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

本研究的主要结果可分为以下三个部分。(1)对横滨市Segami地区下上新世Koshiba组冷渗化学合成群落进行钻孔调查，岩心长度为100m，岩心高度约为40 m，与层理平面垂直，宽度约为20 m，与层理平面平行。岩心的岩相为由Ofuna组上部泥岩向Koshiba组下部泥质砂岩向上细化。这一结果表明，在较长一段时间内，塞伽米地区的渗流持续存在，群落处于沉积旋回的退退阶段。岩心中部具有代表性的岩相，如层理面有斜向岩相边界，若干层位有大型双壳类（可能为Lucinoma sp.）的破碎壳片，少数岩屑层完全被白色碳酸盐岩取代。这些岩相表明，甲烷的爆炸性喷发被认为是在现在的海底观察到的麻袋痕迹的原因。(2)在宫崎县新富镇发现了一个更新世冷渗化学合成群落。该群落暴露在南北向100m、东西向60m、厚度10m范围内，呈向上磨细、退变层序。(3)在北海道Wakkanai市外发现了全新世结核，包括Conchocele sp.和/或Calyptogena sp.。固结物中碳酸盐胶结物的13C缺失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.