Paleoenvironmental reconstruction, paleoecology and sequence stratigraphy of some Nummulites buildups in Egypt

Abstract

The present study deals with microfacies analysis, paleoecology and sequence stratigraphy of the Lower–Middle Eocene rocks in central Nile Valley and west-central Sinai. Four rock units were marked (Minia, Darat, Samalut and Maghagha formations). Eight facies belts were interpreted including lagoon, back bank, main bank, fore bank and open marine outer bank facies and deposited on a gently dipping platform ramp. This ramp might be further divided to three main faunal associations depending on the depth of the water and associated fauna. Four major depositional sequences (DS1–DS4), reflecting third-order cycles and separated by two prominent sequence boundaries (SB1 and SB2) were marked. The record of these sequences reflects the changes in eustatic sea level plus the regional tectonism in the area. Every sequence includes facies associations, which constitute lowstand and/or transgressive and highstand systems tracts. Based on faunal elements and facies analysis, the water salinity, water temperature, nutrients, substrate, water depth and hydrodynamic behavior were discussed. The fine-grain size of the deposits, the loss of good connectedness and the occluding of the Nummulite tests by other minerals could give rise to low reservoir potential. The sedimentation was affected by the tectonic activity of the Syrian orogeny. Moreover, both external and internal mechanisms have controlled the carbonate sedimentation, basin construction and sequence bounding surfaces.