Abstract
Abstract
A total of 763 rock samples from the Tumaco and San Juan-Atrato basins, located along the Colombian Pacific continental margin, were evaluated for total organic carbon (TOC), rock-eval pyrolysis (RE-Py), and vitrinite reflectance (Ro) to determine the type, origin, paleodepositional environment, and thermal maturity of the organic matter (O.M.). In both basins, the TOC content ranges from 0.77 and 2.43%, considered to be within the “acceptable” range. Rock-Eval pyrolysis results indicate that S1 peak (free hydrocarbons) ranges between 0.02 and 1.09 mg HC/g rock, while S2 peak varies between 1.10 and 1.29 mg HC/g rock. The average Tmax ranging between 398 and 417°C, classify the organic matter in its early maturity to thermally immature, which is confirmed by the petrographic measurements with values ranging between 0.1978 to 0.5418%. Geochemical indices derived from the TOC and RE-Py data show hydrogen index (HI) values between 300 and 600 mg HC/g TOC, classifying the organic O.M. as predominantly Type III and/or mixed Type II/III kerogen. This suggests that the primary generated products are gas and/or oil–gas mixtures, particularly within the deeper intervals of the column, reflecting a transitional composition derived from mixtures of marine and terrestrial organic matter. The maturity indices calculated from screening parameters suggest that the O.M. did not originate from a single kerogen source, but rather reflects significant variations in paleodepositional environments and maturity stages.