Taking varves to bits: Scanning electron microscopy in the study of laminated sediments and varves |
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Authors: | Jean M Dean Alan ES Kemp David Bull Jennifer Pike Gunilla Patterson Bernd Zolitschka |
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Institution: | (1) Department of Oceanography, University of Southampton, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH, UK;(2) Department of Environmental Health, Umeå University, S-901 87 Umeå, Sweden;(3) GeoForschungsZentrum Potsdam, PB 3.3 - Sedimente und Beckenbildung, Telegrafenberg C327, D-14473 Potsdam, Germany |
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Abstract: | Conventional high resolution studies of varved sediments are able to identify clastic and biogenic laminae, but are often unable to resolve the nature of fine-scale lamination contained therein. This intra-annual signal provides us with the highest potential resolution from the sedimentary record and can be resolved using scanning electron microscopy (SEM). Six case studies from lacustrine and marine settings are presented to illustrate the combination of clastic and biogenic fabric types typically found in laminated sediments. Clastic laminae fabrics include those which originate through grain settling and those which are event deposits. The correct identification of event deposits is essential if varves are to be used chronologically. SEM-based biogenic laminae fabric studies have identified seasonal faunal successions where individual laminae may be less than 100 thick and most recently, deep chlorophyll maxima (DCM) summer diatom floras, providing an insight into seasonal scale processes. High resolution lamina fabric studies can provide a basis for generating records of seasonal and inter-annual variability, thus contributing to our understanding of lacustrine and marine processes and palaeoenvironmental interpretation. |
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Keywords: | laminated sediments varves palaeoceanography palaeolimnology palaeoclimatology backscattered electron imagery |
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