Computer-integrated polarisation (CIP) in the analysis of fossils: a case of study in a Palaeozoic coral (Sinopora, Syringoporicae, Carboniferous)

Abstract

Computer-integrated polarisation (CIP) method has been applied satisfactorily in the study of fossils skeletons of Sinopora (tabulate coral, Auloporida and Carboniferous). A previous characterisation of sample by scanning electron microscopy, atomic force microscopy and cathodoluminescence (CL) with the purpose of distinguishing the diagenetical alteration was done. Subsequently, a crystallographic comparison between CIP and electron-backscattering diffraction has been made getting a very good correlation between both methods. The CIP method allows obtaining c-axis orientation images, pole figures, and measure and mapping the misorientation of uniaxial biominerals in recent and fossil skeletons. This technique can only be used in uniaxial biominerals (calcite, quartz and hydroxylapatite), limiting its use for biaxial or bimineralic and polimineralic biominerals. CIP method has good spatial resolution (limited by camera); in our example 90 nm. The main advantage of this technique, versus other with similar properties, is the fast acquisition of data in low and high magnifications. This method does not require special treatment of samples and can be very useful for the analysis of microstructures in thin and ultra-thin sections. CIP method detects diagenetic alterations in fossil skeletons by modifications in the inner arrangement of biominerals, which combined with CL offers valuable geochemical and crystallographic information.