西藏洞错硼砂芒硝层的发现及其古气候意义

Discovery of Borax-bearing Mirabilite Beds in Tontso Lake, the Northern Tibet and Its Palaeoclimatic Significance

通过调查藏北高原腹地盐湖——洞错的Ⅰ级阶地湖相化学沉积,首次发现硼砂及赋存5层纯芒硝层的完整沉积剖面,依据韵律层的沉积特征研究和^(14)C测年,针对剖面中出现的冷相盐类矿物——芒硝,应用比较盐湖学的理论和方法,指出洞错在全新世早、中期经历了潮湿温暖期(>8470 a BP,可能至10500 a BP±)→寒冷干旱期(8470～8170 a BP)→潮湿温暖期(8170～7590 a BP)→气候频繁波动期(7590～7400 a BP,寒冷大背景下三干三湿的气候演替)→寒冷干旱期(7400～6940 a BP)→潮湿温和期(6940～6620 a BP)→寒冷干旱期(6620～6410a BP)→温暖湿润期(6410 a BP以后)的演变序列。

The Tontso, a saline lake at the center of the northern Tibetan Plateau, was chosen as a study object. Modern chemical sediments are forming in the lake without human-induced pollution. Borax in the mirabilite beds was discovered in the second bottom of the Tontso lake and a sedimentary sections with five layers of pure mirabilite was seen. This is significant for the appraisal of resources and prospecting in the area as well as palaeoclimatic and palaeoenvironmental study. Research on the five layers of mirabilite and the whole section with comparative salinology of saline sedimentary environment study confirmed that, as a cold saline mineral, mirabilite is a delicate and effective indicator for reconstructing palaeoclimate and palaeoenvironment. High-res-olution analyses based on reliable age scale sensitively rebuilt the palaeoclimatic environment in which saline chemical sediments were formed. It is pointed out that, during the early-middle Holocene (>8470-6410 a BP), a series of dry/wet and cold/warm climate changes occurred as fellows;>8470 a BP, probable to 10500 a BP?: generally warm &. wet.8470-8170 a BP: frigid &. arid (lasting 300 a).8170-7590 a BP: warm &. wet (lasting 580 a).7590-7400 a BP: frequently fluctuating (lasting 190 a). Under frigid background, a fluctuating climate of three arid and three wet periods alternating.7400-6940 a BP: frigid &. arid (lasting 540 a).6940-6620 a BP: warm &. slightly wet (lasting 320 a).6620-6410 a BP frigid &. arid (lasting 210 a).After 6410 a BP: generally warm & wet ( As the upper part of sections did not appear in this climate, the lasting time of the stage cannot be determined).The palaeoclimatic environment is fully comparative and consistent with that revealed in the synchronous records of neighbouring lakes, e.g., the retreating trace and pollen in the Chabyer Caka, drilling data in the Bangkog Co, the δ 18O value in Siling Co, pollen and diatom in Lungmu Co and Sumxi Co, and the Quaternary spreading of Stage V of arid climate (salinization) with the Qaidam-eastern Tarim area as the center in western China. Meanwhile, with high precision of sections from the Tontso, the palaeoclimate and palaeoenvironment of this period can be divided in more detail.