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|Comparison of microstructures of recent sediments (Schelde river and North Sea) and pleistocene estuarine deposits (Turnhout clay member)|
Son, T.H. (2000). Comparison of microstructures of recent sediments (Schelde river and North Sea) and pleistocene estuarine deposits (Turnhout clay member). MSc Thesis. VUB: Brussel. 103 pp.
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The advent of the Environmental Scanning Electron Microscope (ESEM) allows to have a close look inside the material in its natural state. In this study, the author has performed clay fabric analysis on the ESEM together with other methods, i.e. field observation and description, X-ray radiography and grain size analysis, to carry out a research on the recent sediments ( the North Sea and Schelde river) and Pleistocene deposits (the Turnhout Clay Member). The obtained results reveal several interesting aspects.The results of grain size analysis showed that all the sediments have very fine grain sizes, falling in the range of fine silt or clay. Normally, the clay content is fairly high, between 30-50%, the sand content is low, less than 5%, whereas the silt content is high, more than 50%. This implies that in this case the sediment supply comes mainly from the river, especially in the case of the Turnhout Clay Member, where the silt content is up to 70%. Besides, the results of grain sizing could be used to re-define the stratigraphical units in the sampling profile.The results of the study on clay fabric showed that the samples in the North Sea have an EF fabric configuration, whereas the samples from the Schelde river have both EF and FF fabrics with dominance of the FF. In the Schelde river, the further the sampling site is from the river mouth, the larger the flocs are both in suspension and in bottom sediments. The Turnhout Clay Member shows a non-constant alternation of EF, FF and silt coating fabrics, as well as the special "stressed" gas void structures. This feature implies that there was a periodic change in the depositional environment. It shifts from brackish to fresh water and vice versa again and again, with presence of turbulent currents. This information, together with the information from the field observation and grain size analysis would draw the author to a conclusion that the sediments of the Turnhout Clay Member were likely deposited in a "tidal flat" environment. Besides, the ESEM could be a good tool to give a better resolution on stratigraphical profiles, even when other methods, i.e. X-ray or grain sizing, showed a homogeneous feature.