Reconstruction of sub-bottom section of geologic methane-seep site - variety of seep activity indicated by fossil chemosynthetic communities

这项研究明确了始新世波罗奈组和中新世森莱组的地质过去甲烷渗漏点的亚底剖面，这两个组都是半深海粉砂岩，在日本北部的北海道发现了丰富的泡囊类化石。对它们的化石产状和渗漏碳酸盐岩块(规模、形状、岩石学和内部结构)的详细观察表明，这两个渗漏点在渗流活动方式上是相反的，波罗奈渗流是沟道化聚焦流，其特征是流体超压导致岩性破裂，而莫赖渗流是通过凝结泥浆空间扩散和静态的，没有这种破裂结构。这些结果表明，化学合成的囊泡菌文蛤利用了这两种渗漏。这与他们在半动物群生活状态下的高流动性有关，这为解决他们为什么能在后白垩纪取得成功和繁荣提供了一把钥匙。

This study made clear sub-bottom cross-sections of the geological past methane-seep sites in the Eocene Poronai Formation and the Miocene Morai Formation, both of which are bathyal siltstones yielding abundant vesicomyid fossils in Hokkaido, north Japan. Detail observations of their mode of fossil occurrences and seep-carbonate blocks (scale, shape, petrology, and internal textures) indicate that the two seep-sites are contrast in style of seepage activity.The Poronai seep is channelized focused-flow characterized by its fractured lithology due to fluid overpressure, whereas the Morai seep is diffusive and static through interspaces of clotted-mud, without such fracturing texture. These results show that chemosynthetic vesicomyid clams have utilized both types of seepage. This is related with their high mobility in semi-infaunal life position, which can provide a key to solve the question: why they have made success and flourish in the post-Cretaceous age.