Ediacara Obscura: Unveiling Hidden Magnetisations in the Fen Complex, Southern Norway

Abstract

Paleomagnetic directions found in Ediacaran (635–539 Ma) rocks are widely dispersed, which has led to conflicting hypotheses about tectonic regimes and geomagnetic field behavior during this period, and raised doubts about the fidelity of the paleomagnetic record. In particular, data from eastern and western Baltica show large and rapid changes in paleopole positions which are difficult to explain if we assume a geocentric axial dipole field operated in the Ediacaran. We present new paleomagnetic data from 214 samples across 18 sites of the Fen carbonatite-alkaline rock complex (583 (Formula presented.) 15 Ma) in southern Norway, coupled with detailed petrographic observations using transmitted and reflected light, scanning electron and quantum diamond microscopy, alongside conventional rock magnetic and mineralogical analyses. Our results indicate that the Fen complex and its associated intrusions were pervasively overprinted in the Permian (ca. 270 Ma), during tectono-magmatic activity of the nearby Oslo Rift, which complicated previous paleomagnetic interpretations. However, after removing secondary overprints, we find that 7% of our specimens preserve weak, shallow paleodirections interpreted as primary. The outlier directions are found in rock types not previously studied, mainly damtjernites (ultramafic lamprophyre intrusions). Based on specimen directions from these preserved units, we define a new paleopole at 266.6 (Formula presented.) E, −1.7 (Formula presented.) N ((Formula presented.) = 4.5 (Formula presented.), K = 77.4, N = 15), which places Baltica at low/equatorial latitudes during the mid-Ediacaran (ca. 583 Ma). Our findings have significant implications for understanding the nature of the geomagnetic field and Baltica's paleogeography in the late Neoproterozoic.