Palaeomagnetic chronology and paleoenvironmental records of late Neogene Wuqi paleolake in northern Chinese Loess Plateau

Aeolian red clay and loess deposited in northern China since late Neogene is an ideal palaeoclimate recorder. A profile consisting of loess, lacustrine deposits and red clay was found at Wuqi County in northern Chinese Loess Plateau. Primary investigations were carried out on the typical Tufosi section in order to provide the age constraints of the lacustrine deposits (namely Wuqi paleolake). Rock magnetic results demonstrate that the magnetic carriers of the characteristic remanent magnetization of lacustrine deposits are mainly magnetite and hematite. The correlation between magnetic polarity sequence and Geomagnetic Polarity Time Scale is very well. The age of the bottom of the section is 4. 28 Ma B. P. approximately. Wuqi paleolake formed at about 3. 0 Ma B. P. and died out around 1. 2 Ma B. P. The regional environment became colder and drier during this period as implied by the variations of lithology, magnetic susceptibility, grain size and sedimentation rates. The evolution history of Wuqi paleolake can be divided into three stages: the paleolake was formed during the period of 3. 0 similar to 2. 5 Ma B. P. and the water body was relatively deep; the lake became shallow markedly as the result of palaeoclimate change during 2. 50 similar to 2. 05 Ma B. P., during 2. 05 similar to 1. 20 Ma B. P., reduction of the water body led to the extinction of the lake. Climatic deterioration in this region around 1. 2 Ma B. P. was the main reason for the end of Wuqi paleolake, and the headward erosion of North Luohe River caused by regional tectonism was probably a factor, too.