Magnetic signatures of Heinrich-like detrital layers in the Quaternary of the North Atlantic

Channell, J.E.T. and Hodell, D. A. (2013) Magnetic signatures of Heinrich-like detrital layers in the Quaternary of the North Atlantic. Earth and Planetary Science Letters, 369–37. pp. 260-270. ISSN 0012-821X DOI 10.1016/j.epsl.2013.03.034

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Abstract

Abstract Magnetic parameters are useful for distinguishing North Atlantic Heinrich-like detrital layers from background sediments. Here we compare magnetic properties with XRF scanning data back to 700 ka and 1.3 Ma at IODP Sites U1302–U1303 and U1308, respectively. Multi-domain magnetite, with grain sizes >20 µm, is characteristic of both Ca- and Si-rich detrital layers, as defined by XRF core scanning, confirming the contribution of ice rafting. Reflectance spectra and magnetic parameters distinguish Ca- and Si-rich IRD layers due the presence of high coercivity hematite in Si-rich layers. Heinrich layer 6 (H6) at Site U1302–U1303 is unlike other detrital layers, being marked by a 45-cm thick homogeneous cream-colored clay layer underlain by a thin (5-cm) graded coarse-sand. Comparison of Site U1302/03 and Site U1308 detrital layers implies a dominant Laurentide source for both Ca- and Si-rich detrital layers. At Site U1308, low benthic δ13C values during stadials are in-step with magnetic grain-size coarsening associated with Si-rich detrital layers back to 1.3 Ma, indicating a link between deep-sea ventilation and ice rafting. The surface-sediment tan-colored oxic layer (~2 m thick at Site U1308) yields magnetic hysteresis ratios that are offset from the single-domain to multi-domain (SD–MD) magnetite mixing-line in hysteresis-ratio diagrams. This offset is attributed to maghemite grain-coatings, that form on magnetite in surface sediment, and undergo dissolution as they pass through the oxic/anoxic boundary.

Item Type:	Article
Uncontrolled Keywords:	2013AREP, IA66,
Subjects:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title:	Earth and Planetary Science Letters
Volume:	369–37
Page Range:	pp. 260-270
Identification Number:	10.1016/j.epsl.2013.03.034
Depositing User:	Sarah Humbert
Date Deposited:	07 Jul 2013 00:49
Last Modified:	08 Aug 2013 12:12
URI:	http://eprints.esc.cam.ac.uk/id/eprint/2816

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