Middle Cretaceous cores from the prolific oil fields of the Golden Lane and Poza Rica trends in eastern Mexico were studied to determine the environment of deposition of the reservoir and associated rocks and to compare these with similar middle Cretaceous carbonate rocks along the Gulf Coast.

The Golden Lane fields produce from the El Abra Limestone, which was deposited in a shallow shelf or lagoon with scattered rudistid patch reefs. The structurally lower Poza Rica trend fields are 5-8 mi west and southwest of the Golden Lane, and contain rocks of the Tamaulipas and Tamabra Formations. The Tamabra Formation is composed largely of shallow-water coral-rudistid reefs, debris derived from the reefs and deposited in shoal-water nearby, and forereef talus mixed with basinal carbonate mudstone of Tamaulipas facies. Production in the Poza Rica trend is mainly from the reef debris. No coral-rudistid reef was recognized in the small amount of core examined from the Golden Lane, and available data do not support the prevalent view that the materials comprising the Tamabra Formation were transported 5-8 mi from the Golden Lane.

The carbonate rocks of the Golden Lane and Poza Rica trends and of the "Deep Edwards" trend in south Texas are of approximately the same age and, broadly speaking, were deposited under similar environmental conditions on a shallow shelf and at the shelf edge, adjacent to a basin. The Golden Lane and Poza Rica trends are only 30-40 mi from the Sierra Madre Oriental, a major early Tertiary orogenic belt, whereas the "Deep Edwards" trend is hundreds of miles from the same belt. Thus, although depositional environments of the Lower Cretaceous in south Texas parallel those of eastern Mexico, the subsequent geologic histories of the two regions differ markedly.

End_of_Article - Last_Page 706------------