Abstract: On the basis of an analysis of the lithology, facies indicators and biological features, it is considered that two marine transgressions took place during this period of time. The first transgression resulted in the formation of littoral-neritic carbonate rocks with terrigenous clastics. From below upward five sedimentary facies may be distinguished, continental margin clastic rocks, platform tidal flat, platform-margin shoal, open platform and platform intertidal zone. The second trasgression was more extensive in scale, producing neritic chert band-bearing carbonate rocks. From below upward four sedimentary facies are recognized: open platform, platform slope, platformfront organic reefs and platform intertidal flat.