It is generally observed that precipitation is gradually depleted in 18O and 2H isotopes as elevation increases (‘altitude’ effect) or when moving inland from seacoasts (‘continental’ effect); the regionally accurate estimation of these large-scale effects is important in isotope hydrological or paleoclimatological applications. Nevertheless, seasonal and spatial differences should be considered. Stable isotope composition of monthly precipitation fallen between January 2016 and December 2018 was studied for selected stations situated along an elevation transect and a continental transect in order to assess the isotopic ‘altitude’ and ‘continental’ effects in modern precipitation across the Adriatic–Pannonian region. Isotopic characteristics argue that the main driver of the apparent vertical depletion of precipitation in heavy stable isotopes is different in summer (raindrop evaporation) and winter (condensation), although, there is no significant difference in the resulting ‘altitude’ effect. Specifically, an ‘altitude’ effect of −1.2‰/km for δ18O and −7.9‰/km for δ2H can be used in modern precipitation across the Adriatic–Pannonian region. Isotopic characteristics of monthly precipitation showed seasonally different patterns and suggest different isotope hydrometeorological regimes along the continental transect. While no significant decrease was found in δ18O data moving inland from the Adriatic from May to August of the year, a clear decreasing trend was found in precipitation fallen during the colder season of the year (October to March) up to a break at ~400 km inland from the Adriatic coast. The estimated mean isotopic ‘continental’ effect for the colder season precipitation is −2.4‰/100 km in δ18O and −20‰/100 km in δ2H. A prevailing influence of the Mediterranean moisture in the colder season is detected up to this breakpoint, while the break in the δ18O data probably reflects the mixture of moisture sources with different isotopic characteristics. A sharp drop in the d-excess (>3‰) at the break in precipitation δ18O trend likely indicates a sudden switch from the Mediterranean moisture domain to additional (mainly Atlantic) influence, while a gradual change in the d-excess values might suggest a gradual increase of the non-Mediterranean moisture contribution along the transect.
A tatai Kálvária-dombon feltáruló alsó-jura mészkőben korábban nem azonosított dolomit testet ismertünk fel. A dolomit test egy repedés mentén jelenik meg és egy szintben a Pisznicei Mészkő réteglapjával párhuzamosan is kiterjed, így „gomba” metszetet mutat. A dolomit finom-középkristályos, és helyenként nyeregdolomit is megjelenik. A dolomittestet breccsazóna harántolja. A klasztokat több generációs fehér-szürke-sárga kalcit cementálja, amelyben zárványként apró dolomittörmelék is megfigyelhető. A dolomittest nem breccsásodott, hanem rétegződéssel párhuzamos kalciterek vágják át. Dolomit utáni kalcit pszeudomorfózát (dedolomitot) is azonosítottunk a Pisznicei Mészkő breccsazóna melletti szakaszán. A három különböző dolomit (finom-középkristályos helyettesítő dolomit, nyeregdolomit cement, törmelékes dolomit zárványok a kalcitban) valamint a később kalcittal helyettesítődött dolomit képződése is feltételezhetően ugyanahhoz a dolomitosodási eseményhez köthető. A repedés mentén áramló, esetenként réteglap mentén elszivárgó fluidum szövetromboló módon dolomitosította a mellékkőzetet. Ennek a dolomit fázisnak a törmelékét találjuk meg a breccsazónát cementáló kalcit zónái között. A dolomitosodás repedéshez kötötten ment végbe. A stabilizotóp értékek betemetődéskor végbement folyamatot valószínűsítenek. Az anyaoldat lehetett az ekkor jelenlévő pórusvíz vagy hidrotermális fluidum. A törések poszt-szediment jellege, és breccsát cementáló kalcit meteorikus eredete alapján a dolomitosodási esemény a késő-jura és késő-kréta–paleogén között mehetett végbe.
Abstract Retrograde clay mineral reactions (reverse weathering), including glauconite formation, are first-order controls on element sequestration in marine sediments. Here, we report substantial element sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 3 ± 2 mmol·cm − ²·kyr −1 for K, Mg and Al, 16 ± 9 mmol·cm − ²·kyr −1 for Si and 6 ± 3 mmol·cm − ²·kyr −1 for Fe, which is ~2 orders of magnitude higher than estimates for deep-sea settings. Upscaling of glauconite abundances in shallow-water (0–200 m) environments predicts a present-day global uptake of ~≤ 0.1 Tmol·yr −1 of K, Mg and Al, and ~0.1–0.4 Tmol·yr −1 of Fe and Si, which is ~half of the estimated Mesozoic elemental flux. Clay mineral authigenesis had a large impact on the global marine element cycles throughout Earth’s history, in particular during ‘greenhouse’ periods with sea level highstand, and is key for better understanding past and present geochemical cycling in marine sediments.
The middle Anisian extensional tectonics of the Neotethyan realm developed a small, isolated carbonate platform in the middle part of the Balaton Highland (western Hungary), resulted in the deposition of uranium-bearing seamount phosphorite on the top of the drowned platform and produced some epigenetic fluorite veins in the Middle Triassic sequence. The stable C-O isotope data of carbonates are shifted from the typical Triassic carbonate ranges, confirming the epigenetic-hydrothermal origin of veining. Primary fluid inclusions in fluorite indicate that these veins were formed from low temperature (85–169 °C) and high salinity NaCl + CaCl2 + H2O type (apparent total salinity: 15.91–22.46 NaCl wt%) hydrothermal fluids, similar to parent fluids of the Alpine-type Pb-Zn deposits. These findings indicate that the Triassic regional fluid circulation systems in the Alpine platform carbonates also affected the area of the Balaton Highland. This is also in agreement with the previously established palinspatic tectonic reconstructions indicating that the Triassic carbonate and basement units in the Balaton Highland area were a part of the Southern Alpine. Similar fluorite veining in phosphorite deposits is also known in the Southern Alpine areas (e.g., Monte San Giorgi, Italy). Raman spectroscopic analyses detected H2 gas in the vapor phase of the fluid inclusions and a defect-rich fluorite structure in violet to black colored growth zones. This unique phenomenon is assumed to be the result of interaction between the uranium-rich phosphorite and the parent fluids of the epigenetic fluorite veins.
Abstract In this study, already published and new monitoring data are compiled from the Baradla and Béke caves in the Aggtelek Karst, from the Vacska Cave in the Pilis Mountains as well as from the Szemlőhegy and Pálvölgy caves in the Buda Hills. Recent investigations (2019–2020) include monitoring of climatological parameters (e.g., temperature, CO 2 ) measured inside and outside the caves, and the chemical, trace element and stable isotopic compositions of drip waters. In the Baradla Cave, the main focus of the investigation was on the stable isotope composition and the temperature measurements of drip water. In the Vacska Cave, which belongs to the Ajándék-Ariadne cave system, CO 2 measurements and drip water collection were conducted in order to perform chemical and stable isotope measurements. In the Szemlőhegy and Pálvölgy caves, the chemical and stable isotope compositions of drip waters at six sites were determined. These datasets were used to characterize the studied caves and the hydrological processes taking place in the karst, and to trace anthropogenic influences. Climatological investigation revealed seasonality in CO 2 concentration related to outside temperature variation, indicating a variable ventilation regime in the caves. In addition, the contributions of the winter and summer precipitation to the drip water were also estimated, in order to evaluate the main infiltration period. The knowledge of these parameters plays a crucial role in constraining the carbonate precipitation within the cave. Thus, the dataset compiled in this study can provide a basis for the interpretation of speleothem-based proxies.
ABSTRACT The carbonate-dominated Mesozoic sequence of the Transdanubian Mountain Range contains Triassic, uranium-enriched phosphorite layers and Cretaceous, REE -enriched nodular phosphorite. Detailed investigation of these deposits may have an economic benefit because of their large U and REE contents. The dominant minerals in the Triassic phosphorite are carbonate-bearing fluorapatite (CFA) and calcite. According to the electron-probe microanalysis (EPMA) the U is mainly associated with the CFA crystals. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) measurement shows that CFA contains 137–612 ppm U and 113–261 ppm total REE + Y. The LA-ICP-MS U-Pb age of the uppermost phosphorite horizon is 237 ± 11 Ma, which conforms with the stratigraphic age of the host limestone. The Cretaceous nodular phosphorite occurs on the base of an Aptian crinoid-bearing limestone mostly in the form of encrustations around bio- and silicic-clasts, but the clasts also contain phosphorite. The main minerals in these crusts are CFA, calcite, quartz, glauconite and Fe-oxide-hydroxides. Based on EPMA the REE enrichment is related to CFA and LA-ICP-MS measurements show that it contains 748–2953 ppm total REE + Y. The redox-sensitive proxies and the shape of NASC normalized REE patterns indicate that both phosphorites formed in anoxic environments. There are significant differences between these deposits such as appearance, rock-forming minerals, and U and REE contents which indicate differences in their sedimentary environments. The present results suggest that the Triassic phosphorite was formed by inorganic precipitation in a reducing environment close to sea-mounts. The Cretaceous occurrence resulted from a concentric growth mechanism in cold, ascending seawater at the continental margin environment during the anoxic Selli Event (OAE 1a) and/or Paquier Episode (OAE 1b). The critical raw material contents were derived from other sources.
Available data (Sr, Nd and Pb isotope systematics) for the Proterozoic Samalpatti–Sevattur (Tamil Nadu, India) carbonatite complexes indicate ultimately a mantle origin of these carbonatites. However, for both intrusions various degrees of mixing between mantle and crustal components of the parent carbonatite fluid have been evidenced based on stable C–O and noble gas (He, Ne, Ar) isotope compositions. An integrated petrographic, noble gas (He, Ne, Ar), clumped isotope and trace element geochemical study has been performed to further constrain their genesis and provide additional constraints on their evolution. Oriented texture of calcite, formation of subgrains, grain boundary bulging as well as sheared and inclined calcite twins indicate dynamic deformation; whereas triple junctions and polygonal mosaic texture indicate static recrystallization of the carbonatites. Although the metamorphism may have had significant effect on the ordering of C and O atoms, clumped isotope analyses (expressed as D 47 ) indicate temperatures < 250°C for Sevattur carbonatites. The obtained low crystallization temperatures are in line with the compatible/incompatible element ratios. High Ho/Y, U/Th and Y/Ce ratios support the carbothermal origin of the carbonatites and the fractionation of the fluids from the footwall syenitic rocks. Plots of Ba/Mn vs. Nb/Th and Ba/La vs. Nb/Pb, however, do not support their fractionation or immiscibility from the host pyroxenite rocks. Crustal-like R/R A values (~0.05) of Sevattur are slightly different from the Samalpatti ratios (~0.2) and imply a higher (2-3% vs 0.1%) mantle contribution to the magma formation of the Samalpatti carbonatites. Two samples from Samalpatti have mantle-plume-like 20 Ne/ 22 Ne (10.5 and 11.8) and 21 Ne/ 20 Ne (0.030 and 0.035) ratios. Model calculations prove that the high 4 He and 21 Ne concentrations cannot be explained with decay of the U and Th hosted by the apatite and calcite crystal lattice, but they were trapped from the mineralizing fluids in the fluid inclusions. High ΣREE (>1000 ppm) and Ba concentrations of Sevattur compared to Samalpatti as well as the low 87 Sr/ 86 Sr ratios (~0.0705) and high Ba/Th ratios (1000/10000) suggest the melting of an enriched Subcontinental Lithospheric Mantle (SCLM) which was previously enriched in incompatible LILE elements deriving from the hydrothermally altered ocean floor (sediments). Although volumetrically not comparable, most of the geochemical parameters and hence the magma genesis makes the Sevattur carbonatite comparable with the world-class REE deposits in China. In turn, the low ΣREE (<100 ppm), the high 87 Sr/ 86 Sr ratios (0.706–0.708), the average Ba concentrations (~110) and the low Ba/Th ratios (~100) suggest the melting of the SCLM or mantle which was enriched in sedimentary carbonates. Noble gases indicate that compared to the Sevattur complex the fraction of the mantle (-plume) derived magma could have been higher compared to the Sevattur complex. Our study has proven, that in spite of the close spatial proximity (2 km) the neighboring carbonatite complexes have experienced basically contrasting syn- and post emplacement history and have different magma sources.
