Macrobioerosion and Microbioerosion in Marine Molluscan Shells from Holocene and Modern Beaches (39°–40°S, South of Buenos Aires Province, Argentina)

Abstract

The marine sediments of the area of Verde Peninsula – Jabali Island (39°28′S/62°19′W–40°28′S/62°11′W) 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 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 constant with different abundance in the modern beaches, and increasing representation 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.

Bioerosion in Ostrea lamellosa shells from the Messinian of the Tafna basin (NW Algeria)

“…Entobia producers (sponges) are chemical borers, which prefer carbonate substrates such as the bivalve shells (RADWAŃSKI et al, 2011). However, similar Entobia borings have been observed on the shells of bivalves from the upper Eocene of Egypt (RASHWAN et al, 2019), the Miocene (GIANNETTI et al, 2020) and Pliocene of Spain (GI- BERT et al, 1998), and the Holocene of Argentina (CHARÓ et al, 2017).…”

“…Remarks: Trypanites is a cylindrical, unbranched, bioerosional trace fossil, produced by sipunculans and polychaetes and belonging to the ethological category domichnia (GIBERT et al, 2012;CHARÓ et al, 2017). It is recorded from the Cambrian (JAMES et al, 1977) to the Holocene.…”

“…It is recorded from the Cambrian (JAMES et al, 1977) to the Holocene. Trypanites borings occur in biogenic substrates such as brachiopods (VINN, 2005) and bivalve shells (CHARÓ et al, 2017;RASHWAN et al, 2019), but also in hardgrounds. It gives its name to the Trypanites ichnofacies.…”

Bioerosion on Late Pleistocene Marine Mollusks: A Paleoclimatological and Paleoecological Comparison of MIS 7 and MIS 5e with Modern Beaches (Río Negro, Argentina)

“…The boring is made by a bivalve excavating the substrate both mechanically and chemically. It is mostly produced by animals of the Family Mytiladae (Charó et al, 2017) and is represented here by Gastrochaenolites torpedo on C. iudicai (Fig. 8).…”

“…Bioerosion is an indicator of both water environmental conditions and the benthonic community related to the hard substrate interaction, of bivalves and gastropods in this case, becoming paleoclimatic proxies (Charó et al, 2017).…”