ABSTRACT

The Parras and Sabinas basins in Coahuila and Nuevo Leon and the Ojinaga basin in northeastern Chihuahua were the principal sites of Late Cretaceous sedimentation in northeastern Mexico. Comparative study of these basins provides insight into the Late Cretaceous geologic history of the area. Inter-basin similarities suggest first-order regional patterns; whereas, differences are the product of second-order local causes.

The three basins contain a similar sequence of deltaic deposits that show the same sense of progradation (west to east). The deltaic sequence is older (Campanian) in the Ojinaga basin and younger in the Parras and Sabinas basins (Campanian and Maestrichtian). Regional uplift, continuous sediment input, and shifting depositional sites from Campanian through Maestrichtian time produced these eastward shifting deposits.

The deltaic sequence differs from basin to basin. It is 1,000 feet thick in the Ojinaga basin, 3,000 feet thick in the Sabinas basin, and 10,000 feet thick in the Parras basin. Coal deposits are part of the sequence in the Ojinaga and Sabinas basins but absent in the Parras basin. Sediments in the Ojinaga and Sabinas basins were deposited during a single major progradational event; whereas, the sediments in the Parras basin were deposited during multiple progradational and retrogradational cycles. These differences in the anatomy and thickness of the depositional sequences were produced by local tectonic events. The relatively thin, deltaic sequence with associated coal deposits of the Ojinaga and Sabinas basins suggest low subsidence rates together with low sediment input rate in these areas. The thick, cyclic, non-coal bearing, progradational-retrogradational sequence of the Parras basin suggests a high rate of subsidence and sediment input concomitant with tectonic instability south and west of the depositional area.