CGRG Bibliography of Canadian Geomorphology
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Author : Enkin, R.J.; and Barendregt, R.
Date : 2007.
Title : Paleomagnetic dating of glacial and periglacial sediments.
Publication : CANQUA Ottawa 2007. Canadian Quaternary Association Conference, June 4-8, 2007. Carleton University, Ottawa, Ontario, Canada.
Issue :
Page(s) :
Abstract
Glacial and periglacial sediments are difficult to date. Many studies concern sediments much older than the 50 ka limit for 14C dating, but even recent sediments are often void of datable organics because of the harsh environment in which they were deposited. Paleomagnetic methods can offer unique age control, and are most useful when combined with complementary dating methods (e.g., fission track dating of ash layers or 14C of recent organics). Glacial tills are imperfect recorders of paleomagnetic remanence, however careful selection of the finest-grained material usually can lead to reliable polarity determination. Care must be taken to separate primary normal polarity remanence from recent normal polarity overprints. Consequently, even noisy reverse polarity units may be more reliable than apparently well-behaved normal polarity units. Sample collection should avoid where possible, sediments which have been substantially altered by secondary processes, either syn- or post-depositionally. These processes might include glacial deformation, dewatering, unloading, oxidation/reduction, lightning, etc. Most glacial/interglacial sediments can be sampled using plastic sample vessels inserted directly into the cleaned outcrop. Some, however, are too cemented or indurated, and must be carved into stubs which are then inserted and fixed in the sample cylinder. The low energy depositional environment of loess, or the chemical remanence of interbedded paleosols, provide more reliable magnetic remanences, leading to a high fidelity paleoclimate signal. Magnetic remanence directions of Late Pleistocene sediments from caves or slack water flood deposits can be compared to reference paleomagnetic secular variation records from well-dated lake sediments to help date deglaciation events, and provide an indication of the magnitude and frequency of such events. We will provide examples of the successes and pitfalls of paleomagnetic dating of glacial sediments deposited from North American icesheets.
Bibliography of Canadian Geomorphology