MACROBIOEROSION AND MICROBIOEROSION IN MARINE MOLLUSCAN SHELLS FROM HOLOCENE AND MODERN BEACHES (39°- 40º S, SOUTH OF BUENOS AIRES PROVINCE, ARGENTINA)

CHARO MELISA; CAVALLOTTO, JOSE LUIS; ACEÑOLAZA, GUILLERMO

ACTA GEOLOGICA SINICA-ENGLISH EDITION

WILEY-BLACKWELL PUBLISHING, INC

Año: 2017 vol. 91 p. 801 - 840

1000-9515

The marine sediments of the area of Verde Peninsula ? Jabali Island ( 39º28´S/62º19´W 24 25 40º28`S/62º11W) Holocene in age (3 - 2 ky), and modern beaches contain a significant amount of bioeroded mollusc shells. Fifteen sites were analyzed, in which 20.11% of the mollusc shells (2168 valves) presented bioerosion traces, in 54 species (30 bivalves 31 32 and 24 gastropods). Fourteen ichnogenera were reported: Entobia, Maeandropolydora, Iramena, Caulostrepsis, Pennatichnus, Pinaceocladichnus, Trypanites, and Gastrochaenolites (Domichnia), Gnathichnus and Radulichnus (Pascichnia), Finichnus and Centrichnus (Fixichnia), Oichnus (Praedicnia) (macrobioerosion), y Semidendrina (microbioerosion), the latter is first reported in mollusc shells in Argentina. Eleven ichnospecies were identified Finichnus peristroma, Maeandropolydora sulcans, Gnathichnus pentax, Pinaceocladichnus onubensis, Caulostrepsis taeniola, Centrichnus eccentricus, Radulichnus inopinatus, Oichnus simplex, Oichnus paraboloides, Oichnus gradatus, and Gastrochaenolites torpedo (lithic remains). The dominant ichnogenera in the Holocene deposits are Iramena, Entobia and Oichnus. The same ichnogenera are 53 54 constant with different abundance in the modern beaches, and increasing representation 55 56 57 of Pinaceocladichnus and Pennatichnus. The dominant ichnofacies in the Holocene deposits is Trypanites, revealing a benthonic marine community composed of cheilostome bryzoans, clionaid sponges, predator gastropods, regular echinoids, polychaete annelids, bivalves, thallophytas and fungi. Generally, the area was described as a sublittoral, low energy, stable environment with high rate of oxygenation, and sandy bottoms, with rocky bottoms at Villalonga locality.