Stratigraphy in mountain belts

Abstract

The importance of stratigraphical research for the understanding of the structure and genesis of complex mountain chains was stressed and some of its special problems were discussed. The main part of the lecture dealt with the sedimentary history of the Alps, from Upper Carboniferous to Lower Cretaceous time, and with its implications for the crustal development in the geosyncline. Continental Upper Paleozoic and uniformly shallow-water Triassic formations point to the existence of a normal continental crust before the onset of subsidence. Deeper basins, probably bordered by normal faults, developed gradually during the Jurassic, and in late Jurassic and early Cretaceous time the geosyncline may have been comparable to some of the present smaller ocean basins. This implies thinning of the original continental crust; nevertheless, large remnants of granitic basement are present even beneath eugeosynclinal sediments and ophiolitic volcanics. In the Alps, the stratigraphical sequence is better compatible with the hypothesis of oceanization (replacement of the lower part of the crust by denser matter) than with the mechanism of ocean-floor spreading according to the Atlantic model.