The origin and significance of the distribution of crude oils with different maturation levels in the Baise Basin, southern China

Abstract

This study distinguishes some of the major late Pleistocene and Holocene lithofacies in the northeastern Nile Delta of Egypt by evaluating quantitatively the texture and the coarse fraction composition of 375 samples in 14 cores. Seventeen petrologic variables (three textural and 14 mineralogical, faunal and floral) were considered for each of the samples. For facies discrimination the raw data were evaluated with descriptive statistics and with numerous (>300) computer-generated bivariate and ternary diagrams. This treatment, and Q-mode factor analysis, were applied separately to two facies groups: one comprised coastal-organic rich, lagoonal/marsh, delta-front, prodelta and alluvial delta plain muds; the other comprised upper Holocene progradational coastal sands, lower Holocene transgressive coastal sands and late Pleistocene alluvial sands. Discrimination of the five mud facies is generally good (except that of the upper Holocene lagoonal/marsh muds), while that of the three sand types is only moderately successful.As a test of the method used here for facies analysis, we were able to satisfactorily identify and interpret the origin of 38 small “unknown” samples in two additional poorly-preserved cores in the study area. Having identified most of the facies, normalized factor components were used to correlate some of the sedimentary sections between cores. The investigation indicates that discrimination of Nile Delta facies and their correlation from core-to-core are most precise when the textural and compositional data are merged with the visually more obvious features (sedimentary structures, hardness, color, etc.), and when the petrologic data are placed within a chronostratigraphic framework of radiocarbon-dated subsurface sequence.