Calcite Isotope Research Articles

Cave monitoring in the Peruvian Andes reveals monsoon climate preserved in speleothem calcite

Speleothem paleoclimate records from the Peruvian Andes have been interpreted to reflect the strength of the South American monsoon. While these interpretations have been verified through comparison with other regional and global climate records, the mechanics of the cave environment that facilitate the preservation of this signal with such consistency remain unstudied. Here, we present four years of environmental data from Huagapo and Pacupahuain cave, and one year from Antipayarguna cave. The data reveal that the cave environment is very stable with little to no change in temperature and 100% relative humidity year-round. This stability in cave air is juxtaposed with the monsoonal drip water pulse that increases drip rates over 40 times on average across all seven monitored drip sites. Compared to the amount-weighted precipitation average δ18Oprecip value, the cave drip water δ18ODW values are evaporatively 18O enriched during infiltration through the soil/epikarst. As the monsoonal precipitation pulse fades and drip rates decrease, changes in the drip water chemistry (trace elements Mg/Ca and Sr/Ca, dissolved inorganic carbon δ13CDW, and δ18ODW values) indicate that prior calcite precipitation (PCP) drives the trace element and δ13CDW variability. The δ13Cc and δ18Oc values of farmed slide calcite are highly variable. However, high drip rate and lower cave air pCO2 during the monsoon combine to increase calcite precipitation rates. This causes speleothem records from these caves to be weighted toward annual monsoon conditions. Calcite isotope values from actively growing stalagmite tops support this finding. These results suggest that speleothems from these caves are sensitive to changes in monsoon precipitation amount, because it determines the duration of the monsoon drip water pulse, and therein, the extent of dry season PCP. Further, these data indicate that heterogeneity in the dolomitic limestone massif causes offsets between the carbon isotopes and trace metal concentrations between the caves, highlighting the need to normalize these datasets when chronology-stacking these proxies.

Unified 200 kyr paleohydrologic history of the Southern Great Basin: Death Valley, Searles Valley, Owens Valley and the Devils Hole cave

We present a hydroclimate synthesis of the southern Great Basin over the last two glacial-interglacial cycles focused on paleolakes in Death Valley (core DV93-1), Searles Valley (core SLAPP-SRLS17), Owens Valley (core OL92), and the Devils Hole cave. There is close agreement between the occurrence of lakes in Death Valley and the height of the water table in the Devils Hole (50 km east of Death Valley) during the last 200 kyr. Death Valley and Devils Hole have adjacent, partly overlapping, drainage areas and most likely did over the last 200 kyr. When the water table in the Devils Hole was above the threshold level of ∼5 m higher than the modern, permanent lakes existed in Death Valley. At water table elevations less than 5 m above the modern, ephemeral lakes, saline pans, and mudflats occurred in Death Valley. The close temporal agreement between inferred paleoenvironments from the sediments in the Death Valley core and the paleowater table elevation in Devils Hole suggests a common forcing and provides insight into climate variability in the southwestern United States over the last 200 kyr. Owens Valley and Searles Valley, which derived inflow waters from the Sierra Nevada via the Owens River, contain paleohydrologic records which match those from Death Valley and the Devils Hole in terms of timing and direction of water availability over the last 200 kyr, indicating a similar paleohydrologic history for the entire southern Great Basin region. Near the end of Marine Oxygen Isotope Stage 6 (MIS 6), 140 ka - 130 ka, Lake Manly in Death Valley became shallow and hypersaline, and ultimately dried up at 127.1 ka ±4.3 ka. The transition from glacial to interglacial vegetation, which involved the loss of Juniperus pollen and an increase in Quercus (oak) pollen, occurred in Death Valley core DV93-1 at 131.3 ka ±4.0 ka. Following the glacial to interglacial pollen shift, a large alkaline lake formed in Death Valley. Similar conditions (freshwater, high productivity, and a mixed, deeply oxygenated water column indicated by biomarkers) existed in Searles Lake between 135.3 +2.7/-2.9 ka and 130.1+2.7/-2.6 ka, also following the juniper-oak pollen transition. Sr isotopes in calcite and sulfate minerals (gypsum, glauberite, thenardite), and the rare occurrence of the sodium carbonate mineral northupite with a low 87Sr/86Sr ratio in core DV93-1, together with organic geochemical proxies from Searles core SLAPP-SRLS17, all suggest that at this time, late MIS 6 Lake Manly in Death Valley received alkaline water via spillover from Searles Valley into Death Valley through Panamint Valley. The hydrologic connection between Searles Valley, Panamint Valley, and Death Valley at Termination II (130 ka) is documented here for this system of pluvial lakes for the first time. The Devils Hole water table decreased to +6.5 m at 140.8 ka ±3.2 ka, rose briefly to +8 m at 137.6 ka ±0.5 ka, and then dropped 8 m by 120.36 ka ±0.45 ka, when it reached an elevation similar to the modern. The pluvial lakes in Death Valley and Searles Valley may have coincided with the rise of the Devils Hole water table at ∼137.6 ka ±0.5 ka years ago, although the age models for core DV93-1 and core SLAPP-SLRS17 during the end of MIS 6 carry large uncertainties.

Clumped and in situ carbon and oxygen isotopes of calcite as tracers for oxidation of hydrocarbons in deep siliciclastic strata

The oxidation of hydrocarbons, including methane, is part of interrelated hydrogeochemical reactions affecting the carbon budget in Earth’s crust. To investigate these processes in deep siliciclastic strata, we analyzed core samples from Lower Triassic red beds in the Mahu Sag (Junggar Basin, northwest China) by coupling petrological observations with high-resolution in situ secondary ion mass spectroscopy stable carbon and oxygen isotope analyses and clumped isotopes (Δ47) of authigenic calcite. The strata contain variable oil and gas content as well as abundant high-valence Fe and/or Mn oxides. Three sequential generations of cement occur, which are characterized as (1) non-luminescent, early diagenetic calcite (MnO <0.3%, δ13CVPDB [Vienna Peedee belemnite] = −5.6‰ to −4.1‰); (2) bright-orange luminescent late-stage I calcite (0.75%−5.23% MnO, δ13C = −51.4‰ to −25.8‰); and (3) dull-orange late-stage II calcite (4.10%−12.93% MnO, δ13C = −91.4‰ to −30.9‰). Clumped isotopic thermometry reveals that the calcite precipitation temperature increases successively from <40 °C, to 81−107 °C, to finally 107−132 °C, corresponding to three precipitation time periods: before the Late Triassic, from the Early Jurassic to the Early Cretaceous, and from the Early Cretaceous to the present, respectively. δ13C values of −55.7‰ to −25.8‰ indicate that late-stage I calcite is the final product of oxidation of both methane and C2+ hydrocarbons, whereas δ13C values as low as −91‰ indicate that late-stage II calcite is mainly derived from the thermochemical oxidation of methane (δ13C = −46.8‰ to −39.3‰) induced by high-valence Mn and/or Fe oxides. For late-stage I calcite, hydrocarbon oxidation was most likely promoted by high temperatures, although microbial oxidation cannot be completely ruled out. The higher precipitation temperature of late-stage II calcite demonstrates that the oxidation of methane requires higher activation energies than oxidation of C2+ hydrocarbons. We provide reliable geochemical evidence for thermally induced sequential oxidation of hydrocarbons within deep siliciclastic strata.

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

The history of calcite diagenesis and origin of exceptionally negative oxygen isotope values in chalks of the Niobrara Formation, Denver Basin, USA

AbstractThe Niobrara Formation of north‐east Colorado, USA, has anomalously negative δ18O values compared to all other Cretaceous chalks. These unique δ18O values have been attributed to elevated heat flow and/or freshening of the Cretaceous Western Interior Seaway. This work utilises clumped isotopes of calcite (Δ47), peak burial temperatures estimated from pyrolysis data, and strontium and neodymium isotopes of carbonate to re‐evaluate the origin of the calcite's18O‐depletion. Peak temperatures indicate lateral variability in geothermal gradients ofca20°C/km at the tens of kilometre scale, and corroborate prior studies proposing locally elevated palaeotemperatures. Greater insight is provided by numerical models of calcite recrystallisation and oxygen isotope evolution that are constrained by measured Δ47‐derived temperatures, calcite δ18O values and inferences from the87Sr/86Sr and εNd values. The models indicate that (1) sea water in the seaway had normal marine δ18O values of −1 (VSMOW) except on the eastern margin of the basin where some freshwater dilution yielded −2 to −3‰ (VSMOW) water, and (2) the main driver of the anonymously negative calcite δ18O values was a semi‐open hydrologic system that provided a few percent by pore volume of meteoric groundwater derived from post‐Laramide recharge into the basin. Minor contributions were a Laramide‐aged heat pulse related to the underlying Colorado Mineral Belt, the thermal insulating effects of now eroded coals, and a small flux of compaction‐driven Cretaceous sea water evolved by smectite dehydration. However, those three factors alone were insufficient drivers of the calcites'18O depletion. High burial temperatures are interpreted to have caused clumped isotope reordering in at least one well, but those temperatures cannot yield the observed calcite δ18O values. The study illustrates the unique attributes of the Niobrara's diagenetic system that results in its anomalous δ18O values, and reaffirms the value of clumped isotopes in unravelling the diagenetic history of chalk systems.

Stalagmite evidence of Last Glacial Maximum to early Holocene climate variability in southwestern Iran

ABSTRACTGlacial 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.

Oxygen isotopes of calcite precipitated at high ionic strength: CaCO3-DIC fractionation and carbonic anhydrase inhibition

Background electrolytes affect calcite precipitation and dissolution rates and hence have the potential to impact kinetic isotope fractionation between calcite and the dissolved inorganic carbon (DIC) species. We grew inorganic calcite from NaCl-CaCl2 solutions (T = 25 °C, pH = 8.3, and crystal growth rate = 10−6.3 ± 0.3 mol m−2 s−1) to test for potential ionic strength effects on the oxygen isotope fractionation between calcite and an isotopically equilibrated inorganic carbon pool (αc/EIC). Calcite was grown in the presence of the enzyme carbonic anhydrase from bovine erythrocytes (bCA) to promote isotopic equilibration of the DIC pool.No evidence of an ionic strength effect on αc/EIC was found for NaCl concentrations up to 0.35 M (1000lnαc/w = 28.0 ± 0.1; n = 7). For experiments conducted with [NaCl] > 0.35 M, the DIC pool could not be maintained in isotopic equilibrium with water due to the inhibitory effect of NaCl on bCA. The use of other types of CA may be required to maintain isotopic equilibration of DIC in solution with ionic strength close to or above that of seawater.The oxygen isotope results were modeled successfully with an isotopic box model for a CO2-fed solution that tracks the isotopic composition of each DIC species and CaCO3. The experimental and modeling results suggest that the efficacy of bCA decreases exponentially with increasing [NaCl]. We quantify the salt effect on the quantity kcat/KM, which relates the catalyzed rate constant for CO2 hydration to the concentration of bCA. The salt effect can be implemented in models of biomineralization with potential to extend our knowledge of oxygen isotope vital effects in marine organisms.

Fluid source of seismogenic accretionary body based on calcite isotope ratio, Shimanto complex, Shikoku, southwest Japan

Fluid source of seismogenic accretionary body based on calcite isotope ratio, Shimanto complex, Shikoku, southwest Japan

Differentiating early from later diagenesis in a Cretaceous sandstone and petroleum reservoir of the Cedar Mountain Formation, Utah

ABSTRACT Previously published anomalous whole-rock stable isotopic values from the Poison Strip Sandstone Member of the Cretaceous Cedar Mountain Formation (CMF) of eastern Utah are of uncertain origins. This study investigated the diagenetic history and the processes responsible for these anomalous data. Accordingly, we integrated photomicroscopic techniques including polarized light microscopy, epifluorescence and cathodoluminescence (CL) imaging, micromilling of stable isotope samples, and fluid-inclusion heating and freezing measurements to this end. The key observations involved the microscopic mapping of calcite cement stratigraphy using CL imaging to permit the analysis of stable isotopes of calcite cements that crystallized during early and late diagenesis. The mapping of calcite cement zones of sufficient submillimeter size to mill out and isolate microgram-sized stable isotope samples enabled this discrimination. Early diagenetic calcite cements have the most positive δ18O values (-10 to -8.5‰ Vienna Pee Dee Belemnite [VPDB]) of all components. The pattern of δ13C and δ18O variation in this early diagenetic cement indicates affinities with early meteoric diagenesis previously documented in published literature on the CFM. The late diagenetic calcite cements yield the most negative δ18O values (-18 to -16‰ VPDB). We interpret the late diagenetic cements to be responsible for the anomalously low whole-rock δ18O values previously reported from the Poison Strip Sandstone Member. Our discoveries of bitumen in late-stage pore fillings and liquid petroleum in the fluid inclusions of late diagenetic calcite cements of the Poison Strip Sandstone Member explain the lower whole-rock organic matter δ13C values and anomalous Δ13C values reported from the unit. Comparatively lower carbonate δ18O and organic δ13C values originally derived from whole-rock analyses of samples from the Poison Strip Sandstone Member resulted from high-temperature basinal diagenesis (hydrothermal circulation and/or petroleum migration), rather than the alternative interpretation of early diagenesis related to a Cretaceous paleoclimatic perturbation. Our results are illustrative of methods to resolve the long-standing geologic problem of discriminating and characterizing products of early vs. late diagenesis in terrigenous clastic sedimentary strata.

Ore-fluid geochemistry of the Hehuashan Pb–Zn deposit in the Tongling ore district, Anhui province, China: Evidence from REE and C–H–O isotopes of calcite

Calcite is the main gangue mineral of the Hehuashan lead–zinc deposit, which is located in the Tongling ore district, Anhui Province, East China. The ore bodies of the Hehuashan deposit are hosted by dissolution breccia of the Lower Triassic carbonate sediments. We report petrography, rare earth elements (REE), and C–H–O isotope data of four generations of calcite recognized in the Hehuashan deposit, namely the pre-ore stage calcite (Cal-1), early ore-forming stage calcite (Cal-2), late ore-forming stage calcite (Cal-3) and post-ore stage calcite (Cal-4). In addition, we also report C–H–O isotopes data of dolostone from the Lower Triassic carbonate sediments. All four calcite generations show a low ∑REE content (13–50 ppm on average), indicating that the related ore-forming fluids may not have been derived a magmatic fluid but rather be derived from the carbonate sediments or basinal brines. Low LREE/HREE ratio (1.1–6.1 on average) of all four calcite generations implies that no significant REE fractionation happened during the mineralizing processes. The wide distribution of Y/Ho ratios (17–70) of calcite indicates a result of fluids mixing. The δ13C values of calcite (1.4‰ to 4.2‰) are comparable to marine carbonates, but the δ18O values are lower, indicating possibly a result of carbonates dissolution. Calculated δ18O of the fluid in equilibrium with calcite vary from –3.1‰ to –0.1‰, combining the δDV-SMOW (–100‰ to –81‰), implying a fluid mixing of a brine fluid and meteoric water or diagenetic pore water for the mineralization of the Hehuashan deposit.

Rare earth elements and carbon-oxygen isotopes of calcite from the Tongjiachong Cu deposit, South China: Implications for fluid source and mineral precipitation

Calcite is a major gangue mineral in many types of hydrothermal deposits, and its chemical and carbon-oxygen isotopic signatures can shed light on the metallogenic evolution. The Tongjiachong Cu deposit, located in the northern margin of the Yangtze Block in South China, is hosted by dolostone of the Ediacaran Doushantuo Formation. Empirical geothermometric calculation indicates that the pre-ore chlorite was formed at 265–305 °C. Copper mineralization occurs mainly as veinlets in a calcite-chalcopyrite-bornite ± ankerite assemblage. Exsolution lamellae of chalcopyrite from bornite indicate that both minerals were formed coevally at 200–250 °C. Mineral chemical analysis on the syn-ore hydrothermal calcite from Tongjiachong suggests that all the calcite samples are enriched in rare earth elements and yttrium (REYs) (ΣREY = 53.7–119.9 ppm). They have similar Y/Ho (38.3–42.3) and varying La/Ho (21.8–86.7), and display consistent convex PAAS-normalized REY patterns. The distinct positive Eu anomalies (2.38–3.45) and lack of Yb anomalies (0.92–1.05) suggest initial fluid temperatures of 250 to 420 °C and calcites deposition temperatures of <250 °C. The lack of negative Ce anomalies reflects suboxic to anoxic conditions of the ore-forming fluids.Dolomite samples from the dolostone ore host show a marine carbonate C-O isotopic affinity (13CPDB = −4.0 to −2.7‰; δ18OSMOW = +19.8 to +20.2‰). Comparatively, the hydrothermal calcite contains lower 13CPDB (−7.4 to −6.1‰) and δ18OSMOW (+14.1 to +14.8‰), and display a positive 13CPDB vs. δ18OSMOW correlation. Simulated calculations of water-rock (W/R) interactions and ore geological constraints suggest that the initial fluids were likely originated from organic-rich formation water. We proposed that W/R reactions may have been the main drive for calcite precipitation at Tongjiachong, whilst decreasing temperature and W/R reactions may have led to the chalcopyrite precipitation.

Trace elements and C-O isotopes of calcite from Carlin-type gold deposits in the Youjiang Basin, SW China: Constraints on ore-forming fluid compositions and sources

The Carlin-type gold deposits in the Youjiang Basin, SW China can be further classified into three sub-types; strata-bound, fault-controlled, and diabase-associated. The compositions and sources of the ore-forming fluids for each deposit type are evaluated using the texture of calcite by CL (Cathode luminescence), its chemistry by EMPA (Electron probe microanalysis) and LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry), and its C-O isotopic compositions by SIMS (Secondary ion mass spectroscopy). The studied deposits are the stratabound Zimudang deposit, the fault-controlled Lannigou deposit, and the diabase-associated Badu deposit. Calcite in the Zimudang and Lannigou deposits formed at three different stages: pre-ore stage pore-filling and massive calcite (Cal 1), late-ore stage vein calcite (Cal 2) associated with realgar and pyrite, and post-ore stage vein calcite (Cal 3). Calcite in the Badu deposit formed in two stages: ore stage vein and replacement calcite (Cal 2) associated with pyrite and post-ore stage calcites (Cal 3). Calcite with brighter red CL color has higher Mn and lower Fe content than calcite with darker red CL color. Furthermore, the higher the total REE content, the brighter the CL color. The host rocks are characterized by light REE (Rare earth element) enrichments. In contrast, the ore stage calcite shows middle REE enrichments. The ore stage calcite has higher concentrations of Fe, Mn, Mg, Si and Sr, and lower concentrations of Cu, Sb and Zn than both the pre- and post-ore calcite. The ranges of carbon (PDB) and oxygen (SMOW) isotope compositions of calcite are from −11.29 to 6.89‰ and from 16.49 to 22.60‰ for the Zimudang deposit, from −13.31 to 2.80‰ and from 9.12 to 29.71 for the Lanningou deposit, and from −11.94 to 0.49‰ and from 10.51 to 18.97‰ for the Badu deposit. Generally, the ore stage calcite has a wider range of δ13C and δ18O values than the other stage calcite. The isotope data indicate that a deep crustal fluid was involved in the formation of all of these three deposits. Meteoric water containing abundant organic matter was also involved in the formation of the Badu deposit as well as the Zimudang deposit, whereas a basin brine was also involved in the formation of the Lanningou deposit.

Insight into Heterogeneous Calcite Cementation of Turbidite Channel-Fills from UAV Photogrammetry

Diagenesis is a key controlling factor on sandstone porosity and permeability. Understanding type, paragenetic sequence and spatial patterns of cements is thus important for assessing sandstone hydrocarbon reservoir properties. In this study Unmanned Aerial Vehicle (UAV) photogrammetry is used to evaluate the shape and spatial distribution of calcite concretions developed within the sand-prone fill of a turbidite channel. The studied channel-fill is entrenched into hemipelagic marlstones and include a lower conglomeratic sandstone loaded with marlstone rip-ups and an upper fill featuring a range of turbidite bed types, which, up-section and off the channel axis, are progressively finer grained and less amalgamated. Concretion shape analysis highlighted a continuum of equant to oblate shapes with flat-lying major axes and a cumulative volume fraction of ca. 22%. Equant to sub-equant concretions are ubiquitous and occur at different heights within beds, often developing around marlstone rip-ups. Conversely, elongated concretions are either strata-bound concretions or completely cemented beds which become volumetrically dominant up section and off the channel axis. The interparticle pore-space of concretions represents on average ca. 22% and is tightly filled by poikilotopic and blocky calcite cement precipitated near to maximum burial depth, whereas host sandstones lack calcite cements and show smectite clay cement and an average preserved porosity of ca. 15%. The oxygen and carbon isotopes of calcite cements point to the marlstone as the main source of carbonate ions, suggesting concretions developed during burial by either diffusion from rip-ups and mud caps or recrystallization of, matrix micrite. Results suggest that the process by which the carbonate-rich component was eroded from the substrate and trapped within the channel-fill is a key control on spatial distribution of calcite concretions, likely to reflect on spatial variability of reservoir properties.

Zoning of Faults and Secondary Mineralization of Host Rocks of Kimberlites of the Maiskoe Diamond Deposit, Nakyn Field, Yakutia

Study of faults and secondary mineralization of host rocks of diamond-bearing kimberlites yields important data for local prediction of kimberlite bodies. Of special methodological interest are exploration data on deposits where the study of host rocks is based on a dense observation network. Factual material for this paper was collected from cores of all inclined exploration boreholes of the Maiskoe diamond deposit found in the Nakyn field in Yakutia in 2006. The paper shows a nonuniform distribution of tectonic deformations, stringer mineralization, O and C isotopes of calcite, and CO2 content of Lower Paleozoic host carbonate rocks of kimberlites. Our data agree with different diamond potentials of two areas of the Maiskoe kimberlite body, which can be used to search for and explore deposits.

The source and evolution of ore fluids in the Heiniuwa gold deposit, Baoshan block, Sanjiang region: Constraints from sulfide trace element, fluid inclusion and stable isotope studies

The Heiniuwa gold deposit is located in the northwestern segment of the Longyang Au–Fe–Pb–Zn polymetallic ore cluster in the northern Baoshan block, Sanjiang region, SW China. This ore cluster is characterized by skarn Fe–Pb–Zn mineralization (∼120 Ma) in the central part and Au mineralization in the distal part. The genesis of the Heiniuwa deposit and its relationship with the skarn deposits remain unclear. All orebodies in Heiniuwa are hosted in the Upper Cambrian calcareous slate and siltstone of the Hetaoping Formation, and are controlled by the NS-striking faults. Three main paragenetic stages of mineralization have been recognized based on petrographic observation including, from early to late, a pyrite – arsenopyrite – quartz stage (stage I), a pyrite – pyrrhotite – sphalerite – galena – chalcopyrite – quartz – calcite stage (stage II), and a quartz – calcite – chlorite stage (stage III). Three types of fluid inclusions were identified in the quartz and calcite from the stage I to III in Heiniuwa, including liquid-rich (L-type), vapor-rich (V-type) and solid-bearing (S-type) inclusions. The S-type inclusions only occur in stage I quartz. The fluid inclusions from stage I homogenized at 185–326 °C (concentrating at 220–250 °C), with eutectic temperatures of −48.5 °C to −36.7 °C, final ice-melting temperatures of −11.34 °C to −0.8 °C and salinities ranging from 1.4 to 17.2 wt% NaCl equiv. The inclusions from stage II homogenized at 155–281 °C (concentrating at 190–230 °C), with eutectic temperatures of −51.6 °C to −37.5 °C, final ice-melting temperatures of −10.6 °C to −0.5 °C and corresponding salinities ranging from 0.9 to 14.6 wt% NaCl equiv. The inclusions from stage III homogenized at 116–202 °C (concentrating at 150–170 °C), with eutectic temperature of −45.5 °C to −37.5 °C, final ice-melting temperatures of −4.3 °C to −0.6 °C and salinities ranging from 1.3 to 7.2 wt% NaCl equiv. The microthermometry reveals that the ore-forming fluid of Heiniuwa gold deposit is a typical H2O–NaCl–CaCl2 fluid system. The carbon and oxygen isotopes of calcite show that δ13CPDB and δ18OSMOW values respectively range from −13.4‰ to −6.8‰ and 9.1‰ to 9.6‰ in stage II, and from −8.1‰ to −1.5‰ and 6.4‰ to 8.2‰ in stage III. The bulk marble and calcareous slate samples have δ13CPDB and δ18OSMOW values from −3.0‰ to −0.7‰ and 7.8‰ to 11.9‰, respectively. This suggests that the carbon in the ore-forming fluid was probably from a magmatic source. The δ18Ofluid values of ore-forming fluid vary from 1.6‰ to 2.5‰ in stage I, from −6.2‰ to 0.6‰ in stage II and from −10.8‰ to −2.5‰ in stage III. This indicates that the fluid in stage I is dominantly magmatic, whereas the fluid in stage III is close to meteoric water. The decrease of Na/Ca ratios of ore-forming fluid from stage I to stage III suggests that the interaction with carbonate wallrock is significant during fluid evolution. The sulfide δ34S values range from −5.7‰ to +4.6‰ (mean = +0.3‰, n = 19), agreeing with the explanation based on C–O isotopes and fluid inclusions that the ore-forming fluids are mainly magmatic in origin. In addition, LA-ICP-MS analysis of sulfides also supports this opinion. The stage I pyrite has Cu/Ni ratios greater than 1, and a high concentration of gold; in contrast, the stage II pyrrhotite samples display a very low concentration of gold. This suggests that gold mineralization mainly occurred in stage I. The mixing between magmatic hydrothermal fluid and meteoric water is considered to be a key factor controlling the gold deposition.

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.

The modern and Last Glacial Maximum hydrological cycles of the Eastern Mediterranean and the Levant from a water isotope perspective

The isotopic composition of precipitation (δP) is one of the most widely used and informative terrestrial paleoclimate proxies. δP integrates a series of hydrological processes; therefore, any interpretation of paleohydrology using δP requires a thorough understanding and quantification of the full hydrological cycle. In this paper, we use modern data to analytically model the full isotopic hydrological cycle of the Eastern Mediterranean and the Southern Levant, including oceanic evaporation, distillation during transport and precipitation over land. This model allows us to determine the important factors controlling this system. The model results underscore the significance of the isotopic distillation process driven by the land–sea temperature gradient as a significant factor controlling the long-term average isotopic composition of precipitation across Israel. Based on the understanding of the processes that govern the modern system, we model the isotopic composition of precipitation from the Last Glacial Maximum (LGM) using published data for speleothem oxygen isotopes in calcite, oxygen and hydrogen isotopes in fluid inclusions and clumped isotope values from Soreq Cave and the isotopic composition of East Mediterranean planktonic foraminifera G. ruber. The data and model results indicate two plausible scenarios for the LGM that entail changes in the magnitude of distillation over Israel, in normalized humidity over the Mediterranean and possible shifts of the moisture trajectories over the Mediterranean. The results presented in the paper illustrate the importance of understanding the full local hydrological cycle when reconstructing and interpreting the isotopic composition of precipitation.

Ore-fluid geochemistry and metallogeny of the Dunde iron–zinc deposit in western Tianshan, Xinjiang, China: Evidence from fluid inclusions, REE and C–O–Sr isotopes of calcite

The Dunde iron–zinc deposit is a typical submarine volcanogenic iron oxide deposit in the eastern Awulale Metallogenic Belt of the western Tianshan. We report new petrography, rare earth elements (REE), and fluid inclusion microthermometry and C–O–Sr isotopes of the calcite from the skarn and the magnetite ores from the Dunde deposit. Calcite from both the skarn and magnetite ores displays high LREE/HREE (44–172), implying significant REE fractionation. We infer that the complexation of Cl (±F) during the fluid circulation and mineralogical control of calcite at the depositional sites were important for the LREE enrichment in the Dunde calcite. The restricted Y/Ho (26.7–32.1) suggests that calcite in the skarn and magnetite ores was co-genetic and the superchondritic Y/Ho may have resulted from the preferential incorporation of Y over Ho in calcite. Positive Eu anomaly (1.23–1.63) of the skarn calcite may have been inherited from the parental fluids, while the negative or slightly positive anomaly (0.65–1.04) of the magnetite ore calcite may have been resulted from the high Sr2+ content that suppressed Eu2+ in calcite.Fluid inclusion microthermometric results exhibit a wide range of homogenization temperatures (106°C–364°C) and salinities (0.2wt.%–41.5wt.% NaCl equiv.). Three kinds of ore-forming fluids can be distinguished, i.e., high-salinity (>35wt.% NaCl equiv.), medium-salinity (10wt.%–35wt.% NaCl equiv.) and low-salinity (<10wt.% NaCl equiv.) fluids. The high-salinity fluid was likely to be magma-derived and occurred in both the skarn- and magnetite ore calcite. The low-salinity fluid, possibly seawater-derived, was found only in the skarn calcite. The medium-salinity fluid, mainly of CaCl2–H2O aqueous- and brine-featured fluids, may have been the product of the fluid–rock interactions as the magmatic fluids and seawater circulated through the strata. The Dunde calcite has δ13C comparable to marine carbonates, but δ18O substantially lower, suggesting possibly a result of limestone dissolution. Calculated δ18O of the fluids in equilibrium with calcite vary from −0.78‰ to 5.46‰ (−0.78‰–1.85‰ and 2.15‰–5.46‰ for skarn calcite and magnetite ore calcite, respectively), implying magmatic fluids and seawater mixing. The Dunde calcite 87Sr/86Sr (0.7071 to 0.7078) correlate positively with 1/Sr, implying that two sources, i.e., basaltic/andesitic volcanic wall rocks (87Sr/86Sr: 0.7056–0.7066) and limestones/seawater (87Sr/86Sr: 0.7075–0.7089), may have been involved in the mineralization. Mass-balance calculation between fresh basaltic tuff and its neighboring skarn showed that extra Ca, Mg and Fe were added to the basaltic tuff during the hydrothermal alteration. The limestone dissolution during the fluid–rock interactions may have added Ca to the ore-forming fluids, while Fe and Mg may have been introduced from the deep-seated magmatic system via the heated Cl-rich fluid circulation.

Tracing formation and durability of calcite in a Punic–Roman cistern mortar (Pantelleria Island, Italy)

Ancient hydraulic lime mortar preserves chemical and isotopic signatures that provide important information about historical processing and its durability. The distribution and isotopic composition of calcite in a mortar of a well-preserved Punic–Roman cistern at Pantelleria Island (Italy) was used to trace the formation conditions, durability, and individual processing periods of the cistern mortar. The analyses of stable carbon and oxygen isotopes of calcite revealed four individual horizons, D, E, B-1 and B-2, of mortar from the top to the bottom of the cistern floor. Volcanic and ceramic aggregates were used for the production of the mortar of horizons E/D and B-1/B-2, respectively. All horizons comprise hydraulic lime mortar characterized by a mean cementation index of 1.5 ± 1, and a constant binder to aggregate ratio of 0.31 ± 0.01. This suggests standardized and highly effective processing of the cistern.The high durability of calcite formed during carbonation of slaked lime within the matrix of the ancient mortar, and thus the excellent resistance of the hydraulic lime mortar against water, was documented by (i) a distinct positive correlation of δ18Ocalcite and δ13Ccalcite; typical for carbonation through a mortar horizon, (ii) a characteristic evolution of δ18Ocalcite and δ13Ccalcite through each of the four mortar horizons; lighter follow heavier isotopic values from upper to lower part of the cistern floor, and (iii) δ18Ocalcite varying from −10 to −5 ‰ Vienna Pee Dee belemnite (VPDB). The range of δ18Ocalcite values rule out recrystallization and/or neoformation of calcite through chemical attack of water stored in cistern.The combined studies of the chemical composition of the binder and the isotopic composition of the calcite in an ancient mortar provide powerful tools for elucidating the ancient techniques and processing periods. This approach helps to evaluate the durability of primary calcite and demonstrates the importance of calcite as a proxy for chemical attack and quality of the ancient inorganic binder.

Fracture zone-scale variation of trace elements and stable isotopes in calcite in a crystalline rock setting

With an aim to increase the understanding about the isotopic and chemical heterogeneity of calcites in water-conducting fracture zones with different crystalline wall rock compositions at different depths, we present trace element chemistry, isotopic composition (δ18O, δ13C, 87Sr/86Sr) and biomarkers of euhedral low-temperature fracture-coating calcite. Paleohydrogeological fluctuations and wall rock influence on the hydrochemistry in the deep groundwater are explored. Samples are from several fracture zone sub-fractures (at −360 to −740m), retrieved during an extensive core drilling campaign in Sweden.Calcite generally showed fracture zone specific values of δ13C, δ18O and 87Sr/86Sr, which indicates precipitation from relatively homogeneous fluid (similar to the modern groundwater at the site) at the same event in each fracture zone. δ18O and δ13C in the different fracture zones were consistent with precipitation from waters of different salinity and decreasing organic input with depth, respectively. The latter is also supported by biomarkers showing clear indications of SRB-related organic compounds (e.g. iso- and anteiso-C17:0-branched fatty acids), except in the deepest zone. In contrast to the isotopes, variation in trace elements within the fracture zones was generally up to several orders of magnitude. Manganese and REE, as oppose to the other metals, were higher in the shallow fracture zones (112–1130 and 44–97ppm, respectively) than in the deeper (28–272 and 5–11ppm, respectively), in agreement with the groundwater composition. Although the rock types varied between and within the different fracture zones, this had insignificant influence on the trace element chemistry of the calcites. Co-variation was generally relatively large for many trace elements, with isometric logratio correlation generally better than 0.75, which indicates that their variation in the calcites is due to variation of Ca in the fracture water, but other local factors, especially uptake in co-precipitating minerals (clay minerals, barite, pyrite and zeolites), but also microbial activity and metal speciation may have influenced the metal incorporation into calcite. These detailed studies of fracture calcite are of importance for the understanding of variation in fluid chemistry and trace metal uptake in fracture zones, adding together with hydrochemical studies detailed information optimal for site characterisation.