Javier García-Veigas

X-ray microanalysis of fluid inclusions and its application to the geochemical modeling of evaporite basins

Direct access to brines trapped in halite is possible by freezing and breaking halite crystals on a cooling stage inside a scanning electron microscope. Quantitative analyses of major solutes (Na, Mg, K, Ca, Cl and SO4) in natural brines were obtained by means of X-ray microanalysis of the frozen fluid inclusions using frozen droplets of brines with known composition as standards. Precision errors were estimated to be lower than 10%. and detection limits vary from below 0.02 mol/L for Ca, K, and SO4 to 0.55 mol/L for Na. Analyses of several inclusions of sizes larger than 20 μm were performed for each cross section of halite. The composition of primary fluid inclusions in halites from a drill core in the Messinian basin of Lorca, SE Spain, were used to constrain the parameters of a geochemical model of the evolution of the basin. A computer program to simulate evaporation paths was developed using thermodynamic equilibrium and mass balance as constraints. The halite sequence was interpreted as resulting from the evaporation of initial seawater in a hydrologically open basin, with seawater replacing the evaporated water and a small fraction of basinal brine leaking out. In the middle of the sampled sequence, the basin was closed to the sea and only continental water flowed into the basin, reworking part of the halite deposited in the margins. In contrast with these results, only very poor information would have been obtained from the mineralogical record alone, consisting mainly of halite and minor gypsum.

The chemical and hydrological evolution of an ancient potash-forming evaporite basin as constrained by mineral sequence, fluid inclusion composition, and numerical simulation

The chemical evolution of the brine in a potash evaporite basin has been investigated by X-ray microanalysis of frozen primary inclusions trapped in halite. A Computer program based on thermodynamic equilibrium and mass balance principles has been used to simulate evaporation paths. The comparison between the results of calculations, the observed mineralogy and mineral sequence, and the solute content in fluid inclusions has placed constraints on the hydrological evolution of the basin. The upper Eocene basin of Navarra, southern Pyrenees, Spain, began as a marine basin, evolving from a moderate to a high degree of restriction, depositing first a basai anhydrite horizon, and then a thick sequence of massive halite. An additional inflow of CaCl2 in the basin during seawater evaporation is proposed as the process responsible for the sulfate depletion required for sylvite instead of Mg-sulfates to form. Mixing of seawater with continental waters, bacterial sulfate reduction and “in situ” dolomitization are discarded. The basin subsequently closed to the sea and evolved with decreasing volume. Alternating bands of clays-halite-sylvite and then clays-halite-carnallite were deposited under the influence of seasonal continental recharge. Before reaching total desiccation the residual brine was diluted by continental water. The basin then evolved under an endoreic regime, where continental recharge and the recycling of previously-formed halite led to deposition of alternating beds of clays and halite.

Evolution and geochemical signatures in a Neogene forearc evaporitic basin: the Salar Grande (Central Andes of Chile)

Abstract The Salar Grande is a 45-km-long (N–S axis), 4–5-km-wide, fault-bounded (pull-apart) Neogene forearc evaporitic basin, located in the Cordillera de la Costa of northern Chile whose sedimentary record is composed almost exclusively of a massive halite salt body. Underground waters coming from the east (now the Precordillera and Altiplano) were progressively enriched in solutes by interaction with volcanic rocks. These fluids drained into a lacustrine system located in the Depresion Central (in the Llamara–Quillagua area) and thick sequences of diatomites, carbonates, evaporites and clastic sediments were deposited. These lacustrine areas eventually dried out and became a salar with anhydrite and halite. During this stage (Late Miocene–Pliocene), evolved brines of the Llamara–Quillagua area migrated eastwards through structural paths, reaching the Salar Grande basin which acted as a final sink. A proof of this connection is the anhydrite level that links the western Llamara and southeastern Salar Grande areas. The accessory minerals and geochemical signatures in the rock salt are a record of the inputs arriving to the former lake and reflect variations in climate, and in tectonic and volcanic activity. The arrangement of halite textures along the sequence shows an evolution from a very shallow ephemeral saline lake (some cm–dm deep on average) to a salar where interstitial processes controlled by phreatic brines dominate. This evolution is coherent with a slight increase in the terrigenous content of the rock salt, and documents the increasing aridity of the climate as a response to the tectonic uplift of the Andean Ranges. In Pliocene times pore brines were definitively lost as a response to the downfall of the water table generated by the beginning of the exorheism due to the opening of the Loa River canyon towards the sea. The aim of this paper is to describe the Salar Grande through the study of its geological setting and its salt record. A detailed description of the salar will enable us to reach valuable conclusions about environmental conditions in the area during the Neogene, prior to the opening of the hydrologic system to the Pacific Ocean.

Analyses of fluid inclusions in Neoproterozoic marine halite provide oldest measurement of seawater chemistry

We analyzed primary fluid inclusions in halite from marine evaporites in the ca. 830 Ma Browne Formation of the Officer Basin in Western Australia using the cryogenic scanning electron microscopy– energy dispersive X-ray spectrometry analysis technique. The concentrations of the major ions, except K + and possibly SO 4 2– , fall within the range of Phanerozoic seawater. This is the first direct measurement of the composition of mid-Neoproterozoic seawater, and extends present-day knowledge of seawater chemistry by ∼300 m.y. Our estimates suggest that mid-Neoproterozoic marine sulfate concentrations were lower (∼90%) than modern values. By the terminal Neoproterozoic, fluid inclusions in halite and evaporite mineralogy indicate seawater sulfate levels rose significantly, to 50%–80% of modern concentrations, which parallels increases in atmospheric and oceanic oxygen.

A model for the diagenetic formation of sandstone-hosted copper deposits in Tertiary sedimentary rocks, Aragón (NE Spain): S/C ratios and sulphur isotope systematics

Abstract Numerous small, noneconomic copper deposits are associated with syntectonic sandstones of Tertiary age (Campodarbe and Uncastillo Formations) in the South Pyrenean foreland basin (SPFB). Sulphides, native metal, and their oxidation products occur within elongate lenses in fluvial sandstones and conglomerates. In all cases, the geometry of the ore is highly consistent with the primary depositional and biogenic structures of the host sandstones. Copper ores replace wood debris and diagenetic pyrite or, more frequently, appear as intergranular cement replacing previous diagenetic calcite cement. Sulphide sulphur and organic carbon distribution shows that pyrite-rich sandstones are the copper ore precursor, and that mineralizing processes provoked the depletion of both reduced S and organic C as a consequence of interaction with an oxidized Cu-bearing fluid. On the other hand, low δ34S values are consistent with bacteriogenic derivation of sulphur after Pyrenean evaporites. Petrographic studies, sulphide sulphur and organic carbon concentrations, and δ34S values suggest that Cu-rich fluids were introduced into reduced sediments during diagenesis. Mineralizing processes took place in two different periods: the first one related to the filling of the Jaca Basin during erosion of the Pyrenean basement and the second one related to the emplacement of a thrust ramp which initiated the erosion of the previously formed cupriferous sandstones.

Further insights in trichothiodistrophy: a clinical, microscopic, and ultrastructural study of 20 cases and literature review.

Background: Trichothiodistrophy (TTD) is a rare autosomal recessive condition that is characterized by a specific congenital hair shaft dysplasia caused by deficiency of sulfur associated with a wide spectrum of multisystem abnormalities. In this article, we study clinical, microscopic, and ultrastructural findings of 20 patients with TTD with the aim to add further insights regarding to this rare condition. Additionally, analyses of our results are compared with those extracted from the literature in order to enhance its comprehensibility. Materials and Methods: Twenty cases of TTD were included: 7 from Mexico and 14 from Spain. Clinical, microscopic, scanning electron microscopy (SEM) studies and X-ray microanalysis (XrMa) were carried out in all of them. Genetic studies were performed in all seven Mexican cases. Patients with xeroderma pigmentosum and xeroderma pigmentosum/TTD-complex were excluded. Results: Cuticular changes and longitudinal crests of the hair shaft were demonstrated. These crests were irregular, disorganized, following the hair longest axis. Hair shaft sulfur deficiency was disposed discontinuously and intermittently rather than uniformly. This severe decrease of sulfur contents was located close to the trichoschisis areas. Only five patients did not show related disturbances. Micro-dolichocephaly was observed in five cases and represented the most frequent facial dysmorphism found. It is also remarkable that all patients with urologic malformations also combined diverse neurologic disorders. Moreover, three Mexican sisters demonstrated the coexistence of scarce pubic vellus hair, developmental delay, onychodystrophy, and maxillar/mandibullar hypoplasia. Conclusions: TTD phenotype has greatly varied from very subtle forms to severe alterations such as neurologic abnormalities, blindness, lamellar ichthyosis and gonadal malformations. Herein, a multisystem study should be performed mandatorily in patients diagnosed with TTD.

Influence of magmatic-hydrothermal activity on brine evolution in closed basins: Searles Lake, California

Evaporites in a 700-m-long core (KM-3) from Searles Lake, California, preserve a record of the chemical evolution of inflow waters. Chemical analyses of fluid inclusions in halite and evaporite minerals show that the major ion composition of inflow waters to Searles Lake was changed by distant hydrothermal activity associated with magmatism at Long Valley caldera between 1.27 and 1.0 m.y. ago. Below core depths of 291 m, the evaporites consist of Ca-bearing sulfates (anhydrite, glauberite) and halite; fluid inclusions in the halite show that parent waters were Na+-Cl−-SO42−-rich waters. Above 291 m, the evaporites include sodium carbonates (pirssonite, trona) and halite, and fluid inclusion brines are Na+-K+-HCO3−-CO32−-Cl−-SO42−-rich. These fluctuations in mineralogy and brine chemistry document an alkalinity spike beginning between 1.27 and 1.0 Ma, when inflow waters to Searles Lake crossed the CaCO3 chemical divide and began to produce alkaline brines that precipitated trona upon evaporation. The Owens River is a modern chemical analog for inflow water into Searles Lake beginning between 1.27 Ma and 1.0 Ma. A major contributor of solutes to the Owens River is Hot Creek in Long Valley caldera, which is fed by hydrothermal springs with high alkalinity from magmatically derived CO2. The timing of magmatism in Owens Valley and the appearance of sodium carbonate minerals in core km-3 suggest a causal relationship. Volcanism and hydrothermal activity provided CO2 and elevated alkalinity to Searles Lake inflow waters 0.5−0.2 m.y. before the eruptions that formed the Bishop Tuff and Long Valley caldera.

Evaporite evidence of a mid-Holocene (c. 4550–4400 cal. yr BP) aridity crisis in southwestern Europe and palaeoenvironmental consequences

Sedimentological evidence for an abrupt dry spell in south-eastern Spain during the middle Holocene, from c. 4906 to 4384 cal. yr BP, is presented. This phase was determined primarily from halite beds deposited between muddy slimes in a lagoon system of Puerto de Mazarrón (Murcia province) with a peak phase from c. 4550 to 4400 cal. yr BP. A multi-core, multi-proxy study of 20 geotechnical drills was made in the lagoon basin to identify the main sedimentary episodes and depositional environments. The results suggest that this halite bed, more than 80 cm thick, was conditioned by climate change and was accompanied by a generalized drying-out of the basin. Halite precipitation was linked with palaeoecological changes, including forest and mesophyte depletions and increasing cover and diversity of xerophytic plant species. Archaeological evidence indicates a demise of the population at this period probably due to resource exhaustion. An overall picture of the biostratigraphy and palaeoclimates of the region is given in a broader geographical context.