我国志留系的划分和对比,过去长期地以三峡剖面为标准,以小达尔曼虫层之上最早出现的礁相地层作为中志留统的底界。经近年的深入研究,发现过去划归中志留统的罗惹坪组,甚至过去划归上志留统的纱帽组的中、下部仍属早志留世沉积,因而认为过去的中、下统界线大大地偏低。随着三峡“标准剖面”的厘正,全国志留系的划分、对比,出现了重新认识的局面。陕甘宁地区不少地方过去同样出现过中、下统划界偏低的现象,将志留系中几乎所有礁 In the past, the division and contrast of Silurian in China were based on the Three Gorges section in the past, and the reef-facies strata that appeared above the Little Dalmatian layer served as the bottom of the Middle Silurian. After a thorough study in recent years, it has been found that the middle and lower parts of the Yarlung Ping Formation previously classified by the Central Zhi-li-Tuo and even the Yarn-hat Formation previously classified by the Upper Silurian are still of the Early Silurian sediments. Therefore, Boundary greatly lower. With the correction of the “standard profile” of the Three Gorges and the division and comparison of national records of Silurian, a new understanding has emerged. In many parts of the Shaanxi-Gansu-Ningxia region, the phenomenon of low demarcation of the middle and lower dens occurred in many places in the past and almost all reefs in the Silurian