Lakes act as outdoor laboratories for the observation and understanding of natural processes. Every process has its own signature. If science looks at processes occurring today and their respective characteristics, then the door opens for understanding past processes that have similar characteristics and signatures. Sediments in lakes are the primary diagnostic source for determining paleoclimate, paleoenvironment and for developing a general understanding of lake processes. In particular carbonate sediments are unique archives for looking at a lake's specific chemical and environmental history. (Kelts and Talbot, 1990.) However it is necessary to look at a combination of factors other than carbonates and use various means of gathering data to fully understand a lake's history. Familiarity with the different sources of carbonate, the preservation processes and the general isotopic interpretation will provide bounds of information about biotic and abiotic interactions in the lake and local environmental change.
[...] Darker bands usually consist of mostly organic matter and diatoms from the fall and winter seasons when carbonate production does not occur. Some lakes freeze during the winter seasons and thus fine-grained suspended clay and silt settle out into the profundal sediments and add to this darker layer. Preserved laminated couplets can be interpreted as annual varves. Varves can be counted to determine lake chronology, however it may be difficult to distinguish annual couplets from seasonal couplets (Eugster and Kelts, 1983). [...]
[...] Kelts, K., and Hsu, K.J Freshwater carbonate sedimentation. In: Lerman, A. (eds.), Lakes: Chemistry, Geology, Physics . Springer-Verlag, Berlin p. 295-320. Kelts, K., and Talbot, M Lacustrine carbonates as geochemical archives of environmental change and biotic/abiotic interactions. In: M.M. Tilzer and C. Serruya (eds.), Ecological Structure and Function in Large Lakes. Science Tech. Publications, Madison WI, USA, p.290-317. Pearson, F.J., and Coplen, T.B Stable isotope studies of lakes. In: A. Lerman (eds.), Lakes: Chemistry, Geology, Physics. Springer-Verlag, Berlin p. 325-336. [...]
[...] As the lake reaches its deepest point, the profundal zone, sedimentation is dominated by the basin wide carbonate blankets and fine grain sediments that settle out in the deep, silent waters. The profundal zone is especially noteworthy for its ability to create rhythmic laminations. In order for these laminations to exist there must be a variable chemical, biological or physical signal and an environment that favors sediment and preservation (Eugster and Kelts, 1983). Many times non-glacial laminated sediments are found as dark and light banded couplets. [...]
[...] Sources of Carbonate in Lake Systems Kelts and Hsu (1978) describe four types of carbonate sources that are commonly found in lacustrine sediments: allochtonous clasts from the drainage area, bioclastic carbonates, inorganically precipitated carbonate minerals or primary carbonate, and diagnenetic minerals occurring post deposition. Allochtonous clasts, also known as detrital carbonates, may contribute to the carbonate load if the lake's drainage basin is predominated by carbonate rocks. Glacial lakes may have a significant amount of detrital carbonate from glacial erosion of carbonate bedrock. [...]
[...] Carbonate lacustrine sediments are simply a sliver of the possible paleoenvironmental indicators used in lake study. As demonstrated in the Moon Lake case study, often different proxies will show contrasting explanations of past lake environment, thus a greater understanding of multiple lake processes is necessary to fully analyze paleoenvironment. References Eugster, H.P., and Kelts, K Lacustrine chemical sediments. In: A.S. Goudie and K. Pye (eds.), Chemical sediments and Geomorphology. Academic Press, London p. 321-368. Glenn, C.R., and Kelts, K. Sedimentary rhythms in lake deposits. [...]
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