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

A geochemical study of the vertical variations of organic matter in th e Guayuta Group (Querecual and San Antonio Formations) has been conduc ted on a series of samples taken from a sedimentary sequence outcroppi ng in the Interior Mountain Belt. The results indicate that despite ve ry high thermal maturity, the organic matter content in the samples is still very high and shows geochemical characteristics related to anox ic paleoenvironmental conditions of sedimentation. Based on micropaleo ntological data, mineralogical data. and trace metal (V/Ni) ratio of k erogen, the analysis of the sequence shows stronger anoxic depositiona l conditions toward the base of the section and an increase of clastic sediments toward the top. The total organic carbon of the sediments i ncreases toward the base of the sequence. In addition, there are pseud ocyclic patterns and heterogeneities of the organic carbon content dis tribution at the meter-scale. The results indicate that the lower part of this sedimentary sequence represents a major anoxic event, that ca n be correlated with other sequences of middle and upper Cretaceous ag e.