Sedimentation in macrotidal estuary
Speaker:
Ming-Wei Liao
Date:2012/12/27Abstract
An occurrence of inclined heterolithic stratification (IHS) is described from a tidal point bar in a 40-m-deep distributary of the macrotidal (tidal range 3.6–7.8 m), Han River delta, Korea. The vertical succession of IHS is approximately 25 m thick and dips into the channel with angles reaching 14° and consists of interstratified fine sand, sandy silt, and silt with an upward-fining textural trend. Tidal rhythmites are well developed in the middle and upper intertidal zone, and may also be present in the subtidal zone, but are poorly developed near the low-water level because of wave action.
Well-developed rhythmic climbing-ripple cross-lamination (RCRL) was described from estuarine tidal channels in Gomso Bay, west coast of Korea. Associated with upper intertidal point bars of closely spaced meandering channels, RCRL occurs between mean sea level and mean neap high-water level. RCRL is typically less than 40 cm thick, and constitutes the upper part of fining-upward channel-fill successions. Climbing patterns are dominantly supercritical and less commonly subcritical. Flood-oriented RCRL is developed in the landward part of ?the meander bend, while ebb-oriented RCRL is developed in the seaward part. RCRL demonstrates rhythmic change in cross lamination thickness, which resembles various hierarchical tidal cycles, such as diurnal inequality, synodic neap–spring tidal cycle, and anomalistic tidal cycle. These study highlight the significance of well-preserved tidal rhythmicities in the reconstruction of paleodepositional environment and paleoelevation in terms of tidal frame.