SHELLS OF PIRENELLA CINGULATA (GASTROPODA, POTAMIDIDAE) AS ENVIRONMENTAL ARCHIVES - A TAPHONOMIC, SCLEROCHRONOLOGICAL AND MICROCHEMICAL STUDY

Shells of Pirenella cingulata were studied for its potential as environmental indicators by looking at environmental records preserved in the shells. This study was important because coastal areas are particularly affected by environmental contaminants and Pirenella cingulata is one of the most abundant gastropods in coastal environments and estuaries. The shells were subjected to taphonomic characterization to study the impact on environmental, physical and biological factors on the shells, microstructural study to see how the environment influenced the growth and development of the shells, using the optical microscope and elemental mapping, and microchemical study, using Raman microspectroscopy, to understand the role the chemistry of the environment played in the biomineralization process that formed the shells. Taphonomic studies showed that the shells were affected by different physical and biological processes including bioerosion, weathering, encrustation, cracking and loss of external lustre, resulting in different taphonomic grades for the shells. Microstructural optical study of the shells revealed a discordant growth pattern of the shells, they formed a sequence where the older growth increments eventually end on the outer shell, while new ones are added in the inner shell. Microchemical study of the shells revealed that they are composed of carbonate minerals, aragonite and calcite, and organic materials such as carotenoids, and polyenes, including polyenic chain molecules. There is noticeable heterogeneity and variability in the biochemical composition of the shells, and this can be attributed to a number of factors. Elemental mapping of Mn, Sr, S, Mg and Fe in the shells was done to check the composition and other information that could be incorporated into the already available data to better understand the shell structure and chemistry. This study shows that Pirenella cingulata have high potentials as environmental indicators and can be used for environmental and contaminant studies especially in coastal areas and estuaries that are susceptible to environmental contamination.