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Zechstein marine deposits in the Wleń Graben (North Sudetic Synclinorium, SW Poland) : new insights into the palaeogeography of the southern part of the Polish Zechstein Basin

Kowalski A., Durkowski K., Raczyński P.

Annales Societatis Geologorum Poloniae

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2018

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Vol. 88, No. 4

321--339

EN

This paper presents the results of sedimentological studies of Zechstein marine deposits occurring in the Wleń Graben, a tectonic unit located in the southeastern part of the North Sudetic Synclinorium (NSS; Western Sudetes, SW Poland). Owing to poor exposure, small thickness, and lack of palaeontological data, the stratigraphy and age of these rocks were determined solely on the basis of analogies with adjacent areas. New findings described here, including faunal remains (remains of bivalves, including Liebea sp.), geopetal structures, clastic fills of halite crystals, moulds and bioturbation, shed new light on the environmental interpretations of the Zechstein in this part of the NSS. It should be assumed that at least two types of deposit may be assigned to the marine Zechstein in the Wleń Graben area, namely sparitic and microsparitic dolomite (PZ3) and the overlying deposits of the heterolithic series (PZt). These deposits were formed during the late Zechstein transgression, when the study area was in the marginal southwesternmost part of a newly formed shallow-marine bay of the Polish Zechstein Basin. In the central part of the present-day Wleń Graben, a shallow-marine bay (lagoon?) was dominated by carbonate sedimentation. A north-dipping mud plain, periodically flooded by a shallow sea, occurred in the southern part of the area. The paper summarises the present state of research on Permian deposits in the Wleń Graben, the first comprehensive lithostratigraphic scheme is suggested, and a new concept of the palaeogeographic evolution of the area in the Early and Late Permian is proposed.

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Oil- and gas-bearing sediments of the Main Dolomite (Ca2) in the Międzychód region: a depositional model and the problem of the boundary between the second and third depositional sequences in the Polish Zechstein Basin

Jaworowski K., Mikołajewski Z.

Przegląd Geologiczny

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2007

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Vol. 55, nr 12/1

1017-1024

EN

The Polish Zechstein Basin was a tideless sea dominated by storms. Main Dolomite deposits of the Miedzychód region were deposited: a) on the carbonate platform (in the environments of the outer barrier, inner barrier and high- and low-energy platform flat); b) on the platform slope; c) at the toe-of-slope; d) on the basin floor. The best reservoir properties are recorded in shallow-marine deposits of the outer and inner barriers and in deep-sea sediments of the toe-of-slope (turbidites and debrites). Rich reserves of crude oil and natural gas were discovered both on the carbonate platform (the Miedzychód and Grotów deposits) and at its toe-of-slope (the Lubiatów deposit). The Main Dolomite sediments are wholly included in the second depositional sequence (PZS2 sensu Wagner & Peryt, 1997). The maximum flooding surface of the PZS2 sequence within the platform, its slope and toe-of-slope, runs along the A1g/Ca2 boundary. In the basinal zone, its correlative equivalent is a hard ground observed within the Main Dolomite carbonate rhythmites. The boundary between the second and third (PZS2/PZS3) depositional sequences (corresponding to the ZS3/ZS4 sequence boundary in the German Basin) runs on top of the Main Dolomite carbonates (on the platform slope, at the toe-of-slope and on the basin floor) and above top of the Main Dolomite carbonates, within the lower part of the Basal Anhydrite (on the platform).

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Paleogeografia utworów poziomu dolomitu głównego polskiego basenu cechsztyńskiego w aspekcie poszukiwań węglowodorów

Zych I.

Technika Poszukiwań Geologicznych

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2005

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R. 44, nr 3

35-43

PL

Dolomit główny jest perspektywicznym poziomem roponośnym cechsztynu na Niżu Polskim. Pierwsze złoże ropy naftowej w dolomicie głównym zostało odkryte w 1961 roku w miejscowości Rybaki. Do najważniejszych odkryć należy zaliczyć między innymi złoża: Kamień Pomorski, Jeniniec oraz BMB (ryc.5). Aby określić własności zbiornikowe utworów dolomitu głównego, wykonano analizę paleogeograficzną tego poziomu. Sedymentacja dolomitu głównego odbywała się w pięciu strefach, o różnym wykształceniu litofacjalnym: w strefie głębokowodnej, lokalnych spłyceń, przedbarierowej, barierowej oraz lagunowej. Wyróżniono cztery główne facje węglanowe: madstony, węglanowe facje ziarnowe, wakstony i pakstony muszlowe i muszlowce oraz biolity (Gąsiewicz i inni, 1989). Wtórne procesy diagenetyczne ograniczają pierwotną porowatość i przepuszczalność utworów węglanowych. Większość złóż ropy naftowej i gazu ziemnego występuje wzdłuż krawędzi platformy węglanowej. Migrujące węglowodory spotkały na swej drodze szczelne zamknięcia litologiczne, w wyniku czego doszło do powstania szeregu pułapek (Pikulski, 2004).

EN

Main Dolomite structures are important target of hydrocarbon search in the Polish part of Zechstein Basin. In 1961 in the Rybaki first deposit of crude oil in Main Dolomite struktures was uncovered. The most important discoveries of hydrocarbons deposits were: Kamień Pomorski, Jeniniec and BMB (ryc. 5). Paleogeographical analysis of the Main Dolomite unit in the Polish Zechstein Basin area have been described. Zones of the sedimentation of the carbonate structures have been defined: open marine, major offshore bank, shelf margins and shelf lagoon (ryc. 3). Following four main carbonate lithofacies have been distinguished: mudstones, carbonate sandy facies, bioclaslastic wackestones and packstones, and lumachells, as well as biolithites. These lithofacies are charakterized by different values of porosity and permeability (Gąsiewicz et al., 1989). The discovery of other big hydrocarbon fields in the Main Dolomite in Polish Zechstain Basin can be expected.