藏南沉错地区近1400年来的介形类与环境变化

Environmental Changes and Ostracoda in the Chen Co Lake of Southern Tibet in Recent 1400 Years

通过分析藏南沉错CC1孔的介形类动物群所提供的古环境信息,探讨近1400年来的湖泊演化。CC1孔介形类共计7属15种。据其属种、数量及生态特征,可划分为7个组合,同时发现1400年来沉错环境变化可分为3个时期:(1) 公元6世纪末～14世纪下半叶沉错主要为较深水湖,其中大约在708～780年和1199～1213年湖泊迅速扩大加深;(2) 14世纪下半叶～19世纪末沉错主要为浅水湖,其中大约在1454～1525年、1645～1670年和1803～1891年3个时段湖泊强烈退缩,环境极不稳定,而大约在1731～1803年湖泊发生逆向转化,湖水增多,湖面抬升;(3) 19世纪末至今沉错由较深水湖转变为浅水湖,20世纪60年代以前为较深水湖,其中大约在1929～1935年湖泊急剧加深,20世纪70年代以来湖泊退缩,湖水变浅。

The CC1 core, with a length of 216 cm, was drilled in the western part of Chen Co Lake in Tibetan Plateau. The 210 Pb and 137 Cs test indicated that it was a continuous sedimentary sequence since ca. 1400 years. A total of 15 species of ostracodes belonging to 7 genera in the core sediments had been identified. The ostracoda assemblages and their ecological features, together with the sediments dating decision were used to infer the past ca. 1400 years environmental changes as follows: (1) from the end of the 6th century to the 1370s Chen Co was a deeper water lake. The replenished water that flew into the lake increased obviously and the lake water deepened during ca. 708-780 AD; (2) from the 1370s to the 1890s Chen Co gradually became a shallow water lake. However, the lake level still experienced intensive fluctuation in this period. The lake water impetus was stronger in two stages from ca. 1454 to 1525 AD and from ca. 1803 to 1891 AD, during which sediments were subjected to disturbance, transportation and redeposition. The lake shrank and became a shallow water environment. During the stage of ca. 1645-1670 AD the lake environment deteriorated, which led ostracoda fauna not to be able to live. The lake level rose while the depth of the lake increased relatively during ca. 1731-1803 AD; and (3) from the 1890s to the present Chen Co had evolved from a deeper water lake before the mid-1960s to a shallow one at present. The lake had been shrinking since the mid-1960s and became a shallow water lake environment.