Tidal drawdown: A mechanism for producing cyclic sediment laminations in glaciomarine deltas

A process for generating sediment laminations by tide-controlled storage and release of delta-plain sediment is described, using data from two glacier-fed deltas in Glacier Bay, Alaska. Intertidal mudflats and lower channel reaches store fluvial bed load and suspended load when the lower delta plain is flooded, which occurs periodically during spring intervals and continuously during neap intervals. Spring lower low tides expose the channel mouths at the delta lip and the entire delta plain, which causes abrupt transport pulses of stored sediment into the basin. Each pulse and ensuing flood tide forms a coarse and fine laminated couplet in the fjord-head basin. Neap-generated deposits are either structureless or faintly laminated.