The prosperity and decay and the three dimensional reconstruction of chemosynthetic autotrophic communities in shelf environments.

本研究的主要成果可分为以下三个部分。(1)对横滨市濑上更新世小芝组冷泉化能合成群落进行钻探,岩心长度共计100m,垂直于层理面高度约40m,平行于层理面宽度约20m。岩心岩相由大船组上部泥岩向小芝组下部泥砂岩向上变细。这一结果显然表明濑上的渗流持续了很长一段时间，群落发生在沉积旋回的退行阶段。岩心中部具有代表性的岩相，例如层理面的倾斜岩相边界，多个层位中大型双壳类（可能是 Lucinoma sp.）的破碎壳碎片，以及一些火山渣层完全用白色碳酸盐取代了其基质。这些岩相表明甲烷的爆炸性喷发，这被认为是在目前海底观察到的麻点痕迹的原因。(2)在宫崎县新富町发现了更新世冷泉化学合成群落。该群落出露南北方向100m，东西方向60m，厚度10m，呈向上变细、海退的顺序。(3)全新世结核，包括Conchocele sp。和/或Calyptogena sp。是在北海道稚内市附近发现的。结核中碳酸盐胶结物的 13C 耗尽表明这些群落依赖于甲烷渗漏。

The main results of this study can be divided into the following three parts.(1) A boring investigation, totally 100m in core length, for a cold-seep chemosynthetic community in the lower Plesitocene Koshiba Formation at Segami, Yokohama City indicates that it has about 40 m in height, normal for the bedding plane, and about 20 m in width, parallel for the bedding plane. The litho-facies of the core are of upward fining from mudstone, the upper part of the Ofuna Formation, to muddy sandstone, the lower part of the Koshiba Formation. This result evidently suggests that the seepage at Segami continued for a long period of time, and the community occurred in a regressive phase in the depositional cycle. The middle part of the core has a representative litho-facies, such as an oblique litho-boundary for the bedding plane, crashed shell fragments of large bivalves, probably Lucinoma sp., in several horizons, and a few scoria beds entirely replaced their matrix with white carbonates. These litho-facies suggest an explosive eruption of methane that has been considered to be a cause of pock marks observed on the present oceanic floor.(2) A Pleistocene, cold-seep chemosynthetic community is discovered from the Shintomi Town, Miyazaki Prefecture. This community is exposed in the range of 100m in N-S direction, 60m in E-W, and 10m in thickness, and occurs in the upward fining, regressive sequence.(3) Holocene concretions including Conchocele sp. and/or Calyptogena sp. are discovered from off Wakkanai City, Hokkaido. The depleted 13C of the carbonate cements of the concretions suggests that these communities were depended upon the methane seepage.