The disintergration of the Zhenzhumen Formation and the reconstruction of the paleo-middle Proterozoic Group

The paleo-middle Proterozoic strata are both best exposed in the eastern Liaoning and southern Jilin Provinces. However, their correlation is very difficult for different classification schemes used by the two provinces. By comparison of the magnesium marble of the Zhenzhumen Formation in rock association, tectonic sequence, REE geochimestry, chronostratigraphy and paleo-biology in both Ⅰand Ⅱareas, it is concluded that these marbles were formed in different geologic periods and different tectonic settings. The marbles in Ⅰarea were formed in middle Proterozoic while the marbles in Ⅱarea were formed in palaeo-Proterozoic. A new classification scheme is proposed for the palaeo-middle Proterozoic strata in southern Jilin Province by the present authors, in which the middle Proterozoic strata contain two formations:Dahongyu and Gaoyuzhuang Formations while the palaeo Proterozoic strata include Ji'an, Linjang, and Dalizi Groups.