Middle Pleistocene ice‐marginal sedimentation at a constrained ice‐sheet margin, East Anglia, UK

Abstract

This paper presents a reconstruction of the marginal zone of the Anglian (Elsterian, 480-420 ka BP) age ice sheet in the Danbury-Tiptree area, East Anglia, UK. The research area is a unique locality where the ice front abutted against a 30km-long and 100-m-tall ridge in an otherwise lowland area. Observations from three main field localities (Danbury quarry, Royal Oak pit and Tiptree quarry) are complemented with ground penetrating radar survey data, borehole data analysis, laboratory analyses and geological map interpretation. A four-stage model of the evolution of the landscape in the Danbury-Tiptree area is presented. The results are of broader importance, in that the sedimentary record sheds light on the processes operating at a constrained ice-sheet margin. The paper identifies the most important characteristics of the depositional environments at an ice front terminating within this type of setting: (i) high temporal and spatial variability of energetic depositional conditions, resulting in the presence of a vast array of distinct depositional sub-environments; (ii) mechanisms promoting differential erosion leading to enhanced topography, and (iii) unusually high overburden pressure in the topographically constrained ice margin within the otherwise lowland area influencing the ice-sheet-bedrock interaction in this particular research area, inducing postglacial seismicity.

Bedforms and sedimentary structures related to supercritical flows in glacigenic settings

“…The slope break at the transition may trigger hydraulic jumps in supercritical density flows, leading to the formation of isolated scours filled by backsets or massive deposits, which may be incised into finergrained delta-foreset or toeset deposits (Fig. 7E) (Winsemann et al, 2007b(Winsemann et al, , 2018Leszczynska et al, 2018). Increased sedimentation rates downflow of hydraulic jumps may cause the accumulation of thick successions featuring climbing-dune cross-stratification and climbingripple cross-lamination in the delta toeset (Winsemann et al, 2011(Winsemann et al, , 2018.…”

“…Hornung et al ., 2007; Winsemann et al ., 2009, 2011, 2018; Lang & Winsemann, 2013; Pisarska‐Jamroży & Zieliński, 2014; Lang et al ., 2017b) and British–Irish ice sheets (e.g. Lee et al ., 2015; Leszczynska et al ., 2017, 2018) in Europe and the Laurentide Ice Sheet in North America (e.g. Brennand, 1994; Russell & Arnott, 2003; Johnsen & Brennand, 2004; Dietrich et al ., 2016, 2017).…”

“…Proximal gravel‐rich fan lobes are interpreted as the mouth bars of the glacigenic jet flow and are unconformably overlain by more distal sand‐rich lobes deposited by sustained density flows on the lee side of and between the gravelly mouth bars (Hornung et al ., 2007; Winsemann et al ., 2009; Lang & Winsemann, 2013; Lang et al ., 2017b). Deposits of supercritical flow are very common within gravelly and sandy subaqueous ice‐contact fan deposits and may be considered characteristic facies for these systems (Figs 3, 7 and 8) (Brennand, 1994; Russell et al ., 2003; Hornung et al ., 2007; Russell et al ., 2007; Winsemann et al ., 2009; Lang & Winsemann, 2013; Leszczynska et al ., 2017, 2018; Lang et al ., 2017b).…”

“…7C and D) (Lang et al ., 2017b). Sheet‐like deposits consist of low‐angle cross‐stratified, subhorizontally or sinusoidally stratified gravel formed by breaking or non‐breaking antidunes (Brennand, 1994; Russell & Arnott, 2003; Leszczynska et al ., 2017, 2018; Lang et al ., 2017b). Planar and trough cross‐stratified gravel indicates the migration of 2D and 3D gravel dunes under high‐energy subcritical flows (Russell & Arnott, 2003; Hornung et al ., 2007; Winsemann et al ., 2009; Lang et al ., 2017b).…”

“…Upper‐flow‐regime bedforms commonly occur within deposits of glacifluvial deltas (Fig. 3; Table 1) (Postma et al ., 1983; Winsemann et al ., 2011, 2018; Girard et al ., 2012a,b; Dietrich et al ., 2016, 2017; Moreau & Joubert, 2016; Nehyba et al ., 2017; Normandeau et al ., 2017; Lang et al ., 2017b; Hanáček et al ., 2018; Leszczynska et al ., 2018; Kostic et al ., 2019). The successions are very similar to those described from non‐glacigenic coarse‐grained deltas (e.g.…”