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1.
Michael Houmark-Nielsen 《Sedimentary Geology》1983,36(1):51-63
Four major sedimentary facies are present in coarse-grained, ice-marginal deposits from central East Jylland, Denmark. Facies A and B are matrix-supported gravels deposited by subaerial sediment gravity flows as mudflows (facies A) and debris flows (facies B). Facies C consists of clast-supported, water-laid gravels and facies D are cross-bedded sand and granules. The facies can be grouped into three facies associations related to the supraglacial and proglacial environments: (1) the flow-till association is made up of alternating beds of remobilized glacial mixton (facies A) and well-sorted cross-bedded sand (facies D); (2) the outwash apron association resembles the sediments of alluvial fans in containing coarse-grained debris-flow deposits (facies B), water-laid gravel deposited by sheet floods (facies C) and cross-bedded sand and granules (facies D) from braided distributaries; (3) the valley sandur association comprises water-laid gravel (facies C) interpreted as sheet bars and longitudinal bars interbedded with cross-bedded sand and granules (facies D) deposited in channels between bars in a braided environment.The general coarsening-upward trend of the sedimentary sequences caused by the transition of bars and channel-dominated facies to debris-flow-dominated facies indicate an increasing proximality of the outwash deposits, picturing the advance and still stand of a large continental lowland ice-sheet. The depositional properties suggest that sedimentation was caused by melting along a relatively steep, active glacier margin as a first step towards the final vanishing of the Late Weichselian icesheet (the East Jylland ice) covering eastern Denmark. 相似文献
2.
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. 相似文献
3.
Variable style of transition between Palaeogene fluvial fan and lacustrine systems, southern Pyrenean foreland, NE Spain 总被引：1，自引：0，他引：1
Two Palaeogene fluvial fan systems linked to the south‐Pyrenean margin are recognized in the eastern Ebro Basin: the Cardona–Súria and Solsona–Sanaüja fans. These had radii of 40 and 35 km and were 800 and 600 km2 in area respectively. During the Priabonian to the Middle Rupelian, the fluvial fans built into a hydrologically closed foreland basin, and shallow lacustrine systems persisted in the basin centre. In the studied area, both fans are part of the same upward‐coarsening megasequence (up to 800 m thick), driven by hinterland drainage expansion and foreland propagation of Pyrenean thrusts. Fourteen sedimentary facies have been grouped into seven facies associations corresponding to medial fluvial fan, channelized terminal lobe, non‐channelized terminal lobe, mudflat, deltaic, evaporitic playa‐lake and carbonate‐rich, shallow lacustrine environments. Lateral correlations define two styles of alluvial‐lacustrine transition. During low lake‐level stages, terminal lobes developed, whereas during lake highstands, fluvial‐dominated deltas and interdistributary bays were formed. Terminal lobe deposits are characterized by extensive (100–600 m wide) sheet‐like fine sandstone beds formed by sub‐aqueous, quasi‐steady, hyperpycnal turbidity currents. Sedimentary structures and trace fossils indicate rapid desiccation and sub‐aerial exposure of the lobe deposits. These deposits are arranged in coarsening–fining sequences (metres to tens of metres in thickness) controlled by a combination of tectonics, climatic oscillations and autocyclic sedimentary processes. The presence of anomalously deeply incised distributary channels associated with distal terminal lobe or mudflat deposits indicates rapid lake‐level falls. Deltaic deposits form progradational coarsening‐upward sequences (several metres thick) characterized by channel and friction‐dominated mouth‐bar facies overlying white‐grey offshore lacustrine facies. Deltaic bar deposits are less extensive (50–300 m wide) than the terminal lobes and were also deposited by hyperpycnal currents, although they lack evidence of emergence. Sandy deltaic deposits accumulated locally at the mouths of main feeder distal fan streams and were separated by muddy interdistributary bays; whereas the terminal lobe sheets expand from a series of mid‐fan intersection points and coalesced to form a more continuous sandy fan fringe. 相似文献
4.
R. DOUGLAS ELMORE 《Sedimentology》1983,30(6):829-842
Laminated cryptalgal carbonates occur in the Precambrian Copper Harbor Conglomerate of northern Michigan, which was deposited in the Keweenawan Trough, an aborted proto-oceanic rift. This unit is composed of three major facies deposited by braided streams on a large alluvial-fan complex. Coarse clastics were deposited in braided channels, predominantly as longitudinal bars, whereas cross-bedded sandstones were deposited by migrating dunes or linguoid bars. Fine-grained overbank deposits accumulated in abandoned channels. Gypsum moulds and carbonate-filled cracks suggest an arid climate during deposition. Stromatolites interstratified with these clastic facies occur as laterally linked drapes over cobbles, as laterally linked contorted beds in mudstone, as oncolites, and as poorly developed mats in coarse sandstones. Stromatolites also are interbedded with oolitic beds and intraclastic conglomerates. Stromatolitic microstructure consists of alternating detrital and carbonate laminae, and open-space structures. Radial-fibrous calcite fans are superimposed on the laminae. The laminae are interpreted as algal in origin, whereas the origin of the radial fibrous calcite is problematic. The stromatolites are inferred to have grown in lakes which occupied abandoned channels on the fan surface. Standing water on a permeable alluvial fan in an arid climate requires a high water table maintained by high precipitation, or local elevation of the water table, possibly due to the close proximity of a lake. Occurrence of stromatolites in the upper part of the Copper Harbor Conglomerate near the base of the lacustrine Nonesuch Shale suggests that these depositional sites may have been near the Nonesuch Lake. 相似文献
5.
南襄盆地泌阳凹陷深凹区核三段沉积特征及演化 总被引：1，自引：0，他引：1
通过测井、录井、粒度分析资料,结合区域地质资料、前人研究成果、岩心描述和地震反射资料,认为核三段发育辫状河三角洲、近岸水下扇、滑塌浊积扇及湖泊沉积,并进一步识别出5个亚相及6个微相。其中,近岸水下扇发育于研究区西南部和东南部的控边断层处,辫状河三角洲发育于东北部,滑塌浊积扇发育于辫状河三角洲前端的半深湖-深湖区域。近岸水下扇岩性主要为灰白色中、细砾岩,砾石成分复杂,分选差,磨圆程度低。辫状河三角洲发育平行层理、交错层理及冲刷充填构造,垂向上构成间断正韵律,其岩性为浅灰色砾岩、砾质砂岩、砂岩,中-厚层或块状,自然电位曲线和电阻率曲线呈钟形或箱型。辫状河三角洲前缘砂体失稳,产生滑塌,在深湖区形成滑塌浊积扇,其岩性为细砂岩、粉砂岩、泥质粉砂岩,多呈正韵律,发育块状层理、液化变形层理、波状层理及泥岩撕裂屑、槽模、沟模构造等,电测曲线表现为钟形、箱形、漏斗形等。湖泊沉积主要发育于三角洲前缘和近岸水下扇前方的深凹区。从H38-H31研究区经历了水体由深到浅再略加深的沉积演化。 相似文献
6.
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
7.
Sequences of wave-enhanced sediment-gravity flows (WESGFs) have been widely recognized in the marine shelf environment. In this study, we show observations of WESGF deposits in lacustrine settings using well core and thin section data from the Paleogene in the Jiyang sub-basin, Bohai Bay basin, eastern China. The findings of this study include the following: 1) the sequence of WESGFs in the lacustrine basin is similar to that of marine; it consists of three units, MF1 unit: siltstone with basal erosion surface, MF2 unit: silt-streaked claystone, and MF3 unit: silty-mudstone; and 2) prodelta sand sheets are found in the lacustrine WESGF sequence and are classified as the MFd unit: clay-streaked siltstone. However, because the system size and variability in hydrodynamic conditions are different between the lacustrine and marine basins, lacustrine WESGFs do appear to have three distinguishable features: 1) the sediment grain size and sand content are slightly higher than those of the marine WESGFs; 2) lacustrine WESGFs may contain prodelta sediments or sedimentary sequences of other types of gravity flows, such as hyperpycnal flows; and 3) the scale of the sedimentary structures for lacustrine WESGFs is smaller. The WESGFs found in the continental lacustrine basin provide a new model for sediment dispersal processes in lake environments and may be helpful to explain and predict the distribution of sandy reservoirs for oil and gas exploration. 相似文献
8.
9.
Outcrop-scale acoustic facies analysis and latest Quaternary development of Hueneme and Dume submarine fans, offshore California 总被引：6，自引：1，他引：5
The uppermost Quaternary deposits of the Hueneme and Dume submarine fans in the Santa Monica Basin have been investigated using a closed-spaced grid of boomer seismic-reflection profiles, which give vertical resolution of a few tens of centimetres with acoustic penetration to 50 m. Acoustic facies integrated with geometry define six architectural elements, some with discrete subelements that are of a scale that can be recognized in outcrops of ancient turbidite systems. In the Santa Monica Basin, the relationship of these elements to fan morphology, stratigraphy and sediment source is precisely known.
The width of upper Hueneme fan valley has been reduced from 5 km since the last glacial maximum to 1 km at present by construction of laterally confined sandy levees within the main valley. The middle fan comprises three main subelements: thick sand deposits at the termination of the fan valley, low-gradient sandy lobes typically 5 km long and < 10 m thick, and scoured lobes formed of alternating sand and mud beds with many erosional depressions. The site of thickest lobe sediment accumulation shifts through time, with each sand bed deposited in a previous bathymetric low (i.e. compensation cycles). The lower fan and basin plain consists of sheet-like alternations of sand and mud with shallow channels and lenses.
Variations in the rate of late Quaternary sea level rise initiated changes in sediment facies distribution. At lowstand, and during the approximately 11 ka stillstand in sea level, the Hueneme Fan was fed largely by hyperpycnal flow from the Santa Clara River delta, depositing high sediment waves on the right hand levee and thick sandy lobes on the middle fan. At highstand of sea level, most turbidity currents were generated by failure of silty prodelta muds. In contrast, the smaller Dume Fan was apparently always fed from littoral drift of sand through a single-canyon point source. 相似文献
The width of upper Hueneme fan valley has been reduced from 5 km since the last glacial maximum to 1 km at present by construction of laterally confined sandy levees within the main valley. The middle fan comprises three main subelements: thick sand deposits at the termination of the fan valley, low-gradient sandy lobes typically 5 km long and < 10 m thick, and scoured lobes formed of alternating sand and mud beds with many erosional depressions. The site of thickest lobe sediment accumulation shifts through time, with each sand bed deposited in a previous bathymetric low (i.e. compensation cycles). The lower fan and basin plain consists of sheet-like alternations of sand and mud with shallow channels and lenses.
Variations in the rate of late Quaternary sea level rise initiated changes in sediment facies distribution. At lowstand, and during the approximately 11 ka stillstand in sea level, the Hueneme Fan was fed largely by hyperpycnal flow from the Santa Clara River delta, depositing high sediment waves on the right hand levee and thick sandy lobes on the middle fan. At highstand of sea level, most turbidity currents were generated by failure of silty prodelta muds. In contrast, the smaller Dume Fan was apparently always fed from littoral drift of sand through a single-canyon point source. 相似文献
10.
Moutaz A. Al-Dabbas Jassim A. Al-Jassim Amanj I. Qaradaghi 《Arabian Journal of Geosciences》2013,6(12):4771-4783
The depositional facies and environments were unraveling by studying 21 subsurface sections from ten oilfields in the central and southern Iraq and a large number of thin sections of the Nahr Umr (siliciclastic deposit) Formation (Albian). This formation is mainly composed of sandstone interlaminated with minor siltstone and shale, with occurrence of thin limestone beds. Nahr Umr Formation is subdivided into three lithostratigraphic units of variable thicknesses on the basis of lithological variations and log characters. Mineralogically and texturally, mature quartz arenite and sandstones are the common type of the Nahr Umr Formation. The sandstones are cemented by silica and calcite material and have had a complex digenetic history. Compaction, dissolution, and replacements are the main diagenetic processes. Prodelta, distal bar, distributary mouth bar, distributary channel, over bank, and tidal channel are the main depositional environments recognized for the Nahr Umr Formation, within the studied wells. This formation was deposited in shallow marine and fluvial–deltaic environments and exhibit progradational succession of facies. Eight sedimentary facies that have been identified in the Nahr Umr Formation include claystone lithofacies, claystone siltstone lithofacies, lenticular-bedded sandstone–mudstone lithofacies, wavy-bedded sandstone–mudstone lithofacies, flaser-bedded sandstone–mudstone lithofacies, parallel and cross lamination sandstone lithofacies, trough cross-bedded sandstone lithofacies, and planar cross-bedded sandstone lithofacies. The depositional model of the Nahr Umr Formation environment was built based on the lithofacies association concepts. 相似文献
11.
The Dibdibba Formation is of Pleistocene age and consists of a fluviatile sequence of ungraded, often cross-bedded sand and gravels intercalated with minor sandy clay layers. It occurs in the northern desert of Kuwait as subparallel elongated ridges trending NE-SW. Structures and mineralogy of the Dibdibba deposits suggest that they have been derived from the basement complex of the northeastern area of Saudi Arabia as sheet floods and deposited in the alluvial fan of the Wadi Ar-Rimmah-Al Batin valley system. Floods transporting these deposits were intermittent; the gravelly bands were deposited during severe floods and the sandy beds during relatively quiet floods. 相似文献
12.
K. Stingl 《International Journal of Earth Sciences》1994,83(4):811-821
The Eibiswald Bucht is a small subbasin of the Western Styrian Basin exposing sediments of Lower Miocene age. In the past the entire sequence exposed in the Eibiswalder Bucht has been interpreted as being of fluvial/lacustrine origin; here, results are presented of detailed sedimentological investigations that lead to a revision of this concept. The lowermost siliciclastic sedimentary unit of the Eibiswalder Bucht sequence is the Radl Formation. It is overlain by the Eibiswald Beds, which are subdivided into the Lower, Middle and Upper Eibiswald Beds. The Radl Formation and the Lower Eibiswald Beds are interpreted as a fan delta complex deposited along NNW-SSE striking faults. Based on the sedimentary facies this fan delta can be subdivided into a subaerial alluvial fan facies group, a proximal delta facies group and a distal delta/prodelta facies group. The Radl Formation comprises the alluvial fan and proximal delta facies groups, the Lower Eibiswald Beds the distal delta/prodelta facies group. The alluvial fan and the proximal delta consist of diverse deposits of gravelly flows. The distal delta/prodelta consists of wave-reworked, bioturbated, low density turbidites intercalated with minor gravelly mass flows. The prodelta can be regarded as as the basin facies of the small and shallow Eibiswalder Bucht, where marine conditions prevailed. The basin was probably in part connected with the Eastern Styrian Basin, the contemporary depositional environment of the Styrian Schlier (mainly turbiditic marine offshore sediments in the Eastern Styrian Basin). Analysis of the clast composition, in conjunction with the paleotransport direction of the coarse delta mass flows of the Radl Formation, shows that the source rocks were exclusively crystalline rocks ranging from greenschists to eclogites. 相似文献
13.
渤南洼陷古近系沙河街组为一套冲积－湖泊沉积，由曲流河三角洲相、辫状河三角洲相、扇三角洲相、水下扇相和湖泊相组成，可分出14个亚相，35个微相，其中辫状河三角洲最发育，其特征显著，明显有别于其它四种类型的三角洲。研究区辫状河三角洲由辫状河三角洲前缘及前三角洲构成，辫状河三角洲前缘的主体是由含砂岩及中粗粒砂岩组成的水下分流河道砂坝，三角洲中交错层理发育，其中尤以水道砂坝侧向迁移加积而形成的侧积交错层异常发育为标志。 相似文献
14.
The Doumsan fan-delta system in the Pohang Basin (Miocene), SE Korea comprises tripartite components of Gilbert-type topset, foreset, and bottomset environments with an extended prodelta in the deeper part (a few hundred metres deep). The present study documents sedimentologic features and origin of a gravel body (here interpreted as a gravel lobe) formed in the prodelta region of the Doumsan fan delta. The gravel lobe lies on sandy mud deposits and is capped by a thick massive sand bed. It extends for more than 1.5 km with a height of up to 30 m and shows a narrow tongue-like geometry. Eight sedimentary facies have been distinguished to describe characteristic features of the gravel lobe and the associated deposits. Of these, three types of gravelly sedimentary facies are important with regard to volumetric contribution and depositional processes: (1) crudely stratified pebble-grade conglomerate; (2) disorganized, clast-rich pebble(-to-cobble)-grade conglomerate; and (3) matrix-rich, bimodal cobble-grade conglomerate. The former two types dominate the central part of the lobe where they are not accompanied by sand beds, whereas the latter, as subordinate units, is prevalent in the fringe which otherwise is dominated by thick sandy mud deposits. The stacked successions of crudely stratified pebble-grade conglomerate are representative of the active aggradational phases of the gravel lobe, whereas the occurrence of channels within the lobe reflects that the gravel lobe prograded under the influence of subaqueous channel systems. The gravel lobe resulted from catastrophic disturbance (slumping) on the foreset region that further caused the development of channel systems, promoting efficient transport of gravelly sediments. This type of deposit may represent an important additional category of low-efficiency subaqueous fans. 相似文献
15.
KEVIN T. PICKERING 《Sedimentology》1983,30(2):181-199
ABSTRACT Three transitional submarine fan environments are recognized in the late Precambrian, 3-2 km thick Kongsfjord Formation in NE Finnmark, North Norway, namely: (1) middle to outer fan; (2) fan lateral margin, and (3) fan to upper basin-slope deposits. Middle to outer fan deposits have a high proportion of sandstones, typically showing Bouma T bede with T a in the thicker beds. Deposition was mainly from sheet flows with rare shallow channels. Middle to outer fan deposits are an association of sandstone packets less than 10 m thick but commonly only a few metres thick, interpreted as channels or lobes. Interchannel and fan fringe deposits occur as discrete packets of beds between the thicker bedded and coarser grained channel or lobe deposits. Fan lateral margin deposits are recognized on the basis of their stratigraphic position adjacent to inner/middle fan deposits. They are characterized by: (a) a relatively high proportion of fine-grained sandstone/siltstone turbidites compared to other major fan environments; (b) relatively small channels oriented at various angles to the regional basin slope; (c) lobes associated with channels, and (d) abundant clastic dykes and other soft-sediment deformation. Fan lateral margin deposits are distinguished from the outer fan/basin plain successions on account of the very high proportion of siltstone turbidites comparable with middle fan inter-channel deposits. Fan to upper basin-slope deposits occur at the top of the formation as an alternation of sandstone turbidites, most of which are laterally discontinuous, and very thin-bedded upper basin-slope siltstones with slide deposits. 相似文献
16.
Hueneme and Dume submarine fans in Santa Monica Basin consist of sandy channel and muddy levee facies on the upper fan, lenticular sand sheets on the middle fan, and thinly bedded turbidite and hemipelagic facies elsewhere. Fifteen widely correlatable key seismic reflections in high-resolution airgun and deep-towed boomer profiles subdivide the fan and basin deposits into time-slices that show different thickness and seismic-facies distributions, inferred to result from changes in Quaternary sea level and sediment supply. At times of low sea level, highly efficient turbidity currents generated by hyperpycnal flows or sediment failures at river deltas carry sand well out onto the middle-fan area. Thick, muddy flows formed rapidly prograding high levees mainly on the western (right-hand) side of three valleys that fed Hueneme fan at different times; the most recently active of the lowstand fan valleys, Hueneme fan valley, now heads in Hueneme Canyon. At times of high sea level, fans receive sand from submarine canyons that intercept littoral-drift cells and mixed sediment from earthquake-triggered slumps. Turbidity currents are confined to ‘underfit’ talweg channels in fan valleys and to steep, small, basin-margin fans like Dume fan. Mud is effectively separated from sand at high sea level and moves basinward across the shelf in plumes and in storm-generated lutite flows, contributing to a basin-floor blanket that is locally thicker than contemporary fan deposits and that onlaps older fans at the basin margin. The infilling of Santa Monica Basin has involved both fan and basin-floor aggradation accompanied by landward and basinward facies shifts. Progradation was restricted to the downslope growth of high muddy levees and the periodic basinward advance of the toe of the steeper and sandier Dume fan. Although the region is tectonically active, major sedimentation changes can be related to eustatic sea-level changes. The primary controls on facies shifts and fan growth appear to be an interplay of texture of source sediment, the efficiency with which turbidity currents transport sand, and the effects of delta distributary switching, all of which reflect sea-level changes. 相似文献
17.
《Sedimentology》2018,65(6):2117-2148
The origin of the fourth member of the Eocene Shahejie Formation in the northern steep slopes of the Minfeng Sub‐sag, Dongying Sag, China, was investigated by integrating core studies and flume tank depositional simulations. A non‐channelized depositional model is proposed in this paper for nearshore subaqueous fans in steep fault‐controlled slopes of lacustrine rift basins. The deposits of nearshore subaqueous fans along the base of steep border‐fault slopes of rift basins are typically composed of deep‐water coarse‐grained sediment gravity‐flow deposits directly sourced from adjacent footwalls. Sedimentation processes of nearshore subaqueous fans respond to tectonic activities of boundary faults and to seasonal rainfall. During tectonically active stages, subaqueous debris flows triggered by episodic movements of border‐faults dominate the sedimentation. During tectonically quiescent stages, hyperpycnal flows generated by seasonal rainfall‐generated floods, normal discharges of mountain‐derived rivers and deep‐lacustrine suspension sedimentation are commonly present. The results of a series of flume tank depositional simulations show that the sediments deposited by subaqueous debris flows are wedge‐shaped and non‐channelized, whereas the sediments deposited by hyperpycnal flows generated by sporadic floods from seasonal rainfall are characterized by non‐channelized, coarse‐grained lobate depositional bodies which switch laterally because of compensation sedimentation of hyperpycanal flows. The hyperpycnal‐flow‐deposited non‐channelized lobate depositional bodies can be divided into a main body and lateral edges. The main body can be further subdivided into a proximal part, middle part and frontal part. Normal mountain‐derived river‐discharge‐deposited sediments are characterized by thin‐bedded, fine‐grained sandstones and siltstones with a limited distribution range. Normal mountain‐derived river‐discharge‐deposited sediments and deep‐lacustrine mudstones are commonly eroded in the area close to boundary faults. A nearshore subaqueous fan can be divided into three segments: inner fan, middle fan and outer fan. The inner fan is composed of debrites and the proximal part of the main body. The middle fan consists of the middle part of the main body and lateral edges, normal mountain‐derived river‐discharge‐deposited fine‐grained sediments and deep‐lacustrine mudstones. The outer fan comprises the frontal part of the main body, lateral edges, and deep‐lacustrine mudstones. Based on the non‐channelized depositional model for nearshore subaqueous fans, criteria for stratigraphic subdivision and correlation are discussed and applied. 相似文献
18.
Ancient stream-dominated (‘wet’) alluvial fan deposits have received far less attention in the literature than their arid/semi-arid counterparts. The Cenozoic basin fills along the Denali fault system of the northwestern Canadian Cordillera provide excellent examples of stream-dominated alluvial fan deposits because they developed during the Eocene-Oligocene temperate climatic regime in an active strike-slip orogen. The Amphitheatre Formation filled several strike-slip basins in Yukon Territory and consists of up to 1200 m of coarse siliciclastic rocks and coal. Detailed facies analysis, conglomerate: sandstone percentages (C:S), maximum particle size (MPS) distribution, and palaeocurrent analysis of the Amphitheatre Formation in two of these strike-slip basins document the transition from proximal, to middle, to distal and fringing environments within ancient stream-dominated alluvial-fan systems. Proximal fan deposits in the Bates Lake Basin are characterized by disorganized, clast-supported, boulder conglomerate and minor matrix(mud)-supported conglomerate. Proximal facies are located along the faulted basin margins in areas where C:S = 80 to 100 and where the average MPS ranges from 30 to 60 cm. Proximal fan deposits grade into middle fan, channelized, well organized cobble conglomerates that form upward fining sequences, with an average thickness of 7 m. Middle fan deposits grade basinward into well-sorted, laterally continuous beds of normally graded sandstone interbedded with trough cross-stratified sandstone. These distal fan deposits are characteristic of areas where C:S = 20 to 40 and where the average MPS ranges from 5 to 15 cm. Fan fringe deposits consist of lacustrine and axial fluvial facies. Palaeogeographic reconstruction of the Bates Lake Basin indicates that alluvial-fan sedimentation was concentrated in three parts of the basin. The largest alluvial-fan system abutted the strike-slip Duke River fault, and prograded westward across the axis of the basin. Two smaller, coarser grained fans prograded syntaxially northward from the normal-faulted southern basin margin. Facies analysis of the Burwash Basin indicates a similar transition from proximal to distal, stream-dominated alluvial fan environments, but with several key differences. Middle-fan deposits in the Burwash Basin define upward coarsening sequences 50 to 60 m thick composed of fine-grained lithofacies and coal in the lower part, trough cross-stratified sandstone in the middle, and conglomerate in the upper part of the sequence. Upward-coarsening sequences, 90–140 m thick, also are common in the fan fringe lacustrine deposits. These sequences coarsen upward from mudstone, through fine grained, ripple-laminated sandstone, to coarse grained trough cross-stratified sandstone. The upward-coarsening sequences are basinwide, facies independent, and probably represent progradation of stream-dominated alluvial-fan depositional systems. Coal distribution in the Amphitheatre Formation is closely coupled with predominant depositional processes on stream-dominated alluvial fans. The thickest coal seams occur in the most proximal part of the basin fill and in marginal lacustrine deposits. Coal development in the intervening middle and distal fan areas was suppressed by the high frequency of unconfined flow events and lateral channel mobility. 相似文献
19.
扇三角洲沉积体系及其与油气聚集关系 总被引：23，自引：2，他引：21
扇三角洲沉积体系是断陷盆地中极为发育的一种沉积体系,主要由扇三角洲平原组合、扇三角洲前缘组合和前三角洲沉积构成,可识别出9种成因相。受沉积物供给速率、可容空间增长速率及盆缘断裂产状等因素控制可划分出退积型、加积型、前积型、陡坡型和缓坡型5种扇三角洲类型。位于扇三角洲平原的辫状分流河道砂体及其位于扇三角洲前缘的与之有成因联系的水下分流河口坝、洪水型重力流砂体等物性好,可以构成优质储层。含油性勘探成果亦证实各主力油层段平面上主要分布于扇三角洲前缘及分流间湾区,小部分位于扇三角洲平原区。受埋藏深度和成岩场的影响,不同地区、不同层位主力油层段的物性与岩性相关性各异。因此,应用沉积体系分布与油气聚集规律挖掘剩余油层及进行远景区预测是有效的与可行的。 相似文献
20.
《Quaternary Science Reviews》2007,26(22-24):2883-2896
In the El Minia district of northern Upper Egypt, the Pleistocene deposits of the Nile Valley include (?)Early Pleistocene conglomerates of the Armant Formation and (?)Middle Pleistocene sands of the Qena Formation. These sediments are exposed along both sides of the valley in terraces at different heights, unconformably overlying Eocene limestones. Field observations suggest that the conglomerate facies of the Armant Formation was deposited in proximal and mid-alluvial fans. The sands of the Qena Formation are differentiated into two facies: a cross-bedded sandstone, representative of alluvial fan—braided stream environments, and a facies of sand interbedded with mud that may have been deposited by a meandering river. The heavy minerals of the Armant Formation are markedly different from those of the Qena Formation, suggesting derivation from different sources. Surface textures of quartz grains from the Qena sands, observed by SEM, exhibit chemical features, attributed to a fluviatile origin. Sand from the Armant Formation is characterized by mechanical and chemical surface textural features that suggest original aeolian derivation followed by later fluvial sedimentation. 相似文献