Insect trace fossils from paleosols of the Sarmiento Formation (Middle Eocene-Lower Miocene) at Gran Barranca (Chubut Province)

BELLOSI, E. S. AND J. F. GENISE

Fieldtrip Guidebook. First International Congress on Ichnology

Museo Paleontológico E. Feruglio

Lugar: Trelew; Año: 2004; p. 15 - 29

ABSTRACT Gran Barranca is the classical paleontological mammal-bearing locality (fig. 1) of the Sarmiento Formation (Middle Eocene - Lower Miocene) where it is possible to observe superb exposures with one of the most abundant and stratigraphically continuous terrestrial ichnofaunas from Cenozoic times. At present, the assessment of these associations of continental invertebrate trace fossils is in an early stage of development (Bellosi at al. 2001; Genise et al, in press). The study of these ichnologic associations, occurring with abundant fossil mammals in the tuffaceous paleosols of the Sarmiento Formation, provides a unique opportunity to improve our knowledge of the ancient terrestrial ecosystems, particularly of the earliest grassland-type paleoenvironments, also documented by the numerous phytoliths. Gran Barranca locality is a clear example of the high diversity and abundance that reached insect constructions in Southamerican paleosols by Paleogene times, when all groups of modern insects were already diversified. The observable evolution along different localities of this trip begins with Jurassic paleosols almost deprived of invertebrate trace fossils, continues with Lower Cretaceous paleosols bearing an ichnofauna of uncertain affinities, which can be envisaged as a more or less ichnological static background that is recorded also in Upper Cretaceous and Paleogene paleosols. This background highlights the evolution of insect trace fossils as a changing foreground, which began with the first and few insect constructions known in the Upper Cretaceous paleosols of the Laguna Palacios Formation, and continues with one of the best examples worldwide of the cenozoic abundance, diversity and dominance of insect constructions at Gran Barranca.  Gran Barranca is also one of the most typical examples of the Coprinisphaera ichnofacies (Genise et al., 2000), bearing numerous paleosols with a typical association of dung-beetle and bee nests indicating a palaeonvironment dominated by herbaceous communities. IMPORTANTE: No se adjuntan figuras y láminas de fotos en el archivo "Full text", debido al tamaño final que alcanza el mismo, siendo rechazado por el sistema. La versión completa se presenta en forma  impresa.