudstone sequence overlain by a channellized conglomerate package. Conglomeratic bounding surfaces truncate successions of interbedded turbiditic sandstones and mudstones both vertically and laterally. Thick-bedded, massive sandstones are interbedded with conglomerates. Facies architecture, palaeocurrent indicators, slump features, sandstone percentages and sandstone bed thickness trends lead to the interpretation that these elements comprise channel and overbank facies. A vertical sequence with conglomerate at the base, followed by thick-bedded sandstone, and capped by interbedded turbiditic sandstone and mudstone form a fining-upward lithofacies association that is interpreted as a single channel-fill/overbank system. Three similar lithofacies associations can be related to autocyclic processes of thalweg migration and submarine fan aggradation or to allocyclically driven changes in sediment calibre.     

准噶尔盆地南缘上三叠统黄山街组辫状河三角洲沉积

准噶尔盆地南缘上三叠统黄山街组主要为砾岩、含砾砂岩、砂岩、粉砂岩和泥岩构成的一套碎屑岩组合,野外沉积特征研究确定为典型的辫状河三角洲沉积。通过对沉积相、亚相、微相的详细研究,认为辫状河三角洲具有类似曲流河三角洲的层序结构和微相类型,但两者间也存在很大的差别。与曲流河三角洲相比,辫状河三角洲的三角洲平原亚相不仅沉积物的粒度较粗,而且辫状河道沉积较发育,河道间洪泛平原沉积不发育。辫状河三角洲前缘亚相也可以识别出水下分流河道、河口坝、席状砂和水下分流河道间等微相,水下分流河道沉积为主体。根据野外露头的追索研究,建立了准噶尔盆地南缘上三叠统黄山街组辫状河三角洲的沉积模式。从沉积物的岩性特征看,辫状河三角洲砾岩和含砾粗砂岩体具有分布较稳定、展布较广、储集物性较好的特点。     

Old red sandstone sedimentation—an example from the brownstones (highest lower old red sandstone) of south central wales

The Brownstones form the highest Lower Old Red Sandstone in South Wales and the Welsh Borderlands. Sections from the Brecon Beacons of Central South Wales consist of laterally extensive sheets of interbedded sandstone and siltstone. Facies sequence A consists of parallel laminated sheet sandstones and siltstones and is interpreted as a sandy sheetflood and distal muddy floodflat association. Facies sequence B comprises sheet sandstones composed of multistorey channel fills, small calcrete-clast filled channels and massive siltstones with thin interbedded sandstones. This sequence is interpreted as low sinuosity channel deposits merging laterally and downslope into a muddy flood-basin, with calcrete clasts infilling intrabasinal channel systems. Facies sequence C consists of multistorey sandstones and is interpreted as a proximal low sinuosity channel system. The Brownstones of the Brecon Beacons formed on an extensive alluvial plain with low sinuosity sand-bed channels merging downslope into sheetfloods and muddy floodflats, in a system broadly analogous to that of the Eyre Basin of South Australia.     

济阳坳陷牛庄洼陷沙三段三角洲前缘浊积岩特征

根据地质、测井、地震资料的综合分析,对济阳坳陷牛庄洼陷沙河街组三段三角洲前缘的浊积岩特征进行了研究。结果表明,该区存在砂质浊积岩体和细粒浊积岩体两种浊流沉积物。其中砂质浊积岩体粒度较细、结构成熟度和成分成熟度较低,结构和构造均反映了砂体具有滑塌再沉积的特点,可用Bouma序列来描述,常发育CDE,BCD,ABCD型浊流组合。砂质浊积岩体可进一步划为有根式和无根式两类。有根式砂体常呈扇形,可分为内扇槽道、中扇辫状水道、水道间、水道前缘和外扇无水道五种微相;无根式砂体常呈片状、舌状,可分为中心微相和边缘微相两个相带。细粒浊积岩属于低密度流的产物,不能用Bouma序列来解释,主要发育递变纹层泥岩和不均匀的块状泥岩两种细粒浊积岩。根据两类沉积物的沉积特征,建立了该区三角洲一浊积岩体综合沉积模式。论述了三角洲前缘浊积岩的成因及石油地质意义。     

湖南邵阳地区茅口期晚期重力流沉积的发现及意义*

湖南邵阳市邵阳大道两侧出露的龙潭组下段(中二叠世茅口期晚期)发育一套地质特征典型、沉积序列明显的重力流沉积。重力流沉积以块状砂岩、粉砂岩及泥岩互层为主,砂岩底面发育有重荷模、槽模、工具痕及冲刷充填构造,砂岩内部有块状层理、平行层理、包卷层理及粒序层理,互层的泥岩中见类似于古网迹的痕迹化石。可识别出砂质碎屑流、浊流与滑塌沉积。剖面下部含泥砾块状砂岩发育,剖面中上部以发育薄到中厚层砂岩、粉砂岩与泥岩互层为特点。根据重力流沉积物特征及其垂向序列特征,建立了重力流沉积模式,将海底扇划分出内扇、中扇与外扇。通过与附近的短陂桥矿区的龙潭组下段沉积特征进行对比研究,结合华南地区岩相古地理特征,认为位于华南盆地范围的邵阳地区,在中二叠世茅口期晚期(龙潭组下段)发育的重力流沉积,可能意味着华南盆地在扬子陆块和华夏陆块之间的深大断裂在中二叠世末期曾经发生拉张,形成裂谷盆地。     

NON-GREYWACKE "TURBIDITE" SANDSTONES IN THE WELSH GEOSYNCLINE

In contrast with the commonly accepted notion regarding ancient turbidites, non-greywacke sandstones are not uncommon in the typically graded turbidite facies of the Cambrian and Silurian sediments in north Wales. The sandstones are the arkosic and lithic types of PETTIJOHN (1957) or the feldspathic and lithic arenites of GILBERT (1954) and occur at the bottom of graded beds when the grain size tends to be above medium grade. Petrological features suggest that debris forming the sandstones in north Wales was not significantly modified during transportation and original provenance characters are well preserved. The occurrence of such sandstones implies that: (1) the current concept of ancient graded greywackes in the turbidite facies should be revised; (2) non-greywacke sandstones in ancient turbidites are comparable in petrological features to recent deep-sea sands; (3) these sandstones are important in connection with the origin of the clay matrix in greywacke.     

广西来宾-合山一带晚二叠世海底扇浊积岩相

广西来宾蓬莱滩及合山马滩两地的晚二叠世地层中发育有典型的重力流沉积构造,如粒序层理、包卷层理、槽模、重荷模、碟状构造和滑塌褶皱等。通过对蓬莱滩合山组和大隆组以及马滩剖面的大隆组岩相特征的详细研究,提出来宾蓬莱滩晚二叠世合山组和大隆组以及合山马滩晚二叠世大隆组形成于海底扇环境,划分出具碟状构造的块状砂岩(B１)、块状砂岩(B2)、近基浊积岩(C)、远基浊积岩(D)、不规则互层的砂泥岩(E)、滑塌褶皱层(F)及含浮游生物化石的页岩、硅质岩(G)等岩相类型,同时归纳出外扇相组合、中扇舌状体相组合、中扇水道相组合、斜坡相组合及深切谷水道相组合等,还对这些海底扇浊积岩系的古地理意义做了讨论。桂中碳酸盐岩台地相区和云开古陆之间在晚二叠世为一发育海底扇浊积岩的深水盆地,其中来宾-合山一带在大隆组沉积期处于水深约300～1 000 m的深水盆地环境,合山一带火山活动提供的火山物质及来自东侧云开古陆的陆源物质构成该区浊积岩的主要物源。     

Depositional facies of the subsurface Neogene Surma Group in the Sylhet Trough of the Bengal Basin,Bangladesh: record of tidal sedimentation

The Bengal Basin, in the north-eastern part of the Indian subcontinent, contains a thick (± 22 km) early Cretaceous-Holocene sedimentary succession. The Neogene succession in the Sylhet Trough of the basin reaches a thickness of more than 6 km of which the Surma Group contains important sandstone reservoirs. Lithologically, the group consists of a succession of alternating shales, siltstones, sandy shales and sandstones, with minor conglomerates. This research work is a sedimentological analysis of the subsurface Neogene succession encountered in the petroleum exploration wells in the Sylhet Trough of the Bengal Basin. Detailed lithologic logs of the cores, based on considering texture and sedimentary structure, permit a subdivision into eight lithofacies, e.g., a shale-dominated facies, interbedded fine sandstones and mudstones, ripple-laminated sandstones, parallel-laminated sandstones, massive sandstones, cross-bedded sandstones, cross-bedded sandstones with pebble/granule lag and conglomerates. Characteristic sedimentary structures of the Surma Group, such as flaser-, wavy- and lenticular-bedding, bipolarity of ripple cross-stratification, evenly laminated sand/silt-streaked shales, reactivation surfaces within cross-bedded sandstone sets, mud-drapes on foreset laminae and herringbone cross-stratification as well as small-scale vertical sequences (several fining-upward cycles) are diagnostic for tidal influence. On the basis of the lithofacies associations and prograding character of the deposits revealed from the electrofacies associations, the Surma Group sediments have been interpreted as representing deposits of tide-dominated deltaic depositional setting.     

Eocene fan delta-submarine fan deposition in the Wagwater Trough, east-central Jamaica

ABSTRACT The Wagwater Trough is a fault-bounded basin which cuts across east-central Jamaica. The basin formed during the late Palaeocene or early Eocene and the earliest sediments deposited in the trough were the Wagwater and Richmond formations of the Wagwater Group. These formations are composed of up to 7000 m of conglomerates, sandstones, and shales. Six facies have been recognized in the Wagwater Group: Facies I-unfossiliferous massive conglomerates; Facies II—channelized, non-marine conglomerates, sandstones, and shales; Facies III-interbedded, fossiliferous conglomerates and sandstones; Facies IV—fossiliferous muddy conglomerates; Facies V—channelized, marine conglomerates, sandstones, and shales; and Facies VI—thin-bedded sheet sandstones and shales. The Wagwater and Richmond formations are interpreted as fan delta-submarine fan deposits. Facies associations suggest that humid-region fan deltas prograded into the basin from the adjacent highlands and discharged very coarse sediments on to a steep submarine slope. At the coast waves reworked the braided-fluvial deposits of the subaerial fan delta into coarse sand and gravel beaches. Sediments deposited on the delta-front slope were frequently remobilized and moved downslope as slumps, debris flows, and turbidity currents. At the slope-basin break submarine fans were deposited. The submarine fans are characterized by coarse inner and mid-fan deposits which grade laterally into thin bedded turbidites of the outer fan and basin floor.     

Facies analysis of the Plateau Sandstones (Eocene to early Miocene?), Bako National Park,Sarawak, Malaysia

Sandstones, located in the Kuching area, western Sarawak, are known as the ‘Plateau Sandstones’ (of possible Eocene to early Miocene age). However, based on a number of factors, including: (i) anomalous kerogene compositions; (ii) proximity of the on-lap surface; and (iii) palaeocurrent direction (generally to the NNE), it is thought that the sands exposed on the Bako Peninsula are unrelated to the Plateau Formation (located to the south of the Bako Penisula) and therefore a new name is coined; the Bako Sandstones, which form a subgroup of the Bako Sandstone Group. The Bako Sandstones form the Bako Peninsula, a flat-topped cliffed plateau which extends into the South China Sea at a latitude of 1°30′N. The plateau has a gently dipping surface, sloping northwards from a height of about 300 to 150 m. The sandstones form a succession of very thick bedded sandstones (up to 6 m thick), with lenses of conglomerates and subordinate sandy mudstones. The sandstones consist of pebbly coarse-medium grained sands, interbedded with polymictic pebble conglomerates. The sandstones are mainly lithic arenite, poorly to moderately sorted and consist of subangular to subrounded grains. Isolated pebbles are common throughout the sandstones. The most common structure in both sandstones and conglomerates is cross-bedding; planar cross-bedding and trough cross-bedding, together with thick sequences of climbing ripples. These structures suggest extensive tractional transport, forming both ripple and dune structures along the base of the channel. The geometry of the sands is either (i) lensoidal, or (ii) tabular, with the channel-fill interpreted as scour-fill channels or migrating dunes, respectively. Both types are commonly stacked vertically or amalgamate laterally to form thick interconnected units. The conglomeratic lenses, scour-fill features and rip-up shale clasts are related to higher energy erosional events, whilst the mud-draped ripples, ripple rejuvenation surfaces and two-tiered channel margins indicate a lower energy and stasis period. Slope instabilities at the channel margin are inferred from the slump structures present and shale clast slurries. The sandstones at Bako are thought to have formed within a braided channel environment (subject to exposure, from the presence of mud cracks within the formation).     

东濮凹陷濮卫环洼带层序划分与沉积体系

根据地层基准面原理,通过对岩心、测井、录井资料的综合分析,将研究区Es3.3-Es3.2层段的地层划分出4个中期地层旋回（层序）：MSC1,MSC2,MSC3,MSC4。其中大致发育2种类型的层序,即陆源碎屑岩层序和膏盐岩层序。陆源碎屑岩层序多形成于基准面上升期,以发育泥质岩夹浊积砂体、三角洲前缘砂质沉积为主;膏盐岩层序多形成于基准面下降期,以发育厚层的盐岩、膏盐岩、膏岩、泥膏岩、膏泥岩夹浊积席状砂为特征。识别出3种类型的沉积体系：较深水湖－浊积扇、较深水盐湖、浅湖－三角洲体系,并在层序格架内分析了各旋回的沉积体系构成和储层砂体的发育情况。综合分析生、储、盖条件后认为,在垂向上,MSC2上升半旋回为本区最有利的储集层段;在平面上,本区的油气勘探应主要寻找洼陷东、西两侧断层下降盘的浊积砂体,主要储层砂体类型为浊积水道及浊积席状砂。