ARTÍCULO

Provenance of the Jurassic Huayacicotla Formation and Alamitos Sandstone, Central Mexico: paleogeographic and paleoclimatic changes

Ocampo-Díaz, Y.Z.E., Torres-Sánchez, S.A., Augustsson, C., Barboza-Gudiño, J.R., García-Díaz, J.L., Talavera-Mendoza, O., Aceves-de Alba J., Castro-Larragoitia, J., Martínez-Paco, M., Saucedo, R., Aguillón-Robles, A.
Chemie der Erde Geochemistry, 79(2), 369-383. https://doi.org/10.1016/j.chemer.2019.05.004, 2019.

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ABSTRACT:

We present a modified model for the paleogeographic evolution of Mexico during Early and Late Jurassic time that is constrained by the tectonic setting and the weathering conditions of the Early Jurassic Huayacocotla Formation and Late Jurassic Alamitos Sandstone basins in state San Luis Potosí in central Mexico. Framework petrography constrains feldspato-quartzose sandstone (mean of Q68F22L10) and litho-quartzose (mean of Q75F6L19) sandstone compositions for the two units, respectively. The abundant lithic fragments are totally dominated by volcanic fragments. Quartz cathodoluminescence colours and textures from the Alamitos Sandstone supports a large input of volcanic material, but also indicates the presence of metamorphic quartz. Similarly, the geochemical composition is more mafic for the Huayacocotla Formation (Th/Sc: ˜0.6 and Cr/Th: ˜10) than for the Alamitos Sandstone (Th/Sc: ˜1.1 and Cr/Th: ˜48). Also the weathering conditions were less intense during the Early (CIA: ˜60, PIA: ˜61) than the Late Jurassic (CIA ˜85, PIA ˜97). Well preserved lithic fragments and feldspar grains, particularly in the Huayacocotla Formation, indicate that weathering indeed was minor for this unit. We interpret the difference between the two units as a combined result of climate change and tectonic setting. During the Early Jurassic, transport of volcanic detritus probably dominated from the active Nazas arc in the west. Later, additional sources from the metamorphic basement of Mexico were included. During Late Jurassic time strike-slip faulting related to the opening of the Gulf of Mexico may have re-directed the sediment-transport systems. Finally, the degree of weathering was affected by drastic climatic change from arid to humid tropical conditions during the Middle to Upper Jurassic, possibly related to the first incursions of Gulf of Mexico marine environments linked to the rotation of the Yucatan block.