The Vizcaíno terrane: another occurrence of Upper Triassic shallow-marine carbonates in Mexico

Abstract

Outcrops of Upper Triassic carbonates of shallow-marine character are rare in Mexico. Another locality, next to the Antimonio depositional system (ADS) in Sonora, is found on the Vizcaino terrane (Baja California Sur), near the village of San Hipolito. The outcropping formation is named after the nearby village and represents an arc-ophiolite assemblage. The formation comprises a limestone breccia, which includes re-worked Upper Norian shallow-water limestone. In addition, questionable lowermost Rhaetian radiolarians have been found in some clasts of the breccia. Accordingly, the breccia member possibly deposited during the uppermost Norian–lowermost Rhaetian. Based on their preservation, 43 clasts representative of the main lithologies have been sampled along a 550-m-long outcrop surface. Some authors proposed the Vizcaino to have been in close relation to the ADS in north-western Sonora. It has been proposed that the Antimonio served as the source of the limestone clasts contained within the San Hipolito Formation. Petrographic analysis and micropaleontologic evidences, however, indicate a more distal relationship between the two systems. Furthermore, the microfacies proposed by the hierarchical clustering include some rather poorly constraint facies. This could be explained by the facts that (a) the samples have derived from clasts that not necessarily represent a stratigraphic succession and (b) multiple systems could have contributed to the assemblage.