Preliminary lithofacies studies of upper Paleozoic rocks in Yunnan, Guizhou, and Guangxi Provinces indicate three stages of crustal change, beginning in the Devonian.

1. In the slow-transgression stage, up to 5,000 m of Devonian sediment was deposited on the fault blocks resulting from Caledonian deformation. In the East Yunnan-central Guizhou area and in the foreland of the elevated Jiangnan, these fault blocks formed narrow, rapidly subsiding zones or troughs. Bioherms, commonly developed along the boundaries between elevated and depressed blocks, account for the lateral distribution of the source and reservoir rocks.

2. In the extensive-transgression stage, open-marine continental-shelf sediments predominate. No rocks of marginal facies have been reported. On some elevated areas, bioherms are present. During the Dongwu movement between the Early and Late Permian, basalts were extruded along the Xiaojiang fault and the whole area was gradually uplifted, ending the transgression.

3. In the slow-regression stage, sedimentation was progressively restricted to the topographic lows in the eastern part of the area. The platform margin is very narrow and bioherms are well developed. Analysis of widespread oil and gas shows suggests that exploratory efforts should be directed first to this area.

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