Stratigraphic architecture, depositional environments and geochronology of the Olinalá Formation (late Permian), northeastern Guerrero, Mexico

Abstract

The Olinalá Formation is a marine-continental Permian sedimentary succession of ~ 860 m thick exceptionally exposed in the northeast of Guerrero, in southern Mexico. The stratigraphic architecture of this sedimentary succession corresponds to a homoclinal carbonate ramp system with siliciclastic influence. This succession contains a wide diversity of siliciclastic continental and marine facies, and carbonate marine facies that indicate its development in warm waters under marine conditions. Siliciclastic facies include: conglomeratic sandstone, cross-stratification polymictic conglomerate, trough cross-stratification sandstone, quartz-crinoid conglomerate, and graded quartz-sandstone. Shallow marine and outer shelf facies include: bioturbed sandstone and black shales. Carbonate facies represent predominantly shelf margin environments and include: crinoid-bryozoan-brachiopod grainstone, coralline red algae biohermal, muddy brachiopod packstone, fusulinid wackestone, and radiolarian wackestone.

The Olinalá Formation is a marine-continental Permian sedimentary succession of ~860 m thick, which is exceptionally exposed in the northeast of the Guerrero state, in southern Mexico. The depositional architecture of this sedimentary succession indicates a mixed carbonate-siliciclastic homoclinal ramp system. The U-Pb ages of detrital zircon grains set from two basal sandstones of the Olinalá Formation yielded a weighted mean maximum deposit age of 268±5 Ma, which agrees with a Wordian biostratigraphic age based on ammonoids collected at its base. Wide continental siliciclastic facies diversity was identified in this sedimentary succession that represents a prominent fluvial incision valley of 130 m depth, at least. Instead, the siliciclastic and carbonate marine facies indicate a ramp system developed in warm waters and normal salinity conditions. The superposition of different environments in the Olinalá Formation through time allows us to deduce sea-level changes of a different magnitude, which partly controlled the sedimentary evolution of this unit.