Depositional phases of Neogene rocks based on palynofacies and inorganic geochemical analyses in Nile Delta, Egypt: A focus on organic matter accumulation

Abstract

The depositional phases of the Nile Delta are investigated based on the palynofacies and geochemical analyses in samples from two studied wells Baltim-1 and NDOB-1 wells. These depositional phases determine the ability to produce and preserve the organic carbon. The Nile Delta's hydrocarbon system is based mainly on the Neogene rocks, particularly those ranging from the Late Miocene to the Pleistocene, where environmental conditions governed organic matter accumulation. The depositional history in this region is related to the activity of sediment input by the different phases of the Nile River and their ability to transfer the sediments and terrigenous organic matter. Multivariate statistical analyses of the palynofacies revealed four types, namely distal-high oxic type A, proximal-suboxic type B, proximal-dysoxic type C, and distal-oxic type D. In addition, proximal-distal and oxygen depletion trends were identified based on the values of the principal components analysis (axis 1). The characterization of the palynofacies types incorporated inorganic geochemical analysis of trace elements to determine environmental gradients, were compared to the values of organic matter (0.27–1.18 wt% TOC). Organic matter concentrations were low during most depositional phases despite the active influx of the terrigenous organic matter and the productivity of marine organic matter. These results can be attributed to the Nile Delta region's depositional phases identified from the palynofacies types and major element oxides. It is inferred that the Nile River delivered a high rate of sediments into the basin, in addition to nutritious material that increased the sea surface paleoproductivity of marine organic matter. However, the high sedimentation rate during the different depositional phases did not attain the optimum threshold to preserve organic carbon in high concentrations.