Stromatolite Declines and Molar-Tooth Carbonates：Origin and Advancement

Stromatolite and Molar-tooth structure are of interest for geologists.Stromatolites underwent five major declines occurring at 2000 Ma,1250Ma,1000 Ma,675Ma and 450 Ma.Recently,according to a non-stromatolitic sedimentary succession in Yanshan area,there might be another stromatolite decline occurring at 1450Ma.Thus,there are six stromatolite declines during geological time and they are comparatively scarce at the present day.The success of stromatolites depends upon synsedimentary lithification and calcification,which are essential for the accretion and preservation to occur.Calcification reflects environmental constraints especially seawater chemistry.Both metazoan influence and seawater saturation state have combined to determine the abundance of stromatolites throughout Phanerozoic.