Earthworm calcite granules: a new tracker of millennial-timescale environmental changes in Last Glacial loess deposits

Earthworm calcite granules (ECG) are secreted by several earthworm species, mostly Lumbricus terrestris and Lumbricus rubellus, which release them at the surface and in the upper part of soil horizons. For a long time, they have been found in various calcareous Quaternary deposits, but more recently in Western European loess sequences where they can be abundant in specific layers. In this study, we present the first continuous record of ECG abundance variations from two loess sequences in northern France dating from the last glacial period. The aim of this research is to evaluate the reliability of ECG as a new palaeoenvironmental proxy for the study of loess environments. ECG counts reveal a link between their abundance and the nature of stratigraphic units, i.e. very high abundances in tundra gley and boreal brown soil horizons and almost none in typical calcareous loess. These abundance variations are similar to those of terrestrial molluscs. The ECG signal thus suggests, along with sedimentological parameters (grain size index, calcium carbonate, total organic carbon), that milder climatic conditions occurred during the development of tundra gleys during the Upper Pleniglacial (approximate to 20-35 ka), and of boreal brown soils during the Middle Pleniglacial (approximate to 35-40 ka).