Geoquímica microestructural en Praeradiolites ciryi (Hippuritacea, Bivalvia, Cretácico Superior de Gredilla de Sedaño, Norte de Burgos, España)

Abstract

The detailed geochemical evolution along two transects of the shell of one specimen of Praeradiolites ciryi is examined along annual, seasonal and fortnightly («doublet») sclerochronological records. The analyzed specimen is thought to have suffered a low diagenetic degree because it mostly retains the original composition of both cellular and compact microstructures of the shell. So it can be deduced from the .«saw-tooth» geochemical profiles, the Mg-Sr high mmol/mol values, the Mn-Fe low mmol/mol values and the unequal distribution of luminescence that accurately follows shell microstructural features. The organic control upon the geochemistry of the shell is still observable because two zones, each one having a characteristic cationic trend, can be distinguished within a «doublet». This fact is reinforced by changes in the luminescence indicating some periodic phenomenon of fortnightly cyclicity. The decrease in cationic content and increase in organic matter content towards the upper half of the «doublets» could be related to metabolic activity changes preparatory for the construction of a new growth line