New idea of the Meso-and Neoproterozoic chronostratigraphic chart and tectonic environment in Sino-Korean Plate

Abstract

Located in the northern Sino-Korean plate,the Yanliao aulacogen is a region of very thick Meso-Neoproterozoic sediments.The Meso-Neoproterozoic consists of the Changchengian(1800-1600 Ma),Jixianian(1400-1200 Ma)and Qingbaikouan(1000-800 Ma)systems.The above-mentioned stratigraphic division is the consensus reached by Chinese geologists through their long-term study.In 2000,the National Commission on Stratigraphy of China issued a proposal document about it and the Chinese Geological Survey implemented it in geological survey and mapping in China.The Qingbaikouan System consists in ascending order of the Xiamaling,Longshan and Jing'eryu formations.Because a SHRIMP U-Pb zircon age of 1368±12 Ma was gained from bentonite in the Xiamaling Formation,the 1000 Ma age for the lower boundary of the Qingbaikouan System and even the Meso-and Neoproterozoic chronostratigraphic time scale in China are challenged.Chinese geologists must face the new age of the Xiamaling Formation,abandon the traditional idea of the division and redefine the boundary ages of various systems and formations in the Meso-and Neoproterozoic chronostratigraphic time scale of northern China.In the paper the authors propose the following new time scale:the age range of 1800-1600 Ma for the Changchengian System,1600-1400 Ma for the Jixianian System,1400-1200 Ma for the newly established Xishan System,1200-1000 Ma for a system to be named and 1000-800 Ma for the new Qingbaikouan System,including the Longshan and Jing'eryuformations.Because bentonite in the Xiamaling Formation reflects an arc tectonic environment,the Xiamaling Formation and the whole of the Mesoproterozoic Erathem in the northern Sino-Korean plate may be reconstructed as a backarc basin in the trench-arc-basin system,i.e.the traditional Yanliao aulacogen is the product of backarc spreading.The trench-arc-basin system can systematically explain the dynamic genesis of the Yanliao aulacogen,various earthquake events,volcanic activities and geological setting of stratabound ore deposits.The new dating data of the Xiamaling Formation reflects a depositional break of 300 or 200 Ma between the Xiamaling and Longshan formations.The break impels petroleum geologists to reconsider petroleum prospects in anoxic sediments(black shale and black siliceous rocks)in the Xiamaling Formation.