Paleomagnetism of Jurassic Carbonates from Germany

Abstract:

Although the distribution of paleomagnetic data for the Jurassic of stable Europe is notorious for its wide spread and lack of any recognizable age control of pole positions it was only recently that the Jurassic has moved closer to the focus of paleomagnetic research (Kent and Irving, 2010; Muttoni et al. 2013). Here we present paleomagnetic data for carbonate rocks of early and late Jurassic age from southern (Franconia and Swabia) and northern Germany. A total of 406 samples from 37 localities in northern Germany and 180 samples from 19 localities in southern Germany were collected and subjected to detailed demagnetization experiments. All localities are dated biostratigraphically covering the Oxfordian to Tithonian (northern Germany) and the Pliensbachian (southern Germany) in time. After removal of a component of magnetization of secondary origin, stable magnetizations could be identified in 176 samples from 17 sites in northern Germany (D=003.2°, I=53.2°, k=79.4, α₉₅=4.5°). Similar directions (D=001.2°, I=43.3°, k=18.6, α₉₅=13.2°) were isolated in 108 sampled from 8 sites of coeval rocks from southern Germany. Positive fold and reversal tests support our interpretation that the resulting mean direction of is of primary origin e.g. late Jurassic in age. Unfortunately, however, the situation for the early Jurassic of southern Germany is less favourable. Here, only 15 samples from 2 sites yielded magnetizations which were interpreted to be of primary origin (D=025.3°, I=59.4°, k=51.0, α₉₅=11.2°) . The resulting paleo north pole positions for the Lower and Upper Jurassic of Germany plot at comparable latitudes (70°N) but are separated in longitude by roughly 60°. This is compatible with the apparent polar wander path proposed by Kent and Irving (2010). Taking into consideration that the only reliable paleopole for the middle Jurassic of stable Europe is indistinguishable from the late Jurassic paleopole lends additional support to the proposed late Jurassic jump connecting the connecting the early/mid Jurassic standstill to the Jurassic/Cretaceous hook of the Kent and Irving (2010) apparent polar wander path.