The Karsts of Yunnan

Yunnan is the most westerly province of S China and nearly 26% of the whole province of 97 000 km2 is karstic. The easterly parts of Yunnan form the western sectors of the Yangtse platform with folds generally NE-SW and NNE-SSW. However, from Kunming, the capital of Yunnan, westwards, the structure lines are N-S or NNW-SSE (Figs. 3 and 4). Western Yunnan is the region where the eastern Himalayas and the mountains of Assam and Burma impinge on the South China paraplatform and where high ridges separate the deep valleys of the rivers which have risen in Tibet — the Mekong, Salween, and Irrawaddy and the Red river which flows to Hanoi. There are three main areas of karst in Yunnan: (1) in the west and south in the N-S ranges adjacent to the Burmese and Vietnam borders; (2) the graben or karst basins aligned N-S in the Kunming and Nanpan river areas; (3) the undulating plateau area in E Yunnan which is a continuation of the Guizhou plateau, but at a higher altitude where the famous “Stone forest” of Lunan is situated. The Indo-Sinian (or Neo-Cathaysian) folds affected the rocks in Yunnan as they did in Guizhou and Guangxi. However, the effects of the Cenozoic and later the Quaternary uplifts are much greater in Yunnan than in the more easterly provinces. The proximity of W Yunnan to SE Tibet is the most important aspect of the relief. Carbonate rocks of the Palaeozoic and the Triassic are predominant in E Yunnan; in W Yunnan, the carbonates are mainly Permian and Triassic, but in some areas, older metamorphic limestones (Ordovician) occur, as at Dali.