Stratigraphic Evolution of Latest Cretaceous to Early Tertiary Difunta Foreland Basin in Northeast Mexico<subtitle>Influence of Salt Withdrawal on Tectonically Induced Subsidence by the Sierra Madre Oriental Fold and Thrust Belt</subtitle>

Abstract

The latest Cretaceous to Eocene Difunta Group in the Parras, La Popa, and the southern part of the Sabinas Basins in the states of Coahuila and Nuevo Len in northeast Mexico once occupied an extensive basin in the foreland to the Sierra Madre Oriental fold and thrust belt. The Difunta foreland basin records a complex history of initial Cretaceous deformation in the Sierra Madre Oriental and subsequent early Tertiary salt withdrawal in the region covered by the salt basin in the western part of the Gulf of Mexico. As a result of rapid facies transitions in the Difunta Group, stratigraphic correlation between the three structural basins is complex. Only one regionally extensive lithostratigraphic unit occurs in the Difunta Group, namely, the Maastrichtian Caon del Tule Formation in the Parras Basin and the correlative Muerto Formation in La Popa Basin and the southern part of the Sabinas Basin. Detailed sedimentologic and sequence stratigraphic studies of the Caon del Tule and Muerto formations have led to dramatic revisions in correlations in the Difunta Group. The Difunta Group is now subdivided into five informal stratigraphic cycles termed SC1, SC2, SC3, SC4, and SC5, each composed of marine mudstone and sandstone with overlying red fluvial mudstone. Stratigraphic cycles SC1 to SC3 were deposited in the latest Cretaceous in response to tectonic loading by encroaching thrust sheets in the Sierra Madre Oriental. In the southeastern Parras Basin, near the Sierra Madre Oriental frontal zone, the foredeep fill is at least 3677 m thick, thinning to 922 m, 150 km (structurally unrestored) to the north in the southern Sabinas Basin. Sediment dispersal was from west to east along the axis of the Difunta foredeep with a dissected volcanic arc provenance presumed to be the Guerrero composite terrane. Exceptionally high subsidence rates of 1 m/1000 years caused sediment to be trapped in the southern part of the foredeep, adjacent to the thrust belt, preventing early deltaic complexes in SC1 and SC2 from prograding eastward. The contemporary Mendez shale in the Tampico-Misantla foredeep, which was connected to the Parras–La Popa Basins across the Monterrey salient, represents a starved, underfilled equivalent of the Difunta foredeep to the southeast. In the distal northern part of the Difunta foredeep, in northern La Popa and southern Sabinas Basins, stratigraphic cycles are characterized by forced regression caused by limited subsidence. By the Paleocene and Eocene, thrusting in the Sierra Madre Oriental and accompanying foreland basin subsidence had ceased. In the region of the Parras Basin, no more sediment accumulated in the Difunta Group. In La Popa Basin and the southern part of the Sabinas Basin, which overlie the western extension of the Gulf of Mexico salt basin, growth of salt diapirs and associated salt withdrawal resulted in accumulation of more than 2300 m of sediment in structural minibasins. Large volumes of volcaniclastic detritus continued to be supplied from the west, filling the salt minibasins with fluvial and shallow-marine sediment. These Tertiary sequences represent cycles SC4 and SC5 in the Difunta Group. By the Paleocene, in the Tampico-Misantla portion of the Difunta foredeep, axially derived sands were deposited in the Chicontepec paleochannel. Only limited carbonate clastic input from the Sierra Madre Oriental highland was received in the Tampico-Misantla Basin in the Tertiary, and at no time did the Sierra Madre Oriental supply detritus to the Parras or La Popa Basins. Some time after the Eocene, probably in the early Oligocene, the region covered by the Difunta foredeep was deformed, uplifted, and eroded, leading to the present outcrop pattern of structural basins and highs. This episode of uplift resulted in large volumes of sediment being deposited in the western Gulf of Mexico Basin and led to substantial progradation of the northeast Mexican continental margin and establishment of a large, early Oligocene depocenter.