Sedimentary Characteristics of Stromatolites in Cambrian Strata in Songzi Liujiachang Area and Its Paleoenvironmental Significance

Stratiform, irregularly stratiform and columnar stromatolites are found in the third section of Qingjiamiao Group, while columnar and hemispherical stromatolites are found in Sanyoudong Group in Cambrian strata in Songzi Liujiachang area. 1) From the stratiform and columnar stromatolites to hemispherical stromatolites, the internal plaster content is decreasing. And from obvious layer characteristics to intermittent layer characteristics, they reflect that the hydrodynamic conditions are strengthening gradually. 2) From the perspective of sedimentary petrology and the classification of stromatolites, it is concluded that the combinations of stromatolites in different sedimentary environments are different and the main sedimentary facies of different types are different: a) Stratiform (including irregularly statiform) and columnar stromatolites are mainly distributed in the upper tidal zone; columnar and hemispherical stromatolites mainly distribute in the intertidal zone. b) The stratiform stromatolites are mainly found in the upper tidal zone with weak hydrodynamic conditions, while the columnar and hemispherical stromatolites are mainly found in powerful hydrodynamic conditions of the lower intertidal zone. 3) A mass extinction of part of the metazoan is the main reason for the growth of stromatolites in Cambrian strata in Songzi.