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Hyperpycnal-fed turbidite lobe architecture and recent sedimentary processes: A case study from the Al Batha turbidite system, Oman margin 总被引：3，自引：0，他引：3
J. Bourget S. Zaragosi J.-L. Schneider A. Van Toer N. Ellouz-Zimmermann 《Sedimentary Geology》2010,229(3):144-159
The main sediment depocenter along the Oman margin is the Al Batha turbidite system that develops in the Gulf of Oman basin. It is directly connected to the wadi Al Batha, and forms a typical sand and mud rich point source system that acts as regional sediment conduit and feeds a ~ 1000 km2 sandy lobe.The Al Batha lobe depositional architecture has been investigated in detail using very high-resolution seismic, multibeam echosounder data and sediment cores. Several scales of depositional architecture can be observed. The Al Batha lobe is composed of several depositional units, made of stacked elementary sediment bodies (thinner than 5 m) that are each related to a single flow event. The lobe is connected to the feeder system through a channel-lobe transition zone (CLTZ) that extends on more than 25 km. The lobe can be divided into proximal, middle and distal lobe areas. The proximal lobe is an area of erosion and by-pass with small axial feeder channels that rapidly splay into several small distributaries. They disappear in the mid-lobe area where deposits consist of vertically stacked tabular to lens-shaped sediment bodies, with a lateral continuity that can exceed 10 km. The distal lobe fringe shows a classical facies transition towards thin-bedded basin plain deposits.Sub-surface deposits consist of sandy turbidites and hyperpycnites, interbedded with fine-grained deposits (thin turbidites, hyperpycnites, or hemipelagites). Although these distal deposits are mainly related to flow transformations and concentration evolution, they highlight the importance of flooding of the wadi Al Batha on the sediment transfer to the deep basin. The thick sandy hyperpycnites recovered in such a distal area are also possibly related to the initial properties of gravity flows, in relation to the flooding characteristics of mountainous desert streams.Finally, the Al Batha lobe depositional architecture is typical of sand-rich lobes found within “small”, sand and mud rich turbidite systems fed by mountainous “dirty” rivers. Turbidite sedimentation in the Al Batha system appears to be primarily controlled by the strong climatic and geomorphic forcing parameters (i.e. semi-arid environment with ephemeral, mountainous rivers subjected to flash-flooding). 相似文献
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The Liard Lobe formed a part of the north‐eastern sector of the Cordilleran Ice Sheet and drained ice from accumulation areas in the Selwyn, Pelly, Cassiar and Skeena mountains. This study reconstructs the ice retreat pattern of the Liard Lobe during the last deglaciation from the glacial landform record that comprises glacial lineations and landforms of the meltwater system such as eskers, meltwater channels, perched deltas and outwash fans. The spatial distribution of these landforms defines the successive configurations of the ice sheet during the deglaciation. The Liard Lobe retreated to the west and south‐west across the Hyland Highland from its local Last Glacial Maximum position in the south‐eastern Mackenzie Mountains where it coalesced with the Laurentide Ice Sheet. Retreat across the Liard Lowland is evidenced by large esker complexes that stretch across the Liard Lowland cutting across the contemporary drainage network. Ice margin positions from the late stage of deglaciation are reconstructed locally at the foot of the Cassiar Mountains and further up‐valley in an eastern‐facing valley of the Cassiar Mountains. The presented landform record indicates that the deglaciation of the Liard Lobe was accomplished mainly by active ice retreat and that ice stagnation played a minor role in the deglaciation of this region. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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The glacial geomorphology of the Waterville Plateau (ca. 55 km2) provides information on the dynamics of the Okanogan Lobe, southern sector of the Cordilleran Ice Sheet in north‐central Washington. The Okanogan Lobe had a profound influence on the landscape. It diverted meltwater and floodwater along the ice front contributing to the Channeled Scabland features during the late Wisconsin (Fraser Glaciation). The glacial imprint may record surge behaviour of the former Okanogan Lobe based on a comparison with other glacial landsystems. Conditions that may have promoted instability include regional topographic constraints, ice marginal lakes and dynamics of the subglacial hydrological system, which probably included a subglacial reservoir. The ice‐surface morphology and estimated driving stresses (17–26 kPa) implied from ice thickness and surface slope reconstructed in the terminal area also suggest fast basal flow characteristics. This work identifies the location of a fast flowing ice corridor and this probably affected the stability and mass balance of the south‐central portion of the Cordilleran Ice Sheet. Evidence for fast ice flow is lacking in the main Okanogan River Valley, probably because it was destroyed during deglaciation by various glacial and fluvial processes. The only signature of fast ice flow left is the imprint on the Waterville Plateau. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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This study integrates newly acquired stratigraphic data, geologic mapping, and paleocurrent data to constrain the stratigraphic evolution of the oldest channel-lobe complex in the Upper Cretaceous Cerro Toro Formation in the Silla Syncline area of the Magallanes Basin, termed the Pehoe member. The Pehoe member ranges in thickness from 60 m in the north to at least 410 m farther down system and comprises three separate divisions (A, B, and C). A lower conglomerate unit and an upper one, termed Pehoe A and C divisions respectively, represent the fill of major incised submarine channels or channel complexes. These are separated by stratified sandstone of the Pehoe B division, representing a weakly confined lobe complex, either transient or terminal.The integration of new data with observations from previous studies reveal that the three main coarse-grained conglomerate and sandstone members in the Cerro Toro Formation in the Silla Syncline include at least seven distinct submarine channels or channel complexes and two major lobe complexes. The thinning and disappearance of these units along the eastern limb of the syncline reflect confinement of the flows to a narrow trough or mini-basin bounded to the east by a topographic high. This confinement resulted in unidirectional paleocurrents to the south and southeast in all deposits. Changes in depositional geometries are interpreted as reflecting changes in sediment supply and relative confinement. Submarine channels were from 700 m to 3.5 km wide and occupied a fairway that was 4-5 km wide. Flows moving south and southeast in this mini-basin probably crossed the eastern topographic high south of the present exposures and joined those moving southward along the axis of the foreland basin at least 16 km to the east. 相似文献
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Subaqueous sediment gravity flow is the volumetrically most important process transporting sediment across our planet, which forms its largest sediment accumulations (submarine fan). Based on the previous studies, we tried to clear up the concept, classification and identification of subaqueous sediment gravity flow, and introduced the progress of modern direct observation and submarine fan model. Turbidity current and debris flow are two of the most important parts of the gravity flow, the former deposits layer by layer with normal gradation while the latter is en masse settling with chaotic disorder. The turbidity current transformed into the debris flow during the transportation is called hybrid flow. The hyperpycnal flow is the turbidity current formed by flood discharges into the ocean/lake. Modern direct observations show that the turbidity current can contain dense basal layers and last for a week. The structure of turbidity current can be different from those surge-like turbidity current observed in laboratory. Submarine fans are mainly composed of channel, levee, lobe, background deposits and mass transport deposits, which should be studied by architecture analysis and hierarchical classification. The channel deposits extend narrowly with abundant erosion structures; levee deposits are composed of thin layer mud-silty turbidites, wedge thinning laterally; the lobe deposits extend well laterally with narrow range of grain size. The hierarchy of channel deposits is channel unit, channel complex and channel complex system. The hierarchy of lobe deposits is bed, lobe element, lobe and lobe complex. 相似文献
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现代黄河三角洲叶瓣的划分和识别 总被引：7，自引：0，他引：7
黄河分流河道摆动频繁,自1855年以来形成了8个三角洲叶瓣。1904-1929年的三角洲沉积物划归一个叶瓣较为合适。1934-1938年和1947-1964年也应该划归一个叶瓣。叶瓣活动时间短,平均活动时间只有16年。单个叶瓣形成的沉积物厚度有限。一个钻孔剖面上的三角洲沉积物常常分层于数个叶瓣。叶瓣废弃后改造时间短,还没有形成较粗的改造,沉积物便被新的叶瓣所覆盖。两个叶瓣的界线不很清楚。但根据沉积结构和构造,微体化石,210pb测年方法,土壤层以及历史记录,可以识别出不同的叶瓣。 相似文献
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The role of internal and external forcing of sedimentation in turbidite systems remains a subject of debate. Here we propose new insights from the quantitative analysis of architectural parameters of the Congo Axial Fan.Fifty-two channel-levee-lobe systems, spanning the last ca. 200 ka, are visible on the seafloor, most of them having slightly elongated lobe complexes at their termination. Volumes of lobe complexes (usually 3–196 km3) are highly variable in time and space. The cumulative volume of the lobe complexes represents approximately 30% of the volume of the Axial Fan.The Axial Fan is sequentially divided into periods of increasing/decreasing channel lengths and basinward/landward migrations of avulsion points, representing successive prograding/retrograding architectural patterns called architectural cycles. These cycles are either symmetrical saw toothed and bell-shaped with progressive progradation and retrogradation phases, or asymmetrical, with long-lasting progradation phases and abrupt retrogradation phases that correspond to channel avulsions occurring high up on the fan.Our study points to the interplay between internal and external factors controlling the architecture of the Congo Axial Fan. The local topographic constraint is a major factor in the fan's stacking pattern. However, cyclic evolution of the architecture reveals major shifts in the deposition site that are linked to very upfan avulsion events. These events are interpreted to be driven by external factors (e.g. climate and/or eustatic sea-level change) that were able to drastically increase and/or coarsen the sediment supply to the fan. 相似文献
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Loess has been recognized on the glacial land surface of the Green Bay Lobe for over 100 yr, but no systematic explanation of the source of the loess has been advanced. Intriguingly, the loess on the Green Bay Lobe land surface is thicker than predicted by regional thinning trends from the Mississippi Valley and is geographically separated from much loess of southwest Wisconsin by a sandy region devoid of loess. Mapping based on soil survey interpretation indicates that the loess occurs above an escarpment marking the eastern end of the sandy loess-free region. Particle size fining trends demonstrate that the loess was transported by northwesterly winds. Clay mineralogy of the Green Bay Lobe loess is distinctly different than glaciogenic sediments and matches loess of the Mississippi Valley, indicating a regional source and long distance transport of the loess. We propose the loess was transported from the regional source along a surface of transport produced by migration of eolian sand through low-relief landscapes including the glacial Lake Wisconsin basin. Eolian sand migration caused repeated entrainment of dust leading to east-southeastward transport. The loess accumulated above an escarpment that limited sand mobility and re-entrainment of loess beyond this topographic barrier. 相似文献