位于河北元氏县北的元北勘探区,构造复杂,对比的标志层少。我们在用岩矿鉴定寻找标志层时,发现在太原组中下部小青灰岩与中青灰岩间有一层沉凝灰岩,颜色灰绿,遇水膨胀,俗称“糟砂岩”,正粒序层理,厚度8m左右,产状稳定。镜下见有明显的凝灰结构,火山碎屑物主要是半棱角状、有泥化现象但结构可辨的安山岩屑,含量30％,粒径0.1～1mm;晶 It is located in the Yuanbei exploration area north of Yuanshi County, Hebei Province. It has a complex structure with fewer sign layers. When we used the identification of rock and mineral resources to find the sign layer, we found that there is a layer of tuffaceous limestone in the middle and lower part of Taiyuan Formation, which is gray-green and water-swelling, commonly called “bad sandstone” Thickness of about 8m, stable shape. Microscopic see the obvious tuff structure, volcanic detrital material is mainly half angular, mud phenomenon but structural discernible andesite debris content of 30%, particle size 0.1 ~ 1mm; crystal