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PaleolimnologyThe History and Evolution of Lake Systems$
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Andrew S. Cohen

Print publication date: 2003

Print ISBN-13: 9780195133530

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195133530.001.0001

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Paleoecological Archives in Lake Deposits I: Problems and Methods

Paleoecological Archives in Lake Deposits I: Problems and Methods

(p.273) 10 Paleoecological Archives in Lake Deposits I: Problems and Methods

Andrew S. Cohen

Oxford University Press

Fossils provide some of the most detailed sources of information for environmental reconstruction available to the paleolimnologist. The use of lacustrine fossils to infer paleoenvironmental conditions is fundamentally based on inferences derived from modern correlations between the distribution of organisms and environmental variables, coupled with an understanding of taphonomy, the study of the fossilization process. No single group of organisms provides a comprehensive picture of lake ecosystems or environmental change, so it is always desirable to gather paleoecological records from multiple clades and habitats in a paleolimnological study. Analysis of multiple clades provides a means of establishing or testing ecological hypotheses that may not be possible from the study of one group alone. For example, many limnological processes affect the plankton, littoral organisms, and benthos in predictable sequences, and with predictable intensities. The most comprehensive study of fossil data and data analysis will be meaningless if the fossils studied are misidentified. A good taxonomic framework is an essential element of paleoecological studies. Accurate identification of described species, and the curation of voucher specimens, photographs, and other descriptive materials of undescribed species is important, to insure the quality of a paleolimnologist’s ongoing work, and to avoid future errors based on previously misidentified fossil specimens. Using fossils to interpret lacustrine paleoenvironments requires not only an understanding of modern organism distributions, but also an understanding of four additional factors we did not consider in chapter 5: (1) ecological causality and scale, (2) taphonomy and time-averaging, (3) historical contingency, and (4) evolutionary processes. One of the most common uses of fossil data in lakes is to try and reconstruct changes in some physical or biological forcing process from changes in abundance or morphology of the fossil organisms affected by the process. We might be interested in reconstructing changes in nutrient flux to the lake, based on changes in the relative abundances of some fossil animals. However, these animals actually responded to nutrient load only indirectly, through the effect of nutrient load on autotrophs and/or organic detritus. Now suppose that our ultimate objective is not really to understand productivity changes or nutrients, so much as to understand climate changes that may be driving productivity changes.

Keywords:   Alkalinity, Bioturbation, Calcium carbonate, Deltas, Ecological causality, Fecal pellets, Historical contingency, Insects, Jackknifing, Miocene

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