The Messinian halite of Italian Peninsula : facies analysis, rheological parameters and paleoclimatic reconstruction

Abstract

The scientific and economic interest on rocksalt is well known for a long time. Mining industry, hydrocarbons research companies, academic institutions have spent great effort in studying such a unique rock, its peculiarity and how to use it. Indeed, rocksalt deposits are useful in several ways, from the pure academic interest to the possibility of halite extraction itself, to the oil and gas research, often linked with salt and related tectonic effects, until the attractiveness as nuclear or others waste long term storage. Nevertheless, there are various rocksalt characteristics still unclear, poorly investigated or debatable. In fact, has to be noticed that one of the main halite feature, besides the low density and deformation proneness, is the great facies variability, mirrored by the relative rheological properties. Moreover, fluid inclusions, that are always present within and between salt crystals, are an aknowledged paleotemperature data source, very useful for paleoclimatic reconstruction purposes. Within this framework, this PhD thesis has dealt with the Messinian halite of Italian Peninsula, previously almost never studied. Referring, for further informations, to the introductions of each chapter, arranged as scientific articles, here we would explain briefly our work. In the first chapter we present the results of a paleotemperature and geochemical study using primary fluid inclusions in halite from five italian sites. Gathered data allowed to suggest the average climatic conditions and water chemical characteristics at salt deposition time, that is the acme of the so called Messinian Salinity Crisis, still discussed and uncertain. The first chapter was published in the G-Cubed journal on 12/2013. During rocksalt sampling for fluid inclusions analysis we recognized a great salt facies variability in every sites, so, as written in the second chapter, we decided to quantitatively analyze the characteristics of our samples, a point of view often neglected in halite studies. Our analyses allowed to identify some useful facies-characterizing parameters, to define four facies end-members related to different salt deformation degree, to test in laboratory these facies in order to verify the effect of salt characteristic on its overall rheology and eventually to understand the complex salt facies arrangement in the Volterra Basin sampling site. Finally, in the third chapter, we presents the results of thermal expansion experiments on halite crystals with different fluids contents. As previously said and also hightlighted in the first and second chapter, fluids are always present within rocksalt crystals. We found that these fluids exert a considerable influence on rocksalt expansion amount during heating, affecting also halite density. This could be of great interest in salt mobility study and in those applications, as neclear waste storage, involving heat production. The third chapter is meant as preliminary to a wider and detailed study to be concluded next.