The Unexpected Discovery of Paleocene? Coals in Outcrops Thought to Be Cambrian, Al Huqf, Oman

Abstract

Two brown organic deposits were encountered whilst investigating kaolinitic claystones thought to occur at the base of a Cambrian formation at outcrop. The age of these organic deposits is probably Paleocene from palynology. Organic petrography shows that they are subbituminous coals with some oil source potential. Vitrinite reflectance measurements of 0.53–0.56%R_o indicate a thermal maturity that is approaching the early oil window and imply burial to about 1600 m and subsequent uplift back to near surface. The kaolinitic claystones are interpreted to have been weathered from the outcrops of the Cambrian Thumaylah Formation and to have accumulated in small terrestrial basins along with organic matter of both allochthonous and autochthonous origin. These kaolinitic claystones and coals may be equivalent to terrestrial deposits which occur at the base of the early to middle Paleocene Shammar Member of the Umm er Radhuma Formation in northwest Oman. They may also be equivalent to kaolinite deposits of Paleocene age which occur on Masirah Island. It seems likely that further evidence of Paleocene organic deposits will be discovered in Oman where there are the conditions for preservation from erosion and oxidation.