Probing Pedogenetic Imprints and Functional Properties of Moroccan Clayey Materials Through FFC NMR Relaxometry

Abstract

Understanding how soil formation processes influence the microstructure and the dynamic behavior of clay-rich materials is essential for both pedological interpretation and technological assessment. In this study, we applied fast field cycling nuclear magnetic resonance (FFC NMR) relaxometry to investigate the microstructural heterogeneity of Moroccan clays developed under diverse pedogenetic conditions. Nuclear magnetic relaxation dispersion (NMRD) profiles were processed using a model-free inversion algorithm to retrieve the distribution of correlation times. The latter provides a phenomenological mapping of proton-surface interactions across distinct dynamic domains. Complementary indicators of micro-scale hydrological connectivity were, then, computed from the T₁ distributions, integrating both structural (SCI) and functional (FCI) heterogeneity. While the former indicates the breadth of molecular environments experienced by water across the system, the latter captures the dynamic contrast between fast- and slow-relaxing populations associated with variations in surface accessibility and magnetic heterogeneity. The results showed that the clay sample from Khemisset exhibited the greatest relaxation heterogeneity, consistent with advanced pedogenetic reorganization related to redox-driven redistribution of paramagnetic metals. In contrast, the clay samples from Berrechid and Tiflet displayed a more ordered architecture and lower magnetic heterogeneity, reflecting earlier-stage pedogenetic development. This study demonstrated that FFC NMR relaxometry reveals the microstructural memory encoded into water dynamics, offering a powerful tool to infer the pedogenetic pathways leading to soil formation. Beyond its relevance for pedological studies, the method also offers valuable insights into the technological behavior of clays, supporting the selection of raw materials for industrial purposes based on their microstructural properties.