Middle Oxfordian ammonite biostratigraphy of the Lower Santiago Formation at Tamán, San Luis Potosí, Mexico — with notes on Mexico-Caribbean ochetoceratins

Abstract

Bed-by-bed sampling of ammonites from clayey to calcareous siltstones of the basal part of the Santiago Formation at the type section in Tamán, San Luis Potosí (Mexico) is first reported. Ammonites belonging to assemblages described by Burckhardt (1912), usually interpreted as Middle to Upper Oxfordian, are restricted to the lower Middle Oxfordian Plicatilis Zone, Antecedens Subzone. Perisphinctes (Dichotomosphinctes) durangensis (Burckhardt, 1912) is revised and its biostratigraphic interpretation constrained by its co-occurrence with Gregoryceras. Evidence for the occurrence of Perisphinctes (Perisphinctes), Perisphinctes (Otosphinctes), and Passendorferia or Sequeirosia is first reported from Mexico within a precise biostratigraphic context. Burckhardt’s Oxfordian ochetoceratins are re-examined and their affinity with Cuban counterparts is approached. From a paleobiogeographical point of view, metapopulation dynamics and potentially involved events (e.g., temporary, ancillary, selective vicariancy and subsequent ecological capture) well apply for understanding the biogeographical significance of the ammonite assemblies described.