Commune: Trzebinia (pow. chrzanowski, woj. małopolskie)
Framework element or context represented:
Primary geological/geomorphological interest:
Middle Triassic dolomite forming on unique hardrock raising above the old plantation surface.
Comparative assessment justification:
The representative outcrop of Diplopora Beds (Diplopora Dolomites) is typical of the middle part of Muschelkalk. It is ussual for comparative studies within the area of German Basin. The site is the one and only tor of the Triassic dolomite/limestone in southern Poland (in Poland at all). It is also the most persistent outcrop of the Diplopora Dolomite rich in oncoids.
Protection status and accessibility:
Nature monuments since 1948, protection status amended in 2002; site very accessible is situated on the flat ridge-crest among the cultivated agriculture area.
Character of site: Natural outcrop.
Area: 0.5 ha
Altitude: 350 m a.s.l.
Lithology: limestones, dolostones
Discipline: Palaeobiology, Stratigraphy of Phanerozoic
Process Age: *all periods
Bedrock Age: Triassic, *all periods
Description of primary interest:
The dolomitic tor up to 8 m. high with the base 10x30 m. The yellow dolomite and dolomitic limestone are distinctly bedded, cavernous with numerous oncoids and green algae. Scars remains of fossil are visible to. There are many small gastropods and crinoid debris. The shape and surface of the tor reflect the unequal lithification of the rock. Some holes and fissures are filled with coarse-crystalline wax-yellow calcite. The general shape of the tor resembles a castle ruins well marked on the flat ridge-crest. The site is situated in the Upper Silesian area and represents Diplopora Beds of Anisian age of Middle Triassic (middle part of Muschelkalk). These beds are described as Diplopora Dolomite, too. There are sediments of the southern part of Triassic Germanic Basin called Peri-Tethys. In the Anisian time (245-236 Ma) this part of the basin has been directly influenced by the Tethys rifts through the Silesian-Moravian Gate. The Diplopora Dolomite a few lithofacies presents of littoral and sublittoral environments. The tor in Bolęcin is formed by the oncoid grainstone of high intergranular porosity, typical for very shallow and moderately agitated sublittoral environment.
ALEXANDROWICZ S.W. 1996–Recent and subfossil molluscan fauna of the tor in Bolęcin near Chrzanów (English sum.). Chrońmy Przyr. Ojcz. 52,6: 27-40. MYSZKOWSKA J. 1992–Lithofacies and sedimentation of Diplopora Dolomite (Middle Muschelkalk) in the east part of the Cracovian-Silesian Region (English sum.). Ann. Soc. Geol. Pol. 62,1: 19-62. SIEDLECKI S. 1951–Une roche triasique prés de Bolęcin (French sum.). Zabytki Przyrody Nieożywionej 1(4): 35-37. SIEDLECKI S. 1952–Utwory geologiczne obszaru między Chrzanowem a Kwaczałą (Polish and Russian only). Biuletyn PIG 60: 5-230. SZULC J. 2000–Middle Triassic evolution of the northen Peri-Tethys area as influenced by early opening of the Tethys Ocean. Ann. Soc. Geol. Pol. 70: 1-48.