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黑色页岩是富含有机质和硫化矿物的特殊沉积岩,但人们对其风化过程的元素活动性及矿物风化机制关注较少.为探讨不同地形位置的黑色页岩化学风化过程,采集了渝东北城口某山脊(A)、近山顶(B)和沟谷(C)的下寒武统水井沱组黑色页岩风化剖面岩样,利用XRD、XRF和化学分析手段对采集样品的矿物成分、主量元素进行测定分析.元素和矿物的质量迁移系数(τ)和质量迁移通量(M_(j,flux))的计算结果表明,黑色页岩风化过程中Ca、Mg和Na元素具有明显的贫化现象,近地表处存在Al元素的富集现象;矿物成分方面,黄铁矿和有机质氧化后形成的酸性水环境,造成方解石、白云石、斜长石等不稳定矿物溶解,并生成含水石膏、铁质氧化物、黏土矿物等次生矿物.不同赋存位置的黑色页岩风化程度有所差异,Na/K-CIA、K/Ca*-Al/Na、A-CN-K和A-CNK-FM图解显示:A剖面处于脱Ca过程的初级风化阶段,B剖面处于脱Ca、Na初期的初等-中等风化阶段,C剖面已发生脱Ca、Na过程,并伴随脱Si作用的中等-强烈风化阶段,结合不同风化指数(如:CIA、CIW、PIA、MWPI等),得出各剖面的化学风化强弱程度依次为C>B>A.
Black shale is a special sedimentary rock rich in organic matter and sulfide minerals, but people pay less attention to its elemental activity and mineralization mechanism of weathering.For exploring the chemical weathering process of black shale at different topographic positions, The rock profiles of black shale weathering sections of the Lower Cambrian Shui-Tuo Formation in the vicinity of the ridge (A), near the summit (B) and the valley (C) were analyzed by XRD, XRF and chemical analysis. The mineral composition, Element.The results of mass transfer coefficient (τ) and mass flux (M_ (j_flux)) of elements and minerals show that the elements of Ca, Mg and Na are obviously depleted during the weathering of black shale Phenomenon, there is Al element enrichment phenomena near the surface; mineral composition, pyrite and organic acid oxidation of the formation of acidic water environment, resulting in calcite, dolomite, plagioclase and other unstable minerals dissolved and generate hydrated gypsum, Iron oxides, clay minerals and other secondary minerals.Different occurrences of black shale weathering degree is different, Na / K-CIA, K / Ca * -Al / Na, A-CN-K and A-CNK The -FM diagram shows that section A is in the primary weathering stage of the Ca-removal process , The B section is in the middle-intense weathering stage of Ca-Na initial primary-intermediate weathering stage, the Ca-Na stage has been removed in the C section, and accompanied by the desilication of Si. Combined with different weathering indices (such as CIA, CIW, PIA , MWPI and so on), the degrees of chemical weathering of each section are given as C> B> A.