ASGP (2007), vol. 77: 161-170

BOSITRA LIMESTONES - A STEP TOWARDS RADIOLARITES: CASE STUDY FROM THE TATRA MOUNTAINS

Renata JACH

Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, 30-063 Kraków, Poland, e-mail: jach at ing.uj.edu.pl

Jach, R., 2007. Bositra limestones - a step towards radiolarites: case study from the Tatra Mountains. Annales Societatis Geologorum Poloniae, 77: 161-170.

Abstract: Bositra limestones of Aalenian–Lower Bathonian age crop out in the Krížna unit in the Western Tatra Mountains (Poland). They are sandwiched between pelagic red limestones and radiolarites and display lateral facies variation. Four facies were distinguished: (i) Bositra packstones/grainstones, (ii) crinoidal packstones/ grainstones, (iii) Bositra-crinoidal packstones, and (iv) Bositra-radiolarian wackestones. The Bositra packstones/ grainstones were laid down in high-energy setting, while Bositra-radiolarian wackestones in calm condition. Crinoidal packstones/grainstones represent density current deposits. Bositra-crinoidal packstones resulted from intense bioturbation and mixing of crinoidal packstones/grainstones with background Bositra-rich deposits. Topographic gradient affected the lateral facies variation. Taphonomic factors strongly controlled by energy of the sedimentary environment, ecological factors which caused domination of Bositra bivalves in benthos assemblage and dissolution eliminating non-calcitic bioclasts could resulted in formation of the Bositra limestones. The eutrophication of water column and remodelling of the Krížna Basin, which finally led to deposition of radiolarites seem to be of considerable importance. Hence, Bositra limestones can be regarded as the record of the interme- diate stage of the basin evolution towards radiolarite formation.