Yuri Dublyansky

Speleogenetic history of the Hungarian hydrothermal karst

The hydrothermal karst of Hungary displays at least two principal stages of development in two differing environments. Caves of an early stage were formed within a deep zone of low thermal gradient. These caves (vugs) are small (tens of centimeters) and lined with scalenohedral crystals of calcite that are often in association with barite. Calcite yields fluid inclusion temperatures of 55–95°C and is depleted in18O (−11.2 to −17.6 per mil PDB). The caves were formed by ascending thermal waters charged with CO2. Solubility of CaCO3 in such a system gradually increases with the ascent of the fluid (solutional zone) but drops sharply at a depth of −250 m to −500 m below the water surface (depositional zone). Caves formed in the solutional zone may be shifted into the depositional zone due to tectonic uplift, and calcite lines their walls. Large caves (tens to thousands of cubic meters) of a late stage were formed within a shallow zone of high thermal gradient immediately below and above the thermal water table. The calcite of the phreatic crusts has a rhombohedral habit, displays lower fluid inclusion temperatures (35–55°C and less), and a depletion in18O of −9.5 to −14.6 per mil PDB. Several powerful cave-forming processes may operate there including convection, mixing/cooling corrosion, and condensation corrosion. Due to differences in the rate of tectonic uplift, rate of hydrothermal system decay, and hydrogeologic pattern, these caves were either filled with water for a long period of time (phreatic calcite crusts are formed) or partly dewatered early in their history (waterline and subaerial speleothems are formed). The zones of thermal cave formation recognized in Hungary may have a universal character. Very similar features are found in other hydrothermal karst areas of the world (Kirghizia, Algeria, South Dakota).

Hydrogen and oxygen isotopes of water from inclusions in minerals: design of a new crushing system and on-line continuous-flow isotope ratio mass spectrometric analysis

An analytical line for stable isotope analyses of water recovered from fluid inclusions in minerals was built and successfully tested. The line is based on the principle of continuous-flow analysis of water via high-temperature reduction on glassy carbon. It includes a custom-designed set of high-efficiency crushers and a cryo-focusing cell. This paper provides details of the line design and discusses strategies for line conditioning and mitigation of memory effects. The line allows measurements of hydrogen and oxygen isotopes during a single acquisition. The precision of the analyses depends on the amount of water released from the inclusions. The best results are obtained for samples containing at least 0.1-0.2 microL (0.06-0.11 micromol) H(2)O. For such samples precision is better than 1.5 per thousand for deltaD and 0.5 per thousand for delta(18)O (1sigma). Smaller amounts of water can be measured but at lower precision. Analyses of modern calcite formed under stable conditions in a deep cave allowed assessment of the accuracy of the analyses. The deltaD values measured in fluid inclusions of this working standard match the deltaD value of the parent water, and the oxygen isotope values agree within ca. 0.5 per thousand. This indicates that fluid inclusions trapped in calcite at near-ambient temperatures (e.g. speleothems and low-temperatures phreatic calcite) faithfully preserve the original isotopic composition of the parent waters.

Traces of epigenetic hydrothermal activity at Yucca Mountain, Nevada: preliminary data on the fluid inclusion and stable isotope evidence

Samples of opal–quartz–calcite crusts from the 7.8-km-long tunnel excavated under Yucca Mountain were studied to determine their origin. Calcite in these crusts commonly forms relatively large (up to 1.5 cm), euhedral crystal terminations. In some crusts, layers of chalcedony and patches of opal alternate with calcite layers. Chalcedony commonly grades into euhedral quartz crystals. Quartz also forms microdruses of individual crystals up to 8 mm in size. Fluorite was identified in four samples. Fluid inclusion studies on calcite revealed formation temperatures of 35–85°C. Gas-filled inclusions are apparently of low-density (P<1 bar at room temperature) and contain aromatic hydrocarbons. In four studied calcite samples, values of δ18O remain virtually constant across crusts (−10.6‰ to −12.1‰ V-PDB). In one sample, the earliest part of calcite had δ18O of −19‰; in this part of the sample, the highest fluid inclusion temperatures, 70–85°C, were measured. The secondary calcite found at Yucca Mountain is commonly interpreted as being formed through a “pedogenic” process from rain waters percolating in the vadose zone and carrying dissolved carbonate from overlying soils [e.g., Stuckless, J.S., Peterman, Z.E., Muchs, D.R., 1991. U and Sr isotopes in ground water and calcite, Yucca Mountain, Nevada: evidence against upwelling water. Science 254, 551–554; NAS/NRC, 1992. Ground Water at Yucca Mountain: How High Can It Rise? National Academy Press, Washington, DC; Roedder, E., Whelan, J.F., Vaniman, D.T., 1994. Fluid inclusion studies of calcite veins from Yucca Mountain, Nevada, tuffs: environment of formation. High-Level Radioactive Waste Management. Proc. Int. Conf., Am. Nucl. Soc. La Grande Park, IL, pp. 1854–1860]. Our data indicate that the calcite–opal–quartz (with minor fluorite) crusts from the presently unsaturated (vadose) zone of Yucca Mountain were formed from low-temperature hydrothermal aqueous fluids in the saturated (phreatic) environment. The issue has direct bearing on the suitability of Yucca Mountain as a site for permanent geological disposal of the high-level nuclear waste.

Overview of calcite/opal deposits at or near the proposed high-level nuclear waste site, Yucca Mountain, Nevada, USA: Pedogenic, hypogene, or both?

Calcite/opal deposits (COD) at Yucca Mountain were studied with respect to their regional and field geology, petrology and petrography, chemistry and isotopic geochemistry, and fluid inclusions. They were also compared with true pedogenic deposits (TPD), groundwater spring deposits (GSD), and calcite vein deposits (CVD) in the subsurface. Some of the data are equivocal and can support either a hypogene or pedogenic origin for these deposits. However, Sr-, C-, and O-isotope, fluid inclusion, and other data favor a hypogene interpretation. A hypothesis that may account for all currently available data is that the COD precipitated from warm, CO2-rich water that episodically upwelled along faults during the Pleistocene, and which, upon reaching the surface, flowed downslope within existing alluvial, colluvial, eluvial, or soil deposits. Being formed near, or on, the topographic surface, the COD acquired characteristics of pedogenic deposits. This subject relates to the suitability of Yucca Mountain as a high-level nuclear waste site.

Reconciliation of the Devils Hole climate record with orbital forcing.

The difference is all in the water Glacial cycles are in part controlled by the pattern of incident solar energy determined by the geometry of Earths orbit around the Sun. The classic record of the penultimate deglaciation from Devils Hole, Nevada, did not reconcile the presumption of so-called orbital forcing, however, suggesting that deglaciation began ~10,000 years too early. Moseley et al. present analyses of a new set of data from Devils Hole that show that the deglaciation indeed occurred at the time expected on the basis of orbital forcing. The age offset displayed by the older samples apparently was caused by interaction with groundwater, which preferentially affected the deeper original samples but not the new shallower samples. Science, this issue p. 165 Groundwater effects misled us about the Devils Hole climate record for nearly three decades. The driving force behind Quaternary glacial-interglacial cycles and much associated climate change is widely considered to be orbital forcing. However, previous versions of the iconic Devils Hole (Nevada) subaqueous calcite record exhibit shifts to interglacial values ~10,000 years before orbitally forced ice age terminations, and interglacial durations ~10,000 years longer than other estimates. Our measurements from Devils Hole 2 replicate virtually all aspects of the past 204,000 years of earlier records, except for the timing during terminations, and they lower the age of the record near Termination II by ~8000 years, removing both ~10,000-year anomalies. The shift to interglacial values now broadly coincides with the rise in boreal summer insolation, the marine termination, and the rise in atmospheric CO2, which is consistent with mechanisms ultimately tied to orbital forcing.

Identification of the deep-seated component in paleo fluidscirculated through a potential nuclear waste disposal site: Yucca Mountain, Nevada, USA

Using a combination of mineralogical, fluid inclusion and stable isotope techniques, chemical data have been obtained thathelp characterize the hydrogeochemistry of paleogroundwaters that circulated through the vadose zone of Yucca Mountain, Nevada, USA—a prospective site for geological disposal of high-level nuclear waste. The results depict unidirectional evolution of groundwaters from reducing to oxidizing states concomitantly with an overall cooling from ∼ 85 °C to < 35–50 °C. Early calcite has strongly positive δ13C values (up to +9 %o PDB), which are interpreted as an indication of the partitioning between reduced and oxidized dissolved carbon species in anoxic (reducing) environment. Reducing character of fluids is further supported by the chemistry of gases trapped in inclusions (dominant CH4, CO2, very little O2). The maximum homogenization temperatures of fluid inclusions and reconstructed paleoheat flows form a non-uniform field with prominent maximum near the block-bounding Paintbrush fault. The data support the model of invasion(s) of the deep-seated thermal fluids, into the vadose zone, along the permeable fault zone. Chemical properties of early portions of the fluid were acquired during its long residence in the deep-seated part of the Earths crust. At advanced stages, the fluid evolved in response to the overall cooling and mixing with oxidized waters from shallow aquifers.

Design of two crushing devices for release of the fluid inclusion volatiles

Two crushing cells have been described for the release of volatiles from fluid inclusions in minerals in vacuum, static gas, and gas-flow applications. To minimize the adsorption of released volatiles on the freshly created mineral surfaces, both devices employed heated crushing. In the MTSN (Museo Tridentine di Scienze Naturali) crusher, samples were disintegrated by a piston driven by an induction coil. For efficient crushing, the electromagnet operated in dynamic impulse mode. In the LFU (Leopold-Franzens-Universität) crusher, the sample was disintegrated through the combined action of compression (manually operated hydraulic ram) and attrition. Crushers are able to be used in off-line and on-line modes, in gas chromatographic and mass spectrometric analyses.

Evidence of thermophilisation and elevation-dependent warming during the Last Interglacial in the Italian Alps

Thermophilisation is the response of plants communities in mountainous areas to increasing temperatures, causing an upward migration of warm-adapted (thermophilic) species and consequently, the timberline. This greening, associated with warming, causes enhanced evapotranspiration that leads to intensification of the hydrological cycle, which is recorded by hydroclimate-sensitive archives, such as stalagmites and flowstones formed in caves. Understanding how hydroclimate manifests at high altitudes is important for predicting future water resources of many regions of Europe that rely on glaciers and snow accumulation. Using proxy data from three coeval speleothems (stalagmites and flowstone) from the Italian Alps, we reconstructed both the ecosystem and hydrological setting during the Last Interglacial (LIG); a warm period that may provide an analogue to a near-future climate scenario. Our speleothem proxy data, including calcite fabrics and the stable isotopes of calcite and fluid inclusions, indicate a +4.3 ± 1.6 °C temperature anomaly at ~2000 m a.s.l. for the peak LIG, with respect to present-day values (1961–1990). This anomaly is significantly higher than any low-altitude reconstructions for the LIG in Europe, implying elevation-dependent warming during the LIG. The enhanced warming at high altitudes must be accounted for when considering future climate adaption strategies in sensitive mountainous regions.

Cryogenic Mineral Formation in Caves

Abstract Freezing of karst water in caves forces the segregation of solutes, a process of rejection of dissolved ions by the advancing ice-water front during the growth of ice crystals. This process causes supersaturation of the unfrozen residual part of the solution and precipitation of some of dissolved compounds as minerals. Water evaporation and solution degassing additionally enhance the mineral formation. The cryogenic cave minerals constitute a variety of speleothems, which differ in practically all aspects from their counterparts formed in caves unaffected by freezing. The morphology and mineralogy of cryogenic cave minerals largely depend on the initial chemical composition of the karst water, the thickness of the water layer that freezes, and the freezing rate. The most common cryogenic minerals in the ice caves of limestone karst are fine-grained (powdery) carbonates produced by rapid water freezing in thin water layers. In contrast, slower freezing of large water volumes at cave temperature near 0°C produces coarse-grained cryogenic cave carbonates, which are typically associated with present or past permafrost conditions. Overall, the cryogenic cave carbonates are characterized by C and O isotope signatures different from that of speleothems in temperate environments. Apart from the cryogenic carbonates, several other freeze-related minerals have been identified in caves. By far, the richest diversity of cryogenic minerals occurs in gypsum-hosted ice caves.

High Resolution Isotopic Monitoring of Cave Air CO2

RATIONALE CO2 is the main driver of many chemical processes in cave environments. Understanding CO2 fluxes in a given cave system through monitoring campaigns has become a standard procedure in a wide variety of fields such as paleoclimatology or show cave management. However, conventional methods lack the resolution of isotopic data to capture many transient processes occurring in caves. METHODS A novel approach using isotope ratio infrared spectrometry (IRIS) to monitor cave air pCO2 , δ13 C and δ18 O values in situ was tested and compared with conventional monitoring methods (handheld pCO2 meter and discrete cave air samples for conventional isotope ratio mass spectrometry). This also involved the development of a field-deployable experimental setup to operate the equipment in rough cave environments. RESULTS Comparison between data obtained by means of a Thermo Fisher Scientific Delta Ray IRIS instrument shows overall good agreement with conventional monitoring methods in terms of pCO2 and δ13 C values. In addition, IRIS allows the δ18 O values of cave air CO2 to be measured. CONCLUSIONS IRIS allows identification and tracking of processes at various timescales ranging from transient visitor impact on the cave atmosphere to seasonal trends in cave ventilation. However, the need for an uninterrupted power supply (110/220 V AC) and the relatively large dimensions of the equipment (698 × 1092 × 704 mm, 80 kg) limit the number of caves where deployment of the instrument is feasible. Copyright