Taking varves to bits: Scanning electron microscopy in the study of laminated sediments and varves

Conventional high resolution studies of varved sediments are able to identi fy clastic and biogenic laminae, but are often unable to resolve the nature of fine-scale lamination contained therein. This intra-annual signal provi des us with the highest potential resolution from the sedimentary record an d can be resolved using scanning electron microscopy (SEM). Six case studie s from lacustrine and marine settings are presented to illustrate the combi nation of clastic and biogenic fabric types typically found in laminated se diments. Clastic laminae fabrics include those which originate through grai n settling and those which are 'event deposits'. The correct identification of event deposits is essential if varves are to be used chronologically. S EM-based biogenic laminae fabric studies have identified seasonal faunal su ccessions where individual laminae may be less than 100 mu thick and most r ecently, deep chlorophyll maxima (DCM) summer diatom floras, providing an i nsight into seasonal scale processes. High resolution lamina fabric studies can provide a basis for generating records of seasonal and inter-annual va riability, thus contributing to our understanding of lacustrine and marine processes and palaeoenvironmental interpretation.