Análisis de microfacies y de isótopos estables del Carbonífero de la sección La Joya en Sierra Agua Verde, Sonora, México

摘要

In the Sierra Agua Verde in central-eastern Sonora, Mexico, a sequence of paleozoic rocks crops out, deposited in a carbonate platform environment with a marine biota consisting of phylloid algae, fusulinid foraminifera, Chaetetes sponges, tabulate corals, gastropods, bryozoans, brachiopods, and crinoids. In this region, a Mississippian-Pennsylvanian section, corresponding to the Santiago and La Joya formations, was studied to analyze the microfacies and reveal the paleoenvironmental evolution of the area. Nine facies associations were described, based on the composition and texture of the sample, and were linked to standard microfacies and facies zones according to the modified Wilson model. The section was analyzed for 13C and 18O stable isotopes, which revealed a series of excursions that can be related both to a global or regional-local scale events, as well as with the defined facies belts. The results indicate the section was deposited in a series of marine environments including reefal margin, sand banks, and open and restricted lagoons. The C and O positive excursions might be related to marine regression events, which are product of glacial episodes. Such events characterized important time intervals during the Late Paleozoic. Also, the carbon and oxygen excursions are related, to an influx of waters proceeding from the continent that partially masked the δ13C and δ18O global excursion patterns. The study is relevant as it is pioneer in analyzing stable isotope excursions for Sonora, and opens a window to more exhaustive research about the excursion patterns that could be related to global climate changes in a region with abundant Upper Paleozoic outcrops in Mexico.