Modern Meteoric Water Research Articles

Saline groundwater in the Münsterland Cretaceous Basin, Germany: clues to its origin and evolution

Saline groundwater (TDS up to 250,000mg/l) occurs in subsurface coal mines, wells, and artesian springs in the area of the halite-free Münsterland Cretaceous Basin (MCB) in Germany. The origin and evolution of the saline groundwater in the MCB are poorly understood. An investigation of the hydrochemistry and stable isotope (O, H, Sr) composition of a small sample set of present-day saline groundwater from the MCB has been carried out to improve our understanding of its origin and evolution within the framework of the complex geological history of the area.The data provide evidence for: (1) halite dissolution, (2) water–rock interaction of highly saline fluids with siliciclastic sediments, (3) mixing of highly saline fluids with less saline waters of marine isotopic composition, (4) fault-controlled upward movement of warm saline 87Sr-enriched groundwater from the Paleozoic bedrock into the overlying Late Cretaceous limestone aquifer, (5) water–rock interaction of ascending saline groundwater with the limestone aquifer, and (6) dilution by meteoric water. For the investigated sample set, the subrecent processes of mixing of different saline groundwaters, water–rock interaction, and dilution by modern meteoric water are volumetrically predominant, so that inferences about the early groundwater-forming processes have to rely mainly on our present understanding of the geological history of the area.The results of this study have a bearing on questions related to the timing and origin of Pb–Zn and strontianite mineralizations within and in the periphery of the MCB, and are of direct interest to the small, but vibrant, salt-water spa industry in the area.

Origin and migration of brines from Paleozoic strata in Central Tarim, China: constraints from 87Sr/ 86Sr, δD, δ 18O and water chemistry

Chemistry of major and minor elements, 87Sr/ 86Sr, δD, and δ 18O of oilfield waters, and 87Sr/ 86Sr of whole rock were measured from Paleozoic strata in the Central Tarim basin, NW China. The aim is to elucidate the origin and migration of formation water and its relation to petroleum migration. High salinity oilfield waters in Carboniferous, Silurian and Ordovician reservoirs have maintained the same Na/Cl ratio as seawater, indicative of subaerially evaporated seawater. Two possible sources of evaporitic water are Carboniferous (C II) and Cambrian, both of which contain evaporitic sediments. Geographic and stratigraphic trends in water chemistry suggest that most of the high salinity water is from the Cambrian. Strontium, H and O isotopes as well as ion chemistry indicate at least 3 end member waters in the basin. High-salinity Cambrian evaporitic water was expelled upward into Ordovician, Silurian and Carboniferous reservoirs along faults and fractures during compaction and burial. Meteoric water has likely invaded the section throughout its history as uplift created subaerial unconformities. Meteoric water certainly infiltrated Silurian and older strata during development of the C III unconformity and again in recent times. Modern meteoric water enters Carboniferous strata from the west and flows eastward, mixing with the high salinity Cambrian water and to a lesser degree with paleometeoric water. The third end member is highly radiogenic, shale-derived water which has migrated eastward from the Awati Depression to the west. Enrichment of Ca and Sr and depletion of K, Mg, and SO 4 relative to the seawater evaporation trajectory suggest waters were affected by albitization of feldspars, dolomitization, illitization of smectite, and SO 4 reduction. The mixing of meteoric water occurred subsequently to seawater evaporation, main water-rock interactions, and brine migration. The direction of brine migration is consistent with that of petroleum migration, suggesting water and petroleum have followed the same migration pathways.

Geochemical Evolution of Ground Water in the Great Plains (Dakota) Aquifer of Nebraska: Implications for the Management of a Regional Aquifer System

AbstractThe Great Plains (Dakota) aquifer system is one of the most extensive in North America extending from the Arctic Circle to New Mexico, and underlies approximately 94% of Nebraska. In Nebraska, we do not have the physical ground water monitoring data at the scale that is necessary to manage ground water flow systems. However, first‐order management strategies for this regional aquifer can be developed by understanding the geochemical evolution of the ground water. Using major‐ion water chemistry data from 203 wells in 19 counties in eastern Nebraska, reconnaissance δ180, δD, and δ87Sr data, and two geochemical models, PHREEQC and SNORM, we determine that modern meteoric water, NaCl brines from underlying formations, and cold glacial melt water are the primary sources for the water in the Dakota Aquifer. Based on these three water sources and the geochemical evolution of the various water types, the following first‐order management strategies are suggested. In areas where CaSO4 and Ca‐Na SO4 type water occur, Pleistocene‐age glacial meltwater is the source. This water supply is not easily renewable. It is recommended that detailed water resource evaluation be conducted before extensive development occurs. The source of Ca (± Mg) HCO3 type water is from recharge by local precipitation and should be managed to maintain them as a renewable resource. In mixed ground water type areas, the ground water chemistry reflects the interaction of two distinct water types, one of which is meteoric water and the other is either CaSO4 and Ca‐Na SO4‐type water or NaCl‐type water. If the relatively fresh ground water is extracted at a rate that changes the location of the interface between the endmembers, then monitoring changes in water chemistry in a well over time could be used as an early warning system for the onset of potential problems related to overpumping.

Recharge and Preservation of Laurentide Glacial Melt Water in the Canadian Shield

AbstractGround water inflows to drifts ranging from 700 to 1615 m below ground surface at the Con Mine, Yellowknife, Northwest Territories, Canada, were used to study deep hydrogeological flow regimes in Shield terrain. Salinity trends are due to mixing between low‐TDS ground water and deep Ca(Na)‐C1 brines (>290 g/L) likely derived from Devonian sea water. C1‐−δ18O relationships demonstrate that all inflows are a mixture of three distinct components: modern meteoric ground water (δ18O ∼−18.9 ± 0.1%o), brine (δ18O ∼−10%o), and an isotopically depleted water (δ18O ∼−28%o). The origin of this third endmember is attributed to glacial melt water injected into the subsurface during ablation of the Laurentide Ice Sheet at ca. 10 ka. A mechanism is proposed where high hydrostatic pressure in the ablation zone imposes strong downward gradients beneath the ice sheet margin. Numerical simulation with the SWIFT II finite‐difference code recreates the observed salinity gradients within a modeled 50‐year interval, corresponding with the rate of retreat of the ice sheet across the landscape at this time. The persistence of this melt water in the subsurface for some 10,000 years following retreat of the ice and decay of the steep hydraulic gradients highlights the importance of gradient, in addition to permeability, as a major control on ground water flow and transport in deep crystalline settings.

Brines in the Carboniferous Sydney Coalfield, Atlantic Canada

Formation waters within Upper Carboniferous sandstones in the sub-sea Prince and Phalen coal mines, Nova Scotia, originated as residual evaporative fluids, probably during the precipitation of Windsor Group (Lower Carboniferous) salts which underlie the coal measures. Salinity varies from 7800 to 176,000 mg/l, and the waters are Na–Ca–Cl brines enriched in Ca, Sr and Br and depleted in Na, K, Mg and SO 4 relative to the seawater evaporation curve. Br:Cl and Na:Cl ratios suggest that the brine composition corresponds to an evaporation ratio of as much as 30. The brines lie close to the meteoric line on H/O isotopic plots but with a compositional range of δ 18O from −4.18 to −6.99 and of δD from −42.4 to −23.5, distant from modern meteoric or ocean water. Mine water composition contrasts with that of nearby salt-spring brines, which are inferred to have originated through dissolution of Windsor Group evaporites by modern meteoric waters. However, a contribution to the mine waters from halite dissolution and from Br in organic matter cannot be ruled out. Present concentrations of several elements in the brines can be explained by water–rock interaction. The original Windsor brines probably moved up into the overlying coal-measure sandstones along faults, prior to the Late Triassic. The high salinity and irregular salinity distribution in the Phalen sandstones suggests that the brines have undergone only modest dilution and are virtually immobile. In contrast, Prince waters show a progressive increase in salinity with depth and are inferred to have mixed with surface waters. Basinal brines from which these modern formation fluids were derived may have been important agents in base-metal and Ba mineralisation from the mid-Carboniferous onwards, as saline fluid inclusions are common in Zn–Pb sulphide deposits in the region.

Groundwater mixing dynamics at a Canadian Shield mine

Temporal and spatial variations in geochemistry and isotopes in mine inflows at the Con Mine, Yellowknife, are studied to access the impact of underground openings on deep groundwater flow in the Canadian Shield. Periodic sampling of inflow at 20 sites from 700 to 1615 m depth showed that salinities range from 1.4 to 290 g/l, with tritium detected at all depths. Three mixing end-members are identified: (1) Ca(Na)–Cl Shield brine; (2) glacial meltwater recharged at the margin of the retreating Laurentide ice sheet at ∼10 ka; and (3) modern meteoric water. Mixing fractions, calculated for inflows on five mine levels, illustrate the infiltration of modern water along specific fault planes. Tritium data for the modern component are corrected for mixing with brine and glacial waters and interpreted with an exponential-piston flow model. Results indicate that the mean transit time from surface to 1300 m depth is about 23 years in the early period after drift construction in 1979, but decreases to about 17 years in the past decade. The persistence of glacial meltwater in the subsurface to the present time, and the rapid circulation of modern meteoric water since the start of mining activities underline the importance of gradient, in addition to permeability, as a control on deep groundwater flow in the Canadian Shield.

Catastrophic and dangerous inflows to salt mines in Poland as related to the origin of water determined by isotope methods

Tritium, 14C, δ13C, δ18O and δD measurements indicated as early as 1973 the existence of inflows of modern meteoric water to the Wapno salt mine in a Zechstein diapir. In spite of these early warnings, the continuation of improper exploitation led, in 1977, to sudden flooding of the mine followed by catastrophic land subsidence. The lesson learned from that catastrophe, as well as the results of isotope investigations performed in the Inowroclaw salt mine, led to the decision to flood the mine artificially in order to avoid a similar land subsidence. The Klodawa mine was not regarded to be in danger of flooding due to a thick clay cap. In fact, a large number of usually short-lasting water occurrences had the isotopic composition characteristic for evaporated ocean water. However, since 1956 an inflow has existed with δ18O and δD values close to that of pre-Quaternary saline waters and brines in the Mesozoic formations adjacent to the diapir. Two other inflows have recently occurred with the initial δ18O and δD values of modern waters. As a consequence, the mine is regarded to be in danger, and the exploitation of salt in the areas of inflows has been stopped. The Wieliczka mine, southern Poland, exploits Miocene salts overthrusted together with the Carpathian flysch from the south. The most dangerous and catastrophic inflows were caused by human errors. Isotope data show the water to be of glacial or Holocene age stored in Tertiary, slightly cemented rocks of low permeability, which neighbor the mine from the north. Owing to specific geology, the mine has survived for a long time, in spite of relatively large and long-lasting inflows. However, its existence is in permanent danger.

Terrestrial stable isotope records of Late Quaternary paleoclimates in the eastern Mediterranean region

Terrestrial stable isotope records ( 13C/ 12C, 18O/ 16O, and D/H ratios) of late Quaternary paleoclimates in the eastern Mediterranean region are reviewed. Significant paleoclimatic reconstructions come from a variety of isotopic studies. Paleogroundwaters, although they cannot be accurately dated, show oxygen and hydrogen isotopic compositions highly depleted in heavier isotopes compared to modern meteoric waters in arid regions of southern Israel, Sinai and northeastern Africa and attest to a major difference in climatic regime some time in the Pleistocene. Th-U dating of land snails showing a similar 18O depletion indicates ages of 100,000 yr and ≥300,000 yr for this climatic regime in the Negev Desert of southern Israel. Carbon isotope records of organic matter have not been studied extensively in the region, except for the record of Holocene land snails in the Negev. These document a southward shift in pure C 3 plant communities in the middle and early Holocene relative to their present distribution and indicate wetter conditions at those times. An oxygen isotope curve for the Holocene, reflecting changes in the isotopic composition of precipitation, has been established from analysis of carbonate materials—land snail shells and speleothems. The curve indicates a depletion of ca. 2‰ in 18O centered around 7000 cal yr bp, with modern levels being reached by 5000 cal yr bp. Carbon isotope analysis of soil carbonates in paleosols developed in loess in the Negev show the existence of dramatic north–south climatic gradients at the times of formation of the soils (ca. 13,000, 28,000, and ≥37,000 14C yr bp), as occur also today due to the waning influence of Mediterranean to the south. Some isotopic methods, widely used in other regions, have received little or no attention in the eastern Mediterranean region. These include oxygen and hydrogen isotopes in wood, phosphate oxygen and organic carbon in bones and teeth, and carbon in soil organic matter.

Ground-water, large-lake interactions in Saginaw Bay, Lake Huron: A geochemical and isotopic approach

Delineating the nature and extent of ground-water inputs is necessary to understand the hydrochemistry of large lakes. Characterizing the interaction between ground water and large lakes (e.g., the Great Lakes) is facilitated by the use of geochemical and isotopic data. In this study, pore waters were extracted from sediment cores collected from Saginaw Bay and the surrounding Saginaw lowland area; the geochemistry and stable isotope signature of these pore waters were used to identify sources for the water and solutes. Cores from Saginaw Bay and the Saginaw lowland area yielded strong vertical gradients in chloride concentrations, suggesting that a high-chloride source is present at depth. The spatial distribution of cores with elevated chloride concentrations corresponds to the regional distribution of chloride in ground water. Most of the Saginaw lowland area cores contain water with significantly lower δ 18 O values than modern meteoric water, suggesting that the water had been recharged during a much cooler climate. The δ 18 O values measured in pore waters (from Saginaw Bay cores) containing high chloride concentrations are similar to modern meteoric water; however, values lighter than modern meteoric water are encountered at depth. Chloride:bromide ratios, used to distinguish between different chloride sources, identify formation brine as the likely source for chloride. Transport models indicate that a combination of advection and diffusion is responsible for the observed Saginaw lowland area pore-water profiles. Pore-water profiles in Saginaw Bay sediments are produced primarily by diffusion and require significantly less time to evolve. An upward flux of solutes derived from formation brine could occur elsewhere within the Great Lakes region and significantly affect the geochemical cycling of chloride and other contaminants (e.g., trace metals).

Diagenetic history of Cambrian quartzarenites, Ras Dib–Zeit Bay area, Gulf of Suez, eastern desert, Egypt

In the northern corner of the El Zeit range, 370 m of sandstone overlie Precambrian granite and underlie Cretaceous marine strata. The sandstones include the marine Lower Cambrian(?) Araba Formation and the overlying, dominantly fluvial, Upper Cambrian(?) Naqus Formation. The framework compositions of both sandstones are almost entirely quartz, with trace amounts of muscovite, K-feldspar and heavy minerals. Up to 21% oversize pores, some filled with younger cements, attest to extensive dissolution loss of detrital grains. Because the final mineralogical maturation of these quartzarenites reflects diagenesis, they are diagenetic quartzarenites. During burial diagenesis, the introduction of up to 8% quartz cement (inhomogeneously distributed, mean = 3%) was followed by local, pore-occluding calcite cement, which halted compaction. Sandstones without calcite cement underwent additional mechanical and chemical compaction sufficient to develop sutured quartz grain contacts and reduce porosity (∼27%). These events were followed by: (1) extensive dissolution loss of carbonate cement, detrital feldspars, micas, and heavy minerals; (2) formation of local patches of kaolinite (mean = 3%); and (3) formation of extensive iron-oxide cements, including specular hematite. These features suggest extensive invasion by oxidizing meteoric water. The timing of this event can only be dated as post-Cambrian(?) and pre-Cenomanian. Some outcrop samples contain pore-occluding gypsum cement, or mixtures of gypsum and halite. Sr 87/Sr 86 ratios of four samples of gypsum cement have values (0.7079 and 0.7085) that indicate Miocene and slightly younger seawater. Evaporites were evidently leached by modern meteoric water from nearby outcrops of Miocene and younger marine evaporite-bearing strata, transported in surface and ground water to the topographically low terrain where the Cambrian sandstones crop out, and reprecipitated by evaporation. Initial primary porosity (45%) was reduced to ∼27% by compaction in sands with minor quartz cement; compaction ceased where calcite was precipitated. Subsequent dissolution of some calcite cement and unstable detrital grains generated considerable secondary porosity.

Fossil isotope records of seasonal climate and ecology: Straight from the horse's mouth

Isotope analysis of a bulk fossil tooth gives a “snapshot” impression of paleoclimatic conditions—a single point in time. However, hypsodont teeth grow over a period of a year or more, so that stable carbon and oxygen isotope variations along their length are a “tape recorder” of short-term seasonal variations from the distant past. We have used a new in situ micro-laser sampling method to determine submillimeter carbon and oxygen isotope variations in the enamel of individual fossil horse teeth to assess ancient annual meteoric water variations and feeding patterns. The δ18O values from a 6.8 Ma fossil horse tooth ( Astrohippus ansae ) from Texas vary cyclically along the 6 cm length of the tooth with a smoothed amplitude of >4‰, similar to the monthly averaged amplitude measured in modern meteoric waters from the region. The seasonal δ18O values are ∼3‰ to 4‰ higher than those calculated from modern meteoric water data, suggesting either a higher local meteoric water value in the Miocene of Texas, or that the animal received a high proportion of its dietary water from plants or highly evaporated water. A Holocene horse tooth from the shores of Glacial Lake Agassiz, North Dakota ( Equus sp.), also has isotopic variations with the same 35 mm periodicity, but a smoothed amplitude of only 2‰. This horse most likely had a buffered drinking supply. The calculated δ18O of the water in equilibrium with this tooth is the same as the modern measured annual average. The variations within a single tooth can be as large as those generally observed in entire stratigraphic sections of fossil teeth analyzed by bulk methods. The new method provides an important technique for evaluating fossil diagenesis; conventional bulk analyses of teeth fragments may not be representative of the whole tooth, thus explaining analytical scatter that has been previously attributed to diagenesis.

96/05127 Advances in solar energy, Volume XI

Friedrichsen, H., 1981. Geothermal systems in the Upper Rhine graben and northern Black Forest: a chemical and stable isotope study. In: J.H. Illies (Editor), Mechanism of Graben Formation. Tectonophysics, 73: 125–140.The reservoir temperatures of 22 hot spring waters from 9 localities in the Upper Rhine graben and the northern Black Forest have been determined using 4 different geothermometers (SiO2, Na-K, Na-K-Ca and 18O-sulphate). The 18O-sulphate thermometer and the SiO2 thermometer yield concordant temperatures in those thermal waters which have not been diluted by near-surface ground water components. Deviations of the SiO2 thermometer from the 18O-sulphate thermometer can be applied to estimate the near-surface water components in hot spring waters. The alkali content of these waters can not be used for geothermometry.The highest reservoir temperatures have been calculated for the hot springs of Baden-Baden (156°C). All other hot springs have substantially lower reservoir temperatures (115 to 65°C).The δ 18O and δ D values of the hot water component are comparable with the mean of the δ 18O and δ D values of modern meteoric waters from higher elevations of the Black Forest; the cold components have stable isotope ratios of local precipitation.

Environmental isotopic evidence for the origins of ground and surface water in a prairie discharge wetland

Ground, surface, and soil waters from a 500-ha wetland surrounding Lunby and Stewart Lakes, approximately 24 km northwest of Grand Forks, ND, have a large range of δD and δ18O values and appear to be mixtures of infiltrating modern meteoric water, evaporated modern meteoric water, and ancient water upwelling from the artesian regional aquifer system (“Dakota aquifer”), which subcrops some 30–50 m beneath the low-permeability glaciolacustrine silty clays underlying the wetland. The Dakota component is brackish and has δD≈−135%., δ18O≈−18%. Its isotopic composition indicates that it probably originated primarily as Pleistocene glacial ice. The stable isotope evidence suggests that shallow ground waters are richest in modern meteoric and evaporated meteoric water, but also that a substantial component (up to ≈65%) of Dakota water has reached the vicinity of the water table at some well sites. Upwelling and evaporation of this Dakota water probably account for the high salinity of soils and some shallow ground waters in the wetland. Although δD and δ18O values indicate that the proportion of modern meteoric water decreases with depth, a modern meteoric component has evidently penetrated to at least 13 m, the depth of the deepest borings on site. The deep penetration of modern water in spite of dominantly upward hydraulic gradients is also indicated by the presence of bomb tritium in one of the deeper monitoring wells. The wetland’s budget of surface and soil waters seems currently to be dominated by meteoric components; ground water upwelling from the Dakota aquifer is evidently subsidiary.

Petrogenesis of the Proterozoic Athabasca Basin, northern Saskatchewan, Canada, and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology

In the Athabasca Basin Proterozoic sandstones unconformably overlie Archean and Aphebian rocks. Multiple fluid events, involving isotopically- and chemically-distinct fluids which have migrated laterally for considerable distances and along fault zones, have produced a paragenetically-identifiable assemblage of clay, silicate and oxide minerals in the basin and basement rocks. Altered sandstones and the underlying metasedimentary rocks proximal to fault zones host high-grade UNiCo unconformity-type uranium ore deposits and contain an alteration assemblage of highly crystalline 2M/3T illite, 1M kaolinite, clinochlore and sudoite, hematite, dravite and euhedral quartz. In the sandstones, δ 18O-values of coeval quartz-hematite, quartz-illite, quartz-dravite, illite-hematite and kaolinite-hematite, fluid inclusion temperatures in diagenetic quartz, and δD-values of 1M kaolinite, 2M/3T illite, dravite and in fluid inclusions in the quartz indicate formation from a basinal fluid that had δD-values of ∼ −60±10‰ and which underwent salinity, temperature and 18O increases from 5 to 34 wt% NaCl, 120° to 240°C, and −5 to +3‰, respectively, as a result of increasing burial depth and sustained water-rock interactions with the basinal sediments over substantial time periods. 18O 16O and D/H ratios of sudoite and clinochlore in meta-sedimentary basement rocks within the alteration haloes indicate formation from a basement-derived fluid with δ 18O- and δD-values of +4±4 and +30±10‰, respectively, that was isotopically distinct from the basinal fluids. δ 18O- and δD-values of late kaolinites in reactivated fault zones indicate formation mainly from low-temperature (50-25 °C) fluids having δ 18O- and δD-values of −16 and −130‰, respectively, similar to relatively modern meteoric waters in the area. Some kaolinites have δ 18O- and δD-values which suggest they formed from meteoric waters at mid-latitudes and have experienced varying degrees of oxygen and hydrogen isotope exchange with relatively modern meteoric waters. In the re-activated faults, illite, sudoite and dravite have δD-values that vary by 100‰ without concurrent changes to their δ 18O-values, indicating preferential hydrogen isotope exchange with relatively modern meteoric waters at low temperatures and under conditions of high integrated water/rock ratios. RbSr isochron and model ages of 1477±57 and 952 Ma, respectively, for the crystalline 2M/3T illites indicate the timing of the high-temperature basinal fluid events associated with fluid mixing. RbSr and KAr ages on illites with the lowest δD-values are as young as 300 Ma and indicate late-stage resetting of their radiogenic isotope systematics as a result of substantial interactions with relatively modern meteoric waters. The evolution of Sr isotopic compositions of fluids in the basin and basement rocks, as reflected by the 87Sr 86Sr ratios of chlorite, illite and dravite, indicates that mixing of two isotopically-distinct fluids in the vicinity of faults was the process by which uranium was precipitated, similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals. ϵ Nd ratios in the high-temperature diagenetic and hydrothermal clay and silicate minerals and the cogenetic uranium ores suggest they all have formed from similar fluids which have interacted substantially with the basin sediments. In general, the isotopic, chemical, microthermometric and petrologic data indicate that the Athabasca Basin has had a protracted fluid history comparable to that documented for more modern sedimentary basins. The data clearly show that the major sandstone aquifers have been affected by widespread lateral flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross-formational fluid flow near active fault zones.

Stable isotope study of fluid inclusions in fluorite from Idaho: Implications for continental climates during the Eocene

Research Article| March 01, 1993 Stable isotope study of fluid inclusions in fluorite from Idaho: Implications for continental climates during the Eocene Robert R. Seal, II; Robert R. Seal, II 1U.S. Geological Survey, 954 National Center, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar Robert O. Rye Robert O. Rye 2U.S. Geological Survey, 963 Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information Robert R. Seal, II 1U.S. Geological Survey, 954 National Center, Reston, Virginia 22092 Robert O. Rye 2U.S. Geological Survey, 963 Denver Federal Center, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1993) 21 (3): 219–222. https://doi.org/10.1130/0091-7613(1993)021<0219:SISOFI>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Robert R. Seal, Robert O. Rye; Stable isotope study of fluid inclusions in fluorite from Idaho: Implications for continental climates during the Eocene. Geology 1993;; 21 (3): 219–222. doi: https://doi.org/10.1130/0091-7613(1993)021<0219:SISOFI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Isotopic studies of fluid inclusions from meteoric water-dominated epithermal ore deposits offer a unique opportunity to study paleoclimates because the fluids can provide direct samples of ancient waters. The oxygen and hydrogen isotope compositions of meteoric waters vary because of changes in climatic variables such as mean annual temperature of precipitation, relative humidity, origin and history of air masses, and the isotope composition of the oceans. Inclusion fluids found in fluorite (CaF2) are especially useful because their host is devoid of oxygen or hydrogen, thus precluding postentrapment isotope exchange. Fluorite-hosted fluid inclusions from the Eocene (51-50 Ma) epithermal deposits of the Bayhorse mining district, northeastern Idaho, have low salinities, most less than 0.6 equivalent wt% NaCl, and low to moderate homogenization temperatures (98 to 146 °C), indicating meteoric origins for the fluids. Oxygen and hydrogen isotope data on inclusion fluids are almost identical to those of modern meteoric waters in the area. The equivalence of the isotope composition of the Eocene inclusion fluids and modern meteoric waters indicates that the Eocene climatic conditions were similar to those today. This conclusion supports the climate modeling of Sloan and Barron, who suggested that the climates of continental interiors do not reflect the magnitude of warming preserved by the deep-ocean paleoclimate record during the Eocene. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Chemical and isotopic variations in an iron-rich lava flow from the Kirkpatrick Basalt, north Victoria Land, Antarctica: implications for low-temperature alteration

Chemical and isotopic (Sr, O, H) variations have been examined in an iron-rich lava flow of the Kirkpatrick Basalt from the Mesa Range in north Victoria Land, Antarctica. The flow is homogeneous with respect to the less mobile elements, whereas variations observed in K, Na, Si, Fe, and Rb result largely from alteration of glassy matrix material. Whole-rock Rb−Sr isotope data fall along a poorly-defined 103 Ma array attributed to secondary mobilization of Rb during the mid-Cretaceous. Alteration at that time is suggested by paleomagnetic data and would also account for discordant K−Ar dates. Whole-rock δ18O values vary from +5.8 to +8.2‰ and a plagioclase separate has a δ18O value of +5.6‰, reflecting the original composition of the magma. The range of δ18O values for the whole-rock samples results from low-temperature alteration occurring primarily in the Jurassic and/or mid-Cretaceous. Whole-rock δD values (-201 to -243‰) are markedly depleted, approaching equilibrium with modern meteoric water. In light of these data, variable Sr and O isotopic ratios in the underlying sequence of flows, previously interpreted in terms of an assimilation-fractionation model, may largely reflect post-magmatic alteration.

Contributions to the solute and isotopic groundwater geochemistry, Antelope Island, Great Salt Lake, Utah

The 110 km 2 Antelope Island is predominantly composed of Precambrian gneiss similar to rocks in the Wasatch Range 32 km to the east. Three types of island groundwater systems have been identified on the basis of aquifer composition and dissolved solute content. The systems include ground waters which discharge from either crystalline or sedimentary rocks. Sedimentary groundwater systems contain ground water which is either Na-Cl rich or poor. All island ground water has anomalously high Na +, Cl, or SO 2 4 concentrations when compared with ground waters that issue from similar bedrock in nearby areas. Island groundwater systems may be statistically distinguished from each other and from other ground water in the region. The solute chemistry of island ground water cannot be accounted for by the simple dissolution of aquifer minerals, and the water does not plot along fault controlled thermal water-precipitation or parent aquifer-precipitation Cl − SO 2− 4 mixing lines. Discharge elevations and Cl − SO 2− 4 also rule out mixing with residual salts from paleo Lake Bonneville or brines of the Great Salt Lake for most island ground water. Tritium values (> 40 tritium units (TU)) suggest that island groundwater systems are primarily recharged from modern meteoric water. Stable isotopic δ 2H and δ 18O data plot along an evaporation line which indicates that recharge water contains a component of evaporated Great Salt Lake water. Temporal variations in spring discharges, tritium concentrations, and discharge temperatures of less than 20°C indicate short flow paths and shallow circulation. Excess Cl − and SO 2− 4 concentrations are attributed to the deposition of aerosols of wind-blown dust from nearby evaporate deposits and sea spray. Sulfur isotope data suggest contributions to crystalline systems of reduced sulfur from nearby smelter or other industrial plumes.

Oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate

Because meteoric water δ 18 O values decrease with decreasing ambient temperature and increasing latitude, δ 18 O values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures. To test this, we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from Devonian to modern and in paleolatitude from 3.5° to 83°. Mean δ 18 O values for meteoric cements and speleothems both show the same negative correlation with paleolatitude. The δ 18 O vs. latitude trend for these carbonates is almost identical to that predicted for modern inland environments, but differs from the trend for coastal environments. This suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge. If it is assumed that the modern meteoric water δ 18 O vs. temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation, then coastal and inland paleotemperatures can be calculated from the δ 18 O values of meteoric calcite (δ 18 O mcl ) and seawater (δ 18 O sw ) by using the equations T coastal =13.3 ±32.6[-0.231- 0.0613(δ 18 O mcl + δ 18 O sw ) ½ and T inland =17.8 ±16.2[-0.572 - 0.1233(δ 18 O mcl + δ 18 O sw ) ½ , where T is temperature in °C. Calcite precipitated from coastal meteoric water at temperatures between 0 and 25 °C will exhibit a narrow range in δ 18 O(-6‰ to -4‰, where δ 18 O sw = 0‰). The δ 18 O of calcite precipitated from inland meteoric water will be sensitive to paleotemperature, ranging from -14‰ to -5‰ (where δ 18 O sw = 0‰) for temperatures of 0 to 25 °C.

Geochemical studies of the Tongyoung gold-silver deposits, Republic of Korea; evidence of meteoric water dominance in a Te-bearing epithermal system

Epithermal gold-silver vein mineralization of the Tongyoung mine was deposited in five stages (I to V) of quartz-rhodochrosite-calcite-sulfide veins (0.3-7.0 m thick) which fill fault planes in Cretaceous volcanic rocks of the Gyeongsang basin. K-Ar dating of alteration sericite (72.9 + or - 1.2 Ma) indicates a Late Cretaceous age for ore mineralization. Stages I and II are Au-Ag-bearing, whereas stages III, IV, and V are barren. Ore grades average 12 g/metric ton gold with a gold/silver ratio of 1:11. Stage II is composed of five rhythmically banded substages which show a progressive change in ore mineralogy with increasing paragenetic time: electrum (68 wt % Au) --> electrum (65 wt % Au) + argentitc --> electrum (50 wt % Au) + Ag tellurides --> Ag tellurides + native silver. The shift in mineralogy reflects decreases in temperature and fugacity of sulfur, with a concomitant increase in fugacity of tellurium.Fluid inclusion data indicate a history of progressive cooling and dilution of ore-forming fluids. During stages I and II, higher temperature and salinity fluids (260 degrees C, 6 equiv wt % NaCl) mixed with cooler, less saline waters, resulting in most ore deposition from fluids of intermediate temperature and composition (190 degrees -230 degrees C, 2.5-4.5 equiv wt % NaCl). Continued cooling and dilution (coupled with decreasing fugacity of sulfur) resulted in deposition of Ag-Te mineralization and ultimately in barren stage III and IV quartz and stage V calcite. Stable isotope compositions of mineralizing fluids from Tongyoung (delta D = -44 to -61ppm; delta 18 O = -6.8 to -9.4ppm) are similar to modern meteoric and thermal spring waters in the area and indicate meteoric water dominance during all stages of the Au-Ag-Te mineralizing system. Comparison of Tongyoung to other Au-Ag-(Te) deposits indicates that its complex sequence of mineralization is a natural consequence of repeated inundation of a hydrothermal system by progressively cooler meteoric waters.

Stable-isotope geochronology of the Australian regolith

Australian regolith profiles can be assigned to one of three post-Palaeozoic age groups on the basis of the oxygen-isotope composition of authigenic clay minerals developed in the profile. Systematic variations in the isotopic composition of meteoric waters, and therefore of the authigenic regolith minerals that formed in equilibrium with them, are a result of the continent's drift from high to low latitudes and changes in global climate. Residual clays (collected in situ from regolith profiles) of post-mid Tertiary age have δ 18 O values between +17.5 and +21.3%., with the exception of samples from northern Australia (north of approximately 20°S), which have anomalously low values because meteoric waters in northern Australia are largely derived from monsoonal rain. The high δ 18 O, values of post-mid Tertiary residual clays are consistent with Australia's northward drift to low (warm) latitudes during this time, compared with the much higher latitudes it occupied for most of its post-Palaeozoic history. Late Tertiary residual clays have δ 18 O values that are indistinguishable from all other post-mid Tertiary clays, indicating that further subdivision of the sample groups is not feasible on a continent-wide scale. Comparison with hypothetical “modern” clays in equilibrium with modern meteoric waters confirms that there has been very little change in the isotopic composition of meteoric waters in Australia since the mid-Tertiary. Pre-mid Tertiary clays have lower δ 18 O values, between +10.0 and +17.5%., which are consistently lower than post-mid-Tertiary clays. δ 18 O values of less than +14 to +15%. are thought to reflect weathering events during much earlier geologic periods, perhaps early or mid Mesozoic, when Australia was at high latitude and the Australian climate was humid and cool to cold. Several workers have documented the existence of very old regolith profiles and land surfaces in Australia and support for the above hypothesis comes from three analyses of clays from profiles of stratigraphically demonstrable pre-late Mesozoic age which have δ 18 O values between +10.2 and +12.3%.. Regolith profiles composed of low- 18O clays (< +15%.) are widespread in Australia, and it is possible that a much greater part of the modern landscape than previously recognized developed in the early- or mid-Mesozoic. The δ 18 O values of transported (i.e., sedimentary) kaolinites reveals that the major source for many Tertiary kaolinitic sediments was this postulated pre-late Mesozoic low- 18O regolith. The stableisotope evidence that much of the Australian regolith formed in comparatively cold conditions suggests that, contrary to some traditional interpretations, lateritization and deep weathering phenomena are not solely the result of weathering in tropical or sub-tropical climates. The hydrogen-isotope composition of the clays range from −115 to −50%.; however, it is inferred that the majority of clays have undergone some post-formational hydrogen-isotope exchange which renders their δD composition unsuitable for dating purposes.