Climate changes on the Jurassic/Cretaceous bonduary on the geochemical indicators - new data from the Slovenian Basin

The pelagic succession from the Slovenian Basin (Petrovo Brdo section) covers the lower Tithonian to upper Berriasian interval (ca. 40 m). At 5 m of the section a sharp transition is observed between clay rich radiolarian cherts of Tolmin Fm and calpionellid limestones of Maiolica Fm.  Calpionellid associations are not numerous and poorly preserved, therefore only rough biostratigraphic dating is possible.  Crassicollaria (upper Tithonian) was documented between 8 and 13 m of the section, while the  beginning of the Calpionella alpina Subzone (present day J/K boundary) is situated at ca. 20 m.  Transition between Tolmin and Maiolica Fm  falls in the UAZ 12 radiolarian Zone (Gorican et al. 2012) which is close to the lower/upper  Tithonian boundary. Despite poor dating, the section supplied high-resolution magnetic susceptibility, as well as chemostratigraphic data (δ¹³C, main and trace elements), acquired with portable XRF device, gamma ray spectrometer and verified with ICP-MS laboratory measurements. Lithogenic elements (Al, K, Rb, Ti, Zr etc.) and MS show prominent decrease between Tolmin and Maiolica Fm, reaching minimum values in the upper Tithonian and lower Berriasian. Lithogenic input increases again  from ca 30 m of the section. As in numerous Tethyan sections (e.g. Western Carpathians, Northern Calcareous Alps, Western Balkan) the increase of marly sedimentation starts in the lower part of the Calpionellopsis Zone (magnetozone M16n), this level is tentatively interpreted as being close to the lower/upper Berriasian boundary. Relative variations of K and Ti content  (K/Ti, Ti/Al ratios) indicate enrichment of K  and depletion in Ti in the upper Tithonian/lower Berriasian interval  which accounts for decreased chemical weathering in the provenance areas. Additionally, the interval is enriched in redox sensitive trace metals (Cu, Zn, Cd) and decreased δ¹³C values, which accounts for bottom water stratification. The overall palaeoenvironmental trends might be interpreted in favor of aridification trend throughout the upper Tithonian and lower Berriasian and more humid episodes in the lower Tithonian and upper Berriasian. The trends seems to correlate throughout the Western Tethys domain and might be related with large-scale palaeoenvironmental perturbations.