Microbial Structures in Neoproterozoic Cap Carbonates

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." Microbial structures in Neoproterozoic cap carbonates Tanja Bosak MIT, EAR-0843358 ABSTRACT Life 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.