Quaternary calcretes in Fez plain, Saïs basin–Morocco: Origin and paleoclimatic implications

This study investigates calcrete profiles in the Saïs Basin (Fez Plain, Morocco), formed at the top of the Pleistocene fluvial and overbank deposits, with the aim of understanding their origin, formation processes, and paleoclimatic implications. Field observations revealed a vertical succession of carbonate horizons, including chalky, nodular, laminar, and hardpan layers, topped by a pisolithic horizon rich in rhizoliths and brecciated carbonate fragments. X-ray diffraction identified calcite as the dominant mineral, with minor quartz and goethite, indicating detrital input and pedogenic oxidation. Petrographic analysis showed evidence of both diagenetic and pedogenic processes, including calcite recrystallization and iron oxide accumulations near root traces, suggesting alternating dry and wet conditions. Scanning Electron Microscopy revealed biogenic structures, including plant tissues and varied calcite morphologies, indicating biological influence on calcite precipitation. Stable isotope signatures for δ¹³C range from −9.8 to −8.33 ‰VPDB and from −4.8 to −2.52 ‰VPDB for oxygen, suggesting a predominance of C3 plants with small inputs of C4 vegetation and influence of meteoric waters under moderate evaporation. The weak δ¹³C–δ¹⁸O correlation revealed multiple processes involved in calcretes genesis. These calcretes are of pedogenic origin, formed under semi-arid to dry sub-humid climates during Quaternary, offering valuable insights into pedogenic processes and paleoclimatic conditions.