La zona de los lagos Pueyrredón y Posadas, Provincia de Santa Cruz

Abstract

The following formations are described: pre-mesozoie phyllites and quartzites; Jurassic porphyritic vulcanites; lower and middle marine Cretaceons strata containing a fauna rich in number of species (Lago Pueyrredón series); Upper Cretaceous continental formation (Chubutense; Upper Cretaceous or lower Tertiary granitic intrusion (C. San Lorenzo plutonites); Upper Cretaceous of lower Tertiary hypabyssal mesosilisic rocks ol Cerros Indio and Negro; Tertiary vulcanites of (C. San Lorenzo; lower Tertiary olivine-Basalt (Basalto Posadas); Patagoniense marine transgression with a rich fauna; continental strata of the so called
Santaerucenee stage; plateau basalt (Basalto Belgrano); and finally Quaternary deposits. Two tectonic areas can be defined: one to the north of lakes Pueyrredon and Posadas of mild folding composed of voleanie rocks; the other, to the south of
the depression characterized by the andine and extraandine environment. The first are characterized by pre-mesozoic metamorphie formation strongly folded, intruded and covered of mesozoic and tertiary formations overlaining the older
rocks with vertical to horizontal dips in the vicinity of lake Posadas. The most important fracture bines are N-S.