共查询到20条相似文献，搜索用时 15 毫秒
1.
PATRICIA A. McCRORY 《Sedimentology》1995,42(2):223-247
The Neogene Humboldt (Eel River) Basin is located along the north-eastern margin of the Pacific Ocean within the Cascadia subduction zone. This sedimentary basin originated near the base of the accretionary prism in post-Eocene time. Subduction processes since that time have elevated strata in the south-eastern portion of the basin above sea level. High-resolution chronostratigraphic data from the onshore portion of the Humboldt Basin enable correlation of time-equivalent lithofacies across the palaeomargin, reconstruction of slope-basin evolution, and preliminary delineation of climatic and tectonic influence on lithological variation. Emergent basin fill is divided into five lithofacies which clearly document shoaling of the inner trench slope from deep-water environments in early Miocene time to paralic environments in Pleistocene time. The oldest strata consist of hemipelagic mudstones and minor debris-flow breccias deposited in a deep-water setting during elevated sea level. These strata are overlain by glauconite-rich, fine-grained turbidites which heralded an increasing influx of terrigenous detritus. Water depths shoaled earlier in the eastern basin area as the palaeoshoreline prograded seaward. Turbidite deposition ceased in the eastern basin area at about 2-2 Ma, whereas 22 km to the west, turbidite deposition continued until about 1-8 Ma. Lithofacies at the western study site change abruptly across a middle Pleistocene unconformity from outer shelf to paralic deposits. In the east, a more complete Pleistocene section records transition from outer to inner shelf, beach and fluvial environments. The Humboldt Basin lithofacies sequence is overprinted by eustatic control of sediment source. Comparison of sediment character with palaeoceanographic conditions indicates dominance of hemipelagic facies during periods of elevated sea level in the middle Miocene and early Pliocene when depocentres were isolated from terrigenous sediment. Glauconite-rich facies were mobilized from an upper slope setting following these periods of elevated sea level and redeposited in a deep-marine environment. Pleistocene shoreline lithofacies display glacio-esutatic control of depositional environment by recording several cycles of nearshore to fluvial progressions. General models of accretionary prism behaviour and trench-slope basin evolution are compatible with the overall coarsening-upward lithofacies sequence filling the Humboldt Basin. Early structural barriers precluded deposition of terrigenous material except from locally derived debris flows; subsequent shoaling and burial of deactivated thrust-folds enabled turbidity flows to reach the basin floor. However, late-stage tectonism apparently controlled the onset of coarse-grained deposition in this sequence. Significant sand-rich turbidite deposition began in the middle Pliocene, synchronous with tectonic uplift of the southern basin margin. Conversely, cessation of turbidite deposition in the eastern basin area in latest Pliocene time was synchronous with growth of anticlinal structures which again blocked widespread dispersal of turbidity flows. This middle Pliocene to Holocene period of crustal shortening is synchronous with continued reduction in spreading rate along the southern Juan de Fuca ridge, and probably reflects partial coupling between the subducting lithosphere and the overlying accretionary prism. 相似文献
2.
Mixed carbonate-siliciclastic sediment gravity flow deposits of Late Pennsylvanian to Early Permian age are exposed in the Death Valley - Owens Valley region of east-central California. The Mexican Spring unit constitutes the upper part of the Keeler Canyon Formation and is characterized by turbidites, debris flow deposits and megabreccias, all of mixed carbonate-siliciclastic composition. The mixed composition of the Keeler Canyon Formation provides an opportunity to link facies architecture to controls on depositional system development. Depositional relationships indicate that the deposits represent a non-channellized base of slope carbonate apron system with inner, outer and basinal facies associations. These gravity flow deposits are characterized by repeated stacked, small scale (<15 m) coarsening and thickening upward cycles with superimposed medium scale (>100 m) coarsening and thickening upward cycles. Contemporaneous outer shelf and upper slope deposits of the Tippipah Limestone are exposed at Syncline Ridge on the Nevada Test Site. The deposits consist of carbonate buildups directly overlain by cross bedded, quartz-rich sandstone and conglomerate which filled channels that traversed across the previously existing carbonate shelf. Detritus was transported to the west, down the upper slope by gully systems that fed the temporally persistent base of slope apron of the upper part of the Keeler Canyon Formation. This style of deposition differs from point-sourced siliciclastic submarine fan depositional systems. However, the Keeler Canyon system has lithofacies similar to some sandy siliciclastic turbidite systems, such as the delta-fed submarine ramp facies model, which is a line-sourced, shelf-fed system that is not supply limited. The mixed clastic apron systems of the Keeler Canyon Formation differ from classical carbonate aprons in that the former is characterized by an abundance of sedimentary cycles. Controls on the development of these cycles and of the facies distribution may have resulted from changes in type and rate of sediment supply, relative sea level changes and/or tectonic events. Interpretation of the data is focused on relative changes in sea level as the most significant control on development of the depositional system. Relative sea level changes serve two important functions: (1) they provide a mechanism for bringing coarse siliciclastic and bioclastic grains together on the outer shelf, and (2) shelf margin collapse may be initiated during relative lowstands allowing for transport of the sediment to the deep basin and development of deep basinal cycles. Therefore, an abundance of mixed clastic gravity flow deposits such as these in the rock record may be an indicator of periods of high frequency changes in relative sea level, which is a characteristic of Late Palaeozoic sea level history. 相似文献
3.
4.
Quaternary coastal lithofacies,sequence development and stratigraphy in a passive margin setting,North Carolina and Virginia,USA 总被引：3，自引：0，他引：3
PETER R. PARHAM STANLEY R. RIGGS STEPHEN J. CULVER DAVID J. MALLINSON W. JACK RINK KEVIN BURDETTE 《Sedimentology》2013,60(2):503-547
Lithofacies analysis is fundamental to unravelling the succession of depositional environments associated with sea‐level fluctuations. These successions and their timing are often poorly understood. This report defines lithofacies encountered within the north‐eastern North Carolina and south‐eastern Virginia Quaternary section, interprets their depositional environments, presents a model for coastal depositional sequence development in a passive margin setting and uses this understanding to develop the stratigraphy and Quaternary evolutionary history of the region. Data were obtained from numerous drill cores and outcrops. Chronology was based on age estimates acquired using optically stimulated luminescence, amino acid racemization, Uranium series and radiocarbon dating techniques. Geomorphic patterns were identified and interpreted using light detection and ranging imagery. Since lithofacies occurrence, distribution and stratigraphic patterns are different on interfluves than in palaeo‐valleys, this study focused on interfluves to obtain a record of highstand sea‐level cycles with minimal alteration by fluvial processes during subsequent lowstands. Nine primary lithofacies and four diagenetic facies were identified in outcrops and cores. The uppermost depositional sequence on interfluves exhibits an upward succession from shelly marine lithofacies to tidal estuarine lithofacies and is bounded below by a marine ravinement surface and above by the modern land surface. Older depositional sequences in the subsurface are typically bounded above and below by marine ravinement surfaces. Portions of seven depositional sequences were recognized and interpreted to represent deposition from late middle Pleistocene to present. Erosional processes associated with each successive depositional sequence removed portions of older depositional sequences. The stratigraphic record of the most recent sea‐level highstands (Marine Isotope Stage 5a and Marine Isotope Stage 3) is best preserved. Glacio‐isostatic adjustment has influenced depositional patterns so that deposits associated with late Quaternary sea‐level highstands (Marine Isotope Stages 5c, 5a and 3), which did not reach as high as present sea‐level according to equatorial eustatic records, are uplifted and emergent within the study area. 相似文献
5.
Debris flow deposits are the principal component of Quaternary continental slope sediments between the north-east Newfoundland Shelf and central Orphan Basin. In seismic profiles, these deposits occur as shingled, elongate, acoustically transparent lenses with their long axes orientated downslope. Deposits of individual flows form positive mounds on the sea floor; subsequent flows were diverted by the pre-existing topography into bathymetric lows between older debris flow deposits. These deposits show a large variation in the area of sea floor covered by individual flows (about 60–1000 km2), average thickness of deposits (9–37 m) and volume of sediment displaced (1–27 km3). The ratio of average thickness to a measure of deposit diameter, termed the aspect ratio, has a threefold variation from 0·0006 to 0·0021. Very low depositional slopes and low aspect ratios suggest relatively low viscosities, probably due to inmixing of water during downslope transport. Stratified sediments form three distinct horizons and are locally interbedded with the debris flow deposits. These are mainly hemipelagic deposits. The slope and rise to the west of the Orphan Basin are constructional in character. The apparent absence of upper slope erosional features and the abundance of debris flow deposits on the slope suggest that the supply of sediment to the continental slope occurred predominantly during times of maximum extent of Quaternary glacial ice. The ice sheet grounding line during several glacial maxima must have been situated at or near the present shelf break, supplying vast amounts of sediment directly to the upper slope. Oversteepening and subsequent slope failures fed material into deeper water. 相似文献
6.
Evolution of the Galicia Interior Basin over the last 60 ka: sedimentary processes and palaeoceanographic implications 
下载免费PDF全文
下载免费PDF全文 Anxo Mena Guillermo Francés Marta Pérez‐Arlucea Till J. J. Hanebuth Vera B. Bender Miguel A. Nombela 《第四纪科学杂志》2018,33(5):536-549
The Galicia Interior Basin (GIB; NW Iberian Peninsula) is located near a critical transition between the subtropical (temperate) and subpolar (cold) gyres of the North Atlantic. It therefore witnesses oceanographic changes driven by global climatic events. This study reports on the recent (latest Pleistocene) sedimentary, palaeoceanographic and palaeoclimatic history of the basin. We integrated analysis of deep‐sea sediment cores retrieved from an E–W transect across the GIB. The analysis indicated three types of sedimentary processes recording glacial (Marine Isotope Stage 2–4) and deglacial events: along‐slope bottom currents (forming contourite deposits), pelagic and hemipelagic sedimentation, and gravitational dislocation. Variation in depositional patterns and sedimentation rates indicate distinctive transport (along‐slope and down‐slope) and depositional processes. These in turn reflect climatic and oceanographic drivers. We interpret changes in sea level from core evidence showing changes in sediment supply. The cores exhibited conspicuous sedimentary evidence of Heinrich events (HEs). The stratigraphic intervals associated with HEs showed significant lateral variation. We suggest that the lateral variation may result from the development of an oceanographic boundary between surface water masses with different temperature and salinity parameters or changes in surface currents which may have introduced relatively warmer water into the GIB during the last glacial period. 相似文献
7.
Tectonic, eustatic and environmental controls on mid-Cretaceous carbonate platform deposition, south-central Pyrenees, Spain 总被引：2，自引：0，他引：2
Cenomanian–Turonian strata of the south‐central Pyrenees in northern Spain contain three prograding carbonate sequences that record interactions among tectonics, sea level, environment and sediment fabric in controlling sequence development. Sequence UK‐1 (Lower to Upper Cenomanian) contains distinct lagoonal, back‐margin, margin, slope and basin facies, and was deposited on a broad, flat shelf adjacent to a deep basin. The lack of reef‐constructing organisms resulted in a gently dipping ramp morphology for the margin and slope. Sequence UK‐2 (Upper Cenomanian) contains similar shallow‐water facies belts, but syndepositional tectonic modification of the margin resulted in a steep slope and deposition of carbonate megabreccias. Sequence UK‐3 (Lower to Middle Turonian) records a shift from benthic to pelagic deposition, as the shallow platform was drowned in response to a eustatic sea‐level rise, coupled with increased organic productivity. Sequences UK‐1 to UK‐3 are subdivided into lowstand, transgressive and highstand systems tracts based on stratal geometries and facies distribution patterns. The same lithologies (e.g. megabreccias) commonly occur in more than one systems tract, indicating that: (1) the depositional system responded to more than just sea‐level fluctuations; and (2) similar processes occurred during different times throughout sequence development. These sequences illustrate the complexity of carbonate platform dynamics that influence sequence architecture. Rift tectonics and flexural subsidence played a major role in controlling the location of the platform margin, maintaining a steep slope gradient through syndepositional faulting, enhancing slope instability and erosion, and influencing depositional processes, stratal relationships and lithofacies distribution on the slope. Sea‐level variations (eustatic and relative) strongly influenced the timing of sequence and parasequence boundary formation, controlled changes in accommodation and promoted platform drowning (in conjunction with other factors). Physico‐chemical and climatic conditions were responsible for reducing carbonate production rates and inducing platform drowning. Finally, a mud‐rich sediment fabric affected platform morphology, growth geometries (aggradation vs. progradation) and facies distribution patterns. 相似文献
8.
Naohisa Nishida Taku Ajioka Ken Ikehara Rei Nakashima Hajime Katayama Tomoyuki Sato Seishiro Furuyama Toru Tamura 《Sedimentology》2020,67(1):559-575
Sandy shelf sediments are important elements of clastic sedimentary systems because of their wide distribution in the geological record and their significance as hydrocarbon reservoirs. Although many studies have investigated shelf sediments influenced by waves or tidal currents, little is known about shelf sediments influenced by oceanic currents, particularly their lithofacies characteristics and stratigraphic evolution. This study investigated the stratigraphic evolution of shelf sediments off the Kujukuri strandplain facing the Pacific Ocean, which is influenced by the strong Kuroshio Current. Sediment cores were obtained from six locations on the Kujukuri shelf (34 to 124 m water depth) using a vibrocorer. The dominant lithofacies is mud-free sand with low-angle cross-lamination associated with alternating beds of finer and coarser sand with cross-lamination. These display depositional processes influenced by storm waves and the Kuroshio Current, respectively. This finding is consistent with the previously presented modern and historical observations of the Kuroshio Current and estimates of the storm-wave base. Radiocarbon dates show that the sediment succession formed during the last transgressive and highstand stages after 13·1 ka. The depositional processes during the stages represent a transition from storm waves with abundant sediment supply to both storm waves and the Kuroshio Current with sediment starvation mainly due to its trapping in the strandplain. Comparison to other Holocene–Modern shelf systems suggests that the sandy shelf successions are strongly influenced by oceanic currents under conditions of limited riverine input and open coastal geometry. The resultant sand-dominated succession is characterized by reversal of the proximal to distal grain-size trend compared to the fining for most other recognized wave/storm-dominated shelf successions. This is because of seaward increase in the influence of the Kuroshio Current. Thus, shelf deposits are naturally complex, and these may be further complicated by the additional influence of oceanic currents above the usual wave-dominated and tide-dominated end members. 相似文献
9.
Deep-water Depositional Features of Miocene Zhujiang Formation in Baiyun Sag,Pearl River Mouth Basin
Eleven lithofacies and five lithofacies associations were indentified in the Miocene Zhujiang Formation on the basis of detailed core analysis.It could be determined that three depositional types developed,namely submarine fan,basin and deep-water traction current.Six microfacies were further recognized within the fan,including main channels in the inner fan,distributary channels in the middle fan,inter-channels,levees and the outer fan.The lower Zhujiang Formation,mainly sandstone associations,was inner fan and inner-middle fan deposits of the basin fan and the slope fan. The middle part,mainly mudstone associations,was outer fan deposits.With the transgression,the submarine fan was finally replaced by the basinal pelagic deposits which were dominated by mudstone associations,siltstone associations,and deep-water limestone associations.During the weak gravity flow activity,the lower channels,the middle-upper outer fans and basin deposits were strongly modified by the deep-water traction current.The identification of the deep-water traction deposition in Miocene Zhujiang Formation would be of great importance.It could be inferred that the deep-water traction current had been existing after the shelf-break formation since the Late Oligocene (23.8 Ma) in the Baiyun sag,influencing and controlling the sediment composition,the distribution, and depositional processes.It would provide great enlightenment to the paleo-oceanic current circulation in the northern South China Sea. 相似文献
10.
南海盆地是东南亚陆缘最大的、含有丰富油气等资源的边缘海盆地.对于南海大陆斜坡带的发育、沉积演化与南海盆地构造作用及动力学过程的响应关系等方面缺乏深入认识.依据地震、测井及岩心等丰富资料,对南海珠江口盆地东南部陆架边缘斜坡带的层序地层、沉积-地貌演化及其对构造、海平面和沉积物供应变化的响应关系开展了系统性的研究.研究表明盆地的沉积充填可划分为由区域性不整合所限定的7个复合（二级）层序（CS1-CS7）.复合层序CS3-CS7（上渐新统-第四系）均由区域性的海侵-海退旋回构成;其内可进一步划分出由局部不整合或水退-水进的转换面为界的20个次级层序（三级）.研究识别出包括外陆架至陆架边缘三角洲、前三角洲-斜坡扇、陆架边缘前积体、单向迁移的横向底流-斜坡重力流复合水道、大型斜坡下切峡谷、泥质斜坡扇、斜坡滑塌泥石流复合体以及大规模软沉积物变形体等沉积体系或沉积复合体,它们在不同层序具有特定的时空分布,构成多种沉积样式.短周期（三级）的沉积旋回变化与Haq的海平面变化曲线总体上可对比,但长周期的海侵和海退则明显不同,受到了构造隆升和沉降等的控制.陆架边缘沉积演化可划分出裂后早期海底扩张沉积（破裂层序）、裂后晚期海底扩张沉积、后海底扩张等构造-沉积演化阶段.裂谷作用晚期的热隆起、构造差异沉降、裂后热衰减沉降以及上新世以后的东侧碰撞等对主要不整合的形成和海侵-海退产生了重要的影响.晚渐新世至中中新世发育的复合层序（CS3和CS4）记录了裂后海底扩张到停止的大陆斜坡沉积过程;而裂后早期的沉积层序（CS3）为破裂层序,以发育大型的陆架边缘三角洲-前三角洲斜坡扇体系构成的前积层为特征.气候变化和季风加强可能增强了晚渐新世-早中新世和更新世沉积期的沉积物供应,为大规模陆架边缘三角洲体系的发育提供了充足的物源供给.发育于陆架边缘的三角洲-滨岸碎屑体系和共生的前三角洲斜坡扇体系构成区内最重要的油气勘探对象. 相似文献
11.
Cross-platform architecture of a sequence boundary in mixed siliciclastic-carbonate lithofacies, Middle Cambrian, southern Great Basin, USA 总被引：1，自引：0，他引：1
Stratigraphic analysis of mixed siliciclastic-carbonate lithofacies within the Middle Cambrian Bonanza King Formation of the southern Great Basin reveals three distinct facies associations that record a range of depositional environments from semi-arid tidal flats to deeper subtidal, restricted lagoons. Stratigraphic trends, cross-platform facies variations and correlation of individual surfaces across 250 km of the study area suggest that these mixed lithofacies were deposited in three temporally distinct phases. (1) Extensive progradation of mixed peritidal environments culminated in a prolonged episode of subaerial exposure marked by an areally extensive intraclast breccia (0·5–1·2 m thick) that we interpret to be a major Type 1 sequence-bounding disconformity. (2) Abrupt flooding of the exposed platform resulted in the deposition of mixed deeper subtidal lithofacies, including a condensed interval of fissile, fossiliferous shale. (3) Progressive shallowing and aggradational accumulation was accompanied by a decrease in siliciclastics and a shift to pure carbonate deposition. Deep-water siliciclastics and megabreccias record deposition along the base-of-slope off the Middle Cambrian shelf-edge, and are interpreted to represent lowstand deposits emplaced during the prolonged episode of subaerial exposure of the shallow shelf. The presence of fine siliciclastics in both peritidal facies and sharply overlying deeper subtidal facies of the study interval within the Bonanza King suggests a variable, but relatively continuous, influx of terrigenous material throughout an extended period of accommodation change, apparently asynchronous with respect to the predictive model of reciprocal sedimentation. We suggest that the primary siliciclastic source changed with relative sea-level position. During lowered sea level, aeolian processes acting upon the unvegetated Cambrian craton transported fine siliciclastics onto peritidal and shallow-subtidal environments. During higher sea level, coastal siliciclastic reservoirs supplied sediment that was transported for long distances by geostrophic currents flowing along the submerged platform. As opposed to many Cambro-Ordovician grand cycles that are commonly interpreted to consist of a transgressive shaly half-cycle grading upward into a regressive carbonate half-cycle, the sequence boundary within this Middle Cambrian succession occurs within siliciclastic-rich, mixed lithofacies rather than in adjoining purer carbonates, implying that some ‘grand cycles’ should not be considered synonymous with ‘sequences’. Interbasinal correlations of the Type 1 sequence boundary within the mixed unit are speculative, primarily because of the inherent imprecision of available trilobite biostratigraphy. However, there is evidence that an extended episode of subaerial exposure may have been continent-wide during the Ehmaniella trilobite biochron. 相似文献
12.
Late Quaternary marine deposition in New South Wales and southern Queensland — An evolutionary model
From new data on coastal and continental shelf morphology, sediments, stratigraphy and chronology, it is possible to formulate a general model of late Quaternary marine sedimentation, for New South Wales and southern Queensland. This model integrates various factors influencing deposition in coastal and shelf environments, in relation to glacio‐eustatic sea level oscillations. The model involves several components, including (i) very slow to negligible continental margin subsidence during the Quaternary, (ii) an inherited geomorphic framework; (iii) oscillations of sea level of c 100 m amplitude every 100 000 years, with interglacial high sea levels being close to present and only the Last Interglacial being significantly higher; and (iv) a wave climate that induces a potential south to north littoral sand transport at all sea level positions. Terrigenous sediment that is moved from the hinterland through embayments to the shelf is either stored as barrier, estuarine or inner shelf deposits, or lost to depositional sinks on the continental slope or into coastal dune fields. Over many glacial‐interglacial cycles, sand has been progressively moved northward and has accumulated in vast aeolian sand deposits in southern Queensland. Littoral sand transport was especially effective during sea levels lower than present. The relatively shallow and lower gradient shelf north of Newcastle (33°S) has encouraged preservation at the coast of a wide range of depositional morphologies, including Pleistocene barriers, whereas the steeper southern shelf has induced net sediment loss seawards and shoreline erosion, excpt in the Holocene. To account for Holocene barrier development in the southern region, the model invokes reworking of sand deposits stranded high on the inner shelf at the end of the Pleistocene Epoch. These were in disequilibrium with Postglacial marine processes that operated at a lower level of the sea than did those during the Last Interglacial maximum. 相似文献
13.
利用多个地震数据体的地震反射特征,分析了孟加拉湾若开盆地深水沉积体系的不同沉积结构单元类型(峡谷、水道及水道复合体、天然堤—漫溢沉积、朵体以及块体搬运沉积)的典型地震响应特征、及其发育的位置,构建了研究区陆架—陆坡—盆底的沉积结构单元演化模式。研究表明,一个深水沉积体系垂向上自下而上的组合样式为:底部块体搬运沉积及厚层大规模朵体沉积,上覆水道复合体沉积,之后为水道—天然堤复合体沉积、以及一些小规模朵体沉积,顶部为薄层深海泥岩沉积。横向上自陆架向深海盆地的发育模式表现为:陆架/上陆坡峡谷—上陆坡侵蚀型水道—下陆坡侵蚀沉积型水道—沉积型水道—盆地朵体。 相似文献
14.
Mohammad Ali Kavoosi 《Geological Journal》2016,51(4):523-544
Upper Callovian to Tithonian (late Jurassic) sediments represent an important hydrocarbon reservoir in the Kopet‐Dagh Basin, NE Iran. These deposits consist mainly of limestone, dolostone, and calcareous mudstone with subordinate siliciclastic interbeds. Detailed field surveys, lithofacies and facies analyses at three outcrop sections were used to investigate the depositional environments and sequence stratigraphy of the Middle to Upper Jurassic interval in the central and western areas of the basin. Vertical and lateral facies changes, sedimentary fabrics and structures, and geometry of carbonate bodies resulted in recognition of various carbonate facies related to tidal flats, back‐barrier lagoon, shelf‐margin/shelf‐margin reef, slope and deep‐marine facies belts. These facies were accompanied by interbedded beach and deep marine siliciclastic petrofacies. Field surveys, facies analysis, parasequences stacking patterns, discontinuity surfaces, and geometries coupled with relative depth variation, led to the recognition of six third‐order depositional sequences. The depositional history of the study areas can be divided into two main phases. These indicate platform evolution from a rimmed‐shelf to a carbonate ramp during the late Callovian–Oxfordian and Kimmeridgian–Tithonian intervals, respectively. Significant lateral and vertical facies and thickness changes, and results obtained from regional correlation of the depositional sequences, can be attributed to the combined effect of antecedent topography and differential subsidence related to local tectonics. Moreover, sea‐level changes must be regarded as a major factor during the late Callovian–Tithonian interval. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
Anatomy of shelf deltas at the edge of a prograding Eocene shelf margin, Spitsbergen 总被引：1，自引：0，他引：1
Abstract Although shelf‐edge deltas are well‐imaged seismic features of Holocene and Pleistocene shelf margins, documented outcrop analogues of these important sand‐prone reservoirs are rare. The facies and stratigraphic architecture of an outcropping shelf‐edge delta system in the Eocene Battfjellet Formation, Spitsbergen, is presented here, as well as the implications of this delta system for the generation of sand‐prone, shelf‐margin clinoforms. The shelf‐edge deltas of the Battfjellet Formation on Litledalsfjellet and Høgsnyta produced a 3–5 × 15 km, shelf edge‐attached, slope apron (70 m of sandstones proximally, tapering to zero on the lower slope). The slope apron consists of distributary channel and mouth‐bar deposits in its shelf‐edge reaches, passing downslope to slope channels/chutes that fed turbiditic lobes and spillover sheets. In the transgressive phase of the slope apron, estuaries developed at the shelf edge, and these also produced minor lobes on the slope. The short‐headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf, and the shelf‐edge position of the discharging deltas, made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin. The abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion. Evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane‐parallel laminae within turbidite beds in the slope channels, and thick spillover lobes with repetitive alternations of massive and flat‐laminated intervals. The examined shelf‐edge to slope system, now preserved mainly below the shelf break and dominated by sediment gravity‐flow deposits, has a threefold stratigraphic architecture: a lower, progradational part, in which the clinoforms have a slight downward‐directed trajectory; a thin aggradational zone; and an upper part in which clinoforms backstep up onto the shelf edge. A greatly increased density of erosional channels and chutes marks the regressive‐to‐transgressive turnaround within the slope apron, and this zone becomes an angular unconformity up near the shelf edge. This unconformity, with both subaerial and subaqueous components, is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level. The studied shelf‐margin clinoforms accreted mostly during falling stage (sea level below the shelf edge), but the outer shelf later became estuarine as sea level became re‐established above the shelf edge. 相似文献
16.
《Journal of African Earth Sciences》2005,41(1-2):79-101
Integrated sedimentologic, macrofossil, trace fossil, and palynofacies data from Paleocene-Middle Eocene outcrops document a comprehensive sequence stratigraphy in the Anambra Basin/Afikpo Syncline complex of southeastern Nigeria. Four lithofacies associations occur: (1) lithofacies association I is characterized by fluvial channel and/or tidally influenced fluvial channel sediments; (2) lithofacies association II (Glossifungites and Skolithos ichnofacies) is estuarine and/or proximal lagoonal in origin; (3) lithofacies association III (Skolithos and Cruziana ichnofacies) is from the distal lagoon to shallow shelf; and (4) shoreface and foreshore sediments (Skolithos ichnofacies) comprise lithofacies association IV. Five depositional sequences, one in the Upper Nsukka Formation (Paleocene), two in the Imo Formation (Paleocene), and one each in the Ameki Group and Ogwashi-Asaba Formation (Eocene), are identified. Each sequence is bounded by a type-1 sequence boundary, and contains a basal fluvio-marine portion representing the transgressive systems tract, which is succeeded by shoreface and foreshore deposits of the highstand systems tract. In the study area, the outcropping Ogwashi-Asaba Formation is composed of non-marine/coastal aggradational deposits representing the early transgressive systems tract. The occurrence of the estuarine cycles in the Palaeogene succession is interpreted as evidence of significant relative sea level fluctuations, and the presence of type-1 sequence boundaries may well be the stratigraphic signature of major drops in relative sea level during the Paleocene and Eocene. Sequence architecture appears to have been tectono-eustatically controlled. 相似文献
17.
This study utilized three-dimensional exposures to evaluate how sea-level position and palaeotopography control the facies and geometries of heterozoan carbonates. Heterozoan carbonates were deposited on top of a Neogene volcanic substrate characterized by palaeotopographic highs, palaeovalleys, and straits that were formed by subaerial erosion, possibly original volcanic topography, and faults prior to carbonate deposition. The depositional sequence that is the focus of this study (DS1B) consists of 7–10 fining upward cycles that developed in response to relative sea-level fluctuations. A complete cycle has a basal erosion surface overlain by deposits of debrisflows and high-density turbidity currents, which formed during relative sea-level fall. Overlying tractive deposits most likely formed during the lowest relative position of sea level. Overlying these are debrites grading upward to high-density turbidites and low-density turbidites that formed during relative sea-level rise. The tops of the cycles consist of hemipelagic deposits that formed during the highest relative position of sea level. The cycles fine upward because upslope carbonate production decreased as relative sea level rose due to less surface area available for shallow-water carbonate production and partial drowning of substrates. The cycles are dominated by two end-member types of facies associations and stratal geometries that formed in response to fluctuating sea-level position over variable substrate palaeotopography. One end-member is termed ‘flank flow cycle’ because this type of cycle indicates dominant sediment transport down the flanks of palaeovalleys. Those cycles drape the substrate, have more debrites, high-density turbidites and erosion on palaeovalley flanks, and in general, the lithofacies fine down the palaeovalley flanks into the palaeovalley axes. The second end-member is termed ‘axial flow cycle’ because it indicates a dominance of sediment transport down the axes of palaeovalleys. Those cycles are characterized by debrites and high-density turbidites in palaeovalley axes, and lap out of strata against the flanks of palaeovalleys. Where and when an axial flow cycle or flank flow cycle developed appears to be related to the intersection of sea level with areas of gentle or steep substrate slopes, during an overall relative rise in sea level. Results from this study provide a model for similar systems that must combine carbonate principles for sediment production, palaeotopographic controls, and physical principles of sediment remobilization into deep water. 相似文献
18.
The Palaeoproterozoic Frere Formation (ca 1.89 Gyr old) of the Earaheedy Basin, Western Australia, is a ca 600 m thick succession of iron formation and fine‐grained, clastic sedimentary rocks that accumulated on an unrimmed continental margin with oceanic upwelling. Lithofacies stacking patterns suggest that deposition occurred during a marine transgression punctuated by higher frequency relative sea‐level fluctuations that produced five parasequences. Decametre‐scale parasequences are defined by flooding surfaces overlain by either laminated magnetite or magnetite‐bearing, hummocky cross‐stratified sandstone that grades upward into interbedded hematite‐rich mudstone and trough cross‐stratified granular iron formation. Each aggradational cycle is interpreted to record progradation of intertidal and tidal channel sediments over shallow subtidal and storm‐generated deposits of the middle shelf. The presence of aeolian deposits, mud cracks and absence of coarse clastics indicate deposition along an arid coastline with significant wind‐blown sediment input. Iron formation in the Frere Formation, in contrast to most other Palaeoproterozoic examples, was deposited almost exclusively in peritidal environments. These other continental margin iron formations also reflect upwelling of anoxic, Fe‐rich sea water, but accumulated in the full spectrum of shelf environments. Dilution by fine‐grained, windblown terrigenous clastic sediment probably prevented the Frere iron formation from forming in deeper settings. Lithofacies associations and interpreted paragenetic pathways of Fe‐rich lithofacies further suggest precipitation in sea water with a prominent oxygen chemocline. Although essentially unmetamorphosed, the complex diagenetic history of the Frere Formation demonstrates that understanding the alteration of iron formation is a prerequisite for any investigation seeking to interpret ocean‐atmosphere evolution. Unlike studies that focus exclusively on their chemistry, an approach that also considers palaeoenvironment and oceanography, as well the effects of post‐depositional fluid flow and alteration, mitigates the potential for incorrectly interpreting geochemical data. 相似文献
19.
The Upper Ordovician rocks of Hadeland, Norway, form a sequence of thin bedded nodular limestones (wackestones) and shales, hosting five distinctive sedimentary breccia complexes. These breccias contain blocks of varying sizes and shapes in a wackestone and grainstone matrix. Blocks differ in lithology, and in their included biotas and cement sequences. The thin bedded limestones are interpreted as turbidites, deposited against a background of hemipelagic calcareous shales. The breccias occupy channels cut into this sequence. The lithologies and biotas of blocks in the breccias record deposition in differing sedimentary environments, whereas their cements are the results of contrasting diagenetic histories. Blocks were eroded from a diverse and mature carbonate platform, close to sea level, which probably lay 5–10 km east of Hadeland. The breccias are interpreted as debris flow deposits, transported as channellized flows. Following channel cutting events, perhaps triggered by sea level change, channels were characterized by deposition rather than erosion. Wackestones and grainstones associated with the breccias also reflect resedimentation, their less diverse biota suggesting local derivation on the slope. The reworking of calcarenaceous muds locally produced clean washed calcarenites (now grainstones). A fall in sea level resulted in emergence of the upper slope and erosion of the debris flow complex to form caverns and fissures. As sea level rose again crinoidal calcarenites, now grainstones, were deposited within these cavities. Cement sequences in blocks record early marine and burial conditions on the shelf, and also precipitation of new marine cements following downslope transport. Those cements in lithologies formed in situ document later shallowing, culminating in emergence. The localized dissolution of cements in both blocks and associated grainstones reflects the infiltration of ‘aggressive’meteoric waters through permeable channel deposits. A subsequent rise in sea level is recorded in the generation of an additional marine cement with final burial reflected in the deposition of blocky calcite. The debris flow deposits therefore maintained their distinctive character from deposition through diagenesis. 相似文献
20.
NOEL P. JAMES CAROLYN H. EYLES† NICHOLAS EYLES‡ ERIC E. HIATT§ T. KURTIS KYSER 《Sedimentology》2009,56(2):367-397
Uplifted during the 1964 Alaskan earthquake, extensive intertidal flats around Middleton Island expose 1300 m of late Cenozoic (Early Pleistocene) Yakataga Formation glaciomarine sediments. These outcrops provide a unique window into outer shelf and upper slope strata that are otherwise buried within the south‐east Alaska continental shelf prism. The rocks consist of five principal facies in descending order of thickness: (i) extensive pebbly mudstone diamictite containing sparse marine fossils; (ii) proglacial submarine channel conglomerates; (iii) burrowed mudstones with discrete dropstone layers; (iv) boulder pavements whose upper surfaces are truncated, faceted and striated by ice; and (v) carbonates rich in molluscs, bryozoans and brachiopods. The carbonates are decimetre scale in thickness, typically channellized conglomeratic event beds interpreted as resedimented deposits on the palaeoshelf edge and upper slope. Biogenic components originated in a moderately shallow (ca 80 m), relatively sediment‐free, mesotrophic, sub‐photic setting. These components are a mixture of parautochthonous large pectenids or smaller brachiopods with locally important serpulid worm tubes and robust gastropods augmented by sand‐size bryozoan and echinoderm fragments. Ice‐rafted debris is present throughout these cold‐water carbonates that are thought to have formed during glacial periods of lowered sea‐level that allowed coastal ice margins to advance near to the shelf edge. Such carbonates were then stranded during subsequent sea‐level rise. Productivity was enabled by attenuation of terrigenous mud deposition during these cold periods via reduced sedimentation together with active wave and tidal‐current winnowing near the ice front. Redeposition was the result of intense storms and possibly tsunamis. These sub‐arctic mixed siliciclastic‐carbonate sediments are an end‐member of the Phanerozoic global carbonate depositional realm whose skeletal attributes first appeared during late Palaeozoic southern hemisphere deglaciation. 相似文献