Leaching of Legacy Paper mill Sludge promotes Lithification through cementation of fluvial sediments

This study explores the formation of anthropogenic conglomeratic rock caused by the lithification of fluvial sediment through calcium leaching from historical paper mill sludge (PMS) deposits near Penicuik, Scotland. Calcium-rich waste generated by historic paper mill activities accumulated along the stream bank, resulting in localized cementation of sediment. Field observations identified lithified stream bed deposits beneath the PMS heaps, where natural sedimentary clasts were bound by calcium carbonate (CaCO₃). Microstructural analysis using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX) revealed that the cementing material is predominantly calcite. This was further corroborated by X-ray Diffraction (XRD), confirming a calcite-rich mineralogical composition. Stable isotope analysis (δ¹³C and δ¹⁸O) suggested a mixed carbon source, with approximately 40% derived from atmospheric CO₂ and 60% from lithogenic origins, highlighting complex geochemical processes. The results demonstrate that calcium ions (Ca²⁺) leached from PMS dissolved into pore water, subsequently migrating into adjacent fluvial sediments. This facilitated the precipitation of calcite, binding sediment grains into a cohesive structure and forming an anthropogenic conglomerate. This process mimics natural lithification mechanisms but occurs at the Earth's surface over significantly shorter timescales, bridging natural and anthropogenic geological systems. This anthropogenic lithification challenges conventional sedimentary rock classifications and has broader implications for waste management, pollutant immobilization, and carbon sequestration. By illustrating the interaction of industrial waste with natural sedimentary environments, the study emphasizes human influence on geological processes and provides insights into the evolving role of industrial byproducts in shaping modern sedimentary systems.