摘要
【目的】白垩纪在地质历史上曾发生过极端温室气候、全球大洋缺氧以及富氧事件,在此时期出现的白垩纪红层蕴含着重要的古气候和古环境信息,对理解地球表层系统具有十分重要的意义。【方法】以中国东部北黄海盆地白垩纪发育的一套湖相红色厚层泥岩为主要研究对象,对取自钻井的中侏罗统至下白垩统的红色和灰色泥岩岩心样品分别开展了X射线衍射(XRD)与漫反射光谱(DRS)分析,半定量—定量分析岩石中致色矿物的组成及含量;结合普通薄片、扫描电镜等方法观察泥岩中致色矿物的赋存特征,如含铁矿物的形态、分布、晶型大小等;运用DRS二阶导数法计算泥岩样品中的赤铁矿和针铁矿的含量;并结合样品中铁氧化物的含量及其比值变化获取红色泥岩沉积期的古气候与古环境信息。【结果】红色泥岩致色矿物有赤铁矿和针铁矿,其中以赤铁矿为主,最高含量可达14%,而灰色泥岩中不含赤铁矿和针铁矿;红色泥岩在显微镜下可见赤铁矿集合体,局部可见蚀变现象;扫描电镜下可见赤铁矿呈颗粒状或板状集合体。DRS二阶导数法求出红色样品中赤铁矿平均含量为1.25 g/kg,最高可达2.62 g/kg。针铁矿含量平均为0.62 g/kg,最高可达1.19 g/kg。赤铁矿与针铁矿含量变化特征表明,晚侏罗世至早白垩世早期气候相对湿润,早白垩世中期至晚期气候以炎热干旱为主。【结论】结合岩性特征和北黄海盆地及其邻区资料,发现在研究区内利用铁氧化物反映古气候变化的方法具有可行性,综合分析认为白垩纪红色泥岩中的致色矿物具有一定的古气候与古环境指示意义。
[Objective]During the Cretaceous period,extreme greenhouse climate,global oceanic anoxia,and oxy⁃gen enrichment events occurred.The Cretaceous red beds that appeared during this period contain important informa⁃tion related to the paleoclimate and paleoenvironment that aid in our understanding of stratigraphic surface systems.[Methods]In this study,a set of red mudstones developed during the Cretaceous in the North Yellow Sea Basin of eastern China were taken as the object of study.X-ray diffraction(XRD)and diffuse reflectance spectroscopy(DRS)analyses were conducted on the red and grey mudstones of the Middle Jurassic to Lower Cretaceous to semiquantitatively and quantitatively analyze the composition and content of chromogenic minerals in the rocks.We also combined the ordinary thin section and scanning electron microscope methods to observe the characteristics of chro⁃mogenic minerals in the red mudstone,such as the morphology,distribution,and crystalline size of iron-containing minerals.The DRS second derivative method was used to calculate the contents of hematite and goethite in mudstone samples.The paleoclimate and paleoenvironment information of red mudstone during its deposition period was obtained by combining the content and ratio of iron oxides in the samples.[Results]XRD results show that the chromogenic minerals in the red mudstone are hematite and goethite,of which hematite is the main content.The high⁃est content can reach 14%,whereas the grey mudstone does not contain hematite;hematite aggregates can be seen under the microscope in the red mudstone,and alteration phenomena can be seen in the local area;hematite can be seen as granular or plate aggregates under the scanning electron microscope;The DRS second derivative method cal⁃culated that the average content of hematite in red samples was 1.25 g/kg,and the highest was 2.62 g/kg.The average content of goethite was 0.62 g/kg,and the highest was 1.19 g/kg.Using the changes in hematite and goethite content,the climate was found to be relatively humid from the Late Jurassic to the Early Cretaceous,and hot and dry from the Middle to Late Early Cretaceous.[Conclusions]Combined with the paleoclimate data of the North Yellow Sea Basin and its adjacent areas,the method of using iron oxides to reflect the paleoclimate changes in the study area was found to be feasible.A comprehensive analysis suggests that the chromogenic minerals in the red mudstone of the Lower Cretaceous have indicative significance for the paleoenvironment and paleoclimate.
作者
岑欣
王任
殷科
石万忠
李顾盼
胡小强
CEN Xin;WANG Ren;YIN Ke;SHI WanZhong;LI GuPan;HU XiaoQiang(Key Laboratory of Tectonics and Petroleum Resources,Ministry of Education,China University of Geosciences(Wuhan),Wuhan 430074,China;School of Earth Resources,China University of Geosciences(Wuhan),Wuhan 430074,China;School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,China;Guangzhou Marine Geological Survey,Guangzhou 510075,China)
出处
《沉积学报》
北大核心
2025年第6期1978-1991,共14页
Acta Sedimentologica Sinica
基金
国家自然科学基金项目(42202121)。
关键词
红色泥岩
致色矿物
古环境
白垩纪
北黄海盆地
red mudstone
chromogenic minerals
paleoenvironment
Cretaceous
North Yellow Sea Basin
