Tagelus plebeius (Lightfoot, 1786) (Mollusca: Bivalvia) bioturbations in a Holocene estuarine environment (Quequen Grande river, Buenos Aires Province, Argentina)

Elongated traces, showing a lower v-shape closed end have been identified in mid Holocene estuarine deposits exposed along the lower reach of the Quequen Grande River, Argentina (38degrees34'35" S and 58degrees42'45" W) associated with shells in life position of the infaunal bivalve Tagelus plebeius (Lightfoot). These traces, located in a stratigraphic level dated in circa 6,900 years C-14 B.P., were originated by the burrowing activity of T. plebeius based upon the comparison of their morphological characteristics (width, general shape, colour) with those of T. plebeius and the traces resulting from its burrowing activity at present estuarine environments of the region. The high percentages of the estuarine gastropod Heleobia australis (d'Orbigny) found in the sedimentary filling of the traces come from the overlying strata, abundant in Heleobia australis remains. The traces are stratigraphically transgressive within a depth interval of up to 80 cm.