Traces fossils in marine molluscan shells from Holocene in Buenos Aires Province, Argentina.

M. P. CHARO, J.L., CAVALLOTTO, G. ACEÑOLAZA AND G. D. CHARO

Valencia

Congreso; 2nd Palaeontological Virtual Congress; 2020

Universidad de Valencia

The shells of bivalves and gastropods found in Holocenemarine sediments of the south of BuenosAires Province show bioerosion traces. Ten sitesfrom three areas were analyzed: Colorado Riverdelta (CRD) (39º15?S / 39º55?S) (6.9 ? 2.1 ka); BahiaAnegada (BA) (39º55?S /40º31?S) (5.9 - 3.6 ka) andBahia San Blas (BSB) (40º31?S /40º37?S) (7.5 ? 2.1ka). These sites are reported (N= 2.640 valves).Twelve ichnogenera were identified: Entobia,Iramena, Pinaceocladichnus, Pennatichnus, Maeandropolydora,Caulostrepsis, Gastrochaenolites(Domichnia); Finichnus and Centrichnus (Fixichnia);Gnathichnus and Radulichnus (Pascichnia)and Oichnus (Praedichnia), as well as eight ichnospecies:P. onubensis, F. peristroma, C. eccentricus,G. pentax, R. inopinatus, O. simplex, O. paraboloides,and O. smiley. The highest percentagesof bioerosion traces were found in the depositsof BSB with 18.21%, followed by CRD with 4.30and BA with 3.70%. The dominant ichnogenerain CRD are Pennatichnus, Pinaceocladichnus,and Iramena, which reveal the existence of ctenostomatebryozoans suggesting water currentsand large availability of phyto- and zooplanktonin the environment. The most represented ichnogenerain BA are Entobia and Iramena, whichindicate a high temperature range with a sublittoralenvironment of low sedimentation rate,water currents, high availability of suspensionparticles and high oxygenation of the water.While those of BSB are Entobia, Maeandropolydoraand Oichnus, which suggest long periods ofexposition, low energy enviroment, and sandybottoms with polychaete annelids and carnivorousgastropods. Bioerosion is among the mostrelevant taphonomic features when interpretingspecific environmental characteristics that suggestpalaeoecological and palaeoenvironmentalconditions during the Late Quaternary.