河北三河上更新统——全新统磁化率变化旋回分析

为了获取河北三河地区上更新统-全新统古气候和古环境变化，在该区实测一地层剖面，采集磁化率样品进行测试，以磁化率变化为沉积环境代用指标，在前人研究确立的地质年代框架下，运用频谱分析、演化谱分析等方法对地层垂向磁化率变化进行旋回分析。结果表明研究区冲积沉积中存在23ka的岁差尺度旋回，由于剖面较短未识别出更长周期的斜率和偏心率旋回。根据分析结果计算出剖面沉积时限为4-45ka，属于晚更新世晚期至全新世早期河流砂坝和泛滥平原沉积，平均沉积速率为24cm/ka。磁化率的变化与粒度变化具有正相关性，粗粒沉积磁化率较高、细粒沉积磁化率较低；磁化率的变化受岁差驱动气候变化影响，岁差高值时大气降水对河流补给增多，陆源碎屑增多提高了沉积物中磁性矿物的含量，反之，则磁性矿物少，磁化率低。岁差驱动气候变化在河流冲积物中的发现，为河流冲积沉积天文驱动气候变化研究提供参考依据，为第四纪冲积沉积和地质事件研究提供新的年龄约束手段。

Cyclostratigraphic analysis of the change of magnetic susceptibility based on the upper Pleistocene-Holocene strata in Sanhe, Hebei

In order to obtain the paleoclimate and paleoenvironment changes of the upper Pleistocene-Holocene in Sanhe city, Hebei province, one section was clearly measured and samples were collected at 1cm interval. Magnetic susceptibility is chosen as the parameter of environmental change. Based on the geological ages in previous studies, the cyclostratrigraphic analysis of the vertical MS change were carried out using spectral analysis and evolutionary spectral analysis. Combined with lithology and grain size, the changes of paleoclimate and paleoenvironment are discussed. The results suggest that 23ka precession cycles exist in the section, and the obliquity and eccentricity are not recognized due to the short profile. According to the results, the duration of the section is from 4 to 45ka, and the sedimentary environment are river bar and flood plain deposits from late Pleistocene to early Holocene. The average sedimentary rate is 24 cm per ka. The magnetic susceptibility (MS) of coarse-grained sediments is higher and that of fine-grained sediments is lower. The change of magnetic susceptibility is influenced by precession-driven climate change. When the precession is high, atmospheric precipitation increases the recharge of rivers, and the increase of terrigenous debris increases magnetic minerals in sediments. Conversely when the precession is low, minerals are few and magnetic susceptibility is low. The discovery of precession-driven climate change in fluvial sediments provides a reference for astronomical driven climate change study and new geological time constraint of fluvial sediments.