晚第四纪湖泊沉积物盐类与碎屑矿物反相关关系的沉积学解释

湖泊沉积物中矿物组合是古气候环境研究的敏感性指标之一,充分认识湖泊沉积物中各类矿物组合类型、沉积过程,对正确解释矿物学指标有重要意义.我国晚第四纪湖泊沉积记录中,盐类矿物与碎屑矿物含量普遍存在反相关关系,影响了矿物组合作为气候指标的解释和应用.从地球科学的角度正确理解这种关系,可以为湖泊动力学以及古气候环境定量研究提供重要的科学依据.选择甘肃民勤盆地石羊河下游终端湖猪野泽不同位置5个全新世剖面,在明确湖泊沉积物来源、搬运方式和沉积动力机制的基础上,研究了以碳酸盐矿物为主的盐类矿物含量与粒度指标之间的关系.结果表明:猪野泽各剖面砂层富含的中砂、细砂沉积物主要是来自于巴丹吉林沙漠和腾格里沙漠的风成砂;水动力作用主导了湖相沉积层200μm以下沉积物的沉积,风力作用对20~70μm粉砂组分沉积也有所贡献.同时,猪野泽湖相沉积层中高含量的碳酸盐主要来自于流水搬运,湖相沉积层位200μm以下的粉砂和极细砂是碳酸盐的主要富集区.综上所述,干旱区湖泊沉积物中盐类矿物含量与其沉积过程密切相关,盐类矿物在全球变化研究中的应用要建立在充分研究其沉积动力机制的基础上.

A sedimentological interpretation of the inverse correlation between saline mineral and detritals mineral in the Late Quaternary lake sediments

Mineral assemblages in lake sediments are sensitive indicators of palaeoclimates, whose types anddeposit processes have important significances to interpretations of mineralogical proxies.The ubiquitous inverse correlation between saline minerals and detrital minerals in the Late Quaternary lake sediments has disturbed the interpretation and application of mineral assemblages as a paleoclimate proxy. A correct understanding of the relationship from the perspective of earth sciences can provide important scientific basis for hydrodynamics of lake and quantitative research of palaeoclimate. In this paper,five sections from different positions of Zhuye Lake (Sections QTH01, QTH02, XQ, SKJ and JTL) were chosen to conduct a comparative study on saline mineral contents and grain sizes in order to make clear the sedimentary models of saline minerals and detrital mineralsunder different hydrodynamic conditions. The results revealed that in the aeolian layers, sediments above 200 μm mainly are aeolian sands from the Badain Jaran Desert and the Tengger Desert. In lake sediments, wind force slightly contributes to the deposition of silt between 20 μm and 70 μm, but silt and sand under 200 μm are dominated by hydrodynamic effect, and carbonate mineral enriches in this grain size interval. Meanwhile, sedimentary processes of saline mineral show different patterns under different sedimentary conditions. Sedimentary environment at Sections QTH01 and QTH02 was stationary, and carbonate content was significantly high; Section XQ had strong hydrodynamic condition. At the same time, Sections SKJ and JTL were far away from the estuary, and carbonate content was relatively low. Sedimentary environment at Sections QTH01, QTH02 and XQ were dominated by runoff, where there was high value of carbonate content in the lake sediments corresponding to a finer average grain size; Sections SKJ and JTL were influenced by local environment, so the high value of carbonate content was corresponding to coarse particles. Above all, saline mineral contents in lake sediments of arid areas were closely related to the sedimentary process; therefore, the application of the saline minerals in global change research should be established on the basis of the full study of the sedimentary dynamic mechanism.