Lower Eocene carbonate facies, environments and sedimentary cycles in Upper Egypt: evidence for global sea-level changes

Abstract

The Lower Eocene carbonate succession in the Eastern Desert between Qena and Sohag (Upper Egypt) exhibits four major coastal subenvironments. The tidal flat, oyster nearshore and nummulite bank facies form the Thebes Formation and the open-shelf lagoon and bars (shoals) facies build up the Drunka Formation. During the Early Eocene, pure and dolomitized lime muds with ostracodes accumulated on the tidal flats of regional gentle-inclined seaward shelf platform in the E and S of the area. Penecontemporaneously, the larger foraminifera (nummulites, operculines and discocyclines) constructed bank facies between the normal and storm wave base. During that time, an active external influx of reworked older Paleocene planktonic foraminifera took place across the tidal inlets and distributary channels. At the same time, codiacean and dasycladacean algal open shelf lagoon facies (with intermittent water energy) dominated the parts in the NW. On the outer shelf platform a series of submarine oolitic and bioclastic bars accumulated under high water energy conditions. The bars were developed with their axes trending NE-SW, suggesting a paleocoast strike running in the same direction. The fluctuations in mean sea level in the study area are demonstrated by models exhibiting the evolution of the sedimentary basin during the Early Eocene. Four relatively major phases of transgressive episodes separated by very short durations of regressions are recorded. It is believed that, the Early Eocene sea level changes in Upper Egypt have been controlled by a true eustatic change of the global sea level without significant regional tectonic events during that time.