Print this pageInfluence of Intermittent Salt Diapirism and Madrean Thrusting on Late Cretaceous-Paleogene Sedimentation Patterns, La Popa Basin, Mexico
LAWTON, T. F. and GILES, K. A.
Stratal geometries and lithofacies distribution in La Popa basin of northern Mexico record coeval Late Cretaceous foreland basin deposition and salt diapirism succeeded by Paleogene fold-thrust disruption of the foreland. In Maastrichtian time La Popa basin lay in the distal part of the Madrean foreland basin system, probably within the forebulge depozone. Localized flexural extension at the forebulge permitted diapiric rise of Jurassic evaporite that created favorable sites for carbonate deposition in a basin otherwise flooded with siliciclastic mud. At El Papalote diapir, rimming foram-rich carbonate grainstones and rudstones thin radially away from the diapir and interfinger with fine-grained siliciclastics of the Potrerillos Formation. Carbonate facies distribution and geometry are asymmetric about the diapir reflecting a oceanward versus leeward depositional setting. Carbonate strata on the oceanward flank form numerous horizons that are upturned adjacent to the diapir, truncated and unconformably overlain by boulder conglomerate beds containing clasts eroded from underlying units and the diapir itself. Beds of gypsum on the order of 10 m thick are interbedded in the conglomerate-limestone section and represent episodic lateral expansion of the evaporite mass. Folding and truncation of successive beds comprise a progressive unconformity that records intermittent rise, exposure and erosion of the diapiric mass and flanking strata Only two carbonate horizons are present on the leeward side and intercalated evaporites are not present Diapir-deformed strata are overlain by undeformed Paleogene strata that postdate the youngest major salt tectonism.
Diapiric stratal geometries are presently exposed in cross section on the northern flank of a large, southwest-verging, thrust-cored anticline that postdates diapirism. Southerly vergence is consistent among La Popa basin structures, but contrasts with E- NE vergence m the Sierra Madre thrust belt to the south. Southwest-directed thrusting resulted from Paleogene inversion of the Cretaceous Sabinas basin directly to the north.