Loess formation and chronology at the Palaeolithic key site Rheindahlen, Lower Rhine Embayment, Germany

Abstract

Abstract. The loess–palaeosol sequence and intercalated Palaeolithic find layers at the former brickyard of Rheindahlen are matters of ongoing scientific dispute. The age of different palaeosols and loess layers, hence their correlation with the global climate cycles, and the timing of repeated Neanderthal occupations have been hotly debated. These disagreements should be solved because the exceptional sedimentary and Palaeolithic sequences at Rheindahlen provide a unique opportunity to study diachronic changes in Neanderthal behaviour within the context of past climate change. We thus revisited one of the key loess sections of the Rheindahlen site to improve our understanding of loess formation processes and provide a more reliable chronostratigraphic framework for the sequence. High-resolution grain size analyses and micromorphology show that the Erkelenz Soil and the Rheindahlen Soil are characterized by more strongly developed Bt horizons than the modern soil. While these soils represent interglacial phases, the lowermost palaeosol likely formed during an interstadial and has been overprinted by weak clay illuviation during the formation of the Rheindahlen Soil. Sedimentary features of prolonged frost characterize loess and palaeosols below the modern soil and give indirect evidence for a Holocene age of the uppermost part of the sequence. Our luminescence dating approach corroborates this correlation and adds several Last Glacial deposition ages for the upper metres of the sequence. Previous correlation of this part of the sedimentary sequence with the penultimate glacial is thus rejected, whereas placing the Middle Palaeolithic inventories A3, B1, and B2 into the Last Glacial is confirmed. Luminescence measurements for the parental loess of the Erkelenz Soil and for loess layers below did not provide reliable ages probably related to signal saturation. The age of this part of the sequence thus remains open, hence the timing of human occupation testified by Palaeolithic inventories B3, B4/5, C1, and D1. The new findings provide an improved base for stratigraphic correlation of the Rheindahlen loess sequence and for investigating diachronic change in Neanderthal behaviour against the background of past climate change.

MiGIS: micromorphological soil and sediment thin section analysis using an open-source GIS and machine learning approach

“…The feature classes were established based on material screening and conventional micromorphological analysis under the microscope. Corresponding results and interpretations are described in detail in Kehl et al (2024). Pore space as observed in TSs under the microscope is less than the total porosity within a sediment or soil horizon due to geometry-related effects such as the Holmes effect or wedging effects (Stoops, 2020).…”

“…), B7 was taken from a second Bt (Erkelenz soil) at a depth of 305 cm b.s., and C5 belongs to the third Bt (Rheindahlen soil) extracted from a depth of 524 cm b.s. (Kehl et al, 2024). Since in some cases individual methods, feature classifications, or phenomena are more illustrative in other classified TSs from Rheindahlen, some of these additional results (Appendix B) appear in the figures.…”

“…The TSs were prepared and analysed in stratigraphic order allowing observations on changes in the type and intensities of soil formation with time. These have already been micromorphologically analysed in detail and described using conventional methods in Kehl et al (2024). The Rheindahlen sediment sequence contains three different palaeosols characterised by pedogenic illuviation of clay (Bt horizons), which were interpreted to have formed during warmer phases (i.e.…”

“…interglacials) of the Middle and Late Quaternary. These palaeosols are intercalated in diverse loess deposits that are associated with colder and drier phases (glacials) in the past (Kehl et al, 2024). Undisturbed Bt horizons typically contain coatings of oriented clay minerals (clay coatings), whose specifications and distribution are basically of micromor- phological interest because they are evidence of the pedogenic process of clay illuviation (Stoops, 2020;IUSS Working Group (WRB), 2022).…”

“…As a case study, we selected a well-described loesspalaeosol sequence from Rheindahlen in Germany (Kehl et al, 2024). The aim was to classify and quantify the pore space and main micromorphological constituents: four different groundmass types (Gm); coarse constituents, such as medium sand and fine gravel grains (Sg); clay granules (Cg); charred organic material (Ch); and pedofeatures including different clay coating types (Cc, Cci, Ccd) and iron hydroxide (Fe)-and manganese oxide (Mn)-dominated constituents.…”