Non-uniform across-shelf variations in thickness, grain size, and frequency of turbidites in a transgressive outer-shelf, the Middle Pleistocene Kakinokidai Formation, Boso Peninsula, Japan
Non-uniform across-shelf variations in thickness, grain size, and frequency of turbidites in a transgressive outer-shelf, the Middle Pleistocene Kakinokidai Formation, Boso Peninsula, Japan
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DOI：
10.1016/j.sedgeo.2009.07.002
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发表时间：
2009-09-15
影响因子：
2.8
通讯作者：
Ito, Makoto
中科院分区：
文献类型：
--
作者：
Horikawa, Keiji;Ito, Makoto
从中更新世（约1000年）开始，研究了海侵外陆棚序列中砂岩层厚度、粒度和频率的跨陆棚变化。0.7日本房总半岛的Kakinokidai组。海侵沉积物一般为泥质，并含有滑塌和滑塌疤痕。夹层砂岩床被解释为已形成浊流作为一个响应的侵蚀和再悬浮的砂桥复杂的沉积物在西南部的上坡地区在风暴事件。火山灰层和海侵表面在该地层的基础上的映射允许详细的层间对比的外架砂岩层。尽管总体而言，砂岩层的厚度、粒度和频率沿下坡方向减小，但某些砂岩层局部变薄并变粗，与周围泥质沉积物中的滑塌疤痕有关。这些砂岩层随后变粗变细，最后在更远的下坡区域变薄。除了砂岩层的局部变薄之外，砂岩层的频率在更远的离岸方向上先减小然后增大。从这一证据，我们得出结论，这些不均匀的模式，在厚度，粒度和频率的砂岩层的跨外大陆架的变化是由当地增加流速和随后的扩展和降低速度的浊流，沿着与当地增加海底梯度，这是由海侵外大陆架地板滑塌疤痕的发展。这些地文特征的外架被解释为不允许单调的下坡变薄和细化的砂岩床，与床形模型的消耗浊流和与邻近的趋势，从现代和古代的高位阶段的货架系统的货架砂岩。(C)2009 Elsevier B.V.保留所有权利。
Across-shelf variations in thickness, grain size, and frequency of sandstone beds in a transgressive outer-shelf succession were investigated from the Middle Pleistocene (ca. 0.7 Ma) Kakinokidai Formation on the Boso Peninsula, Japan. The transgressive deposits are generally muddy and contain slumps and slump scars. The intercalated sandstone beds are interpreted to have been formed from turbidity currents as a response to erosion and resuspension of sandridge-complex deposits in the southwestern upslope area during storm events. Mapping of volcanic ash beds and a transgressive surface in the base of the formation permits detailed bed-by-bed correlation of the outer-shelf sandstone beds. Although, overall, thickness, grain size, and frequency of sandstone beds decrease in the downslope direction, some sandstone beds locally thin out and coarsen in association with slump scars in the surrounding muddy deposits. These sandstone beds subsequently thicken and fine, and finally thin out in the farther downslope area. In addition to the local thinning of sandstone beds, the frequency of sandstone beds first decreases and then increases in the farther offshore direction. From this evidence, we concluded that these non-uniform patterns of across-outer-shelf variations in thickness, grain size, and frequency of sandstone beds were caused by the local increases in flow speeds and subsequent expansion and reduced speeds of turbidity currents, along with a local increase in the seafloor gradient that was induced by the development of slump scars in the transgressive outer-shelf floor. These physiographic features in the outer shelf are interpreted not to have permitted monotonous downslope thinning and fining of sandstone beds, compared with the bed-shape models of depletive turbidity currents and with the proximality trend of shelf sandstones from modern and ancient highstand-stage shelf systems. (C) 2009 Elsevier B.V. All rights reserved.