A revised paleomagnetic age of the Nihewan Group at the Xujiayao Palaeolithic Site, China

The age of the Nihewan Group lacustrine sediments (Shanxi province. China) has been a matter of dispute For decades. The sediments were initially assi gned a lower Pleistocene age, which was subsequently extended to Late Pleis tocene based on Palaeolithic evidence and mammal fossils, A short zone of r eversed paleomagnetic polarity was proposed to represent the Blake geomagne tic excursion (0.117 Myr) in accord with a Late Pleistocene age (Liu. C., S u, P., Jin, Z., 1992. Discovery of Blake Episode in the Xujiayao Paleolithi c Site. Shanxi, China. Scientia Geologica Sinica 1, 87-95). We report on a high-resolution palaeomagnetic investigation of two stratigraphic sections at Xujiayao based on progressive thermal demagnetisation experiments. Alter ations of magnetic minerals occur during heating (susceptibility-crisis), b ut experiments indicate no significant effects on remanence properties. The uppermost ca. 15 m carries a normal-polarity magnetisation overlying a rev ersed-polarity zone extending to the base of the sampled sections. The reve rsed-polarity zone is too extensive (6-12 m) to represent a geomagnetic exc ursion, and is proposed to represent the Matuyama Chron. The Nihewan Group at Xujiayao Palaeolithic must hence be older than Late Pleistocene, in gene ral accord with palaeomagnetic results of Nihewan-type sections at Dadaopo, some 50km NE from Xujiayao. (C) 2001 Elsevier Science Ltd. All rights rese rved.