首页|Implications of the Precambrian Non-stromatolitic Carbonate Succession Making up the Third Member of Mesoproterozoic Gaoyuzhuang Formation in Yanshan Area of North China
Implications of the Precambrian Non-stromatolitic Carbonate Succession Making up the Third Member of Mesoproterozoic Gaoyuzhuang Formation in Yanshan Area of North China
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A particular non-stromatolitic carbonate succession making up the third member of the Mesoproterozoic Gaoyuzhuang Formation might demonstrate that a stromatolite decline of the Mesoproterozoic occurring at ca. 1 450 Ma besides other three events of the Proterozoic, respectively, occurred at ca. 2 000 Ma, ca. 1 000 Ma, and ca. 675 Ma. The forming duration of this non-stromatolitic carbonate succession can be generally correlative to that of a similar depositional succession in North America, i.e. a non-stromatolitic carbonate succession made up by the Helena Formation of the Belt Supergroup, which suggests that the stromatolite decline occurring at ca. 1 450 Ma may be a global event. This information endows the non-stromatolitic carbonate succession making up the third member of the Gaoyuzhuang Formation in the Yanshan area with important significance for the further understanding of Precambrian sedimentology. The Mesoproterozoic Gaoyuzhuang Formation in Yanshan area is a set of more than 1 000 m thick carbonate strata that can be divided into four members (or subformations). The first member (or the Guandi subformation) is marked by a set of stromatolitic dolomites overlying a set of transgressive sandstones; the second member (or the Sangshu'an subformation) is a set of manganese dolomites with a few stromatolites; the third member (or the Zhangjiayu subformation) is chiefly made up of leiolite and laminite limestones and is characterized by the development of molar-tooth structures in leiolite limestone; the fourth member (or the Huanxiusi subformation) is composed of a set of dolomites of stromatolitic reefs or lithoherms. Sequence-stratigraphic divisions at two sections, i.e. the Jixian Section in Tianjin and the Qiangou Section of Yanqing County in Beijing demonstrate that a particularly non-stromatolitic succession making up the third member of the Mesoproterozoic Gaoyuzhuang Formation is developed in the Yanshan area of North China, in which lots of grotesque matground structures (wrinkle structures and palimpsest ripples) are developed in beds of leiolite limestone at the Qiangou Section and lots of molar-tooth structures aredeveloped in beds of leiolite limestone at the Jixian Section. The time scale of the Gaoyuzhuang Formation is deduced as 200 Ma (from 1 600 Ma to 1 400 Ma). The duration of an obvious hiatus between the Gaoyuzhuang Formation and the underlying Dahongyu Formation is deduced as 50 Ma to 100 Ma, thus the forming duration of the GaoyuzhuangFormation is thought as 100 Ma (1 500 Ma to 1 400 Ma). Furthermore, the age of the subface of the third member of the Gaoyuzhuang Formation that is just in the mid position of the Gaoyuzhuang Formation can be deduced as about 1 450 Ma, which is the basis to infer a stromatolite decline of the Mesoproterozoic occurring at ca. 1 450 Ma. Importantly, several features of both the molar-tooth structure and the stromatolite, such as the particular forming environment, the important facies-indicative meaning, and the episodic distribution in the earth history, might express the evolutionary periodicity of the surface environment of the earth and can provide meaningful clues for the understanding of the Precambrian world, although their origin and forming mechanism is highly contentious.
non-stromatolitic carbonatedepositional successionGaoyuzhuang FormationMesoproterozoicYanshan area
Mei Mingxiang
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State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
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