Robert O. Rye

Carbon, hydrogen, and oxygen isotope studies of the regional metamorphic complex at Naxos, Greece

Abstract At Naxos, Greece, a migmatite dome is surrounded by schists and marbles of decreasing metamorphic grade. Sillimanite, kyanite, biotite, chlorite, and glaucophane zones are recognized at successively greater distances from the migmatite dome. Quartz-muscovite and quartz-biotite oxygen isotope and mineralogie temperatures range from 350 to 700°C. The metamorphic complex can be divided into multiple schist-rich (including migmatites) and marblerich zones. The δ 18 O values of silicate minerals in migmatite and schist units and quartz segregations in the schist-rich zones decrease with increase in metamorphic grades. The calculated δ 18 O H 2 O values of the metamorphic fluids in the schist-rich zones decrease from about 15‰ in the lower grades to an average of about 8.5‰ in the migmatite. The δD values of OH-minerals (muscovite, biotite, chlorite, and glaucophane) in the schist-rich zones also decrease with increase in grade. The calculated δD H 2 O values for the metamorphic fluid decrease from −5‰ in the glaucophane zone to an average of about −70‰ in the migmatite. The δD values of water in fluid inclusions in quartz segregations in the higher grade rocks are consistent with this trend. Theδ 18 O values of silicate minerals and quartz segregations in marble-rich zones are usually very large and were controlled by exchange with the adjacent marbles. The δD values of the OH minerals in some marble-rich zones may reflect the value of water contained in the rocks prior to metamorphism. Detailed data on 20 marble units show systematic variations of δ 18 O values which depend upon metamorphic grade. Below the 540°C isograd very steep δ 18 O gradients at the margins and large δ 18 O values in the interior of the marbles indicate that oxygen isotope exchange with the adjacent schist units was usually limited to the margins of the marbles with more exchange occurring in the stratigraphic bottom than in the top margins. Above the 540°C isograd lower δ 18 O values occur in the interior of the marble units reflecting a greater degree of recrystallization and the occurrence of Ca-Mg-silicates. Almost all the δ 13 C values of the marbles are in the range of unaltered marine limestones. Nevertheless, the δ 13 C values of most marble units show a general correlation with δ 18 O values. The CO 2 H 2 O mole ratio of fluid inclusions in quartz segregations range from 0.01 to 2. Theδ 13 C values of the CO 2 range from −8.0 to 3.6‰ and indicate that at some localities CO 2 in the metamorphic fluid was not in carbon isotopic equilibrium with the marbles.

Climatic and Hydrologic Oscillations in the Owens Lake Basin and Adjacent Sierra Nevada, California

Oxygen isotope and total inorganic carbon values of cored sediments from the Owens Lake basin, California, indicate that Owens Lake overflowed most of the time between 52,500 and 12,500 carbon-14 (14C) years before present (B.P.). Owens Lake desiccated during or after Heinrich event H1 and was hydrologically closed during Heinrich event H2. The magnetic susceptibility and organic carbon content of cored sediments indicate that about 19 Sierra Nevada glaciations occurred between 52,500 and 23,500 14C years B.P. Most of the glacial advances were accompanied by decreases in the amount of discharge reaching Owens Lake. Comparison of the timing of glaciation with the lithic record of North Atlantic core V23-81 indicates that the number of mountain glacial cycles and the number of North Atlantic lithic events were about equal between 39,000 and 23,500 14C years B.P.

A test of geographic assignment using isotope tracers in feathers of known origin

We used feathers of known origin collected from across the breeding range of a migratory shorebird to test the use of isotope tracers for assigning breeding origins. We analyzed δD, δ13C, and δ15N in feathers from 75 mountain plover (Charadrius montanus) chicks sampled in 2001 and from 119 chicks sampled in 2002. We estimated parameters for continuous-response inverse regression models and for discrete-response Bayesian probability models from data for each year independently. We evaluated model predictions with both the training data and by using the alternate year as an independent test dataset. Our results provide weak support for modeling latitude and isotope values as monotonic functions of one another, especially when data are pooled over known sources of variation such as sample year or location. We were unable to make even qualitative statements, such as north versus south, about the likely origin of birds using both δD and δ13C in inverse regression models; results were no better than random assignment. Probability models provided better results and a more natural framework for the problem. Correct assignment rates were highest when considering all three isotopes in the probability framework, but the use of even a single isotope was better than random assignment. The method appears relatively robust to temporal effects and is most sensitive to the isotope discrimination gradients over which samples are taken. We offer that the problem of using isotope tracers to infer geographic origin is best framed as one of assignment, rather than prediction.

STABLE HYDROGEN ISOTOPE ANALYSIS OF BAT HAIR AS EVIDENCE FOR SEASONAL MOLT AND LONG-DISTANCE MIGRATION

Abstract Although hoary bats (Lasiurus cinereus) are presumed to be migratory and capable of long-distance dispersal, traditional marking techniques have failed to provide direct evidence of migratory movements by individuals. We measured the stable hydrogen isotope ratios of bat hair (δDh) and determined how these values relate to stable hydrogen isotope ratios of precipitation (δDp). Our results indicate that the major assumptions of stable isotope migration studies hold true for hoary bats and that the methodology provides a viable means of determining their migratory movements. We present evidence that a single annual molt occurs in L. cinereus prior to migration and that there is a strong relationship between δDh and δDp during the molt period. This presumably reflects the incorporation of local δDp into newly grown hair. Furthermore, we present evidence that individual hoary bats are capable of traveling distances in excess of 2,000 km and that hair is grown at a wide range of latitudes and elevations. Stable hydrogen isotope analysis offers a promising new tool for the study of bat migration.

Chemical, crystallographic and stable isotopic properties of alunite and jarosite from acid—Hypersaline Australian lakes

Abstract Chemical, crystallographic and isotopic analyses were made on samples containing alunite and jarosite from the sediments of four acid, hypersaline lakes in southeastern and southwestern Australia. The alunite and jarosite are K-rich with relatively low Na contents based on chemical analysis and determination of unit cell dimensions by powder X-ray diffraction. Correcting the chemical analyses of fine-grained mineral concentrates from Lake Tyrrell, Victoria, for the presence of halite, silica and poorly crystalline aluminosilicates, the following formulas indicate best estimates for solid-solution compositions: for alunite, K0.87Na0.04(H3O)0.09(Al0.92Fe0.08)3(SO4)2(OH)6 and for jarosite, K0.89Na0.07(H3O)0.04(Fe0.80Al0.20)3(SO4)2(OH)6. The δD-values of alunite are notably larger than those for jarosite from Lake Tyrrell and it appears that the minerals have closely approached hydrogen isotope equilibrium with the acidic regional groundwaters. The δD results are consistent with a fractionation ∼60–70‰ between alunite and jarosite observed in other areas. However, interpretation of δD results is complicated by large variability in fluid δDH2O from evaporation, mixing and possible ion hydration effects in the brine. δD-values of water derived from jarosite by step-wise heating tend to be smaller at 250°C, at which temperature hydronium and other non-hydroxyl water is liberated, than at 550°C, where water is derived from the hydroxyl site, but the differences are not sufficiently different to invalidate measurements of total δD obtained by conventional, single-step heating methods. δ34S-values for alunite and jarosite from the four lakes (+19.7 to +21.2‰ CDT) and for aqueous sulfate from Lake Tyrrell (+18.3 to +19.8‰) are close to the values for modern evaporites ( +21.5 ±0.3‰ ) and seawater ( +20±0.5‰ ) and are probably typical of seawater-derived aerosols in arid coastal environments. δ34-S-values slightly smaller than that for seawater may reflect a minor contribution of sulfate from pyrite oxidation in the Parilla Sand or a reservoir effect from removal of gypsum enriched in 34S. δ18OSO4-values for alunite from three Western Australia lakes (+17.8 to +18.3‰ V-SMOW), for alunite and jarosite from Lake Tyrrell (+22.6 to +24.9‰) and for aqueous sulfate from Lake Tyrrell (+17.3 to +19.0‰) are much larger than the average value for seawater (+9.6‰). The data suggest an approach to 18O-16O equilibrium between aqueous sulfate and groundwater, which is known from experimental studies to be possible at low pH and low temperatures, but has not been previously documented in nature. A residence time of ∼0.1–1 kyr for sulfate in acidic water (pH 3–4) is needed to achieve the apparent partial oxygen exchange, using previously published data of R.M. Lloyd.

Genesis of sediment-hosted disseminated-gold deposits by fluid mixing and sulfidization: Chemical-reaction-path modeling of ore-depositional processes documented in the Jerritt Canyon district, Nevada

Integrated geologic, geochemical, fluid-inclusion, and stableisotope studies of the gold deposits in the Jerritt Canyon district, Nevada, provide evidence that gold deposition was a consequence of both fluid mixing and sulfidization of host-rock iron. Chemical-reaction-path models of these ore-depositional processes confirm that the combination of fluid mixing, including simultaneous cooling, dilution, and oxidation of the ore fluid, and wall-rock reaction, with sulfidization of reactive iron in the host rock, explains the disseminated nature and small size of the gold and the alteration zonation, mineralogy, and geochemistry observed at Jerritt Canyon and at many other sediment-hosted disseminated gold deposits.

Distribution of Oxygen and Carbon Isotopes in Fossils of Late Cretaceous Age, Western Interior Region of North America

The oxygen isotope composition of both calcite and aragonite of the pelecypod Inoceramus is lighter than the composition of the aragonite of associated baculites and other cephalopods from the western interior region, the Gulf and Atlantic Coastal Plains, parts of Canada, and West Greenland. This difference cannot be explained by biotic and oceanographic factors or by postdepositional alteration of original isotopic compositions. Metabolic fractionation of oxygen isotopes by Inoceramus is strongly implied by the data and is not contradicted by what is known of the processes involved in the biologic deposition of shell carbonate. In addition, the oxygen isotope compositions of the inocerams and of some baculites are so light as to indicate temperatures greater than 30° C, which is too high for mollusks to tolerate. The unreasonable range of the indicated temperatures seems to be partly the result of metabolic fractionation of oxygen and partly the result of the Late Cretaceous sea in the western interior region having had a light oxygen isotope composition because of dilution with fresh water. The carbon isotope composition of the aragonite from Inoceramus is consistently heavier than that of the calcite in the same specimen by amounts ranging from 1 to 3 per mil. Metabolic fractionation of carbon isotopes within Inoceramus thus is indicated. The carbon isotope composition of the aragonite from baculites and other cephalopods is consistently lighter than that in either the aragonite or calcite in Inoceramus, indicating either that the cephalopods fractionated carbon isotopes from the dissolved carbonate in sea water differently than did inocerams or that the cephalopods utilized carbon of a different isotopic composition, probably from their food source, for their metabolic processes. While oxygen isotope data from the inocerams are not useful for paleotemperature interpretations, the oxygen isotope data from the baculites, if taken at face value, suggest either warmer temperatures for the western interior sea than around the periphery of Cretaceous North America, or water of oxygen isotope composition lighter than world oceans, or both. Data from British Columbia, southeastern Alaska, and West Greenland to the Gulf Coastal Plain do not indicate a well-developed latitudinal distribution of temperature in Late Cretaceous time. A general decline in temperatures during late Campanian and early Maestrichtian time is not evident.

Sulfur and oxygen isotopic systematics of the 1982 eruptions of El Chichón Volcano, Chiapas, Mexico

Abstract Thermometers based on sulfur and oxygen isotopic compositions of anhydrite, pyrrhotite, titanomagnetite, and plagioclase crystals from fresh pumices of the 1982 eruptions of El Chichon Volcano indicate a pre-eruption temperature of 810 ± 40°C, confirming textural evidence that the anhydrite precipitated directly from the melt. The isotopic composition of sulfate leached from fresh ashfall samples shows it to be a mixture of anhydrite microphenocrysts and adsorbed sulfate derived from oxidized sulfur (SO 2 ) in the eruption plume. The leachate data show no evidence for rapid oxidation of significant amounts of H 2 S in the eruption cloud even though the fugacity ratio of H 2 S/SO 2 in the gas phase of the magma was >400. This may indicate kinetic inhibition of H 2 S to SO 2 conversion in the eruption cloud. Prior to eruption, the magma contained an estimated 2.6 wt. % sulfur (as SO 3 ). The estimated δ 34 S of the bulk magma is 5.8‰. Such a high value may reflect assimilation of 34 S-enriched evaporites or the prior loss of 34 S-depleted H 2 S to a fluid or gas phase during formation of a small prophyry-type hydrothermal system or ore deposit. In either case, the original magma must have been very sulfur rich. It is likely that the initial high sulfur content of the magma and at least some of its 34 S enrichment reflects involvement of subducted volcanogenic massive sulfides deposits during Benioff-zone partial melting. Isotopic data on mineralized, accidental lithic fragments support the possible development of a porphyry-type system at El Chichon.

Carbonate deposition, Pyramid Lake Subbasin, Nevada: 4. Comparison of the stable isotope values of carbonate deposits (tufas) and the Lahontan lake-level record

Abstract In this paper, the fundamental importance of changes in hydrologic balance and hydrologic state on the δ18O and δ13C values of water and dissolved inorganic carbon (DIC) in lakes of the Lahontan basin is illustrated. Abrupt changes in δ18O and δ13C values of carbonate deposits (tufas) from the Pyramid Lake subbasin, Nevada, coincide with abrupt changes in lake-level and hydrologic state. Minima in lake-level at ∼26,000, ∼15,500 and ∼12,000 yr B.P. are associated with relatively heavy δ18O and δ13C values; maxima in the lake-level record at ∼14,000 and ∼10,500 yr B.P. are associated with relatively light δ18O and δ13C values. We believe that the correlation between maxima and minima in the lake-level and δ18O records reflect the fundamental effect of lake-level dynamics on the δ18O value of lake water. Evaporation increases the δ18O value of lake water, whereas, streamflow discharge and on-lake precipitation decrease the δ18O value. Variation in the δ18O value of lake water, therefore, indicates change in the hydrologic balance; increases in δ18O accompany decreases in lake volume and decreases in δ18O accompany increases in lake volume. Covariance of δ13C and δ18O indicates that change in δ13C values of DIC also accompany change in lake volume. We offer the hypothesis (first put forward by J.A. McKenzie) that change in the productivity (photosynthesis) respiration balance is responsible for much of the observed variation in δ13C. Most Great Basin lakes, including Lake Lahontan, experienced changes in hydrologic state during the late Wisconsin. When a lake becomes hydrologically open, the residence time of water decreases. The greater the rate of spill, the greater the volume of evaporated (18O-enriched) water removed from the spilling lake and the more negative the δ18O value of water remaining in the spilling lake. The concentration of DIC, as well as the concentrations of photosynthesis limiting nutrients (e.g., phosphorus, nitrogen, silica, molybdenum) decrease as spill increases. Increasing rates of spill, therefore, lead to overall decreases in photosynthetic rates relative to respiration rates and, as a consequence, the δ13C values of DIC become more negative.

The origin and isotopic composition of dissolved sulfide in groundwater from carbonate aquifers in Florida and Texas

The δ34S values of dissolved sulfide and the sulfur isotope fractionations between dissolved sulfide and sulfate species in Floridan ground water generally correlate with dissolved sulfate concentrations which are related to flow patterns and residence time within the aquifer. The dissolved sulfide derives from the slow in situ biogenic reduction of sulfate dissolved from sedimentary gypsum in the aquifer. In areas where the water is oldest, the dissolved sulfide has apparently attained isotopic equilibrium with the dissolved sulfate (Δ34S = 65 per mil) at the temperature (28°C) of the system. This approach to equilibrium reflects an extremely slow reduction rate of the dissolved sulfate by bacteria; this slow rate probably results from very low concentrations of organic matter in the aquifer. In the reducing part of the Edwards aquifer, Texas, there is a general down-gradient increase in both dissolved sulfide and sulfate concentrations, but neither the δ34S values of sulfide nor the sulfide-sulfate isotope fractionation correlates with the ground-water flow pattern. The dissolved sulfide species appear to be derived primarily from biogenic reduction of sulfate ions whose source is gypsum dissolution although upgradient diffusion of H2S gas from deeper oil field brines may be important in places. The sulfur isotope fractionation for sulfide-sulfate (about 38 per mil) is similar to that observed for modern oceanic sediments and probably reflects moderate sulfate reduction in the reducing part of the aquifer owing to the higher temperature and significant amount of organic matter present; contributions of isotopically heavy H2S from oil field brines are also possible.