AAPG Middle East Region Geoscience Technology Workshop

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Provenance of Cambrian Sandstones from Oman: Implications for the Consolidation of Gondwana and the Early Paleozoic Petroleum Systems of Arabia

Abstract

Clastic sediments of the Cambrian Nimr and lower Haima Groups in Oman were studied from both outcrops and the subsurface in terms of heavy minerals and detrital zircon geochronology to try to understand sediment provenance and distribution patterns. The Nimr and base Haima clastics include reservoir rocks in Oman, and were deposited in predominantly continental alluvial to fluvial settings in the context of Gondwana consolidation. The Nimr clastics are syntectonic, while the base Haima clastics are post-orogenic; they are separated by the Angudan Unconformity. Heavy minerals ratios offer information on the nature of the rocks exposed in the clastic sediment source areas, while detrital zircon geochronology offers information on the age of these terranes, as well as the magmatic events in a basin. Together, and integrated with sedimentological data and paleocurrent information, allow for an understanding of basin paleogeography and plate tectonic setting and evolution. The Nimr clastic sediments show heavy mineral associations rich in apatite, probably of syn-magmatic origin, while the base Haima heavy mineral associations are very mature, and are interpreted to represent recycled sediments. The detrital zircon geochronology spectrums are virtually identical for both units: they show old Paleoproterozoic and Archean age sources (~1900 and ~2500Ma peaks) and Tonian-Cambrian age sources (peaks at ~1000, ~830, ~620 and ~525 Ma). The results have been compared to equivalent data from the Precambrian succession of Oman, to understand provenance changes in geological time, and with other Cambrian samples from across the region, to understand paleogeography. The Cambrian signal of Oman is different from the Cryogenian-Ediacaran signal from East Oman, but resembles Ediacaran samples from West Oman and the UAE. Regionally, comparison with Cambrian-Ordovician samples from Pakistan, Iran, and Saudi Arabia, shows similarities and the same pattern of strongly intermixed sediment sources. The main detrital zircon age peaks however, are strongly controlled by the age of the local basement: Tonian (~830 Ma) for Pakistan and Oman, and Ediacaran (~620 Ma) from Iran and Arabia. Based on these observations, we support the presence of the final East-West Gondwana suture along the Western (Angudan) Deformation Front, a Cambrian orogenic belt now buried in the subsurface of Oman. This was a narrow fold and thrust belt which formed a regional high during the Early Paleozoic, and supplied clastic sediments to the retro-and pro-foreland basins of Oman, Saudi Arabia