Weathered crust and sedimentary intercalation are indicative of volcanic intervals.Extrusive and volcanogenitic sedimentary facies are the end-members of an eruption cycle.

• 风化壳层之上和沉积夹层之上的火山岩是新的喷发旋回的开始，而火山沉积相和侵出相的出现往往标志着一个火山喷发旋回的结束。