Unusual sauropod slipping tracks preserved on a biostabilized tidal flat from the Lower Cretaceous of northern Patagonia, Argentina

HEREDIA A.M.; PABLO J. PAZOS; FERNANDEZ D.E,

GEOLOGICAL SOCIETY OF LONDON SPECIAL PUBLICATION

Geological Society

Lugar: London; Año: 2023 vol. 522

0305-8719

Several elongated and other crescent-shaped impressions interpreted asdinosaur tracks and preserved on Lower Cretaceous tidal flat deposits fromthe Agrio Formation (northern Patagonia, Argentina) are studied in detail. These tracks were documented on a palaeosurfaceshowing palaeotopographic differences over a short distance, related to the lateral migration of a tidalchannel. A genetic order between biostabilization and bioturbation of the palaeosurface is recognized. Ripples generatedwithin the channel during the flood tide were first biostabilized; there, horseshoe crabtrace fossils were produced. Then, the area bearing the tracks studied here was subaerially exposed, with the biostabilized substrategenerating a slippery surface. Scanning electron microscope analysis of the rims indicates that the microbial mat wasdisturbed by the trampling. Finally, microbial mats recovered, and some tracks preserved wrinkle marks insidethe tracks. Taking into account the substrate properties and track features analysed (morphology, size,depth and orientation), it is concluded that the tracks were produced by dinosaurs, probably small sauropods,trampling on a slippery surface and moving parallel to the channel margin. This study is an unusual case ofslipping tetrapod tracks preserved on a biostabilized tidal flat developed in a mixed carbonate–siliciclasticenvironment.