Facies framework and depositional setting of the Middle-Upper Eocene Hamra Formation, north of Bahariya Oasis, Western Desert, Egypt

Abstract

The Middle-Upper Eocene Hamra Formation, covering the northern plateau of the Bahariya Oasis, northwestern Desert, comprises two informal (lower and upper) members; the lower member (Upper Middle Eocene, 34.5-m thick) is made up entirely of fossiliferous limestone rocks (Nummulites gizehensis, Nummulites champolioni), while the upper member (Late Eocene, 38-m thick) consists of an intercalation of limestone with thin beds of sandstone, siltstone, and claystone. The upper member is highly fossiliferous with Turrittella, Carolia palcnoids, and Ostrea multicostata. Seven carbonate and three clastic microfacies have been recognized in five measured sections of the Hamra Formation. The carbonate microfacies were deposited on the proximal ramp setting of a warm and shallow sub-tropical environment. The lower member can be correlated with the (Upper Middle Eocene) Sath El Hadid and Fashn formations, while the upper member is correlated with the Upper Eocene Beni Sueif Formation. The reduced thickness of both members of the Hamra Formation compared with the corresponding rock units to the east reflects the structural uplift prevailed in the north of Bahariya Oasis during sedimentation.