Internal structure and origin of modern salt crust of Salar de Uyuni (Bolivia) salt pan based on tomographic research

This paper presents the results of a study on the internal structure of modern salt crust of Salar de Uyuni in SW Bolivia. Additionally, the structure of desiccation fissure infill was investigated. X-ray microtomography was used as the main analytical method because it enabled the complete structure of the sample's interior to be imaged without its destruction. Based on microtomographic images three layers were distinguished in the crust between the surface and its base: a halite shell at the top, a cellular halite layer in the middle and a large-pore halite layer at the base. Results revealed that the desiccation fissures are filled with extremely porous bubble-halite. Distribution of mud in the sample as well as wash-out of the surfical halite crystals indicate the cyclicity of halite dissolution, its crystallisation and mud accumulation. These observations provide an explanation for low rate salt accumulation in the salt pan. This leads to the conclusion that the observed layering in the rocks does not reflect annual sedimentation-evaporation cycles but rather long-term cycles

Salt tectonics in front of the Outer Carpathian thrust wedge in the Wieliczka area (S Poland) and its exposure in the underground salt mine

Salt deposits in the Wieliczka area (Wieliczka Salt Deposit – WSD) in southern Poland comprise salt-rich strata belonging to an evaporite succession that originated in the Carpathian Foredeep basin in the Middle Miocene Badenian (Serravallian) times, ca 13.81–13.45 Ma. Although they have been mined since the 13th century and decades of investigations provided abundant data on their origin and structure, some aspects of their geological evolution are still not fully understood. This study presents current concepts on the lithostratigraphy and tectonics of the WSD. The salt-bearing facies developed near to the southern basin margin, delineated by the Carpathian orogenic front. Such a location triggered the redeposition of sediments and gravity-driven deformation followed by tectonic deformation related to the forelandward advancement of the Carpathian thrusts. As a result, the WSD consists of folds and slices composed of two main salt members: (1) the stratified salt member, with intercalating salt, sulphates and siliciclastics, and (2) the boulder salt member, built of clays with large, isolated blocks of salt. The stratified member contains abundant meso-scale tectonic structures recording the soft-sediment deformation and deformation related to the northward tectonic push exerted by the advancing Carpathian thrust wedge. The boulder member originated due to the syntectonic erosion of evaporites along the basin margins and their redeposition during progressive northward migration of the Carpathian front. Recent interpretations of seismic data imply that the WSD constitutes the core of a triangle zone developed at the contact of the Carpathian orogenic wedge with the backthrust-displaced foredeep sedimentary fill. Meso-scale examples of sedimentary and tectonic structures in the salt-bearing succession exposed in the underground Wieliczka Salt Mine are described and their formation modes discussed

Struktura wewnętrzna i geneza współczesnej pokrywy solnej solniska Salar de Uyuni (Boliwia) w świetle badań tomograficznych Internal structure and origin of modern salt crust of Salar de Uyuni (Bolivia) salt pan based on tomographic research /

Tyt. z nagłówka.Bibliogr. s. 228.W pracy przedstawiono rezultaty badań budowy wewnętrznej współczesnej pokrywy solnej solniska Salar de Uyuni w południowo-zachodniej Boliwii. Analizie poddano również budowę wypełnień szczelin z wysychania. Podstawową techniką badawczą była mikrotomografia rentgenowska, obrazująca pełną strukturę wewnętrzną prób bez ich destrukcji. Badania wykazały trójdzielność struktury pokrywy: obecność powłoki halitowej na powierzchni, warstwy halitytów komórkowych poniżej powłoki oraz warstwy halitytów wielkoporowych w części spągowej pokrywy. Szczeliny z wysychania wypełniają halityty pęcherzykowate. Rozmieszczenie materiału mułowego w próbie oraz rozmycia kryształów przypowierzchniowych wskazują na wielokrotność cykli rozpuszczania soli, krystalizacji halitu i depozycji mułów. Na tej podstawie sformułowano wniosek, iż obserwowane w skałach warstwowanie nie odzwierciedla rocznych cykli sedymentacyjno-ewaporacyjnych, lecz cykle wieloletnie. Tłumaczy to niskie średnie tempo przyrostu osadów na solnisku.This paper presents the results of a study on the internal structure of modern salt crust of Salar de Uyuni in SW Bolivia. Additionally, the structure of desiccation fissure infill was investigated. X-ray microtomography was used as the main analytical method because it enabled the complete structure of the sample's interior to be imaged without its destruction. Based on microtomographic images three layers were distinguished in the crust between the surface and its base: a halite shell at the top, a cellular halite layer in the middle and a large-pore halite layer at the base. Results revealed that the desiccation fissures are filled with extremely porous bubble-halite. Distribution of mud in the sample as well as wash-out of the surfical halite crystals indicate the cyclicity of halite dissolution, its crystallisation and mud accumulation. These observations provide an explanation for low rate salt accumulation in the salt pan. This leads to the conclusion that the observed layering in the rocks does not reflect annual sedimentation-evaporation cycles but rather long-term cycles.Dostępny również w formie drukowanej.SŁOWA KLUCZOWE: Salar de Uyuni, współczesne osady solne, poligony z wysychania, mikrotomografia rentgenowska. KEYWORDS: Salar de Uyuni, modern salt deposits, desiccation polygons, X-ray microtomography

Chemical composition of Badenian brines from primary fluid inclusions in halite (Transcarpathian Basin, Ukraine)

The primary fluid inclusions, which may be helpful in detemining the chemical composition of brines in the Badenian evaporite basin, were found in the chevron halite crystals from the Transcarpathian Basin (Ukraine). Fluid inclusions in sedimentary halite were examined with the use of ultra-microchemical analysis. Concentration of brines was high - close to the middle stage of halite sedimentation. The content of ions: K+ ranged from 10.6 g/l to 17.6 g/l, Mg2+ from 31.4 g/l to 58.3 g/l, and SO4 2- from 22.4 g/l to 39.0 g/l. Based on the chemical composition of major ions it was concluded that the brine from the Transcarpathian basin was saturated (to the stage of halite crystallization) and was similar to the Badenian brines from other basins

Geomorphometric and Geophysical Constraints on Outlining Drained Shallow Mountain Mires

Long-term draining of peatlands results in transformation of vegetation and obliteration of their morphological features. In many areas, efforts are made to restore the original ecosystems and increase their water retention potential. Using combined analyses of a LiDAR-based digital terrain model (DTM), colour-infrared (CIR) imagery data, ground-penetrating radar (GPR) data and electrical resistivity tomography (ERT) data, we tested the applicability of these methods in outlining the extent and subsurface structure of drained mires located in the Stolowe Mountains National Park area, Poland. The LiDAR-DTMs enabled parameterisation of physiographic features of the mires and determination of their extent, runoff directions and potential waterlogging areas. CIR analysis enabled classification of vegetation types. GPR prospecting revealed the bedrock morphology, thickness and internal structure of the peat deposits, showing that this technique can also provide data on variability in the decomposition of phytogenic deposits. The obtained ERT sections indicate both the thickness of peat deposits and variability in the bedrock internal structure. The results show that integrated analyses of data obtained with different methods can be an effective tool in outlining the original extent of peatlands, with potential application in the planning of peatland ecosystem restitution