Bryozoans and borings from Destacamento Río Salado Member (Buenos Aires Province, Argentina): Systematics and palaeoenvironment

Abstract

This study describes and discusses bryozoan taxa and borings associated with carbonate fragments and bioclasts from Destacamento Río Salado Member, Canal de las Escobas Formation, mid-Holocene of northeastern Buenos Aires Province, Argentina. Three species of encrusting bryozoans were found co-occurring with borings: Biflustra puelcha, Conopeum reticulum and Electra arcuata comb. nov. In addition, bilaminar fragments of Hippomonavella charrua showing considerable surface abrasion were also found among the carbonate clasts. C. reticulum, formerly regarded as a cryptogenic species in Argentine harbours, is present in the Southwest Atlantic at least since the mid-Holocene, so it should be considered as a native species in the area. Borings comprise Gastrochaenolites isp., Trypanites isp., Maeandropolydora isp., Entobia isp. and Caulostrepsis isp. The co-occurrence of bryozoans and borings suggests that the carbonate fragments were transported from an abrasion platform when they were already bored, and then they were encrusted by the bryozoans at the study site, a tidal flat depositional environment.