他念他翁山中段第四纪冰川沉积物时空分布特征与环境

Spatiotemporal characteristics and the environment of Quaternary glacier deposits in the middle Tenasserim Chain

他念他翁山中段位于横断山脉西部,保留着良好的第四纪冰川遗迹,论文以该地区第四纪冰川沉积物为主要研究对象,通过光释光(Object-source lighting, OSL)测年、粒度、磁化率、矿物及化学元素分析等方法,探讨研究区第四纪冰川沉积物在不同时期的沉积学、矿物学、环境磁学以及元素地球化学特征,结合相关环境指标分析该区的环境特点。研究表明:①冰川沉积物总体沉积特征是大小混杂、无层理、无分选、风化程度由倒数第二次冰期到新冰期依次减弱。②研究区冰川沉积物细粒部分在粒度频率曲线上主要呈现双峰或多峰,反映出沉积物的物质来源复杂、形成动力多样。冰碛物的平均粒径在空间上表现出距冰川作用源头越远粒径越小的规律,主要是受冰川作用强度和风化时间长短的影响。③冰川沉积物的磁化率值为8.72×10-8~298.00×10-8m3·kg-1,其中冰水沉积物磁化率的平均值(178.51×10-8m3·kg-1)和波动幅度(17.43×10-8~298.00×10-8m3·kg-1)要大于冰碛物(平均值19.82×10-8m3·kg-1,波动幅度8.72×10-8~42.95×10-8m3·kg-1),反映出磁铁矿集中分布的粒级与冰水沉积物组成的粒级相似。④地球化学和矿物学指标反映青古隆地区古气候的总体特征为寒冷干燥,其中在末次冰盛期时气候最为干旱,末次冰期中冰阶时气候较为干旱、降水量相对于末次冰盛期有所增加,倒数第二次冰期降水量相对于末次冰盛期和末次冰期中冰阶较多,但气温较低。

Vestige of the Quaternary glaciation is well preserved in the middle Tenasserim Chain located in the west of the Hengduan Mountains.In this study,we investigated Quaternary glacial deposits in this area using the methods of luminescence dating,grain size,magnetic susceptibility,and mineral and chemical elements analyses,discussing the characteristics of sedimentology,mineralogy,environmental magnetism,and element geochemistry aspects of Quaternary glacial deposits during different periods in the study area.We also combined the related environmental indicators to analyze the environmental characteristics of this area.The results display that:1)The overall sedimentary characteristics of glacial sediments are mixed size,no bedding,no sorting,and the degree of weathering weakened from the MIS6 to the MIS1.2)Fine particles of glacial deposits in the study area show bimodal and multimodal spectra in frequency curves,which reflects that glacial deposits have complex sources.The average grain size of moraines shows that the farther away from the source of glaciation,the smaller the grain size-it was mainly affected by the intensity of glaciation and the duration of weathering.3)The magnetic susceptibility of glacial deposits in the study area ranges from 8.72×10-8 m3·kg-1 to 298.00×10-8m3·kg-1.The average value(178.51×10-8m3·kg-1)and amplitude of fluctuation(17.43×10-8-298.00×10-8m3·kg-1)of the magnetic susceptibility of ice water deposits are greater than moraines(average value:19.82×10-8m3·kg-1,amplitude of fluctuation:8.72×10-8-42.95×10-8m3·kg-1),which reflects that the grain size of centralized distribution of magnetite is similar to the grain size of ice water deposits.4)The analysis of geochemical indicators of elements and minerals show that the overall characteristics of the paleoclimate in the Qinggulong area was cold and dry;the climate was the driest during the MIS2,but precipitation of the MIS3 b was higher.The precipitation of MIS6 was more than the MIS2 and MIS3 b,but the temperature was lower.