Geochemistry of the frost mound’s ice in the Sentsa River Valley (Oka plateau, East Sayan Mnt.)

¹ Institute of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk, Russia
² Irkutsk state university, 664003 Irkutsk, Russia

^* Corresponding author: lalex@crust.irk.ru

Abstract

The authors have studied the chemical composition of ground ice sampled from the frost mounds located in the unconsolidated sediments of the Sentsa River valley (Oka plateau, Eastern Sayan Mountains) to reconstruct the formation history of these cryogenic creations. Numerous frost mounds of various sizes are mainly composed of clayey silts with interlayers of heavy silts and ice lenses. It is found that the chemical composition of the melt ice sampled from lenses and layers within the frost mounds is HCO₃ Ca, SO₄-HCO₃ Ca and NH₄-HCO₃ Ca with 6.5–15.6 mg/L salinity and pH = 5.6÷6.1. Whereas, the salinity of the melt texture-forming ice sampled from the ice with fractions of enclosing clayey silts was much higher: from 50 up to 792.5 mg/L. River and lake water is ultra-fresh HCO₃ Ca with 99–132 mg/L salinity. The geochemical features of ground ice depend on a water-rock interaction, a presence of organic matter in the unconsolidated sediments and a repeated volcanic activity. The frost mounds are confined to a lacustrine sediments area in the backwater zone that was formed by the Late Pleistocene end moraine. The frost mounds have probably a mixed segregation-injection genesis.