ABSTRACT: Holocene paleomagnetic secular variation and relative paleointensity proxies from the Laurentian Channel (Gulf of St-Lawrence): Preliminary results.

CGRG Bibliography of Canadian Geomorphology
Search Results

Author :

Date :

Title :

Publication :

Issue :

Page(s) :

Abstract

Here we present the paleomagnetic results of three sedimentary cores recovered on board the Coriolis II in 2005 in the Laurentian Channel in order to develop a Holocene regional magnetostratigraphy using paleomagnetic secular variation (PSV) and relative paleointensity proxy (RPI) records. Preliminary physical and magnetic properties including low-field volumetric magnetic susceptibility and bulk density of cores COR0503-37PC, COR0503-36PC and COR0503-35PC (hereinafter referred to as cores 37PC, 36PC and 35PC) were initially performed on board using a Multi Sensor Core Logger. Cores 37PC, 36PC and 35PC were subsequently split, photographed and described, and sub-sampled with u-channels. The magnetic properties of these u-channels were measured at 1 cm intervals at ISMER using a 2G Enterprises high-resolution cryogenic magnetometer. The natural remanent magnetization (NRM) was measured and stepwise demagnetized in order to isolate the characteristic remanent magnetization (ChRM). The ChRM inclinations of all cores fluctuate around the expected inclination calculated using the geocentric axial dipole model. An anhysteretic remanent magnetization (ARM) and two isothermal remanent magnetizations (IRM) were induced in order to characterize the magnetic mineralogy and grain size. ChRM of all cores is principally carried by pseudo-single domain magnetite, although the presence of a high-coercivity magnetic component is compatible with the observed low IRM0.3T/IRM0.95T ratio in some intervals of cores 35PC and 37PC. All paleointensity determinations were made by normalizing the NRM by ARM or IRM, yielding almost identical results with both normalizers, suggesting that all cores are suitable for relative paleointensity determinations. AMS 14C-based age models were determined by interpolation of six (cores 35PC and 36PC) and five (core 37PC) calibrated ages and the identification major lithological units. The RPI proxy of core 36PC depicts a similar trend when compared to the expected paleointensity at the core site using the recent spherical harmonics model CALS7K of geomagnetic field variations during the last 7000 cal BP. Furthermore, millennial-to centennial-scale features of both the directional and paleointensity records can be correlated between the three cores and with core MD99-2220 from the St-Lawrence Estuary. These preliminary results corroborate the idea that cores 35PC, 36PC and 37PC record a coherent PSV and RPI signal and they also open the possibility of constructing a regional paleomagnetic master curve for Eastern Canada.

Bibliography of Canadian Geomorphology