Magnetostratigraphy of drill-core SG-1b in the western Qaidam Basin (NE Tibetan Plateau) and tectonic implications

The Qaidam Basin is an ideal archive to study long-term climate and erosion histories at the NE Tibetan Plateau. We present a magnetostratigraphic study of the 723 m deep drill-core SG-1b of lacustrine sediments at the Jianshan anticline in the western Qaidam Basin. The polarity sequence shows 18 normal and 19 reverse polarity zones which can be readily correlated with chrons C1n-C3Br of the Geomagnetic Polarity Time Scale 2004 (GPTS 2004), dating the core at about 7.3-1.6 Ma. The resulting mean sediment accumulation rate (SAR) between polarity boundaries ranges from 6.5 to 30.4 cm ka(-1). High SARs occur within the intervals of > 7.3-6.0, 5.2-4.2 and 3.6-2.6 Ma indicating three episodic phases of higher erosion. From the derived variation of SARs and previous results, we conclude that growth strata at the Jianshan anticline started to develop at similar to 1.6 Ma by limb rotation. All this we relate to pulse tectonic uplift of the NE Tibetan Plateau and fault-propagation-folding in the Qaidam Basin.