Resumen

OCAMPO-DIAZ, Yam Zul Ernesto; GUERRERO-SUASTEGUI, Martín  y  JENCHEN, Uwe. Petrography and source for the Galeana sandy member (Taraises Formation, Valanginian-early Hauterivian), Sierra Madre Oriental, NE Mexico. Bol. Soc. Geol. Mex [online]. 2012, vol.64, n.3, pp.335-352. ISSN 1405-3322.

Extensional systems are characterized by multiphase reactivation of faults that are conducive to erosion, redistribution of sediments within the basin and affect the composition of the sandstones. The provenance analysis of these sedimentary sequences documents the stages of evolution of these systems, as well as the composition of the buried basement blocks. This paper is based on a rigorous petrographical analysis and point counting in 58 samples of sandstones from the Galeana sandstone member, Taraises Formation (Early Cretaceous). It documents the composition and location of source areas that led to the origin of the sandstones, and the petrotectonic evolution of the southern region of the Monterrey Trough during the Early Cretaceous. Petrographically, the Galeana sandstone member can be divided into three petrofacies and two provenance sequences that are closely related to the sedimentary environment in which they were deposited. Sedimentoclastic petrofacies A corresponds to tidal facies deposits and represents the erosion of preexisting rocks from the pre-Early Cretaceous, with a moderate influence of basement rocks of granitic and/or granodioritic and schistose composition. Sedimentary-plutonoclastic petrofacies B corresponds to a shift in lateral facies from petrofacies A (north-south). It shows a higher recycling index associated with the subaqueous dune sedimentary environment, changes in the source area composition, and internal recycling (intraformational or cannibalism). Petrofacies C marks the deposition of a second provenance sequence, represented by an east-west lateral change in petrofacies A and B. The sandstones represent the greatest exposure and erosion of deep basement rocks. The compositional differences between the lithic assemblages suggest that a sedimentary transport event occurred during the Early Cretaceous, from the Tamaulipas Arch and Terán Island in the east to the Monterrey Trough, favoring the erosion of the sedimentary cover, and to a minor degree plutonic, volcanic and low to medium-grade metamorphic rocks. Such erosion led to the deposition of the first provenance sequence (petrofacies A and B). On the other hand, the early Hauterivian represents a second provenance sequence (petrofacies C), and the major period of block exhumation. Therefore, this paper proposes that during the early Valanginian-middle Hauterivian, the Monterrey Trough was exposed to extensional processes related to strike-slip systems that produced the exhumation of basement rocks.

Palabras llave : provenance; sedimentary petrography; Sierra Madre Oriental; Taraises Formation; Galeana sandstone member; NE Mexico.

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