The Kimmeridgian/Tithonian boundary in the “Barranquito del Alacrán” section at Cuencamé (Durango, Mexico); its biostratigraphy and ecostratigraphic interpretation

Abstract

The data obtained from a new section of the Upper Jurassic in the Mexican Altiplano, studied bed-by-bed, reveal the presence of a fauna of Hybonoticeras, the absence of Mazapilites, and the recorded FAD of Subplanitoides siliceum (QUENSTEDT), which together show that the Kimmeridgian/Tithonian boundary in this part of Mexico is not related to the FAD of Mazapilites. The taphonomic analysis, sedimentological observations and the control of macroinvertebrate assemblages permit the interpretation of the eco-sedimentary evolution in a low-energy, moderately shallow, and relatively proximal environment, which was confined at least to the lower waters. In this monotonous succession of siltstones, the ecostratigraphic analysis reveals difficulties for the recognition of a sequence boundary coinciding with the Kimmeridgian/Tithonian boundary, as considered in recent proposals of the sequence stratigraphy.