末次间冰期以来洛川黄土天然剩磁记录的可靠性

地磁倒转和漂移不仅是研究地球动力学的重要手段之一,也能使地磁年代框架更加准确。通过对洛川黄土剖面L1、S1进行详细的岩石磁学、古地磁研究,结果表明:L1、S1中主要的载磁矿物是磁铁矿,但赤铁矿也可能携带稳定的特征剩磁;洛川黄土剖面能够记录Blake漂移,并发生于(123±2)ka。通过S1中1 092~1 240cm处6套平行样品的古地磁结果,表明洛川黄土难以记录Blake漂移的形态学特征;L1未记录到Mono Lake和Laschamp漂移,但是在175cm处识别出1次明显的地磁异常事件,年代约17.9ka。我们认为该地磁异常事件应为Hilina Pali/Tianchi漂移。此外,导致同一极性事件在不同地区记录产生差异的可能原因有中国黄土存在千年尺度的沉积间断、较低的沉积速率及黄土剖面所处地理位置的不同。同一剖面平行样品间地磁漂移形态学存在差异,可能是由于极性漂移期间较低的古地磁场强度抑制了黄土剩磁记录能力所致。

The Reliability of the Natural Remanet Magnetization Recorded Since the Last Interglacial in Luochuan Loess

The study of the paleomagnetic reversal and excursion events is not only one of the important methods to study the geodynamics, but also can ensure the framework of the paleomagnetic timescale more accurate.In this study, high resolution and multi-sets of parallel samples were collected in the Luochuan loess section.By detailed rock magnetism and paleomagnetic analysis, it can be conclude thatthe main magnetic carrier of L1, S1 in the Luochuan loess section is magnetite, and the hematite may also carry stable characteristic remanence in few samples.The Blake excursion event have been identified in the lower part of S1with an age of about (123±2) ka.Six subsets of parallel samples at 1 092～1 240 cm in S1 have also been measured.The paleomagnetic results show that the Luochuan loess might record the Blake excursion event,but the morphology within the polarity excursion is rather questionable.The Mono Lake and Laschamp geomagnetic excursion events have not been identified in L1.There are 3 samples at 175 cm can record an obvious geomagnetic anomaly.It can be considered that the geomagnetic anomaly can be compared with Hilina Pali/ Tianchi geomagnetic excursion.In addition, the fact that one polarity event displays different morphology recorded in different regions in Chinese Loess Plateau may be caused by such several factors, as millennial scale depositional break in loess, low loess deposition rate, geographical location of different loess sections.Moreover, the reason why parallel samples from one section display different morphology may be lower relatively ancient magnetic field intensity which could reduce the alignment of magnetic carriers along the ancient geomagnetic field while dust deposition.