The interpretation of pollen records of colluvial deposits is subjected to additional problems (van Mourik, 2001). Firstly, the pollen content of the basic layer (as paleosol in mardels) is post-sedimentary. Under stable and vegetated conditions pollen will infiltrate by bioturbation and survive decay in protecting soil AGN 195183 (van Mourik, 2003). Consequently, the age of the sediments is older than the palynological age. Secondly, the pollen composition of the sediment is a mix of the regular aeolian pollen influx and pollen, present in eroded and transported material. Consequently, older eroded and redeposit pollen grains are mixed with the regular pollen influx and species occurring on eroded slopes can be overrepresented in pollen extractions of colluvial deposits.
4.2. Mardels and landscape evolution
Mardels (CDs) in the Gutland can be the result of historical clay extraction (from the li3 and the km3 formations), the development of sinkholes, related to joint patterns (in the Luxembourger sandstone formation) and soil subsidence caused by subsurface dissolution of gypsum veins (present Keuper formations). Natural mardels (in sinkholes and subsidence basins) may develop during the whole Holocene (Barth, 1996 and Thoen and Hérault, 2006), and anthropogenic mardels (in abandoned quarries) are the result of clay extraction in Roman Time (Etienne et al., 2011) or later (Schmidt, 1995).