“南郑页岩”时代的再认识

<正> “南郑页岩”是卢衍豪(1959)建立的一个地层单位,用以代表奥陶纪宝塔灰岩之上,志留纪龙马溪页岩之下约6m厚的一段地层,产以Dalmanitina为主的三叶虫,及笔石、瓣鳃类等化石。“南郑页岩”的时代,卢衍豪(1943)最初曾“疑其为上奥陶纪产物”,在正式命名时(1959)认为“放在志留纪底部为宜”。此后,对其时代归属的问题争论颇多,有

Review on the age of the "Nanzheng Shale

The "Nanzheng Shale" is well known for its bearing the Dalmanitina fauna together with abundant graptolites and other fossils. Recent biostratigraphic study at the type locality in Nanzheng, Shaanxi Province has ed to the following conclusions: The name of "Nanzheng Shale" is better to be replaced by Nanzheng Formation. As a regional lithostratigraphic unit, it represents the marine deposits along the idannan old landmass during the Late Ordovician Wufengian stage. The Nanzheng Formation can be correlated with the Wufeng Formation widely distributed in the Yangtze platform area, with the top corresponding to the Diplograptus bohemicus zone-(W6) and the lower part being correlative with the Dicellograptus szechuanensis zone (W2). In this regard, the Dalmanitina fauna in Nanzheng, Shaanxi is also Late Ordovician in age. It reveals that most of the Dalmanitina fauna in China occur in the Late Ordovician, ranging from the Dieratograptus mirus zone (W4) up to the Diplograptus bohemicus zone (W6). Biostratig-raphically, the sequence between Nanzheng Formation and the overlying stratum, the Early Silurian Lungmachi Formation with index graptolite Glyptograptus lungmaensis is continuous and is in accordance with the chronostratigraphic boundary between Ordovician and Silurian.