甘蒙北山地区海相二叠系时代及其区域对比

Chronostratigraphy and Regional Comparison of Marine Permian System in the Beishan Region,North China

甘蒙北山地区海相二叠系是中亚造山带最年轻的海相地层之一,但其精确时代尚缺少高精度年龄数据约束。此次研究获得北山地区双堡塘组火山岩LA-ICP-MS锆石U-Pb年龄285.7±2.9 Ma、280.9±2.8 Ma、279.2±4.8 Ma和272.7±2.6 Ma。同位素年龄和古生物组合证明北山海相二叠系时间延限为早二叠世亚丁斯克期—中二叠世卡匹敦期(Artinskian-Capitanian,286~265Ma),其中双堡塘组、菊石滩组和金塔组时代分别主要为亚丁斯克—沃德期(Wordian)、沃德期和卡匹敦期。区域对比表明中亚造山带新疆北部地区的海相沉积最终消失在早二叠世空谷期(Kungurian)之前(>288Ma),而甘蒙北山和内蒙古地区海相沉积可持续至中二叠世卡匹敦期(265Ma)。

Marine Permian system in the Beishan Region,North China is one of the youngest sequences in the Central Asian Orogenic Belt.But its precision time has not been constrained due to lacking high-resolution isotopic age data.This study obtained four LA-ICP-MS zircon U-Pb ages for the volcanic rocks from the Shuangbutang Formation,285.7±2.9 Ma,280.9±2.8 Ma,279.2±4.8 Ma and 272.7±2.6 Ma.Isotopic and paleontological evidence indicates that the marine Permian in the Beishan region ranges from Artinskian to Capitanian（286-265 Ma）,with the Shuangbotang,Jushitan and Jinta formations occurring in Artinskian, Wordian and Capitanian,respectively.Regional comparison shows that the marine deposition in the northern Xinjiang region ceased before the Kungurian（288 Ma）of early Permian,while the marine deposition in the Beishan and ancient Inner Mongolian regions continued until the Capitanian（265 Ma）.