Geochemical characterization of potential source rocks and oils from the Cariaco area in the northeastern offshore margin of Venezuela

The Cariaco offshore area, located along the northeastern margin of Venezuela, represents a key segment for understanding the petroleum systems associated with the Caribbean-South American plate boundary. This study integrates organic geochemical analyses of 130 rock samples from eight exploratory wells and six oil samples (including three natural seeps) to evaluate the hydrocarbon generation potential, source rock characteristics, and genetic relationships between oils and potential source rocks in the Tuy-Cariaco, La Tortuga, and La Blanquilla basins. Rock-Eval and total organic carbon (TOC) results indicate that most Miocene and Oligocene shales contain Type II-III and III-II kerogen, deposited under suboxic to dysoxic conditions, with localized high TOC values (>2 wt.%) in the La Tortuga and northern Tuy-Cariaco basins. Thermal maturity parameters indicate that Paleogene units reached the oil window, whereas Neogene successions are marginally mature. Molecular and isotopic data reveal two distinct oil families: (i) Miocene-derived oils from the Tuy-Cariaco Basin characterized by δ 13 C values around -21‰ and transitional marine-terrigenous signatures, and (ii) Oligocene-derived oils from the La Tortuga Basin with lighter δ 13 C values (≈ -26‰) and stronger terrestrial input. Biomarker correlations indicate that Miocene source rocks within the Cariaco Trough likely generated the oils accumulated in the Tuy-Cariaco Basin, while Oligocene shales from the La Tortuga Basin charged local accumulations and the condensate found in La Blanquilla. These results highlight the coexistence of multiple petroleum systems along the northeastern Venezuelan margin, with potential for additional hydrocarbon resources in the deeper sectors of the Cariaco area.