Sulfur and Oxygen Isotope Compositions of Seawater Sulfate as Recorded in Marine Barite

全球气候和大气化学的变化与硫和碳沉积旋回密切相关。海洋硫酸盐和碳的同位素记录提供了沉积储层之间大规模S和C转移的证据。S和C储层之间的耦合维持了一个稳定的大气氧储层。因此，硫化物氧化速率的增加必须由有机碳埋藏速率的增加来补偿，从而导致海洋中硫代硫酸盐和碳代碳酸盐之间整体呈反比关系，正如所观察到的那样。存在高分辨率海相碳酸盐岩13C年龄曲线。在显生宙，海水硫酸盐S、O同位素组成有明显波动的证据，主要是基于海洋蒸发岩硫酸盐的综合同位素数据；但海洋蒸发岩的地质记录是断断续续的，间隔数百万年。蒸发岩也容易受到成岩作用的影响，它们的年龄控制可能有问题，一些纯粹的海洋起源是值得怀疑的；因此，确定另一种可靠地记录和维持海水硫酸盐S和O同位素组成的海洋相是很重要的。海相重晶石是深海沉积物中随处可见的小相，连续沉积，伴生沉积年代可测定，在含氧沉积物中不易发生成岩蚀变，可靠地记录了海水Sr同位素组成；它似乎是一种非常适合这项研究的矿物质。因此，本研究的目的是：(1)确定海相重晶石是可靠的海水硫酸盐S和O同位素记录；(2)建立详细、连续、定年准确的过去65 m.y的海水硫酸盐S和O同位素记录；(3)利用定年准确的深海沉积物，在3个特殊时间间隔(1)墨西尼亚事件、（2)白垩纪-第三纪界线和(3)34S明显的Albian-Aptian界线附近的最小值）建立高分辨率的S和O同位素记录。海水硫酸盐的S和O同位素曲线将与海洋碳酸盐的13C记录联系起来，并根据控制海洋S和C输入和输出通量动态平衡的过程进行解释。通过将本研究的数据与现有的12C/12C和87Sr/86Sr海水数据相关联，还将评估风化通量增加的作用，特别是喜马拉雅隆起在过去-40 m.y的作用。这项工作的重点将放在重晶石上，重晶石将从全新世到65Ma的沉积物中分离出来，间隔大约100万年到200万年。全新世至38ma的重晶石样品之前已经被我们分析了它们的sr同位素组成。对于三个“特殊”地质时间间隔，将以约0.5微米的间隔进行高分辨率采样。将通过扫描电镜研究重晶石晶体的习性，并对分离的重晶石的Sr同位素组成进行可能的成岩作用测试。通过分析海相重晶石，连续记录海水硫酸盐S和O同位素值，并与现有的高分辨率海洋C和Sr同位素年龄曲线进行对比，将有助于揭示这三个重要地质事件期间的气候-构造耦合。

Kastner 9628479 Global changes in climate and atmospheric chemistry are intimately related to the sulfur and carbon sedimentary cycles. Evidence for large scale transfers of S and C between the sedimentary reservoirs is provided by the isotope records of oceanic sulfate and carbon. Coupling between the S and C reservoirs maintains a steady-state atmospheric oxygen reservoir. Thus, an increase in the rate of sulfide oxidation must be compensated by an increase in the rate of organic C burial, resulting in an overall inverse relationship between marine 34Ssulfate and 34Scarbonate, as observed. A high resolution marine carbonate 13C age curve exists. The evidence that S and O isotope compositions of seawater sulfate have fluctuated significantly through the Phanerozoic, is mostly based on the comprehensive isotope data obtained from marine evaporite sulfates; but the geological record of marine evaporites is episodic, with gaps of millions of years. Evaporites are also susceptible to diagenesis, their age control could be problematic, and the purely marine origin of some is questionable; it is therefore important to identify another marine phase that reliably records and maintains seawater sulfate S and O isotope compositions. Marine barite is a readily available ubiquitous minor phase in deep-sea sediments, it is continuously deposited, its associated sediment ages can be determined, it is not susceptible to diagenetic alteration in oxic sediments, and has been shown to record reliably seawater Sr isotope composition; it seems to be a very suitable mineral for this study. Thus, the objectives of this research are: (I) to confirm that marine barite is a reliable recorder of seawater sulfate S and O isotope values, (II) to construct detailed, continuous, well dated seawater sulfate S and O isotope records over the past 65 m.y., (III) to construct high resolution S and O isotope records during three special time intervals (1) the Messinian event, (2) the Cretaceous-Tertiary boundary , and (3) the distinct minimum in 34S near the Albian-Aptian boundary, using well dated deep-sea sediments. The refined S and O isotope curves of seawater sulfate will be related to the oceanic 13C record of carbonates and interpreted in terms of the processes controlling the dynamic balance between the oceanic S and C input and output fluxes. The role of increased weathering fluxes, especially from the Himalayan uplift over the past -40 m.y., will also be evaluated by correlating data from this research with the existing 12C/12C and 87Sr/86Sr seawater data for this time interval. The emphasis of the work will be on barite that will be separated from sediments of Holocene to 65Ma age, at about 1 to 2 million year intervals. Barite samples from the Holocene to 38 Ma have previously been analyzed by us for their Sr-isotope composition. For the three "special" geologic time intervals higher resolution sampling will be carried out at an interval of about 0.5 m.y. The habit of the barite crystals that will be studied by SEM, and Sr- isotope composition of the separated barites will be tests for possible diagenesis. Continuous records of seawater sulfate S and O isotope values, by analyses of marine barite, and their correlation with existing high resolution oceanic C and Sr isotope age curves, should help to unravel the climate-tectonic coupling during these three important geological events.