Hanna MATYJA

SUMMARY

This report contains the results of both early analyses and the Zechstein strata (Jamno IG 1). The Zechstein deposits recent stratigraphic, sedimentological, petrographical and geo- were analysed for petrographical microfacies and diagenetic chemical investigations based on modern research methods and investigations. Some informations were also presented on within the chronostratigraphic units recommended by the Inter- the Zechstein salt deposits in the Jamno IG 1 section. national Commission on Stratigraphy. The Mesozoic succession is represented by the , , , , Triassic, , Cretace- Jurassic and . ous and Neogene and/or Quaternary deposits were encountered Triassic deposits of all the boreholes seem to be represen- in the Jamno IG 1, Jamno IG 2 and Jamno IG 3 boreholes. ted by the almost complete stratigraphic range of the system. The oldest rocks drilled in the boreholes are Ordovician Thirteen lithostratigraphic units of group, formation and beds deposits represented by strongly tectonically deformed rank have been identified within the succession. These are fine-grained siliciclastics (mostly claystones and mudstones) (from oldest to youngest): Lower Buntsandstein (Baltic For- characterized by the presence of thin clayey siderite interbeds, mation), Middle Buntsandstein (Pomorze and Po³czyn forma- lenses and concretions as well as small crystalline pyrite con- tions), Upper Buntsandstein (Barwice Formation), Lower, cretions and aggregates. Graptolite fauna found in claystones Middle and Upper Muschelkalk, Lower Keuper (Sulechów indicates the gracilis Zone (Jamno IG 2) and the multidens Beds) and ?Upper Keuper (?Red Sandstein), and Drawno, Jar- Zone (Jamno IG 1 and Jamno IG 2), corresponding to the lo- kowo, Zb¹szynek and Wielichowo beds. The Jamno IG 2 sec- wer portion of the Caradoc stage in Britain. tion seems to be stratigraphically complete although there are No uppermost Ordovician, and almost entire Lo- signs of tectonic activity. Within the Jamno IG 1 and Jamno wer Devonian sections were encountered in all of the analysed IG 3 sections, only Carnian deposits are missing. boreholes. Jurassic deposits were identified in all the boreholes, al- Upper Ordovician (Caradoc) rocks are directly overlain by though none is complete. The Lower Jurassic was encounte- Devonian deposits: ?Lower, Middle and Upper (only part of red in Jamno IG 1, Jamno IG 2 and Jamno IG 3. It is represen- Frasnian) Devonian in Jamno IG 1, ?Lower and part of Mid- ted by the Hettangian, Sinemurian and Pliensbachian (Jamno dle Devonian in Jamno IG 2 and Jamno IG 3. Four lithostrati- IG 1, Jamno IG 2, Jamno IG 3) and Toarcian (Jamno IG 2 and graphic units have been distinguished within this stratigraphic Jamno IG 3). The Middle Jurassic was also encountered in all range. These are (from oldest to youngest): the Jamno Forma- the boreholes, however the presumed Aalenian deposits are tion represented by conglomerates, sandstones and mudstones suggested only in the Jamno IG 3 borehole, upper Bajocian is (Jamno IG 1, Jamno IG 2 and Jamno IG 3), the Sianów For- observed in Jamno IG 2, and variably complete Bathonian and mation represented mainly by carbonates and mixed silicicla- Callovian deposits are represented in all the boreholes. Upper stic-carbonate series (Jamno IG 1), the Wyszebórz Formation Jurassic rocks, represented by the Oxfordian and Kimmerid- characterized by dominant conglomerates, sandstones and gian, occur in the Jamno IG 3 section. The Lower Jurassic mudstones (Jamno IG 1) and the Kocza³a Formation com- succession consists of 7 lithostratigraphic formations. These posed of carbonates and mixed siliciclastic-carbonate series are: the Zagaje, Sk³oby, Ostrowiec, £obez, Komorów, Cie- (Jamno IG 1). The Devonian deposits were analysed for bio- chocinek and Borucice formations. No lithostratigraphic units stratigraphic, microfacies, petrographical and diagenetic inve- have been identified within the Middle Jurassic succession re- stigations. Biostratigraphic research based on miospores and presented by the presumed Aalenian (Limnic series), upper conodonts. Palynological analysis shows that basal parts of Bajocian, Bathonian and lower Callovian. The middle and the Devonian succession cannot be older than the uppermost upper Callovian deposits are included in the £yna Formation. Emsian and younger than the middle Eifelian. The topmost Its uppermost part belongs partly to the Oxfordian. The Upper Devonian strata were dated by conodonts and miospores as Jurassic is represented by 4 lithostratigraphic units: the £yna, lower and middle Frasnian. No Upper Devonian was encoun- Chociwle, Brda and Pa³uki formations. tered in the boreholes. The gap also comprises the Carbonife- Cretaceous deposits were encountered only in the Jamno rous and Lower Permian. Middle (Givetian) or Upper (lower IG 1 borehole. The section falls within the Upper Cretaceous and middle Frasnian) Devonian is overlain directly by the comprising the Cenomanian through upper Maastrichtian Upper Rotliegend deposits belonging to the Dar³owo Forma- stages. No lithostratigraphic units are identified within tion (Jamno IG 2) or Miastko Formation (Jamno IG 3) or to the sequence. 276 Summary

The Mesozoic succession is capped in the Jamno IG 1, posits contain organic matter derived mostly from decomposi- Jamno IG 2 and Jamno IG 3 boreholes by rocks of presumed tion of algae and bacteria, and a certain amount of humic ma- Neogene and/or Quaternary age. terial. More humic-type organic matter is observed in the Lo- The most organic-rich Paleozoic deposits are the Upper Or- wer Jurassic rocks. The Lower Triassic rocks are conspicuous dovician clay shales composed of a sapropel-type organic-mi- by a low humic material content. The Upper Triassic and Mid- neral association, bitumen, infrequent zooclasts and inertinite dle Jurassic series are more abundant in humic-type organic represented mostly by algae and cyanobacteria. The other orga- matter in relation to the amount of sapropel-type matter. nic matter-rich horizon is the Upper Devonian carbonates com- The degree of organic matter alteration in the Mesozoic rocks posed mostly of vitrinite-like material, sapropel-type orga- is low in this region. nic-mineral association accompanied by alginite and relatively The suite of wireline logs included caliper, sontaneous po- frequent nituminous impregnations. The Upper Permian clay- tential, resistivity, radiometric and temperature logs. The ba- stones contain increased amounts of organic matter in relation sic goals of the borehole geophysical measurements compri- to the carbonates. The organic matter is composed chiefly of vi- sed determination of lithology and depth to individual strata, trinite macerals and rare liptinite. Humic organic matter obser- determination of geothermal parameters (heat flow and geo- ved in the Mesozoic deposits is represented by vitrinite, inerti- thermal degree), identification of formations showing reser- nite and liptinite (both in situ and redeposited) occurring in voir properties as well as determination of depth-related the greatest abundance in the Middle Jurassic rocks. changes in physical parameters of rocks. Wireline logs from Thermal maturity of the Upper Ordovician through Mid- the Jamno boreholes enabled construction of lithological logs dle Cretaceous rocks is low. The degree of authigenic organic and determination of petrophysical properties of rocks indica- matter alteration increases with the burial depth and age of de- ting formations of the best reservoir properties. posits – from immature for hydrocarbon generation (Cretace- Drill stem tests performed in the boreholes aimed at exami- ous–Jurassic) at the maximum reflectance of 0.42–0.48% RO, nation of the Palaeozoic and Mesozoic reservoir horizons in to the main phase of oil generation in the Upper Per- terms of possibility for crude oil, natural gas and industrial gro- mian–Upper Ordovician rocks (0.5–0.75% RO). The maximum undwater occurrences. Test horizons were selected based on palaeotemperatures were <90°C. the results of wireline logging and bitumen shows detected du- Geochemical data indicate that the Paleozoic and Meso- ring drilling operations. In the Jamno IG 1 borehole, 7 reser- zoic rocks are poor in organic matter. The Ordovician and voir horizons were tested: the connected Ordovician– Devonian Devonian deposits show features of “poor” source rocks for horizon (no flow), 5 Devonian horizons and 1 Lower Triassic hydrocarbon generation. They also contain small amount of horizon. In the Jamno IG 2 borehole, 4 reservoir horizons were labile components. The Permian and Triassic rocks also exhi- tested: 1 Devonian horizon and 3 Permian horizons. In the bit features of “poor” source rocks. The Middle and Lower Ju- Jamno IG 3 borehole, 7 reservoir horizons were tested: 1 Devo- rassic deposits contain abundant but unevenly distributed or- nian horizon, the connected Zechstein–uppermost Devonian ganic matter. They are considered “good” rocks for hydrocar- horizon, 2 Zechstein horizons, 2 Triassic horizons and 1 Juras- bon generation. The Upper Jurassic deposits have been analy- sic horizon. The boreholes are situated within an area prospec- zed relatively poorly. The Cretaceous rocks from Jamno IG 1 tive for hydrocarbon accumulation. Although no hydrocarbon contain low percentages of organic carbon, as they are repre- shows were observed during drilling, it is indicated by the pro- sented mostly by carbonates. Thus they are considered “poor” perties of brines analysed from the boreholes. source rocks for hydrocarbon generation. The degree of orga- The Devonian and Permian (Zechstein) rocks are of the gre- nic matter alteration in these rocks is very low. atest interest. They contain strongly metamorphosed brines se- Organic matter found in the Ordovician and Devonian parated from other water-bearing horizons. The hydrochemi- deposits originated from algal and bacterial decomposition. cal indices indicate the possibility of bitumens accumulations. Organic matter originating from decomposition of vascular The hydrochemical indices of Permian groundwater show plants was observed only in the Upper Devonian rocks of a proximity to hydrocarbon fields. Strongly isolated metamor- the Jamno IG 1 borehole. However, the degree of its alteration phosed brines are also observed in the Triassic rocks. The hy- is low. A mixed-type of organic matter was found in the Trias- drochemical parameters do not preclude the hydrocarbon sic and Jurassic rocks. Upper Triassic and Lower Jurassic de- accumulations.