Cyanobacteria in Jurassic geothermal deposits from Patagonia, Argentina

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

Mendoza

Congreso; 4th International Paleontological Congress; 2014

This paper describes morphologically variable, structurally preserved cocoid and filamentous cyanobacteria from Jurassic hot springs in Patagonia. Fossils are silicified and preserved in their original context in fossiliferous cherts from the two best known geothermal localities of La Matilde Formation (Bahia Laura Group) in the Deseado Massif, Santa Cruz, Argentina. Coccoid forms are represented by individual, spherical or nearly spherical cells arranged in up to three perpendicular planes forming morphologically variable, tri-dimensional colonies of numerous units that lived epibiotically on different organic substrates. Filamentous forms consist of individual trichomes of variable length and diameter that occur as isolated units in the chert matrix or grouped in dense clusters forming hemispherical or spherical colonies on decayed plant stems, roots and other organic remains. Based on the morphological, anatomical and habit variability displayed, the fossils resemble different taxa extant Croococcales, Nostocales and Oscilatoriales. This record is among the few known of structurally preserved cyanobacteria in in-situ and in-life position from Phanerozoic non-marine terrestrial paleoecosystems. The presence of cyanobacteria in the geothermal deposits from La Matilde Formation in the Deseado Massif is consistent with extreme physical and chemical parameters known in modern comparable settings. Most importantly, this record helps fill in the gap in the distribution of cyanobacteria in the geological record and provides a reference point for their evolution, structural diversity and roles in Mesozoic terrestrial ecosystems.