Weathering and abrasion of Fe–Ti oxides during rock degradation and fluvial transport: implications for sedimentary provenance studies

Abstract

Physical and chemical degradation of individual grains of titanomagnetite and ilmenite during rock weathering and fluvial transport processes in the River Eden catchment, Eastern Scotland, have been traced using backscattered electron images and electron probe microanalysis. Magnetic characteristics have been used to detect differences in magnetic mineralogy concentration, paragenesis and grain size between rock samples showing different stages of weathering, and between different sources and sediment samples. Results have shown higher physical and chemical durability of ilmenite during this segment of the geological cycle than titanomagnetite, which is rapidly altered. During progressive subaerial weathering of a dolerite, the increasingly intensive and extensive oxidation and development of internal fractures in titanomagnetite are observed. However, under subaqueous conditions, titanomagnetite was found to be progressively replaced by titanite and Ti‐impoverished magnetite due to hydrocirculation. Neither the total physical nor the total compositional degradation of titanomagnetite is achieved under rock weathering and fluvial transport processes. Thus, the importance of titanomagnetite as a provenance indicator remains despite its degradation during the geological processes studied in the River Eden catchment.