ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    基于pXRF岩心扫描的扬子地台宜昌地区水井沱组黑色页岩地球化学特征

    Geochemical Characterization and Paleoenvironmental Analysis of Black Shale of the Shuijingtuo Formation in Yichang Area, Yangtze Platform, Based on pXRF Core Scanning

    • 摘要: 本研究以扬子地台宜昌地区针对寒武纪大爆发时期生态系统演化研究配套的全取心钻井岩心为研究对象,采用手持X射线荧光分析仪 (pXRF) 对水井沱组完整岩心中的地球化学元素进行高分辨率(采样间隔0.05 m)样品采集与分析,重建了水井沱组沉积时的古气候、古盐度、古氧化还原条件、古水深和古生产力特征。研究结果表明:Rb/Sr值变化指示沉积时期气候总体为温暖湿润,由水井沱组底部向顶部气候逐渐转为炎热干旱;Th/U<2反映沉积水体整体为海相咸水环境,但盐度存在波动变化,可能与局部海平面变化和沉积环境封闭性有关;V/(V+Ni) >0.5和V/Cr>2表明沉积水体长期处于贫氧至缺氧的还原性环境;Zr/Rb<2揭示沉积环境位于浅海台地边缘至外陆棚区域,水深较深;Ni/Al和Cu/Al值的峰值与多金属富集层段耦合。多种古环境的地球化学替代指标综合显示,水井沱组黑色页岩沉积时期为温暖湿润的还原环境,这种环境为有机质和多金属元素的富集创造了条件,同时也为清江生物群的形成和埋藏提供了关键的地质背景。本研究为扬子地台宜昌地区寒武纪早期古环境和生态系统重建提供了初步的地球化学证据,并为分析关键层位的古环境提供了一种准确高效的研究实例。

       

      Abstract: This study focuses on fully cored drilling samples from the Yichang area of the Yangtze Platform, targeting the evolution of ecosystems during the Cambrian Explosion. High-resolution geochemical element analysis (sampling interval: 0.05 m) was performed on intact core samples of the Shuijingtuo Formation using a portable X-ray fluorescence spectrometer (pXRF). This allowed for the reconstruction of paleoenvironmental characteristics during the deposition of the Shuijingtuo Formation, including paleoclimate, paleosalinity, paleoredox conditions, paleowater depth, and paleoproductivity. The results demonstrate the following: Variations in the Rb/Sr ratio indicate an overall warm and humid climate during the depositional period, with a gradual transition to a hotter and more arid climate from the base to the top of the Shuijingtuo Formation. Th/U<2 suggest a predominantly marine saline environment with fluctuating salinity, likely linked to local sea-level changes and the degree of environmental confinement. V/(V+Ni) >0.5 and V/Cr >2 reflect long-term suboxic to anoxic conditions in the depositional water column. Zr/Rb<2 reveal a depositional setting at the margin of a shallow marine platform to the outer shelf, characterized by relatively deep water depths. Peaks in Ni/Al and Cu/Al correlate with polymetallic enrichment intervals. Integrated geochemical proxies indicate that the black shales of the Shuijingtuo Formation were deposited in a warm, humid, and reducing shallow marine environment. These conditions promoted the enrichment of organic matter and polymetallic elements, while also providing critical geological prerequisites for the formation and exceptional preservation of the Qingjiang biota, a Burgess Shale-type fossil Lagerstätte. This study establishes preliminary geochemical evidence for reconstructing early Cambrian paleoenvironments and ecosystems in the Yangtze Platform and proposes an efficient analytical approach for deciphering paleoenvironmental conditions in key stratigraphic intervals.

       

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