COASTAL DEPOSITIONAL ENVIRONMENTS ALONG THE CRETACEOUS TETHYS SEAWAY OF EGYPT

During the sea level highs of the Late Cretaceous, Egypt was transgressed many times by a southward extending arm of the Tethys Seaway. These events produced a diverse set of coastal lithosomes preserved in part in the Cenomanian Bahariya Formation. These deposits are well exposed in the ablated Bahariya Oasis (320 km southwest of Cairo) and record a complex depositional history along a sheltered, low-energy, epeiric bight.

Diminished energy conditions along this coast allowed for the development of mangrove communities, occupied partly by Weichselia reticulata, a mangrove tree fern. Where these communities were well-established, mangrove deposits prograded into transgressing seas. Where mangroves were absent or not well established, small barrier islands developed and migrated landward over paralic sediments.

The Cenomanian transgressions occurred over a very low gradient coastal plain, producing very wide back-barrier environments. The resulting paralic deposits account for most of the volume of the Bahariya Formation and include open-water lagoon, tidal flat, mangrove, and tidal channel facies. These deposits also preserve a rich fauna, including bivalves, gastropods, sharks, bony fish, turtles, crocodyliforms, plesiosaurs, and five dinosaurs, Spinosaurus, Carcharodontosaurus, Bahariasaurus, Aegyptosaurus, and Paralititan.

Similar coastal behavior can be seen today along the Ten Thousand Islands region of the Florida Gulf coast, where Holocene transgression over a gently sloping coastal plain has produced extremely wide back-barrier environments. Along very low energy reaches of this coast, mangroves occupy the foreshore and have prograded up to 8 km seaward during the past 3,000 years of sea level rise. Where wave energy is locally elevated, small barrier islands form and migrate landward over paralic environments. The lateral and vertical relationships produced by advancing and retreating segments along this coast serve as a useful analog for the development of the complex coastal record of the Baharyia Formation.