The Cuo E (CE) core contains the entire Quaternary stratigraphy of the Cuo E Lake (31°24′ - 31°.32′ N, 91°28′ - 91°33′E, Tibetan Plateau, China). Here, we study the magnetic properties of 1748 samples from the CE core, combined with scanning electron microscopy and X-ray energy dispersive spectrometer analysis on selected samples. The main magnetic minerals appear to be magnetite and greigite. To further quantify the presence of greigite in CE core, 84 samples were rock magnetically analyzed in more detail including: susceptibility (χ) vs. temperature, coercivity component analysis of acquisition curves of the isothermal remanent magnetization (IRM), and Principal component analysis (PCA) of the first-order reversal curve (FORC) diagrams.
The greigite content and saturation IRM over susceptibility (SIRM/χ) appear to be exponentially related. SIRM/χ can be used as greigite concentration indicator. We also propose a rapid way to identify greigite in the CE core: When the SIRM/χ value increases and anhysteretic remanent susceptibility (χARM) increases only slowly, the sample contains greigite. Samples with SIRM/χ < 15kAm-1 also obey this relation. This method has a lower limit of detection than the traditionally used SIRM/χ parameter for greigite detection. It is also faster than FORC analysis and thus particularly suitable for analysis of large sample collections. Twenty greigite-bearing layers were identified in the CE core using this method. The location of the Jaramillo subchron in the CE core is controversial in the currently available magnetostratigraphy, possibly related to the presence of greigite in this core interval.