PALEO-PACIFIC TRIASSIC-JURASSIC CONTINENTAL SLOPE DEPOSITS TO THE GULF SEDIMENTARY RECORD IN THE SIERRA DE CATORCE, NORTHEASTERN MEXICO

In the Sierra de Catorce, an uplifted block in southernmost Basin and Range province in northern San Luis Potosí, the exposed succession includes Upper Triassic fine-grained sandstone and shale, interpreted as lateral equivalents of deep marine turbidites of the Zacatecas Formation to the west. Upwards, the deposits become chaotic and are product of flow events, accord to strong sin-sedimentary deformation, including Interlayered greenstone horizons and quartz-litharenites which change upwards in to fine-grained yellow and red-purple sandstone and siltstone layers. The succession, which is deep marine in their lower part and change gradually upwards up to marine marginal, is not present in other Triassic-Jurassic exposures in the region. It was informal named Cerro El Mazo beds and is probably comparable to beds mapped in northern Zacatecas, as Taray Formation or partly as Rodeo Formation. The outcrops in Sierra de Catorce include strata that allow interpreting the tectonic-paleogeographic evolution of the ancient pacific margin of Mexico during Late Triassic-Early Jurassic time. The Cerro El Mazo beds in their lower part, may be represent deposition at a Paleo-Pacific continental slop, southeast of outcrops of the Triassic El Alamar fluvial system, placed in the actual geography in southern Nuevo León and east of the exposures of deep marine turbidites of the Zacatecas Formation, in Charcas and La Tapona areas, in western San Luis Potosí. While in most of the known Triassic-Jurassic outcrops in the Mesa Central province, the Carnian-Norian Zacatecas Formation unconformable underlie Early Jurassic volcanic rocks of the Nazas Formation, in Real de Catorce, the Cerro El Mazo beds build a gradual change between the Zacatecas Formation and the Nazas Formation. In turn, volcanic rocks of the Early-Middle Jurassic Nazas Formation, underlie breccia-conglomerate and red sandstone of La Joya Formation, that represents an erosional (break-up) unconformity related to rifting and probably initial sea floor spreading in the Gulf of Mexico.