Interpreted depositional conditions of balanced-fill lake basin strata incorporating vertebrate and invertebrate trace fossils, Triassic Santa Clara sub-basin, Cuyana rift basin, Argentina

Abstract

The Santa Clara Abajo and Santa Clara Arriba formations host a diverse assemblage of trace20 fossils that record a wide range of behaviors and a broad array of ecological niches during the21 Middle Triassic—a critical period in the evolution of continental fauna with the diversification of22 both synapsids (cynodont and dicynodont) and archosauromorphs (dinosaurs, pterosaurs, andJSRPre-PrintDraftDownloaded from http://pubs.geoscienceworld.org/sepm/jsedres/article-pdf/doi/10.2110/jsr.2021.124/6013339/benevente.pdfby Consejo Nacional de Investigaciones Cientificas y Tecnicas CONICET useron 21 November 20232crocodilians) that represent post-Permian faunal recovery. The Santa C 23 lara formations are part of24 the continental infill of the Cuyana rift Basin in Argentina and represent a lacustrine system with25 fluvial input and delta development. Sedimentological characteristics of these units as well as26 their stacking patterns characterize a “fluctuating profundal” facies association typical of a27 balanced-fill lake basin. The lacustrine and associated terrestrial environments preserve a rich28 record of invertebrate traces with 26 ichnogenera from ethological classes of fodichnia,29 domichnia, repichnia, pascichnia, and cubichnia occupying all continental tiers (subaerial and30 subaqueous, surficial/very shallow, shallow, mid, and deeper) and ecological niches31 (epiterraphilic, terraphilic, hygrophilic, and hydrophilic). In association with the invertebrate32 traces, two taphonomic modes of tetrapod footprints have been found: a moderate fidelity mode33 and a high fidelity mode. Physical sedimentary features, burrows, trails, and tracks, and their34 stratigraphic positions are integrated to interpret the main factors involved in footprint35 preservation in these subsettings. The most significant and variable preservational factor found is36 water-table fluctuations controlled by the paleohydrology of a balanced-fill lake system. These37 data show that in balanced-fill lake systems, diverse trace assemblages occur in the lake and38 associated subsettings such as delta plains, and lake-margin settings whereas trace fossils can be39 totally absent in coeval lake-center strata, particularly if anoxic lake bottom conditions occur, as40 probably occurred in the meromictic Santa Clara lake system.