EVIDENCE OF SEMI-DIURNAL TIDES ALONG THE AFRICAN COAST OF THE CRETACEOUS TETHYS SEAWAY: BAHARIYA OASIS, EGYPT

The Bahariya Bight was a costal embayment along the African shore of the Cenomanian Tethys Seaway and was bordered by a high-productivity mangrove ecosystem. The sedimentology of foreshore and shoreface lithosomes along this sheltered coast indicates an extremely low-energy wave regime. Tidal energy along this coast, however, appears to have been more robust.

Tide generated couplets are common in Bahariya sediments in flaser, wavy, and lenticular deposits. Large-scale mud drapes are also present, indicating the likelihood of mesotidal conditions, and representing sedimentation during slackwater periods. Tidal bundles can be delineated where mud drapes alternate with more angular foresets and record neap-spring cyclicty. In one particularly well-preserved outcrop, a neap-spring cycle is represented by approximately 28 bundles of 4-element drapes followed by approximately 14 bundles of 2-element drapes. This sequence corresponds to deposition by semi-diurnal tides over an approximately 14 day period.

The Bahariya deposits preserve a mangrove flora which includes the tree fern Weichselia reticulata and a rich fauna, that includes bivalves, gastropods, sharks, bony fish, turtles, crocodyliforms, and at least five genera of dinosaur. The strong flushing action afforded by semi-diurnal mesotides over the gently sloping Bahariya coastal plain would have provided a high-volume pathway for the delivery of nutrients to this biome and would have aided the cycling of gases throughout the ecosystem. This, in part, explains the high bioproductivity evident in this paleoecosystem.