Tetrapod tracks taphonomy in eolian facies from the Permian of Argentina

Abstract

Ancient desert deposits preserve a copious ichnofossil record, particularly Permian-age deposits where the record of tetrapod footprints is present and abundant in almost all desert settings. We propose to analyze, from a taphonomic perspective, Permian footprints preserved in eolian deposits from Argentina with a detailed sedimentological study of the trackway-bearing levels, in order to find evidence of processes that may have enhanced their preservation. We defined four taphonomic modes based on preservation quality, and the morphological and extra-morphological features of the footprints. Mode 1 includes footprints with detailed impressions of the palm, digits and claws. Mode 2 includes tracks with palm and digit impressions associated with small bulbous-shape marginal rims. Mode 3 includes tracks characterized by large, bulbous, marginal rims and randomly preserved palm impressions. Mode 4 includes footprints with shallow digit and palm impressions associated with sand-crescent marginal rims. The Los Reyunos footprints suggest preservation in: (1) dry sand, evidenced by sediment slipping down-slope structures and (2) subsurface damp sand, evidenced by digit impressions and claw drag traces. Also, we found vertical water content variations along the dune foresets, evidenced by a varying amount of sediment slipping down-slope in the same trackway. Moreover, differences in the time of entombment are suggested by the morphology of rims (bulbous-shape or sand-crescent). The stratigraphic genetic framework resulting from the Los Reyunos taphonomic analysis supports changes in the interstitial subsurface water and rapid entombment of the tracking surface due to a high rate of sediment supply as the main factor for footprint preservation.