Diagénesis en las conchas de inocerámidos de la Isla de Castro (Coniaciense final-Santoniense inferior, Cuenca Vasco-Cantábrica): evidencias petrológicas e isotópicas

Abstract

Pétrographie and isotopic (á!80 and a13C) analyses have been carried out on inoceramid shells from shallow-marine limestone-marl couplets at the Castro Island section (latest Coniacian-lower Santonian, Basque-Cantabrian Basin), in order to determine their diagenetic alteration. Results show that the prismatic microstructure of the shells was mainly affected by silica replacement during diagenesis, but very little compaction, cementation and recrystallization occurred. However, these changes do not seem to have modified largely the isotopic composition of the inoceramids, as supported by the low luminescence intensity that show all the shells. In addition, à780 and al3C mean values from inoceramids included in limestones are heavier than those from inocermids in marls, which confirms that the isotopic values were influenced by a paleoceanographic circulation model with estuarine and anti-estuarine regimens