Fossil cold seep assemblages in shallow water deposits do occur in regressive facies !?

浅水沉积物中的化石冷泉组合确实出现在海退相中！？

• 批准号: 13640468
• 负责人: MAJIMA Ryuichi
• 金额: $ 2.5万
• 依托单位: Yokohama National University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640468/
• 关键词: Japan; Glacio-eustatic change; Early Pleistocene; Chemoautotrophic assemblage; Methane seep; Carbonate concretion; Carbon stable isotope; Regressive facies; 炭素の安定同位体比; 海退相; 高鍋層; 棚層; 安定同位体比; ポックマーク

Fossil chemoautotrophic assemblages in Japan can be divided into three types, based on species composition, mode of occurrence, and palaeobathymetric distribution. Type 1 is dominated commonly by vesicomyid bivalves and/or tube worms, and characterised by its allochthonous or parautochthonous mode of occurrence in deep-water settings, along with tectonically-or sedimentologically-induced structures such as faults, slumps, diapirs, or debris flows. Some Type 1 assemblages are comparable to modern cold-seep communities around Japan at depths of more than about 500 m, living on scarps and talus deposits, whereas other Type 1 assemblages are seemingly related to slope failures and sediment collapses caused by the drastic decomposition of gas hydrates. Type 2 assemblages are also dominated by vesicomyid bivalves, but usually the species differ from those in Type 1. In contrast with Type 1 assemblages, Type 2 assemblages are characterised by autochthonous occurrences in muddy sediments in le … More ss than 1,000 m water depth. Type 3 assemblages are dominated by Lucinoma and/or Conchocele and are characterised by autochthonous occurrences in muddy sediments at water depths of less than 300 m. No living community comparable with Types 2 and 3 assemblages has yet been observed in the seas around Japan. It is noteworthy that no tectonically-or sedimentologically-induced structures, such as faults, slumps and/or debris-flow deposits, have been observed in and around Type 2 and 3 fossil localities, although the muddy sediments sometimes show brecciated facies that suggest an explosive effusion of methane. Occurrences of Types 2 and 3 may have been synchronous with sea-level changes that triggered methane-hydrate decomposition and/or the upward migration of methane gas. This working hypothesis may also explain why there in no comparable modern community made up of these types : present-day sea level is stable compared to the ancient sea levels when Type 2 and 3 fossil assemblages flourished. Less

日本的化石化能自养组合根据物种组成、出现方式和古水深分布可分为三种类型。第1类通常以囊虫类双壳类和/或管蠕虫为主，其特征是在深水环境中出现异地或准原地模式，沿着构造或沉积学诱导的结构，如断层、滑塌、底辟或泥石流。一些1型组合相当于现代冷泉社区在日本周围的深度超过约500米，生活在悬崖和岩屑沉积物，而其他1型组合似乎与边坡破坏和沉积物崩塌所造成的气体水合物的剧烈分解。第2型组合也以泡壳类双壳类为主，但通常与第1型组合的种类不同。与第1类组合不同，第2类组合的特征是原地产出于低海拔地区的泥质沉积物中 ...更多信息 水深超过1,000米。3型组合主要由Lucinoma和/或Conchocele，其特征是在水深小于300米的泥质沉积物中原地发生。在日本周边海域还没有观察到与第2和第3类组合相媲美的生物群落。值得注意的是，没有构造或沉积诱导的结构，如断层，滑塌和/或碎屑流沉积物，已观察到在和周围的2型和3型化石地点，虽然泥质沉积物有时显示角砾岩相，这表明甲烷的爆炸性渗出。类型2和类型3的发生可能与海平面变化同步，海平面变化引发甲烷水合物分解和/或甲烷气体向上运移。这一假说也可以解释为什么没有类似的现代群落由这些类型组成：与2型和3型化石组合繁荣时的古代海平面相比，现在的海平面是稳定的。少

项目成果

Nobuhara, T., Majima, R., Hikida, Y., Kitazaki, T.: "Carbonate rocks of fossil chemosynthetic assemblages in Japan."Paleontological Research. 7・4. 277 (2003)

Nobuhara, T.、Majima, R.、Hikida, Y.、Kitazaki, T.：“日本化学合成化石组合的碳酸盐岩”。古生物学研究 7・4 (2003)。