Microstructures, subglacial till deposition, and shear band development revealing up-section changes in shear–A study from Weissbach, Austria John Menzies a, *, Jürgen M. Reitner b a Department of Earth Sciences, Brock University, St. Catharines, Ontario, L2S 3A1, Canada b Geologische Bundesanstalt /Geological Survey of Austria, Neulinggasse 38, A-1030, Wien, Austria A R T I C L E I N F O Article history: Received 5 April 2018 Received in revised form 7 November 2018 Accepted 12 November 2018 Available online xxx Keywords: Sedimentology Stratigraphy Quaternary Geology Geomorphology A B S T R A C T Tills from an exposure in Wildschönau Valley, northern Austria were examined using micro- sedimentological techniques. The tills exhibit a range of microstructures indicative of soft sediment deformation within temperate subglacial bed conditions. The tills can be subdivided at the macroscale into a lower grey and upper red till both of which exhibit some sedimentological variations; however, at the micro-level the tills appear essentially identical. The microstructures in the tills are illustrative of structures developed during deformation both during and following their emplacement. Of note are the microshears within these tills that are demonstrative of changes in applied stress. Both low (<25  ) and high angle (>25  ) microshears were mapped and their fabric data analyzed. The microshears show a change in stress levels ascending through successive till units. The changes in stress are demonstrative of spatially and temporally changing rheological conditions undergone by the subglacial tills during deformation, ongoing deposition/ emplacement and stress localization. These findings indicate that microstructures reveal local deformation conditions in tills and a more detailed micro-history of paleo- stress. © 2018 The Geologists' Association. Published by Elsevier Ltd. All rights reserved. 1. Introduction The rheological behavior of tills deforming within a subglacial soft sediment layer beneath an ice mass has been the subject of considerable interest over the past decades (Piotrowski et al., 2004, 2006;Kjær et al., 2006; Truffer and Harrison, 2006; Schomacker and Kjær, 2007; Larter et al., 2009; Smith and Murray, 2009; Narloch et al., 2012; McCracken et al., 2016; Spagnolo et al., 2016; Phillips et al., 2018a, b). With the discovery of “deforming soft sediment packages” beneath modern ice masses, it has been commonly acknowledged that similar subglacial conditions more than likely prevailed beneath Quaternary and Pre-Quaternary ice masses. However, the detection of soft beds in the ancient record remains challenging (cf. Busfield and Le Heron, 2018). Compre- hension of the mechanics of just how subglacial tills are deposited and/or emplaced remains imperfect. Although macrofabric ele- ments of tills have been well established for over 60 years (cf. Holmes, 1941; Evans et al., 2006; Menzies et al., 2018), the genesis and kinematic evolution of microstructures indicative of both brittle and ductile shear within tills formed and forming during shear, and the link to bulk rheological properties remain poorly understood (Phillips et al., 2013a, b, 2018a, b; van der Meer et al., 2003; Roberts and Hart, 2005; Benn and Prave, 2006; Reinardy and Lukas, 2009; van der Meer and Menzies, 2011; Phillips et al., 2011; Denis et al., 2010; Arnaud, 2012; Clerc et al., 2012; Busfield and Le Heron, 2013; Ravier et al., 2014; Le Heron, 2015; Menzies et al., 2016a, b; Cowsill et al., 2016; Phillips et al., 2018a, b). This paper investigates microstructures in subglacial till formation and their development from a site at Weissbach in the Wildschönau Valley, northern Austria with an emphasis on the analyses of microshears that occur within these tills. The development of a method of microshear analyses in tills has been discussed in the past (e.g., Thomason and Iverson, 2006; Narloch et al., 2012) utilizing microshear length rather than geometry. This paper introduces an alternate method of microshear analyses showing, in an experimental manner, the potential value of such studies. The paper sets out to detect the level of localized change in stress within a specific near-vertical till exposure using microshear analyses and provides a better understanding of till deformation and depositional/ emplacement mechanics. * Corresponding author. E-mail address: jmenzies@brocku.ca (J. Menzies). https://doi.org/10.1016/j.pgeola.2018.11.001 0016-7878/© 2018 The Geologists' Association. Published by Elsevier Ltd. All rights reserved. Proceedings of the Geologists’ Association xxx (2018) xxx–xxx G Model PGEOLA 730 No. of Pages 14 Please cite this article in press as: J. Menzies, J.M. Reitner, Microstructures, subglacial till deposition, and shear band development revealing up- section changes in shear–A study from Weissbach, Austria, Proc. Geol. Assoc. (2018), https://doi.org/10.1016/j.pgeola.2018.11.001 Contents lists available at ScienceDirect Proceedings of the Geologists’ Association journa l homepage : www.e lsevier.com/loca te/pgeola