Geology of the Central Ridges of Southern Chubut. Between Parallels 45 and 46 S lat.

Abstract

Geological formations of the mountainous zone of central Chubut, between parallels 45 and 46 S lat. are described. The most antique stratigraphic complex corresponds to the sediments of the upper Cretacic (Chubutian), in which it is possible to identify five sections with their own lithological characters, covered on a reduced sector by marine sediments belonging to the Salamanquense, the entrance of which marks the end of the Mesozoic.

The Terciary is made up essentially of sedimentary deposits which begin directly with the Riochiquense, followed by the Tobas de Koluel Kaike and Tobas de Sarmiento, all of them continental formations. A new atlantic marine ingression is represented by the Patagoniense which supports itself indistinetly on any of the mencioned terms and passes its turn concordantly and insensibly to a new continental deposit (bed) of wide distribution in the Patagonia, which is the Santacrucense.

The eruptive rocks are represented by intrusions of basic rocks (diabases), existing also potent and vast buckings of olivinic basalts which cover a wide region. Both of them must have appeared in more than a cycle, but this has not yet been perfectly determined.

The most modern geological elements are represented by the Rodados Patagónicos at different levels (the inferior, redeposited), as well as terraced and non-terraced alluvions, and actual formations of sand-banks.