Microbial communities and their primary to early diagenetic mineral phases; the record from Neoproterozoic microbialites of Qarn Alam, Oman
M. Mettraux, P. Homewood, C. Dos Anjos, M. Erthal, R. Lima, N. Matsuda, A. Souza, S. Al Balushi, 2015. "Microbial communities and their primary to early diagenetic mineral phases; the record from Neoproterozoic microbialites of Qarn Alam, Oman", Microbial Carbonates in Space and Time: Implications for Global Exploration and Production, D. W. J. Bosence, K. A. Gibbons, D. P. Le Heron, W. A. Morgan, T. Pritchard, B. A. Vining
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The 10 m-scale shallowing-up Neoproterozoic carbonate cycles at Qarn Alam (Oman) provide a record of microbial textures and the communities responsible for them. This is documented for four major microbialite facies. Despite their age, these microbialites show extremely fine preservation of microbial fossils and mineral associations (primary calcite and dolomite with minor phosphate, glauconite, palygorskite, hematite and goethite) and they are the record of a suite of microbial communities, from pellicular biofilms (planar laminites) to mats and gels (crinkly laminites, and stromatolitic layered and massive thrombolites) and a more complex microbial community in bushy thrombolites possibly involving a sponge-like form. Mineralized extra-cellular polymeric substances (EPS) resembles that of modern microbial mats. The mineral associations, as well as cathodoluminescence attributes, indicate oxic to suboxic conditions during deposition and early diagenesis for planar laminites and crinkly laminites, but more evaporitic to saline conditions during development of thrombolites of the upper part of a cycle. Early cementation under variable redox conditions sealed the organomineralized phases.
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Microbial carbonates (microbialites) are remarkable sedimentary deposits. They have the longest geological range of any type of biogenic limestones, form in the greatest range of different sedimentary environments, oxygenated the Earth’s atmosphere and produce and, furthermore, store large volumes of hydrocarbons. This Special Publication provides significant contributions at a pivotal time in our understanding of microbial carbonates when their economic importance has become established and the results of many research programmes are coming to fruition.
It is the first book to focus on the economic aspects of microbialites and in particular the giant pre-salt discoveries offshore Brazil. The volume contains papers on the processes involved in the formation of both ancient and modern microbialites and the diversity of style in microbial carbonate build-ups. Structures and fabrics from both marine and non-marine settings are discussed from throughout the geological record.