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The International Berriasian Working Group (ISCS) suggested primary and secondary marker “datums” to fix the basal Berriasian boundary and thus to detine the Jurassic-Cretaceous boundary (Wimbledon et al., 2011, 2013). Two primary markers Calpionella, as well as calcareous nannoplankton, are practically unknown in the Boreal Realm. Testing and calibration of these markers, as well as of fossils of radiolarians and other signals, in the most complete sections, were declared as an important task for the near future. In the Tethys, the Jurassic-Cretaceous boundary based on radiolarians falls inside zone UAZ 13 of Baumgartner et al. (1995), whereas in the palaeo-Pacific it corresponds to the boundary between zones 4 and 5 of Pessagno et al. (2009), and in boreal Siberia it probably falls between the biohorizons of Parvicingula haeckeli and P. khabakovi. The radiolarian events at the Jurassic-Cretaceous boundary in the boreal successions of Russia can be proposed to be used as an additional biomarker to help develop new integrated boundary criteria. Thus, as the first appearance of the zonal species Calpionella alpina, which defines the Jurassic and Cretaceous boundary, coincides with the first occurrence of the calcareous dinocyst zonal species Stomiosphaerina proxima (Reháková, 2000), it is logical to propose a calcareous dinoflagellate, widely represented in the Upper Jurassic-Lower Cretaceous Bazhenovo Formation of Siberia, as a secondary marker.
Middle-Upper Jurassic pelagic carbonates and radiolarites were studied in the Krížna Nappe of the Tatra Mountains (Central Western Carpathians, southern Poland and northern Slovakia). A carbon isotope stra- tigraphy of these deposits was combined with biostratigraphy, based on radiolarians, calcareous dinoflagellates and calpionellids. In the High Tatra and Belianske Tatra Mountains, the Bajocian and part of the Bathonian are represented by a thick succession of spotted limestones and grey nodular limestones, while in the Western Tatra Mountains by relatively thin Bositra-crinoidal limestones. These deposits are referable to a deeper basin and a pelagic carbonate platform, respectively. The various carbonate facies are followed by deep-water biosiliceous facies, namely radiolarites and radiolarian-bearing limestones of Late Bathonian-early Late Kimmeridgian age. These facies pass into Upper Kimmeridgian-Lower Tithonian pelagic carbonates with abundant Saccocoma sp. The bulk-carbonate isotope composition of the carbonate-siliceous deposits shows positive and negative S C excursions and shifts in the Early Bajocian, Late Bajocian, Early Bathonian, Late Bathonian, Late Callovian, Middle Oxfordian and Late Kimmeridgian. Additionally, the S13C curves studied show a pronounced increasing trend in the Callovian and a steadily decreasing trend in the Oxfordian-Early Tithonian. These correlate with the trends known from the Tethyan region. The onset of Late Bathonian radiolarite sedimenlalion is marked by a decreasing trend in S13C. Increased S13C values in the Late Callovian, Middle Oxfordian and Late Kimmeridgian (Moluccana Zone) correspond with enhanced radiolarian production. A significant increase in CaCO3 content is recorded just above the Late Callovian S13C excursion, which coincides with a transition from green to variegated radiolarites.
The Upper Jurassic strata of the Krížna 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.
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