Grain-size and microstructure of the loess from closed depressions in the Nałęczów Plateau (East Poland)

The investigation was conducted in the eastern part of the Naleczow Plateau, a region of the Lublin Upland, in eastern Poland. The loess cover of this region was formed mainly during the last glaciation, and loess accumulation lasted until 15,000–12,000 BP. The undulating loess plateau with numerous oval-shaped closed depressions (CDs) is the main landform in the study area. Particle size distribution and SEM analyses were conducted for loess profiles under the bottoms and on the slopes of 4 CDs. Grain-size distribution characteristics as well as qualitative and quantitative micromorphological characteristics of the the loess forming the bottoms and slopes of the depressions were compared and discussed. It was documented that the differences between the loess forming the bottoms and slopes of the depressions are insignificant in the case of clay fraction content, but are considerable in the case of microstructure characteristics. The differences documented result from the impact of syn- and post-depositional diagenetic processes related mainly to suffosion and hydroconsolidation occurring under the influence of water. A quantitative assessment of the morphological effects of these processes was carried out in the context of the origin of closed depressions. The morphological effect of Holocene diagenetic processes was manifested in the deepening of the initial closed depressions formed previously under the influence of primary morphogenetic processes.