Elkina, Daria (2013) Pliocene-Quaternary Sedimentation Rates of the Mendeleev Ridge : Paleomagnetic Studies. (Master thesis), Saint-Petersburg State University ; University of Hamburg, Saint Petersburg, Russia ; Hamburg, 90 pp.

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Abstract

Nowadays the Arctic Ocean is a region of high scientific interest and it’s more and more considered like an essential key to understanding of the Earth paleoclimate. With the lack of biological information and age limitations of radiocarbon method paleomagnetic studies become a crucial tool for marine sediments dating here.
A 9-meter length core was retrieved from the Mendeleev Ridge and subjected to paleomagnetic analysis. Magnetic susceptibilities measurements were performed by different types of equipment. The 6 meters of the core were continuously sub-sampled and measured for natural remanent magnetization (NRM) using a spinner magnetometer JR-6A. Patterns of NRM inclination, NRM intensity and magnetic susceptibility were constructed against depth. Specimens of interest was chosen for following demagnetization procedure to remove viscous overprints based on the revealed NRM inclination reversals. Stepwise thermal demagnetization was performed at 130°C and further in 50°C steps in the 200-500°C temperature range. Characteristic remanent magnetization (ChRM) with maximum anglular deviations (MAD) were calculated by using the principal component analysis method [Kirschvink, 1980]. Alternating field demagnetization was performed in the 5 mT – 100 mT field peak range and NRM results in 20, 30 mT were used as an addition to the ChRM inclination pattern.
The distinct drop from positive to a negative inclination at 123.5 cmbsf is interpreted as a polarity reversal from the Brunhes chron to the Matuyama chron. Prevalence of reverse polarity is supported by demagnetization data up to at 394-397 cmbsf and short positive intervals within zone are probably reflect subchrons of normal polarity. Change from reverse to normal polarity at 394-397 cmbsf is considered as the Matuyama – Gauss boundary. This zone with prevailed normal polarity is traced from 394-397 cmbsf up to 490 cmbsf and its lower bound isn’t clearly definable downward due to lack of demagnetization data and frequent interchanges of polarity.
The decrease of the NRM intensity values is observed in the reverse polarity zone in comparison to normal polarity zones, which is derived from the presence of viscous remanent magnetization (VRM) and its superimposing with the initial one. Spikes of NRM intensity and magnetic susceptibility are discovered near the determined chron boundaries, and it may act as an independent factor for determination of polarity boundaries. The secondary processes occurring in sediments may play some role and affect alterations in the paleomagnetic record.
Calculated mean sedimentation rates during Brunhes and Matuyama chrons are 1.58 and 1.5 mm kyr-1 respectively. These values represent sedimentation rate on the Mendeleev Ridge as low and approach to other studies with the similar estimation [Piskarev et al., 2013, Gusev et al., 2013] Thus the obtained sedimentation rates don’t exceed 1.58 mm kyr-1 for last 2.5-2.6 Myr.

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