VERTICAL VARIATIONS OF ORGANIC-MATTER CONTENT IN GUAYUTA GROUP (UPPER CRETACEOUS), INTERIOR MOUNTAIN BELT, EASTERN VENEZUELA

A geochemical study of the vertical variations of organic matter in the Guayuta Group (Querecual and San Antonio Formations) has been conducted on a series of samples taken from a sedimentary sequence outcropping in the Interior Mountain Belt. The results indicate that despite very high thermal maturity, the organic matter content in the samples is still very high and shows geochemical characteristics related to anoxic paleoenvironmental conditions of sedimentation. Based on micropaleontological data, mineralogical data. and trace metal (V/Ni) ratio of kerogen, the analysis of the sequence shows stronger anoxic depositional conditions toward the base of the section and an increase of clastic sediments toward the top. The total organic carbon of the sediments increases toward the base of the sequence. In addition, there are pseudocyclic patterns and heterogeneities of the organic carbon content distribution at the meter-scale. The results indicate that the lower part of this sedimentary sequence represents a major anoxic event, that can be correlated with other sequences of middle and upper Cretaceous age.