--> Abstract: Geology of Sierra Baluartes Diapir and Sierra de Pajaros Azules, Coahuila, Mexico, by Marshall J. Vinet, Alfred E. Weidie; #90967 (1977).

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Abstract: Geology of Sierra Baluartes Diapir and Sierra de Pajaros Azules, Coahuila, Mexico

Marshall J. Vinet, Alfred E. Weidie

Sierra Baluartes and Sierra de Pajaros Azules are in the Sabinas basin of Coahuila, Mexico. These two areas differ in structural character. Sierra de Pajaros Azules trends northwest-southeast and is an elongate, breached, asymmetric anticline. The Sierra Baluartes area, on the northwesterly plunging nose of Pajaros Azules, is an oval mass of diapiric gypsum flanked on the north and east by a discontinuous ridge of nearly vertical Aurora Limestone. Exotic blocks of various sizes and lithologies are incorporated within the gypsum. Normal faults radiate outward from the diapir. Doming and possibly diapirism occurred in the Baluartes area during the Neocomian, Aptian, and Albian, with possible subaerial exposure during the Neocomian.

Sierra Baluartes and Sierra de Pajaros Azules likewise differ lithologically. A comparison of the Cupido and Aurora limestones in the two areas illustrates their differing Early Cretaceous depositional and tectonic histories. In the Pajaros Azules area, a 6,000-ft (1,828 m) section of the complete Taraises, Cupido, La Pena, and Aurora formations crops out. Units here are low-energy, marine, carbonate rocks and terrigenous mudstones characteristic of this part of the Sabinas basin. Cupido is predominantly miliolid, pellet wackestones and packstones which represent shallow, semirestricted, intertidal-subtidal, marine conditions. The Aurora is a calcisphere, globigerinid- and tintinnid-rich, pellet wackestone which represents "deeper water," open-marine conditions. The Cupido and Aurora ere are indicative of low-energy depositional environments. In comparison, the Cupido Limestone in the Baluartes area is predominantly thickly bedded grainstones rich in lithoclasts (eroded Taraises) and intraclasts. A few intervals are boulder conglomerates. The Cupido rocks represent high-energy, shallow-marine conditions. The Aurora is predominantly oncolite wackestones and packstones indicative of "higher energy" conditions than those of the Pajaros Azules area. The Cupido and Aurora in this area were deposited over a submarine topographic high.

In the Baluartes area, salt tectonics caused domal uplifting, possibly with minor diapirism, in the Early Cretaceous. This doming affected the thickness and lithology of the rocks. Laramide tectonics deformed both areas, forming the Sierra de Pajaros Azules anticline by decollement of the Upper Jurassic evaporites, and causing diapirism and associated faulting in the Baluartes area.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas