ON THE AGE AND STRUCTURAL TYPES OF THE TIEN-SHAN VALLEYS

Abstract

The problems of age of the Tien-Shan valleys and their relations with the structure of this mountain region are hardly dealt with in literature. The inheritance of intermontane depressions from Paleozoic structures and the alluvial character of the Upper-Triassic and the Lower-Jurassic continental thicknessess testify to a profound antiquity of many present longitudinal valleys. In the period of Cenozoic regeneration of the Paleozoic structures of the Tien-Shan and their partial rearrangement, and under the influence of glaciation many river valleys have undergone an essential change.

Six types of valleys can be singled out according to the relation of valleys to the orotectonic structure: simple transverse, complex transverse, longitudinal intermontane. .longitudinal intermontane with a transverse outlet, secondary longitudinal with a transverse antecedent outlet, and complex bead-like valleys. Each type of the valleys has a certain purpose in economy.