Sedimentation Rate and Sedimentary Break in Tidal Deposits

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Based on the study of tidal laminae of non tidal inlet in the Wenchang Formation of northern Zhejiang Province and at the muddy coast facing open sea in the Yangtze Delta region,the sedimentation rates have been calculated,which are close to that of similar study abroad.Field observation and research of coast pragradation rate and tidal flat sedimentation show that the calculated sedimentation rates are unreasonable.The investigation of present tidal flat in the Yangtze Delta reveals that tidal laminae are formed and reworked during a simidiurnal tidal cycle,and laminae preserved in the layer of sixteen days observation cover only 10% of that could be formed,other 90% have been eroded.The small sequence composed of sandy and muddy layers is a storm sequence,which is formed in the condition of alternation of storm and calm weather.Preservation of the small sequence covers about 10% of that could be formed,and other 90% are reworked.The laminae in the small sequence disappeared when the sandy and muddy layers eroded,so that the laminae preserved in tidal flat sequence are only 0 2% of that could be created.Reworked laminae and layer only have erosion surfaces,i.e.diastems.The attention should be paid to the sedimentary breaks,when we are doing high resolution study of the tidal deposits.

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Marine Geology and Quaternary Geology, v. 19

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