Abstract

Our study examines the origin of hydrocarbons in a large exhumed oil field located in the Sierra de El Abra along the eastern margin of the Valles-San Luis Potosi platform and the leading edge of the Sierra Madre Oriental fold-thrust belt. The El Abra Formation is exposed in quarries where it is heavily impregnated with bitumen. Geochemical analyses of stains and fluid inclusions within the quarries suggest that two types of oil are present. The first is a highly mature volatile oil and condensate with thermally degraded biomarker signatures. The second oil is similar in maturity to the Golden Lane oils of the Tuxpan platform but is derived from a more clastic-rich lithofacies. Our integrated paleothermometry data indicate that the El Abra Formation in the quarries was buried by Lower Tertiary sediments to a depth of approximately 5 km and uplifted about 30 Ma. Large volumes of hydrocarbons were generated within the fold-thrust belt during the Paleocene and migrated eastward where they were trapped within the Sierra de El Abra just prior to or during deep burial. A second, smaller charge of hydrocarbons was trapped in the same structure during Eo-Oligocene uplift of the frontal part of the fold-thrust belt and the foreland. The source of this later oil is presently unclear, but most likely came from a more foreland position where lower maturity Upper Jurassic source rocks are preserved. Relatively recent regional uplift and erosion were responsible for breaching the large hydrocarbon accumulation. Our analysis indicates the Sierra Madre Oriental fold-thrust belt played a significant role in the formation of hydrocarbon accumulations along the eastern margin of the Tampico-Misantla basin.