Facies hierarchy and microscopic features of upper Eocene rock succession, northern Eastern Desert, Egypt: inference on frequent subaerial exposure of Tethys platform and relevant palaeoclimates

Abstract

The evolution of the upward stacking pattern of shoaling, which contains microscopic features of paleosols and calcretes in the Upper Eocene Beni-Suef and Maadi Formations along the Beni-Suef-Zaafarana road in the northern Eastern Desert, Egypt, is related to frequent intervals of subaerial exposure. The work was achieved through an integrated approach of outcrop observations and microfacies analysis using polarizing microscopy. The study reveals the presence of sixteen microfacies types grouped into six facies associations, representing a mixed clastics-carbonates ramp setting. The ramp facies belts consist of a back ramp restricted mudflat/supratidal flat and lagoon, protected and low-energy inner ramp, open inner ramp, carbonate shoal, and open middle/outer ramp. The cycles commonly start with open inner ramp carbonate facies and end with mudflat clastic facies/subaerial exposure surfaces. The vertical changes in the depositional environments indicate that the facies were deposited within a highly tectonic active area that was consequently influenced by the transgression and regression of the Tethys. Microscopic features of subaerial exposure, including Microcodium crystal aggregates, crystallaria, rhizoliths, Stromatolite-like structures, sheet cracks, fenestrae, microbial mat laminae and dissolution of bioclasts, commonly occur in the topmost part of the cycles. The documented microfabric features in the study area provide strong evidence of the regular emergence of the southern Tethys platform in Egypt during the Late Eocene. They point to an intermediate palaeoclimate, involving conditions ranging from semi-arid to sub-humid. Subaerial disconformities and associated diagenesis/pedogenesis features, as recorded in the studied units, are not widely reported in the upper Eocene carbonates in Egypt.