桂东北吉维特阶与艾菲尔阶界线碳酸盐岩地球化学特征及古环境意义  

Geochemical characteristics and paleoenvironmental implications of carbonaterocks at the Givertian and Eifelian boundary in northeast Guangxi

作　　者：刘世杰 管琪 潘明[3] LIU Shijie;GUAN Qi;PAN Ming(Hebei Key Laboratory of Strategic Critical Mineral Resources,Hebei GEO University,Shijiazhuang,Hebei 050031,China;Hebei Province Collaborative Innovation Center for Strategic Critical Mineral Research,College of Earth Sciences,Hebei GEO University,Shijiazhuang,Hebei 050031,China;Institute of Karst Geology,CAGS,Guilin,Guangxi 541004,China)

机构地区：[1]河北地质大学,河北省战略性关键矿产资源重点实验室,河北石家庄050031 [2]河北地质大学地球科学学院,河北省战略性关键矿产研究协同创新中心,河北石家庄050031 [3]中国地质科学院岩溶地质研究所,广西桂林541004

出　　处：《中国岩溶》2023年第3期436-447,共12页Carsologica Sinica

基　　金：中国地质调查局地质调查项目(DD20221637,DD20190022)。

摘　　要：依托阳朔县龙岩口艾菲尔阶与吉维特阶界线剖面,采集碳酸盐岩样品10个,通过显微特征、元素组分含量及相关元素的比值特征、碳氧同位素数据等,对该界线附近的古海洋沉积环境进行了分析和探讨。研究表明:①样品YS3层位产牙形刺分子Polygnathus intermedius,可归属于艾菲尔晚期ensensis带,为该层位碳同位素偏移事件、Eiffelian与Givertian界线以及Kačák事件提供了准确的时限约束;②参考Wilson的标准微相沉积模式,结合岩性特征,识别出SMF23、SMF16、SMF4和SMF15共四种微相类型;③通过对碳酸盐岩主、微量元素及其比值分析,得出以下结论:YS1至YS2对应阶段为沉积水体快速变深,且具有一定物源供给的沉积环境,反映了海侵初期,海洋环境由局限-半局限台地相向斜坡相快速转变的地质过程;YS3至YS4阶段低含量的陆源组分反映了水体较深、海平面相对较高的远岸沉积环境,该阶段海洋环境以缺氧为典型特征;YS5至YS10阶段陆源组分含量逐渐增加,出现代表低能环境的放射状鲕粒灰岩,沉积区海平面呈现出明显下降的趋势,剖面中多个向上变厚的进积型层序是良好的沉积学响应;④依据氧同位素,重建了古海水温度演化曲线,研究表明该时期海水平均温度为21℃,为温暖的亚热带气候,与其位于赤道附近的古地理位置相吻合;⑤样品YS3层位碳同位素表现出的负偏移现象与摩洛哥全球界线层型剖面和北美加拿大地区同层位的δ13C值曲线特征相吻合,共同反映了全球尺度海侵背景下的缺氧沉积环境。The Devonian period,marking the initial phase of the Late Paleozoic era,has garnered considerable attention in recent decades.This heightened interest stems from its intricate climatic fluctuations,recurrent global shifts in sea levels,and a series of consequential biological catastrophes.Of particular captivation is the upper Devonian-lower Carboniferous in northeastern Guangxi, characterized by a multifaceted paleogeographicconfiguration known as platform-trench-basin facies. Notably, the stratigraphic progression from basin facies to openplatform facies displays a notable continuity, culminating in the formation of a substantial kilometer-thick carbonaterock layer. This unique geological foundation underpins the development of a renowned karst geomorphic landscape,which is globally significant. Furthermore, this distinctive karst landscape has facilitated the establishment of the international Devonian-Carboniferous boundary auxiliary layer profile, adding another layer of importance to the study of the Devoniansystem in this region. While prior investigations have primarily concentrated on sedimentary facies, paleontology,pivotal organisms, and event layers like the 'F-F' biological catastrophe event and the D/C boundary layer during theLate Devonian, certain critical events, notably the Kačak-Otomari event in the late middle Devonian, have receivedcomparatively less attention. Moreover, a comprehensive global-scale comparative analysis has been lacking. Given these gaps, the present study investigates a critical juncture, the boundary between the Eiffelian andGivertian systems, situated in Longyankou village, Yangshuo county. A meticulous examination was carried out,involving the collection of ten carbonate rock samples from this specific section. Through a comprehensive analysisencompassing microscopic features, elemental compositions, ratios, as well as carbon and oxygen isotope data, thestudy aimed to elucidate and discuss the ancient oceanic sedimentary environments in proximity to this location. Ourfin

关 键 词：桂东北 Kačák事件 碳酸盐岩 古环境 泥盆纪 

分 类 号：P588.245[天文地球—岩石学]