Biostratigraphy and palaeoenvironment of the Kimmeridgian-Lower Tithonian pelagic deposits of the Krížna Nappe, Lejowa Valley, Tatra Mts. (southern Poland)

Abstract

The Upper Jurassic strata of the Križna Unit in the Tatra Mts. comprises pelagic, fine-grained and well-oxygenated deposits. They are represented by red radiolarites and radiolarian limestones (Czajakowa Radiolarites Formation), red nodular limestones (Czorsztyn Limestones Formation) and wavy, platy or nodular light grey and reddish limestones and marlstones (Jasenina Formation). These deposits are mainly wackestones characterized by a succession of the following microfacies: radiolarian, filament- Saccocoma , Saccocoma and Globochaete–Saccocoma . The section comprises four calcareous dinoflagellate zones, i.e. the Late Kimmeridgian Moluccana Zone, and the Early Tithonian Borzai, Pulla and Malmica zones. In the uppermost part of the studied section, the Early Tithonian Dobeni Subzone of the Chitinoidella Zone has been identified. Using these biostratigraphic data, the sedimentation rate for the Late Kimmeridgian (Borzai Zone) and Early Tithonian (Dobeni Subzone of the Chitinoidella Zone) interval is estimated as 3.7 m/my. This is in accordance with the general trend of increasing sedimentation rate through the Tithonian and Berriasian. The increased supply of clastic material in the Jasenina Formation may have been caused by climate changes and continental weathering. The sedimentation was controlled mainly by eustatic changes and fluctuations in ACD and CCD levels. The Upper Jurassic of the Križna Unit in the Tatra Mts comprises pelagic, fine-grained and well oxygenated deposits. They are represented by red radiolarites and radiolarian limestones (Czajakowa Radiolarites Formation), red nodular limestones (Czorsztyn Limestones Formation) and light grey limestones of Maiolica facies (Jasenina Limestone Formation). These deposits are mainly wackestones characterized by a succession of the following microfacies: radiolarian, filament -Saccocoma , Saccocoma and Globochaete - Saccocoma . The section comprises four calcareous dinoflagellate zones, i.e. the Upper Kimmeridgian Moluccana Zone, and the Lower Tithonian Borzai, Pulla and Malmica zones. In the uppermost part of the studied section, the Lower Tithonian Dubeni Subzone of the Chitinoidella Zone has been identified. Using these biostratigraphic data, sedimentation rate for the studied interval is estimated as 3.7 m/my. This is in accordance to the general trend of increasing sedimentation rate through Tithonian and Berriasian. This trend is well correlated with the climatic changes and continental weathering which resulted in accompanied increase in supply of clastic material. The sedimentation was controlled mainly by the eustatic changes and fluctuation of the ACD and CCD levels.