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Spatial and temporal variations in depositional systems in the Kazusa Group: insights into the origins of deep-water massive sandstones in a Pleistocene forearc basin on the Boso Peninsula, Japan
Progress in Earth and Planetary Science ( IF 3.9 ) Pub Date : 2020-08-09 , DOI: 10.1186/s40645-020-00343-1
Akihiko Takao , Keisuke Nakamura , Shinichi Takaoka , Masaya Fuse , Yohei Oda , Yasushi Shimano , Naohisa Nishida , Makoto Ito

A detailed chronostratigraphic framework established by the mapping of tephra key beds and application of oxygen isotopic data allows assessment of the synchroneity and diachroneity of depositional systems formed in coastal and deep-water environments. This framework also allows estimation of the timing of active delivery of coarse-grained sediments beyond the shelf margin in relation to relative sea-level changes. The depositional processes of deep-water massive sandstones (DWMSs) are still enigmatic; their formation is a result of active delivery of sands in association with the supply of organic carbon into deep-water environments. DWMSs are also important as reservoirs for hydrocarbon explorations. This study investigated the origins of DWMSs in the upper Umegase, Kokumoto, and Chonan formations (in ascending order) of the Pleistocene Kazusa Group on the Boso Peninsula, central Japan. Each formation contains several packets of DWMSs that are interpreted to have formed in response to the progradation of gravelly shelf-margin deltas or fan deltas during the falling and lowstand stages of relative sea-level changes controlled primarily by glacioeustasy. The development of DWMSs and associated sandstone beds is interpreted to have been induced by hyperpycnal flows, in association with sediment gravity flows that were initiated by breaching and/or collapse of sandy substrates on the shelf-margin deltas or fan deltas. The timings of the initial and final deposition of the packets vary within and between the formations, and are considered to have been controlled by the interaction between allogenic and autogenic processes operating in the gravelly shelf-margin deltas or fan deltas. A muddy horizon that contains the Lower–Middle Pleistocene Subseries boundary (the base of the Chibanian Stage) in the Kokumoto Formation is also underlain and overlain by the packets and represents a deposit formed in a condensed section in an upper slope environment. This depositional setting may have favored the development of the Global Boundary Stratotype Section and Point (GSSP) for the Lower–Middle Pleistocene Subseries boundary in the formation.


中文翻译:

Kazusa组沉积系统的时空变化:洞悉日本Boso半岛更新世前臂盆地深水块状砂岩的成因

通过对特弗拉关键层的映射和氧同位素数据的应用建立的详细的年代地层学框架,可以评估在沿海和深水环境中形成的沉积系统的同步性和双错性。该框架还允许估算相对于海平面的变化,主动输送超出大陆架边缘的粗粒沉积物的时间。深水块状砂岩(DWMS)的沉积过程仍然是个谜。它们的形成是与向深水环境中提供有机碳有关的,主动输送沙子的结果。DWMS作为油气勘探的储层也很重要。这项研究调查了在Umegase上国库本市的DWMS的起源,日本中部Boso半岛的更新世Kazusa组的Chonan地层(按升序排列)。每个地层均包含数个DWMS数据包,这些数据包被解释为在主要由冰川洋流控制的相对海平面变化的下降和低潮阶段,响应于​​砾石架缘三角洲或扇形三角洲的发展而形成。DWMSs和相关砂岩床的发展被解释为是由高温流引起的,与沉积物重力流有关,后者是由陆架三角洲或扇形三角洲上的砂质基质破裂和/或崩塌引发的。包的初始和最终存放时间在地层内部和地层之间有所不同,并且被认为是由在砾石层缘三角洲或扇形三角洲中进行的同种异体和自体过程​​之间的相互作用所控制。Kokumoto组中包含下-中更新世亚系列边界(Chibanian阶段的底部)的泥泞地层也被包裹层覆盖和覆盖,代表着在较高斜坡环境中的一个冷凝段中形成的沉积物。这种沉积环境可能有利于地层中下更新世亚系列边界的全球边界层型剖面和点(GSSP)的发展。Kokumoto组中包含下-中更新世亚系列边界(Chibanian阶段的底部)的泥泞地层也被包裹层覆盖和覆盖,代表着在较高斜坡环境中的一个冷凝段中形成的沉积物。这种沉积环境可能有利于地层中下更新世亚系列边界的全球边界层型剖面和点(GSSP)的发展。Kokumoto组中包含下-中更新世亚系列边界(Chibanian阶段的基础)的泥泞地平线也被包裹层覆盖和覆盖,代表了在上斜坡环境中的一个凝结部分中形成的沉积物。这种沉积环境可能有利于地层中下更新世亚系列边界的全球边界层型剖面和点(GSSP)的发展。
更新日期:2020-08-09
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