Upper Pleistocene and Holocene deposits at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)

Abstract

An abandoned ozokerite mine (= Ropyshche), where large mammal remains were discovered in the first half of the 20th century, is located in the Velyky Lukavets River valley covered with Quaternary sediments. The catchment area includes a flysch sequence unconformably overlain by salt-bearing Lower Miocene molasses of the Vorotyshcha beds. Both the Upper Pleistocene and Holocene are represented by: channel (gravel, sandy gravel) and overbank alluvium (mud, peat, biogenic mud) and colluvium (mud, sandy mud) as well as by mine wastes. The channel sediments are usually found in the lowest fragments of the borehole logs and represent mainly material deposited in the straight segments of meandering river-beds. The most common, fine-grained (Mz = 61.33 to 7.11 μm), distal floodplain sediments are locally up to 10 m thick and are dominated by massive mud lithofacies, which contain frequent burrows, root hairs or slightly larger root traces and reed rods. These sediments are characterized by rather stable grain size distribution, quite monotonous mineral composition, presence of resistant heavy minerals and quartz grains with traces of chemical weathering. Angular grains with conchoidal fractures and sharp edges also occur. Therefore, textural features show that the main sources of material were, most probably, weathering crusts of various ages developed on relatively poorly lithologically diversified Carpathian flysch strata and on Miocene deposits of the Carpathian Foredeep. With time, an increase of the content of material originating from mechanical weathering (frost action) occurred in the floodplain deposits, which can be linked to an increase of climate severity and reduction of vegetation. However, these changes are not recorded in the deposits, which developed mostly in closed hollows and accumulated mainly from suspension or from low-energy flows. This calm sedimentation was periodically interrupted by supply of more coarse-grained material (sand, gravel). A distinct predominance of overbank deposits in the sections documented by their thickness suggests that the northward flow of the Velyky Lukavets River was blocked as a result of either neotectonic movements or damming of the valley by landslide tongues. From the lithological point of view, the most favourable conditions for preservation of large, extinct mammals still exist in the two selected areas, where the total thickness of Pleistocene muds exceeds 2 metres. The first area is located in the vicinity of boreholes Nos 2, 3, 21, 22, 23, 28, 30 33 and 36N, and the other, smaller one, is placed around borehole No. 42.