Bitumen and salt contents within the Quaternary sediments at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)

Geochemical studies were conducted on bitumen and salts saturating the Pleistocene and Holocene sediments from an abandoned ozokerite mine in Starunia. This location is noted for the discovery of remnants of a mammoth and three woolly rhinoceroses in 1907, and a nearly completely preserved rhinoceros carcass in 1929. The bitumen (oil) and brines (chloride ions) were preserving agents for the large Pleistocene mammals. The main mass of organic carbon hosted in the Pleistocene muds is related to bitumen originating from oil migrating from deep accumulations within the Boryslav-Pokuttya Unit. The highest analysed bitumen content is 9.26 wt%. The chloride ion content, originating from highly concentrated brines ascending from the salt-bearing Miocene Vorotyshcha beds, vary from 0 to 4.66 wt% but this usually does not exceed 1 wt%. The natural pathways of underground fluids (oil, gas and water) migration within the Quaternary sediments were disturbed by intensive ozokerite mining operations run between the last three decades of the 19th century and 1960. Therefore, the present preservation and conservation conditions of large, extinct mammals' remains can be different from those prevailing during the Pleistocene, when the mammals were buried. Taking into consideration the contents of the remaining preservatives: chloride and bitumen, the most favourable zone for fossils conservation and preservation is located close to boreholes Nos 22, 23, 28 and 36N, where the thickness of Pleistocene muds exceeds 2 metres. Generally, the spatial distributions of bitumen and chloride ion contents within the Holocene sediments and salt-bearing Miocene Vorotyshcha beds are very similar to those in the Pleistocene sediments.