Tracing source and paleoweathering conditions of the lower jurassic sandstone from sierra de santa rosa section, Northern Sonora, México

Abstract

The Lower Jurassic sedimentary rocks of the Sierra de Santa Rosa Formation in northern Sonora, Mexico has been deposited in a forearc basin and its age has been assigned based on the fossil assemblages and detrital zircon U–Pb geochronology data. Neverthless, their geochemical characteristics has not undertaken yet. In this study, the whole rock geochemistry (including major oxides, trace, and rare earth elements) of 23 sandstone samples from the Sierra de Santa Rosa Formation is investigated to infer the provenance and paleoweathering conditions of the basin, within the Lower Jurassic paleogeographic framework. The concentration of total rare earth elements (ΣREEs) range between 46.5 and 166.6 ppm (ave. 118.7 ppm), which is lower than the average Upper Continental Crust (UCC) value (147.80 ppm). Chemical index of weathering (CIA), weathering index of Parker (WIP), and A-CN-K diagrams signify the low to moderate chemical weathering in the source region. It suggests that the source regions experienced arid to semi-arid climatic conditions during the deposition of these detritus. The chondrite normalized REE patterns, negative Eu anomaly, bivariate diagrams and elemental ratios like, Eu/Eu*, La/Sc, La/Co, Th/Sc, Th/Co, and Cr/Th indicate that majority of the detritus were derived from the felsic rocks with minor contribution from intermediate source rocks.