【作者】 王书兵；

【导师】 蒋复初；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2005， 博士

【摘要】 对川西黄土进行了岩石地层学、磁性地层学和年代地层学研究。金川黄土以马厂剖面发育最好,黄土-古土壤序列厚15.5m,据岩性、磁性地层,结合磁化率特征可划分为:冰后期S0古土壤,末次冰期L1黄土、末次间冰期S1古土壤、倒数第二冰期L2黄土、倒数第二间冰期S2古土壤等五个成因地层单位。其中S1复合古土壤又可细分为S1SS1、S1LL1、S1SS2、S1LL2和S1SS3等五个次级地层单位。磁性地层结果显示样品全部为正极性,剖面中末出现B/M界线。金川黄土沉积始于中更新世晚期,大约为200kaBP。理县黄土以喇嘛寺剖面最具代表性,其黄土-古土壤序列厚7.3m,自上而下划分为:冰后期S0古土壤,末次冰期L1马兰黄土和末次间冰期S1古土壤。结合热释光年龄,理县黄土-古土壤序列形成于130kaBP。甘孜县城附近雅砻江河谷宽广,各级阶地上均有黄土分布。系统研究了满地和新市区两剖面,它们分别厚23.7m和26.0m。据岩性、磁性地层特征和磁化率测定和光释光测年结果,甘孜黄土可划分为冰后期S0古土壤,末次冰期L1黄土和末次间冰期S1古土壤等三个地层单位。其中,S0为复合型古土壤由S0SS1古土壤、S0LL1黄土和S0SS2古土壤组成;L1黄土又可细分为L1LL1、L1LL2、L1LL3和L1LL4黄土和L1SS1、L1SS2和L1SS3复合型古土壤等七个次级地层单位;S1古土壤在研究剖面上保存不全,上部为发育成熟的古土壤,其磁化率值高,下部为成壤较弱的黄土,磁化率值较低,只能将其分为S1SS1和S1LL1两个次级地层单位。古地磁结果显示,布莱克反向极性亚时记录于底部S1LL1黄土中。甘孜黄土沉积始于晚更新世早期,大约为120kaBP。对川西中部理县黄土、金川黄土、甘孜黄土进行了环境指标的综合研究,并与印度季风、格陵兰冰芯和深海氧同位素记录进行了对比。结果显示磁化率记录的古气候变化,与深海氧同位素曲线变化有较好的一致性,是对全球冰期气候旋回的响应。碳酸盐含量可作为川西高原夏季风的指代指标,与印度季风强度变化基本保持一致;中值粒径是高原冬季风强度的良好替代指标,与印度季风记录耦合关系好于冰芯和深海氧同位素记录。川西中部200kaBP以来的环境演变分为以下几个阶段:①200-189.61kaBP期间夏季风盛行;②189.61-129.84kaBP,以冬季风占主导地位,在140-155kaBP,夏季风异常强大;③129.84-73.91kaBP,冬、夏季风交替显示“三峰两谷”的特征;④73.91-58.96kaBP,冬、夏季风均比较强盛;⑤58.96-24.11kaBP,早期冬、夏季风同步增强,为极端冷湿的气候环境;晚期夏季风盛行;⑥24.11-12.05kaBP,以冬季风占主导地位;⑦12.05-0kaBP,早期是冬季风盛行凉湿气候环境;之后进入全新世高温期;最后为新冰期阶段。晚更新世以来,川西中部发育了一系列的湖相沉积,并先后消失。较场湖相台地沉积物厚101.1m,其中湖相层厚97.0m,上覆黄土厚4.1m;湖相层结束于约10kaBP。加珺湖积层、大平村湖积层和马尔康饶巴湖积层厚度分别为7.6m、44.8m和11.4m。磨西台地形成于全新世时期。晚更新世(约120kaBP至10kaBP期间)是川西中部地区盛行湖相堆积的时期。运用地貌学方法对大渡河、岷江阶地进行了分析。大渡河共发育12级河流阶地;上游河流阶地保存较好,向下游保存状况稍差;其中Ⅰ、Ⅱ、Ⅲ级阶地分别形成于10～20kaBP、30～50kaBP、100～170kaBP,Ⅻ～Ⅳ级阶地形成于早、中更新世。岷江中游发育9级阶地,其中Ⅱ、Ⅲ级阶地分别形成于10kaBP、20～30kaBP。川西中部地区在200kaBP以来发生了三次新构造运动。第一次起始于200kaBP,结束于120kaBP;它导致川西中部气候环境发生重大分异;第二次发生在大约30-50kaBP期间,与川西中部极端冷湿环境的出现一致;最近一次发生在大约10kaBP前后。更多还原

【Abstract】 A preliminarily lithostratigraphic and magnetostratigraphic study of loess in the central western Sicuan Plateau shows that the loess deposition commenced at 200 kaBP, and began to spread out extensively during 120-130 ka B.P. The loess strata in this area can be divided into five units as followings: the postglacial paleosol S0, the last glacial loess L1, the last interglacial paleosol S1, the next to the last glacial loess L2 and the next to the last deglacial paleosol S2. Specifically, the thickness of the loess-paleosol couplets varies at different area.In this thesis, synthesized analyses of paleoenvironmental indicators of loess in the central western Sicuan Plateau are carried out. Magnetic susceptibility, which is regarded as a primary proxy of pedogenic intensity and/or dust accumulation rate, display a high coherency with the deep-sea oxygen isotope records. The carbonate content used as a proxy of the summer monsoon, keeps in line with the Indian Ocean monsoon as reflected by the median lithogenic grain size variations in RC27-61 core. While the median grain size, which is adopted as a proxy of the winter monsoon, shows a higher correlation to the Indian Ocean Monsoon than that to the GRIP records and the deep-sea oxygen isotope records.The paleoclimatic oscillations in this region can be reconstructed as the following stages:①during the time of 200-189.61kaBP, the summer monsoon was dominated;②during the period of 189.61-129.84kaBP, the winter monsoon was dominated with exceptional warmth and humidity during 140-155kaBP;③during the time of 129.84-73.91kaBP, the enhanced summer monsoon and declined winter monsoon displayed the characteristic of“three peaks with two troughs”;④during the period of 73.91-58.96kaBP, the enhanced summer monsoon alternated with the enhanced winter monsoon;⑤during the time of 58.96-24.11kaBP, the enhanced winter monsoon coupled with enhanced summer monsoon at the first sub-stage, showing an extremely cold and humid environment; then the winter monsoon subdued and the summer monsoon began to dominant;⑥during the period of 24.11-12.05kaBP, the winter monsoon was dominated;⑦during the stage of 12.05-0kaBP, the winter monsoon prevailed at the beginning, and then followed by the altithermal period of the mid-Holocene. After that, the Neoglaciation began.During the late Pleistocene, a series of paleolake formed on the central western Sicuan Plateau. The thickness of the lacustrine deposits varies at different place, e.g., the thickness at Jiaocang reaches over 98 m, and only 7.6 m at Jiajun. Furthermore, the thickness of the Taiping lacustrine deposits and the Raoba lacustrine sediments are 44.8 m and 11.4 m respectively. The Moxi terrace formed during the Holocene. The period of 120kaBP-10kaBP is the reign of lacustrine formation on the central western Sicuan Plateau.There are 12 terraces of the Daduhe River, among which T1, T2 and T3 formed at 10～20kaBP, 30～70kaBP and 100～170kaBP respectively, and T4-T12 formed between the Early Pleistocene and mid-Pleistocene. There are 9 terraces of the Min River, among which T2 and T3 formed at 10kaBP and 20～30kaBP respectively.There are three neotectonic movements in the central western Sicuan Plateau during the late Pleistocene. The first one began from 200kaBP, ended at 120kaBP. The second one and the last one occurred during 30-50 ka BP and 10kaBP respectively.更多还原