Cretaceous echinoids in Paleocene reworked tsunamite from Coahuila, NE Mexico

Abstract

The Maastrictian echinoid species Hardouninia mortonis (Michelin, 1850) typical from Upper Cretaceous deposits along the Gulf and Atlantic Coastal plains of USA and Canada, is here reported for the first time for Mexico into a peculiar matrix, which consists of a K/Pg reworked tsunamite deposited during an early Paleocene storm event in the NW portion of the Parras Basin, Difunta Group, NE Mexico. Our specimens have a peculiar small size compared with those reported for Maastrichtian localities in Mississippi amd North Carolina. Small-sized specimens are abundant in late Maastrichtian Las Encinas Formation of the Parras Basin, and are identical to the more than 50 specimens found included in reworked K/Pg tsunamite at Arroyo Amargos, Coahuila. Our interpretation is that the tsunamite was reworked during an early Paleocene storm, forming a channel-like structure of microconglomeratic sandstone, which includes ammonites (Sphenodiscus pleurisepta), the small Hardouinia mortonis, and delicate early Paleocene ostreoids. Other localities with reworked K/Pg tsunamite deposits are found in the adjacent La Popa Basin, interpreted also as deposited by early Paleocene storms in this area of NE Mexico, in Coahuila and Nuevo León states, but mix of Maastrichtian and Paleocene invertebrates has only been observed in Amargos.