关键词: 非叠层石碳酸盐岩, 沉积序列, 高于庄组, 中元古代, 燕山地区

Abstract:

 Within the Mesoproterozoic Gaoyuzhuang Fm. in Yanshan area there is a set of more than 1,000 m-thick carbonate strata, the third member makes up a particular non-stromatolitic carbonate succession. The detail research at two sections, i.e. the Jixian section in Tianjin and the Qiangou section of Yanqing County in Beijing, indicates that this non-stromatolitic succession is a set of limestones of leiolite and laminite with the thickness ranging from 300 m to 600 m, 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 are developed in beds of leiolite limestone at the Jixian section. This non-stromatolitic sedimentary succession might reflect a stromatolite decline event occurring at ca. 1,450 Ma of the Proterozoic besides other three events respectively occurring at ca. 2,000 Ma, ca. 1,000 Ma and ca. 675 Ma. And this non-stromatolitic sedimentary succession can be generally correlative to a similar sedimentary succession in North America, i.e. a non-stromatolitic sedimentary succession of the Helena Formation of the Belt Supergroup, which suggests that the stromatolite decline occurring at ca. 1,450 Ma is a global event. All of these information endows the non-stromatolitic sedimentary succession of the third member of the Gaoyuzhuang Formation in the Yanshan area with important significance. In the secular Precambrian, after most stromatolite declines are frequently developed molartooth deposits, thus both the molar-tooth structure and the stromatolite can provide meaningful clues for the understanding of the Precambrian world, although their origin and forming mechanism remain uncertain and is highly contentious. Therefore, like other three stromatolitic declines respectively occurring at ca. 675 Ma, ca. 1,000 Ma and 2,000 Ma, the identification of the stromatolite decline occurring at ca. 1,450 Ma during the Golden Age of stromatolites (2,800 Ma to 1,000 Ma) has important meaning for the further understanding of the Precambrian evolving carbonate world.

Key words: non-stromatolitic carbonate, depositional succession, Gaoyuzhuang Formation, Mesoproterozoic, Yanshan area