Reconstruction of subglacial depositional conditions based on the anisotropy of magnetic susceptibility: an example from Dębe (central Poland)

Abstract

The analysis of low‐field anisotropy of magnetic susceptibility (AMS) was used to reconstruct the subglacial deposition conditions during the Main Stadial of the Odranian Glaciation (MIS 6) in till deposits from a site in Dębe (central Poland). Based on the AMS parameters, six till beds were identified (intervals 1–6). The declination of the maximum magnetic susceptibility axis (k1) indicates that the ice sheet was moving in from the northwest. The obtained results confirm the thesis about the preferred direction of ice‐sheet transgression during the Odranian Glaciation (MIS 6) in this part of Poland. This interpretation is also confirmed by data obtained from measurements of the long axis of clasts, which agree with the orientation of k1. Based on the AMS results, a significant part of the profile was deformed through simple shear and direct interaction of the ice sheet with the underlying sediment (beds 2–5). The lowest part of the till (bed 6) may have been deposited on a southeast‐trending slope or post‐depositional deformed by uneven loading of the ice cover. The upper part of the profile (especially in interval 1) could be deposited with an impact of pore water.

The Pleistocene ice-sheet dynamics in north-central Poland based on magnetic fabrics of tills and landform analysis

“…The filtration was based on the median and 25% and 75% quartiles. Samples above the level described by the formula Q3 + 1.5 × IQR, where Q3 is the 75% quartile, and IQR is the interquartile range between the 25% and 75% quartiles, were removed due to anomalously high values of the parameters (Hodge and Austin, 2004; Stachowska et al, 2020; Teodorski et al, 2021). The IQR outliers method is not dependent on abnormally high boundary values, unlike the standard deviation method.…”

“…An effective tool for measuring the average orientation of fine grains is the anisotropy of magnetic susceptibility (AMS) method, which has been used to determine not only the directions of movement, but also the mechanism of ice-sheet movement, and to reconstruct processes of subglacial till formation. This method of studying tills has been refined across more than six decades of use (e.g., Fuller, 1962; Stupavsky and Gravenor, 1975; Stewart et al, 1988; Hooyer et al, 2008; Thomason and Iverson, 2009; Gentoso et al, 2012; Fleming et al, 2013; Tylmann et al, 2013; Ankerstjerne et al, 2015; Król and Wachecka-Kotkowska, 2015; Hopkins et al 2016; McCracken et al, 2016; Narloch et al, 2021; Teodorski et al, 2021).…”