title: Unmixing hysteresis loops of the late Miocene-early Pleistocene loess-red clay sequence.
abstract: Magnetic paleoclimatic records often represent mixed environmental signals. Unmixing these signals may improve our understanding of the paleoenvironmental information contained within these records, but such a task is challenging. Here we report an example of numerical unmixing of magnetic hysteresis data obtained from Chinese loess and red clay sequences. We find that the mixed magnetic assemblages of the loess and red clay sediments both contain a component characterized by a narrow hysteresis loop, the abundance of which is positively correlated with magnetic susceptibility. This component has grain sizes close to the superparamagnetic/stable single domain boundary and is attributed to pedogenic activity. Furthermore, a wasp-waisted component is found in both the loess and red clay, however, the wasp-waisted form is more constricted in the red clay. We attribute this component to a mixture of detrital ferrimagnetic grains with pedogenic hematite. The abundance of this component decreases from the base to the top of the red clay, a pattern we attribute to decreased hematite production over the Chinese Loess Plateau (CLP) due to long-term climate cooling. This work demonstrates the potential of hysteresis loop unmixing to recover quantitative paleoclimatic information carried by both low and high coercivity magnetic minerals.
authors.affiliation: MOE Key Laboratory of Western China's Environmental Systems, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 73000, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Faculty of Physics, Paleomagnetic Laboratory, University of Bucharest, N. Balcescu, 1, 010041 Bucharest, Romania.
authors.forename: Cristian
authors.initials: C
authors.lastname: Necula
authors.affiliation: Research School of Earth Sciences, Australian National University, Acton 2601, ACT, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Heslop
authors.affiliation: MOE Key Laboratory of Western China's Environmental Systems, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 73000, China.
authors.forename: Junsheng
authors.initials: J
authors.lastname: Nie