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Book Chapter

Neoproterozoic

Published:
January 01, 2015

Abstract

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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Geological Society, London, Special Publications

Microbial Carbonates in Space and Time: Implications for Global Exploration and Production

D. W. J. Bosence
D. W. J. Bosence
Royal Holloway, University of London, UK
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K. A. Gibbons
K. A. Gibbons
Nexen Petroleum UK Ltd, UK
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D. P. Le Heron
D. P. Le Heron
Royal Holloway, University of London, UK
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W. A. Morgan
W. A. Morgan
Morgan Geoscience Consulting, LLC, USA
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T. Pritchard
T. Pritchard
BG Group, UK
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B. A. Vining
B. A. Vining
Royal Holloway, University of London, UK
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Geological Society of London
Volume
418
ISBN electronic:
9781862397163
Publication date:
January 01, 2015

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