The Stromatolite And Their Significance From The Mantou Formation(cambrian Series 2,3), Mianchi Area,western Henan

The Mantou Formation(Cambrian Series 2,3) well and continuously exposed in Mianchi area of western Henan. Varieties of stromatolites developed in the Formation. The study on research of the macroscopic and microscopic morphological characteristics of stromatolites and their sedimentary features and microbial fossils can provide evidences for reconsturction of sediemntary environments and the life-style of the microorganisms in Cambrian of western of Henan.According to the macroscopic depositional characters, the stromatolites in study area can be divided into five types: half globular, undulating, columnar, fasciculate, and growing around flat-pebble stromatolites. Undulating stromatolites were formed in upper intertidal zone and supratidal zone with the weak hydrodynamic condition. Fasciculate stromatolites occurred in upper and middle intertidal zone with the weak hydrodynamic condition. Those stromatolites which growing around the flat-pebbles and small mound stromatolites were preserved in middle intertidal zone with high hydrodynamic condition. Columnar stromatolites were formed in subtidal zone and middle intertidal zone with changing hydrodynamic condition in which the small columnar stromatolites reflect the weak hydrodynamic condition in upper intertidal zone and the cylindrical stromatolites were formed in lower intertidal zone where the hydrodynamic force is much stronger.Abundant microbial fossils such as Girvanella are found in stromatolites and display four types of distributions: upright, imbricate, latticed and irregular filaments.The study of cortex in stromatolites shows that hydrodynamic condition has the important influence on the change of light and dark laminations of the cortex. The laminations are much clear under high hydrodynamic condition,but the laminations are difficult to recognize and have the high micrite content under weak hydrodynamic condition. The distribution model of depositional environment with the deffirent types of stromatolites has estiblished in Cambrian of Mianchi area, western Henan. It can provide the evidences for the growth condition and depositional environment of stromatolites.