Channel and Floodplain Facies in a Wandering Gravel-Bed River
Published:January 01, 1987
Joseph R. Deslogest, Michael Church, 1987. "Channel and Floodplain Facies in a Wandering Gravel-Bed River", Recent Developments in Fluvial Sedimentology, Frank G. Ethridge, Romeo M. Flores, Michael D. Harvey
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Bella Coola River drains 5050 km2 of glacierized mountains on the central coast of British Columbia. Spring snowmelt and autumn rainstorm floods occur up to 1000 m3s The valley-fill is composed of Quaternary glacial and fluvial sediments, with modern alluvium representing less than 3 percent of the total volume. Proportions of light and heavy minerals in alluvial deposits indicate that headwater volcanic terrain is the dominant sediment source; however, distal tributaries draining plutonic rocks are locally important.
Sedimentation within the modern channel yields medial, lateral and point bars and vegetated channel islands. Avulsions within ‘sedimentation zones’ result in a network of slough channels. Floodplain development occurs in three ways: infilling of sloughs after channel avulsions, lateral accretion of channel bars, and overbank deposition. The most prominent facies assemblage is horizontally and trough cross-stratified sands over massive gravels. Intervening stable reaches are cobble-paved zones through which sediment is transported directly. Facies within these reaches comprise horizontally stratified sands and silts, indicating that floodplain development also occurs by vertical accretion. This association of channel zone and floodplain facies is widespread in mountain valley rivers in the northern Cordillera today. They are not aggrading and would not be prominent in the stratigraphic record.
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Recent Developments in Fluvial Sedimentology
This volume brings together 36 of the manuscripts that were presented at the Third International Fluvial Sedimentology Conference hosted by Colorado State University in August, 1985. Fluvial systems and sedimentary rock sequences discussed range in age from Holocene to Precambrian and include many diverse areas. The principal objective of the volume was to document the recent developments in the application of facies analysis to the reconstruction of the architecture of fluvial systems. Reconstruction of architecture is an integral part of the overall process of basin analysis.