Successive first downhole sporomorph-events: Applied biostratigraphic tool for fault delineation within Baharyia Formation, Abu Sennan area, Abu Gharadig Basin, Egypt

Abstract

Abstract Two hundred and seventy four samples, covered the Bahariya sections encountered in 13 boreholes, drilled in three main fields of the General Petroleum Company concession, Abu Gharadig Basin, north Western Desert, were critically investigated for their palynomorphs content. A standard acid-based palynological processing technique is employed to extract the palynomorphs. Fair to moderate diversity and moderate to good preserved palynomorph assemblage has been recovered. This study yielded 107 species of spores, pollen grains and dinoflagellate cysts. Six remarkable successive first downhole appearance (FDA) sporomorph-events are defined and biostratigraphically utilized for dividing the Bahariya Formation and delineating the Bahariya/Kharita contact. The upper Bahriya unit includes the first Afropollis jardinus event dated latest early Cenomanian, while the middle Bahriya unit comprises the second Elatersporites klaszii event dated early Cenomanian. The lower Bahriya unit, dated early Cenomanian-late Albian, contains the third, fourth, and fifth Cretaceieporites densimurus, Trilobosporites laevigatus and Stellatopollis sp. events, respectively. The contact between Bahriya Formation and the upper part of the underlying Kharita Formation, dated early-middle Albian, is placed on Concavisimisporites punctatus event. The authors found the possibility of these six zones to be widely traced and provide potential bio-correlation tool for the Bahariya sections in Abu Gharadig Basin. According to the presence or absence of such six successive events and their average zonal thicknesses, the intra-formational disconformities and positions of the faults could be allocated with confidence. The remarkable thinning in the thickness of such zones could localize the position of disconformities caused by non deposition or erosion/faulting within the Bahariya sections. The aforementioned six events could be correlated and nicely matched with their equivalent six log-based cycles on the log responses. The authors encourage the Egyptian industrial geologists to follow the presented successive six sporomorph-events in the future palynological-steering exploration and production activities in the Bahariya rock unit and effectively utilize such events as intra- and inter-basinal dating tool and possible correlation control for the Bahariya sections across the northern basins of Egypt.