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1

A Hirnantian deep-water refuge for warm-water ostracods in Baltoscandia

Truuver K., Meidla T.

Geological Quarterly

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2015

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Vol. 59, No. 4

738--749

EN

The latest Ordovician is marked by a severe climate change, the Hirnantian glaciation. This climatic event affected many marine taxa including ostracods. Rich and abundant ostracod assemblages of the Baltic Palaeobasin were severly impoverished. Many of the typical pre-Hirnatian warm-water ostracod species died out, but also some distinct, cold-water species appeared. Two very different but likely coeval latest Ordovician ostracod assemblages are recorded in the Baltic countries and north-eastern Poland. The latest Ordovician Estonian Shelf (inner ramp) is characterized by the Medianella aequa association whilst sections in the Livonian Basin (middle to outer ramp) reveal the Harpabollia harparum association that is thought to represent a cold-water assemblage belonging to the Dalmanitina-Hirnantia Fauna sensu lato. A transitional assemblage composed of a “species mixture” of typical Hirnantian cold-water and some pre-Hirnantian warm-water ostracod species is described for the first time from the Kętrzyn IG1 borehole, north-eastern Poland. The assemblage is dominated by Cryptophyllus pius sp. n. The genus Cryptophyllus is rare in the two other well-known assemblages. The discovery suggests that marginal parts of the Baltic Palaeobasin could serve as a kind of refuge for the last representatives of the ostracod faunas of the inner shelf of Baltic Palaeobasin. The Hirnantian assemblage is replaced by the low-diversity recovery assemblage that is dated as late Hirnantian-Silurian in Estonia and other areas. This suggests that the position of the systemic boundary in the Kętrzyn borehole and elsewhere in north-eastern Poland should be re-evaluated.

2

Palynomorph assemblages from the Upper Ordovician in northern and central

Stempień-Sałek M.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 1

21-61

EN

Palynological studies have been done to compare the Upper Ordovician strata in various geological units of northern and central Poland (epi-Caledonian Platform, East European Platform, Małopolska Block and Holy Cross Mountains–Łysogóry Fold Zone and Kielce Fold Zone). Two distinct palynological assemblages have been distinguished in the studied material: the Caradoc assemblage I and the Ashgill assemblage II (with two sub-assemblages IIa and IIb), thus demonstrating usefulness of the Upper Ordovician palynomorphs for biostrati- graphy. Thermal maturity of organic matter was studied using the TAI method. The palynological analysis, palynostratigraphy, and estimates of thermal maturity were done with the aim at palynological characterization of three ancient units: the Avalonia, Baltica and the Małopolska Block, all now participating in structures of the present-day geological units of northern and central Poland.

3

Potencjał występowania złóż gazu ziemnego w łupkach dolnego paleozoiku w basenie bałtyckim i lubelsko-podlaskim

Poprawa P.

Przegląd Geologiczny

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2010

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Vol. 58, nr 3

226-249

EN

The Lower Palaeozoic basin at the western slope of the East European Craton (EEC) (Fig. 1) is currently recognized as one of the most interesting areas for shale gas exploration in Europe. The Upper Ordovician and/or Lower Silurian graptolitic shale is here the major potential reservoir formation (Figs. 2, 3) (Poprawa & Kiersnowski, 2008; Poprawa, 2009). Moreover, the Upper Cambrian to Tremadocian Alum shale is an additional target locally in the northern part of the Baltic Basin. These sediments are often rich in organic matter (Klimuszko, 2002; Poprawa & Kiersnowski, 2008; Więcław et al., 2010; Skręt & Fabiańska, 2009), as well as silica. Limited data from two wells in the western part of the Baltic Basin show silica contents up to 60-70% (Fig. 4) (Krzemiński & Poprawa, 2006). The advantage of the Lower Palaeozoic shale from the western slope of EEC is its broad lateral extend (Fig. 1) and relatively quiet tectonic setting. The later is particularly true in the case of the Baltic Basin and Podlasie Depression. Structural development becomes to some extent more complex in the case of the Lublin region, where the Lower Palaeozoic shale appears affected by late Famennian to early Visean block tectonics. Development of the organic rich Lower Palaeozoic shale at the western slope of EEC was controlled by several factors. Very important was here the rate of non-organic detritus deposition (Fig. 5). The other factors included organic productivity of the basin, its subsidence, relative sea level changes, basin bathymetry, geochemical conditions at the sea bottom (especially oxygenation), degree of bioturbation, presence of topographic barriers at the sea bottom, leading to development of isolated anoxic zones, sea currents configuration, and climate changes. Organic matter of the Lower Palaeozoic is characterized by presence of II type of kerogen. Appearance of the organic-rich shale within the Lower Palaeozoic section at the western slope of the EEC is diachronic (Fig. 6). From NW towards east and SE, the intervals richest in organic appear related to systematically younger strata, starting from the Upper Cambrian to Tremadocian, as well as the Upper Llanvirn and Caradoc in the Łeba Elevation (northern onshore Baltic Basin; Fig. 7). In central parts of the Baltic Basin and Podlasie Depression as well as NW part of the Lublin region, the intervals richest in organic matter are found in the Llandovery section, while in the eastern part of the Baltic Basin and SE part of the Lublin region the highest TOC contents are found in the Wenlock. Therefore, depending on location at the western slope of EEC, different formations are recognized as the targets for shale gas exploration. The Upper Cambrian to Tremadocian shale, present only in the northern part of the Baltic Basin, is characterized by very high contents of organic matter, with average value for individual sections usually ranging from 3 to 12% TOC. This shale formation is, however, of very limited thickness, not higher than several meters in the onshore part of the basin (Szymański, 2008; Więcław et al., 2010). In onshore part of the studied area, thickness of the Caradoc shale changes from a few meters up to more than 50 m (Modliński & Szymański, 1997, 2008). Contents of organic matter in these sediments are the highest in the Łeba Elevation zone and the basement of the Płock-Warszawa trough, where average TOC contents in individual well sections range from 1% to nearly 4%. Ashgill rocks are characterized by high TOC contents only in the Łeba Elevation zone, where average TOC values for individual well sections rise up to 4,5% at the most. Llandovery shale has high TOC contents, particularly in its lower part, throughout vast parts of the western slope of EEC. The maximum measured TOC contents in those rocks in Podlasie Depression are nearly 20%. Average TOC values for individual sections of the Llandovery are usually equal 1% do 2,5%, except for the Podlasie Depression, where they may reach as much as 6%. Thickness of the Llandovery shale generally increases from east to west to approximately 70 m at the most. However, in the major part of that area it ranges from 20 to 40 m (Modliński et al., 2006). Thickness of theWenlock sediments is also highly variable laterally, from less than 100 m in SE part of the Lublin region to over 1000 m in western part of the Baltic Basin. Average content of organic matter in individualWenlock sections in central and western parts of the Baltic Basin and the Podlasie Depression usually ranges from 0,5% to 1,3% TOC. In the eastern part of the Baltic Basin and in the Lublin region it is higher, rising to about 1-1,7% TOC. The above mentioned TOC values show the present day content of organic matter, which is lower than the primary one. The difference between the present and primary TOC contents increases along with increasing thermal maturity. It is also highly dependant on genetic type of kerogen. Taking into account the II type of kerogen from the analyzed sediments, it may be stated that in the zones located in the gas window the primary TOC was at least one-half greater than indicated by laboratory measurements. From the shale gas point of view, the basins at the western slope of EEC are characterized by a negative relation between depth at present day burial and thermal maturity (Poprawa & Kiersnowski, 2008). In the zones with burial depth small enough to keep exploration costs at very low level (Fig. 8), thermal maturity of shales is too low for gas generation (Figs. 9, 12a). Maturity increases westwards (Fig. 8) along with depth of burial (Fig. 9). Thus, the potential shale gas accumulations in the western part of the studied area occur at depths too high for commercial gas exploration and exploitation (Fig. 12b). Between of the zone of maturity too low for shale gas development and that where depth of burial is too large for its exploration, there occurs a broad zone of the Lower Palaeozoic shale with increased shale gas exploration potential (Fig. 13) (Poprawa & Kiersnowski, 2008; Poprawa, 2009). In that area, there are shale intervals of relatively high thickness and average TOC exceeding 1-2% TOC (Fig. 7, 10, 12c). Thermal maturity of these rocks appears sufficient for generation of gas (Fig. 9, 10), and results of well tests for deeper-seated conventional reservoirs suggest good quality of dry gas with no nitrogen (Fig. 12c). It should be noted that some gas shows have been recorded in the Lower Palaeozoic shale. Moreover, depth of burial is not too large for commercial shale gas exploration (Fig. 8, 10). Hydrocarbon shows and their composition in the Lower Palaeozoic are strictly related to thermal maturity of the source rock. In the zones of low maturity, these are almost exclusively oil shows documented. Further westwards, in the zone transitional to the gas window area, gas is wet and contains significant contribution of hydrocarbon gases higher than methane.Within the gas window zone, the records are almost exclusively limited to methane shows. Moreover, within the zones of low maturity high nitrogen contents were recorded (Poprawa, 2009). In the zones characterized by thermal maturity in the range from 0,8 to 1,1% Ro and very high TOC contents (over 15% at the most), there is a potential for oil shale exploration. The zones with the highest oil shale potential include eastern Baltic Basin in SW Lithuania and NE part of the Podlasie Depression. Some data necessary for entirely firm estimations of potential shale gas resources of the Lower Palaeozoic complex in Poland are still missing. However, preliminary estimates indicate that these shale gas resources may possibly be classified as gigantic (1,400-3,000 bln m3 of recoverable gas; Fig. 15). For comparison, resources of conventional gas in Poland are equal to 140,5 bln m exp.3, and annual domestic gas consumption is at the level of 14 bln m exp. 3. However, it should be noted that some characteristics of the Lower Palaeozoic complexes indicate increased exploration risk. The average TOC contents are here lower than in classic examples of gas shales, like e.g. Barnett shale. Moreover, in the zone of optimal burial depth (less than 3000–3500 m) thermal maturity is lower than in the case of the Barnett shale core area. An important risk factor is also both a limited amount and limited resources of conventional gas fields in the Lower Palaeozoic complex (Fig. 13). Amount and intensity of gas shows in the Lower Palaeozoic shale are also relatively low, and there is no evidences for presence of overpressure in this complex. In the eastern part of western slope of the EEC, there appears an additional risk factor-arelatively high content of nitrogen in gas.

4

Środowiska sedymentacji ordowiku górnego w regionie kieleckim Gór Świętokrzyskich

Trela W.

Biuletyn Państwowego Instytutu Geologicznego

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2005

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nr 417

109-168

PL

W górnym ordowiku, w regionie kieleckim obserwowane są kontrasty facjalne związane z regionalną aktywnością tektoniczną i różnym tempem subsydencji basenu sedymentacyjnego. Efektem synsedymentacyjnych ruchów tektonicznych było powstanie pod koniec środkowego ordowiku wyniesienia podmorskiego, które w późnym ordowiku było miejscem rozwoju skondensowanych facji węglanowych - grejnstonów, pakstonów i wakstonów. W karadoku wyniesienie to graniczyło od południa z głębokim zbiornikiem, który był miejscem rozwoju facji ilastych. Okresowo sedymentacja w tym zbiorniku odbywała się w warunkach deficytu tlenowego wód dennych. Od późnego lanwirnu po początek późnego karadoku warunki ekologiczne i sedymentacyjne, na obszarze wyniesienia podmorskiego, były kształtowane przez prąd oceaniczny płynący między Avalonią a Baltiką, wzdłuż północnego brzegu bloku małopolskiego, oraz związane z nim prądy wstępujące. Zanik oddziaływania tego prądu był zbieżny ze zmianami cyrkulacji oceanicznej spowodowanej stopniowym zamykaniem w późnym ordowiku zachodniej części morza Tornquista, w wyniku dokowania wschodniej Avalonii do Baltiki oraz przesunięciem obu obszarów w kierunku niższej szerokości geograficznej. Abrazja tego wyniesienia przez falowanie sztormowe i oddziaływanie prądu oceanicznego oraz słabszy potencjał wzrostowy chłodnowodnego zespołu faunistycznego, spowodowały spowolnienie tempa depozycji, lub nawet jego okresowe zatrzymanie. Konsekwencją tego jest znaczna kondensacja osadu i rozwój małego "wygłodzonego wyniesienia podmorskiego" (statved seamount). Pod koniec wczesnego karadoku, w efekcie ożywienia regionalnej aktywności tektonicznej, nastąpiła przebudowa planu paleomorfologicznego. W centralnej części regionu kieleckiego ujawniły się tendencje do wzrostu pojemności akomodacyjnej, związane z tektonicznie uwarunkowanym większym tempem subsydencji tej części wyniesienia podmorskiego. Na przełomie karadoku i aszgilu zaznaczył się spadek względnego poziomu morza. Litologicznym wyrazem globalnej regresji w późnym aszgilu są w regionie kieleckim osady klastyczne (waki kwarcowe) związane z grawitacyjnymi spływami osadu, schodzącymi prawdopodobnie ze skłonu delty stożkowej. Utrzymująca się lokalnie w późnym aszgilu tendencja do pogłębiania basenu sedymentacyjnego centralnej części regionu kieleckiego sprzyjała natomiast zachowaniu ciągłości sedymentacyjnej między ordowikiem i sylurem.

EN

The spatial and temporal extent of the Upper Ordovician facies in the Kielce Region indicates regional tectonic controls on its distribution. The sedimentary basin was affected by differential subsidence rate, which probably originated from synsedimentary block faulting in the basement, that resulted in establishment of horst-like submarine palaeohigh with condensed carbonate deposition - grainstones, packstones to wackestons. During the Caradoc, the palaeohigh was bounded, to the south, by a deeper-water basin subjected to much stronger subsidence rate, where claystone facies were deposited. Periodically, the oxygen-deficient conditions occurred at the basin floor. From the latest Llanvirn to the early Late Caradoc the sedimentary and ecological conditions on the palaeohigh were affected by upwelling associated with the oceanic current that flowed south-eastwards along the northern margins of the Małopolska Block. The cessation of that oceanic current activity and then upwelling inflow was coeval with changes in palaeooceanographic circulation related to gradual closare of the western part of the Tornquist Sea during the latest Ordovician due to collision of the Avalonia with Baltica. The hydrodynamic conditions on the palaeohigh were dominated by interaction of storms and the oceanic palaeocurrent that together with slow carbonate production, resulted in low accumulation rate and subsequently in development of small starved seamount with a condensed carbonate sediment. During the end of the early Caradoc there was a rearrangement of the palaeohigh that resulted in establishment of a deeper water basin in the central part of the Kielce Region, with a continuous sedimentation in some places across the Silurian-Ordovician boundary. During the latest Caradoc and earliest Ashgill, the tectonic activity was intensified in the central part of the Kielce Region, resulting in uplifting of some parts of the basin floor, and subsequently a juxtaposition of the shallow and deep-water deposits in this area. The lithological expression of the Late Ashgill regression in the Kielce Region are clastic deposits (quartz wackes) accumulated by sandy debris flow derived from a fan delta.