Palaeoclimatic Changes And Inter-Regional Correlations In The Jurassic/Cretaceous Boundary Interval Of The Polish Basin: Portable Xrf And Magnetic Susceptibility Study

The Jurassic-Cretaceous epicontinental Polish Basin developed along the margin of the East European Platform, as a part of the Central European Basin, connected with the Tethys to the south, and sometimes with the North Sea Basin across northern Germany, and with the Middle Russian Sea to the east. Such a peculiar position in the Jurassic-Cretaceous (J/K) boundary interval resulted in variable influences from both Tethyan, and Sub-boreal/Boreal palaeogeographic provinces, and there was complex faunal exchange and interaction of palaeoclimatic factors. The main aim of this study has been to determine palaeoclimatic changes in the J/K boundary interval as recorded in the sedimentary sequence of the Kcynia IG 2 borehole (central Poland). A high-resolution chemostratigraphic study was perfomed in a c. 320 m thick succession using a portable XRF spectrometer, accompanied by magnetic susceptibility measurements. Stratigraphic calibration is based on ammonites, in the Lower-Middle Volgian (upper Lower Tithonian - lower Upper Tithonian) and Ryazanian (upper Lower Berriasian - Upper Berriasian), and on ostracods in Purbeck facies (uppermost Tithonian - lowermost Berriasian). Elevated values of Ti/K and Zr/Rb ratios, supported by weathering indices (CIA, CPA), Ga/Rb, and clay mineral data, indicate a humid climate in the Early Tithonian and in the Late Berriasian (Ryazanian) to Early Valanginian. Aridification spread in the late Tithonian to early Berriasian (between the early Middle Volgian and earliest Ryazanian). Palaeoclimatic trends correlate very well between Boreal to peri-Tethyan basins from the east (Volga Basin) to the west (S England and SE France, via the Polish and Lower Saxony basins) indicating the potential for climatic stratigraphy in the J/K boundary interval.