PRELIMINARY REDEFINITION OF STRATIGRAPHY OF JURASSIC ROCKS IN SANTO DOMINGO TIANGUISTENGO BASIN, OAXACA, SOUTHEAST MEXICO

The Santo Domingo Tianguistengo basin is located in the center of Sierra Mixteca, southeastern Mexico. In this area is exposed a Paleozoic polydeformed crystalline basement composed by the Acatlán Complex, the Totoltepec pluton and the Santo Domingo Gabbro, these three units are unconformably overlain by a Jurassic-Cretaceous sedimentary succession. We propose here the preliminary stratigraphy of the Mesozoic succession based on field and petrographic data. We recognized four stratigraphic units that, from the base to the top, are: the Tianguistengo, Cazahuate, Magdalena, and Coyotepec formations. The Tianguistengo Formation is made up of flood plain sandstone, shale, and scarce limestone displaying cross-bedding, convolute bedding, lamination and bioturbation, and containing fossil woods and roots. The Tianguistengo formation is unconformably overlain the Cazahuate formation, which we subdivide into three informal members. The Piedra Hueca member is composed by coarse-grained, cross-bedded fluvial sandstone and conglomerate with clasts proceeding from the Paleozoic crystalline basement. The Piedra Hueca member is unconformably overlain by the Santa Cruz and Otlaltepec members. The Santa Cruz member is made up of medium-grained, cross-bedded fluvial sandstone quartz rich. The Santa Cruz and Piedra Hueca members are in turn unconformably overlain by the Otlaltepec member, which consists of medium- to coarse-grained, quartz-arenite with nodules. The Cazahuate unit is unconformably overlain by the Magdalena formation, defined as a succession of conglomerate, sandstone, and shale. Finally, this latter unit grades up section to Albian-Cenomanian limestones of the Coyotepec formation. Base on the ubiquitous presence of syn-sedimentary faults in the Jurassic units, we interpret preliminary that at least the lower stratigraphic part of this Mesozoic succession was deposited in an extensional or transtensional setting. Thus, the angular unconformities documented in this paper could mark the tectonic evolution of growth faults related to the opening of the Santo Domingo Tianguistengo basin.