Relationship between cyclic patterns of organic matter concentrations and their paleoenvironmental controls in the Upper Cretaceous rocks in Abu El Gharadig basin, Egypt: Cyclo-sequence stratigraphic framework

Abstract

Abu El Gharadig Basin includes active petroleum systems that produce petroleum in many fields such as Abu El Gharadig Field. The hydrocarbon source rocks in the Upper Cretaceous of Bahariya and Abu Roash formations play an important role in such petroleum systems. The organic matter concentration is very important parameter to determine the potentiality of source rock occurrences. The understanding of cyclic changes of the organic matter enrichments measured in total organic carbon (TOC) is targeted in the present study together with the paleoenvironmental trends that control their distribution. The paleoenvironmental conditions are determined using the statistical analysis of palynofacies by applications such as cluster and correspondence analyses. These analyses are used to identify the palynofacies types (A, B, C, D and E) with distinctive paleoenvironmental conditions. The correspondence analysis is used to determine the paleoenvironmental trends including proximal-distal trend in axis 2 and oxygenation conditions on axis 1. The palynofacies type D and E are characterized by anoxic to suboxic distal conditions. The measured total organic carbon values are generally low (3.3 wt%) in the studied wells and the higher values have tendency to associate the distal anoxic environment of palynofacies type D. The succession was divided into 15 stratigraphic sequences using the palynofacies analysis which enabled the basinal correlations through the studied wells. Additional trace elements measurements are used to confirm the paleoenvironmental characteristics indicated by the palynofacies analysis. The G-ray log in addition to the proximal-distal trend represented by correspondence axis 2 and organic matter concentrations are subjected to time series analysis by spectral and wavelet transform applications. The analysis revealed similar ratios of the resulted periodicities that indicate existence of a common cyclic pattern. This cyclic pattern is connected to the oscillation orbitallly induced climate changes.