Greigite detected as dominating remanence carrier in Late Pleistocene sediments, Lisan formation, from Lake Kinneret (Sea of Galilee), Israel

Autor(en)

Markus Schwab

Abstrakt

Arock magnetic investigation of three sedimentary cores of Lisan formation of late Pleistocene age from Lake Kinneret (Sea of Galilee) northern Israel demonstrates that the magnetization of these sediments is controlled by various degrees of a secondary chemical remanent magnetization (CRM) carried by greigite (Fe3S4). This CRM is superimposed on a primary detrital remanent magnetization (DRM) that resides in Ti-magnetite. This finding is independently confirmed by X-ray diffraction (XRD) measurements performed on magnetic extracts of the sediments. The domain state of the greigite is largely single domain behaviour (SD), thus dominating the magnetization. Therefore, the magnetic record retrieve from of these sediments is not reflecting geomagnetic variations but rather chemical rock magnetic properties, resulting from diagenetic processes.

The results of our study suggest that paleomagnetic record of greigite bearing sediments should be interpreted with caution because of the following reasons:

1. Geomagnetic secular variations can be biased, due to large coercivity overlap between

magnetite and greigite.

2. Alternating field (AF) demagnetization can produce erroneous directions due to vector

distortion by acquisition of a gyro-remnant magnetization (GRM).

3. Estimation of relative paleointensity can be hampered by large-scale variations in natural

remnant magnetization (NRM) intensity, caused by the acquisition of a secondary CRM of

unknown age and unknown extent superimposed on the DRM. The precipitation of greigite requires reducing conditions at the sediment¿water interface and/or interstitial water, associated with the presence of sulphur and iron oxides. Reducing conditions are typical of stratified lakes and other stratified water bodies, such as the Dead Sea, paleo-Lake Lisan, temporarily the Eastern Mediterranean Sea, the Caspian Sea, the Black Sea and many other marine basins. According to our findings, paleomagnetic records from such environments carried dominantly by greigite therefore should be treated with care.

Organisation(en)

Institut für Geologie

Journal

Geophysical Journal International

Band

170

Seiten

117-131

Anzahl der Seiten

15

ISSN

0956-540X

Publikationsdatum

2007

Peer-reviewed

Ja

ÖFOS 2012

105101 Allgemeine Geologie, 105102 Allgemeine Geophysik

Sustainable Development Goals

SDG 14 – Leben unter Wasser

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/bedf6a96-d996-4092-a316-bd69087e4a4d