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Kryteria identyfikacji obiektów litofacjalnych jako potencjalnych pułapek złożowych w utworach dolomitu głównego (Ca2) u podnóża platform i mikroplatform węglanowych w środkowo-zachodniej Polsce

Kwolek K., Mikołajewski Z.

Przegląd Geologiczny

2010

Vol. 58, nr 5

426-435

In terms of oil reserves of Poland, the Lubiatów oilfield in the Międzychód area is the second largest after BMB oilfield. The discovery of this structural-lithological trap in a toe-of-slope position in relation to the Main Dolomite (Ca2) carbonate platform opened a new hydrocarbon opportunities in this unit. One of the conditions for trap occurrence in the "Lubiatów-type" deposits of the toe-of-slope zone in relation to Ca2 carbonate platforms and microplatforms is the presence of appropriate reservoir facies. These facies are characterized by occurrence of thick packets of porous Main Dolomite rocks (Ca2 lithosomes) composed mostly of sublittoral, redeposited carbonate sands (packstones, floatstones, sporadic rudstones), deposited below wave-base and resulting from activity of traction and suspension currents and gravity flows. The only method to detect such facies is via high resolution seismic images, preferably from three-dimensional (3D) surveys. Unfortunately, intensive exploration studies carried out in this zone between 2005-2008 did not bring measurable effects, that is discovery of new hydrocarbon deposits. Several boreholes drilled in Ca2 lithosomes found water-bearing horizons only. In several other dry holes, none of the facies assumptions made prior to drilling were confirmed. Comparison of seismic images of area of those dry holes made it posssible to find a geometric criterion for seismic detection of Ca2 lithosomes located at the toe-of-slope of carbonate platforms and microplatforms. This geometric criterion, along with the seismological one, should constitute an important interpretational premise in identifying or excluding areas with potential hydrocarbon traps in the Main Dolomite rocks in the area under study.

Source and depositional processes of coarse-grained limestone event beds in Frasnian slope deposits (Kostomłoty-Mogiłki quarry, Holy Cross Mountains, Poland)

Vierek Aleksandra

Geologos

2010

Vol. 16, No. 3

153--168

The Kostomłoty-Mogiłki succession is situated in the Kostomłoty transitional zone between the shallow-water Kielce stromatoporoid-coral platform and the deeper Łysogóry basin. In the Kostomłoty-Mogiłki quarry, the upper part of the Szydłówek Beds and Kostomłoty Beds are exposed. The Middle-Upper Frasnian Kostomłoty Beds are composed of shales, micritic and nodular limestones with abundant intercalations of detrital limestones. The dark shales and the micritic and nodular limestones record background sedimentation. The interbedded laminated and detrital limestones reflect high-energy deposition (= event beds). These event beds comprise laminated calcisiltites, fine-grained calcarenites, coarse-grained grain-supported calcirudites fabrics, and matrix-supported calcirudites. The material of these event beds was supplied by both erosion of the carbonate-platform margin and cannibalistic erosion of penecontemporaneous detrital limestones building the slope of this platform. Storms and the tectonic activity were likely the main causes of erosion. Combined and gravity flows were the transporting mechanisms involved in the reworking and redeposition.