中文摘要：

塔里木盆地的高分辨率环境记录对于理解西部干旱乃至全球变化至关重要。湖泊沉积物的磁学参数能够记录沉积环境和古气候信息。罗布泊地区是受西风影响的典型区域。本文选取罗布泊Ls2孔7.1Ma以来长度达1050.6m的沉积物进行详细的岩石磁学与环境磁学研究。结果表明,磁铁矿和赤铁矿是沉积物中主要载磁矿物。钻孔底部和上部的沉积物磁铁矿含量相对较高,中部强磁性矿物浓度降低导致赤铁矿占主导。磁性矿物以PSD（pseudo-single-domain）颗粒为主,并含有极少量的SP（super-paramagnetic）颗粒。罗布泊Ls2孔的S-ratio比值表明,7.1-5.6Ma气候为相对较干旱和相对较湿润交替出现,5.6-3.6Ma干旱化加剧,3.60-0.74Ma有所缓和,0.74-0Ma干旱化最为强烈,其中5.1Ma和3.6Ma是两个明显的转折点。多磁学参数表明,晚中、上新世以来罗布泊地区的磁性矿物含量的变化,可以反映罗布泊地区气候渐进式的干旱化过程。

英文摘要：

Late Cenozoic fluvio-lacustrine sediments of the Tarim basin are good archives of the paleoclimatic changes in Asian interior.The analysis and interpretation of changes in mineral magnetic signatures from a long Ls2 core（1050.6m in long;39° 46′N,88°23＇18.2″E） recovered from Lop Nur in the northeast Tarim basin in 2004 spanning a timescale of approximately the last 7.1Ma years is reported by Chang et al.[19].A suite of mass specific susceptibility and magnetic remanence measurements were made at regular intervals of 100cm on 1056 samples.Rock magnetic measurements revealed that magnetite and hematite are the dominant magnetic minerals.Magnetite of PSD-size was identified as the main magnetic carrier minerals by temperature-dependent measurements of saturation magnetization and determination of hysteresis parameters. Based on detailed rock magnetic measurements like magnetic susceptibility versus high/low temperature curves,thermal demagnetization curve,hysteresis loops and FORC diagrams,we have investigated the magnetic properties of Lop Nur Ls2 core sediments.The abrupt decrease at about 580℃ in X-T curves revealed that magnetite could be the dominant magnetic mineral in the sediment.What is more,some samples showing decrease after 685℃ revealed hematite signal.FORC diagram displayed a PSD characteristic.Hysteresis loop showed a subtle wasp waist characters which is due to admixture of different coercivity minerals.This could be magnetite and hematite. HIRM and S-ratio records indicate four intervals of hematite variations.Hematite concentration in the Lop Nur fluvio-lacustrine sediments is closely linked to the oxidation of magnetite.From 7.1Ma to 5.6Ma,hematite concentration is relatively low,consistent with a high lake level with weak oxidation of magnetite under a relatively humid climate.Hematite concentration increases from 5.6Ma to 3.6Ma,showing enhanced oxidation of magnetite.This implies strengthened aridification and deceased lake level.From 3.60Ma to 0.74Ma,slight decrease in hematite c