Isotopic and geochemical characteristics of composite wedges from the Batagay lower sand unit

The study focuses on sand-ice wedges from the Batagay Lower Sand and their isotope-geochemical characteristics. The goal of this research is to characterize the isotopic and geochemical properties of composite sand-ice wedge (CW) in the Lower Sand sequence and compare them with similar wedges in the Upper Sand. Ice sampling from lower horizons of the Batagay sequence is extremely difficult due to active soil collapse above as a result of melting of highly ice-rich deposits and their fall from heights of 50–70 meters. Ice sampling of CW exposed in Lower Sand of Batagay slump was conducted on August 14, 2019. Samples were collected every 10–20 centimeters vertically using Makita and Bosch electric drills. Macrocomponent composition of CW ice was determined using a Stayer ion chromatograph. Oxygen and deuterium isotope composition measurements were performed in the CW ice at the Stable Isotope Laboratory of the Geography Faculty of Moscow State University using a Delta-V Plus mass spectrometer and a gas bench complex. The normality of distribution was tested using the Shapiro-Wilk test, Welch's t-test and the Mann-Whitney U-test. Overall, relatively low isotopic composition values were obtained for the CW ice, with δ18O ranging from –36.09 to –32.32 ‰ and δ2H ranging from –257.1 to –230.1 ‰. Very high dexc values, ranging from 22.5 to 42.4 ‰ were obtained for all ice samples. Statistical tests on the isotopic composition of the CW revealed significant differences in the distributions of δ18O and δ2H values in the upper and lower sands, while there were no significant differences in dexc values. The average mineralization value for CW in the Lower Sand was 332 mg / L. Calcium predominates among cations, averaging 66–97 mg/L, and sulfates predominate among anions, averaging 144–273 mg/L. The greatest variation among cations is noted for magnesium (2–255 mg/L) and among anions for nitrates (0.1–111.7 mg/l. A hypothesis has been proposed regarding the significant proximity in origin and, potentially, the formation timing of the CW of the Lower and Upper Sand layers of the Batagay sequence.