Sedimentological and stratigraphically controlled preservation styles and distribution of fossil cetaceans from a new Early Miocene fossiliferous locality, Patagonia, Argentina

ABSTRACT

Prospecting fieldwork in a new fossiliferous locality of the marine Early Miocene Gaiman Formation (Patagonia, Argentina) results in the discovery of abundant fossil cetaceans (n = 29). We analyse stratigraphic, sedimentologic, palaeontologic, and taphonomic data with the aim of understanding the factors that control the preservation and distribution of these specimens. The cetacean sample is dominated by small odontocetes exhibiting five different preservation categories. Based on sedimentological features, three distinct facies were recognised in the stratigraphic section. Stratigraphically condensed deposits of facies C, related to a ravinement surface and subsequent transgressive deposits, enclose 52% of the specimens, grading from isolated postcranial elements to articulated and associated postcranial and cranial elements. In contrast, facies A and B exhibit predominantly isolated postcranial elements. Facies C shows higher degrees of corrosion, encrustation and fragmentation than those specimens from facies A and B, reflecting differences in preservation quality among the facies. The higher abundance and evidence of long exposure times recorded for facies C seems to be resulted mostly from physico-chemical factors after stratigraphic condensation. Finally, intrinsic biological features and ecological preferences of the specimens could explain the dominance of small-sized odontocetes in a restricted inner shelf to lower shoreface environmental setting.

KEYWORDS:

• Taphonomy
• stratigraphic condensation
• physical controls
• odontocetes
• Gaiman formation

Acknowledgments

We wish to specially acknowledge Alejo Irigoyen for sharing the discovery of the CDP locality and Raúl Gimenez for his permissions to access the outcrops. We also thank people who kindly helped during the fieldwork and cetacean identification: Maximiliano Gaetán, Mariana Viglino, Felipe Busker, Santiago Bessone, Lucía Alzugaray, Pablo Raposo, Florencia Barria, Ethel Dening, Nayla and students from UNCH university. We thank Soledad Gouiric-Cavalli for her help in determining ray plates. We thank the organizing committee of the 6^th ICAZ-TWG and 9^th TAPHOS congress for the invitation to this special volume. We thank Giulia Bosio, an anonymous reviewer and editor Gareth Dyke for all the corrections and suggestions that helped impoving the manuscript. We thank the Secretaría de Cultura of Chubut Province for providing permissions for fieldwork and fossils collection. This work was supported by the Agencia Nacional de Promoción Científica y Técnica (Argentina) under grants PICT2019-0390 and PICT2019-00327, and by the Consejo Nacional de Investigaciones Científicas y Técnicas under grant PUE IPGP-CONICET N°22920200100014.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the PUE IPGP-CONICET [N°22920200100014];PICT2019-0390;PICT2019-00327;