Article: Diagenesis and construction of the belemnite rostrum
Diagenetic and morphological studies of transversely sliced rostra of six belemnite species were carried out by means of scanning-electron, cathodoluminescence and blue-light fluorescence microscopy, staining of thin sections, total organic content analysis, as well as x-ray diffractometry. Diagenesis has not destroyed the laminar morphology of rostra in most cases, and diagenetic alterations indicate that the original mineralogy was low-Mg calcite. A revised interpretation of the construction of belemnite rostra is given, where composite radial structures accreting periodically around the surface are suggested as the principal elements. Organic matter is distributed throughout the rostrum, and is probably both inter- and intra-crystalline. Variation in the organic content along radial structures gives rise to a concentric growth pattern. This variation is often subtle, making growth-rings difficult to define. Muller-Stoll's (1936) concept of a rostrum consisting of discrete alternating inorganic and organic layers is thought to be invalid.