GEOCHEMISTRY OF OIL SEEPS AND ROCK SAMPLES OF THE EARLY TERTIARY SECTION FROM THE NORTHANDEAN FLANK OF THE VENEZUELAN ANDES

An organic geochemical study of oil seeps and Early to Middle Tertiary source rocks of the Northandean Flank (NAF) of the Venezuelan Andes r ange was performed to establish the possible contribution of terrestri al source rocks to the oil accumulations in the unexplored southern pa rt of the Maracaibo Basin. Source rocks were identified within the Pal eocene Barco and Los Cuervos Formations, and the Late Eocene-Oligocene Carbonera Formation. Biomarker distributions indicate a terrigenous o rganic source for these units. Geochemical modeling performed by Parna ud et al. (1995), indicated Plio-Pleistocene oil generation for the Or ocue Group and Middle Miocene to Plio-Pleistocene oil generation for t he Carbonera Formation. Geochemical modeling also indicates that the q uantity of crude oil expelled by the Carbonera Formation is four times that expelled by the Orocue Group (Barco and Los Cuervos Formations), A northeast to southwest variation from marine to terrestrial oil see ps was identified based on sterane and terpane distributions. The mari ne oil seeps appear to be derived from the La Luna source rocks. The c haracteristics of the mixed oils suggest contributions from different sources (La Luna and a terrestrial source rock) most likely the Orocue Group or Carbonera Formation coals. Source facies similar to those in the Los Cuervos and Carbonera Formations coals are most likely the ma in source rocks of terrestrial oil seeps in the NAF.