Abstract This study gives valuable insights into the microstructure and pore space characteristics of 17 compositionally variable Visean shale samples from the Ukrainian Dniepr-Donets Basin (the ‘Rudov Beds’). The representative imaging area varies considerably (from 10 000 to >300 000 µm 2 ) as a function of the mineralogy and diagenetic overprinting. The pores hosted in organic matter (OM) are restricted to secondary solid bitumen. Based on high-resolution maps from broad ion beam scanning electron microscopy combined with organic geochemical and bulk mineralogical data, we propose that the amount of OM-hosted porosity responds to the availability of pore space, enabling the accumulation of an early oil phase, which is then progressively transformed to a porous solid bitumen residue. The type of OM porosity (pendular/interface v. spongy) is reflected in the individual pore size distributions: the spongy pores are usually smaller (<50 nm) than the pendular or OM–mineral interface pores. The OM-hosted porosity coincides with differences in the composition of the extract, with high amounts of extractable OM and saturated/aromatic compound ratios indicative of abundant porous solid bitumen. The average circularity and aspect ratio of the mineral matrix pores correlate with the corresponding values for the OM-hosted pores, which show a preferred bedding-parallel orientation, suggesting that compaction influenced both types of pore.

Pollen and lithopedological data were obtained from Upper Paleolithic sites and Upper Pleistocene loess-soil sequences located between the Sea of Azov and the River Donets, and in the foothills of the Crimean Mountains. During the last Middle Pleniglacial interstadial (Upper Vytachiv soil, 30–27 ka), there existed boreal steppe (south-boreal forest-steppe in Crimea). During the Late Pleniglacial, two main phases of loess accumulation occurred, which were separated by the phase of initial pedogenesis. The loess accumulated under subperiglacial xeric steppe (particularly dry at 15–13 ka), and the incipient soils (Dofinivka unit, 18–15 ka) formed under boreal grassland. During the Late Glacial interstadials, there existed boreal and south-boreal forest-steppe with a relatively wet climate (middle Prychernomorsk soil unit, the upper soil 11.8–11.4 ka). During the Younger Dryas, grassland reappeared under a dry and cool climate (10.9–10.5 ka). Paleoclimatic changes demonstrate the same pattern in both studied areas, and they correspond well with Black Sea transgressive-regressive cycles. Regional differences still existed—during all phases, the climate was the mildest in the western foothills of the Crimean Mountains, the coldest in the Donetsk Upland, and the driest near the Sea of Azov.