摘要
为查明六盘山地区白垩纪李洼峡组狼鳍鱼化石的埋藏学特征所表征的古气候和古环境意义,以化石保存层位岩石和其上下层岩石为主要研究对象,对它们进行了全岩X衍射(XRD)、主量元素、微量元素和稀土元素分析.XRD分析显示化石埋藏层位岩石的组成矿物主要以铁白云石(42.70%)和石英(41.50%)为主,其上下层岩石的组成矿物主要以石英(平均含量40.40%)和长石(总平均含量15.98%)为主.主量元素分析显示化石埋藏层位岩石具有较高含量的CaO(平均含量20.61%)和MgO(平均含量10.52%),而其他层岩石具有较高含量的SiO_(2)(平均含量54.58%)和Al2O3(平均含量14.79%).古气候指标MgO/CaO和Sr/Cu指示干热的气候,古盐度指标m值和Sr/Ba指示水体盐度高,古氧化还原环境指标Th/U和V/(V+Ni)指示缺氧和水体分层且底层出现硫化环境.鱼群的大规模死亡是由一次短暂的突发性事件造成,缺氧的水体环境和硫化氢的毒害作用可能是鱼类大规模死亡并得到保存的主要原因.特别需要指出的是,六盘山地区在白垩纪中期出现干热的气候条件以及高盐度、缺氧的水体环境可能是这一时期全球CO_(2)浓度快速升高的结果,也可视为白垩纪Aptian-Albian大洋缺氧事件(OAE1a)在陆相地层的地质响应.
In order to find out the taphonomy and paleoclimate and paleoenvironment significance of Lycoptera-bearing Liwaxia Formation in the Liupanshan area,multiple methods of analyses are used.XRD analysis shows that the fossil-bearing is mainly composed of ankerite(42.70%)and quartz(41.50%),while its overlying and underlying neighbors are mainly composed of quartz(average 40.40%)and feldspar(total average 15.98%).The major elements of the fossil-bearing unit are CaO(average 20.61%)and MgO(average 10.52%),while its neighboring units are enriched in SiO_(2)(average 54.58%)and Al2O3(average 14.79%).The paleoclimate indexes MgO/CaO and Sr/Cu indicate a dry hot climate,the paleo-salinity index m value and Sr/Ba indicate a high salinity environment,and the paleo-redox environment indexes Th/U and V/(V+Ni)indicate a stratified aquatic environment with euxinic bottom water.The mass mortality of fishes was caused by a rapid redox change of the water body and toxicity of H2S.It is likely that the anoxia was a response to OAE1a in the Liupanshan area,and the dry hot climate and high salinity water were caused by the elevated atmospheric CO_(2) concentration in the Middle Cretaceous.Additionally,the euxinic bottom water provides favorable conditions for the preservation of fish fossils.
作者
梁积伟
常小斌
陶文星
冯振伟
李汉林
宗浩
郑萌
Tsogochir Tungalag
Liang Jiwei;Chang Xiaobin;Tao Wenxing;Feng Zhenwei;Li Hanlin;Zong Hao;Zheng Meng;Tsogochir Tungalag(School of Earth Science and Resources,Chang'an University,Xi'an 710054,China;Geological Research Institute,Binnan Oil Production Plant,Shengli Oilfield Company,SINOPEC,Binzhou 256600,China)
出处
《地球科学》
EI
CAS
CSCD
北大核心
2024年第1期189-208,共20页
Earth Science
基金
第二次青藏高原综合科学考察项目(No.2019QZKK0704)。
关键词
六盘山地区
白垩纪
化石埋藏学
主微量元素
古气候
古环境
Liupanshan area
Cretaceous
taphonomy
major and trace element
paleoclimate
paleoenvironment
