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

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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.