A review of the Ediacaran to Early Cambrian (‘Infra-Cambrian’) evaporites and associated sediments of the Middle East
A. G. Smith, 2012. "A review of the Ediacaran to Early Cambrian (‘Infra-Cambrian’) evaporites and associated sediments of the Middle East", Geology and Hydrocarbon Potential of Neoproterozoic–Cambrian Basins in Asia, G. M. Bhat, J. Craig, J. W. Thurow, B. Thusu, A. Cozzi
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The paper reviews the age, location and extent of the late Neoproterozoic to Early Cambrian evaporite basins in the Middle East, NW India and Pakistan. The stratigraphic section discussed includes the largest inorganic negative δ13C excursion known (in the Shuram Formation); six cycles of alternating evaporites and carbonate (Ara Formation) and a unique formation in the middle of the Ara known as the Al Shomou silicilyte, which is a major hydrocarbon source. Tuff/volcanic horizons within the Ara are very well dated, with a precision of <0.15 myr. Extensional faulting was contemporaneous with the deposition of the evaporites, creating basins that at times showed density stratification and anoxia. The Buah Formation, which underlies the Ara, provides an insight into the development of Ediacaran carbonate ramp systems in the absence of bioturbation. A reconstruction of Gondwana brings the Ara and the Hormuz evaporites close to the evaporites of NW India and Pakistan, but leaves a small gap between them, which was probably occupied by a continental sliver, mostly likely part of the Lut block of central Iran. The Ara-Hormuz basins lie on the edge of a major continental collision between India and east Africa that was part of the amalgamation of east Gondwana.
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This volume provides a comprehensive overview of the geology and hydrocarbon potential of the major Neoproterozoic–Cambrian basins of Asia from Oman, across the Middle East and the Indian Subcontinent, to China and SE Siberia, along with new research on the region. Many of these areas (e.g., Oman, Bikaner–Nagaur Basin in India, South China and SE Siberia) host prolific Neoproterozoic–Cambrian petroleum systems with giant to supergiant fields. Three key elements: (1) tectonic stability, (2) relatively late phase of hydrocarbon generation and (3) presence of an effective evaporite seal, seem to be critical for the development of effective Neoproterozoic–Cambrian petroleum systems. These key elements appear of less consequence for the development of ‘unconventional’ hydrocarbons, and the future prospectivity in many of these basins may lie in the exploration for, and production of, shale gas and shale oil directly from the thermally mature, organic-rich source rocks.