Geochemistry and Petrography of Organic Matter in Cretaceous Sediments from the Southeastern Gulf of Mexico, Deep Sea Drilling Project Hole 535—Preliminary Results

Abstract

Organic geochemical and organic petrographic methods were used to study three Lower to middle Cretaceous sediment samples from Hole 535 in the southeastern Gulf of Mexico for organic matter contents and origin and level of maturation. All three samples contain mixed kerogen Type II/III organic matter with a maturity corresponding to about 0.4% vitrinite reflectance. The marine component increases with stratigraphic age, and microbial reworking of the organic matter is significant in each age. The lower two samples of Hauterivian to Valanginian age appear to be impregnated (or contaminated) with soluble polar organic compounds, but there is only a weak indication for the presence of more mature, nonindigenous hydrocarbons.

Geochemical characterization of source rocks, crude oils and gases of Northwest Cuba

“…Five Lower Cretaceous formations were described in the literature as levels of distinct and variable organic rich sediments (Herbin et al, 1984;Rüllkotter et al, 1984). The published data mentions bioturbated organic matter in limestones and marl layers with unusual asphalt filled fractures and adjacent oil stained levels, where the host rocks contain small levels of unstained organic carbon with very different genetic and thermal signatures.…”

“…Part of the study has been focused on a study of outcrops and selected rock samples whose information served as input to geochemical modelling that simulate the generation and expulsion of the source rocks in 1D and 2D by Moretti et al (2004). The rest of the geochemical characterization study concentrated on the origin and maturity levels of gases and oils, and their relationships to a Lower Cretaceous offshore DSDP well impregnated limestone sampled years ago (Herbin, Deroo, & Roucaché, 1984;Rüllkotter, Mukhopadhyay, Hartung, & Welte, 1984). The present newly collected source rocks, gases and oil samples were chosen because they belonged to producing intervals mostly in Upper Jurassic and Lower Cretaceous sedimentary sequences.…”