Fossil organic matrices of the Callovian aragonitic ammonites from Lukow (Poland): location and composition

The micro- and nanostructures of modern and fossil aragonitic nacreous layers of cephalopod shells were studied with scanning electron microscope (SEM) and atomic force microscope (AFM). The nacreous tablets are organized in sectors, composed of acicular units. The acicular units are composed of small granules. The fossil and modern shells show some differences in granule size, but the granules are surrounded by a thin envelope in both samples. Electrophoretic and amino-acid compositions show that organic matrices are present in the fossil shells. Thus, the organic nature of the granule envelopes can be inferred from the two analytical approaches. The AFM microscopy allows us to study the nanostructures of the recent and fossil hard tissues and to observe the diagenetic changes of both the mineral and organic components.