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中文摘要：
白垩纪黑色页岩至大洋红层的转变，预示着古海洋氧化还原条件及海洋-气候系统的改变。海相白垩纪黑色页岩与大洋红层在我国西藏江孜地区广泛发育，其中床得剖面已经成为海相白垩系研究的经典剖面之一，根据岩性的不同以及剖面上所表现出的风化色差异，床得剖面自底部至顶部可分为黑层段、白层段和红层段等岩性单元。本文以床得剖面为代表，分析了江孜海相白垩系黑色页岩至大洋红层样品中铁、铝含量、Fe^3＋／Fe^2＋比值的变化规律、铁的富集特征及其漫反射光谱特性。红层的铁、铝含量及Fe^3＋／Fe^2＋比值均远高于其它层位。红层中铁铝含量呈线性相关，认为红层中的铁元素主要来源于陆源输入，铁在红层中富集，是由于陆源输入的增加造成。而黑层和白层中铁铝相关系数很低，可能的解释是由于这两个层段中常见的黄铁矿化结核而导致铁的流失。漫反射光谱学实验显示黑层段和白层段下部的漫反射光谱略显435nm处针铁矿特征峰值，白层段上部反射光谱的峰值不明显，而红层样品在波长565nm处呈现赤铁矿特征峰值。因而，在红层中铁矿物主要以赤铁矿形式存在，而黑层和白层下部有针铁矿存在，在白层上部没有高价态铁矿物。床得剖面的红层段铁富集程度很高，黑层段和白层下部铁相对较为富集，而在白层上部，铁呈亏损状态。综合以上研究结果，我们认为江孜地区红层沉积时期大洋底层水为富氧状态，而黑层和白层下部可能为弱氧化状态，大洋缺氧沉积出现于白层上部。
英文摘要：
Cretaceous marine sediments spread widely in the Gyangze area, Southern Tibet. The Chuangde Section is one of the most studied sections in this area. According to the lithology, the section is divided into 4 units from bottom to top. black unit, white unit, red beds units , and olistostrome unit. This paper analyzed the contents of Fe and Al, the ratios of Fe^3＋/Fe^2＋ and the characteristic of spectral data of the samples from different units of the Chuangde Section. Fe decreases from the bottom of black unit to the upper part of white unit, but it reaches to a highest value in the red bed. The plot of the content of Al represents a similar trend with that of Fe. Both of them have highest average value in the red beds. The Fe^3＋/Fe^2＋ ratio declines slightly from the black unit to white unit, but it reaches to a highest value in the red bed. By analyzing the ratios for Fe and Al, we believe that the Fe in the red bed was terrigenous. Fe＇s enrichment in the red bed means an increased terrestrial input. The Al and Fe in the black unit and white unit have very low correlation coefficients. Though there is not exact explanation for it, we believe that it was caused by the pyritization. The spectral curves of samples from different units were estimated in this paper. To make the spectral data easier to be interpreted, we calculated the first derivative of the raw spectral curves. First derivative curves for the black unit and white unite have two peaks in the wavelength of 435 nm and 500 nm. In contrast, the samples of red bed have a single prominent peak in the wavelength of 565 nm. It indicates that the red bed is rich in hematite and the other units contain goethite. Combined with previous researches, we believe that the iron in the red bed came from terrestrial input and is oxygenated after precipitation. The bottom water was in a highly oxide state.
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