Research On The Sequence Stratigraphy And Sedimentology Of The Mesoproterozoic Gaoyuzhuang Formation In The Yanshan Region

In the present paper the sequence stratigraphy and sedimentology of the Mesoproterozoic Gaoyuzhuang Formation are studied, and the main conclusions are as follows:1. The Mesoproterozoic Gaoyuzhuang Formation of the Yanshan Region may be divided into 13 third-order sequences (SQ₁ to SQ-(13)) and be grouped into 4 second-order sequences. Six third-order sequences (SQ₁-SQ₆ ) are recognized in the Guandi Subformation, two third-order sequences (SQ₇ and SQ₈ ) are in the Sangshuan Subformation, three third-order sequences (SQ₉ - SQ₁₁) are in the Zhangjiayu Subformation, and two third-order sequences ( SQ₁₂ and SQ₁₃) are in the Huanxiusi Subformation, which greatly increases the resolution of stratigraphic division and precision of stragigraphic correlation.2. The typical Molar Tooth (MT) structures well developed in homogeneous limestones of the Zhangjiayu Subformation in the Jixian Section is preliminary considered to be a type of the microbial induced primary structure related with microorganism developing on matground habitat.3. The bulbs occurring together with the MT structures in the Zhangjiayu Subformation are believed to be body fossils of macroalgae rather than spheroidal MT structures. Four genera may be distinguished. They are Chuaria, Shouhsienia, Tawuia and Phascolites. Of them the Chuaria is abundant4. In both the Jixian section of Tianjin and the Qiangou section of Yanqing County in Beijing the Zhangjiayu Subformation of the Gaoyuzhuang Formation is characterized by a particular non-stromatolitic limestone succession. The non-stromatolitic limestone succession may suggest that there was an event of stromatolite decline occurring at ca. 1450 Ma.