EXCEPTIONALLY PRESERVED TURONIAN CALCAREOUS MICROFLORA FROM TANZANIA: IMPLICATIONS OF PRESERVATION ON TAXONOMY

A major component of Turonian marine sediments are calcareous particles, commonly called “calcispheres” (Pithonelloideae; genera Pithonella, Bonetocardiella) which represent reproductive cysts, probably of dinoflagellates. The taxonomy of these microfossils is based on shape and size of the operculum (an opening) being the highest hierarchical criterion – particularly in calcareous dinoflagellate cyst taxonomy. Wall crystal architecture is the second-most important criterion. We found evidence that these key-traits of taxonomic classification of Pithonelloideae are subject to spectacular re-crystallization during carbonate diagenesis. Here we show a comparison between pristine Pithonelloideae from material recovered by the Tanzanian Drilling Project with Pithonelloideae from the Chalk (northern France). The preservation-states of these two materials differ tremendously so that it is impossible that both represent the original bio-mineralogical wall-architecture equally. However, both have been used in detailed wall-crystallographic analyses resulting in taxonomic description. We find a gradual crystallographic transition from the “Tanzanian preservation” to the “chalk preservation”. Importantly, opercula in the Tanzanian material are spectacularly well preserved as revealed by detailed SEM-study. These observations shed new light on species distinction resulting in “lumping” formerly separated species and revising the existing classification scheme. Furthermore, the exceptional preservation of the Tanzanian material allows for CL-spectral study and geochemical measurements that enable unprecedented insight into the paleoecology of the Pithonelloideae.