The Silurian of south-western margin of the East European Platform (Ukraine, Moldova and Romania): lithofacies and palaeoenvironments

Abstract

1 In sti tute of Ge ol ogy and Geo chem is try of Com bus ti ble Min er als of the NAS of Ukraine, Naukova 3a, 79060 Lviv, Ukraine Radkovets, N., 2015. The Si lu rian of southwest ern mar gin of the East Eu ro pean Plat form (Ukraine, Moldova and Ro ma nia): lithofacies and palaeoenvironments. Geo log i cal Quar terly, 59 (1): 105-118, doi: 10.7306/gq.1211Si lu rian strata, stretch ing along the west ern mar gin of the East Eu ro pean Plat form from the Bal tic to the Black Sea, rep re sent a po ten tial tar get for both con ven tional and un con ven tional hy dro car bon ex plo ra tion. Dis tri bu tion of the black shale fa cies, pro spec tive for shale gas, and the reef fa cies, pro spec tive for oil, has been stud ied in re spect of palaeoenvironments. The Silu rian se quence has been in ves ti gated in the ter ri tory of Ukraine (Volyn-Podillyan Plate, Dobrogean Foredeep) and cor related with the data on Moldova and Ro ma nia (Moldovian Plat form). The oc cur rence of Si lu rian strata, their thick ness, and petrographic and lithological char ac ter is tics al lowed re con struct ing the dis tri bu tion of open-shelf, reef and la goonal fa cies. The reef fa cies mi grated dur ing the Wen lock-Mid dle Pridoli, shift ing to wards the open sea and back to wards the shore, and there fore has been termed a mi grat ing reef fa cies. Cor re spond ingly, the bound ary be tween the open-shelf and reef fa cies was shift ing. The fa cies dis tri bu tion was con trolled by the transgressive-re gres sive cy cles, which caused the fluc tu a tions of the shelf wa ter depth in dif fer ent time in ter vals of the Si lu rian. The shelf wa ter depth of about 100 m, where the top of the ox ygen-min i mum layer im pinged on the sea bot tom, was the boundary between the open-shelf facies, represented by organic-rich sediments, and the reef build ups.

Geodynamics

“…In the deeper part there was no intensive influx of clay material. So these sediments are made up of biodetrital and dolomitized limestones, without the facial zones that existed in Silurian times [Radkovets, 2015]. Petrographic investigation of the Silurian and Lover Devonian (Lochkovian) rocks allowed selecting characteristic types of rocks from different parts of the study area (Fig.…”

“…The formation of the reef facies began in Wenlock. These facies formed the boundary beyond which deep-water clay layers were deposited [Radkovets, 2015].…”

“…Therefore, these deposits are of interest in terms of generation and accumulation of liquid and gaseous conventional and unconventional hydrocarbons. Paleogeographic environments in Lochkovian times of the Lower Devonian within the study area were largely inherited from the Silurian period, which led to the accumulation of clay muds with a significant content of carbonate component and contributed to the accumulation of organic matter in these sediments [Radkovets, 2015, Radkovets, 2016. Therefore, in this paper we consider the Silurian and Lower Devonian deposits as a single facies unit, which should also be considered in view of the prospects of oil and gas exploration.…”

“…The petrographic analysis of the Silurian and Lower Devonian (Lochkovian) rocks allowed us to trace the patterns of the material composition changes of these strata in time and space, and to outline their oil and gas generation prospects. [Radkovets, 2015, Radkovets, 2016.…”

Reconstructing Depositional Rates and Their Effect on Paleoenvironmental Proxies: The Case of the Lau Carbon Isotope Excursion in Gotland, Sweden

“…The Baltic Basin, where the Bodudd section is located, is representative of other Paleozoic tropical‐subtropical basins in terms of facies distribution (Calner et al, 2006; Lazauskienė et al, 2003; Tomczykowa, 1988). The epicratonic basin margin is formed by reefal, bioclastic, and microbial limestones, and the only clastic lithosomes are associated with forced regressive strata (Calner et al, 2006; Eriksson & Calner, 2008; Jarochowska & Kozłowski, 2014; Kozłowski & Sobień, 2012; Radkovets, 2015). The carbonate content decreases down the slope of the carbonate platform, represented by marls and calcareous mudstones, and the deepest parts of the basin are formed by graptolitic shales (Hammarlund et al, 2019; Porębski et al, 2013; Sullivan et al, 2018).…”