Bioerosion on Holocene marine molluscs from the Jabali Island (Buenos Aires province, Argentina): paleoenviromental interpretation

CHARÓ, MELISA PAOLA 1,2,3, CAVALLOTTO, JOSÉ LUIS 1, ACEÑOLAZA, GUILLERMO 2,3 AND CHARÓ, GISELA DANIELA

ACTA GEOLOGICA SINICA-ENGLISH EDITION

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2020

1000-9515

The Jabalí Island, southern Buenos Aires province, Argentina, is composed of beach ridge systems, mostly produced by storms within the transgression-regression events of the last 10,000 years BP. The aim of this work is to analyze and describe 23 Holocene sites across the island from a malacological and taphomomical perspective in order to interpret paleoenvironments and benthic communities, as well as their evolution. As a result, six ichnogenera were reported: Entobia, Maeandropolydora, Pinaceocladichnus and Iramena (Domichnia), Oichnus (Praedichnia), and Radulichnus (Pascichnia), as well as five ichnospecies: O. simplex, O. paraboloides, O. simplex, P. onubensis, and R. transversus. The inner littoral ridges (Ct1) between 7.5-4.1 ka (7-4 m height m a.s.l.), with moderate - high bioerosion are characterized by the abundance of Pinaceocladichnus and Entobia which suggest strong stability, even marine salinity and low sediment suspension, and thus, periods of greater exposition of the air-water interface. The outer littoral ridges (Ct3) between 3.8 ? 2.1 ka (3-2 m height m a.s.l.), resulted in moderate-low bioerosion and abundance of Entobia and Maeandropolydora. Ct3 includes deposits of tidal plains that suggests shallow environments with low energy and low bioerosion, and modern beaches located in the north of the island with Entobia in most sites, followed by Maeandropolydora and Oichnus. Modern beaches (Ct2), with low bioerosion, mostly with Entobia and Maeandropolydora, that suggest environments of low energy with low wave action, no sediment in suspension and optimal oxygenation. We concluded that the different associated taphonomic features, as well as the geographical variables, indicate changes in the local environmental factors and the global environmental changes allowing the settlement of a diverse fauna of boring and incrusting organisms in the Late Quaternary. The higher ichnodiversity suggesting warm water conditions of sites S11, S13 and S14, probably due to the influence of the Brazilian Current, record the Hypsithermal (Mid ? Holocene) in the south of the Buenos Aires province.