3. 1. Spatial distribution and structure of closed depressions
(CDs)
CDs are small landforms, commonly found in the European loess belt
(Kołodyńska-Gawrysiak & Poesen, 2017). 5367 CDs have been mapped in the
Nałęczów Plateau. The total area of the CDs bottoms is 7.26
km2, representing 1.46% of the study area. CDs are
not evenly distributed in the studied region. In some places, their
density reaches 1 CD·ha-1 (max. 1.9
CDs·ha-1). Areas where CDs density does not exceed 1
CD·ha-1 predominate in the Nałęczów Plateau (Figure
4). Fossil soils and colluvial sediments in 5 CDs were studied in detail
and dated (Kołodyńska-Gawrysiak et al., 2017; Kołodyńska-Gawrysiak,
Poesen & Gawrysiak, 2018; Kołodyńska-Gawrysiak, 2019). These CDs are
all filled with a 80-90 cm thick Holocene soil-sediment sequence,
consisting of two colluvial sediment layers (C1 and C2) and a fossil
Colluvisol (S2) Ab2g-Cg (Table 1, Figure 3). This sequence overlies a
fossil soil (S1) Ab1g-Bht-Btg-BtC-C that developed on loess in situ. On
the slopes this soil has the horizons
A-E-Bt1-Bt2-BtC-C-CHCl+ or predominantly
A-Bt1-Bt2-BtC-C-CHCl+ as a result of soil erosion
(Figure 3). Calcareous loess was found below the soil surface of the CD
slopes (Figure 3). Below the CD bottoms, calcareous loess was not
detected. The dating results indicate that fossil soil S1 developed
during along period from the Late Vistulian until the Late Boreal or
Early Atlantic Period (10130± 60 BP until 7.99 ± 0.65 BP). The older
colluvial layer C1 is 30-60 cm thick. The formation of this layer
occurred from the Late Boreal or Early Atlantic Period until the
(Middle)Late Bronze Age or Early Iron Age (7.99 ± 0.65 BP until 3.67 ±
0.33 BP/2.37 ± 0.13 BP). The fossil Colluvisol (S2) Ab2g-Cg developed on
the oldest colluvial layer C1 (Figure 3). This fossil Colluvisol
developed from the Late Bronze Age or Early Iron Age until the Early or
High Middle Ages (3.67 ± 0.33 BP/ 2.37 ± 0.13 BP until
7th–8thc/12th–14th c). At the top of the
CDs infilling younger colluvia C2, 50-70 cm thick with Colluvisol have
been found (Table 1, Figure 3). The younger colluvia C2 layers were
deposited during the last several hundred years, i.e. since the Early
Middle Ages until today (7th–8th c
until today) (Kołodyńska-Gawrysiak, 2019).