In a proglacial marine sequence moulds of pholadid bivalve borings containing shells of Penitella sp. have been observed on the soles of several pebbly sandstone and sandstone beds. The borings penetrate the mudstone substratum to a depth of 10 cm and are filled with coarse sand from the overlying beds. The Penitella community inhabited muddy portions of the sea bottom during fair-weather periods and was buried by rapid sediment gravity flows which repeatedly delivered coarse clastics to this low-energy environment. from Current Antarctic Literature