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对北淮阳晚中生代火山岩的野外调查和K-Ar定年结果表明,该区发生过两期火山喷发作用:主要分布于金寨、鲜花岭和毛坦厂地区的原毛坦厂组火山岩,形成于149～138 Ma;主要分布于舒城一带的原晓天组火山岩K-Ar年龄为132～116Ma。两者之间为含灰色片麻岩、榴辉岩和火山岩砾石的火山沉积砾岩层.砾岩层内火山砾石的地球化学特征与毛坦厂组火山岩一致,而有别于晓天组火山岩.该砾岩层于 138～132 Ma堆积而成,暗示 135 Ma前后北大别灰色片麻岩已从中上地壳折返至地表接受剥蚀,成为北淮阳中生代沉积盆地的重要蚀源区.结合北淮阳地区中生代火山-沉积特征,将该区中生代沉积地层依次划分为防虎山组（>160 Ma）、圆筒山组（三尖铺组中下部,约 160～149 Ma?）、毛坦厂组（周公山组/三尖铺组上部/凤凰台组,约 149～135 Ma,顶部为砾岩层）、晓天组（白大畈组/黑石渡组,底部为砾岩层,135～116Ma）.
The field investigation and K-Ar dating of the Mesozoic volcanic rocks in the northern Huaiyang area show that there are two volcanic eruptions occurring in this area: the volcanic rocks of the Maotanchang Formation, mainly distributed in Jinzhai, Xianghuaoling and Maotanchang areas, 149 ~ 138 Ma. The K-Ar ages of the original Xiaotian Formation volcanic rocks in the Shucheng area ranged from 132 to 116 Ma. They are volcanic-sedimentary conglomerate with gray gneiss, eclogite and volcanic gravel.The geochemical characteristics of volcanic gravel in the conglomerate are consistent with the volcanic rocks in the Moutanchang Formation and distinct from the volcanic rocks in Xiaotian Formation. The conglomerate layer is deposited from 138 to 132 Ma, suggesting that the North Dabie gray gneiss had been eroded from the upper crust to the earth surface for denudation before and after 135 Ma, forming an important source area for the Mesozoic sedimentary basin in the Northern Huaiyang area. Volcanic-sedimentary features, the Mesozoic sedimentary strata in this area are divided into three groups: the anti-tiger group (> 160 Ma), the cylinder group (about 160-149 Ma? In the middle and lower part of the Sanjianpu group) Shanyuan Formation / Upper Triassic Formation / Fenghuangtai Formation, about 149-135 Ma, with conglomerate layers on top), Xiaotian Formation (Bai Dao Formation / Heishidudu Formation, bottom conglomerate formation, 135-116 Ma).