LITHOLOGIC AND ROCK MAGNETIC CYCLOSTRATIGRAPHY IN PLEISTOCENE TERRESTRIAL SEDIMENTS

Rock magnetic cyclostratigraphy has demonstrated the preservation of Milankovich-scale environmental signal in a range of marine depositional environments, however, it remains relatively untested for terrestrial stratigraphic sections with pronounced unconformities and variable deposition rates (Kodama, 2017; Li et al., 2013). We have collected rock magnetic data from a section of terrestrial clastic sediments in an actively subsiding foreland that contains numerous unconformities and changes in the rate of deposition marked by paleosols. The exposure, located along the banks of the Enza River in northern Italy, contains 3 full lithologic cycles consisting of repeating paludal, fluvial, debris flow, and soil-loess deposits in 56 m of measured section. Cosmogenic dating correlates the lithologic cyclostratigraphy as aligning with Pleistocene glacial-interglacial cycles (Gunderson et al., 2014). Initial results indicate that the section preserves sediments contemporary with 5+ marine isotope stages (MIS), including MIS 10, 11, 14-16, and possibly MIS 7-9. Additionally, a preliminary analysis shows that the sediment accumulation rate increases by an order of magnitude from 3 cm/kyr at the base of the section (~860 Ka) to 22 cm/kyr at the top (~290 Ka). A previous rock magnetic cyclostratigraphy study in the lower, marine and near-shore portion of the Enza River exposure revealed a high-resolution magnetic susceptibility time series that recorded Milankovitch frequencies (Gunderson et al., 2012). To extend the rock magnetic cyclostratigraphy record into the Pleistocene terrestrial portion, we collected 137 unoriented sediment samples at 40 cm intervals. The magnetic susceptibility of each sample will be measured using a KLY-3s Kappabridge susceptibility meter. Through establishing how rock magnetic signals propagate across lithologic unconformities and paleosols, this study addresses the century-old question of how periods of depositional inactivity are recorded in strata (Paola et al., 2018).