Earth’s Cryosphere, 2021, Vol. XXV, No. 6, p. 52-61.

SUBPERMAFROST WATERS IN THE EAST CHUKOTKA’S UPLAND

V.E. Glotov

Shilo North-East Interdisciplinary Scientific Research Institute, Far East Branch, Russian Academy of Sciences (NEISRI FEB RAS), Portovaya str. 16, Magadan, 685000, Russia, geoecol@neisri.ru

The purpose of the article is to reveal the conditions of occurrence and formation of subpermafrost waters, which have been encountered by wells in the Paleozoic, Triassic terrigenous rocks and in the Lower Cretaceous granitoids of the Chukotka Upland. In the Paleozoic sequence, confined subpermafrost waters were encountered at depths from 223 to 340 m. The specific flow rates vary from 0.01 to 0.5 L/(s⋅m), the composition of the waters is predominantly chloride, and mineralization ranges from 0.2 to 1.3 g/dm3. In the Triassic rocks, at depths from 100 to 300 m, the piezometric surface of waters is higher than wellhead levels by 3–4 m and up to 58.4 m. The specific yield varies from 0.00001 to 0.25 L/(s⋅m). The waters are chloride, hydrocarbonate and sulphate, salinity ranges from 0.1 to 3.1 g/dm3. In the granitoid massifs, the thickness of permafrost near the sea coast is about 100 m; within the watersheds, it is about 450 m. The specific yield varies from 0.0001 to 0.013 L/(s⋅m). The obtained data, confirmed by magnetotelluric sounding, indicate the development of hydrogeological massifs composed of igneous and metamorphosed rocks in the upland. Structures with quasi-stratum fracture reservoirs, associated with overthrusts and faults, were formed in the terrigenous Triassic sequences. The impermeable fault planes divide the quasi-strata into sections, which are poorly interconnected hydraulically. For this reason, in the Triassic subpermafrost strata, the stagnant or extremely impeded water exchange predominates persisting for more than 400 thousand years; while in the hydrogeological massifs, the water exchange is more active.

Chukotka Upland, permafrost zone, subpermafrost waters, active and extremely impeded water exchange, cryogenic pressure, magnetotelluric sounding.