The White Stone Band of the Kimmeridge Clay Formation, an integrated high-resolution approach to understanding environmental change

The Kimmeridge Clay is a Jurassic mudrock succession that shows Milankovitch Band climatic cyclicity. A key issue is to determine
how the subtle changes that define this cyclicity result from climatic change. Using material from the Natural Environment
Research Council Rapid Global Geological Events (RGGE) Kimmeridge Drilling Project boreholes, the White Stone Band was investigated
at the lamination scale using backscattered electron imagery and quantitative palynofacies. Fabric analysis shows the lamination
to represent successive deposition of coccolith-rich and organic-matter-rich layers. Individual laminae contain unsorted palynological
debris with a consistent ratio of marine and terrestrial components. Such mixed organic matter input is interpreted as the
result of storm transport. Linking water column processes to laminae deposition suggests seasonal input with a coccolith bloom
followed by a more diverse assemblage including dinoflagellates and photosynthetic chlorobiacean bacteria. As the photic zone
extended into the euxinic water column organic matter export to the sea bed underwent minimal cycling through oxidation and
subsequently became preserved through sulphurization with greatly increased sequestration of carbon. This was significantly
increased by late season storm-driven mixing of euxinic water into the photic zone. Increased frequency of storm systems would
therefore dilute the coccolith input to give an oil shale. Hence climatically induced changes in storm frequency would progressively
vary the organic content of the sediment and generate the climate cycle signal.

金梅里奇粘土层是一层侏罗纪的泥岩层序，其中展现了米兰科维奇气候周期性。关键问题在于确定界定此周期性的微妙变化如何由气候变化引起。利用来自自然环境研究委员会快速全球地质事件（RGGE）金梅里奇钻探项目的材料，对白垩石层带在层理尺度上进行了研究，采用了背散射电子成像和定量孢粉学方法。层理分析表明，其代表了一系列富含颗石藻和富含有机质的沉积层。单个层理包含未分类的孢粉学碎片，海洋和陆地成分的比例保持一致。这种混合有机物输入被解释为风暴输送的结果。将水柱过程与层理沉积联系起来，表明季节性输入，以颗石藻水华为先，随后是更为多样的组合，包括隐藻和光合作用的绿硫菌。随着光区延伸至缺氧水柱，有机质向海底的输出经历了最小化的氧化循环，随后通过硫化作用得以保存，碳的储存量显著增加。这通过晚季风暴驱动的缺氧水与光区的混合作用而显著增强。因此，风暴系统频率的增加会稀释颗石藻的输入，从而形成油页岩。因此，气候变化引起的风暴频率变化会逐步改变沉积物的有机含量，并产生气候周期性信号。