Formation and diagenetic alteration of marine, meteoric and biogenic radiaxial calcites

海相放射状纤维状和束状光学方解石是古生代和中生代浅海和上半深海石灰岩中非常常见但知之甚少的填孔胶结物。这些钙化骨水泥的主要诊断特征分别是它们的会聚或发散晶体c轴。这种反常晶体结构的原因目前尚不清楚。由于新生代地层中相对缺乏产出，而第四纪海洋沉积中明显缺乏产出，因此存在争议。尽管存在这些不确定性，但非生物成因的海洋放射状胶结物被认为是古海洋地球化学最可靠的非生物成因碳酸盐档案之一。在波鸿的研究表明，放射状组构也存在于洞穴沉积物中，也许更重要的是，在箭石喙中。需要进一步调查，以了解控制这一档案的物理化学和生物参数。CHARON为这个项目提供了一个优秀的、完全跨学科的研究环境。我们有三个目标：（i）我们打算提出一个机械模型，确定控制这种神秘结构形成的物理化学参数;（ii）由此，我们打算评估现代海洋中这种结构稀缺的原因;（iii）我们将探索-并量化-沉积后成岩蚀变对这种结构的影响。特别是，在德国的洞穴现场降水实验将首次允许在监测条件下观察实际的径向纤维水泥沉淀。

Marine radiaxial-fibrous and fascicular-optic calcites are very common but poorly understood porefilling cements in Palaeozoic and Mesozoic neritic and upper bathyal limestones. The main diagnostic feature of these calcitic cements is their converging or diverging crystal c-axis, respectively. The reasons for this anomalous crystallographic texture are at present unknown. A controversy exists due to the relative lack of occurrences in Cenozoic strata and their apparent lack in Quaternary marine deposits. Despite these uncertainties, abiogenic marine radiaxial cements are thought to be amongst the most reliable abiogenic carbonate archives of ancient ocean geochemistry. Research at Bochum has shown that radiaxial fabrics are also present in speleothems and, perhaps even more significant, in belemnite rostra. Further investigations are required in order to understand the physico-chemical and biological parameters controlling this archive. CHARON forms an excellent, radically interdisciplinary research environment for this project. Our aims are threefold: (i) we intend to come up with a mechanistic model defining the physico-chemical parameters that control the formation of this enigmatic fabric; (ii) from this we intend to assess the reasons for the scarcity of this fabric in modern oceans and (iii), we will explore - and quantify - the impact of post-depositional diagenetic alteration on this fabric. Particularly, field precipitation experiments in caves in Germany will, for the first time, allow for the observation of actualistic radiaxial-fibrous cements precipitated under monitored conditions.