11 Back to the Devonian: Revisiting Milestones of Paleontology and Stratigraphy from 1985 (Posters)

Friday, 28 March 2025
8:30 AM - 5:30 PM
North Great Hall

A PALEOMAGNETIC STUDY OF THE DEVONIAN OLD RED SANDSTONE FROM WOODFJORDEN, SVALBARD

Paper number: 11-2
Program: Theme Sessions
Time: 8:30 AM – 5:30 PM

Authors

Abstract

Paleomagnetism is the study of the magnetic field of prehistoric Earth. The strength and direction of the magnetic field can be recorded in rocks, sediments, and archeological materials. This study investigates the paleomagnetism of early Devonian Old Red Sandstone samples from Woodfjorden, Svalbard, Norway, aiming to isolate primary magnetic signals to gain more knowledge about the Devonian magnetic field. Not much is known about the magnetic field during the Devonian, and previous studies have struggled to isolate primary magnetic signals. Previous studies from Woodfjorden have found signals that could possibly be of Devonian age, which is why this area is of special interest within paleomagnetic research.

We present the results of a paleomagnetic study, including thermomagnetic measurements, anisotropy of magnetic susceptibility (AMS), hysteresis loops, and natural remanent magnetizations (NRM). A Kappabridge was used to measure magnetic susceptibility, which help determine which magnetic mineral is present in the sample. AMS is measured in the Kappabridge and gives information about the magnetic fabric in the samples. The hysteric loops show inductive and remanent magnetization and was created using the J-meter Coercivity Spectrometer. NRM was measured by stepwise thermal demagnetization followed by NRM measurements taken on a WSGI (2G) Model 755 Superconducting Rock Magnetometer. The samples underwent a total of 17 demagnetization steps with temperature intervals of 5-100°C, with the highest temperature being 680°C. The directional data from the NRM measurements were analyzed using Zijderveld diagrams and principal component analysis.

We show that the Old Red Sandstone has hematite as the primary magnetic carrier, alongside another mineral with a very low (~100°C) Curie temperature, possibly goethite. The samples show low-temperature and high-temperature components (isolated above 500°). The magnetic direction of the low-temperature component is similar to what is expected for the present-day magnetic field in Svalbard. The high temperature component has a shallow inclination (~-21°) and a declination of around 200°. These directions likely correspond to a magnetization that was acquired during the early Carboniferous, in a magnetic field that had a reverse polarity

Geological Society of America Abstracts with Programs. Vol. 57, No. 3

doi: 10.1130/abs/2025NE-407489

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