GEOMORPHIC CONTROLS ON FLUVIAL TRAVERTINE MORPHOLOGY

Geomorphic parameters, such as channel slope and width, influence fluvial travertine morphology. Travertine, a sedimentary rock composed of calcium carbonate (CaCO3) formed by chemical precipitation is an integral component of the ambient temperature fluvial landscape in Jiuzhaigou National Nature Reserve, Sichuan Province, China. Jiuzhaigou is listed by UNESCO as a World Natural Heritage Site and holds national and global commendations because of its fluvial stream segments separated by waterfalls over dams composed of travertine, lakes with a dramatic range of blue-green colors, and significant wetlands developed on travertine. To evaluate geomorphic controls on travertine morphology, we quantify slope and width transitions at both the watershed and local scales and examine linkages between travertine morphology and slope. Field measurements quantify local slope and flow velocity variation within a set of travertine bedforms atop a travertine dam (at "Pearl Shoals"). Analysis of a QuickBird satellite image with submeter resolution provided the basis for width measurements, analysis of a 1:100,000 topographic map (Sichuan Bureau of Surveying and Mapping) provided data for comparison to watershed scale slope, and analysis of geologic maps illustrating complex folding, faulting, and lithologic variation of underlying carbonate rocks (Zhang and Ge, 2003) allowed comparison to geologic structures. In Jiuzhaigou, geomorphic parameters influence and are influenced by fluvial travertine morphology at two discrete fluvial scales. Watershed-scale channel slope is highly variable and there is a close correspondence of relatively high slope and narrow width. Moreover, local-scale slope transitions are associated with a set of travertine bedforms that lay atop a travertine dam, which forms a prominent watershed-scale step in the longitudinal profile. Although an array of biogeochemical and hydraulic interactions influence fluvial travertine deposition, our work suggests that geologic structures and lithologic variation may be responsible for watershed scale variation in channel gradient, while the geomorphic parameters slope and width may govern the complex interactions responsible for local travertine morphology.