A new Jurassic chert deposit with exceptionally preserved plants and microorganisms from Patagonia, Argentina

GARCIA MASSINI, J.; ESCAPA, I.; GUIDO, D.; CHANNING, A.

Mendoza

Congreso; 4th International Paleontological Congress; 2014

Jurassic geothermally-related chert deposits in the Deseado Massif, Patagonia, Argentina, have been known for some time, but its associated biota has only been recently revealed in a limited number of localities. Here we report the discovery of a complex of Middle-Upper Jurassic epithermal siliceous deposits represented by fossiliferous cherts preserved in distal paleoenvironments within the geothermal system from La Bajada, northwestern Santa Cruz Province, Patagonia. These well exposed deposit represent a series of several distinct chert-bearing localities with different stages of community development. The deposits are in a volcanic setting and contain an exceptionally well preserved multitude of in-situ and transported silicified microorganisms and plants from middle latitudes in western Gonzdwana. The microorganism assemblage contains vegetative and sexual structures of fungi, fungus-like organisms, such as oomycetes, algae and other protists, cyanobacteria, and numerous remains of unknown affinity. Microorganisms are preserved isolated in the chert matrix or directly associated with plants and other organic remains in mutualistic, parasitic and saprotrophic engagements. Also present are crustacean and other arthropod parts and a large number of coprolites, which, along with the microorganisms, further reveal diversity and trophic relationships. The plant assemblage includes disarticulated as well as organically connected conifer, cycad, fern and sphenophyte organs, preserved in-situ, in-life position or transported. This record represents a unique window into the evolution and diversification of Mesozoic plant and microorganism biota. It provides base line data for an understanding of the composition, trophic interactions and, ultimately, the structure and dynamics of middle Mesozoic terrestrial ecosystems.