Messinian twinned selenite from the Catanzaro Trough, Calabria, Southern Italy: field, petrographic and fluid inclusion perspectives

Abstract

Field, petrographic and fluid inclusions (FIs) studies are used to investigate the formation of Miocene twinned selenite crystals from the Catanzaro Trough (Calabria, Southern Italy). The selenite was formed during the Messinian salinity crisis (MSC) (~ 6 Ma) and is classified into three facies: giant selenite, banded selenite and massive curvilinear selenite. Petrographic studies revealed the presence of alternating growth intervals (i.e. cloudy and clear intervals) in the selenite crystals that are occasionally separated by transition zones (intermediate interval). The giant selenite facies has cloudy intervals rich in primary FIs and organic matter; transition zones with lower abundances of FIs and organic matter have been observed, while clear zones are devoid of FIs. The banded selenite facies has cloudy and clear zones and relatively low abundances of organic matter. The massive selenite facies has cloudy zones with abundant primary FIs and organic matter and clear zones with low abundances of FIs and organic matter. These transition zones may have formed in response to daily or seasonal climate change oscillations, which in turn triggered alternations in selenite growth rates, in tandem with variations in biological activity and salinities. Microthermometric analyses have highlighted a salinity range between 0.18 and 11.34 eq. wt% NaCl. This indicates that the selenite precipitated from brines with a significant proportion of nonmarine waters. This study helps to place the Calabrian selenite into the interpretive framework of the MSC. The results of this study will contribute to a better understanding of the sedimentary processes active during the Messinian evolution of the northeastern sector of the Catanzaro Trough.