THE GENESIS OF LAKE TUGAR-SALGAN IN THE WESTERN FOOTHILLS OF THE SOUTHERN URALS

Abstract

Lake Tugar-Salgan is located on the territory of the Ishimbay Municipal District of the Republic of Bashkortostan,10 km southeast of the city of Sterlitamak, at the foot of Shikhan Toratau (Turataw). Despite the morphometric parameters of the lakeestablished a long time ago, its origin is not fully clear. The genesis of the lake is considered to be karstic, but the formation mechanismand even its belonging to the type of karst based on the composition of the karst rocks have not been established. The purpose of theresearch is to determine the conditions and factors of the formation of Lake Tugar-Salgan, which is a complex natural monument ofrepublican importance. Data from a state hydrogeologic survey, a survey of exogenous geologic processes, and the author's 2022 fieldsurvey served as source data for this article. Research methods employed in the study include morphological and morphometric surveysof the lake bed and of the nearest landforms in its vicinity. It has been established that the lake formation was connected with thedevelopment of karst process in the gypsum of the Kungurian Stage of the Early Permian and the lake is located in the rear part of the third supra-flood terrace of the Belaya River valley. The distribution of surface manifestations of sulfate karst in the lake area is directlydependent on the age of relief elements on which they have been formed and inversely dependent on the thickness of non-karst sediments covering karst gypsum. Along with these, the main factor of the lake formation is the course of relief formation in the NeogeneQuaternary time. The karst basin with the lake is located at the mouth of the modern semi-blind erosion-karst ravine, and in the EarlyPliocene its mouth opened 89 km to the west in the paleovalley of the Belaya River. After the paleovalley had been filled with Plioceneand then Pleistocene sediments, the middle and mouth parts of the ravine and the karst landforms were buried under Quaternary alluvium. It was in the rear part of the third supra-floodplain terrace of the Belaya River valley, in the karst basin only partially filled withclayey Middle Pleistocene sediments, where Lake Tugar-Salgan was formed.