Microbial Structures in Neoproterozoic Cap Carbonates

“这项奖励是根据2009年美国复苏和再投资法案（公法111-5）资助的。”新元古代盖碳酸盐岩的微生物结构——地球上的生命在过去的10亿年里至少经历了两次极端的冰川条件，分别发生在~ 710亿年前和~ 6.4亿年前。该方案旨在限制微生物生命的生存及其在随后的全球融化时期与环境的相互作用，正如在这两次“雪球地球”事件后立即形成的全球石灰岩沉积物中不寻常的微生物产生的结构所记录的那样。在第一次冰期之后，一种未知的机制将微生物结合的深水石灰岩沉积物折叠成厘米大小的卷状结构。在后期全球冰川作用后，覆盖在冰川沉积物上的浅水石灰岩中形成了直径1-3 cm的管状延长亚垂直管状结构。这些管状岩被认为是甲烷或二氧化碳的释放，或者是微生物存在下石灰岩的快速增生，但它们形成的机制仍然存在争议。将通过在纳米比亚北部地球化学和地层学上约束良好的部分进行测绘，并通过分析这些结构的岩石学和碳、氧同位素组成，来调查卷筒岩和管状岩的形成。这项提议的工作还将测试一个新的假设：是否可以通过富氧微生物垫中形成的富氧水泡来模板管状石，通过在实验室中在新元古代后冰期相关的条件下培养现代微生物。这项提议的工作解决了物理、化学和微生物过程如何在岩石记录中留下印记的问题，以及它们是如何在地球历史上一些最极端的时期留下印记的。更好地了解滚雪球或管状石形成的机制将解决微生物群落的组成、碳循环、氧化和沉积速率以及后雪球时期的环境化学问题。该项目将为一名研究生和至少两名女本科生提供跨学科培训。三个不同机构（麻省理工学院、史密斯大学和哈佛大学）的研究人员的合作成果将在年度研讨会上公布。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Microbial structures in Neoproterozoic cap carbonatesTanja BosakMIT, EAR-0843358ABSTRACTLife on our planet endured extreme glacial conditions at least twice in the past billion years starting at ~ 710 and at ~640 million years ago. This proposal seeks to constrain the survival of microbial life and its interactions with the environment during the subsequent times of global melting, as recorded by unusual microbially-produced structures within global limestone deposits that formed immediately after these two 'Snowball Earth' events. After the first glaciation, an unknown mechanism folded microbially-bound deep water limestone sediments to produce cm-sized roll-up structures. After the later global glaciation, tubestones, 1-3 cm diameter elongated, sub-vertical tubular structures formed in shallow-water limestone capping the glacial deposits. The tubestones have been attributed either to the release of methane or carbon dioxide or to the fast accretion of limestone in the presence of microbes, but the mechanisms of their formation remain controversial. The formation of roll-ups and tubestones will be investigated by mapping in geochemically and stratigraphically well-constrained sections in northern Namibia and by analyzing the petrography and carbon and oxygen isotopic composition of these structures. The proposed work will also test a new hypothesis: whether tubestones can be templated by oxygen-rich blisters formed in oxygenic microbial mats, by growing modern microbes in the laboratory under conditions relevant for the later Neoproterozoic post-glacial. The proposed work addresses the questions of how physical, chemical and microbial processes leave a mark in the rock record and how they did it during some of the most extreme times in Earth history. A better understanding of mechanisms that form roll-ups or tubestones will address the composition of microbial communities, carbon cycling, oxygenation and sedimentation rates and the environmental chemistry during post-Snowball deglaciations. This project will provide interdisciplinary training to a graduate student and at least two female undergraduates. The results of collaborative efforts between researchers at three different institutions (MIT, Smith C. and Harvard U.) will be disseminated at an annual symposium.