Intermediate field directions recorded in Pliocene basalts in Styria (Austria): evidence for cryptochron C2r.2r-1

Pliocene volcanic rocks from south-east Austria were paleomagnetically investigated. Samples were taken from 28 sites located on eight different volcanoes. Rock magnetic investigations revealed that magnetic carriers are Ti-rich or Ti-poor titanomagnetites with mainly pseudo-single-domain characteristics. Characteristic remanent magnetization directions were obtained from alternating field as well as from thermal demagnetization. Four localities give reversed directions agreeing with the expected direction from secular variation. Another four localities of the Kloch-Konigsberg volcanic complex (3) and the Neuhaus volcano (1) have reversed directions with shallow inclinations and declinations of about 240 degrees while the locality Steinberg yields a positive inclination of about 30 degrees and 200 degrees declination. These aberrant directions cannot be explained by local or regional tectonic movements. All virtual geomagnetic pole positions are located on the southern hemisphere. Four virtual geomagnetic poles lie close to the geographic pole, while all others are concentrated in a narrow longitude sector offshore South America (310 degrees-355 degrees) with low virtual geomagnetic pole latitudes ranging from - 15 degrees to - 70 degrees. The hypothesis that a transitional geomagnetic field configuration was recorded during the short volcanic activity of these five localities is supported by 9 paleointensity results and Ar-39/Ar-40 dating. Virtual geomagnetic dipole moments range from 1.1 to 2.9.10(22) Am-2 for sites with low VGP latitudes below about 60 degrees and from 3.0 to 9.3.10(22) Am-2 for sites with higher virtual geomagnetic pole latitudes. The new Ar-39/Ar-40 ages of 2.51 +/- 0.27 Ma for Kloch and 2.39 +/- 0.03 Ma for Steinberg allow for the correlation of the Styrian transitional directions with cryptochron C2r.2r-1 of the geomagnetic polarity time scale. Graphic abstract

Automated summary

Paleomagnetic investigation of Pliocene volcanic rocks in southeast Austria revealed anomalous magnetic directions that cannot be explained by local or regional tectonic movements. Virtual geomagnetic pole positions were all located in the southern hemisphere, with some close to the geographic pole and others concentrated in a narrow longitude sector offshore South America. The study supports the hypothesis of a transitional geomagnetic field configuration during the volcanic activity of these regions.