First glimpse of the silicified hot spring biota from a new Jurassic chert deposit in the Deseado Massif, Patagonia, Argentina

GARCIA MASSINI J.L.; ESCAPA I.E.; D. M. GUIDO; A. CHANNING

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2016 vol. 53 p. 205 - 230

0002-7014

Jurassic hot-spring chert deposits in the Deseado Massif, Patagonia, Argentina, have been known for over two decades, but theassociated biota has only begun to be documented recently, and thus far only from a small number of localities. Here we report the discoveryof a large complex of well-exposed Upper Jurassic epithermal siliceous deposits represented by organic-rich cherts preserved withinthe geothermal system from La Bajada, Santa Cruz, Argentina. The chert samples analyzed so far contain exceptionally well-preserved, in situand transported, tri-dimensionally silicified plants, animals and microorganisms. Plants include equisetaleans (Equisetum thermale), ferns andgymnosperms. Among them, well-preserved in situ osmundaceous rhizomes in different developmental stages are the dominant componentof the taphoflora. Conifers are represented by wood, seeds, leaves and pollen tentatively assigned to the families Araucariaceae and Cheirolepidiaceae.The assemblage also contains vegetative and reproductive structures of fungi, oomycetes, cyanobacteria, algae, testate amoebas,ciliates and numerous remains of unresolved taxonomic affinity. Microorganisms are preserved isolated in the chert matrix or directly associatedwith plants and other organic remains in mutualistic, parasitic and saprotrophic engagements. Also present are numerous coprolites and arthropodremains that, along with the named microorganisms, are indicative of trophic relationships in the ecosystem. Altogether, this fossilassemblage suggests that distal paleoenvironments within the geothermal system are preserved at La Bajada. The diversity, abundance, andexceptional preservation of fossils in the La Bajada ecosystem provides a unique window into the geological past that offers a substantialcontribution to the reconstruction of middle Mesozoic terrestrial ecosystems.