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Revised Magnetostratigraphies Confirm Low Sedimentation Rates in Arctic Ocean Cores

Published online by Cambridge University Press:  20 January 2017

William K. Witte
Affiliation:
Lamont-Doherty Geological Observatory, and Department of Geological Sciences, Columbia University, Palisades, New York 10964 USA
Dennis V. Kent
Affiliation:
Lamont-Doherty Geological Observatory, and Department of Geological Sciences, Columbia University, Palisades, New York 10964 USA

Abstract

The general lack of an age-diagnostic biostratigraphy in the Neogene sediments of the abyssal Arctic Ocean has emphasized the importance of magnetostratigraphy in providing chronostratigraphic control in these sediments. Sedimentation rates interpreted from early magnetostratigraphic studies of cores taken from the T3 ice island in the western Mendeleev Plain were estimated to be on the order of 1 mm/103 yr; however, recent amino acid epimerization studies of a core from the same area have suggested sedimentation rates of almost 15 mm/103 yr. This controversy has led us to reexamine the paleomagnetism of several of these cores. Our alternating field demagnetization studies indicate that many of these cores have an intense, high coercivity overprint, acquired after the core was opened, that is adequately removed only after treatment at 20 to 70 mT. We have remeasured samples from two cores after demagnetizations up to 80 mT and can confirm the position of the Brunhes/Matuyama boundary originally identified in the cores. In addition, the Jaramillo and Olduvai subchrons are identified. Average sedimentation rates in these two cores are 2–3 mm/103 yr, similar to the original estimates based on reversal stratigraphy, as well as those determined from recent radiocarbon studies, but incompatible with the amino acid-based dates.

Type
Original Articles
Copyright
University of Washington

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