Unmixing magnetic remanence curves withouta prioriknowledge

Abstract

S U M M A R YMany of the natural materials studied in rock and environmental magnetism contain a mixed assemblage of mineral grains with a variety of different origins. Mathematical decomposition of the bulk magnetic mineral assemblage into populations with different properties can therefore be a source of useful environmental information. Previous investigations have shown that such unmixing into component parts can provide insights concerning source materials, transport processes, diagenetic alteration, authigenic mineral growth and a number of other processes.A new approach will be presented that performs a linear unmixing of remanence data into coercivity based end-members using only a minimal number of assumptions. A non-negative matrix factorization (NMF) algorithm for unmixing remanence data into constituent endmembers is described with case studies to demonstrate the utility of the approach. The shape of the end-members and their abundances obtained by NMF is based solely on the variation in the measured data set and there is no requirement for mathematical functions or type curves to represent individual components. Therefore, in contrast to previous approaches that aimed to unmix curves into components corresponding to individual minerals and domain states, NMF produces a genetically more meaningful decomposition showing how a data set can be represented as a linear sum of invariant parts. It has been found that the NMF algorithm performs well for both absolute and normalized remanence curves, with the capacity to process thousands of measured data points rapidly.

Paleoposition of the Intertropical Convergence Zone in the eastern Pacific inferred from glacial-interglacial changes in terrigenous and biogenic magnetic mineral fractions

“…In natural sediments, several magnetic components of different sources are generally mixed, and it is often diffi cult to characterize individual components; therefore, unmixing of magnetic components has been an issue in environmental magnetic studies (e.g., Egli, 2004a;Heslop and Dillon, 2007;Watkins et al, 2007;Lascu et al, 2010). Egli (2004b) demonstrated that rock magnetic parameters, including the ratio of anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization (k ARM / SIRM), and the coercivity distribution of ARM and IRM, are quite useful for unmixing and characterizing magnetic mineral assemblages in sediments; he identifi ed two magnetically distinct groups of biogenic magnetite, biogenic soft (BS) and biogenic hard (BH), that probably correspond to different magnetosome morphology.…”

A New Tool for Separating the Magnetic Mineralogy of Complex Mineral Assemblages from Low Temperature Magnetic Behavior

“…Remanence acquisition or demagnetization curves and fielddependence of induced magnetization probed through hysteresis loops and first-order reversal curve (FORC) distributions are the dominant magnetic data currently being numerically unmixed to characterize the magnetic mineral components (Robertson and France, 1994;Carter-Stiglitz et al, 2001;Egli, 2003Egli, , 2013Fabian, 2003;Heslop and Dillon, 2007;Lascu et al, 2010Lascu et al, , 2015Heslop, 2015;Church et al, 2016;Fabian et al, 2016;Maxbauer et al, 2016b;Zhang et al, 2016). While important and useful results have emerged, the currently applied methods present important limitations.…”

A Review of Recent Advances in Red-Clay Environmental Magnetism and Paleoclimate History on the Chinese Loess Plateau

“…This hypothesis needs further rock magnetic work to confirm. Nie et al (2014c) recently performed backfield remanence curve unmixing on loess and red-clay using the method developed by Heslop and Dillon (2007), which does not require pre-defined end members. The results reveal that backfield curves of both loess and red-clay can be unmixed as two end members (Figure 10).…”