Int J Earth Sci (Geol Rundsch) (2017) 106:743–761 DOI 10.1007/s00531-016-1328-x ORIGINAL PAPER Petroleum source rock evaluation of the Alum and Dictyonema Shales (Upper Cambrian–Lower Ordovician) in the Baltic Basin and Podlasie Depression (eastern Poland) Paweł Kosakowski1 · Maciej J. Kotarba1 · Adam Piestrzyn´ski1 · Alla Shogenova2 · Dariusz Wie˛cław1 Received: 22 September 2014 / Accepted: 6 April 2016 / Published online: 5 May 2016 © Springer-Verlag Berlin Heidelberg 2016 Abstract We present geochemical characteristics of the origin. The measured content of uranium reached up to Lower Palaeozoic shales deposited in the Baltic Basin 750 ppm and thorium up to 37 ppm. and Podlasie Depression. In the study area, this strata are represented by the Upper Cambrian–Lower Ordovician Keywords Alum Shale · Dictyonema Shale · Baltic Basin · Alum Shale recognized in southern Scandinavia and Pol- Podlasie Depression · Source rock evaluation ish offshore and a equivalent the Lower Tremadocian Dic- tyonema Shale from the northern Estonia and the Podlasie Depression in Poland. Geochemical analyses reveal that Introduction the Alum Shale and Dictyonema Shale present high con- tents of organic carbon. These deposits have the best source Investigation of Alum and Dictyonema Shales (Upper Cam- quality among the Lower Palaeozoic strata, and they are brian–Lower Ordovician) in the Baltic region and adjacent the best source rocks in the Baltic region. The bituminous areas (Fig. 1a) as source of hydrocarbons has been performed shales complex has TOC contents up to ca. 22 wt%. The for over 200 years (Andérsson et al. 1985). The first attempts analysed rocks contain low-sulphur, oil-prone Type-II kero- were connected with solvent extraction of bitumen and before gen deposited in anoxic or sub-oxic conditions. The matu- World War II up to 1966 these rocks were retorted for its oil rity of the Alum and Dictyonema Shales changes gradually, in Sweden (Dyni 2006). Interest in these strata is also con- from the east and north-east to the west and south-west, nected with their potential source for hydrocarbons accumu- i.e. in the direction of the Tornquist-Teisseyre Zone. Sam- lations and multi-elements, especially radioactive elements ples, located in the seashore of Estonia and in the Podlasie enrichment (e.g. Schovsbo 2002; Lippmaa et al. 2009). These region, are immature and in the initial phase of “oil win- strata, especially the Alum Shale, are considered as forming dow”. The mature shales were found in the central off- hydrocarbon accumulations in Polish and Russian offshore shore part of the Polish Baltic Basin, and the late mature and onshore parts of the Baltic Basin (Kanev et al. 1989, and overmature are located in the western part of the Baltic 1994; Brangulis et al. 1992; Karnkowski 1999; Wie˛cław Basin. The Alum and Dictyonema Shales are characterized et al. 2010; Sliaupa and Hoth 2011) and Southern Scandina- by a high grade of radioactive elements, especially ura- via (Pedersen et al. 2007). Generated oils are accumulated nium. The enrichment has a syngenetic or early diagenetic mostly in Paradoxides paradoxissimus Zone of Middle Cam- brian strata (Karnkowski et al., 2010). Apart from the Cam- brian, oil accumulations and shows were also discovered in * Paweł Kosakowski the Precambrian, Ordovician, Silurian and Devonian strata [email protected] in Russia, Lithuania, Latvia and Sweden (Zdanaviciute and Bojesen-Koefoed 1997; Zdanaviciute and Lazauskiene 2004, 1 Faculty of Geology, Geophysics and Environmental Protection, AGH-University of Science and Technology, 2007; Pedersen et al. 2006). Generation of these oils from a Al. Mickiewicza 30, 30‑059 Kraków, Poland source different than the Upper Cambrian–Tremadocian com- 2 Institute of Geology, Tallin University of Technology, plex, especially Lower Silurian rocks, is not excluded (Zdana- Ehitajate tee 5, 19086 Tallinn, Estonia viciute and Lazauskiene 2004, 2007). 1 3 744 Int J Earth Sci (Geol Rundsch) (2017) 106:743–761 As a source of uranium and rare metals, Alum and Dic- contents of organic carbon and presence of radioactive ele- tyonema Shales were partially exploited (Andérsson et al. ments. The bituminous shales complex has TOC contents 1985; Brangulis et al. 1992; Bergh 1994; Lippmaa et al. up to ca. 22 wt% and contains oil-prone Type-II kerogen. 2009). Because of low maturity, the Dictyonema Shale has The maturity of the Alum and Dictyonema Shales changes low potential for thermogenic hydrocarbons, but is inter- from immature phase in the east and north-east to the post- esting from the point of view of the content of radioactive mature in the west and south-west of the study area. The elements and their influence on hydrocarbon generation Alum and Dictyonema Shales are characterized by a high (Bergh 1994; Lippmaa and Maramäe 1999; Dyni 2006). grade of radioactive elements, especially uranium. The Research on these bituminous shales was carried out in enrichment has a syngenetic or early diagenetic origin. The the western part of the Baltic Basin–Västergötland region measured content of uranium reached up to 750 ppm and (south-central Sweden), Skåne region (south Sweden), thorium up to 37 ppm. Öland and Götland (Sweden), and Bornholm (Denmark) In the present study, organic matter (OM) quantity, islands and the Polish offshore of the Baltic Basin (Fig. 1b). genetic type, maturity and its hydrocarbon potential dis- Moreover, the study was also conducted in the eastern part persed in Alum and Dictyonema Shales are discussed of the basin—on the seashore of Estonia and the northern on the basis of results of wide-range geochemical tech- part of Podlasie Depression (Fig. 1a, b). niques (Rock-Eval, stable carbon isotopes, biomark- Bituminous shales were also examined for the presence ers, kerogen elemental composition). The relation of organic matter. These studies showed that these depos- of uranium with OM properties and forms of this ele- its have the best source quality among the Lower Palaeo- ment occurrence are presented as well. The study area zoic strata and they are the best source rocks in the Bal- encompasses the Polish offshore of the Baltic Basin tic region. The Alum and Dictyonema shales show high and adjacent onshore area: southern Sweden, Bornholm A B Fig. 1 a Location of main tectonic units and b location of sampled wells and outcrops in the Polish and Estonia part of the Baltic Basin, and Podlasie basin. CDF Caledonian Deformation Front, Podlasie Dep. Podlasie Depression 1 3 Int J Earth Sci (Geol Rundsch) (2017) 106:743–761 745 (Denmark) and northern Estonia, and the Podlasie In the BB, the Cambrian profile begins poorly sorted Depression which is the northern part of the Lublin- sandstones (quartz and arkosic wackes) and conglomer- Podlasie Basin (Tomczykowa and Tomczyk 1976, 1978; ates of Z˙ arnowiec Formation (Fig. 2). In the middle part of Ulmishek 1990) (Fig. 1). profile are observed fine-grained sandstones, siltstones and sandstone–mudstone heterolithic deposits (Kluki and Łeba formations), and black claystones, dark grey mudstones Geological setting and mudstone–sandstone heterolithic deposits (Sarbsko Formation). The Upper Cambrian strata are represented by The Baltic Basin (BB) and Podlasie Depression (PD) are bituminous shales with thin interbeds and lenses of dark, tectonic units located in the western margin of the East often bioclastic limestones (Słowin´ski and Pias´nica forma- European Craton (EEC; Ulmishek 1990). Development of tions; Fig. 2). The total thickness of these deposits reaches the BB was started in the Ediacaran after breakup of Rod- about 35 m. The shales represent shelf muds deposited in inia. At that time, the basin formed a passive continental anoxic conditions, and they correspond to the Alum Shale margin on the western slope of the palaeocontinent of Bal- of Scandinavia (Andérsson et al. 1985; Bauert 1994). The tica (Torsvik et al. 1992; Andréasson 1994; Torsvik 2003). lowermost Ordovician (Tremadocian) is represented by the The BB was affected by Proterozoic tectonism (early Edi- topmost part of black bituminous shales of Pias´nica Forma- acaran rifting) as well as by Caledonian orogenesis (clo- tion (Fig. 2). On Bornholm, Scania, Öland islands and in sure of the Tornquist Ocean), Permo-Triassic rifting, late Estonia, its equivalents are lower Tremadocian bituminous Jurassic and late Cretaceous uplifts (Flodén 1980; Ulm- shales traditionally referred to as the Dictyonema Shale ishek 1990; Poprawa et al. 1997, 1999; Poprawa 2006a, b; (Lippmaa and Maramäe 1999, 2000, 2001; Bergström et al. Karnkowski 1999). The early Cambrian to early Devonian 2004) (Fig. 2). Their thickness ranges between a few metres sedimentary cycle was terminated with an erosional event, to 10 m. The bituminous shales are covered by transgressive which is observed as a regional unconformity, coinciding shales with glauconite, marly limestones and limestones with a global low-stand of sea level (House 1983; Johnson of the Słuchowo Formation (Modlin´ski and Podhalan´ska et al. 1985). 2010) (Fig. 2). Above this formation, marly limestones of The early to middle Cambrian evolution of the western Kopalino Formation, and black and grey shales often bitu- margin of Baltica was controlled by progressive opening minous of Sasino Formation occur. The uppermost part of of the Iapetus and Tornquist oceans (Nikishin et al. 1996). the Ordovician is assigned to the Prabuty Formation. The These oceans began to close again during middle and late Silurian deposits, with an erosional unconformity, are rep- Cambrian times. The early Ordovician mild tensional tec- resented by a thick monotonous claystones, and mudstones’ tonics may have controlled the development of the linear succession belongs to Pasłek, Pelplin, Kociewie and Puck depocentres of the Baltic Basin (Mäannil 1965; Kaplan formations (Modlin´ski and Podhalan´ska 2010) (Fig. 2). and Suveizis 1970; Rotenfeld et al. 1974; Flodén 1980; In the south-eastern of the Baltic Basin, along the TTZ Suveizis 1982).