Tetrapod tracks and other trace fossils from the Chinches Formation (Andean Precordillera, northern Chile): Indication for Pennsylvanian age and glacial influence

Abstract

The Chinches Formation is an up to 3000 m thick succession of poorly studied Paleozoic sedimentary deposits cropping out in isolated high mountain areas on the southern edge of the Atacama Desert, northern Chile. During a recent scientific expedition to various outcrops of the formation, an abundant array of trace fossils was discovered that provides new insight into the stratigraphic age and depositional environment of the fossil-bearing sedimentary deposits. The recorded ichnofauna of the Chinches Formation includes invertebrate traces (Cochlichnus, Diplichnites, Glaciichnium, Vagorichnus) and vertebrate traces (Undichna, Dimetropus, Dromopus, Limnopus, Matthewichnus) referred to locomotion and feeding activity of annelids, arthropods, fish and tetrapods. The assemblage combines elements of the Scoyenia and Mermia ichnofacies suggesting fluvio-lacustrine depositional conditions, though a marine influence cannot be ruled out for parts of the sequence. Especially the non-tetrapod trace fossils show similarities with typical glacio-lacustrine late Paleozoic Gondwanan ichnofaunas. Based on the mixed amphibian-early amniote tetrapod ichnofauna, a late Carboniferous (Pennsylvanian) age of the Chinches Formation is proposed. The study area yields the only occurrence of Carboniferous tetrapod tracks in the present-day southern hemisphere and gives evidence that Pennsylvanian land vertebrate faunas of the tropics and mid-southern latitudes were basically similar by comprising temnospondyls, lepospondyls, early synapsids and lacertoid-like sauropsids. The Chinches Formation has great potential to study the effect of the Late Paleozoic Ice Age on continental and maybe shallow marine ecosystems in higher paleolatitudes.