Inclined heterolithic stratification in a mixed tidal-fluvial channel: Differentiating tidal versus fluvial controls on sedimentation
Tidal and fluvial processes control deposition and determine the sedimentological and ichnological character of sediments in the mixed tidal-fluvial Middle Arm, lower Fraser River, Canada. Sedimentological trends that define the mixed tidal-fluvial zone include: 1) mud beds present from the intertidal zone to the base of the channel, 2) a downstream increase in the number of mud beds, and 3) a lateral mud-sand-mud profile developed in the intertidal zone of each bar. Non-rhythmic deposition of sand under conditions of elevated river discharge is apparent, although sand beds are interbedded with cm- to dm-scale mud beds deposited during periods of low river discharge and increased tidal influence. In rare cases, mm- to cm-scale rhythmically alternating sand and mud lamina are deposited in successions of 12-14 beds (tidal rhythmites).