Late Quaternary bioerosion pattern controlled by upwelling events at Puerto Lobos (Chubut, Argentina)

Abstract

Bioerosion traces are a powerful tool for reconstructing benthic paleo-communities through the geological record. The late Quaternary marine deposits of Patagonia (Argentina) are elongated ridges parallel to the present coast, rich in sand, gravel and shells, the latter being the main substrate for bioerosion traces. However, the ichnological studies in the Quaternary are scarce in high latitudes of the Southern Hemisphere. This work describes for the first time the bioerosion traces recorded in shells belonging to diverse taxa of mollusc from Quaternary deposits in Puerto Lobos, Southern of San Matias Gulf (Patagonia, Argentina). This study complements the scarce information on bioerosion traces in the Southern Hemisphere. A total of 710 mollusc shells were obtained from four Quaternary beach ridges at Puerto Lobos. As a result, 15 ichnotaxa were recorded for the first time in the site, 13 of them for the first time in the Holocene of San Matías Gulf. Through qualitative analysis, bioerosion patterns were observed in the late Quaternary of Puerto Lobos. The abundance of worm and sponge borings in the Pleistocene could be related to warm and sediment-free waters. On the contrary, the results of the bioerosion study in the Holocene and recent samples were very similar. This could indicate that the same environmental factor controlled both bioerosion patterns. For the Holocene, it was observed that the bioerosion pattern is mainly represented by trace produced by suspension and filter-feeding organisms, such as bryozoans, among others. Together with the increase in ichnodiversity, this could indicate an increase in nutrient availability in the San Matías Gulf associated with upwelling events. Therefore, our results reinforce the hypothesis proposed by previous authors that the upwelling events currently observed in the study area began during the mid-Holocene.