In the lower Ordovician Penglaiba Formation of Tarim basin occur thick strata of interbeded dolostone and limestone,which show a relatively constant petrologic rhythm in Tazhong19 well:three parts can be observed in every rhythm,the upper part is microlite limestone,middle part is dolostone,and lower part is siliceous granular limestone.

Based on the core drilling data,the high-resolution volcanic cycles of the first member of Yingcheng formation in Xujiaweizi fault depression were divided,the volcanic cycle model were built,and the well logging characteristics of different lithology and lithofacies were summarized.