Trace fossil zonation in interdune Lakes: example from the neogene of Eastern Patagonia, Argentina

Abstract

The Upper Miocene-Lower Pliocene Río Negro Formation (Río Negro Province, Argentina) contains diverse and abundant continental trace fossils. The purpose of this contribution is to recognize distinctive trace fossil assemblages in interdune lakes as response to lake expansion and contraction. The interdune deposits host 23 invertebrate, vertebrate, and plant ichnotaxa that are linked to the hydrological dynamics of the lake. During lake expansion a highly diverse subaqueous trace fossil assemblage reflects an infaunal bivalve population living in a littoral zone with swampy vegetation and semiaquatic mammals. The trace fossil assemblage recorded during Lake Highstand is less diverse and mostly linked to bivalve-generated trace fossils reflecting resting, locomotion, and escape/equilibrium behaviour (comparable to the Mermia ichnofacies). The assemblage during lake contraction exhibits high ichnodiversity and is dominated by vertebrate trace fossils reflecting foraging activities of shorebirds, cursorial birds, and herding semiaquatic mammals and ground sloths frequenting water holes. Flat sandy areas with moist substrates marginal to the interdune lake displayed a moderate ichnodiversity and its distinctive components were armadillo meniscate burrows and footprints in cross-section, as well as subvertical calcareous root casts. Neogene interdune lacustrine deposits reflect a particular zonation of trace fossils in response to changing physical conditions.

Keywords:

• Río Negro Formation
• vertebrate footprint
• invertebrate trace fossil
• tetrapod burrow
• rhizolith
• sedimentology

Acknowledgements

The authors are indebted for the detailed and constructive reviews by journal reviewer Spencer Lucas, an anonymous reviewer and co-Editor Luis Buatois.

Disclosure statement

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

Additional information

Funding

Permission to work in the study area has been granted by ‘Secretaría de Cultura’ and ‘Secretaría de Ambiente y Cambio Climático’ both from the Government of the Río Negro Province, Argentina. Nahuel Espinoza is thanked for help during fieldwork. This work was founded by project PICT-2019 0114 from the Agencia Nacional de Promoción Científica y Tecnológica and project PIP 2021–2023 0146 from the Consejo Nacional de Investigaciones Científicas y Técnicas, and project G22 from the Universidad Nacional de La Pampa, to RNM and Fondo para la Investigación Científica y Tecnológica.