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Biostratigraphy, magnetostratigraphy, C and O isotope distribution around the J/K boundary, the Brodno section (Kysuca Unit of the Pieniny Klippen Belt)

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Michalik J. , Rehakova D. , Halasova E. , Lintnerova O.

tom Vol. 4, no. 1

190-191

Detailed litho- and biostratigraphy of the Brodno section in contact zone of the Outer and the Central Western Carpathians was given by Michalík et al. (1990), VaĘíçek et al. (1992). Kimmeridgian and Tithonian condensed sequence of red nodular limestones (the Ammonitico Rosso facies) is referred to as the Czorsztyn Limestone Fm. Calcareous dinoflagellates Carpistomiosphaera borzai and Stomiosphaera moluccana indicate its Kimmeridgian age; Parastomiosphaera malmica, Carpistomiosphaera tithonica and Colomisphaera pulla indicate Early Tithonian age; calpionellids Chitinoidella boneti, Praetintinnopsella andrusovi, Crassicollaria intermedia, Crassicollaria brevis, Crassicollaria parvula, Crassicollaria colomi, confirm Middle to Late Tithonian age of this formation. Lower Berriasian part of this succession is represented by pale biomicritic wackestone (Pieniny Limestone Fm) with abundant Calpionella alpina. Strong subsidence and acceleration of “planktic rain” of nannofossils started on the Early/Middle Tithonian boundary where Polycostella beckmannii appeared. Helenea chiastia together with first small nannoconids are typical of the Middle and Late Tithonian. The Late Tithonian interval was specified by the FO of Rotelapillus laffitei and Litraphidites carniolensis. The Tithonian/Berriasian boundary was characterized by the FO of Nannoconus wintereri together with small nannoconids and by the FO of Nannoconus steinmanni minor. There is good correlation between the calcareous nannofossils distribution and the magnetostratigraphic zonation (HouĘa et al. 1996). In the M 20-M 19 interval, two distinct nannoevents were recognized: the dominance of Polycostella beckmannii (Chitinoidella Zone) and the appearance of calcareous nannofossil association with Helenea chiastia (Crassicolaria Zone). Carbon isotope curve from bulk carbonates of the J/K boundary sequence shows smooth trends resulted from equilibrated measure of bio-productivity and organic matter burial. The ä13C value ranges from 1.3 to 1.5‰ (PDB). The authentic character of the limestone record is underlined by relative high and conservative ä18O values (-2.27 to -0.88) of the same beds. These signals can be useful in global stratigraphic correlation in deep water carbonates.