Deng Chenglong

No apparent lock-in depth of the Laschamp geomagnetic excursion: Evidence from the Malan loess

The first-order chronological framework of the long-term Chinese loess/paleosol sequences was based mainly on magnetostratigraphy. However, there remain arguments on the lock-in ages of the major geomagnetic reversals. This study systematically compared the stratigraphic locations of the Laschamp excursion and Henrich events (H4 at ∼39 ka and H5 at ∼48 ka) recorded by the Luochuan loess profile in the central Chinese Loess Plateau. Results show that the Lascchamp excursion is bracketed well by these two cold events, and the corresponding estimated age is between about 41.7–43.7 ka, which is close to the widely accepted age of ∼40–41 ka for the excursion. Therefore, our new results do not suggest apparent lock-in effects in the last glacial Malan loess.

Identification of magnetic minerals in surface sediments of Miyun Lake, Beijing

Understanding the magnetic properties of natural sediments, which include magnetic concentration, composition and grain size, is fundamental in paleomagnetic and paleoenvironmental studies. Systematic magnetic measurements and non-magnetic methods (e.g., transmission electron microscopy, TEM) provide detailed information of magnetic minerals. In this paper, we established a high efficient magnetic extraction method to separate magnetic minerals from surface sediments of Miyun lake in Beijing. We analyzed the bulk samples, magnetic extracts and residues. Saturation magnetization (M-s), volume magnetic susceptibility (kappa) and saturation isothermal remanent magnetization (SIRM) of the magnetic extracts is about 85%, 75% and 70% of the bulk samples, respectively. Multiple-parameter rock magnetic measurements indicated that the major magnetic minerals in sediments are multi-domain (MD) and single domain (SD) magnetite. TEM analyses revealed detrital MD titano-magnetite, biogenic SD magnetite (magnetofossils) and authigenic superparamagnetic (SP) magnetite. We propose that the combination of rock magnetism and TEM observations is useful to accurately identify the magnetic minerals in sediments.