Morphometry, distribution and Holocene dating of closed depressions, called mardelles, in northeastern France
Résumé
Closed depressions (CDs) are common small landforms in the European loess belt, and how they originated - either geological or human made - is still debated. In northeastern France, closed depressions called “mardelles” are widespread on different geological substrata and present land use. To study their morphometric characteristics and spatial distribution, we used two high-resolution LiDAR surveys to perform an inventory of 1300 CDs. These small landforms are more frequent in present forests (70 %) than in grasslands or croplands. On average, these structures are small, with an average area of 347 m2 (median: 449 m2), and over 80 % are 10 to 30 m in diameter. Closed depressions have been identified on all regional types of geological substratum, i.e., not only on Keuper marlstone. In addition, radiocarbon dating of the 23 deepest available CDs at local and regional scales suggests two different types of landforms with different origins