下三叠统奥伦尼克阶含鱼化石结核地质意义初探  

GEOLOGICAL SIGNIFICANCE OF THE FISH-BEARING CONCRETIONS NEAR THE SMITHIAN-SPATHIAN BOUNDARY,OLENEKIAN,EARLY TRIASSIC

作　　者：周敏[1] 付宛璐[1] 张超[2] 倪培刚 季承[2] 

机构地区：[1]北京大学地质系和地质博物馆,北京100871 [2]中国科学院南京地质古生物研究所资源地层学与古地理学重点实验室,江苏南京210008

出　　处：《地层学杂志》2015年第4期395-402,共8页Journal of Stratigraphy

基　　金：国家自然科学基金(No.41372016);现代古生物学和地层学国家重点实验室开放基金(123102);高校博士点基金(20120001110072);人才培养共建项目-资源共享类项目-北京高校博物馆联盟建设(体制改革项目)资助

摘　　要：早三叠世奥伦尼克期含鱼化石碳酸盐岩结核在许多地区的海相地层中都有发现,如非洲东部的马达加斯加、欧洲北极圈内的斯匹兹卑尔根群岛`以及北美加拿大西部的不列颠哥伦比亚等。在我国安徽巢湖、江苏南京龙潭、句容等地的下三叠统奥伦尼克阶斯密斯亚阶(Smithian)顶部泥岩中也发育有大量含鱼化石的钙质碳酸盐岩结核,俗称"鱼瘤",其中的鱼化石保存完整且精美。安徽巢湖的"鱼瘤层"位于斯密斯亚阶-斯帕斯亚阶(SmithianSpathian,简称S-S)界线之下,围岩为灰色薄层泥质灰岩与灰黑色含瘤泥页岩互层,指示当时沉积期水体安静,相对缺氧,处于还原环境。对"鱼瘤层"的成因分析表明,在酸性的海水中有机体在缺氧条件下分解可形成局部的碱性环境,使碳酸盐围绕有机体沉积形成结核。因此,"鱼瘤层"的存在指示当时的海水为缺氧的沉积环境。研究区"鱼瘤层"对应碳同位素值(δ13 C)为升高趋势,并由负值变为正值,且"鱼瘤层"的存在也可作为识别S-S界线的参考标志之一。基于现有碳氧同位素、孢粉学证据和菊石地理分布及生物多样性的研究,斯密斯期末期全球气候环境发生变化,海水表面温度较高,酸化且缺氧,引发一次小规模生物绝灭事件。"鱼瘤层"的形成、碳同位素正向漂移以及菊石纬度分异度的变化都是斯密斯亚期-斯帕斯亚期之交全球海洋环境事件(S-S事件)的不同表现形式。Fossil-bearing carbonate concretions are found in Early Triassic marine strata of many regions,including Madagascar in southern Africa,Spitsbergen in Europe and British Columbia in North America.In Chaohu of Anhui Province,Longtan near Nanjing of Jiangsu Province,and Jurong of Jiangsu Province,there are many carbonate concretions in uppermost Smithian mudstones,and some of them are fish-bearing and commonly known as＂fish nodule＂.The＂fish nodule layers＂are below the Smithian-Spathian Boundary,and they are preserved in dark gray thin-bedded mudstones.Lithological study shows that the mudstones were deposited in anoxic environments.The carbonate carbon isotope values（δ13C）of＂fish nodule layers＂are positive and show an increasing stratigraphic trend.The ＂fish nodule layers＂is regarded as marker of the Smithian-Spathian boundary.Based on carbon and oxygen isotope data,palynological analysis,global distribution of ammonoids,and biodiversity data,we infer that a significant climatic and environmental change occurred at the end of the Smithian,which caused a biological crisis.The development of fossil-bearing concretions coincides with this environmental change and the Smithian-Spathian crisis.Thus,the＂fish nodule layers＂,the stratigraphic pattern of carbon isotopes,and changes in the latitude distribution of ammonoids are regarded as a manifestation of the Smithian-Spathian global oceanic event.

关 键 词：生物地层 含化石碳酸盐岩结核 S-S全球海洋环境事件 碳同位素 早三叠世 巢湖 安徽 

分 类 号：P534.51[天文地球—古生物学与地层学]