Facies Associations and Depositionai Environments of Miocene and Pieistocene Sedimentary Successions in Eit Area, Red Sea Coastai Piain, Sudan

Abstract

Abstract Eit area lies at about 61 km to the north of Port Sudan town in Red Sea State. It located within Mohamed Qol topographic sheet (No 37 - M), which cover the northern edge of the Red Sea region. Sedimentologically, the Eit succession formed of Miocene and Pleistocene deposits, it consists of continental, transitional and marine sediments. The continental deposits include sandstone sequence and older gravels facies. The marine deposits consist of large - scale carbonate sequence and emergent coralline limestone unit. The transitional deposits include mixed carbonate and clastic sequence, evaporite deposits, bedded calcareous marlstone and dolomitized marlstone sequence. Detailed sedimentological studies had been conducted in the Eit succession. The study reveals seven sedimentary units based on variation in lithology, grain - size and fossil remains. Field measurements of the lithological units, microfacies analysis and modal analysis and as well as geochemical investigation were made to describe and classify the facies associations and depositional environments of the Eit succession. The microfacies analysis of the carbonate sequence revealed that it formed of sorted oosparite, shelly biomicrite, pelecypoda biomicrite, pelecypoda biosparimicrite, foraminiferal biosparite, lithmicrite, lithbiomicrite, dismicrite and biolithite microfacies. The modal analysis of the mixed carbonate - clastic detected that the sequence formed of hematitic quartz arenite petrofacies, siliceous quartz arenite petrofacies, calcitic quartz arenite petrofacies and lithic arenite petrofacies. Microscopic inspection of the sandstone sequence reveals that it formed of quartzwacke petrofacies, greywacke petrofacies and lithic arenite petrofacies. The mixed carbonate - clastic sediments includes quartz arenite petrofacies, which cemented by calcareous, iron oxide and silica overgrowth materials. The gypsum deposit divided according to crystal form to massive alabaster gypsum facies, laminated alabaster gypsum facies, selenite gypsum facies and fibrous satin spar gypsum facies. The geochemical analysis presented the affection of seawater into all the clastic deposits in the area studied. The mudstone horizons in the Eit\ succession appear to be dolomitized marlstone facies and calcareous marlstone facies. Analysis of depositional environments reveals that the continental environment includes fluvial and alluvial fan systems in where the sandstone sequence and the older gravel facies were accumulated. The transitional environment includes marine shoreline, lagoonal and tidal flat systems. The quartz arenite petrofacies, the gypsum facies, the dolomitized marlstone facies and the calcareous marlstone facies were deposited in these environments. The marine environment represented by shallow - marine carbonate deposits and the biolithite microfacies. Three phases of regression and transgression of marine water were recognized in the Eit succession. Before the transgression of the marine water, an alluvial extraformational conglomerate facies, the greywacke facies and the lithic arenite petrofacies were deposited. The large - scale carbonate facies were deposited during the Miocene transgression. Pleistocene transgression characterized by development of the emergent coralline limestone unit.