Integrated mineralogical and colour analysis of the Poznań Clays from the Honoratka dump near Konin in Central Poland

Abstract

The Poznań Clays represent a key lithostratigraphic unit of the Neogene in the Polish Lowlands. They are characterised by pronounced colour variability, ranging from dark grey and black to yellow, brown and red. This study identifies and quantifies the mineralogical and geochemical factors controlling this colour variability and evaluates their significance for palaeoenvironmental interpretation, using samples collected from the Honoratka dump in central Poland. A multimethod approach is applied, including grain-size analysis, Powder X-ray Diffraction (PXRD), 57Fe Mössbauer Spectroscopy (57Fe-MS), Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), and Raman Spectroscopy (RS). The results obtained demonstrate that colour in the Poznań Clays is primarily controlled by the type, distribution, and crystallinity of iron-bearing phases, particularly hematite, goethite and jarosite, as well as by redox conditions, pH, and the presence of organic matter. Red and brown colours are associated with oxidising environments and the formation of hematite and goethite, while dark colours reflect reducing conditions and organic-matter preservation. Pale colours are linked to the dominance of non-pigmenting minerals such as quartz, clay minerals and carbonates. This study corroborates the effective use of sediment colour as an integrated indicator of depositional and post-depositional processes in palaeoenvironmental interpretations, when supported by mineralogical analyses.