Facies Architectural Study of a Distributary Channel System in the Ferron Notom Delta, Southern Utah, U.S.A

Li, Yangyang; Bhattacharya, Janok
University of Houston, Houston, TX.

Delta distributary networks result from successive downstream bifurcations, which split the river discharge and sediment load. Distributary channel bifurcations are commonly uneven, forming asymmetrical channel belts. Asymmetrical bifurcations are ubiquitous and well documented in modern delta studies. Detailed facies architectural studies of ancient outcrop examples, however, are uncommon. This paper documents the geometry and facies architecture of one such example.

A gooseneck-shaped canyon provides 3-D outcrop exposure of a major and subordinate channel belt. The channel belts and their associated levee deposits were correlated and mapped through 27 measured stratigraphic section, high resolution photomosaics, and bedding diagrams. Both channels show an erosional base and are mainly filled with medium-grained, cross-bedded sandstone, meter-scale inclined beds, ripple-cross-laminated sandstone, and finer grained heterolithic abandoned channel fills. Tidal and wave influence is observed locally. Levees thin away from channels and are composed of very fine-grained, planar-laminated and climbing-ripple cross-laminated sandstone. Crevasse splay deposits occur where the subordinate channel become unconfined, and are characterized by a general coarsening upward succession consisting of wave rippled, current rippled and planar bedded very fine grained sandstone with minor erosional surfaces.

The major channel belt has a width of about 200m and preserved thickness up to 6m. Internally it shows a multilateral pattern. The formative channel has a minimum width about 20m and depth of about 5m, as estimated from preserved channel and bar forms. The subordinate channel belt, which splits from the major channel belt, has a width of about 60m and thickness up to 4.5m. Its formative channel has a minimum width of about 15m and depth of about 4m. Internally, it is characterized by a transition from laterally accretion to vertical aggradation, which is interpreted to represent a transition from active to passive channel filling.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012