ABSTRACT: Paleomagnetic dating of Holocene Western Canadian Arctic Sediments: Combined use of secular variation and time-varying spherical harmonic model of the geomagnetic field.

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Abstract

A major problem in Holocene paleoceanographic reconstruction from the Canadian Arctic is the difficulty to derive a robust chronology due to an often poorly constrained radiocarbon reservoir effect and the paucity of both datable material and well-dated paleoclimatic records. Here we assess the potential of using both Holocene regional paleomagnetic secular variation records and atime-varying spherical harmonic model of the geomagnetic field (CALS7K.2) to establish a preliminary age model for a marine sedimentary record recently recovered from the Beaufort Sea. Core 2004-804-650 (hereinafter referred to as core 650) was raised from the Mackenzie Shelf (Beaufort Sea) at a water depth of 246 m. The magnetic properties were studied using a 2G-Enterprises high-resolution cryogenic magnetometer in order to isolate the characteristic remanent magnetization (ChRM). In addition, the anhysteretic and the isothermal remanent magnetizations were induced in order to identify the magnetic mineralogy and grain size. The ChRM is characterized by a stable single component magnetization carried by pseudo-single domain magnetite,implying that core 650 recorded coherent paleomagnetic secular variations. A preliminary age model was constructed for the last ~6000 cal BP utilizing one AMS-14C date and four paleomagnetic tie-points derived from the comparison between core 650 ChRM declination record and the expected magnetic declination computed using the CALS7K.2 model. Based on this age model, a significant inclination low was recorded at ~2500 cal BP and is synchronous with a distinct inclination low observed in radiocarbon-dated Holocene Arctic and North American paleomagnetic secular variation records, further supporting the initial age model of core 650. Finally, the preliminary age model depicts a constant sedimentation rate of ~30 cm/ka during the last ~6000 cal BP, much lower than cores collected closer to the mouth of the Mackenzie River, thus reflecting lower sediment supplies from the Mackenzie River.

Bibliography of Canadian Geomorphology