An Overview of Deep-water Turbidite Deposition
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摘要: 深水浊积岩通常发育在风暴浪基面以下、几十米至数千米的水体深度范围内。当沉积中心位于或接近陆架边缘时，浊流沉积系统往往最为活跃，而且通常与相对海平面下降时期的低位体系域有关。深水沉积事件可细分为低位域早期和低位域晚期。低位域早期以规模不断增大和更频繁的流体（浊流）事件为特征；而低位域晚期则以规模逐渐变小且频率降低的流体（浊流）事件为特征。因此，在低位域早期，流体流量不断增大，水道以侵蚀并逐渐变深为主，仅能残存较少的沉积物。随后，在低位域晚期，流体流量逐渐变小，因而水道内的沉积填充物可以得以保存。浊流体系通常发育3个特征迥异的区域：区域1对应浊流体系的近端（上游），以支流峡谷为特征；区域2为浊流体系的中间部分，以单一补给水道复合体系为特征，因浊流水体的高度比补给水道高，因而常常发育天然堤沉积；区域3为浊流体系的远端，以频繁的决口、砂质溢岸以及水道充填为特征，从地貌学上可以将其描述为末端扇，从沉积过程来看，可将其称为前缘分散体系。从层序地层学的角度来看，低位域沉积常常夹持于富泥的远端高位域和海侵体系域沉积之间。低位域早期—晚期沉积序列往往是以富砂的区域3末端扇沉积被区域2水道—天然堤沉积所覆盖为特征。Abstract: Deep-water turbidites commonly are deposited in water depths below storm wave base. These depths range from a few tens of meters to thousands of meters. Turbidite systems tend to be most active when depocenters lie at or near shelf margins,and this proximity of depocenters to shelf margins tends to be associated most commonly with times of relative sea level lowstand. Deep water depositional episodes can be divided into early and late lowstand time. Deposition during early lowstand is characterized by progressively larger and more frequent flow events,whereas deposition during late lowstand is characterized by progressively smaller and less frequent flow events. Consequently,during early lowstand time,erosion of channels tends to dominate such that channels tend to become progressively deeper with minimal preservation of deposits within feeder channels;successive flows are overfit. Subsequently during late lowstand progressively smaller flows tend to be underfit resulting in preservation of channel fill deposits. Turbidite systems tend to be characterized by three discrete regions:Region 1 corresponds to the most proximal reaches of turbidite systems dominated by canyons that commonly are tributive. Region 2 corresponds to that part of the turbidite system characterized by a single feeder channel complex that was characterized by flows with heights greater than confining walls,hence associated with levees. Region 3 corresponds to that part of the system distally, that is characterized by frequent avulsions and sand-prone overbank as well as channel-fill deposits,which can be described geomorphologically as a terminal fan. From a process perspective,Region 3 can be described as a frontal splay. From a sequence stratigraphic perspective,lowstand deposits commonly are bracketed by mud prone distal highstand and transgressive systems tract deposits. The succession of early to late lowstand deposition commonly is characterized by sand-rich Region 3 fan deposits overlain by leveed channel deposits of region 2.
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Key words:
- turbidity current /
- deep-water gravity flow /
- tributive canyon /
- feeder channel complex /
- levee /
- distributive channel /
- terminal fan /
- overview
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