Paleochannel patterns inferred from alluvial deposits; a critical evaluation

Abstract Interpretation of paleochannel patterns from ancient alluvium involves reconstruction of sinuosity and degree of braiding. It is emphasized here that the geometry, flow, and sedimentary processes of the different channel patterns form a continuum, such that similarities between their deposits are more significant than differences. While many commonly cited sedimentary criteria for distinguishing channel patterns are shown to be invalid, the following are considered useful: 1) proportion of channel fills relative to lateral-accretion deposits, which increases with degree of braiding; 2) mean grain size of channel fills relative to lateral-accretion deposits, which decreases with increasing sinuosity; 3) paleocurrent variance, which may indicate sinuosity; and 4) bankfull discharge, slope, and width/depth of paleochannels throughout the channel belt, as long as they can be quantitatively reconstructed from channel-bar and channel-fill deposits. Utilization of these criteria requires examination of completely preserved sections of channel belts and overbank deposits in large outcrops. Presently existing facies models do not convey the diversity of different channel types and facies; those that are not three-dimensional and lack scales and paleocurrent information are of limited value.