Ichnologic note first occurrence of the microcoprolite Palaxius salataensis in the Aptian (Lower Cretaceous) of northeast Mexico and its paleoecological implications

Abstract

Microcoprolites of Palaxius salataensis are non-skeletal carbonate grains produced by callianassid shrimps. This ichnospecies is recognized by four longitudinal canals arranged around a bilateral plane of symmetry, with crescent outline in cross-section. Palaxius salataensis has been previously reported from other countries and in strata from the late Paleozoic to the Mesozoic. In this study, we describe the first Aptian record of the ichnospecies, the first Cretaceous occurrence in North America, and the fifth occurrence worldwide. Palaxius salataensis was found in a packstone-grainstone with abundant pellets and common gastropod shell fragments and subangular, poorly sorted intraclasts. The paleoenvironment was characterized by shallow-waters with high energy conditions, occurring between fair-weather wave base and storm wave base, close to the platform margin, where well-oxygenated and nutrient-rich conditions predominated. The microcoprolite-rich bed of the La Huasteca Canyon occurs on top of an oolitic grainstone interval in the upper levels of the Cupido Formation, interpreted as the termination of the early Aptian Oceanic Anoxic Event 1a (OAE 1a). The presence of P. salataensis in the upper levels of the Cupido Formation is directly related to the availability of organic matter rather than to oxygen recovery.