A re-evaluation of paleomagnetic data of the Lower Rhine Embayment by assessing the efficiency of the recording of their natural remanent magnetization and paleomagnetic dating of coeval sediments in NW Netherlands.

Abstract

The Tegelen-Reuver area in the southeastern Netherlands and German border area has been studied extensively in a lithostratigraphical and biostratigraphical sense. In order to obtain a better understanding of the ages of the strata in this area, a magnetostratigraphic study was conducted in 2016 by de Weger. The results of that study were in part somewhat controversial. De Weger found sediments of Pliocene and Pleistocene age. Discussion started on the correlation to the Geomagnetic Polarity Time Scale of some of the reversals he found, which he interpreted to be either the Gauss-Matuyama boundary, or from a late Gauss subchron. Here, I attempt to verify the paleomagnetic record of the Lower Rhine Embayment by dating and examining samples taken from identical stratigraphic units and locations in 2017. The Relative Natural Remanent Magnetization acquisition (RNRMa) of these samples proves inconsistent. Classically this approach is used to indicate fluctuations in the paleo intensity of the earth’s magnetic field, by assuming the acquisition mechanism of the natural remanent magnetization (NRM) remains stable. A plausible assumption is that the paleo intensity of the earth’s magnetic field does not change by more than a factor of 2. Larger fluctuations in the RNRMa are found, indicating that multiple NRM acquisition mechanisms are at play in the area. These different mechanisms are associated with different timescales, meaning some of the polarities found in these sediments are not the polarity at of the earth’s magnetic field at a time near deposition. While I am able to confirm the deposition of the Reuver clays and Öbel beds during the Gauss chron, I cannot estimate a precise age of these sediments, because their reversal cannot be reliably interpreted. The Tegelen clays were likely deposited during the Olduvai subchron. Further I construct a low resolution paleomagnetic record of a drillcore from Petten (NW Netherlands), containing the Maassluis Formation, which contains the Olduvai subchron, and possibly the Reunion subchron as well. Magnetic data from this core was of rather poor quality and much of the data may in fact be a magnetic overprint. The core contained greigite, which interfered with the AF demagnetization measurements. Thermal demagnetization patterns were used to distinguish between slowly formed (0.1-1Myr) diagenetic greigite and quickly formed (1-50ka) diagenetic greigite.