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Rhythmic Climbing Ripple Lamination in from Inclined Heterolithic Stratification of Estuarine Intertidal Channel in the Macrotidal Gomso Bay, West Coast of Korea

Choi, Kyungsik 1
1 Earth Systems and Environmental Sciences, Chonnam National University, Gwangju, Korea, South.

Well-developed rhythmic climbing ripple lamination (RCRL) is a key constituent of inclined heterolithic stratification (IHS) in a point bar of tightly meandering estuarine intertidal channel in the macrotidal Gomso Bay, west coast of Korea. The IHS is about 3 m thick and dips into channel with angles ranging from 4-10o. RCRL is as thick as 1.5 m and constitutes middle to lower part of the IHS, occurring mainly between mean neap low and high water level. RCRL consists of mud-draped cross laminae that are continuous along strike-direction of channel for 10-20 m. Wavelength and height of ripple cross laminae are 15-25 cm and 1-3 cm, respectively. Climbing patterns are both supercritical and subcritical. RCRL demonstrate rhythmic change in cross laminae thickness, encompassing various hierarchical tidal cycles, such as diurnal inequality, synodic neap-spring tidal cycle and anomalistic high-low spring tidal cycle. Sedimentation rate inferred from RCRL reaches up to 14 cm per month. Flow directions inferred from RCRL are unimodal with a low variation at one locality. Due to the presence of mutually evasive tidal current pattern, however, they are spatially variable depending on the location within point bar. RCRL on the floodward side of point bar is dominantly ebb-oriented, whereas that on the ebbward side of point bar is mostly flood-oriented. With overall ebb-dominance, master bedding of the IHS inclined toward ebb. As a result, RCRL at the ebbward end of point bar demonstrates up-dip migration on the master bedding of IHS. Series of aerial photographs and temporal measurement of channel profile as well as pervasive occurrence of RCRL confirm that tidal channels in the Gomso Bay have been highly mobile to form extensive channel-related facies. The presence of RCRL coupled with IHS within ancient sedimentary record can be considered as an unambiguous indicator of point bar at tight meander bend in an actively meandering intertidal channel probably within macrotidal setting, where tidal asymmetry is greatest.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009