The Gaoyuzhuang Formation of Mesoproterozoic at the Jixian section in Tianjin is a set of about 1 600 m-thick carbonate strata, which can be divided into four members: The first member is mainly constituted by stromatolitic dolomites; The second member is marked by a set of manganese dolomites; The third member is mainly composed of laminar limestones; The fourth member is a set of stromatolitic-lithoherm dolomites. According to lithofacies and lithofacies succession, several types of meter-scale cyclic sequences, i.e. the L-M type, the subtidal type and the peritidal type can be discerned in the Gaoyuzhuang Formation. There is a regularly vertical stacking pattern for meter-scale cyclic sequences in the third-order sequence. Therefore, the Mesoproterozoic Gaoyuzhuang Formation can be divided into 13 third-order sequences (SQ₁ to SQ₁₃) and still be grouped into 4 second-order sequences. The third member of the Gaoyuzhuang Formation that is marked by laminar limestones can be grouped into 3 third-order sequences (SQ₉ to SQ₁₁); and the molar-tooth structure is developed in the middle part of the third sequence in the third member of Gaoyuzhuang Formation. Several features of this kind of molar-tooth structure, i.e. the particular configuration, containing abundant organic matter, easy silication etc., reflect some characters of carbonate sedimentation in Precambrian as follows: Firstly, stromatolites are chiefly formed in shallow tidal-flat environment and molar-tooth structures are mainly generated in more deep-water environment of carbonate ramp, therefore, similar to stramatolite the molar-tooth structure is also a kind of biosedimentation structure; Secondly, the shallow tidal-flat environment mainly developed stromatolites is propitious to dolomitization, but in the more deep water environment of carbonate ramp is chiefly formed limestones, both of which might reflect
that Precambrian dolomites are appear not primary dolomites. Actually, these features of Precambrian sedimentation also represent the problem of Precambran carbonate sedimentation. With much more detail study, much more truly solution for these problems will be obtain in the future.