皖南石台下奥陶统仑山组的叠层石

扬子区东南台缘下奥陶统特马道克阶仑山组上段多见厚层碳酸盐岩,其中的叠层石礁出露厚度23m,穹窿状叠层石密集生长序列厚度20m,往上部的3m叠层石变得稀少。微相特征显示叠层石的纹层多不清晰,存在不同程度的生物、物理及化学营力的干扰现象,可识别数种成因。生物对藻席表面的啃食和内部的栖居钻孔可破坏纹层;高能水流时常带入的生屑、砂屑堆积能点断叠层石纹层的正常生长;部分叠层石中常见压溶缝合线和白云岩化。区域海退过程抑制了叠层石礁的连续生长。

STROMATOLITE OF THE LOWER ORDOVICIAN LUNSHAN FORMATION IN SHITAI,SOUTH ANHUI PROVINCE,EAST CHINA

Tremadocian(Lower Orodvician)stromatolitic units of the Upper Member,Lunshan Formation are yielded along the southeast margin of the Yangtze Platform(South China Block).They are dominated by massive-bedded microbial bindstone with less macrofossils,and typical of low biodiversity.Major column-shaped stromatolite units with20min total thickness are densely outcropped at the Shitai Middle Shool Section and above them,they sparsely occurr in three meters of the outcrop.Varying biotic,physical and chemical factors are considerably impacting on the morphological reformations of the microfacies of the laminations.Bioturbation could be recognized on the surfaces of algal mats and even in their interior lithified parts.Deposition of bioclastic and sandy debris drived by higher enengy currents significantly punctured the regular growth of the laminations.Pressure solution sutures and dolomitizations are common phenomena within the stromatolitic subfacies.A regional regressional tract is potential in constraining of the stromatolite development.