Depositional paleoenvironment and hydrocarbon source potential of the Oligocene Dabaa Formation, north Western Desert, Egypt: A palynofacies approach

Abstract

A detailed palynofacies study was carried out on 24 shale cutting samples from the Oligocene Dabaa Formation, which was penetrated in the Amana-1X well, Abu El Gharadig Basin, north Western Desert, Egypt. The investigation targeted primarily three main groups of palynological elements: Phytoclasts, palynomorphs, and amorphous marine organic matter (AMOM), using transmitted light microscopy. Two major marine palynofacies were recognized: The oldest is palynofacies 1, made up mainly of AMOM (average abundance 47.5%), phytoclasts (31.6%), and palynomorphs (20.9%). A suboxic to anoxic outer shelf to upper slope paleoenvironment is suggested for this palynofacies. Palynofacies 2 is characterized by poorly preserved translucent phytoclasts (average abundance 61.2%) in addition to palynomorphs (24%), AMOM (14.8%), and opaques (< 10%). This association clearly marks a paleoenvironmental shift toward a more proximal, more oxic marine facies. The overall composition of both palynofacies indicates a general progradational trend interrupted by brief transgressional episodes during the deposition of the Dabaa Formation. The kerogen composition of palynofacies 1 suggests type II-III (mostly oil prone), and palynofacies 2 constitutes type III kerogen (largely gas prone). Spore/ pollen exine colors in the studied Dabaa samples point to immature organic content of no potential for hydrocarbon production.