Resumo

OCAMPO-DIAZ, Yam Zul Ernesto. Petrographic and multivariate statistic analysis for determining source areas of the La Casita Formation (late Jurassic-early Cretaceous) and the Patula Arkose (early Cretaceous) in northeastrn Mexico. Bol. Soc. Geol. Mex [online]. 2013, vol.65, n.3, pp.609-630. ISSN 1405-3322.

During the Late Jurassic to Early Cretaceous, two large sedimentary basins in northeastern Mexico, the Sabinas basin and the Monterrey through, accumulated thick clastic sequences. Two examples of these clastic sequences are the Patula Arkose (Early Cretaceous) and La Casita Formation (Late Jurassic - Early Cretaceous), which were petrographically and statistically analyzed in this study. The Patula Arkose, a feldsphatic arenite (Q₅₄F₃₈L₈,-with a confidence level of the 99%), was deposited into continental blocks with trends to continental transition (Qm₅₄F₄₁L₅, 99% of the confidence level).The petrographic characteristics and the mineralogical relationships suggest that the source rocks of the Patula Arkose were mainly low-grade metamorphic rocks (pelitic or psammitic schists), granite or granodiorite, limestone and sandstone. La Casita Fomation is composed of lithic arenite and feldesphatic arenite (Q₅₂F₂₇L₂₁, with a confidence level of the 99%) deposited in a dissected arc or a continental transition area (Qm₅₂F₆₄L₁₄, with a confidence level of the 99%). The sandstone petrography of La Casita Formation in the Monterrey trough shows a very complex provenance that implicates medium to high grade metamorphic rocks, andesite, rhyolite, limestone, sandstone, and shale sources. A multivariate statistical analysis of the main components, and the application of binary diagrams of petrographic index with additive and centered logratio transformation (alr and clr) confirmed the source rocks composition, suggesting that: i) the Patula Arkose is richer in low-grade metamorphic fragments, which are probably related with the Ouachita Mountains with 99% of confidence level, and with granitic or granodioritic rocks of Permian-Triassic age; ii) La Casita Formation has affinity with the Paleozoic Las Delicias volcanic arc, Permian-Triassic and Early Jurassic arcs, and with medium to high grade metamorphic rocks that were possibly part of the Novillo Complex.

Palavras-chave : Sedimentary petrography; provenance; northeastern Mexico; Early Cretaceous; La Casita Formation; Patula Arkose.