Cretaceous sequences in Jamaica are best exposed in inliers which interrupt the monotonous Tertiary limestone cover that forms the surface geology over most of the island. Surface samples were collected over the major inliers of western, central, and eastern Jamaica. Conventional cores from shallow boreholes enabled sampling of subsurface formations. Cretaceous lithologies include gray to black mudstones and shales (only these were sampled for geochemical analyses) commonly associated with fine-grained sandstones and conglomerates dominated by andesitic clasts.

Total organic carbon values are variable but are generally in excess of 0.5%. Vitrinite reflectance (R_o) measurements for the western and central inliers average 0.80% and are well within the oil-generating zone. The Blue Mountain inlier of eastern Jamaica has R_o values above 1.0%, reflecting the heat flow associated with Cretaceous volcanism.

The organic matter preserved in these sediments consists predominantly of coaly to woody material; exinites are rare and fluorescence studies indicate traces of hydrocarbons and minor amounts of spores. Pyrolysis of selected samples suggests Type III kerogens with fair to poor production indices. Capillary gas chromatography of the saturate fractions of dichloromethane extracts reveals marginally mature to mature sediments with organic matter showing a dominant contribution from higher land plants. All samples analyzed have a low extract yield relative to their total organic carbon contents (< 60 mg/g) indicating a low convertibility of the organic matter to liquid hydrocarbons.

Geochemical analyses of a number of Cretaceous samples to determine maturity and source-rock potential reveal a variable maturity with potential for gas generation (and possibly high-wax crudes) at depth.

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