|Optical dating of tidal sediments: Potentials and limits inferred from the North Sea coast|
|Mauz, B.; Baeteman, C.; Bungenstock, F.; Plater, A.J. (2010). Optical dating of tidal sediments: Potentials and limits inferred from the North Sea coast. Quaternary Geochronology 5(6): 667-678. dx.doi.org/10.1016/j.quageo.2010.05.004|
|In: Quaternary Geochronology. Elsevier: Amsterdam. ISSN 1871-1014, more|
Optical dating; Tidal sediments; North Sea
The accuracy of optical ages derived from tidal sediments depends largely upon the transport processes. These processes constrain the degree of bleaching by the time of deposition and the choice of grain size for dating. This study looks at flow regime, sediment bedding, particle size and suspended sediment concentration (SSC) over tidal flats in order to identify the tidal sub-environment from which reliable multigrain optical ages are most likely to be achieved. The resulting conceptual model is then compared with empirical OSL data obtained from Holocene sediments of the southern North Sea tidal coastal plain of continental Europe. Optical dating of the tidal sediments included single-aliquot-regenerative dose protocol applied to multigrain aliquots of fine sand and fine silt, statistical analysis using weighted skewness, standardised kurtosis and over-dispersion. It is inferred from the model that smaller grains should be better bleached than larger grains. However, because transport and deposition processes are extremely variable in both space and time, unequivocal “bleaching rules” could not be assigned to a particular tidal sub-environment. In this context more than 85% of our samples return accurate ages and around 13% of our optical ages are overestimated when compared with ages from established well-constrained stratigraphic frameworks. The empirical study confirms the concept of “variable bleaching rules”: both accurate and inaccurate ages are obtained from silty and sandy OSL samples regardless of the sub-environment and well-bleached samples may be obtained from all tidal sub-environments. Although our study is based on multiple-grain aliquots it also shows that an independent statistical treatment of equivalent dose data is an indispensable procedure to detect and correct for insufficient bleaching.