Karst of Sterlitamak (BASHKIR) Shikhans and Their Surroundings in Southern Pre-Ural Area

Abstract

Abstract—Shikhans, or lone mountains, is the local name for island mountains in the flat foothills of the Southern Urals. The shikhans are denudation remnants, sometimes with preserved residuals of Miocene-Pliocene planation surface on their tops, which allows estimating the total time of development of karst processes at least 5 million years. Despite more than 200 years of research on the shikhans, karst and its manifestations have received little attention to date. A map of karst in the shikhan territory was drawn up according to the standard methodology of karstological survey. Widespread and quite rare forms of carbonate karst of the shikhans and sulphate karst of their close vicinities were characterised. It was established that along with widespread and known in temperate latitudes karstic features, very rare corrosion wells are developed in the gypsum of the Kungurian Stage in the study area, forming karst fields with the highest density of karst forms known in the East European Plain. Gypsum caves at various stages of formation, as well as semi-blind karst-erosion gullies not typical for the lowland sulphate karst of the region were recorded. For the carbonate karst of the Shikhans in the limestones of the Sakmarian Stage, the highest location of karst caves in the foothills of the Southern Urals and the oldest (earky Middle Pleistocene) age of their foundation were established. The main peculiarity of distribution of both surface and underground karst-holes is a clearly expressed dependence of forms and frequency of their occurrence on the course of formation of relief elements in the Neogene-Quaternary time. The presence in a small area of two types of karst by composition of karst rocks with very rare karst forms predetermines the high scientific, practical and educational significance of the shikhans and their surroundings.