REGIONAL ANALYSIS OF PALEOGEOGRAPHY, DOLOMITE DISTRIBUTION AND BEDROCK CONTROL ON RIVER GEOMORPHOLOGY FROM REMOTE SENSING DATA, NANPANJIANG BASIN, SOUTH CHINA

The Nanpanjiang Basin spans 275,928 km² at the intersection of Guizhou, Guangxi, and Yunnan and is characterized by marine carbonate platforms and siliciclastic turbidite basin facies. Faulted synclines and anticlines dissect the region with NW trends in western Guizhou and N-S trends in eastern Guizhou. Previous studies have not delineated paleogeography and dolomite distribution on a regional scale as attempted in this study. Bedrock control on the evolution of river systems in the region has received little attention in previous studies.

Basinwide mosaics were constructed from LANDSAT imagery and SRTM DEM data. The DEM data were used to generate slope, flow direction, flow accumulation, and stream networks. An existing geologic map was georeferenced and reprojected. ASTER data were mosaicked for several chosen study areas in the basin. Several ASTER SWIR band ratios were used to estimate dolomite distribution.

The contrast between tower karst topography of shallow-marine carbonates and stream-eroded deep-marine siliciclastic turbidites delineates the Yangtze Platform and isolated carbonate platforms in the basin. ASTER data suggests greater distribution of dolomite near the margins of platforms, although this distribution does not precisely match the geologic map.

The Dabang River largely follows the northwest-trending synclines and avoids highly cemented limestones such as those of the Upper Permian. Within less resistant siliciclastic facies in the axis of synclines, the river forms lower slopes (1% to 14% rise). Where the Dabang crosses resistant Lower Triassic dolostone, it forms steep slopes (up to 130% rise) and cascades of falls. The Beipanjiang is an antecedent river that is incised through several major structures and resistant carbonate units forming exceedingly narrow and steep gorges (up to 251% rise). Only in small areas does the Beipan follow a less-resistant strata contouring structure. In eastern Guizhou, major rivers generally follow N-S synclines, except for small parts of the Dongtuo and Nali, where they cut across structure and are deeply incised. Parts of these rivers disappear underground and re-emerge. The Nanpan and Hongshui flow primarily through siliciclastic turbidite facies of the basin and have gentler slopes (under 5%) and more dendritic drainage.