Surface geochemical survey at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)

Abstract

A surface geochemical survey was carried out in an abandoned ozokerite mine in Starunia, where remnants of a mammoth and three woolly rhinoceroses and one almost completely preserved rhinoceros carcass were found in 1907 and 1929. In total, 689 measurement sites were defined within the selected 300×350 m rectangle (ca. 10.5 ha). The analysed soil gases vary in their molecular and isotopic compositions. Several zones with anomalous methane concentrations over 10 vol% were identified in the study area. These anomalous concentrations correlate well with total C2-C5 alkane anomalies (over 1 vol%). The zones with carbon dioxide concentrations over 15 vol% are generally shifted SW of those, where the methane and the sum of C2-C5 alkanes anomalies were identified. High helium concentrations of crustal origin (over 0.001 vol%) are clustered near fault zones. In a majority of cases methane is of thermogenic origin, migrating to the near-surface zone from deep-seated accumulations. Microbial methane, or methane with a high microbial component, is genetically related to recent swamps. The high variability of concentrations of gaseous components together with the highly variable isotopic composition of individual gases in the soil, indicate their thermogenic and/or microbial origin, and point to the lithological diversity of Quaternary sediments in the study area. Several zones with thermogenic gaseous hydrocarbons and helium were delineated. It is likely that during the Pleistocene winters, under a thick ice and snow cover, the tundra lake and swamp zones around outflows of brines, oil, helium and thermogenic gases had a higher temperature, which resulted in melting and cracking of the ice cover. These sites would be more prospective for future search of well-preserved large vertebrates.