Magnetostratigraphy of the Kavur Tepe section (southwestern Turkey): A magnetic polarity time scale for the Norian

Abstract

We present the magnetostratigraphy of the late Triassic pelagic Kavur Tepe section from the Taurides (southwestern Turkey). The section investigated is about 30 m thick and consists of fine-grained whitish limestones. The biostratigraphy, based on the conodont zonation, gives an age from the Lacian 2 zone (lower Norian) to the Sevatian 2 zone (upper Norian). The paleomagnetic analyses indicate very favourable behaviour, with two magnetic components which can be isolated both by thermal and AF demagnetization. The magnetization is carried by magnetite and goethite, which are clearly evident in IRM experiments. The first component of normal magnetic polarity has roughly the direction of the present-day field. The high unblocking temperature component shows directions of both polarities. In total, fifteen magnetic polarity intervals are observed within the Kavur Tepe section. The characteristic calculated Fisherian mean direction is particularly tightly grouped: D = 220.2° and I = 32.1°, with K = 40.9, α 95 = 1.7° and N samp = 179 (after bedding correction). Polarity correlations with two other sections in Turkey and in Austria (Northern Calcareous Alps) show that the Kavur Tepe sediments were deposited in the southern hemisphere. By combining the magnetostratigraphic results from the Bolücektasi Tepe [1] and the Kavur Tepe sections, an almost complete Norian magnetic polarity sequence is established, showing 30 magnetic intervals that are well calibrated with the conodont and ammonoid zonations. A magnetic reversal frequency close to about 2.7 reversals/Myr is derived for the Norian. This medium frequency is in agreement with the hypothesis of a long time constant (150–200 Myr) in the changes of the magnetic reversal frequency since the Kiaman reversed superchron.