Magnetomineralogical approach to distal IRD layers detection and characterization. The case study of the Galician Iberian Continental Margin
Abstract
Ice Rafted Debris (IRD) layers are widely distributed along the Northern Atlantic, representing the discharge of detrital material transported by icebergs released from the major continental ice caps during the Heinrich events (Heinrich et al. 1988, Bond et al. 1992). They provide key information on climatically forced events and are commonly used as tracers holding some chronostratigraphic value. At latitudes ranging the Rudimann belt (40-55 N) (Ruddiman et al. 1977) IRD layers can be identified by magnetic susceptibility values (κ) up to 400x10-6 SI, emerging from background values lower than 100x10-6 SI. At the Galician Continental Margin, thousands of km away from their Laurentide, Greenland and Fenoscandian source areas, the distance-weakened icecap detrital signal is mixed within the continental shelf inputs and depleted and modified by upwelling related redoxomorphic diagenetic processes making their recognition very difficult, when not impossible, by the standard susceptibility measurements and/or mineralogical counting. IRD layers were first detected at the Galician Continental Margin in turbidite-dominated sequences off the Galician Bank deposited during MIS2 by Rey et al. (2008). We propose a magnetomineralogical method based on systematic measurement of the magnetic susceptibility and Anhysteretic Remanent Magnetization to detect IRD-like horizons that are subsequent measurement of hysteresis properties, and low temperature remanence and susceptibility will unequivocally demonstrate or reject the occurrence distally sourced materials transported during the Heinrich events. Furthermore, coercivity spectra analysis of detected IRD layers is used to characterize each Heinrich event by their distinct magnetic signature. This have important consequences to asses their ages and provenance. Bond et al, 1992. Nature 360, 245-249. Heinrich, 1988. Quaternary Res. 29, 142-152. Kissel, 2005. C. R. Geosciences 337, 908-918. Rey et al, 2008. Mar. Geol. 249, 64-9 Robinson, 1986. Phys. Earth. Planet In., 42, 22-47. Rudimann, 1977. Geol. Soc. Am. Bull. 88, 1-12. Contribution to the projects CTM 2007-61227/MAR, PGDIT06TAM31201PR and OILDEBEACH
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMGP41C..08R
- Keywords:
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- 1512 GEOMAGNETISM AND PALEOMAGNETISM / Environmental magnetism;
- 1540 GEOMAGNETISM AND PALEOMAGNETISM / Rock and mineral magnetism;
- 4901 PALEOCEANOGRAPHY / Abrupt/rapid climate change