Middle Pleistocene ice‐marginal sedimentation in the transitional zone between the constrained and unconstrained ice‐sheet margin, East Anglia, England

Abstract

It is uncommon in the North Sea basin and northwestern Europe for the ice‐marginal glacial successions of the Middle Pleistocene, Anglian (Elsterian) age to be well preserved and not overridden by subsequent glaciations. The existence of extensive and thick (˜20 m) Middle Pleistocene sand and gravel successions in East Anglia, England, provide a unique opportunity to reconstruct and understand the palaeoenvironmental conditions in the Anglian ice‐marginal zone, and further across the North Sea basin. This paper uses data from 80 sections in two sand and gravel quarries in East Anglia to provide the first evidence concerning: (i) the character of the ice‐marginal processes in the unique, transitional zone between the topographically constrained and unconstrained Anglian ice‐sheet margin; (ii) the role of meltwater in the re‐shaping of topographically driven preglacial drainage; and (iii) the position and the number of oscillations of the Anglian ice‐sheet margin in the form of a sediment‐landform assemblage. Moreover the current research adds to the discussion on the presence and extent of the proglacial lake in the North Sea Basin during the Anglian glaciation. The sand and gravel successions in the Anglian ice‐marginal zone are primarily reworked proto‐Thames sediments deposited by meltwater. At the beginning of the glaciation, the meltwater followed the preglacial (proto‐Thames) river course. However, as the ice sheet advanced, it was re‐routed, overwhelming and abandoning the old river course and depositing an extensive ice‐marginal subaqueous fan. The succession includes evidence for at least two enhanced meltwater release events, as well as indications of glaciolacustrine sedimentation. The character of the described sedimentary settings is discussed in the wider context of the presence of the North Sea Lake.

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

“…The depositional realm described from the Danbury-Tiptree area, consisting of a mosaic of sedimentary subenvironments, stands in contrast to that described in Birch-Stanway, located directly to the northeast of the current research area (Leszczynska et al 2017). In the Birch-Stanway area, the sedimentary succession is interpreted to be a part of a complex fan feature, indicating the exact position of the Anglia ice-sheet margin, as well as two episodes of enhanced ice-sheet ablation and the presence of a lake at the time of fan formation (Leszczynska et al 2017).…”

“…The typical lithologies associated with this Formation are angular flint, nodular flint and Rhaxella Chert (Hey 1976;Green et al 1980). Only a small fraction of sand and gravel deposits, found to the northeast of the Danbury-Tiptree area (Stanway), have been attributed to the pre-and early Anglian age fluvial Kesgrave Formation associated with the proto-Thames river (Ellison & Lake 1986;Leszczynska et al 2017). The main components of this group are quartz, quartzite, sandstone, siltstone, pinhole chert, Greensand chert, volcanic and igneous rocks (Hey 1965(Hey , 1976(Hey , 1980Hey & Brenchley 1977;Green & McGregor 1978;Green et al 1980Green et al , 1982Bridgland 1983a, b;McGregor & Green 1986).…”

“…The deposits are interpreted as glacifluvial in origin, derived from the Anglian ice sheet: the Lowestoft Formation (Bristow 1985). Only a small fraction of sand and gravel deposits, found to the northeast of the Danbury-Tiptree area (Stanway), have been attributed to the pre-and early Anglian age fluvial Kesgrave Formation associated with the proto-Thames river (Ellison & Lake 1986;Leszczynska et al 2017). Only a small fraction of sand and gravel deposits, found to the northeast of the Danbury-Tiptree area (Stanway), have been attributed to the pre-and early Anglian age fluvial Kesgrave Formation associated with the proto-Thames river (Ellison & Lake 1986;Leszczynska et al 2017).…”

“…Dashed and dotted lines mark the limit of the Anglian (Elsterian) ice sheet (light grey). Contour lines (grey, every 30 m) and shoreline after Ordnance Survey of Great Britain; geology layer based on Bristow & Lake (1975Hart 1992Hart , 1994Gibbard et al 1995;Moreau & Huuse 2013;Leszczynska et al 2017). Question marks indicate areaswhere evidence for the presence of the North Sea Lake is still to be found.…”

“…Contour lines (grey, every 30 m) and shoreline after Ordnance Survey of Great Britain; geology layer based on Bristow & Lake (1975). Hart 1992Hart , 1994Gibbard et al 1995;Moreau & Huuse 2013;Leszczynska et al 2017).…”