【作者】 李响；

【导师】 汪相； 蔡元峰；

【作者基本信息】 南京大学 ， 矿物学、岩石学、矿床学， 2011， 博士

【摘要】 白垩纪是地质历史时期极端气候的典型代表,在此时期相应出现了一些特殊的沉积类型。本论文选取在该时期广泛出现的白垩纪大洋红层(CORB)和含海绿石的沉积岩这两种含铁海相沉积为研究对象,在系统的矿物学研究的基础上,探讨其形成所蕴含的古海洋意义及古环境意义。西藏床得剖面、意大Vispi Quarry剖面以及北大西洋ODP1049C孔高频旋回大洋红层分别代表了CORB在东特提斯、西特提斯和大西洋特提斯的出现。对这些典型剖面的致色铁氧化物类型、致色机制、红层控制因素以及成因的研究可以更好的了解整个特提斯地区在白垩纪时期的古海洋环境。对西藏床得剖面红色页岩、意大利Vispi Quarry剖面红色灰岩和北大西洋ODP1049C孔红色泥灰岩的矿物组成的研究表明,不同地区、不同岩性的白垩纪大洋红层相对于上下地层而言,碎屑矿物组成和粘土矿物组合没有明显的变化,只是组成比例略有不同,这表明陆源输入与红层的形成没有直接的关系。三个剖面的红层与相邻非红色地层比较,明显富集三价铁,而这些三价铁主要以赤铁矿(和／或少量的针铁矿)的形式存在于红层中,主要是赤铁矿引起了红层的红色,但三个地区红层铁氧化物含量有一定差别,其致色机制也稍有不同。西藏床得剖面红色页岩中,赤铁矿含量较高,是唯一的致色铁氧化物。定量分析结果显示,其含量变化范围从3.81%到8.11%。赤铁矿存在两种形态：碎屑状的和细分散状的、结晶差的赤铁矿。碎屑状赤铁矿来源于陆源输入,在氧化的条件下得以保存,而细分散状的、结晶差的赤铁矿则形成于同沉积-成岩早期的氧化环境。后者的致色能力远远高于前者,主要是后者引起了红层的红色。意大利Vispi Quarry剖面红色灰岩中,赤铁矿是主要的致色矿物。赤铁矿含量较低(0.1%左右)且具有陆源和内源两种类型。陆源的赤铁矿与石英、伊利石以及勃姆石等碎屑矿物密切共生,在岩石中分布极不均匀；而内源的铁氧化物在灰岩中的分布则很均匀。这两种类型的铁氧化物共同引起了灰岩的红色。此外,组成该灰岩的方解石中含有少量的Mn2+,而含Mn2+方解石的存在也赋予灰岩一定程度的红色,其致色机制为光致发光致色。北大西洋ODP1049C孔红色泥灰岩中,赤铁矿和针铁矿的出现是导致样品由白色、绿色向红色转变的矿物学原因,但赤铁矿和针铁矿的致色作用不同：赤铁矿致红色,而针铁矿致黄色。赤铁矿相对含量的增加可使沉积物颜色由橙色变为棕色。以床得剖面和意大利Vispi Quarry剖面为代表的长周期(百万年)的大洋红层可能与大洋缺氧事件有关,而以ODP1049C孔沉积物为代表的短周期(万年)高频旋回大洋红层则可能与米兰科维奇旋回导致的太阳辐照量的周期变化有关。红层中赤铁矿主要形成于同沉积-成岩早期的氧化条件,其形成受铁或铁氧化物的供应、沉积时的氧化还原条件以及成岩作用影响。然而,无论受何种因素制约,红层的出现都以底层水中溶解氧含量远大于有机质分解所需耗氧量,以铁氧化物的出现为最终结果。实验表明利用漫反射光谱方法可以快速有效地鉴别红层中的铁氧化物,本文采用漫反射光谱和多元线性回归分析相结合的方法首次对大洋红层中的铁氧化物进行了定量研究,该方法的引入为大洋红层中铁氧化物的致色机理和定量分析提供了新的思路。海绿石是白垩纪海相地层中的常见含铁矿物之一,因其结构中同时含有Fe2+和Fe3+,其形成也受氧化还原条件制约。海绿石在层序地层学和同位素年代学中的成功应用,使其成因研究一直备受关注。本文以我国西藏西南部札达县波林地区夏拉剖面中一套白垩系碎屑岩中的海绿石为研究对象,对其进行了系统的矿物学研究。分析表明,该剖面中的海绿石存在不同演化阶段,可分为高演化海绿石和低演化海绿石。海绿石砂岩和灰岩中的海绿石为高演化的海绿石,其中,海绿石砂岩中的海绿石为原地海绿石,而灰岩中的海绿石为源于下伏地层的异地海绿石。海绿石砂岩的形成可能与Albian晚期印度大陆从澳大利亚-南极大陆的彻底裂解有关。下伏砂岩中不同演化阶段的海绿石的研究表明,海绿石化作用主要表现为交代碱性长石中的富钾组分,该过程是受矿物之间的溶解-沉淀-再结晶机制控制的界面迁移反应。不同演化程度的海绿石中几乎相同且高的K20的含量以及低的TFeO(总铁)的含量,不支持‘’neoformation theory"理论和两阶段模式中提到的先形成富铁贫钾的物质,然后在后期的演化中逐渐富钾的过程。与交代贫钾矿物的过程不同,在交代富钾矿物的初期就有很高的钾含量,不需要后期单独的钾富集的过程。下伏砂岩中,海绿石中高的K20含量与大量钾长石和岩屑的溶解有关,而低的TFeO含量则与当时的氧化还原条件有关。当氧化还原条件趋于弱还原时,Fe主要以Fe2+的形式进入了磁绿泥石的晶格。更多还原

【Abstract】 Cretaceous has been considered as the typical representative of extreme climate for the geological period. A series of special sediments in response to this extreme climate was developed in this period. In this thesis, the author carries out a systematically mineralogical study of Cretaceous Oceanic Red beds (CORBs) and glauconite-bearing beds, which widely appeared in Cretaceous ocean and both contain iron-bearing mineral, to achieve a better understanding of the paleoceanographic environments during their deposition.Three sections, including the Chuangde section in Tibet, the Vispi Quarry section in Italy and the ODP Hole1049C Core from the North Atlantic, are considered as the representatives of CORB in eastern Tethys, western Tethys and Atlantic Tethys, respectively. The studies such as identifying the species and coloration mechanism of pigments, the controlling factors and origin of CORB for these typical sections can provide an insight to acquire the paleoceanographic environmental information of Tethys during Cretaceous time.Based on studies of mineral compositions of Chuangde section, the Vispi Quarry section and the ODP Hole1049C, a detrital mineral and clay mineral assemblage are similar but their amount slightly varied comparing with adjacent non-redbeds of the same section. This may indicate that the formation of CORBs was not directly correlated with terrigenously detrital input. As shown by the element geochemical data, the CORBs have higher ferric iron concentration than adjacent non-redbeds, and ferric iron mainly present in the form of hematite (or goethite). We consider that the red color of CORBs was mainly caused by finely, dispersed ferric oxide, but there are some differences in coloration mechanism and concentrations of ferric oxide in these sections. In Chuangde section, hematite is the unique ferric oxide which endows the shale with red color. Further quantitative analysis reveals that the hematite concentration in shales was fairly high but varied within a range from3.81%to8.11%. Hematite can also be subdivided into two forms:detrital one or finely and poorly crystallized one. The former was directly derived from terrigenous input and preserved under oxidized conditions. The latter precipitated in pores of sediments in a highly oxygenated bottom water during syn-deposition or early diagenesis in the deep ocean basin. The latter one has a much higher coloration ability than the former one, and therefore mainly endow the red color of shales in Chuangde section.In the Vispi Quarry section, hematite present as primary pigment in red limestones. The concentration of hematite estimated about0.1%, was much lower than shales in Chuangde section. The origin of hematite are characterized by its distribution features:the irregularly distributed region was derived form terrigenous input with detrital minerals such as quartz, illite, and boehmite, and the homogenous distributed region was formed under oxidized condition during syn-deposition and early diagenesis. Both of them imparted a red color to the limestones. Mn2+-bearing calcite also endowed the limestones with a pink tinge induced by irradiation.In the marl from ODP Hole1049C in North Atlantic, hematite and goethite are the minerals responsible for the color change of sediment from white, green to red. However, they performed differently in terms of determining the color of sediment: hematite and goethite bring a red or yellow color to sediment, respectively. Relative change in amount between hematite and goethite can cause the color change of sediment from orange to brown.CORBs both in Chuangde section in Tibet and in Vispi Quarry section in Italy are belong to long period CORBs which span a few million years, may appear as possible consequence of Oceanic Anoxic Events (OAEs). High-cyclic CORB in ODP Hole1049C in North Atlantic as the representative of short period CORBs which are comparable with Milankovitch cycle periods, may be associated with the fluctuation in solar insolation arose by Milankovitch cycles. The hematite which endowed red color to sediments was deposited under oxidized condition during syn-deposition and early diagenesis. A supply of iron into a depositional basin which ultimately transforms to red pigmenting hematite, favorable redox condition and diagenesis can also largely influence the formation of hematite. No matter which factor is dominant, the formation of CORB depends on the dissolved oxygen in the bottom water. When the dissolved oxygen content is far greater than the consumption of decomposition of organic matter, the pigment hematite finally appeared or survived.Visible light diffuse reflectance spectroscopy (DRS) proved to be a rapid and precise method for identification of hematite and goethite. In this thesis, the author preformed a quantitative analysis using DRS with multiple linear regression fitting to estimate the absolute concentration of hematite and goethite in CORB from ODP Hole1049C in North Atlantic. The successful application of this method provides a new way for quantitative analysis of iron oxides in CORBs and coloration mechanism of iron oxides.Glauconite is the common mineral in Cretaceous marine strata. As an iron-containing mineral, it contains both reduced Fe2+and oxidized Fe3+. The Fe2+/Fe3+ratio in its structure reflects the redox condition which is decisive for its formation. Increasing attention has being focused on its formation mechanism since the important application of glauconite as facies mineral in sequence stratigraphy and isotopic chronology. Early Cretaceous glauconite from Xiala section in southwestern Tibet, China, has been studied by systematic mineralogical analyses. The investigations revealed that the glauconites are at different stages of glauconitization and both in glauconitic sandstone and limestone are highly evolved. The glauconites in glauconitic sandstone are autochthonous origin, but the ones in limestone may come from the underlying glauconitic sandstone. The autochthonous glauconite may be associated with the final separation of the Indian Continent from the Australian-Antarctic Continent during the Late Albian.Investigation of glauconite at different stages of glauconitisation in the underlying strata reveals that the process of glauconitisation is mainly characterized by the replacing K-rich proportion of alkali feldspar, in which the interface migration reaction controlled by the solution-precipitation-recrystallization processes was the main mineralogical reaction mechanism. The lowly evolved glauconite in quartz sandstones and lithic sandstones has the almost same compositional characteristics, namely higher K2O contents and lower TFeO contents. This implies that the process of glauconitisation in Xiala section does not support the neoformation theory and two-stage model in which the glauconite results primarily from a poorly crystallized low-K, high-Fe smectite-like layer silicate following by the progressive enrichment of K during the long evolution. The replacement of K-rich minerals is different from the replacement of K-poor minerals, as the second step, which result in an enrichment in K, is not necessary. The higher K2O contents were associated with the extensive dissolution of K-rich minerals in the marine environment, and the lower TFeo contents were the indicator of redox environment at that time. When the local micro environments become weak reduced, an overwhelming majority of Fe as Fe2+enter into the lattice structure of berthierine.更多还原