岩石磁学研究对萨拉乌苏组年代归属的意义

通过对萨拉乌苏组沉积物的古地磁学研究发现,该剖面沉积物保存的天然剩磁NRM和Q比值曲线与深海沉积物最后一、二次冰期及末次间冰期的氧同位素δ 18 O曲线有较好的对应关系.根据这种对应关系及深海氧同位素曲线反映的年代值推断,滴哨沟湾萨拉乌苏组的年代大致为中更新世晚期至晚更新世,即(180～10)ka,而位于底部粉砂层中的文化层,其年代应为中更新世晚期.     

Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle

The oxidation state recorded by rocks from the Earth's upper mantle can be calculated from measurements of the distribution of Fe3+ and Fe2+ between the constituent minerals. The capacity for minerals to incorporate Fe3+ may also be a significant factor controlling the oxidation state of the mantle, and high-pressure experimental measurements of this property might provide important insights into the redox state of the more inaccessible deeper mantle. Here we show experimentally that the Fe3+ content of aluminous silicate perovskite, the dominant lower-mantle mineral, is independent of oxygen fugacity. High levels of Fe3+ are present in perovskite even when it is in chemical equilibrium with metallic iron. Silicate perovskite in the lower mantle will, therefore, have an Fe3+/total Fe ratio of at least 0.6, resulting in a whole-rock ratio of over ten times that of the upper mantle. Consequently, the lower mantle must either be enriched in Fe3+ or Fe3+ must form by the disproportionation of Fe2+ to produce Fe3+ plus iron metal. We argue that the lower mantle contains approximately 1 wt% of a metallic iron-rich alloy. The mantle's oxidation state and siderophile element budget have probably been influenced by the presence of this alloy.     

Environmental magnetism and paleoclimatic interpretation of the Sanmenxia loess-paleosol sequence in the southeastern extremity of the Chinese Loess Plateau

This is a report of multi-parameter mineral magnetic results of the Sanmenxia loess-pa-leosol couplets in the SE extremity of the Chinese Loess Plateau (CLP) over the interval of L1- L13 spanning the last 1 Ma. These results show that mass-specific magnetic susceptibility (X), XARM and SIRM and their ratios exhibit parallel stratigraphic variations. Since superparamagnetic (SP) particles have significant contribution to X but no contribution to remanence, e.g., ARM and SIRM, the strong linear correlations between X and remanence (e.g., ARM and SIRM) suggest that the pedogenesis-produced magnetic grains are predominantly in small single domain range. Consequently, the significant contribution of SP particles to the bulk X as supposed in previous studies has been obviously overestimated. XARM/X data in Sanmenxia and median grain size records of typical loess sections from the hinterland of the CLP display a strong resemblance, implying that XARM/X may be regarded as a reliable indicator for monitoring the variations of ferrimagnetic grain sizes. The results of S-ratio and HIRM ((SIRM IRM-0.3T)/2) measurements indicate that there is significant enhancement of both soft magnetite/maghemite and hard hematite/goethite in paleosols associated with pedogenesis.