Macrobioerosion in marine molluscs in the south of Buenos Aires (Argentina) during the Late Pleistocene (MIS 5e).

CAVALLOTTO, JOSE LUIS; ACEÑOLAZA, GUILLERMO; CHARO MELISA

Roma

Workshop; 9th International Bioerosion Workshop; 2017

Instituto Superiore per la conservazione ed il restauro

Bioerosion structures have been investigated mainly on the Holocene age marine mollusc taxa occurring along the coastline of Argentina.The aim of our research is to reveal the bioerosion ichnogenera of two Late Pleistocene age (120 ky) localities situated south to Buenos Aires Province. The first locality can be found at La Bañadera (39°47´10.55"S/62°29´22.04"W), near Villalonga canal. The Late Pleistocene formations are represented here by ten m thick homogeneous silty sediments referring to littoral palaeoenvironment. Maeandropolydora isp. is the most abundant ichnogenera (e.g. in Buccinanops globulosus ) but Oichnus isp. and Pinaceocladichnus. isp. are also present in the examined material. Later Oichnus isp. had been determined as Oichnus simplex. The second locality is situated at Los Pocitos (40°26´S/62°25´W), where 2 m thick parallel stratified littoral deposit composed by clays and sandy layers can be observed. We have found six ichnogenera: Maeandropolydora isp., Entobia isp., Pinaceocladichnus isp., Oichnus isp., Iramena isp. and Caulostrepsis isp. in the molluscan remains of the locality. . Among the dominants are: Maeandropolydora isp and Entobia.isp.are dominant. Most of the Maeandropolydora isp. were found in external side of Ostrea puelchana valves. While the eroded Entobia isp. occurred in the umbonal and central section of the oyster valves. Maeandropolydora isp. is the dominant ichnogenus in the case of both localities. The presence of the different ichogenera reveal the existence of the following bioeroding organisms annelids, ctenostomate bryozoans, clionaid sponges and preadatory gastropods. The abundance of annelids (Maeandropolydora isp.) at both sites and clionaid sponges (Entobia isp.) refer to sublitoral enviroment with sandy bottom, low rate of sedimentation and high oxygen content water during the Late Pleistocene south to Buenos Aires.