康滇古陆西侧龙马溪组黑色页岩地球化学特征及其地质意义  

Black shales from the Longmaxi Formation in western Xikang-Yunnan ancient land: Geochemistry and geological implications

作　　者：张茜[1,2] 王剑[3,2] 余谦[3,2] 王小飞[2] 赵安坤[1,2] 张海全[2] 王正和[2] 

机构地区：[1]成都理工大学,四川成都610059 [2]中国地质调查局成都地质调查中心,四川成都610081 [3]国土资源部沉积盆地与油气资源重点实验室,四川成都610081

出　　处：《沉积与特提斯地质》2017年第1期97-107,共11页Sedimentary Geology and Tethyan Geology

基　　金：国家重大科技专项课题<页岩气勘查评价技术试验与应用推广>支持;课题编号2016ZX05034004

摘　　要：为查明康滇古陆西侧龙马溪组黑色岩系的地质成因及沉积环境,指导区域页岩气勘探开发,对宁蒗盆地东南缘李子河地区龙马溪组岩层开展了详细的元素地球化学研究。结果表明,研究区硅质含量较高(SiO_2值为64.78%~96.89%),Al_2O_3与TiO_2呈正相关,SiO_2/Al_2O_3与Al_2O_3呈负相关,这种相关关系表明该区硅质岩系为非纯硅质岩,含有较高比例的陆源泥质沉积物。Al/(Al+Fe+Mn)值(0.53~0.75)、Fe/Ti值(6.38~14.96)、(Fe+Mn)/Ti值(6.40~18.20)、Si/(Si+Al+Fe)值(0.82~0.99)及Al-Fe-Mn三角图解综合显示出生物沉积硅质岩的特点。MnO_2/TiO_2值(0.005~1.20)、δCe值(0.46~0.92)、相关构造判别图解以及稀土元素分布形式特点均说明源区形成于接近大陆边缘的深水-半深水沉积环境。沉积期水体盐度指标m值(4.96~36.88)、CaO/(Fe+CaO)值(0.017~0.83)以及氧化还原指标δCe负异常、δEu正异常、Ce/La值(1.04~2.09)等元素特征指示其沉积于还原条件下低中等盐度海水环境,这种环境下适合有机质的富集和保存。高有机碳(TOC)与高硅质含量显示弱的负相关,说明生物成因硅质岩是造成高TOC的主要原因,而陆源物质硅对有机质进行稀释和破坏反而降低了TOC含量。受上述成因构造及沉积环境的影响,在宁蒗盆地李子河地区龙马溪组形成一套品质较好的富有机质烃源岩储层,具有一定的页岩气地质评价意义。The detailed element geochemical studies are conducted to ascertain the geological genesis and sedimentary environments of the black shales from the Longmaxi Formation in the southeastern Ninglang Basin on western Xikang-Yunnan ancient land, and to provide helpful information for the shale gas exploration in this area. The black shales have higher Si02 contents ranging between 64. 78% and 96. 89% , positive correlation of A1203 and Ti02 contents and negative correlation of Si02/Al2 03 ratios and Al2 03 contents, suggesting that the siliceous rocks in this area are not pure siliceous rocks but higher proportion of terrigenous argillaceous deposits. The Al/（ A1 ＋ Fe ＋ Mn） （0.53 -0.75）, Fe/Ti （6.38 -14.96）, （Fe＋Mn）/Ti （6.40 -18.20）, Si/（Si ＋ A1 ＋ Fe） （0.82 -0.99） ratios and Al-Fe-Mn triangular diagram indicate that the siliceous rocks mentioned above are biogenetic. The Mn02/Ti02 ratios （0. 005 - 1.20） , 8Ce values （0. 46 -0. 92） , tectonic discrimination diagram and REE distribution patterns also indicate the continental-margin abyssal-bathyal sedimentary environments of the provenances. The salinity index of the sea water （m =4.96 -36.88） , CaO/（Fe ＋ CaO） ratios （0.017 -0.83）, negative 8Ce anomalies and positive 8Eu anomalies, and Ce/La ratios （1.04 -2. 09） indicate the anoxic and low- to moderate-salinity marine sedimentary environments. There are slightly negative correlation between high organic carbon and high Si02 contents, indicating that the biogenetic siliceous roks should be responsible for the high organic carbon contents. The organic-rich source rocks from the Longmaxi Formation in the Lizihe region are interpreted to be favourable for shale gas exploration due to high organic carbon contents, greater shale thicknessand abundant surface oil and gas showings.

关 键 词：龙马溪组 黑色页岩 地球化学特征 地质意义 

分 类 号：P534.43[天文地球—古生物学与地层学]