陕西汉中梁山二叠系乐平统底部吴家坪组王坡页岩新认识  

New Petrographic and Mineralogical Analyses of the Wangpo Shale,Wujiaping Formation(Basal Lopingian,Permian) in the Liangshan Area of Shaanxi

作　　者：郭俊锋[1,2] 宋祖晨 肖良[1,2] 李相传 郑亚娟[1,2] 姚肖永 周雪柔[3] 

机构地区：[1]长安大学地球科学与资源学院国土资源部岩浆作用成矿与找矿重点实验室,西安710054 [2]陕西省早期生命与环境重点实验室(西北大学),西安710069 [3]中国地质大学长城学院地球科学与资源系,河北保定071000

出　　处：《地质论评》2017年第5期1169-1179,共11页Geological Review

基　　金：国家自然科学基金资助项目(编号:41472015);中国国家留学基金管理委员会资助项目(编号:201306565037);中央高校基本科研业务费专项基金资助项目(编号:2013G3274021;2014G3272013)的成果~~

摘　　要：陕西汉中梁山瓜德鲁普统—乐平统界线(GLB)附近的吴家坪组底部王坡页岩段长期以来被认为是古风化壳沉积,代表了茅口期后暴露于地表风化剥蚀的产物。最近对该地层进行了重新研究,采集了系列岩石和化石样品,进行了X射线衍射、古生物学、岩相学和岩石学分析。X射线衍射分析表明该粘土层主要矿物成分为蒙脱石71%,片沸石23%,石英6%,暗示其物质来源于火山玻璃。岩相学分析显示岩石主要由蚀变矿物组成,具有蚀变残留玻屑凝灰质结构,其中蒙脱石、片沸石保留了原岩中的玻屑的塑性形态。粘土层中大量腕足动物化石暗示其为海相环境。研究结果表明王坡页岩是典型的斑脱岩,并非风化壳和长期剥蚀的产物,而是峨眉山大火成岩省火山喷发时火山灰在海相环境下沉积、蚀变的产物。火山灰在正常浅海沉积时对海洋生态系统造成严重破坏,导致了包括腕足动物在内的海洋生物的生存危机。Objectives ：The Wangpo Shale, representing Guadalupian--Lopingian Boundary （GLB） deposits, occurs at the base of the Wujiaping Formation in the Liangshan area of Shaanxi Province. It was traditionally interpreted as a terrigenous shale bed related to a paleo-weathering surface, suggesting a regression event after the Maokouan Stage. Methods： We carried out an investigation in detail for Wangpo Shale and collected the rock and fossil samples, the analysis of X ray diffraction （XRD）, paleontology, petrography and lithology are carried out. Results： X ray diffraction （XRD） analysis shows that the Wangpo Shale consists predominantly of montmorillonite （71%）, heulandite （23%）, and quartz （6%）, suggesting an origin from volcanic glass. Petrographic analysis shows that the Wangpo Shale is primarily composed of altered minerals montmorillonite and heulandite with residual tuffaceous structures and vitric pyroclast. Abundant brachiopod fossils occur in the Wangpo Shale, suggesting deposition in a marine environment. Conclusions： These data indicate that the Wangpo Shale is a typical bentonite, derived from volcanic ash fall that was subsequently altered in a marine environment. Sudden ash fall may have destabilized the shallow marine ecosystems at the Guadalupian--Lopingian Boundary, resulting in an ecological crisis for Permian brachiopods.

关 键 词：王坡页岩 斑脱岩 乐平统 陕西梁山 

分 类 号：P534.46[天文地球—古生物学与地层学]