福建黄塘晚侏罗世长林组硅质岩地球化学特征及其沉积环境意义

福建黄塘地区晚侏罗世长林组发育一套层状硅质岩，夹薄层凝灰岩，产硅质海绵骨针和硅质钙藻，其硅质岩沉积环境复杂，成因一直存在不同认识。本文通过野外地质调查和岩相学研究，以及主量元素、稀土元素和微量元素分析认为，该区硅质岩为非纯硅质岩，在FeMnAl三角图中样品位于生物成因区及附近，Mo和V含量富集、轻稀土富集、Eu弱负异常及U/Th值也都具有典型的生物成因特征，且微观特征显示其受到火山活动的影响。黄塘硅质岩在Fe2O3/TiO2Al2O3/(Al2O3+Fe2O3)、TFe2O3/(100-SiO2)Al2O3/(100-SiO2)和(La/Ce)NAl2O3/(Al2O3+Fe2O3)图解中都投在了大陆边缘及附近。ΣREE值较高、Ceanom值、MnO/TiO2值及(La/Yb)N值等这些地球化学指标一致表明黄塘硅质岩处于受陆源物质影响的大陆边缘浅海沉积环境。在前人研究基础上，认为研究区在晚侏罗世早期开始发生海侵并伴有小规模的火山活动，整体为还原环境，局部可能水体较深，为进一步开展福建、浙江地区的石油地质评价工作提供了依据。

Geochemical characteristics and sedimentary environmental implications of the Late Jurassic siliceous rocks in the Changlin Formation,Huangtang section,Fujian Province

The Changlin Formation in the Huangtang area, Fujian Province developed bedded siliceous rocks consisting of thin-layered tuff and producing siliceous sponge spicules and siliceous calcareous algaes. The sedimentary environment of the siliceous rocks is complex and their origin is still under debate. Here, based on our field geological survey and petrographic study, as well as analyses of major elements, rare earth elements and trace elements, we show that the siliceous rocks have similar phase behavior as non-hydrothermal siliceous rocks in the Fe-Mn-Al diagram. Moreover, findings of enrichment of Mo, V and LREEs, weak negative Eu anomalies and U/Th values concur with typical biogenic characteristics, while microscopic characteristics show influence of volcanic activity. In the major element discrimination diagrams including Fe2O3/TiO2Al2O3/(Al2O3+Fe2O3), TFe2O3/(100SiO2)Al2O3/(100SiO2) and (La/Ce)NAl2O3/(Al2O3+Fe2O3) diagrams, the siliceous rocks are consistent with continental shelf. Geochemical indicators such as high ΣREE value and values of Ceanom, MnO/TiO2 and (La/Yb)N, all indicate that the siliceous rocks deposited in the shallow sea continental shelf under anoxic condition, affected by terrigenous material in the Huangtang area. Combining other researchers work, we believe that transgression in the study area began in the Late Jurassic accompanied by small-scale volcanic activities in an overall reducing environment, producing isolated deep water areas. Our research may guide future developments in petroleum geology assessment of prospective regions in Fujian and Zhejiang Provinces.