Contributions of different parent materials in soils developed from periglacial cover-beds

Soils frequently develop from mixtures of different parent materials. We quantified the contributions of different parent materials to the substrate for recent soil development using trace metal concentrations and Pb isotope ratios as input data for end-member mixing analyses (EMMAs). We examined six transects (320-775 m) at two sites in the Rhenish Slate Mountains. Soil types ranged from acid Cambisols to stagnic Luvisols developed from periglacial cover-beds. Sixteen O, 11 A, 120 B and 10 C horizons were analysed for total trace metal concentrations and partly also Pb-206:Pb-207 ratios. Most metal concentrations in the B horizons were in the background range, except for Pb, which partly had elevated concentrations of up to 135 mg kg(-1). The depth distribution of metal concentrations and 206Pb:207Pb ratios suggested that metals deposited from the atmosphere had hardly reached the B horizons. A principal component analysis (PCA) of the trace element concentrations in the 120 B horizons identified four main metal sources of the B horizons, which we interpreted as bedrock (slate), loess, Laacher See tephra (LST) resulting from the last volcanic eruption in the Eifel mountains and ore veins. The slate was characterized by Cr and Zn, the loess by Zr, the LST by Nb and the ore veins by Pb. Based on EMMAs with four end-members using two different sets of tracers (Set 1: concentration ratios of Zr:Cr, Nb:Cr, Pb:Cr, Set 2: Zr:Zn, Nb:Zn, and Pb:Zn), slate, loess and LST contributed, on average, 39-40, 22-24 and 37-38%, respectively, at Site 1 and 19-21, 53-63 and 18-26%, respectively, at Site 2. In contrast, the ore contribution was consistently estimated at 0%. An additional EMMA with two end-members based on the Pb-206:Pb-207 ratios estimated the contribution of the ore at 0.02%. We conclude that EMMAs based on trace element concentrations and isotope ratios provide a tool for determining the contribution of different parent materials to the substrate from which soils develop, at least at a small regional scale and if an appropriate tracer that distinguishes all the considered substrates is found.