Use of calcite crystal optical properties in the identification of calcareous nannofossils and Didemnid Ascidian Spicules in three stratigraphic sections in the Lut block

Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Calcareous nanoplankton are one of the most abundant calcite unicellular planktonic organisms on the Earth. This group include coccoliths which are formed from calcite crystals. They are one of the most important microfossil groups in biostratigraphic, paleontologyl and oil exploration studies, and their accurate and correct identification is of great importance. Some species belonging to Didemnid Ascidian Spicules resemble nannofossils and their separation from the nannofossils is essential and is necessary for correct age determination of the deposit. For this reason, the use of the optical properties of calcite crystal of coccoliths, that determined by polarizing microscop and the gypsumplate, can lead to the separation of microstructures and the arrangement of nannofossils subunits and can lead to the separation of nannofossils subunits from the mention group. In this study, with using of optical properties of calcite crystal, a number of nannofossil species and number of Didemnid Ascidian spicules investigated and identified.