Middle Miocene Pholadid Borings at the Base of the Isidro Formation, Arroyo Mezquital, Baja California Sur, Mexico

Abstract

Abxxnddinl sediment-infilled clavate (club-shaped) borings, assignable <br /><br />to ichnogenus Gastrochaenolites, are reported from the base of the Miocene Isidro <br /><br />Formation, Baja California Sur, Mexico. The infilled borings were made by pho- <br /><br />ladid bivalves that lived in a nearshore-marine environment on a semi-consoli- <br /><br />dated substrate ("'Glossifungites'' ichnofacies). Some borings are connected by <br /><br />horizontal burrows that are sculptured (Spongeliomorpha) or unsculptured (Tha- <br /><br />lassinoides). The localized pholadid community was short lived and abruptly <br /><br />terminated by an influx of sediment.