Forcing factors of the magnetic susceptibility signal in lagoonal and subtidal depositional cycles from the Zachełmie section (Eifelian, Holy Cross Mountains, Poland)

Abstract

Abstract Eifelian dolomites in the Zachełmie Quarry exhibit metre-scale depositional cyclicity, both in the lower, lagoonal part of the section and in the upper, shallow subtidal portion. Magnetic properties were studied in 30 samples (at c. 1 m intervals), including magnetic susceptibility (MS) and anhysteretic and isothermal remanent magnetization. The rock magnetic parameters are compared with the results of thin-section study and elemental chemistry. The forcing factors driving the MS pattern are identified. The MS signal is mostly related to a finely dispersed hematite, controlled by terrigenous input. Magnetite plays a subordinate role and it is confined to less terrigenous horizons relatively enriched in uranium and phosphorus. Results of high-resolution ( c. 8 cm intervals) MS field measurements show a good correlation with depositional shallowing-upwards cycles, especially in the lagoonal part of the section, where variations of rock magnetic properties and geochemical (redox and productivity) indices are very small. High MS values occur in the bottom part of the cycles and they decrease upwards. Time-series analyses of the MS signal reveal the dominance of c. 1.7 m cycles, grouped into c. 10 m bundles. The former cycles probably reflect precession-driven changes in monsoonal intensity, whereas the latter may have been controlled by 100 kyr eccentricity.