(A) Gravity (Bouguer) anomaly (in mGal) and (B) basement depth (in m below/above sea level) maps of the Limagne Basin (after Morange et al., 1971). Contour lines and point data from Morange et al. (1971) maps were interpolated into a raster map using ArcMap (“Topo to Raster” tool, applying ANUDEM (Australian National University Digital Elevation Model) program; Hutchinson, 1988, 1989) producing continuous data. The distribution of microbial and/or metazoans buildups and Valvatidae gastropods is based on literature data.