Annually-laminated lake sediments and the study of Quaternary environmental changes — a review |
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| Authors: | PE O'Sullivan |
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| Institution: | Department of Environmental Sciences, Plymouth Polytechnic, Plymouth PL4 8AA, U.K. |
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| Abstract: | Annually-laminated lake sediments (non-glacial varves) have in recent years been discovered in increasing abundance, especially since the development of in situ freezer samplers. So far, the majority of examples have been found in three main areas (Eastern North America, Northern and Central Europe, and East and Central Africa). A much more widespread distribution seems highly probable however.The formation of annual laminations in freshwater lakes is governed by a number of factors, the most important of which appears to be morphometry. Seasonality of sediment supply, which may be controlled by physical, biological or even cultural processes in the lake, or in its catchment, is also clearly significant.Four main types of laminations (here termed ferrogenic, calcareous, biogenic and clastic) have so far been recorded, although it is quite clear that others exist. Special field and laboratory techniques are needed in order that the particular properties of varved sediments may be fully exploited.Annually-laminated sediments have so far been applied to the investigation of a number of aspects of the Quaternary. These include the study of (a) geochronology (b) climatic change, (c) vegetation history, especially the role of fire in forest ecosystems, (d) the calculation of rates of sediment influx to lakes, and of rates of erosion from their catchments, and (e) the monitoring of processes in the modern environment such as heavy metal pollution, eutrophication, and ‘acid rain’.Annually-laminated lake sediments combine an internal, independent chronology with the preservation of discrete, visible increments of seasonal and annual sedimentation. Given this unique property, and the likelihood that many more examples will be discovered, the prospects for further applications of studies of these sediments to the investigation of the Quaternary seem very good indeed. |
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