An Example of Asymmetrical Distributary Channel Bifurcation in the Turonian Ferron Notom Delta near Hanksville, Utah
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 belts. 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 large inclined beds, ripple cross laminated sandstone, and finer grained heterolithic abandoned channel fills. Tidal and wave influence is observed locally. Levees thin away from the channel and are composed of very fine grained planar laminated and climbing ripple cross laminated sandstone.
The major channel belt has a width of about 200m and preserved thickness up to 6m. Internally it shows a multilateral pattern. Its forming channel has a minimum width about 20m and depth 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 forming channel has a minimum width about 15m and depth about 4m. Internally, it is characterized by a transition from laterally accretion pattern to vertical aggradation, which is interpreted to represent gradual filling and abandonment of the channel.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California