Die Auswirkungen alter Kryomere auf die 'Rodados Patagónicos' in Nordpatagonien, Argentinien

DARIO TROMBOTTO; ANA LÍA AHUMADA

E & G Quaternary Science Journal (Eiszeitalter und Gegenwart)

Schweizerbart'sche Verlagsbuchhandlung

Lugar: Hannover; Año: 1995 vol. 45 p. 93 - 108

0424-7116

The present study analyses different profiles with structures of freezing and thawing which affected the "Rodados Patagónicos" in the region of Puerto Madryn, Northern Patagonia. The "Rodados Patagónicos" are of fluvial origin and are assigned to the Plio-Pleistocene. Fabricstudies support the hypothesis of a synchronization of certain cold events and some deposition-cycles of the "Rodados Patagónicos". The ice wedge-casts may be of syngenetic as well as epigenetic origin and correspond to the cold episodes which belong to the Penfordd Cryomere. As far as paleoenvironment is concerned, the structures mentioned above required a permanently frozen ground, which is to say a mean annual temperature of at least -4 °C, indicating a temperature increase of nearly 17 °C since formation time. Th e characteristic heterogeneity of the profiles can be described as a system of "columns", subhorizontal levels and layers of impregnation forming a "nougat-structure", composed mainly of CaCO2. volcanic glass and quartz. The structures reveal phenomena of leakage and freezing in the fluvial conglomerate. The analyses of the clast-fabric and architecture of the sites allow to recognize structures and reconstruct the paleoenvironment from the Neogene on; an environment with cold impulses, an important volcanic activity and particularly arid or semiarid climatic conditions alternating with the deposition of the "Rodados Patagónicos" as outstanding features.