Thenardite after mirabilite deposits as a cool climate indicator in the geological record: lower Miocene of central Spain

Abstract

Abstract. Salt deposits are commonly used as indicators of different paleoclimates and sedimentary environments, as well as being geological resources of great economic interest. Ordinarily, the presence of salt deposits is related to warm and arid environmental conditions, but there are salts, like mirabilite, that form by cooling and a concentration mechanism based on cooling and/or freezing. The diagenetic transformation of mirabilite into thenardite in the upper part of the lower Miocene unit of the Tajo basin (Spain) resulted in the largest reserves of this important industrial mineral in Europe. This unit was formed in a time period ( ∼ 18.4 Ma) that, in other basins of the Iberian Peninsula, is characterized by the existence of particular mammal assemblages appropriate to a relatively cool and arid climate. Determining the origin of the thenardite deposits as related to the diagenetic alteration of a pre-existing mirabilite permits the establishment and characterization of the sedimentary environment where it was formed and also suggests use as a possible analog with comparable deposits from extreme conditions such as Antarctica or Mars.

Water Abundance of Dunes in Gale Crater, Mars From Active Neutron Experiments and Implications for Amorphous Phases

“…We assumed 21.26-wt% H 2 O in amorphous ferric sulfate based on TG measurements of synthetic amorphous ferric sulfate prepared by vacuum dehydration (Sklute et al, 2015), but the samples were not allowed a similar amount of time to equilibrate in Martian conditions as were those of Vaniman et al (2004). We assumed K sulfate, Na sulfate, and Ca phosphate were anhydrous because, although water can adsorb to the surfaces of crystalline K sulfate and Na sulfate (e.g., Balić-Žunić et al, 2016;Herrero et al, 2015) and synthetic amorphous Ca phosphate (e.g., Li et al, 2007), SAM data suggest active sands in Gale crater generally lack adsorbed water (Stern et al, 2018). The geochemical abundances of the modeled amorphous phases are summarized in Table S2.…”

Orbital- and suborbital-scale changes in the East Asian summer monsoon since the last deglaciation

“…The deposition of evaporites is primarily related to the salinity and chemical composition of lake waters (Liu et al, 2008). Mirabilite is regarded as a good indicator of cold/dry environments (Herrero et al, 2015; Zheng et al, 2000) and has proven to be very useful in the study of paleoclimate (Grasby et al, 2013; Herrero et al, 2015; Wang et al, 2012). Bloedite and gypsum have been found in various saline lakes in arid or semi-arid regions around the world and are used as indicators in paleoclimatology and sedimentology (Liu et al, 2008; Mees et al, 2011; Sönmez and Çelik, 2016).…”

Temperature-dependent, VIS-NIR reflectance spectroscopy of sodium sulfates

“…The evaporation rate is favored by high temperature, low relative humidity and air movement, while it is inhibited for example by the increase in salinity of the evaporating brine itself. On the opposite also the freezing process, by removing liquid water from the brine with consequent ice formation, can result in the precipitation of certain cryogenic sulfate salts (Babel and Schreiber, 2014;Herrero et al, 2015). With this regard, brines having eutectic temperature below 0°C are defined cryobrines.…”

“…Sodium sulfates are strongly temperature dependent: on Earth, the anhydrous form thénardite typically is formed in hot and arid climatic conditions, while mirabilite is a typical product of cool periods (Herrero et al, 2015). Thus thénardite is found on Earth both in recent and in ancient deposits, as primary precipitation product of warm brines in shallow lakes or as efflorescent crust in playa environments (Herrero et al, 2015). Mirabilite instead is not found in ancient environments: this is due to its high reactivity and sensitivity to temperature changes, as it readily can dehydrate and transform to thénardite.…”