Paleomagnetism of Cretaceous and Paleogene sedimentary rocks from the Kopet-Dagh and its tectonic implications

Abstract

In the Kopet-Dagh Mountains (the northernmost part of the Alpine fold belt east of the Caspian Sea), about 600 oriented samples from 21 sites were taken from the Middle Cretaceous through Oligocene sedimentary series. Prefolding and most probably primary remanence were isolated in Middle Cretaceous terrigenous rocks and Upper Cretaceous-Paleocene limestones and marls after stepwise thermal cleaning; only recent postfolding magnetization was found in Eocene-Oligocene clays. The Middle Cretaceous mean pole (75 °N, 153°E) agrees well with that from extra-Alpine Eurasia. A strong negative correlation between paleomagnetic inclinations and clay content in the Upper Cretaceous-Paleocene sedimentary rocks is interpreted as arising from diagenetic compaction. The limestones least affected by this process also yielded a paleopole (78°N, 179° E) closely matching the Eurasian data. The bends of fold axes in the Kopet-Dagh are primary; tectonic rotations are discovered only within the local wrench zone in the southwestern part of the region. The close agreement of paleopoles from the Kopet-Dagh and extra-Alpine Eurasia suggests that these land masses have been welded together since the Middle Cretaceous.