Application of vertebrate trace fossils to paleoenvironmental analysis

RICARDO NESTOR MELCHOR

Colonia del Sacramento

Simposio; Tercer Simposio Latinoamericano de Icnología (SLIC2015); 2015

Facultad de Ciencias, Universidad de la República

This contribution highlights the prospective contributions of vertebrate trace fossils in the analysis of sedimentary environments and the topics that are poorly known and may be the focus of future research. It is argued that the routine incorporation of a solid sedimentary facies scheme in the description of individual vertebrate trace fossil assemblages or ichnofabrics, will be highly beneficial for the development of new vertebrate ichnological tools and concepts of application to paleoenvironmental analysis. The focus is on significant developments produced in the last three decades, including the application of the ichnofacies concept to vertebrate trace fossils. Recognition of footprints in cross-sectional view may help to identify subaerially-exposed, or relatively shallow subaqueous intervals. The response of different substrates, showing contrasting water content and imprinted by different animals or devices, is compared in terms of the morphology of the resultant footprint. Trackways with sand crescents are typical of aeolian cross-strata and are absent in associated flat-lying to low-angle deposits. Thick packages of highly bioturbated sandy dune and interdune sediments have been interpreted as reflecting periods of increased rainfall. Neoichnological observations in modern lake basins suggest that distinct zones can be recognized in the margin of fossil ponds and lakes, including onshore, shoreline and shallow subaqueous zones. Abundant flamingo-like footprints and flamingo nest mounds are good indicators of alkaline and/or saline lake waters. Hippopotamus trails are found closely associated to modern and fossil freshwater wetlands. Dinosaur and pterosaur swim traces from lacustrine and fluvial deposits can be used to estimate water depth. Turtle, crocodile, amphibian, hippopotamus and fish swim traces allow to infer a subaqueous substrate. Certain modern intertidal fish feeding traces are oriented with the predominant tidal current and can be used as paleocurrent indicators. The preferential orientation of tetrapod trackways in lacustrine and fluvial deposits is analyzed. Vertebrate trace fossils can help to infer discharge variability in fluvial channels. The descriptions of vertebrate ichnofabrics are commonly limited to heavily bioturbated beds due to trampling by vertebrates, and a few examples if ichnofabrics with discrete trace fossils. The nature and implications of the recognized vertebrate ichnofacies are still being debated and have a limited utility in paleoenvironmental analysis. The distinction of a potential vertebrate burrow ichnofacies in carbonate-bearing paleosols is proposed to represent well-drained soils, developed under arid or semiarid climate.