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

ROJAS-MANRIQUEZ, MANUEL A.; FEOLA, SILVERIO F.; MELCHOR, RICARDO N.

ICHNOS-AN INTERNATIONAL JOURNAL FOR PLANT AND ANIMAL TRACES

TAYLOR & FRANCIS INC

Año: 2024 p. 1 - 35

1042-0940

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 torecognize distinctive trace fossil assemblages in interdune lakes as response to lake expansionand contraction. The interdune deposits host 23 invertebrate, vertebrate, and plant ichnotaxathat are linked to the hydrological dynamics of the lake. During lake expansion a highlydiverse subaqueous trace fossil assemblage reflects an infaunal bivalve population living in alittoral zone with swampy vegetation and semiaquatic mammals. The trace fossil assemblagerecorded during Lake Highstand is less diverse and mostly linked to bivalve-generated tracefossils reflecting resting, locomotion, and escape/equilibrium behaviour (comparable to theMermia ichnofacies). The assemblage during lake contraction exhibits high ichnodiversity andis dominated by vertebrate trace fossils reflecting foraging activities of shorebirds, cursorialbirds, and herding semiaquatic mammals and ground sloths frequenting water holes. Flatsandy areas with moist substrates marginal to the interdune lake displayed a moderateichnodiversity and its distinctive components were armadillo meniscate burrows and footprintsin cross-section, as well as subvertical calcareous root casts. Neogene interdune lacustrinedeposits reflect a particular zonation of trace fossils in response to changing physicalconditions.