Formation of a rhizogenic calcrete during a glacial stage(Oxygen Isotope Stage 12): its palaeoenvironmental stratigraphic significance

Abstract

The morphology and micromorphology of a carbonate-cemented horizon within Anglian Stage, Oxygen Isotope Stage (OIS) 12, glaciofluvial outwash deposits at Leet Hill, southern Norfolk are characteristic of a rhizogenic calcrete. The horizon consists of a laterally continuous calcified root mat and an associated vertical rhizolith, both of which contain micro-fabrics typical of biologically precipitated carbonate, i.e. needle fibre calcite, calcified root cells and pelleted micrite. Formation of this calcrete is suggested to relate to the coincident occurrence of a phase of land surface stability and a period of climatic amelioration within the Anglian Stage during which permafrost decayed, a near-surface water table formed and a vegetation cover became established. The period of calcrete formation is tentatively correlated with other evidence for a climatic amelioration during the Anglian Stage in eastern England. The stratigraphic position of the calcrete suggests that this amelioration occurred after the Scandinavian ice had advanced into East Anglia but prior to the overriding of the region by the British ice mass. The discovery of this calcrete represents the first known description of a rhizogenic calcrete from a glacial stage. It presents the possibility that other, previously unstudied, carbonate horizons within Quaternary deposits of northwest Europe may in fact be calcretes and that these may provide further palaeoenvironmental and stratigraphic information.