Magnetic susceptibility and spectral gamma logs in the Tithonian-Berriasian pelagic carbonates in the Tatra Mts (Western Carpathians, Poland): Palaeoenvironmental changes at the Jurassic/Cretaceous boundary

摘要

Upper Tithonian-Berriasian pelagic carbonates in the Central Western Carpathians, Tatra Mts (southern Poland), with well-established bio- and magnetostratigraphy, provide excellent possibilities of testing magnetic and geochemical methods as proxies of palaeoenvironmental changes in the Western Tethys at the Jurassic/Cretaceous boundary. Magnetic susceptibility (MS), field spectral gamma-ray (GRS) as well as CaCO_3, total organic carbon (TOC), and elemental analyzes were performed in the Po?rednie III section. MS reveals very good negative correlation with CaCO_3 content as well as positive correlation with Al, Zr, Ti and other lithogenic elements and therefore it might be interpreted as a proxy of a detrital input into the basin. Abrupt MS variations correlate well with relative sea-level changes and indicate regressive intervals (MS highs) in the upper Tithonian/lowermost Berriasian (M20r to M19n2n) and upper Berriasian (M16n) and transgressive interval (MS low) in the lower to middle Berriasian (M18r to M17r). Long-term MS variations might be linked to a palaeoclimatic-controlled enhanced continental runoff. Geochemical data (P, Th/U, Mn, Cd, Ni, Mo and TOC content) point to a productivity increase and a slight oxygen deficiency in the lower and middle Berriasian, which corresponds to MS low values and typical calpionellid limestone sedimentation. Timing of major palaeoenvironmental turnovers might be correlated also with general palaeoclimatic trends in the Western Tethys and Western Europe: cooling in the late Tithonian followed by a temperature increase throughout the Berriasian and an important humidity increase in the middle Berriasian (M17n).