Damage to speleothems is a common phenomenon in mid-latitude caves, and multiple causes have been proposed. Here we report on one of such type of damage, namely stalagmites that are broken and ...partially sheared near their base but are still in upright position. Such stalagmites occur in the Obir Caves (Austria) associated with cryogenic cave carbonates, demonstrating the former presence of cave ice.
Th dating suggests damage to the speleothems during the Last Glacial Maximum. Numerical modelling combined with laboratory measurements demonstrates that internal deformation within a cave ice body cannot fracture stalagmites, even on a steep slope. Instead, temperature changes lead to thermoelastic stresses within an ice body that reach values equaling to and exceeding the tensile strength of even large stalagmites. Differences in thermal expansion coefficients cause a sharp vertical jump in stress between the stalagmite and the surrounding ice body, and the ice lifts the stalagmite as it expands with increasing temperature. This study refutes the previously accepted model that flow of ice breaks stalagmites, and suggests a link between glacial climate variability and corresponding cooling and warming cycles in the subsurface that weaken and eventually fracture stalagmites due to the opposing thermoelastic properties of calcite and ice.
Carbonate geothermometry is a fundamental tool for quantitative assessment of the geothermal and geochemical evolution of diagenetic and hydrothermal systems, but it remains difficult to obtain ...accurate and precise formation temperatures of low-temperature calcite samples (below ~ 40 to 60 °C). Here, we apply three geothermometry methods (∆
-thermometry, nucleation-assisted fluid inclusion microthermometry-hereafter NA-FIM-and oxygen isotope thermometry) to slow-growing subaqueous calcite spar samples to cross-validate these methods down to 10 °C. Temperatures derived by NA-FIM and Δ
-thermometry agree within the 95% confidence interval, except for one sample. Regression analyses suggest that the real uncertainty of ∆
-thermometry exceeds the 1 SE analytical uncertainty and is around ± 6.6 °C for calcite spar that formed at 10-50 °C. The application of δ
O thermometry was limited to a few samples that contained sufficient primary fluid inclusions. It yielded broadly consistent results for two samples with two other geothermometers, and showed higher temperature for the third spar. We also found that calcite with steep rhombohedral morphologies is characteristic of low temperatures (11-13 °C), whereas blunt rhombohedra prevail in the 10-29 °C domain, and the scalenohedral habit dominates > 30 °C. This suggests that the calcite crystal morphology can be used to qualitatively distinguish between low- and higher-temperature calcite.
The 116 km-long and 1560 m-deep Hirlatzhöhle is one of the major cave systems in the Northern Calcareous Alps (NCA; Austria). It is located in the NW part of the Dachstein, an extensive karst massif ...encompassing 576 km² with its highest point at 2995 m a.s.l. In contrast to most other caves in the NCA, Hirlatzhöhle comprises old (epi)phreatic passages located up to 1 km above the base level as well as two modern major drainage systems. The aim of this study is to define the palaeo- and the active flow conditions in combination with speleogenesis, and the age of the cave levels of Hirlatzhöhle. We use morphological as well as sedimentological studies and correlations with other caves. Another difference from cave systems in the NCA is that the majority of passages in Hirlatzhöhle are not developed within the so-called Giant Cave Level between 1200 and 1800 m a.s.l., but deeper between 800 and 1300 m. Most parts of Hirlatzhöhle developed under epiphreatic conditions as indicated by rills and condensation corrosion cupolas, which is the case for much other cave systems in the NCA. In contrast, paragenetic features like canyons and ceiling channels are relatively rare as are insoluble sediments. Elongated scallops indicate that flow velocities were high and abrasive sediments were abundant. Opposite to the nearby Dachstein-Mammuthöhle and other caves east of it that show a west-directed palaeo-flow, scallops in Hirlatzhöhle indicate a NE-directed palaeo-flow and an autogenic recharge. Modern drainage is autogenic and N- to NE-directed as well. Even though burial age dating did not give reasonable results for Hirlatzhöhle yet, the correlation with other adjacent caves suggests a Late Pliocene to Early Pleistocene age of the main palaeo-phreatic level. This is supported by an infinite U-Th age (>0.6 Ma) of a flowstone.
The relationship between the atmospheric concentration of cosmogenic isotopes, the change of solar activity and hence secondary neutron flux has already been proven. The temporal atmospheric ...variation of the most studied cosmogenic isotopes shows a significant anti-correlation with solar cycles. However, since artificial tritium input to the atmosphere due to nuclear-weapon tests masked the expected variations of tritium production rate by three orders of magnitude, the natural variation of tritium in meteoric precipitation has not previously been detected. For the first time, we provide clear evidence of the positive correlation between the tritium concentration of meteoric precipitation and neutron flux modulated by solar magnetic activity. We found trends in tritium time series for numerous locations worldwide which are similar to the variation of secondary neutron flux and sun spot numbers. This variability appears to have similar periodicities to that of solar cycle. Frequency analysis, cross correlation analysis, continuous and cross wavelet analysis provide mathematical evidence that the correlation between solar cycle and meteoric tritium does exist. Our results demonstrate that the response of tritium variation in precipitation to the solar cycle can be used to help us understand its role in the water cycle.
•Isotope records help studying the recharge-discharge properties of karst aquifers.•The age distributions and response times are constrained by environmental tracers.•Recent recharge has been ...detected by the oxygen isotope ratio time series.•The tritium in precipitation modulated by the solar cycle cannot be detected yet.
Three karst regions in Hungary and Slovakia.
Time series of environmental tracers both in the groundwater recharge and discharge provide important insights into how a karst water system works. The aim of the present work was to study the response of discharging karst waters to recharge using time series of environmental tracers, such as tritium, stable water isotopes, noble gases and SF6.
Our results show that sampling frequency plays a significant role in detecting short residence times (months): the seasonality of 18O isotope composition of a selected karst spring indicates a 10 % contribution of recent water with a residence time of half a year. The contribution of an older component can be proven by the decrease of the tritium content of the waters, which compares to the decreasing trend of the tritium time series of the precipitation. However, the tritium concentrations are just slightly lower than those of the precipitation and the recharge water, hence the residence times of these shallow springs are supposed to be short. 3H/3He and SF6 apparent ages confirm this to be between 0 and 10 years, with a median of 1.4 years. Our study demonstrates that long-term time series are preferable to provide better estimation to the age distribution than individual, short-term investigations.
Coarsely crystalline carbonates that formed cryogenically in caves (CCCcoarse for short) are important paleoenvironmental archives that provide evidence of former perennial ice deposits in currently ...ice-free caves and allow the timing of the past freezing conditions close to 0 °C in the subsurface to be determined. Despite their significance, the mode of formation of these deposits has never been observed in statu nascendi.
We conducted a series of freezing experiments in an Alpine ice cave to test the conceptual model of CCCcoarse formation in freezing pools of water in perennial ice deposits. Our results document a number of features associated with the freezing of such confined water bodies, including ice bulging, cracking and episodic expulsion of water. These observations help explain the degassing of carbon dioxide required to maintain carbonate precipitation in these semi-closed pockets of slowly freezing water. Our experiments yielded a range of morphological types of cryogenic calcite crystals and aggregates comparable to those reported from CCCcoarse from currently ice-free caves elsewhere. The experimentally grown crystals also exhibit the same depleted O isotope composition characteristic of natural carbonates interpreted as being formed subaqueously in a semi-closed pools subject to freezing. The main difference to naturally formed CCCcoarse is their smaller crystal size, reflecting the comparably short freezing time of our experiments of less than two weeks.
This study confirms the conceptual model explaining the formation of CCCcoarse in localized pools in ice and calls for a revision of the currently existing classification scheme for cryogenic cave carbonates.
Hypogene karst caves, formed independently of surface processes, have garnered increasing attention in recent decades, revealing a wider distribution than previously assumed. While most studies have ...relied on morphological observations, this research combines morphological and geochemical approaches to present new insights from the Obir caves in the Northern Karawank Mountains, Austria. These caverns, discovered during mining activities, lack natural entrances and developed along a prominent master horizon about 500 m above the current spring level. Notably, large shafts within the caves originate in narrow fissures and terminate blindly at the top, also suggesting a phreatic regime during their formation, with some areas being modified by vadose waters later on. A comprehensive study of drill cores indicates a stable isotope halo in the first few centimeters of the wall rock, characterized by significantly depleted δ13C and moderately depleted δ18O values compared to the pristine limestone, accompanied by bleaching of the host rock. This geochemical evidence of wall rock alteration is only present where the original phreatic solutional morphology is preserved and absent where vadose waters resulted in rugged cave wall surfaces.
Considering the lack of evidence for the involvement of sulfuric acid or thermal waters, the formation of the Obir caves is attributed to carbonic acid speleogenesis. This interpretation is supported by the observed strong C isotope shift in the wall rock and the presence of CO2-bearing springs both north and south of the Periadriatic Fault. In contrast to previous studies of carbonic acid speleogenesis suggesting large-scale upwelling of aggressive waters, we propose an alternative mechanism: the injection of carbon dioxide gas into limestone situated in the phreatic zone. These injections likely occurred along subvertical tectonic fissures, triggered by the tectonic transpression of the Northern Karawank Mountains during the middle Miocene. Subsequent tectonic uplift and the incision of valleys led to a drop in the groundwater table, widespread collapse of larger cave rooms and localized vadose overprint.
This study highlights the strength of combining mega- to the microscale cave morphological observations with systematic geochemical analyses of wall rock alteration in identifying caves formed by carbonic acid speleogenesis.
Hypogene speleogenesis involves the formation of solution-enlarged permeability structures driven by ascending water acquiring its acidity from deep-seated sources. This process occurs in a wide ...range of geological settings and in different lithologies. Although hypogene speleogenesis has received increasing attention in the last two decades, the identification of former hypogene activity in caves remains challenging, unless unambiguous morphological, mineralogical and/or hydrogeological evidence is available. Here, we document that geochemical analyses (mainly stable oxygen and carbon isotopes) of cave wall rock samples may fill this methodological gap and provide a useful tool to identify hypogene karstification through geochemical fingerprinting of water-rock interaction.
Stable isotope profiles of a comprehensive set of wall rock cores from eight hypogene caves in Austria in both limestone and dolomite settings were investigated. Alteration halos typically a few centimeters wide and characterized by up to 12‰ and 15‰ depletion in δ13C and δ18O, respectively, were identified in limestone and calcite marble caves. Besides isotopic alteration, bleaching and/or staining of the wall rock was observed due to oxidizing conditions of the paleowater. No isotopic change of the wall rock was identified in hypogene caves carved in dolomite, which may be attributed to low Ca/Mg ratios of the paleowater and/or aggressive fluids leading to fast wall rock retreat. On the other hand, dedolomitization was observed in some wall rocks implying the presence paleowaters with elevated Ca/Mg ratios. Similarly to dolomitic caves, no isotopic alteration front was observed in a cave formed by sulfuric acid speleogenesis. A likely explanation is the high rate of wall rock retreat outpacing the rate of isotope exchange in the wall rock. Our study also shows that water-rock interaction during epigene speleogenesis does not lead to isotopic halos.
This geochemical fingerprinting approach offers a powerful tool to test the hypogene origin of caves and may provide additional insights into the temperature and provenance of the paleowater and the source(s) of its dissolved inorganic carbon.
ABSTRACT
Glacial periods and their terminations are useful for assessing the full scale of natural climate variability in the diverse climate regions of West Asia (i.e. deserts, mountains, alluvial ...plains, coastal zones). In this study, we report the first stalagmite stable isotope (δ18O and δ13C) records from the southern Zagros Mountains in southwest Iran. The records partially span the period from the Last Glacial Maximum (LGM) to the early Holocene, 24.2–9.6 thousand years before the present. The southwest Iran stalagmite δ18O and δ13C records indicate that climate and environment in the area differed substantially between the LGM and early Holocene. High stalagmite δ13C values are found at the LGM (7‰ greater compared to the early Holocene), and are attributed to sparse vegetation and reduced soil bio‐productivity, and possibly a greater degree of prior calcite precipitation in the epikarst, as a result of a cold and dry climate. Stalagmite δ18O values are also high at the LGM (4‰ greater compared to the early Holocene), and are attributed to lower temperatures (larger water–calcite isotope fractionation) and higher δ18O values of the moisture sources (Mediterranean and Red Seas). Through the deglaciation, stalagmite δ18O, δ13C and/or growth features coincide with the North Atlantic Heinrich Stadial 1, the Bølling–Allerød warm period and the Younger Dryas cold event, supporting a relationship between southern Zagros climate and the North Atlantic millennial events.
The Dolomites of northern Italy feature some of the most intensively studied carbonate rocks worldwide. Yet, little is known about the long karst history of this mountain range dating back to the ...Miocene. This study scrutinizes three caves (F10, Milchloch and Cioccherloch) in the Fanes-Sennes-Prags Nature Park (Province of South Tyrol) and the adjacent Fosses area in the Natural Park of Ampezzo Dolomites (Province of Belluno, Veneto). Paleo-phreatic passages of these limestone caves mostly follow a NW-SE orientation, similar to the nearby Val Salata fault. A multi-method approach including cave morphological and isotopic analyses of wall-rock cores was applied to reconstruct the multi-stage speleogenetic history of these cavities. Clastic sediments partly cemented to the cave walls and paragenetic features such as ceiling channels and solutional ramps are present in all studied caves. F10 cave shows widespread laughöhle geometries, including inverted cone chambers and horizontal passages with trapezoid cross sections, characteristic of slow water convection in a hypogene regime. Drill cores in F10 cave exhibit a systematic depletion in both oxygen and carbon isotopes close to the cave wall. The thickness of this isotopically altered zone ranges from a few mm to 4 cm and alteration can sometimes also be macroscopically identified. The amplitude of the isotopic shift ranges from 2.0 to 5.0‰ for δ13C and from 1.9 to 4.9‰ for δ18O. One of the wall rock cores from Cioccherloch also shows a thin isotopic halo, while no evidence of isotopic alteration was found in Milchloch. Our results provide strong geochemical evidence of wall rock alteration driven by hypogene water-rock interaction in at least two of the caves. We propose an early hypogene speleogenetic phase, followed by uplift and denudation resulting in the opening of these cavities to the surface that allowed clastic sediment influx. The sediment infill in combination with the abundant paragenetic features records a second phase in the karst evolution. This paragenetic phase did not involve hypogene waters, as indicated by the lack of isotopic alteration in the wall rock of paragenetic features. The latest phase of speleogenesis is represented by vadose morphologies and vadose speleothems locally dating back to at least 650 ka. This study demonstrates that the combination of morphological analyses and geochemical fingerprinting represents a powerful approach to decipher the commonly complex speleogenetic history of limestone caves.
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