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Jurassic hot-spring activity in a fluvial setting at La Marciana, Patagonia, Argentina

DIEGO M. GUIDO^* and KATHLEEN A. CAMPBELL

^* CONICET-UNLP, Instituto de Recursos Minerales, Calle 64 esquina 120, La Plata (1900), Argentina
School of Geography, Geology and Environmental Science, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand

Author for correspondence: ka.campbell{at}auckland.ac.nz

Silicified rocks at La Marciana farm, Deseado Massif, Argentinean Patagonia, represent an ancient hot-spring discharging into an active fluvial setting. Their fortuitous burial–erosion history and minimal post-depositional structural modification provide an unparalleled view of a complete, exhumed, late Jurassic geothermal landscape, and thus an opportunity to illuminate hot-spring geological context and palaeoenvironmental gradients. Geological mapping, stratigraphy and petrography revealed hydrothermal eruption events, the spring vent source, structural relationships, dimensions of the discharge apron, and hot-spring facies distributions. Remarkable similarities to Quaternary analogues from the Taupo Volcanic Zone, New Zealand, and Yellowstone National Park, USA, are apparent with respect to scale, spatial distribution of facies, and types of microbial and other palaeoenvironmentally significant fabrics.

Key Words: Hot-springs • siliceous sinter • microbial fossils • Jurassic • Argentina