Formation of greigite under different climate conditions in the Yellow River delta

Formation and preservation of greigite can indicate the physicochemical characteristics of sedimentary environment. Presence of greigite can be diagnosed in the late Pleistocene fluvio-lacustrine sedimentary layers of 29.4-29.7 and 26.1-27.1 m in core ZK30 of the Yellow River delta, based on analysis of particle size, magnetic properties, scanning electron microscope (SEM) and X-ray diffraction (XRD) measurements. These layers are the transition zones from shallow marine facies to fluvio-lacustrine facies, and from fluvio-lacustrine facies to salt marsh facies in an ascending order, respectively. They are characterized by higher SIRM and SIRM/chi (>30 kA m(-1)) values than those of other layers, suggesting the possible existence of greigite. Both SEM and XRD analyses confirm its presence. However, sediment layer of 29.4-29.7 m are coarser, and greigite coexists with pyrite, but sediment layer of 26.1-27.1 m are finer and the occurrence of greigite is not accompanied by pyrite. The different occurrence of greigite in the two layers suggests that different climate condition and sedimentary environment control its formation and preservation.