Recording of cyclicity in the sediments of the Bajocian and Lower Bathonian on the basis of magnetic susceptibility (Carpathians, Poland).

Investigated section is located on the eastern slope of the Ždiarska Vidla, Tatra Mts. (Slovakia), along the old tourist path.  The section belongs to the Križna nappe and to the Havran and the Bujačí unit. Pelagic and hemipelagic sedimentation of the spotted limestones and marls prevailed on the margin of the Zliechov (Križna) during the Early and Middle Jurassic. The spotted limestones of the Tatra Mts. depending on the authors, are included in the Janovky Formation or in the Sołtysia Marlstone Formation. The investigated Ždiarska Vidla section is 200-m thick. This unit is dated to the Bajocian based on lithological similarity to the Kopy Sołtysie area, where rare ammonite fauna was described. The lithology is composed of spiculite limestones and marly spiculite limestones (with marly spiculite wackestone–packstone, and marly bioclastic filament wackestone microfacies). Field magnetic susceptibility (MS) and gamma–ray spectrometric measurements (indicating content of potassium, K (%); uranium, U (ppm,); thorium, Th (ppm)) have been carried out. The Ždiarska Vidla section has also been sampled for carbon isotopes with resolution of ca. 0.5-1 m. The bulk carbonate obtained carbon isotope curve is characterized by positive shift. It is assigned to the Lower Bajocian as based on data of O’Dogherty (2006). The section is subdivided into three parts (IIA, IIB, III) on the basis of the MS, K, Th, U and δ13C curves. The oldest IIA interval is characterized by a weak positive linear correlation between MS to Th, Th/U and CGR, which suggests an association of MS with the supply of terrigenous elements to basin. The p-values associated with received Pearson R are much above the assumed significance level (0.05), indicating that received results are statistically insignificant. In the IIB and III interval, MS correlates inversely to Th, CGR, Th/U, what it might show that increase MS is related to oxygen deficiency. Within the level IIB, values of Pearson r-value for correlation between MS and Th, CGR, U and K varies between -0.2 and -0.43 with p-values in the range from 0.03 to 0.3 meaning, that only part of the results is statistically significant. The III interval is characterized by a moderate negative linear correlation between MS and Th, K and CGR, where Pearson R reaches values from -0.42 to -0.56 with p-values much below the assumed level of 0.05, meaning that received results are statistically significant. Spectral analyses done on the MS signal in Intervals II and III reveal cycles of 18 m, 4-5 m and 1.3-1.8 m, respectively related to the 405-kyr, 100-kyr and 40-kyr cycles. The duration of Intervals II and III are thus assessed at 4.4 to 4.5 Myr, with a mean sedimentation rate of 4.4 cm/kyr.