塔里木盆地的环境格局与绿洲演化

塔里木盆地是中国最大的内陆盆地,它经过长期海陆变迁和盆山耦合作用形成。从元古代到晚二叠纪,一直处于海洋环境,几经海侵海退,有大量海相沉积。从二叠纪末开始,全区抬升,海水退出,盆地进入陆地发展阶段,以湖相和河流相沉积为主,仅在西部边缘有泻湖相沉积;至渐新世,印度板块与欧亚板块在帕米尔地区碰撞拼合,盆地彻底与古特提斯海分离,形成统一的内陆盆地。盆地的气候环境从晚白垩世就已向干热发展,形成了广泛的红色沉积和膏盐;上新世以来,青藏高原及其他山地快速隆升,对盆地的环境格局产生重大影响,盆地腹地出现荒漠化,风成沙堆积面积扩大;第四纪时,干旱化气候进一步加剧,塔克拉玛干沙漠逐渐形成;一些天然绿洲在盆地周围和河流流域相伴而生,从而奠定了今天塔里木盆地的环境格局。古时绿洲大部分是丝绸之路的连接点和集结地,在距今约2000年前的汉朝还比较繁荣,后来变成了废墟和荒漠,塔克拉玛干沙漠的南缘向南推进约100～150km,而注入盆地(沙漠)的河流向上游收缩几百公里。

EVOLUTION OF THE ENVIRONMENTAL FRAMEWORK AND OASIS IN THE TARIM BASIN

The Tarim Basin is the largest inland basin in China, and it was formed by coupled basin-orogen development. From the Proterozoic era to the Late Permian, the Tarim Basin was dominated by marine environment, having experienced several cycles of regressions and transgressions with abundant marine deposits. From the Late Permian, regional uplift occurred in the Tarim Basin with seawater regressed, and continental deposits dominated. In this period of time a few lagoons developed in the western margin of the basin. To the Oligocene, the Indian Plate collided and integrated with the Eurasian Plate in the Pamirs, the Tarim Basin was completely separated from the Tethys, and became a continental basin. The climate of the Tarim Basin changed to become hot and dry in the Late Cretaceous, and widespread red beds and salts deposits developed. With quick uplift of the Qinghai-Xizang Plateau and other mountains in the Pliocene, the climate over the Tarim Basin changed; desert came into hinterland, and the aeolian deposits extended. In the Quaternary, drought tended to be more and more serious, and the Taklimakan Desert formed. Some oasis occurred in the margins of the desert, and the nowadays environment framework of the Tarim Basin developed. The former oases were the key locations along the Silk Road, which thrived in the Han Dynasty at 2000 years ago. Later the southern boundary of the Taklimakan Desert expanded about 100-150km south, and the former oases diminished. The inward flowing rivers have been shortened for several hundred kilometers.