Abstract
Magnetic susceptibility in sediments has been thoroughly studied as a paleoenvironmental proxy over the last decades. However, it is unknown to what extent magnetic susceptibility variation is also a diagnostic of different sediment sources. Here we investigate if multiple magnetic susceptibility-based parameters can effectively be used as sediment source indicators. New magnetic property data from the Mu Us and Tengger Deserts in China are compared to previously known sediment provenance based on other well-established proxies. To assess the magnetic properties of these deserts, magnetic susceptibility and its out-of-phase component, its dependence on frequency, temperature and low-field amplitude are analyzed. Our results indicate similar sources for the western Mu Us Desert and the Tengger Desert and a distinct source for the eastern Mu Us, in-line with previously hypothesized provenance patterns. However, magnetic properties within the Tengger Desert sediments are homogenous, which may suggest a uniform provenance for the entire Tengger Desert, that the sediments are greatly reworked, or similar magnetic properties in potential multiple source regions. Magnetite is the major magnetic mineral in the study area and the dominant causes for divergence in magnetic properties are the magnetic mineral concentration and domain state. The results here, in particular from the Mu Us, suggest considerable promise for using magnetic susceptibility parameters in desert sediment provenance research.
Highlights
The following calculations were done using data from the Agico Kappabridge MFK1-FA: χfd was calculated as χfd (%) = 100/ χlf where χlf and χhf are the magnetic susceptibilities measured at low and high frequency. χfn represents the normalized version of the frequency dependence and allows better comparison of data obtained using different instruments (Hrouda, 2011). χfn was calculated as χfn (%) = χfd/(ln Fhf - ln Flf) where Flf and Fhf are the low and high operating frequencies used by the magnetic susceptibility meter, respectively. χon measures the out-of-phase contribution to magnetic susceptibility (Hrouda et al, 2013) and was calculated as χon (%) = (200/ π) * tan δlf, where δlf is the phase angle measured at low frequency
This study aims to evaluate if a combination of magnetic susceptibility-based parameters can be used to infer sediment provenance in a semi-arid to arid region
The Mu Us Desert comprises sediments of different origin between its eastern and western parts, as demonstrated in multiple previous studies. This source difference is reflected in multiple magnetic susceptibility parameters
Summary
Magnetic susceptibility (κ) of sediments has been intensely studied during the last decades, mainly as a proxy for paleoenvironment and past climate variations (e.g., Heller and Evens, 1995, Baosheng et al, 2000, Porter, 2001, Dong et al, 2015) or sediment relative age dating through stratigraphic correlation, in loess (e.g., Ding et al, 2001, Hao and Guo, 2007, Marković et al, 2015, Zhao et al, 2016). κ variations through loess sequences are considered to be caused by environmental factors such as soil formation under warm and humid conditions. Χfd enhancement is indicative of the presence of ultrafine (< ~25 nm: Maher, 1988) and highly magnetisable superparamagnetic (SP) particles that are formed in situ, mainly during soil formation (Liu et al, 2005a). In this monsoon marginal Chinese setting, this is associated with warm and humid conditions under a strong summer monsoon favouring biological activity, while low values of χfd are associated with cold and arid conditions and strong winter monsoon where soil formation is limited and sediment input is high (Porter, 2001). This implies that weathering and pedogenesis are not the main controls of χlf and χfd of surface sediments in this region, which may rather be signatures inherited from the source lithology
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