Substrate of Bivalve Borers as Recorded on Phosphatic Fills of Gastrochaenolites, Palaeoenvironmental Context (Bohemian Cretaceous Basin, Czech Republic)

Abstract

Phosphatized Gastrochaenolites fills, derived from the rocky-coast facies of the Late Cenomanian age of the Bohemian Cretaceous Basin, comprised specimens with smooth and ribbed surfaces and with Fremdskulpturen. The ribbing may be simple or complex and its origin interpreted as a function of substrates. Close examination of accessible substrates indicates that oyster and/or gastropod shells are the most probable hosts of respective tracemakers. The formation of borings preceded a phosphogenic episode and subsequent destruction of bored substrates and a release and reworking of phosphatized fills. This scenario functioned during the Rotalipora cushmani Zone or a little earlier, and in part anew during the Praeactinocamax plenus Zone of the Late Cenomanian. Phosphatized fills thus represent the reworked relics of phosphogenic products preserved in basal parts of two successive transgressive sets of sediments that followed the settings with phosphogenesis.