Upper Cretaceous sauropod dinosaur tracks, palaeosols, and sedimentary deposits - Bauru Group, southeastern Brazil

Abstract

The Upper Cretaceous period is known in international literature for its rich diversity of terrestrial life. There is a lot of research on sedimentary deposits and the preservation of vertebrate and invertebrate fossils therein. Another essential data contribution to scientific research is the diagnostic characteristics of palaeosol profiles, such as horizons, structures, and root traces. This research found records of palaeosols, sedimentary deposits, and dinosaur tracks in a single outcrop. The palaeosols were analysed based on macro and micromorphological data. They have Bt and C horizons, and it was possible to reconstruct the pedosedimentary development of composite palaeosols. Facies analysis and interpretation of the depositional environment were carried out to identify and interpret the sediments. These are parallel bedding sedimentary structures with alternation of fine sand and clay. The tracks -bearing layers are tabular, parallel bedding sedimentary structures with fine sand and clay alternation. The tracks in the field were identified according to width, depth, morphology, and dimension, so it was possible to define the moulds and casts. At least nineteen concave structures in four different layers were interpreted as cross-sections of dinosaur tracks, with some preserved at the top of the analysed outcrop. Dinosaur tracks depend on specific conditions to be preserved in the geological record, such as plasticity and consistency of the sediments and the depositional environment. Another series of factors must also be considered, such as how and why these animals came to this place. The palaeosols indicate topographic stability for a period sufficient for the pedogenesis process, while the parallel beddings preserved at the top of the section represent instability of the relief with insufficient time for soil development. Thus, the plasticity in the sediments made it possible to record the tracks. This research contributes to the palaeoecological and environmental reconstruction of the landscape through the use of palaeosols, sediments, and dinosaur tracks records.