Resumo

OCAMPO-DIAZ, Yam Zul Ernesto  e  RUBIO-CISNEROS, Igor Ishi. Sedimentary recycling: compositional analysis associated with unconformities in northwestern Mexico, an Upper Triassic to Lower Cretaceous example. Bol. Soc. Geol. Mex [online]. 2013, vol.65, n.3, pp.553-572. ISSN 1405-3322.

The stratigraphic column of the Monterrey Trough in northeastern Mexico is represented by five Late Triassic to Early Cretaceous clastic sequences that show temporal relations defined by angular-erosive unconformities. This work analyses the composition of these sequences by means of sedimentary petrography, and compositional and recycling indices in order to comprehend the recycling-cannibalism process, the compositional variation between source-lands, and its relation to unconformities. The petrographic analysis, as well as the modal composition and the use of compositional indices (e.g., F, Lm, Qm) for the clastic sediments allows the establishment of three recycling periods or important source-rock addition using the QmFL diagram: 1) Upper Triassic (Qm₇₀F₁₀L₂₀), medium-high grade metamorphic source rock erosion with an elevated Qm content suggesting a high rate of sediment transport; 2) Lower Jurassic (Qm₄₀F₂₂L₃₈), a period with maximum rejuvenation of volcanic and metamorphic sources; and 3) Lower Cretaceous (Qm₅₆F₃₁Lt₁₃), a period of short-lived exhumation for the source areas mainly characterized by granites or granodiorites, volcanic rocks and, to a lesser degree, low-grade metamorphic rocks. The set of interpretations for compositional variations (QFL) and indices suggests the evolution of a recycling process, and allows proposing an empirical sedimentary recycling index (SeReIn). The SeReIn was applied and is described for three cases, demonstrating statistical sensitivity in changes related to sedimentary facies (e.g., high tide or storm deposits), grain size (e.g., tidal channels), and genetic implications in the unconformities within the stratigraphic column of the Monterrey Trough (intraformational cannibalism versus allocyclic controls).

Palavras-chave : rejuvenation; compositional indices; recycling; Northeastern Mexico; sedimentary cannibalism; sedimentary petrography.