Fruergaard, Mikkel5; Pejrup, Morten6; Murray, Andrew S.4; Andersen, Thorbjørn Joest5
1 Geography, Department of Geosciences and Natural Resource Management, Faculty of Science, Københavns Universitet2 SCIENCE Dean's Office, SCIENCE Faculty Office, Faculty of Science, Københavns Universitet3 SCIENCE Faculty Management, SCIENCE Faculty Office, Faculty of Science, Københavns Universitet4 Nordic Laboratory for Luminescence Dating, Risø, DK-4000 Roskilde5 Geography, Department of Geosciences and Natural Resource Management, Faculty of Science, Københavns Universitet6 SCIENCE Faculty Management, SCIENCE Faculty Office, Faculty of Science, Københavns Universitet
We investigate the processes responsible for bleaching of the quartz OSL signal from tidal channel sediment. Tidal dynamics are expected to play an important role for complete bleaching of tidal sediments. However, no studies have examined the amount of reworking occurring in tidal channels and on tidal flats due to the mixing caused by currents and waves. We apply bed level data to evaluate the amount of vertical sediment reworking in modern tidal channels and at a tidal flat. Cycles of deposition and erosion are measured with a bed level sensor, and the results show that gross sedimentation was several times higher than net sedimentation. We propose that tidal channel sediment is bleached either on the tidal flat before it is transported to the tidal channels and incorporated in channel-fill successions or, alternatively, on the shallow intertidal part of the channel banks. Based on the quantitative measures of sediment reworking, we suggest that repeated depositional and erosional cycles allow for complete bleaching of the tidal flat sediment, and we infer that quartz OSL dating can provide accurate ages for shallow tidal channel fill.
Geografisk Tidsskrift/danish Journal of Geography, 2015, Vol 115, Issue 1, p. 57-65
bed level measurements; bleaching; quartz OSL dating; sediment reworking; tidal channel fill