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1.
This study provides an insight into the impact of probably the largest flood ever to have been identified in mainland Britain by examining new sedimentary evidence from the Auchteraw terrace, Fort Augustus, Scotland. Study of three sections reveals a succession consisting of: (1) sheet gravels; (2) large trough-shaped depressions infilled with cross-stratified sands and gravels; (3) smaller-scale, finer-grained cross-strata; and (4) sheet-like, occasionally channelized, bimodal sand and gravel beds. This study shows that both the sedimentology and morphology of the Auchteraw terrace are consistent with jökulhlaup deposition and reveal a greater variety of lithofacies types than identified in previous studies of jökulhlaups from ice-dammed lakes. The fine-grained nature of the sediment discussed in this study emphasizes the importance of sediment supply for the formation of distinctive jökulhlaup successions. The sedimentary evidence recorded here provides a valuable tool for the interpretation of the magnitude and frequency of proglacial meltwater flows associated with Pleistocene ice sheets worldwide.  相似文献   

2.
The Kverkfjöll sandur in north Iceland is the furthest upstream of a suite of fluvial landforms extending for 200 km along the Jökulsá á Fjöllum river. Incision of the sandur exposes over 3 km of sedimentary sections, up to 15 m in height. A sandur wide, well-bedded succession of matrix-rich cobble-gravel and pebble/granule gravel, with individual beds 0.2 to 0.5 m thick indicates that the sandur is primarily the product of sandur-wide sheet-floods, with sediment-rich hyperconcentrated flows and also some debris flows and channelised turbulent flows. This interpretation is evidenced by bedded hyperconcentrated flow deposits occurring as laterally extensive tabular depositional units that dominate the entire sandur, reflecting the unconfined nature of the flow. Clast-supported boulder-gravel units interpreted as the product of macroturbulent flow occur in relatively narrow, but deep channels. The sedimentary succession is interpreted as the product of at least six volcanically generated catastrophic outburst floods (jökulhlaups) during the Little Ice Age. The sedimentology of these Little Ice Age flood deposits, on a small, high-gradient sandur, contrasts strongly with the deposits of volcanically-generated jökulhlaups on large, low-gradient coastal sandar, and sandar associated with retreating glaciers which have been the basis for most previous models of jökulhlaup sedimentation.  相似文献   

3.
Land‐terminating parts of the west Greenland ice sheet have exhibited highly dynamic meltwater regimes over the last few decades including episodes of extremely intense runoff driven by ice surface ablation, ponding of meltwater in an increasing number and size of lakes, and sudden outburst floods, or ‘jökulhlaups’, from these lakes. However, whether this meltwater runoff regime is unusual in a Holocene context has not been questioned. This study assembled high‐resolution topographical data, geological and landcover data, and produced a glacial geomorphological map covering ~1200 km2. Digital analysis of the landforms reveals a mid‐Holocene land‐terminating ice margin that was predominantly cold‐based. This ice margin underwent sustained active retreat but with multiple minor advances. Over c. 1000 years meltwater runoff became impounded within numerous and extensive proglacial lakes and there were temporary connections between some of these lakes via spillways. The ice‐dams of some of these lakes had several quasi‐stable thicknesses. Meltwater was apparently predominantly from supraglacial sources although some distributary palaeochannel networks and some larger bedrock palaeochannels most likely relate to mid‐Holocene subglacial hydrology. In comparison to the geomorphological record at other Northern Hemisphere ice‐sheet margins the depositional landforms in this study area are few in number and variety and small in scale, most likely due to a restricted sediment supply. They include perched fans and deltas and perched braidplain terraces. Overall, meltwater sourcing, routing and the proglacial runoff regime during the mid‐Holocene in this land‐terminating part of the ice sheet was spatiotemporally variable, but in a manner very similar to that of the present day.  相似文献   

4.
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   

5.
The Late Westphalian to Artinskian glaciomarine deposits of the Karoo and Kalahari basins of southern Africa consist of massive and stratified diamictite, mudrock with ice-rafted material, sandstone, silty rhythmite, shale and subordinate conglomerate forming a cyclic succession recognizable across both basins. A complete cycle comprises a resistant basal unit of apparently massive diamictite overlain by softer, bedded stratified diamictite, sandstone and mudrock with a total thickness of as much as 350 m. Four major cycles are observed each separated by bounding surfaces. Lateral facies changes are present in some cycles. The massive diamictites formed as aprons and fans in front of the ice-grounding line, whereas the stratified diamictites represent more distal debris-flow fans. The sandstones originated in different environments as turbidite sands, small subaqueous outwash channel sands and delta front sands. The rhythmites and mudrock represent blanket deposits derived from turbid meltwater plumes. Cycles represent deglaciation sequences which formed during ice retreat phases caused by eustatic changes in the Karoo and Kalahari basins. Evidence for shorter-term fluctuation of the ice margin is present within the major advance-retreat cycles. Hardly any sediment was deposited during lowstand ice sheet expansion, whereas a deglaciation sequence was laid down during a sea-level rise and ice margin retreat with the volume of meltwater and sediment input depending on temporary stillstands of the ice margin during the retreat phase. The duration of the cycles is between 9 and 11 Ma suggesting major global tectono-eustatic events. Smaller cycles probably linked to orbital forcing were superimposed on the longer-term events. A sequence stratigraphic approach using the stacking of deglaciation sequences with the ice margin advance phases forming bounding surfaces, can be a tool in the framework analysis of ancient glaciomarine basin fills.  相似文献   

6.
Anastomosing river plains of the Channel Country, central Australia, have aggraded slowly over the past 100 ka. Channel sediments accumulate mainly as accretionary benches of mud and sand, sandy channel-base sheets and vegetation-shadow deposits. The channels are laterally stable and the sediments have aggraded locally against erosional banks of tough floodplain muds. Channel sediments are profoundly affected by desiccation during dry periods and by bioturbation caused by within-channel trees and burrowing invertebrates, especially crayfish. Excavations show that mud-dominated channel bodies of low width:thickness ratio are generated by a combination of vertical and lateral accretion. Levees and braided surfaces, composed mainly of mud aggregates, border the channels and are activated during valley-wide floods which lay down distal mud sheets. Floodplain muds are converted to vertisols with gilgai, deep desiccation cracks, and impregnations of carbonate and gypsum. A fixed-channel facies model is applicable to the Channel Country river deposits. Anastomosis apparently results from the need for the system to move large volumes of water and moderate sediment loads across low-gradient interior basins.
Channels distant from upland source areas receive an abundant supply of pedogenic, sand-sized mud aggregates generated on adjacent floodplains and reworked into braid bars during valley-wide floods. Some quartz sand is provided from excavation of subsurface Pleistocene sands in deep channels and waterholes and from aeolian dunes on the floodplains. Adjacent gibber plains supply some gravel to the system.  相似文献   

7.
Aeolian dune fields characterized by partly vegetated bedforms undergoing active construction and with interdune depressions that lie at or close to the water table are widespread on Skei?arársandur, Southern Iceland. The largest aeolian dune complex on the sandur covers an area of 80 km2 and is characterized by four distinct landform types: (i) spatially isolated aeolian dunes; (ii) extensive areas of damp and wet (flooded) interdune flat with small fluvial channels; (iii) small aeolian dune fields composed of assemblages of bedforms with simple morphologies and small, predominantly damp, interdune corridors; and (iv) larger aeolian dune fields composed of assemblages of complex bedforms floored by older aeolian dune deposits that are themselves raised above the level of the surrounding wet sandur plain. The morphology of each of these landform areas reflects a range of styles of interaction between aeolian dune, interdune and fluvial processes that operate coevally on the sandur surface. The geometry, scale, orientation and facies composition of sets of strata in the cores of the aeolian dunes, and their relationship to adjoining interdune strata, have been analysed to explain the temporal behaviour of the dunes in terms of their mode of initiation, construction, pattern of migration, style of accumulation and nature of preservation. Seasonal and longer‐term flooding‐induced changes in water table level have caused episodic expansion and contraction of the wet interdune ponds. Most of the dunes are currently undergoing active construction and migration and, although sediment availability is limited because of the high water table, substantial aeolian transport must occur, especially during winter months when the surface of the wet interdune ponds is frozen and sand can be blown across the sandur without being trapped by surface moisture. Bedforms within the larger dune fields have grown to a size whereby formerly damp interdune flats have been reduced to dry enclosed depressions and dry aeolian system accumulation via bedform climb is ongoing. Despite regional uplift of the proximal sandur surface in response to glacial retreat and unloading over the past century, sediment compaction‐induced subsidence of the distal sandur is progressively placing aeolian deposits below the water table and is enabling the accumulation of wet aeolian systems and increasing the likelihood of their long‐term preservation. Wet, dry and stabilizing aeolian system types all co‐exist on Skei?arársandur and the dunes are variously undergoing coeval construction, accumulation, bypass, stabilization and destruction as a result of interactions between localized factors.  相似文献   

8.
The Drawa sandur, which is the largest, coarse‐grained sandur in Poland, dates from the Pomeranian phase of the Weichselian glaciation (c. 16 ka BP). Using Markov chain analysis we infer that five cycles and five rhythms occur in its proximal part. The cycles dominated by Gt and St lithofacies in the lower part of the sandur succession and by a GDm lithofacies in the upper part, are fining‐upward cycles deposited in braided channels during large ablation floods. Three groups of cycles are distinguished based on their genesis: (i) cycles due to channel‐sheet evolution during large floods; (ii) cycles due to braid‐bar development during initial and advanced diminishing of floods; and (iii) cycles developed in the thalweg or interbar channels. The succession as a whole forms a large‐scale coarsening‐up megacycle (‘sandur megacycle’) which corresponds to a phase of ice‐sheet advance. Because the cyclicity was evident from Markov chain analysis of the sedimentary succession, we suggest that this statistical tool is valuable for reconstruction of glacifluvial sedimentary conditions, particularly as it can shed new light on the palaeogeographical development of sandar.  相似文献   

9.
During decay of the Cordilleran Ice Sheet, ˜13 000–10000 cal. yr BP, numerous ice-dammed, ribbon-shaped lakes developed within the moderately deep valleys of the Interior Plateau of British Columbia. We describe the pattern and characteristics of lake sediments within the Thompson Valley, propose a palaeoenvironmental model for glacial lakes Thompson and Deadman and explore their implications for the palaeogeography of Cordilleran Ice Sheet decay. Seventeen glaciolacustrine lithofacies are identified within deltas, subaqueous fans and lake-bottom beds. Sediments accumulated at high rates and by a diversity of sediment dispersal and depositional processes: hyperpycnal and surge-type turbidity currents, grain flows and debris flows. Megascale subaqueous failures (tens of metres thick) were facilitated by high sedimentation rates. The palaeoenvironmental model highlights: (i) high rates of basin infilling; (ii) the dominant role of tributary rivers, rather than valley-occupying ice, in delivering water and sediment to lakes; and (iii) the role of melt cycles, jökulhlaups and hyperpycnal flows in sediment delivery. These conditions, in combination with a lack of organics and a fining upward sequence in lake sediments, suggest that glacial lakes Thompson and Deadman were coeval with dwindling plateau ice.  相似文献   

10.
The Fiskarheden quarry, situated in NW Dalarna, central Sweden, reveals thick coarse‐grained sediments of Scott type facies association representing a sandur deposited in an ice‐proximal proglacial environment. Optically Stimulated Luminescence (OSL) dating of the sandur sediments suggests a pre‐Last Glacial Maximum (LGM) age. Most acquired ages are pre‐Saalian (>200 ka) and we regard each of these ages to represent non/poorly bleached sediment except for one small‐aliquot OSL age of 98±6 ka. This age comes from the top surface of an arguably well‐bleached sand bed deposited on the lee‐side of a braid‐bar, putting the sandur build‐up into the Early Weichselian. Large‐scale glaciotectonic structures show an imbricate thrust fan involving both ductile and brittle deformation. The deformation was from the WNW, which largely coincides with the formative trend of the predominating streamlined terrain and Rogen moraine tracts surrounding Fiskarheden. It is suggested that the deformation of the sandur sediments took place when the advancing glacier approached and pushed its own proglacial outwash sediment, during an ice‐marginal oscillation either at the inception of one of the Early Weichselian glaciations in the area, or during a general ice retreat amid a deglacial phase. The Fiskarheden sandur deposits are covered by a subglacial traction till deposited from the NE/NNE. This direction corresponds with younger streamlined terrain flowsets cross‐cutting the older NNW–SSE system and probably represents deglaciation in the area following the LGM. This study will add to the understanding of the formation and deformation of Pleistocene sandur successions and their relationship to past ice‐sheet behaviour.  相似文献   

11.
Philip M.   《Earth》2005,70(3-4):203-251
Proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies. Little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments. This paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective. The nature of the meltwater inputs can be characterised as low-magnitude–high-frequency, primarily controlled by ablation inputs from the source glacier, or high-magnitude–low-frequency, primarily controlled by ‘exceptional’ inputs. The most important high-magnitude–low-frequency inputs are catastrophic outburst floods, often referred to by the term jökulhlaup (Icelandic for glacier-burst). Glacier surges are an additional form of cyclical variation impacting the proglacial environment, which briefly alter the volumes and patterns of meltwater input. The sedimentary consequences of low-magnitude–high-frequency discharges are related to frequent variations in stage, the greater directional variability that sediment will record, and the increased significance of channel confluence sedimentation. In contrast, the most significant characteristics of high-magnitude–low-frequency flooding include the presence of large flood bars and mid-channel ‘jökulhlaup’ bars, hyperconcentrated flows, large gravel dunes, and the formation of ice-block kettle hole structures and rip-up clasts. Glacier surges result in a redistribution of low-magnitude–high-frequency processes and products across the glacier margin, and small floods may occur at the surge termination. Criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics. Studies of Quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record. Consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime, sediment supply, the pattern of glacier advance or retreat, and proglacial topography. A model of sandur development is suggested, which shows how discharge magnitude and frequency, in combination with sandur incision and aggradation (controlled by glacier advance and retreat) can control sandur stratigraphy.  相似文献   

12.
High-quality subsurface data provide new insights into the formation of Oak Ridges Moraine (ORM), an ~80 km3 sequence of stratified meltwater deposits resting >200 m above adjacent Lake Ontario. The ORM sedimentary succession comprises a three-part regional architecture: (i) ~north–south channel sand–gravel; (ii) channel-capping rhythmites; and (iii) east–west ridge sediments. The ORM depositional sequence overlies a regional unconformity with a cross-cutting channel network resulting from ~north–south meltwater floods that transitioned progressively (falling stage) from a ~NNE to ENE flow direction (parallels Lake Ontario depression). Seismic profiles delineate the channels and channel fill characteristics of bank-to-bank channel sedimentation of thick gradational gravel–sand–mud sequences. Channel-capping mud (~100–236 rhythmites) within multiple channels beneath the ORM landform mark a widespread interval of low-energy, seasonally controlled subglacial pond deposition. During this quiescent period ice-sheet thickness adjusted to flood-induced stretching/thinning and re-profiled slopes. New ice gradients led to east–west flow and deposition of the overlying third element, a sequence of high-energy confined esker–fan sediments along ORM ridge. Close, sequential timing (~329 varve years) of channel, basin and ridge-forming architectural elements supports naming this assemblage the ORM formation. Proposed ORM floods are analogous to Icelandic jökulhlaups based on the size, geometry and sedimentology. The observed rhythmite interval between flood events represents a short period (~236 years) of regional meltwater storage prior to east–west ORM flooding. The ORM channel and overlying esker-fan sediment ridge represent two closely timed meltwater drainage events rather than formation by coalescing ice streams. The scale and timing of the ORM flood events are linked to rapid sea-level rise, ~13.5 ka BP. This high-resolution ORM sedimentological record may provide insights into depositional and glaciogenic controls of other large, stratified moraines. The ORM data indicate deposition in response to hydrodynamic events (outbreak floods, re-profiled ice) rather than direct climate forcing.  相似文献   

13.
Glacial outburst floods or ‘jökulhlaups’ are a key part of deglaciation of both alpine mountains and of ice sheet margins. They produce widespread and intense landscape change through erosion and deposition and are a hazard to populations and infrastructure. This article reviews these aspects with an emphasis on the current ‘state of play’ of research on the phenomena. Three case studies are presented: the 2010 Eyafjallajökull and 2007 Mt Ruapehu events, and the recent jökulhlaups in western Greenland. These illustrate that, where there is sufficient lead‐in time for the development of projects, the application of modern technology and of multi‐disciplinary research teams enables unprecedented acquisition quality, resolution and extent of data to be gained. These exciting data should enable development of new insights towards jökulhlaup impacts and flow phenomena.  相似文献   

14.
滕卫卫  王辉 《新疆地质》2021,(1):99-103
玛湖西部斜坡区二叠系乌尔禾组发育厚层砂砾岩储层,且油气储量巨大,但目前对于该套砂砾岩储层成因的认识尚不统一。在岩心、测井和地震资料分析的基础上,认为该区乌尔禾组发育冲积扇相和辫状河三角洲相。冲积扇分布在乌尔禾组下部,由于扇体不断前积,形成进积型冲积扇,纵向上沉积物粒度呈反韵律。辫状河三角洲相主要分布在乌尔禾组上部,划分为平原和前缘亚相,其中平原亚相以数层煤层和碳质泥岩为特征。乌尔禾组沉积过程为湖平面不断上升的过程,表现为由下部冲积扇相向上变为辫状河三角洲相。沉积相类型对储层物性具明显的控制作用,辫状河三角洲前缘储层物性较好,冲积扇储层物性较差。  相似文献   

15.
The classical model of trough mouth fan (TMF) formation was developed in the Polar North Atlantic to explain large submarine fans situated in front of bathymetric troughs that extend across continental shelves to the shelf break. This model emphasizes the delivery of large volumes of subglacial sediment to the termini of ice streams flowing along troughs, and subsequent re‐deposition of this glacigenic sediment down the continental slope via debris‐flow processes. However, there is considerable variation in terms of the morphology and large‐scale sediment architecture of continental slopes in front of palaeo‐ice streams. This variability reflects differences in slope gradient, the relative contributions of meltwater sedimentation compared with debris‐flow deposition, and sediment supply/geology of the adjacent continental shelf. TMF development is favoured under conditions of a low (<1°) slope gradient; a passive‐margin tectonic setting; abundant, readily erodible sediments on the continental shelf ‐ and thus associated high rates of sediment delivery to the shelf edge; and a wide continental shelf. The absence of large sediment fans on continental slopes in front of cross‐shelf troughs should not, however, be taken to indicate the former absence of palaeo‐ice streams in the geological record.  相似文献   

16.
The style of Pleistocene outwash sedimentation in the foreland of the central European Mountains (the Carpathians and Sudetes) was controlled to a large extent by the topography. The deposits of three outwash plains formed in various morphological situations in front of the Upper Odra Lobe during the Odranian glaciation (older Saalian) are described here to show the conditions of their development and to reveal the relation between outwash plain sedimentology and proglacial topography. One outwash plain was formed between the mountain front and the ice-sheet margin, which advanced into the zone of fore-mountain alluvial fans. This outwash, deposited parallel to the ice margin, was under the considerable influence of extraglacial rivers flowing from the mountains. The second outwash was deposited in a small valley dipping away from the ice sheet and successively buried by glaciofluvial sediments. It evolved from a narrow valley sandur to an unconfined outwash plain. The third one was formed in a relatively broad, dammed valley dipping towards the ice sheet, where proglacial lake base level controlled the pattern of outwash channels as well as the character of the sedimentation. The studied outwash plains have different sedimentary successions. Their sedimentary profiles differ from each other even in the neighbouring valleys, indicating that distinct depositional conditions existed at the same time in closely spaced areas. It is suggested that the glaciomarginal deposition was controlled mostly by the orientation of the valleys and the inter-valley areas relative to the ice-sheet front. Size and morphology of valleys and interfluves were also important. Depending on their orientation, the outwash plains were fed by meltwaters in various ways; the dip of their surfaces was markedly different and the dynamics of the proglacial river systems were diverse.  相似文献   

17.
通过对博格达山东北缘西大龙口剖面与水西沟剖面上二叠统进行详细观察和精细测量,详细分析了地层特征与沉积相特征,建立了沉积演化模式。结果表明:博格达山东北缘上二叠统自下而上发育泉子街组、梧桐沟组与锅底坑组;泉子街组沉积期,西大龙口剖面与水西沟剖面分别发育冲积扇、曲流河,冲积扇砂砾岩体内有大量的砂岩砾石与油页岩砾石,为博格达山周缘地区中二叠统红雁池组与芦草沟组被剥蚀后在山前沉积的产物;梧桐沟组沉积期,博格达山隆升为物源区,西大龙口剖面与水西沟剖面分别发育辫状河、曲流河,辫状河砂砾岩体内火山岩砾石较多;锅底坑组沉积期,西大龙口剖面与水西沟剖面主要发育曲流河泛滥平原,以紫红色粉砂质泥岩、泥岩为主。  相似文献   

18.
Extant models predict delta front environments down‐drift of river mouths as unfavourable for organisms because of the physico‐chemical stresses caused by sediment and fresh water influx. This study, however, finds evidence for near‐optimal living conditions down‐drift of contemporaneous mouth bars and distributary channels, as well as at the tops of abandoned lobes, in part of the asymmetrical ‘Notom Delta’ complex of the Ferron Sandstone (Turonian, south‐eastern Utah, USA). Presented herein is a sedimentological and ichnological model using thirty‐two detailed measured sections along a 16 km transect through two continuously exposed, ca 10 m thick allomembers containing delta front, mouth bar and distributary channel facies. Azimuths from sedimentary structures show south‐eastward deflection of near‐shore palaeocurrents relative to the inferred north–south shoreline, as well as minor reversal of flow. Two end‐member trace fossil suites are recognized in delta front sandstones: (i) a stressed suite of low abundance, low diversity, diminutive traces reflecting mobile deposit feeding, resting and locomotion behaviours; and (ii) a comparatively unstressed, high abundance, moderate diversity suite with a regular, heterogeneous distribution of deep, vertical or U‐shaped suspension‐feeding burrows which, in places, thoroughly homogenize the sandstones. The down‐drift side of the delta was colonized by suspension feeders during seasonal reversal of the seaway gyre when mud plumes were swept northward or when river‐derived nutrients were sufficiently concentrated relative to fresh water and sediment input. During normal seaway circulation, very high sedimentation rates and mud‐laden, wave‐dampened waters down‐drift of the river mouths heightened the preservation potential of the pervasively bioturbated facies. Up‐drift of the river mouths, these bioturbated facies were either not preserved or not developed until the lobe was abandoned. This alternative model for delta planform asymmetry contributes to the refinement of facies models for deltaic systems and provides a framework for predicting the distribution of bioturbation‐enhanced porosity and permeability in lobe‐deflected deltas.  相似文献   

19.
新疆中天山侏罗纪盆地群沉积演化   总被引：3，自引：0，他引：3       下载免费PDF全文
侏罗纪时中天山地区沉积盆地由伊-昭盆地，尤尔都斯盆地及焉-库盆地构成，其内沉积了一套厚度巨大的冲积和湖泊成因的碎屑岩沉积体，可识别出6种相类型。18种亚相及44种微相，早侏罗世至中侏罗世西山窑期，气候潮湿，植物繁盛，沼泽密布，形成多层煤层；中侏罗世头屯河期开始，气候变为干燥，下侏罗统三工河组及西山窑组中，辫状河和辫状河三角洲沉积发育，其砂体为好的储集体，下侏罗统八道湾组深湖-半深湖相黑色页岩及煤层是好的生油岩。  相似文献   

20.
Jasper Knight   《Sedimentary Geology》2003,160(4):291-307
Temporal changes in meltwater abundance, distribution and characteristics (controlling subglacial processes and ice sheet dynamics) can be inferred from subglacial sediment successions. Field evidence for changes in subglacial meltwater characteristics over time is presented from two sites (Doonan, Drummee) near a former late Weichselian (Devensian) ice centre in the north of Ireland. On a macroscale, both sites investigated show subglacial diamicton overlying glacially planated bedrock platforms. In more detail, primary sedimentary structures and facies variability show a complex relationship between depositional processes and meltwater characteristics at the ice/bed interface (IBI). Sedimentary evidence suggests sediment transport and deposition took place by low-viscosity subglacial slurries (mobile sediment–meltwater admixtures), which are part of a continuum between the processes of subglacial sediment deformation and subglacial meltwater flooding. Subtle changes in meltwater abundance and distribution at the IBI controlled slurry rheology, mechanisms of particle support and detailed sediment depositional processes.  相似文献   

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