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251.
Turbidites deposited on Southern Central Chilean seamounts: Evidence for energetic turbidity currents 总被引:2,自引:0,他引:2
Gravity cores obtained from isolated seamounts located within, and rising up to 300 m from the sediment-filled Peru–Chile Trench off Southern Central Chile (36°S–39°S) contain numerous turbidite layers which are much coarser than the hemipelagic background sedimentation. The mineralogical composition of some of the beds indicates a mixed origin from various source terrains while the faunal assemblage of benthic foraminifera in one of the turbidite layers shows a mixed origin from upper shelfal to middle-lower bathyal depths which could indicate a multi-source origin and therefore indicate an earthquake triggering of the causing turbidity currents. The bathymetric setting and the grain size distribution of the sampled layers, together with swath echosounder and sediment echosounder data which monitor the distribution of turbidites on the elevated Nazca Plate allow some estimates on the flow direction, flow velocity and height of the causing turbidity currents. We discuss two alternative models of deposition, both of which imply high (175–450 m) turbidity currents and we suggest a channelized transport process as the general mode of turbidite deposition. Whether these turbidites are suspension fallout products of thick turbiditic flows or bedload deposits from sheet-like turbidity currents overwhelming elevated structures cannot be decided upon using our sedimentological data, but the specific morphology of the seamounts rather argues for the first option. Oxygen isotope stratigraphy of one of the cores indicates that the turbiditic sequences were deposited during the last Glacial period and during the following transition period and turbiditic deposition stopped during the Holocene. This climatic coupling seems to be dominant, while the occurrence of megathrust earthquakes provides a trigger mechanism. This seismic triggering takes effect only during times of very high sediment supply to the shelf and slope. 相似文献
252.
博兴洼陷油气勘探已进入隐蔽油气藏为主的勘探阶段,储集砂体的分布,尤其是能够形成地层岩性油藏的有利储集砂体的分布,是油气勘探的关键.研究区主要发育有浊积扇、辫状三角洲前缘和近岸水下扇三种类型的储集砂体,其中浊积扇扇体是岩性圈闭勘探的最有利砂体.通过已发现油气藏的地层位置分析,发现MSC8、MSC7、MSC6、MSC5、MSC2旋回的上升半旋回是有利储集砂体发育的主要层段,浊积扇砂体发育,且具有有利的油气成藏条件.平面上,MSC8旋回的有利储集砂体主要发育在高青断层东南侧的狭长区域内,MSC5、MSC6、MSC7旋回的有利储集砂体发育在坡折带之下的洼陷区.综合上述分析,预测了坡折带下部洼陷区、高青断裂下降盘和高24-高27井间区域3个岩性和构造-岩性圈闭勘探有利区. 相似文献
253.