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1.
Raymond V. Ingersoll 《Sedimentary Geology》1978,21(3):205-230
The Upper Cretaceous part of the Great Valley Sequence provides a unique opportunity to study deep-marine sedimentation within an arc-trench gap. Facies analysis delineates submarine fan facies similar to those described from other ancient basins. Fan models and facies of Mutti and Ricci-Lucchi allow reconstruction of the following depositional environments: basin plain, outer fan, midfan, inner fan, and slope. Basin plain deposits are characterized by hemipelagic mudstone with randomly interbedded thin sandstone beds exhibiting distal turbidite characteristics. Outer fan deposits are characterized by regularly interbedded sandstone and mudstone, and commonly exhibit thickening-upward (negative) cycles that constitute depositional lobes. The sandstone occurs as proximal to distal turbidites without channeling. Midfan deposits are characterized by the predominance of coarse-grained, thick, channelized sandstone beds that commonly are amalgamated. Thinning-upward (positive) cycles and braided channelization also are common. Inner fan deposits are characterized by major channel-fill complexes (conglomerate, pebbly sandstone, and pebbly mudstone) enclosed in mudstone and siltstone. Positive cycles occur within these channel-fill complexes. Much of the fine-grained material consists of levee (overbank) deposits that are characterized by rhythmically interbedded thin mudstone and irregular sandstone beds with climbing and starved ripples. Slope deposits are characterized by mudstone with little interbedded sandstone; slumping and contortion of bedding is common. Progressions of fan facies associations can be described as retrogradational and progradational suites that correspond, respectively, to onlapping and offlapping relations in the basin. The paleoenvironments, fan facies associations, and tectonic setting of the Late Cretaceous fore-arc basin are similar to those of modern arc—trench systems. 相似文献
2.
The 400 m of Blomidon redbeds accumulated in a semi-arid rift valley in the subtropics. At St Mary's Bay, these redbeds are 64% sandy mudstone (playa mudflats), 25% graded beds (sandflats at the toes of alluvial fans), 10% fissile claystone (playa lakes), and 1% channel sandstone (stream channels). Flash floods in mountains south of the valley flowed down alluvial fans to spread out to the north-east as sheet flows on sandflats and playa mudflats. Deceleration of the sheet flows deposited graded beds 2–83 cm in thickness on the sandflats and thin layers of mud on the playas. Nine sequences, consisting of arrangements of six lithologies, compose 90% of the graded beds. In order of decreasing abundance, these are: ripple cross-laminated siltstone → horizontally laminated mudstone; fining-upward, ripple cross-laminated siltstone; ripple cross-laminated sandstone → horizontally laminated mudstone; cross-bedded sandstone horizontally laminated mudstone; ripple cross-laminated sandstone → ripple cross-laminated siltstone; rippledrift cross-laminated siltstone horizontally laminated mudstone; fining-upward, ripple-drift cross-laminated siltstone; cross-bedded sandstone → ripple cross-laminated siltstone; and cross-bedded sandstone → ripple cross-laminated siltstone → horizontally laminated mudstone. The sheet flows, perhaps up to 1 m in depth, had a high concentration of suspended load. Deposition was dominantly during lower flow regime conditions and moderate to rapid flow deceleration. There are 32 thinning and fining-up cycles where a sandflat package of graded beds is transitionally followed by a playa package of sandy mudstone. The cycles range in thickness from 1·3 to 13·3 m, averaging 4·6 m. Each cycle is initiated by avulsion to a new active channel network on a fan. Gradual abandonment of the channel network produces the thinning and fining-up cycle. The cycles are grouped in three 60–70 m fining-up megacycles. Upwards within each megacycle, the packages of sandy mudstone compose a progressively larger proportion of the cycles. Each megacycle evidently was initiated by a brief period of tectonic movement on the border faults that produced greater relief of the highlands relative to the valley floor. Subsequent erosion gradually lowered the relief to yield a fining-up megacycle. 相似文献
3.
《Australian Journal of Earth Sciences》2013,60(5):811-825
The mid‐Silurian Major Mitchell Sandstone of the Grampians Group outcrops at Mt Bepcha, western Victoria, represent a prograding fluviodeltaic sequence comprising four lithofacies and five ichnofacies. The stratigraphically lowest Interbedded Sandstone/Siltstone Facies is characterised by thin sandstone and siltstone beds with soft‐sediment deformation and scours with gravelly lag deposits. This lithofacies contains Thalassinoides, Palaeophycus, Rhizocorallium and intrastratal burrows, together indicative of the Cruziana Ichnofacies, and is interpreted as a shallow‐marine depositional environment on a low‐energy delta front with minor tidal influences. The overlying Massive Sandstone Facies lacks silt, and consists of predominantly massive and some plane‐laminated sandstone, abundant Skolithos linearis , rare Palaeophycus and a single small Cruziana problematica ; the trace‐fossil assemblage is assigned to the Skolithos Ichnofacies. This facies is believed to have been deposited in a marine high‐energy shoreface environment with continuously shifting sands, affected by periodic flooding events from the mouth of a nearby river. Above this is the Trough Cross‐bedded Facies, which contains trough cross‐bedding with gravelly lag deposits, a northwest palaeocurrent direction and large Taenidium barretti burrows (Burrowed Ichnofacies). This facies also contains abundant plane‐laminated sandstone with a northeast‐southwest palaeocurrent direction and ichnofossils of Scoyenia and Daedalus , representing the Scoyenia Ichnofacies. The Trough Cross‐bedded Facies is interpreted to have been deposited in shallow low‐sinuosity channels by overbank‐flooding events, most likely on a delta plain. The uppermost facies, the Plane‐laminated Facies, contains thin beds of current‐lineated, plane‐laminated graded coarse to fine sandstone that preserve arthropod trackways (Arthropod Ichnofacies). This facies was deposited on a periodically sheet‐flooded, subaerially exposed delta plain. 相似文献
4.
The Uhangri Formation forms part of the Cretaceous sedimentary sequence deposited in a series of inland basins in the south-western Korean Peninsula. It comprises an approximately 400-m-thick epiclastic sequence of conglomerate, (gravelly) sandstone, cherty mudstone and black shale. The entire sequence can be represented by 16 distinctive sedimentary facies organized into four facies associations. Facies association I is characterized by thick homogeneous brownish siltstone, wedge-shaped disorganized conglomerate and thinly interlayered gravelly sandstone units. The siltstone units were formed by large floods submerging the alluvial fan fringe (floodplain), whereas the conglomerate and gravelly sandstone units were deposited by sheetfloods and debris flows. Facies association II consists of stratified conglomerate — gravelly sandstone, laminated sandstone and sandstone/siltstone couplets which form fining-upward cycles. Some facies units are low-angle trough cross-bedded and show broad channel geometries. This association represents subaqueous delta lobes fed by high- and low-concentration turbidity currents in the distal delta realm. Facies association III is characterized, by wedged conglomerate and gravelly sandstone facies with interfingered massive sandstone bounded by scoured bases. It represents a delta front where distributary channels and mouth bars are dominant. Facies association IV consists of laterally continuous sequence of laminated black shale, crudely stratified sandstone and convoluted sandstone/cherty mudstone. This facies association is suggestive of depositional processes controlled by chemical equilibrium resulting from an interaction between density inflows and lake water. The cherty mudstone resulted from inorganic precipitation from siliceous solution provided by acidic volcanism. The Uhangri sequence generally shows a fining-upward trend with a transition from alluvial fan fringe, coarse-grained subaqueous delta, to shallow lake. The retrogradation was probably due to continuous subsidence related to continental rifting in the oblique-slip mobile zone. 相似文献
5.
鄂尔多斯盆地白垩系洛河组至环河华池组沉积相特征研究 总被引：1，自引：1，他引：0
通过研究构造背景、野外露头、岩性组合、沉积构造、古生物特征和测井曲线特征,分析和总结鄂尔多斯盆地白垩系洛河组至环河华池组沉积相、相带分布范围和沉积特征。洛河组主要沉积了冲积扇相、风成沉积相、辫状河相和沙漠相;而在环河华池组主要沉积了湖相、三角洲相、曲流河相及风成砂岩夹层。平面上沉积相带的变化规律性较强,由盆地边缘的冲积相、冲积—河流相砾岩向盆内渐变为河流相—滨浅湖—半深湖相泥岩。沉积特征受构造运动影响和沉积相带控制,洛河组是从山缘向盆地内砂岩厚度迅速变薄、尖灭;环河华池组岩性变化表现为北粗南细、东粗西细,在北部砂体呈现东薄西厚,东北向西南增厚,在南部砂体呈近南北向展布,东薄西厚,南薄北厚。 相似文献
6.
7.
Westphalian B (Duckmantian) alluvial Coal Measures along the Northumberland coast, NE England, comprise coal-capped coarsening-upward crevasse-splay sequences of shale, siltstone and sandstone, interbedded with a number of major distributary channel sandbodies, including the Table Rocks Sandstone. Lithofacies, architectural analysis and outcrop geometries divide the Table Rocks Sandstone into flaggy sandstone, massive sandstone, heterolithic, and mudstone facies associations, each comprising up to 7 lithofacies types. The three sandy facies associations are characterised by lenticular bed geometries on different scales producing a hierarchy of lensoid packages and associated bounding surfaces, all showing typical offset stacking patterns: (1) lenses, represent individual lenticular cross-bed sets, bounded by 1st order surfaces; (2) packages of lenses, called lens clusters are bounded by 2nd order surfaces, and are the basic architectural building block of the sandy facies associations; and (3) vertically stacked lens clusters called amalgamated lens clusters, bounded by 3rd order surfaces. The Table Rocks sandbody has a laterally extensive, irregular, lobate subsurface plan geometry, it displays a radial palaeocurrent pattern with 180° dispersion, and it forms part of a 14-m thick coarsening-upward regressive sequence. It is interpreted as a composite, lobate crevasse-splay delta system that prograded into a shallow interdistributary fresh to brackish water lake up to 14 m deep. The shallow lake water, fluvial input, and extensive development of traction structures such as cross-bedding and ripple cross-lamination suggests a friction-dominated delta, in which the four facies associations can be interpreted in terms of discrete elements of the mouth bar environment. The flaggy sandstone facies association represents the main, axial part of the mouth bar system, the erosively based massive sandstone facies association major subaqeous distributary channels, the lithologically more variable heterolithic facies association the medial mouth bar, and the mudstone facies association the distal mouth bar fringe and prodelta. Within this environmental setting amalgamated lens clusters are interpreted as small, discrete mouth bar sand lobes, whose offset, imbricate stacking pattern reflects channel spacing and bifurcation, the rate of channel shifting, or shallow depths and lack of accommodation space. Thus, lens clusters are interpreted as discrete growth elements of the mouth bar sand lobes, and lenses as individual bedforms making up these growth elements. Because of the high rate of channel shifting, lack of extensive erosion of the mouth bar lobes, and deposition of low discharge fines, the lobes retained much of their original depositional geometry, thereby providing advantageous gradients for offset deposition and stacking of adjacent sand lobes. Although the delta complex was maintained by frequent crevassing from the feeder channel, and by subsidence due to contemporaneous compaction and/or local tectonism, it was deeply incised on two occasions by subaqeous channels in response to high magnitude floods or falling lake level. 相似文献
8.
The Hunghae Formation, SE Korea: Miocene debris aprons in a back-arc intraslope basin 总被引：1，自引：0，他引：1
ABSTRACT During early to middle Miocene times a sudden opening of the Ulleung (Tsushima) back-arc basin in the East Sea (Sea of Japan) led to the development of intraslope basins along the rifted southwestern margin (southeast Korea). Abrupt subsidence resulted in the deposition of the 200 m thick Hunghae Formation (middle Miocene), a sand/mudstone sequence that can be divided into five facies. Facies I (sand and mudstone couplet) and II (coarse sand) are turbiditic in origin, as evidenced by massive, graded, crudely-layered and parallel-laminated sand beds. Facies III (homogeneous mudstone) is characterized by various lignite and plant fragments, clastic and biogenic grains that are randomly oriented, suggestive of hemipelagic deposition. Facies IV (chaotic deposit) is characterized by the disruption of beds, the presence of isolated siltstone blocks (or balls) and large clasts in the muddy matrix, indicative of retrogressive rockfall and slide/slump. Facies V (conglomerate) is of debris flow origin, as evidenced by clast- and matrix-supported features, floating large clasts and absence of traction structures. Individual facies are organized into two types of facies association: (1) homogeneous mudstone (facies III) associated randomly with the rest (facies I, II, IV and V), indicative of hemipelagic and episodic sediment-gravity flow processes, respectively; (2) conglomerate (facies V), coarse sand (facies II) and sand/mudstone couplet (facies I), representing the flow transformation from debris flow to high- and low-concentration turbidity currents. These facies associations are similar in many respects to modern and ancient debris (or slope) aprons found elsewhere. Numerous isolated slide/slump blocks, wedged conglomerates with armoured mudstone balls, discontinuous lignite-containing sand/mudstone beds, chaotic structure and growth faults suggest that the deposition occurred on a steep slope (intraslope basin) off coalescing fan-deltas, mainly by unchannellized sediment-gravity flows. Ancient deposits with irregular facies sequences can be viewed as debris-apron systems, which provide alternatives to submarine-fan models in many clastic basins with a line rather than point source. 相似文献
9.
Devonian lacustrine shore zone architecture: Giving perspective to cliff exposures with ground penetrating radar 
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下载免费PDF全文 Lake margin sedimentary systems have been the subject of only limited study. The cyclic Middle Devonian lacustrine succession of Northern Scotland contains repeated developments of shore zone sandstones and thus provides an ideal location for the study of these units. The cycles comprise deep lake, shallow lake, playa and shore zone facies. Detailed field observations are presented alongside ground penetrating radar data which has aided large‐scale and three‐dimensional characterization of the shore zone sand bodies. Loading and discrete channel forms are recognized in thin‐bedded sandstones within the lower portion of the lake shore zone successions. Up‐section, the sandstone beds appear to become amalgamated, forming subtle low angle accretionary bar complexes. Where imaged on the radar profiles, the repeated development of shoreward migrating features succeeded by more shallow angled lakeward accreting surfaces is recognized; these are ascribed to washover and swash–backwash processes, respectively. The orientation of these features is similar to palaeocurrent measurements from oscillation ripples, suggesting an alignment of the shore zone bars perpendicular to the prevailing wind direction. Further loaded sandstone beds and sand‐filled shallow channel features overlie the bar forms. The context of the shore zone facies allows the controls on its formation to be examined. The shore zone sandstones overlie playa facies which contain abundant desiccation horizons, reflecting the most arid phase in the climatically controlled lacustrine cycle. As climatic conditions ameliorated, the rejuvenation of fluvial systems resulted in the transport of sand out into the basin. Initial deposition was limited to intermittent events where sediment was laid down on a water‐saturated substrate. High resolution fluctuations in lake level resulted in periodic short‐lived reworking events along the lake margins which produced amalgamated sands, forming low relief bars. Shore zone reworking is likely to have occurred over a wide area as the lake margin migrated back and forth, and gradually transgressed. 相似文献
10.
Sedimentation and palaeoenvironments of Late Cretaceous crater-lake deposits in Bushmanland, South Africa 总被引：1，自引：0，他引：1
R. M. H. SMITH 《Sedimentology》1986,33(3):369-386
A large diameter borehole core from an epiclastic kimberlite remnant on the farm Stompoor in the Prieska district, Cape Province, contains a continuous 76 m section of fossiliferous sediments interpreted as having accumulated within a crater-lake during the Late Cretaceous. Three distinct facies associations reflect depositional processes that prevailed in offshore areas of the original lake. Facies Association A: matrix-supported pebble conglomerates comprising a chaotic assemblage of pyroclastic, basement and country rocks set in a fine-grained matrix. Flat, non-erosional basal surfaces with ‘frozen’ rip-up clasts, the protrusion of matrix-supported clasts above the upper surfaces and a direct relationship between maximum clast size and bed thickness suggest deposition from debris flows that originated subaerially on pyroclastic talus cones surrounding the crater. Facies Association B: alternating thin beds of matrix-supported granule conglomerate, structureless fine-grained sandstone and parallel laminated mudrock. Small fining-upward sequences within these beds are comparable to turbidite Bouma Tade, Tde. Numerous partings display petrified fish and frog skeletons, as well as bivalve, gastropod and ostracode shells, leaf impressions, insect wings and a possible bird bone. These beds were deposited by thin debris-flows and turbidity underflows interspersed with periods of ‘pelagic’ sedimentation. Facies Association C: microlaminated mudstone beds containing scattered ‘dropstone lapilli’. The lamination is imparted by alternating Ca-rich/Ca-poor layers which may reflect climatic seasonality. They are interpreted as the result of seasonally influenced suspension settling through a thermally stratified water column. Short-term periodicities in conglomerate bed thicknesses are interpreted as the result of successive block caving of a slump scar giving rise to several debris flows from the same source area. Seismic shock from nearby volcanism may have simultaneously triggered slumps on both subaerial and subaqueous slopes. Dropstone lapilli in Type C beds and the preponderance of load casting in Type B beds support this interpretation. An estimate of the time span involved in accumulating 76 m of crater lake sediments based on the possible seasonal imprint of Type C beds gives a figure of some 220,000 yr. 相似文献
11.
基于对东濮凹陷97口钻井岩心的详细观察和分析,在古近系沙河街组沙三中亚段湖相沉积中识别出滑动、滑塌、碎屑流和浊流共4种类型的重力流沉积。各种类型沉积的主要判识特征如下: (1)滑动沉积以保留部分原始沉积构造、层内准同生小型断裂构造及较大角度的地层倾角(陡倾构造)发育、伴生Skolithos-Palaeophycus遗迹组合或Planolites-Taenidium遗迹组合为主要特征; (2)滑塌沉积以砂岩层顶、底面均与暗色泥岩呈突变接触以及岩层内部发育各种同生软沉积物变形构造(如包卷层理、火焰状构造、泄水构造、液化脉和各种撕裂屑等)为主要鉴别特征;(3)碎屑流沉积以砂岩呈块状构造、顶部发育漂浮砾石、底部泥岩撕裂屑发育并可见“泥包砾”现象、砂岩顶、底面均与暗色泥岩突变接触为特征;滑塌沉积和碎屑流沉积序列的上部常常伴生Mermoides-Parapaleodictyon遗迹组合; (4)浊流沉积以发育完整或不完整的鲍马序列为主要特征,浊积砂体下部见正粒序层理,底面见有冲刷痕、不规则槽模、重荷模等沉积构造,中上部发育深湖沉积中常见的Semirotundichnus-Puyangichnus遗迹组合。综合分析上述各种重力流沉积特征和伴生遗迹化石组合所体现的水深变化规律,认为遗迹化石组合随着湖水深度的增加呈分带性,与重力流沉积随水深增加而出现的滑动—滑塌—碎屑流—浊流沉积序列具有明显的一致性,且伴随重力流沉积而产生的生物扰动作用是增强的。因此,生物扰动构造(遗迹化石)的研究不仅对湖相沉积中储集层物性的分析具有重要意义,而且针对重力流沉积类型的判识还能提供重要的生物遗迹学信息。 相似文献
12.
中国白垩纪大陆科学钻探松科1井南孔连续取姚家组岩心长157.67m,岩心收获率为99.96%。上白垩统姚家组对应着三冬阶和坎潘阶下部。松科1井南孔姚家组岩心的精细描述,揭示其岩性-岩相-旋回的沉积序列及其过程。姚家组中可识别基本岩石类型11种,相类型为浅湖、半深湖和三角洲前缘3种亚相,白云岩沉积、泥质灰岩沉积、浅湖和深湖浊流沉积、河口坝、远砂坝、席状砂、分流间湾、水下滑塌沉积、浅湖和深湖静水泥沉积11种沉积微相。姚家组可识别的米级旋回(六级旋回)有8种类型,可划分出151个米级旋回。这些米级旋回叠加成45个五级旋回、9个四级旋回和3个三级旋回。完整组段厘米级刻画为高精度沉积过程研究提供了可能。姚家组红层厚度占姚家组总厚度的43%,作为该时期已被揭示的全球为数不多的陆相红层之一,厘米级刻画的姚家组大套陆相红层为全球白垩纪富氧事件研究提供了可能的立典剖面。 相似文献
13.
Gravity flow deposits associating with ichnoassemblages within the middle Member 3 of Paleogene Shahejie Formation in Dongpu sag,Henan Province 下载免费PDF全文
下载免费PDF全文 Based on the observation and analyses of 97 exploratory well cores in Dongpu sag,four types of gravity flow(including sliding,slumping,debris flow and turbidity current)deposits in lacustrine facies have been recognized within the middle Member 3 of the Paleogene Shahejie Formation. Their main identification marks are outlined as follows: (1)the sliding deposits are characterized by the partial preservation of primary sedimentary structures,the development of small penecontemporaneous fracture or fault in sandstone beds,and steep dip of strata,with Skolithos-Palaeophycus ichnoassemblage and/or Planolites-Taenidium ichnoassemblage,which commonly occurred in the shore and shallow lake environments. (2)General characteristics of slumping deposits mainly are the abrupt contact between sandstone beds(top and bottom)and dark mudstone beds,and development of all kinds of penecontemporaneous soft-sediment deformation structures such as convolution bedding,flame structure,water-escape structure,liquefied vein and tearing debris. (3)The sandy debris flow deposits are mainly marked by the massive sandstone,abrupt contact between sandstone beds(top and bottom)and dark mudstone beds,as well as developing floating gravels near the top of sandstone beds and tearing mudstone debris in the bottom of sandstone beds,sometimes with occurring the mud-coated intraclasts. Meanwhile,slumping and sandy debris flow deposits commonly associated with the Mermoides-Parapaleodictyon ichnoassemblage produced in semi-deep water lake environment. (4)The turbidity deposit is mainly indicated by the complete or incomplete Bouma sequences,normal-graded bedding,and all kinds of sole marks such as scour marks,irregular flute casts and load casts,and the Semirotundichnus-Puyangichnus ichnoassemblage frequently occurred in the middle to upper parts of the turbidite beds that formed in deep-water lake environment. After comprehensive analyses of above four types of gravity flow deposits and water-depth variation reflected by different ichnoassemblages,it can be considered that ichnoassemblage changes appear a zonation with the depth of the lake,which is consistent with variations in gravity flow deposits from sliding-slumping-debris flows to turbidity currents,and the bioturbation generated with gravity flow deposits is enhanced. Therefore,the research of bioturbation structures(ichnofossils)is not only of great significance to study the physical property of sandstone reservoir in lacustrine deposits,but also to provide important ichnological information for discerning various types of gravity flow deposits. 相似文献
14.
Hybrid event beds dominated by transitional‐flow facies: character,distribution and significance in the Maastrichtian Springar Formation,north‐west Vøring Basin,Norwegian Sea 下载免费PDF全文
下载免费PDF全文 Sarah J. Southern Ian A. Kane Michał J. Warchoł Kristin W. Porten William D. McCaffrey 《Sedimentology》2017,64(3):747-776
Hybrid event beds comprising clay‐poor and clay‐rich sandstone are abundant in Maastrichtian‐aged sandstones of the Springar Formation in the north‐west Vøring Basin, Norwegian Sea. This study focuses on an interval, informally referred to as the Lower Sandstone, which has been penetrated in five wells that are distributed along a 140 km downstream transect. Systematic variations in bed style within this stratigraphic interval are used to infer variation in flow behaviour in relatively proximal and distal settings, although individual beds were not correlated. The Lower Sandstone shows an overall reduction in total thickness, bed amalgamation, sand to mud ratio and grain size in distal wells. Turbidites dominated by clay‐poor sandstone are at their most common in relatively proximal wells, whereas hybrid event beds are at their most common in distal wells. Hybrid event beds typically comprise a basal clay‐poor sandstone (non‐stratified or stratified) overlain by banded sandstone, with clay‐rich non‐stratified sandstone at the bed top. The dominant type of clay‐poor sandstone at the base of these beds varies spatially; non‐stratified sandstone is thickest and most common proximally, whereas stratified sandstone becomes dominant in distal wells. Stratified and banded sandstone record progressive deposition of the hybrid event bed. Thus, the facies succession within hybrid event beds records the longitudinal heterogeneity of flow behaviour within the depositional boundary layer; this layer changed from non‐cohesive at the front, through a region of transitional behaviour (fluctuating non‐cohesive and cohesive flow), to cohesive behaviour at the rear. Spatial variation in the dominant type of clay‐poor sandstone at the bed base suggests that the front of the flow remained non‐cohesive, and evolved from high‐concentration and turbulence‐suppressed to increasingly turbulent flow; this is thought to occur in response to deposition and declining sediment fallout. This research may be applicable to other hybrid event bed prone systems, and emphasizes the dynamic nature of hybrid flows. 相似文献
15.
A. W. Mode P. A. Chikezie O. C. Ekwenye O. A. Anyiam I. C. Okwara 《Arabian Journal of Geosciences》2017,10(24):548
A high-resolution study involving the integration of cores, wireline logs and reflection seismic dataset was used to unravel the facies assemblages, reservoir quality and hydrocarbon potential of E1 and H9 reservoirs in the “PAC” field, Offshore Niger Delta. Facies analysis of the cored PAC-14 well shows six lithofacies: massive mudstone, parallel-laminated mudstones with sideritic bands, fine-grained parallel-laminated sandstone, medium-grained parallel-laminated sandstone, fine-grained ripple laminated sandstone, and coarse massive sandstone. These lithofacies were grouped into five facies associations: channel story axis (CSA), channel story margin (CSM), inter-channel thin beds (ICTB), mud-rich thin beds (MRTB) and injectites (INJ). These facies associations are typical of a confined channel and basin floor fan deposit of a deep-water turbidite depositional environment. Reservoir unit E1 was dominated by the facies association CSA while the H9 reservoir consists mainly of the facies associations MRTB and INJ. The observed sand injectites are suggested to have formed due to overloading of compacted sands leading to upward remobilization of sand into the overlying shale. Seismic horizons and faults were mapped to understand the structures, trend and reflections within the study area. Results from petrophysical volumetrics estimated the net hydrocarbon pore volume for the E1 and H9 reservoirs as 456 MMBBL and 378 MMBBL, respectively. Exploration for deep-water reservoir mainly targets high amplitude and bright seismic reflectors and ignores the low amplitude reflectors (dim loops) which are typically interpreted as non-reservoir units. However, this study shows a low-amplitude reflector containing medium-grained sand injectite unit, which has high porosity (31.7%) and permeability (4472 mD) values, and contains recoverable hydrocarbon. 相似文献
16.
Lithofacies in the mid‐Permian Nowra Sandstone indicate a middle/upper shoreface to foreshore environment of deposition under the influence of storm‐generated waves and north‐northeasterly directed longshore currents. Palaeogeographic reconstruction for the Nowra Sandstone portrays a sand‐dominated high energy shelf and offshore shoal forming a sequence thickening seaward away from the western shore of the Sydney Basin. The shoal‐crest at the outer edge of the shelf trends north‐northeast. It is characterized by fine‐ to medium‐grained sandstone with upper flow regime structures and a high proportion of conglomerate, whereas coarser sandstone with lower energy bedforms occurs along the seaward side of the shoal. In the deeper water to the east, the lower Nowra Sandstone becomes rapidly thinner as it passes seaward, via bioturbated storm redeposited sandstone beds, into the shelf deposits of the Wandrawandian Siltstone. This sequence accumulated during a regressive event and the base of the formation becomes progressively younger eastward. The sand may have been supplied by rivers along the western coast but the major source was south of the study area. The lower Nowra Sandstone is separated from the upper part of the formation by an extensive ravinement surface overlain by the Purnoo Conglomerate Member. In contrast to the lower unit, the upper Nowra Sandstone forms a westward thickening wedge that represents a backstepping nearshore sand facies that accumulated during a transgression. The upper Nowra Sandstone passes vertically and laterally eastward into the Berry Siltstone. Thus both boundaries of the Nowra Sandstone are diachronous, first younging eastward and then westward as a response to a regressive‐transgressive episode. 相似文献
17.
Hayfaa Abdul Aziz Enrique Sanz-Rubio† Jose P. Calvo‡ Fredirik J. Hilgen Wout Krijgsman 《Sedimentology》2003,50(2):211-236
ABSTRACT The middle Miocene sedimentary fill of the Calatayud Basin in north‐eastern Spain consists of proximal to distal alluvial fan‐floodplain and shallow lacustrine deposits. Four main facies groups characteristic of different sedimentary environments are recognized: (1) proximal and medial alluvial fan facies that comprise clast‐supported gravel and subordinate sandstone and mudstone, the latter exhibiting incipient pedogenic features; (2) distal alluvial fan facies, formed mainly of massive mudstone, carbonate‐rich palaeosols and local carbonate pond deposits; (3) lake margin facies, which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system, i.e. front (lithofacies A), comprising massive siliciclastic mudstone and tabular carbonates, or lateral (lithofacies B) showing laminated and/or massive siliciclastic mudstone alternating with tabular and/or laminated carbonate beds; and (4) mudflat–shallow lake facies showing a remarkable cyclical alternation of green‐grey and/or red siliciclastic mudstone units and white dolomitic carbonate beds. The cyclic mudflat–shallow lake succession, as exposed in the Orera composite section (OCS), is dominantly composed of small‐scale mudstone–carbonate/dolomite cycles. The mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods, the deposits evolving either under subaerial exposure or water‐saturated conditions, depending on their location on the lacustrine mudflat and on climate. The dolomite intervals accumulated during lake‐level highstands with Mg‐rich waters becoming increasingly concentrated. Lowstand to highstand lake‐level changes indicated by the mudstone/dolomite units of the small‐scale cycles reflect a climate control (from dry to wet conditions) on the sedimentation in the area. The spatial distribution of the different lithofacies implies that deposition of the small‐scale cycles took place in a low‐gradient, shallow lake basin located in an interfan zone. The development of the basin was constrained by gradual alluvial fan aggradation. Additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of δ18O and δ13C values varying from ?7·9 to 3·0‰ PDB and from ?9·2 to ?1·7‰ PDB respectively. More negative δ18O and δ13C values are from carbonate‐rich palaeosols and lake‐margin carbonates, which extended in front of the alluvial fan systems, whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment. The results show a clear trend of δ18O enrichment in the carbonates from lake margin to the centre of the shallow lake basin, thereby also demonstrating that the lake evolved under hydrologically closed conditions. 相似文献
18.
Luis A. Spalletti 《Geological Journal》1993,28(2):137-148
The Sierra Grande Formation (Silurian-Early Devonian) consists of quartz arenites associated with clast supported conglomerates, mudstones, shales and ironstones. Eight sedimentary facies are recognized: cross-stratified and massive sandstone, plane bedded sandstone, ripple laminated sandstone, interstratified sandstone and mudstone, laminated mudstone and shale, oolitic ironstone, massive conglomerate and sheet conglomerate lags. These facies are interpreted as shallow marine deposits, ranging from foreshore to inner platform environments. Facies associations, based on vertical relationships among lithofacies, suggest several depositional zones: (a) beach to upper shoreface, with abundant plane bedded and massive bioturbated sandstones; (b) upper shoreface to breaker zone, characterized by multistorey cross-stratified and massive sandstone bodies interpreted as subtidal longshore-flow induced sand bars; (c) subtidal, nearshore tidal sand bars, consisting of upward fining sandstone sequences; (d) lower shoreface zone, dominated by ripple laminated sandstone, associated with cross-stratified and horizontal laminated sandstone, formed by translatory and oscillatory flows; and (e) transitional nearshore-offshore and inner platform zones, with heterolithic and pelitic successions, and oolitic ironstone horizons. Tidal currents, fair weather waves and storm events interacted during the deposition of the Sierra Grande Formation. However, the relevant features of the siliciclastics suggest that fair weather and storm waves were the most important mechanisms in sediment accumulation. The Silurian-Lower Devonian platform was part of a continental interior sag located between southern South America and southern Africa. The Sierra Grande Formation was deposited during a second order sea level rise, in which a shallow epeiric sea flooded a deeply weathered low relief continent. 相似文献
19.
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. 相似文献
20.
The Raniganj Formation (late Permian) forms the uppermost economic coal-bearing unit of the Gondwana succession. The dominant facies interpreted from analysis of cores from the Raniganj formation are classified as Sandstone dominated facies, Sandstone - shale heterolith facies, Shale facies and Coal facies. The natural Gamma response of Raniganj Formation shows predominance of repetitive fining upwards cycles. Integration of core analysis and geophysical log data of the Raniganj formation indicates meandering fluvial environment. The lower part of Raniganj Formation is channel dominated which corresponds to thick amalgamated sand bodies while the upper part represent overbank shows predominance of channel avulsion indicating a gradual change in accommodation space. Five major fining upward depositional sequences, bounded by sub-aerial unconformities (sequence boundaries) have been dentified in Raniganj formation, based on changes in depositional style that are correlated regionally. Each sequence comprises of Low accommodation system tract (LAST) at base and high accommodation system tract (HAST) at top. LAST is characterized by vertically stacked, multistory amalgamated channel sandstone dominated facies, while floodplain dominated facies characterize HAST. The coal seams deposited in LAST are thicker and relatively more continuous than the frequent thin seams of HAST. Such facies distribution study would be helpful for the development strategy for CBM blocks based on production priority. 相似文献