Styles, origins and implications of syndepositional deformation structures in Ediacaran microbial carbonates (Nama Basin, Namibia)
G. Winterleitner, D. P. Le Heron, B. Mapani, B. A. Vining, K. J. W. McCaffrey, 2015. "Styles, origins and implications of syndepositional deformation structures in Ediacaran microbial carbonates (Nama Basin, Namibia)", 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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Outstanding exposures of Ediacaran-aged thrombolite–stromatolite bioherms and biostromes crop out in the Nama Basin, SW Namibia. Fieldwork, dovetailed with remote sensing and a terrestrial laser scanning (LiDAR) survey, allow the fracture network of this succession to be characterized, and the relative age of fracture sets and families to be determined. The results show that the microbial carbonates were affected by intense syndepositional brittle and ductile deformation. Early brittle fracturing was favoured where early lithification of microbialites took place upon deposition. Such deposits were prone to gravitational collapse due to internal weaknesses during early lithification. Timing of syndepositional fracturing of bioherms and biostromes is demonstrated by contemporaneous microbial overgrowth over brecciated material in open-mode fractures. Ductile deformation occurs preferentially around massive thrombolite domes and columns, represented by folding of mud-dominated sediments in inter-column fill. Secondary fractures developed during the long-lived structural history of the Nama Basin, resulting in a complex fracture network of syndepositional fractures overprinted by secondary fractures. These findings have important implications for carbonate reservoir characterization in microbial reservoirs and subsurface fluid-flow estimations. The observed syndepositional fractures form due to body forces that are intrinsic to the microbial system and thus do not require an external tectonic driver.
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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.