关键词: 华北克拉通, 扬子克拉通, 中元古代, 大火成岩省, 真核生物群, 宏观藻类, 超大陆

Abstract:

Following synthesis of recent advances in geochronological research, the GTS2012 (The Geological Time Scale 2012) Mesoproterozoic (1780850 Ma) chronostratigraphic subdivision of the typical areas both on the North China Craton (NCC) and the Yangtze Craton (YC) of China have been revised thoroughly. It is now know that the early Mesoproterozoic deposits of NCC, between ~1780 Ma and ~1350 Ma, developed initially near the junction of HenanShanxiShaanxi Provinces, and then expended gradually northwards to the Yanshan Mountains and the adjacent areas along the TransNorth China Orogen (TNCO). However, the middle Mesoproterozoic, ~1350 Ma~1100 Ma, are all absent through out the entire craton. In addition to the southwestern Henan (south NCC) and the Yanshan Mountains (north NCC), the late Mesoproterozoic, younger than ~1100 Ma, occurs mainly in the elongated riftrelated basin in the eastern NCC, named the JiaoLiaoXuHuai Sea, in the west Shandong, the southeast Liaoningeast Jilin, the north Jiangsu, and northeast Anhui Provinces. On the other hand, both the early (~1750 Ma~1450 Ma)and the late(<1100 Ma) Mesoproterozoic deposits are developed near the border of Sichuan and Yunnan Provinces, i.e. the KangDian area, along the western margin of YC. The middle Mesoproterozoic, ~1400 Ma~1150 Ma, outcrops mainly in the Shennongjia area, west of Hubei Province, in the northern YC. It means that the Mesoproterozoic successions from the two cratons of China could complement each other to cover the entire proposed GTS2012 Mesoproterozoic Era, 1780 Ma850 Ma. Some relevant fundamental issues emerging from the updated chronostratigraphic framework are discussed in short: (1) Precambrian Stratigraphy: Due to the only one ~1.0 Ga long Rodinian Period proposed for the Mesoproterozoic Era with the same duration in the GTS 2012, a quadripartite intrasubdivision of the Systems (Periods) in this Erathem (Era) has been suggested by the author. All the new Systems (Periods) would be defined by the GSSPs (Global Standard Stratotype Sections and Points) constrained by the sedimentary records of certain LIPsmantle plume events with potentially global influence during this 1.0 Ga. According to the studies of the Phanerozoic Era, such as around the PT boundary and others, these sorts of events should cause significant coupled responses or trigger largescale crises in the multiple spheres of the Mesoproterozoic Earth. It should fit well the definition of the “key causative events” for the use as the Precambrian timescale division under the philosophy of the GTS2012. Covering the entire ~1780 Ma~850 Ma chronostratigraphic framework in the two cratons of China means that, in future research on the suggested quadripartite intrasubdivision of the GTS2012 Mesoproterozoic Erathem (Era), the Chinese researchers would have ample opportunities to define the possible GSSP candidates of each new System (Period), and should contribute uniquely for the Precambrian research; (2) Early evolution of the Eukaryota: With the chronostratigraphic subdivision mentioned above, the horizon of the largescale acanthomorphic acritarch association, i.e. Tappania and others, in the Beidajian Formation of the Ruyang Group at the Shuiyougou section of Yongji, Shanxi Province, southern Zhongtiao Mountains of NCC, should be ~1650 Ma in age. It is the earliest horizon of the unambiguous eukaryotic fossils currently on record around the world. Further, with the distribution elsewhere of Tappaniabearing strata in space and time, it might be inferred that, possibly from ~1650 Ma to ~1450 Ma, i.e. during the initial breakup of the Supercontinent Columbia＼Nuna, the NCC should have been neighbored successively with India, Australia, Laurentia and Siberia; (3) Sedimentological and tectonic evolution: The deposition during the GTS2012 Mesoproterozoic Era both in NCC and YC has followed the same threestage style, and the subsidence and uplift areas have alternated in a seesaw pattern, with the time of each turning point, including that of the Jinning Orogen, correlated fairly well. All of these indicate that probably both NCC and YC have been affected by the same tectonic stresses during this Era. Further, combining with the foreland basin setting of the ~1.38 Ga Kbentonitebearing black shale succession in the Xiamaling Formation in Yanshan Mountains, and the Chuariabearing macroalga both in NCC and YC from ~1.1 Ga to ~0.8 Ga, as well as the abundant Grenvillianage detrital zircons in the successions of the eastern NCC during this period, it may be inferred that, the latest around ~1.1 Ga, the eastern NCC might have collided and even assembled with the YangtzeCathaysia blocks along the east or southeast margins of the NCC, and with the microcratons or massifs, including the Silinhot (Inner Mongolia) and the Hutag UulTsagaan Uul (Mongolia), at the northern margin of the NCC. It would have formed a probable hooflike Grenvillian orogen along the eastern NCC connected with Laurentia, Australia, Baltica, Siberia, and other cratons, to witness the terminal assemblage of the Supercontinent Rodinia and its initial breakup.

Key words: North China Craton, Yangtze Craton, Mesoproterozoic Era, LIPs, Eukaryota, macro-alga, supercontinents