sign in sign up
<<
Home , East European Platform, Emsian, Geology of Romania, Lochkovian, Pragian, Velyki Mosty

Estonian Journal of Earth Sciences, 2016, 65, 4, 207–220 doi: 10.3176/earth.2016.18

Lower lithofacies and palaeoenvironments in the southwestern margin of the East European (, Moldova and Romania)

Natalia Radkovets

Institute of Geology and Geochemistry of Combustible Minerals of the NAS of Ukraine, Naukova 3a, 79060 , Ukraine; [email protected]

Received 8 July 2016, accepted 22 September 2016

Abstract. Lower Devonian palaeoshelf deposits extend along the western margin of the from the Baltic Sea to the . These deposits have been studied on the territory of Ukraine (Volyn-Podillyan Plate, Dobrogean Foredeep) and correlated with coeval deposits in Moldova and Romania (Moldovian Platform). The investigation of the Lower Devonian deposits, their thickness, petrographic and lithological characteristics allowed reconstruction of two types of lithofacies and distinguishing two different depositional environments. The first lithofacies belonging to the , consists of clayey-carbonate rocks and represents a continuation of the Upper marine strata. The other lithofacies encompassing the – comprises terrigenous reddish-brown rocks, which are roughly equivalent to the Old Red Sandstone, completes the Lower Devonian section. Establishing the occurrence and thickness distribution of the terrigenous lithofacies across the study area is important, because it forms potential reservoir rocks for both conventional and unconventional (tight gas) hydrocarbons. Gas accumulation in these reservoir rocks has been discovered at the Lokachi field.

Key words: Early Devonian, Ukraine, petrographic characteristics, borehole sections, shelf of .

INTRODUCTION western Ukraine and adjacent areas. The study utilizes also relevant data from Moldova and Romania (Barbu Forty ago researchers recognized that large-scale et al. 1969; Paraschiv et al. 1983; Prodan 1987; Mutihac hydraulic fracturing could unlock natural gas held in et al. 2007; Seghedi 2012), as well as from Poland, low-permeability (tight) rocks. Today tight gas is a signi- Lithuania, Latvia and Estonia (Pożaryski et al. 1982; ficant and growing part of USA natural gas production. Turnau & Jakubowska 1989; Kleesment & Mark-Kurik The development activities and production of gas from 1997; Poprawa et al. 1999; Racki & Turnau 2000; tight gas reservoirs in Canada, Australia, Mexico, Shogenova et al. 2009; Narkiewicz 2011; Filipiak et al. Venezuela, Argentina, Indonesia, China, Russia, Saudi 2012; Mark-Kurik & Põldvere 2012). Arabia and Egypt has been observed during the past decade (Holditch 2006; Gutiérrez et al. 2009; Sahin 2013). GEOLOGICAL BACKGROUND Lower Devonian deposits (Pragian–Emsian redbeds) of the East European Platform also represent an important The area under study spans the following tectonic units exploration target for the conventional and unconventional in the southwestern margin of the East European gas in Europe (Shogenova et al. 2009). In Ukraine they Platform: the Volyn-Podillyan Plate, Moldovian Platform host gas accumulations in two gas fields in Lower– and Dobrogean Foredeep (Fig. 1). The sedimentary cover Middle Devonian of the Volyn-Podillyan Plate – Velyki in this territory overlying the Archean– base- Mosty and Lokachi, where one of gas-bearing horizons ment is composed of igneous and metamorphic rocks. occurs in Pragian–Emsian terrigenous reddish-brown The basement crops out within the and rocks (Fedyshyn 1998; Galabuda et al. 2007). dips homoclinally towards the Teisseyre–Tornquist Zone. The objective of this study is to provide petrographic The maximum thickness of the sedimentary cover description of the Lower Devonian deposits of Ukraine reaches 10 km in the Volyn-Podillyan Plate and 7 km (Volyn-Podillyan Plate, Dobrogean Foredeep), establish in the Dobrogean Foredeep (Kruglov & Tsypko 1988; their lithofacies patterns and depositional environments Chebanenko et al. 1990). The sedimentary succession is within the southern Baltic shelf, construct lithostrati- represented by the Neoproterozoic, Palaeozoic (, graphic sections and thickness maps for Lochkovian and , Silurian, Devonian and Pragian–Emsian strata, and correlate them between the deposits in the Volyn-Podillyan Plate, Moldovian Platform © 2016 Author. This is an Open Access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International Licence (http://creativecommons.org/licenses/by/4.0).

207 Estonian Journal of Earth Sciences, 2016, 65, 4, 207–220

Fig. 1. Location map, showing the generalized distribution of Lower Devonian rocks in the southwestern margin of the East European Platform and the locations of boreholes. For the location of lithological sections see Fig. 4. Boreholes: Bch, Buchach; Bl, Baluchyn; Blb, Balabanivsk; Br, ; Bsh, Byshiv; Bt, Berestechko; Bzh, Berezhany; Chr, Chernivtsi; Db, Dublyany; Dr, Darakhiv; Gl, Glynyany; Gr, Gorokhiv; IvF, Ivano-Frankivsk; Iv, Ivanesti; Khm, Khmelivka; Km, Kremenets; Kn, Konopkivka; KP, Koropets-Pyshkivtsi; Kr, ; Lk, Lokachi; Lm, Lyman; Ls, Lishchyny; Lt, Litovezh; Lts, Lutsk; Mn, Myrne; NV, Novyi Vytkiv; Og, Ogladiv; Ol, ; P, Valya-Perzhey; Pch, Povcha; Pg, Pidgaytsi; PK, Kangaz; Pr, Peremyshlyany; Rg, Rogatyn; Rm, Roman; RR, Rava-Ruska; Sk, ; Sr, Sarata; Ssh, Sushne; St, Stremin; TK, Tlumach-Kolomya; V, Vugilna; Vch, Verchniakivtsi; Vl, Volodymyrivka; VlV, Volodymyr-Volynsky; VM, Velyki Mosty; Vt, Voyutyn; Yr, Yargara; Zch, ; Zg, Zagoriv; Zl, Zalozhtsi; Zp, Zagaypil; Zv, Zavadivka.

208 N. Radkovets: Lower Devonian of the SW of the East European Platform

The CaCO3, СаMg(СО3)2 and clayey material rock- content has been calculated from chemical analyses, performed in the Institute of Geology and Geochemistry of Combustible Minerals of the NAS of Ukraine (Lviv, Ukraine). Thin sections were examined under a polarizing microscope Carl Zeiss Jena. Well-log data along with the results of analytical and petrographic analyses of rocks were used for the lithostratigraphic correlation of the examined sections.

LOWER DEVONIAN LITHOFACIES Fig. 2. Stratigraphic scheme of the Lower Devonian deposits of the Volyn-Podillyan Plate (after Nikiforova et al. 1972; Petrographic characteristics Tsegelnyuk 1994). The clayey-carbonate facies is represented by marl- and Dobrogean Foredeep), ( and stones, dolomitized limestones and biodetrital limestones. deposits in the Dobrogean Foredeep; Marlstones (Fig. 3IID, E, G, H; Fig. 4IIE, G) are and deposits in the Volyn-Podillyan Plate, dark grey, clayey, with thin calcite veinlets, pyritized Moldovian Platform and Dobrogean Foredeep) and streaks of organic matter and dolomitized. The content of Cenozoic (Palaeogene, and Quaternary deposits). calcite is 48–52%, clayey material amounts to 34–48% The Lower Devonian sequence conformably rests on and dolomite to 5–10%. Locally, accumulations of silt- Upper Silurian deposits. Its lower part is represented by size quartz grains and identified relicts of calcareous clayey-carbonate rocks, whereas the upper part consists bioclasts, such as ostracods and tentaculites, are observed. of terrigenous rocks. The thickness of this sequence Dolomitized limestones (Figs 3IIF, 4IIF) are dark- increases gradually to the west towards the Teisseyre– grey and consist of 40–47% calcite, 40–45% dolomite and Tornquist Zone, where it reaches the maximum thickness 10–15% clayey material. The rocks often contain stylolitic of over 1900 m. sutures 1–3 mm in thickness. These are composed of There are different opinions as to the completeness dolomite crystals (0.1–0.3 mm), which usually have of the Lower Devonian stratigraphic strata within the rhombohedral shape and calcite. Volyn-Podillyan Plate. Nikiforova et al. (1972) recognized In dolomitized limestones a significant amount of there the Lochkovian only, whereas Drygant (2000) organic matter is present. It is often pyritized and locally argued that Pragian and Emsian deposits are present represented by strongly recrystallized bioclasts. as well. We accepted the subdivision of Tsegelnyuk Biodetrital limestones (Fig. 4IIC, D) are grey, rich (1994), who concluded that the Lower Devonian platform in skeletal debris dominated by tentaculites, ostracods, strata in Ukraine are represented by the Lochkovian, brachiopods and subordinately by corals. There are also which is subdivided into the Rukshyn and Tyver stages, single grains of quartz, up to 0.05 mm in size, large and Pragian to Emsian referred to as the Dnister stage phosphate matter accumulations (1–5%) and disseminated (Fig. 2). pyrite. Chemical analysis showed that the CaCO3 content in these limestones ranges between 63% and 83%. The matrix is microcrystalline to fine-crystalline clayey- ANALYTICAL METHODS carbonates. The terrigenous facies is made up of light grey, The study is based on the analysis of well-logs, core greenish-grey and brownish-red, non-calcareous sand- samples and thin sections. Thirty-one representative stones that locally are interbedded with siltstones and core samples of Lochkovian deposits (marlstones, bio- mudstones. detrital limestones, dolomitized limestones) and Pragian– Sandstones (Fig. 3IIA, B, C; Fig. 4IIA) are fine- Emsian siliciclastics (sandstones, siltstones and mud- grained with a contact-porous and contact-hydromica stones) were selected for petrographic examination matrix, saturated with iron hydroxide. Clastic material (Table 1). The samples come from the following bore- is semi-rounded, 0.05–0.2 mm in size, represented by holes: Buchach-2 (Bch-2), Chernivtsi-1 (Chr-1), Krekhiv-1 quartz grains (to 80%), feldspar (5–7%) and muscovite (Kr-1), Lokachi-2, -6 and -9 (Lk-2, -6 and -9), Lyman-1 flakes (1–3%). Some quartzite and siliceous clasts are (Lm-1), Peremyshlyany-1 (Pr-1), Sarata-6 (Sr-6), Yargara-1 also recorded. Accessory minerals, such as zircon and (Yr-1) and Zalozhtsi-1 (Zl-1) (see Fig. 1 for their epidote, are observed sporadically. Compositionally, silt- locations). stones are similar to sandstones.

209 Estonian Journal of Earth Sciences, 2016, 65, 4, 207–220

210 N. Radkovets: Lower Devonian of the SW of the East European Platform

Fig. 3. (I) CaCO3 content in the Lower Devonian sequence of the boreholes (Volyn-Podillyan Plate). (II) Photomicrographs of the Lower Devonian rocks from the Krekhiv-1, Lokachi-2 and Buchach-2 boreholes (Volyn-Podillyan Plate). Photomicrograph B was made without analyser, all the rest – with analyser. A, B, C, sandstones with hydromica matrix saturated with iron hydroxide (hmih), quartz (q), feldspar (f) and muscovite (m): A – depth interval 1916.2–1918.6 m, B – depth interval 1267.5–1268 m, C – depth interval 1337–1337.8 m; D, E, G, H, marlstones with pyritized streaks of organic matter (om): D – calcite veinlet (cv), depth interval 453–459 m, E – problematic bioclasts (bc), depth interval 555–560 m, G – depth interval 3405.1–3414.7 m, H – depth interval 3486.6–3497.6 m; F – dolomitized limestones with dolomite grains (dg) and organic matter (om), depth interval 3348.7–3356.6 m.

211 Estonian Journal of Earth Sciences, 2016, 65, 4, 207–220

Fig. 4. (I) CaCO3 content in the Lower Devonian sequence of the Lyman-1 borehole (Dobrogean Foredeep). (II) Photomicrograph of the Lower Devonian rock of the Lyman-1 borehole (Dobrogean Foredeep). Photomicrograph A was made without analyser, all the rest – with analyser. A, sandstones with hydromica matrix saturated with iron hydroxide (hmih), quartz (q) and feldspar (f), depth interval 1406–1412 m; B, mudstones, composed of hydromica saturated with iron hydroxide (hih) and quartz (q), depth interval 1479–1481 m; C, D, biodetrital limestones: C – ostracods (o), depth interval 1565–1571 m, D – coral fragment (cf), depth interval 1816–1821 m; F – dolomitized limestones with stylolitic sutures (ss) and dolomite grains (dg), depth interval 2170–2180 m; E, G – marlstones with calcite veinlet (cv) and pyritized streaks of organic matter (om): E – depth interval 1979–1981 m, G – depth interval 2180–2200 m.

212 N. Radkovets: Lower Devonian of the SW of the East European Platform

Mudstones (Fig. 4IIB) are composed of thin flakes the river valley related to the construction of the Dnister of hydromica with oriented texture. As a rule, the rock hydroelectric power plant. is saturated with iron hydroxide. Clastic material (0.01– The correlation shows (Fig. 5) that the Lochkovian 0.07 mm) is unevenly distributed in the mudstones, from sequence (clayey-carbonate lithofacies) dips mono- a few grains to 25–32% in different parts of the rock. It clinally and its uppermost part was partly eroded away is mainly represented by quartz. Feldspar and muscovite (boreholes Ogladiv-1, Brody-1, Zalozhtsi-1, Vugilna-7). grains are less common. Small amounts of rhombohedral The Pragian–Emsian deposits of terrigenous lithofacies dolomite grains, as well as fine pyrite, are observed. are spread to a lesser extent than Lochkovian and are K-bentonites (tuffites) occur as numerous, 0.05–3 m more eroded (Chebanenko et al. 1990). Despite , thick intercalations throughout the Lower Devonian in the deeper part of the section the Pragian–Emsian succession (Fig. 5). They are especially common in deposits reach a significant thickness to over 800 m. clayey-carbonate lithofacies, similarly to the Upper This fact is very important because we are considering Silurian sequence within the study area (Radkovets 2015). the terrigenous reddish-brown rocks as potential gas For the basic section of Podillya, K-bentonites are shown reservoir rocks as in the Lokachi field (Fedyshyn 1998; after Nikiforova et al. (1972). For the remaining sections Galabuda et al. 2007). they are indicated based on petrographic investigations, well-log analysis and correlation with the basic section Distribution of lithofacies of Podillya. Hence K-bentonites of the Dnister Basin in Podillya occur in the Upper Silurian as well as in the The Lower Devonian strata within the study area were Lower Devonian. Huff et al. (2000) have interpreted the subdivided on the basis of our investigation into two Ludlow and Pridoli K-bentonites of the Dnister Basin in lithofacies: the clayey-carbonate Lochkovian and the Podillya as indicative of active volcanic arcs along the terrigenous Pragian–Emsian facies, which are roughly margin of the Rheic Ocean. equivalent in age to Devonian continental deposits, A total of 97 K-bentonite levels in the form of so-called Old Red Sandstones, occurring westwards of altered airfall volcanic ash beds (Histon et al. 2007) the Ukrainian Shield towards the Teisseyre–Tornquist have also been recorded from the Upper Ordovician Zone. The clayey-carbonate lithofacies represents the (Ashgill) to Lower Devonian (Lochkov) sequences of continuation of the Upper Silurian strata. The terrigenous the Carnic Alps, Austria. These ash beds suggest wide- lithofacies completes the Lower Devonian section. spread rifting-related volcanism in the enigmatic Palaeo- Previous studies (Drygant et al. 1982; Chebanenko Tethys (von Raumer et al. 2002, 2003), which opened et al. 1990; Drygant 2000; Kurovets et al. 2012) have during the Silurian period between the northern margin shown different thicknesses and boundaries between the of Gondwana and the composite Hun Superterrane. It clayey-carbonate and terrigenous deposits within the may have lasted until the end of the Middle Devonian, Volyn-Podillyan Plate. when these amalgamated and the closure of the The thickness maps (Fig. 6A, B) of the Lower Rheic Ocean began. Lower to Middle Devonian marine Devonian were constructed on the basis of our strata in the Appalachian foreland basin feature up to investigations of well-log data, core samples, thin 80 or more thin K-bentonites that represent ancient sections and stratigraphic subdivision of the Lower volcanic ashes. According to Ver Straeten (2004), the Devonian for the Volyn-Podillyan Plate by Nikiforova middle Lochkovian, early Emsian and early et al. (1972) and Tsegelnyuk (1981, 1994) and for the were times of peak volcanic activity in eastern North Dobrogean Foredeep by Safarov & Kaptsan (1967), America, related to times of increased tectonism in the Grishchenko et al. (1986), as well as the information Acadian orogen. contained in the above-mentioned publications, which were compared with the data from Romania and Moldova Correlation of borehole sections (Barbu et al. 1969; Paraschiv et al. 1983; Prodan 1987; Kruglov & Tsypko 1988; Gnidets et al. 2002; Mutihac Figure 5 shows the lithological features and spatial et al. 2007; Seghedi 2012). distribution of Lower Devonian lithofacies in twelve Figure 6A represents the occurrence of the clayey- well sections. Stage boundaries are based on well-log carbonate lithofacies (Lochkovian) and its thickness data, distribution of K-bentonite beds and the results of within the area from the border of Ukraine with Poland petrographic investigations. The main reference section and Belarus to the Black Sea. Clayey-carbonate litho- for correlation is that from Podillya (Nikiforova et al. facies continuously cover the entire territory under study. 1972) that was constructed on the basis of 87 outcrops In the territory of Romania and Moldova the Lochkovian along the Dnister River and its tributaries. These out- deposits are partly eroded, as well as within the Dobrogean crops are now under water as a result of the damming of Foredeep. At monoclinal dipping the thickness of this

213 Estonian Journal of Earth Sciences, 2016, 65, 4, 207–220

) (see Fig. 1 for location). 1 ) and Dobrogean Foredeep (B–B 1 succession in the Volyn-Podillyan Plate (A–A Lithological sections through the Lower Devonian

Fig. 5.

214 N. Radkovets: Lower Devonian of the SW of the East European Platform

margin of the East European Platform. within the southwestern ) Pragian–Emsian, terrigenous facies B ) Lochkovian, clayey-carbonate facies and ( A

Thickness maps of (

Fig. 6.

215 Estonian Journal of Earth Sciences, 2016, 65, 4, 207–220 lithofacies increases gradually up to 700 m within the areas trees and seed plants evolved and forests appeared Dobrogean Foredeep and to over 1100 m at the Volyn- for the first time (Algeo & Scheckler 1998). During the Podillyan Plate. Silurian to Early Devonian, the Acadian–Caledonian Figure 6B shows that the Pragian–Emsian terrigenous took place as a result of the closure of the lithofacies experienced much more advanced erosion southern Iapetus Ocean and collision of Baltica with than the clayey-carbonate strata so that it now occurs as Laurentia (Torsvik et al. 1996; Ver Straeten 2004). a narrow band along the Teisseyre–Tornquist line. On This collision produced the Caledonian mountains in the background of general monoclinal dipping of the Greenland, Scandinavia and the British Isles, and the rocks five local morphostructures are distinguished, Appalachians in the eastern USA. The new large super- which stretch across the Pragian–Emsian strata from continent, which resulted from this collision and existed northeast to southwest, being almost parallel to each during Early Devonian times, is sometimes called other and representing ancient river valleys (RV in Laurussia or Euramerica or the ‘Old Red Continent’ Fig. 6B). According to our petrographic investigations (Golonka 2007; Golonka & Gawęda 2012). Extensive and to Chebanenko et al. (1990) and Tsegelnyuk (1981, shallow sandy bays, deltas and inlets across the Old Red 1994), the sediments of the terrigenous lithofacies are Continent provided a prosperous milieu for strange the product of erosion of the basement rocks of the armoured jawless fishes and placoderms (Young 2010). Ukrainian Shield (quartz, feldspars, muscovite, zircon, During the Early Devonian, the study area lay in low epidote), which accumulated in the sedimentary basin southern latitudes (45–52ºS) within the southeastern shelf due to the river transport, which had its source from the basin of Baltica (Fig. 7A). In the Lochkovian (Fig. 7B, B’), Ukrainian Shield. In Romania, similarly to Moldova, this sedimentary basin was a continuation of the Late these strata occur only within the area adjacent to the Silurian basin, although the sea level had slightly fallen. Dobrogean Foredeep part. The thicknesses of the The clayey-carbonate sediments with numerous inter- terrigenous lithofacies are significantly smaller than calations of K-bentonites (tuffites) had accumulated those of the clayey-carbonate facies. The thickness of as in the Pridoli. In the Silurian and Lochkovian, the the terrigenous lithofacies reaches 400 m within the climate and tectonic conditions remained the same. It was Dobrogean Foredeep and over 800 m at the Volyn- a warm greenhouse period typified by high atmospheric Podillyan Plate. CO2 levels (Berner 2001; Royer 2006). Figures 3I, 4I and Table 1 show the lithofacies- A different depositional story began in the Pragian, related CaCO3 content in the Lower Devonian sequence showing a dramatic change in climatic and tectonic for both the Dobrogean Foredeep (Lyman-1 borehole) conditions. From the Lochkovian to Emsian, tempera- and the Volyn-Podillian Plate (Krekhiv-1, Buchach-2 tures decreased (Kiessling 2002) and the sea level fell and Lokachi-2 boreholes). The difference of its value (Vail et al. 1977; Berner & Kothavala 2001; Simon et for two different lithofacies is evident. For the clayey- al. 2007; Haq & Shutter 2008; Joachimski et al. 2009). carbonate lithofacies (Lochkovian) CaCO3 content is Cooler climate conditions, with intermediate tempera- significant over the entire succession, ranging from 40% tures of about 23 to 25°C, decreasing atmospheric CO2 to 87%, whereas in the terrigenous lithofacies (Pragian– and accordingly increasing O2 concentrations, have been Emsian) a decrease in CaCO3 content is observed, established. Dahl et al. (2010) indicate two episodes of varying from 18% to as low as 2%. Hence we can state global ocean oxygenation in the Earth’s history. The that for the rocks of the clayey-carbonate lithofacies the first one took place in the 550–560 million minimum CaCO3 content is 40%, while for the rocks of years ago and the second, perhaps larger oxygenation, the terrigenous lithofacies its maximum content is 18%. occurred in the Early Devonian at about 400 Ma. This indicates quite different depositional environments in the Lower Devonian. In the Lochkovian favourable Depositional environments environments existed for carbonate sedimentation, but in Pragian–Emsian time – for the intense deposition of The depositional environments within the southeastern terrigenous material. shelf basin of Baltica (Fig. 7B, B’) have been recon- structed using the maps compiled on the basis of the FACIES PATTERN IN RELATION TO EARLY author’s materials, and published data (Kleesment & DEVONIAN OCEANOGRAPHY AND SEA- Mark-Kurik 1997; Narkiewicz 2011; Mark-Kurik & LEVEL CHANGES Põldvere 2012), occurrence of the clayey-carbonate Global and regional events facies of the Lochkovian series (Fig. 7C) and the terrigenous facies of the Pragian–Emsian series (Fig. 7C’) The Devonian was one of the most interesting and at the southwestern margin of the East European enigmatic periods in the Earth’s history. On the land Platform.

216 N. Radkovets: Lower Devonian of the SW of the East European Platform ’) C

da 2012). Sketch maps show the model of southern ę ) clayey-carbonate facies of the Lochkovian series; ( C ’) – terrigenous facies of Pragian–Emsian time. B e East European Platform show: ( in the southwestern margin of th howing the position of study area within Baltica (after Golonka & Gaw ) – clayey-carbonate facies of Lochkovian time; ( B

) Early Devonian palaeogeography, s

A ( Maps of Lower Devonian occurrence with

Fig. 7. of Baltica with the occurrence ( shelf terrigenous facies of the Pragian–Emsian series.

217 Estonian Journal of Earth Sciences, 2016, 65, 4, 207–220

The Lochkovian epicontinental basin (Fig. 7B) was favourable environments for the development of calcareous a typical carbonate platform (cf. Kiessling et al. 2003), biocenosis and organic matter fossilization. Hence, the which supported a variety of calcareous biocenoses. Lochkovian showed still no significant change in warm

These contained abundant brachiopods, pelecypods, greenhouse climate with high atmospheric CO2 and in tentaculites and ostracods, as well as crinoids, rugose tectonic conditions, which occurred since the Late and tabulate corals, gastropods, trilobites, graptolites Silurian. In turn, the Pragian and Emsian comprise and (Nikiforova et al. 1972; Tsegelnyuk 1981, distinctly terrigenous sequences, which are reddish-

1994). As a result, sediments with a significant content brown in colour with a small amount of CaCO3 (from of CaCO3 (48–87%) accumulated. The presence of 2 to 18%), manifesting a different depositional history numerous streaks of pyritized organic matter in dark with oxygenated environments and dramatic change in grey marlstones indicates favourable conditions for climatic and tectonic conditions, which started in the organic matter fossilization. Although a deep-water anoxic Pragian. In spite of different depositional environments, environment similar to that of the Silurian organic-rich the Pragian–Emsian strata, whether of terrestrial or marine graptolitic shales (Radkovets 2015) is not evident there, origin, have a common feature – a reddish-brown colour, oxygen-poor environments must have existed locally. which gives evidence of the oxic environments within In the Pragian, the sedimentary basin reduced its size the entire supercontinent Laurussia independently of the (Fig. 7B’), the carbonate accumulation ceased and the tectonic setting. terrigenous sedimentation begun instead. Numerous rivers The terrigenous lithofacies is widespread within the supplied clastic material from the Baltic and Ukrainian study area and its thickness reaches over 1000 m. These shields and generated a thick sediment wedge composed terrigenous deposits are an important tight-gas exploration of sandstones, siltstones and mudstones. The wedge was target in Europe and USA. Thus there is a good reason erosionally reduced during the late Emsian, but the to consider these strata of the study area as prospective thickness of preserved sediment generally exceeds for conventional as well as unconventional hydrocarbons, 1000 m. These sediments are reddish-brown in colour and because these reddish-brown terrigenous rocks of were deposited in oxygenated environments irrespective Pragian–Emsian age are the reservoir rocks for gas of the source of clastic material, sediment composition accumulation at the Lokachi field (Volyn-Podillyan as well as tectonic and depositional settings, similarly to Plate). Besides, numerous oil and gas shows and four the case of the Old Red Sandstone facies widespread in oil and gas fields have been discovered in the Middle– the North Atlantic region (Friend 1969; McClay et al. Upper Devonian within the Ukrainian territory (Volyn- 1986; Friend et al. 2000; Blomeier et al. 2003). Podillyan Plate, Dobrogean Foredeep).

Acknowledgements. The author is grateful to the reviewers CONCLUSIONS Paweł Kosakowski (Kraków, Poland) and Ģirts Stinkulis (Riga, Latvia) for many helpful comments on an earlier version Based on the study of well-log data, and lithological and of this manuscript. Kostiantyn Grygorchuk, Volodymyr Gnidets petrographic investigations of Lower Devonian strata and Dmytro Machalskyi (Lviv, Ukraine) are kindly acknow- within the Volyn-Podillyan Plate and the Dobrogean ledged for providing access to the data. Foredeep and their correlation with coeval deposits of the adjacent territories of Moldova and Romania REFERENCES (Moldovian Platform), Poland, Lithuania, Latvia and

Estonia, an integral concept of the extent of the Lower Algeo, T. J. & Scheckler, S. E. 1998. Terrestrial-marine tele- Devonian, regularities of thickness changes, petrographic connections in the Devonian: links between the evolution composition of rocks and distribution of two facies of land plants, weathering processes, and marine anoxic within the southwestern margin of the East European events. Philosophical Transactions of the Royal Society Platform was developed. These lithofacies belong to of London, Series B, 353, 113–130. Barbu, C., Mehmet, N. A & Cornelia, C. 1969. Paleozoicul different age ranges: the clayey-carbonate facies to the din Vorlandul Carpaţilor Orientali, între Valea Buzăului Lochkovian, the terrigenous facies to the Pragian and şi graniţa de nord a Republicii Socalste Romănia Emsian. They have been formed in different palaeo- [ Foreland of the Eastern Carpathians, between environments. An abrupt change is observed in the Buzau valley and the northern border of the Romanian petrographic composition of rocks. Socialist Republic]. Petrol şi Gaze, 20, 863–867 [in The Lochkovian sequence is represented by clayey- Romanian]. Berner, R. A. 2001. Modeling atmospheric O2 over Phanero- carbonate sediments with numerous streaks of pyritized zoic time. Geochimica et Cosmochimica Acta, 65, 685– organic matter and CaCO3 content of 48–87%, reflecting 694.

218 N. Radkovets: Lower Devonian of the SW of the East European Platform

Berner, R. A. & Kothavala, Z. 2001. GEOCARB III: a revised Fore-Black Sea area. Tektonika i Stratigrafiya, 27, 52–59 model of atmospheric CO2 over Phanerozoic time. [in Russian, with English summary]. American Journal of Science, 301, 182–204. Gutiérrez, C., Felipe, T., Osorio, N. & Restrepo, D. P. 2009. Blomeier, D., Wisshak, M., Joachimski, M., Freiwald, F. & Unconventional natural gas reservoirs. Energética, 41, Volohonsky, E. 2003. Calcareous, alluvial and lacustrine 61–72. deposits in the Old Red Sandstone of central north Haq, B. U. & Schutter, S. R. 2008. A chronology of Paleozoic Spitsbergen (Wood Bay Formation, Early Devonian). sea-level changes. Science, 322, 64–68. Norwegian Journal of Geology, 83, 281–298. Histon, K., Klein, P., Schönlaub, H. P. & Huff, W. D. 2007. Chebanenko, I. I., Vishnyakov, I. B. & Vlasov, B. I. 1990. Lower Palaeozoic K-bentonites from the Carnic Alps, Geotektonika Volyno-Podolii [Geotectonics of the Austria. Austrian Journal of Earth Sciences, 100, 26–42. Volyno-Podolia]. Naukova Dumka, Kiev, 244 рр. [in Holditch, S. A. 2006.Tight gas sands. SPE. 103356. Journal of Russian]. Petroleum Technology, 58, 86–93. Dahl, T. W., Hammarlund, E. U., Anbar, A. D., Bond, D. P. G., Huff, W. D., Bergström, S. M. & Kolata, D. R. 2000. Silurian Gill, B. C., Gordon, G. W., Knoll, A. H., Nielsen A. T. K-bentonites of the Dnestr Basin, Podolia, Ukraine. & Canfield, D. E. 2010. Devonian rise of atmospheric Journal of the Geological Society, 157, 493–504. oxygen correlated to the radiations of terrestrial plants Joachimski, M. M., Breisig, S., Buggisch, W., Talent, J. A., and predatory fish. Proceedings of the National Academy Mawson, R., Gereke, M., Morrow, J. M., Day, J. & of Sciences of the USA, 107, 17911–17915. Weddige, K. 2009. Devonian climate and reef evolution: Drygant, D. M. 2000. Lower and Middle Paleozoic of the insights from oxygen isotopes in apatite. Earth and Volyn-Podillyan margin of the East-European Platform Planetary Science Letters, 284, 599–609. and Carpathian Foredeep. Naukovi Zapysky Derzhavnoho Kiessling, W. 2002. Secular variations in Phanerozoic reef Pryrodoznavchoho Muzeyu, 15, 24–87 [in Ukrainian, with ecosystem. In Phanerozoic Reef Patterns (Kiessling, W., English summary]. Flügel, E. & Golonka, J., eds), SEPM Special Publication, Drygant, D. M., Gavrylyshyn, V. I. & Gynda, V. A. 1982. 72, 625–690. Verkhnij dokembrij-nizhnij paleozoj Srednego Pridnestrovya Kiessling, W., Flügel, E. & Golonka, J. 2003. Patterns of [Upper –Lower Paleozoic of the Srednee Phanerozoic carbonate platform sedimentation. Lethaia, Prydnistrovya]. Naukova Dumka, Kiev, 108 pp. [in 36, 195–226. Russian]. Kleesment, A. & Mark-Kurik, E. 1997. Devonian. Lower Fedyshyn, V. O. (ed.). 1998. Atlas of Oil and Gas Fields of Devonian. Middle Devonian. In Geology and Mineral Ukraine. Vol. 4. Ukrainian Oil and Gas Academy, Lviv, Resources of Estonia (Raukas, A. & Teedumäe, A., eds), 328 pp. pp. 65–72. Estonian Academy Publishers, Tallinn. Filipiak, P., Zatoń, M., Szaniawski, H., Wrona, R. & Racki, G. Kruglov, С. С. & Tsypko, A. K. 1988. Tektonika Ukrainy 2012. Palynology and microfacies of Lower Devonian [Tectonics of Ukraine]. Nedra, Moscow, 254 pp. [in mixed carbonate–siliciclastic deposits in Podolia, Ukraine. Russian]. Acta Palaeontologica Polonica, 57, 863–877. Kurovets, І., Drygant, D., Naumko, I., Kurovets, S. & Koltun, Y. Friend, P. F. 1969. Tectonic features of Old Red sedimentation 2012. Geological and physical-chemical characteristics in North Atlantic borders. The American Association of of Lower Paleozoic deposits of Volyno-Podillya, Western Petroleum Geologists Memoir, 12, 703–710. Ukraine. Biuletyn Państwowego Instytutu Geologicznego, Friend, P. F., Williams, B. P. J., Ford, M. & Williams, E. A. 449, 119–130. 2000. Kinematics and dynamics of the Old Red Mark-Kurik, E. & Põldvere, A. 2012. Devonian stratigraphy in Sandstone basins. In New Perspectives on the Old Estonia: current state and problems. Estonian Journal of Red Sandstone (Friend, P. F. & Williams, B. P. J., eds), Earth Sciences, 61, 33–47. Geological Society, London, Special Publication, 180, McClay, K. R., Norton, M. G., Coney, P. & Davis, G. H. 29–60. 1986. Collapse of the Caledonian orogen and the Old Galabuda, M., Krupsky, Y., Pavlyuk, О. & Chepil, P. 2007. Red Sandstone. Nature, 323, 147–149. History of investigation of geological structure and Mutihac, V., Stratulat, M. I. & Fechet, R. M. 2007. Geologia oil and gas bearing perspectives of Volyno-Podillya. României []. Editura Didactică şi Geologiya i Geokhimiya Goryuchykh Kopalyn, 3, 5–18 Pedagogică, Bucureşti, 249 pp. [in Romanian]. [in Ukrainian, with English summary]. Narkiewicz, M. 2011. Lithostratigraphy, depositional systems Gnidets, V. P., Grigorchuk, K. G., Polukhtovych, B. M. & and transgressive-regressive cycles in the Middle Fedyshyn, V. O. 2002. Lithogenesis of Devonian Deposits Devonian to of the Łysogóry-Radom Basin of Dobrogea Foredeep (Palaeooceanography, Sedimentary (south-eastern Poland). Prace Państwowego Instytutu Cyclicity, Reservoir Rocks’ Formation). UkrDGRI, Lviv, Geologicznego, 196, 7–52 [in Polish, with English 85 рр. [in Ukrainian, with English summary]. summary]. Golonka, J. 2007. Phanerozoic paleoenvironment and paleo- Nikiforova, O. I., Predtechensky, N. N., Abushik, A. F., lithofacies maps. Late Paleozoic. Geologia, 33, 145–209. Ignatovitch, M. M., Modzalevskaya, T. L., Berger, A. Y., Golonka, J. & Gawęda, A. 2012. Plate tectonic evolution of Novoselova, L. S. & Burkov, Y. K. 1972. Opornyj razrez the southern margin of Laurussia in the Paleozoic. In silura i nizhnego devona Podolii [Basic Section of the Tectonics – Recent Advances (Sharkov, E., ed.), pp. 261– Silurian and Lower Devonian of Podolia]. Nauka, 282. InTech. Leningrad, 262 pр. [in Russian]. Grishchenko, V. P., Gurevich, K. Y. & Polukhtovych, B. M. Paraschiv, D., Dăneţ, N., Popescu, M. & Dumitrescu, V. 1983. 1986. New data on Palaeozoic deposits of the Western The present stage of pre-Jurassic deposits knowledge in

219 Estonian Journal of Earth Sciences, 2016, 65, 4, 207–220

South Dobrogea. Anuarul Institutului de Geologie şi storage of CO2. Estonian Journal of Earth Sciences, 58, Geofizică, 59, 29–37. 259–267. Poprawa, P., Sliaupa, S., Stephenson, R. & Lazauskiene, J. Simon, L., Godderis, Y., Buggisch, W., Strauss, H. & 1999. Late Vendian–Early Palaeozoic tectonic evolution Joachimski, M. 2007. Modeling the carbon and sulphur of the Baltic Basin: regional tectonic implications from isotope composition of marine sediments: climate evolution subsidence analysis. Tectonophysics, 314, 219–239. during the Devonian. Chemical Geology, 146, 19–38. Pożaryski, W., Tomczyk, H. & Brochwicz-Lewiński, W. 1982. Torsvik, T. H., Smethurst, M. A., Meert, J. G., Van der Voo, R., Tectonics and paleotectonic evolution of the pre-Permian McKerrow, W. S., Brasier, M. D., Strut, B. A. & Paleozoic between Koszalin and Toruń (Pomerania). Walderhaug, H. J. 1996. Continental break-up and collision Przegląd Geologiczny, 30, 658–665 [in Polish, with in the Neoproterozoic and Palaeozoic: a tale of Baltica English summary]. and Laurentia. Earth-Science Reviews, 40, 229–258. Prodan, J. 1987. Prezenţa gedinianului in platforma Moldovenească Tsegelnyuk, P. D. 1981. To stratigraphy of Lower Devonian [The presence of Gedinian in the Moldavian Platform]. of the south-western margin of the East-European Geologie, 32, 90–98. platform. Tektonika i Stratigrafiya, 21, 3–16 [in Russian, Racki, G. & Turnau, E. 2000. Devonian series and stage with English summary]. boundaries in Poland. Courier Forschungsinstitut Tsegelnyuk, P. D. 1994. Stratigraphy of the Lower Devonian Senckenberg, 225, 145–158. Deposits of Volyn-Podolia. Geologicheskij Zhurnal, 1, Radkovets, N. 2015. The Silurian of southwestern margin of 46–57 [in Ukraine, with English summary]. the East European Platform (Ukraine, Moldova and Turnau, E. & Jakubowska, L. 1989. Early Devonian miospores Romania): lithofacies and palaeoenvironments. Geological and age of the Zwoled formation (Old Red Sandstone Quarterly, 59, 105–118. facies) from Ciepielów IG-1 borehole. Annales Societatis Royer, D. L. 2006. CO2-forced climate thresholds during the Geologorum Poloniae, 59, 391–416. Phanerozoic. Geochimica et Cosmochimica Acta, 70, Vail, P. R., Mitchum, R. M. & Thompson, S. 1977. Seismic 5665–5675. stratigraphy and global changes of sea level, part 4: Safarov, E. I. & Kaptsan, V. K. 1967. O stratigrafii devonskikh i global cycles of relative changes of sea level. AAPG kamennougol´nykh otlozhenij osnovaniya severnogo Memoir, 26, 83–97. borta Preddobrudzskogo progiba [The Devonian and Ver Straeten, C. A. 2004. K-bentonites, volcanic ash pre- Carboniferous stratigraphy of the sediments of the servation, and implications for Lower to Middle basement of the northern edge of Dobrodgean foredeep]. Devonian volcanism in the Acadian Orogen, Eastern Paleontologiya, Geologiya i Poleznye Iskopayemye North America. GSA Bulletin, 116, 474–489. Moldavii, 2, 10–15 [in Russian]. Von Raumer, J. F., Stampfli, G. M., Borel, G. & Bussy, F. Sahin, A. 2013. Unconventional Natural Gas Potential in 2002. The organization of pre-Variscan basement areas Saudi Arabia. Paper SPE 164364 presented at the SPE at the north Gondwanan margin. International Journal of Middle East Oil and Gas Show and Conference, Manama, Earth Sciences, 91, 35–52. Bahrain, 10–13 March. http://dx.doi.org/10.2118/164364-MS. Von Raumer, J. F., Stampfli, G. M. & Bussy, F. 2003. Seghedi, A. 2012. Palaeozoic formations from Dobrogea and Gondwana-derived microcontinents – the constituents Pre-Dobrogea – An overview. Turkish Journal of Earth of the Variscan and Alpine collisional orogens. Sciences, 21, 669–721 [in Turkish, with English summary]. Tectonophysics, 365, 7–22. Shogenova, A., Sliaupa, S., Vaher, R., Shogenov, K. & Young, G. C. 2010. Placoderms (Armored Fish): dominant Pomeranceva, R. 2009. The Baltic Basin: structure, vertebrates of the Devonian period. Annual Review of properties of reservoir rocks, and capacity for geological Earth and Planetary Sciences, 38, 523–550.

Alam-Devoni litofaatsiesed ja paleokeskkond Ida-Euroopa platvormi edelapiiril (Ukrainas, Moldovas ja Rumeenias)

Natalia Radkovets

Alam-Devoni šelfil tekkinud kivimid levivad Ida-Euroopa platvormi läänepoolsel äärealal alates Läänemerest kuni Musta mereni. Neid kivimeid uuriti Ukraina piires (Volõõnia-Podoolia platoo, Dobrogi äärenõos) ja korreleeriti sama- vanuseliste kivimitega Moldovas ning Rumeenias (Moldova platvormil). Alam-Devoni kivimite uurimine, nende paksus, petrograafiline ja litoloogiline iseloom võimaldavad rekonstrueerida kaks litofaatsieste tüüpi ning eristada kaks erinevat sedimentatsiooni keskkonda. Esimene faatsies kuulub Lochkovi lademesse, mis koosneb savikatest karbonaatkivimitest, jätkates Ülem-Siluri mereliste setete kujunemise laadi. Teine faatsies kuulub Praha ja Emsi lade- messe ning koosneb punakaspruunidest terrigeensetest kivimitest, mis on Alam-Devoni ülemisest osast tuntud Old Redi liivakivi analoog. Terrigeense litofaatsiese leviku ja paksuse uurimine on oluline, kuivõrd see on potentsiaalne reservuaar nii traditsiooniliste kui ka ebatraditsiooniliste (kinnisgaas) süsivesinike maardlate kujunemiseks. Niisuguseid gaasimaardlaid on avastatud Lokachi piirkonnas.– –

220