Zircon U-Pb dating of tuff bed from Luoyukou Formation in western Henan Province on the southern margin of the North China Craton and its stratigraphic attribution discussion

Luoyu Group and Ruyang Group are cropped out extensively along the southern margin of the North China Craton (NCC), and are mostly composed of sandstone with minor shale and dolostone. Based on field investigation along Luoyukou and Yangpo Village section, Ruzhou City, Henan Province, a few interbedded tuff layers were found in the upper part of the Luoyukou Formation. By means of LA-MC-ICPMS zircon U-Pb dating, the ages of the volcanic eruption, 1638±9 Ma and 1634±10 Ma from Luoyukou Village and Yangpo section, were respectively obtained. These data mean that Luoyukou Formation was formed during Mesoproterozoic Changcheng period rather than during Meso-Neoproterozoic Jixian period and Qingbaikou period as previously held. According to the new dating data, the Luoyu Group and Ruyang Group which conformably underlies Luoyu Group ought to belong to the Mesoproterozoic Changcheng period, because Luoyukou Formation is at the uppermost part of Luoyu Group. This discovery has great significance for Meso-Neoproterozoic stratigraphic redivision and correlation in the NCC, and for the study of the relationship between the tectonic evolution history of the Late Paleoproterozoic to Early Mesoproterozoic geological records in the NCC and the breakup of the Columbia Supercontinent as well as for the evolution of the early life on the Earth.