Palynological and palaeoenvironmental analyses of the upper Albian-Cenomanian succession in Gindi Basin, Egypt: Implication for transgressive/regressive systems tracts

Abstract

The current contribution illustrates the advantage of the use of quantitative palynological data to palaeoenvironmentally differentiate the similar-looking monotonous, thick clastic interval of the Kharita, Bahariya and Abu Roash “G” units in Gindi Basin, Egypt. The present study aims also to the utilization of the upper Albian-Cenomanian quantitative palynological and palynofacies data and their integral interpretation in a sequence stratigraphic context. The recovered palynomorph assemblages with moderately diverse sporomorphs and dinoflagellate cysts, show poor to fair preservation. Around 47 species of pollen grains, 37 of dinoflagellate cysts and 36 species of pteridophytic spores have been recorded from two sections encountered in El Sagha-1A and BRE 6-1 wells drilled in Gindi Basin; however, achritarchs, microforaminiferal test linings and freshwater algae are impoverished and sparsely documented through the studied intervals. Based on the first downhole appearances (FDAs) of the recovered marker taxa, the encountered Abu Roash “G”, Bahariya and the upper Kharita units are palynologically dated as late Cenomanian, early-middle Cenomanian and late Albian, respectively. Relative sea level fluctuation is particularly relevant and deduced from various palynological parameters mainly the terrestrial:marine (T:M) ratio and the palynological marine index (PMI). Based on the vertical stratigraphic distribution of the palynofacies along with the relative variations of the terrestrial versus marine palynomorphs, five complete (SQ1-SQ5) third order transgressive-regressive sequences and incomplete one are defined in El Sagha-1A in comparison to six complete (SQ2-SQ7) and one incomplete (SQ1) are constructed in BRE 6-1. Reliance on distinctive palynofacies assemblages, differentiated based on the relative composition of particulate organic matter constituents, four depositional palaeoenvironments were interpreted for the studied intervals. The Kharita and Bahariya formations were elucidated to be deposited in fluctuating marginal-shallow and proximal inner neritic marine environments. However, the sea level remarkably showed a continued rising which brought the inner-middle neritic conditions of the Abu Roash “G” Member during late Cenomanian.