Facies architecture and controlling factors induced depositional model of the Quaternary carbonate eolianites in the northwestern Mediterranean coast of Egypt
The present paper focuses on the facies and allogenic controlling factors affecting the eolianite depositional system on a semi-arid carbonate ramp. Facies analysis and stratal architecture are integrated with earlier age-dating data to develop a depositional model of the landmark eolianite ridges in the northwestern Egyptian coast. Nine genetically related eolianite units, separated by eight eolianite-bounding surfaces and paleosol/protosol horizons are recognized. Twelve depositional facies belonging to three main facies associations have been identified. The eolianite facies association comprises cross-stratified oolitic and bioclastic grainstones. The inter-eolianite facies association includes paleosols, protocols and calcretes. The intra-eolianite facies association is represented locally by marine boulders of grainstone and rudstone (possibly reworked and imbricated by storm and tsunami waves) in the Coastal and Maryut eolianite ridges. Depositional development of the carbonate eolianites is strongly controlled by the Quaternary paleoclimate and glacio-eustatic sea-level cycles under mild tectonics on a gentle-slope carbonate ramp. The suggested depositional model matches well with the worldwide age-dating data of the carbonate coastal dunes, which generally indicate contemporaneous periods of eolianite deposition. The studied eolianite units are attributed herein to periods of highstand and stillstand, which can be correlated to the Marine Isotope Stages (MIS) of the middle Pleistocene ‘MIS 9 and 7′, the late Pleistocene ‘MIS 5e’ and ‘MIS 5c-5a’, and finally the Holocene ‘MIS 1′. The paleosols were mostly best developed during periods of lowstand. The Holocene immature paleosol ‘Ps1′ represents an example of the generation of protosol/paleosol during a highstand period. This supports the idea that the Pleistocene paleosols may be initiated during wet periods of the highstand and developed later during subsequent lowstand episodes. Collectively, the results imply that the generated eolianites along the carbonate ramp are strongly controlled by glacio-eustasy and paleoclimate, in addition to other autogenic factors in the depositional system.