Sr Ca Ratios Research Articles

Molecular paleoclimatology: reconstruction of climate variabilities in the late Quaternary

Lipid class compounds were studied in the deep-sea surface sediments from the central Pacific across a latitudinal transect at 175°E (48°N-15°S) and a box core from the western tropical Pacific to discuss their utility as paleoclimatological indicators. Higher concentrations of C 25C 35 n-alkanes were observed in the higher latitudes in the north Pacific. Their latitudinal distributions are similar to the spatial distributions of the observed soil dust concentrations observed in the central-north Pacific atmosphere, suggesting that the sedimentary C 25C 35 n-alkanes are atmospherically transported from terrestrial higher plants, and can be used as an indicator of terrestrial input to ocean environments. Downcore distributions of total C 25C 35 n-alkanes suggest that terrestrial input doubled over the western tropical Pacific at the LGM and decreased by a factor of two at the last deglaciation period in comparison with the Holocene. The latitudinal distributions of C 17C 20 n-alkanes and pristane are higher in the high latitudes and equatorial region, probably reflecting the higher primary productivity in surface waters of these oceans. The downcore profiles of these compounds, as well as total organic carbon, long-chain alkenones and dinosterol suggest that biological production decreased significantly during the deglaciation period and slightly increased during the LGM compared with that of the Holocene. The downcore UK 37 record suggests that the SST was almost constant over the last 20 000 y, which agrees well with the CLIMAP results and foraminifera δ 18O, although it disagrees with results from coral Sr Ca ratios and δ 18O records.

Formula omitted] and [formula omitted] ratios in skeletal calcite of Mytilus trossulus: Covariation with metabolic rate, salinity, and carbon isotopic composition of seawater

Minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity. Although molluscan calcite is secreted at or near oxygen isotope equilibrium, the influence of metabolic activity (i.e., vital effects) on skeletal SrCa ratios and δ 13C values is not well known. We present measurements of skeletal chemistry from (a) consecutive samples milled in chronological order from the organism's final year of growth and (b) adjacent samples within three separate growth bands of the marine mussel Mytilus trossulus to investigate chemical disequilibrium effects among different parts of the shell.Seawater temperature and salinity were monitored for one year at Squirrel Cove, British Columbia. At the end of the year, a young, rapidly growing mussel (mussel A) and an old, slowly growing mussel (mussel B) were harvested from this site. Growth bands within the shells were sampled to provide a chronological record of shell carbonate chemistry. Results from consecutive samples show (1) a significantly higher average SrCa ratio in mussel A than that in mussel B and (2) δ 13C values that correlate well with salinity in mussel A but not in mussel B. Results from time-equivalent, adjacent samples show (1) higher SrCa and δ 13C values near the ventral margin than at time-equivalent regions on lateral margins of the shell and (2) little or no variation in δ 18O values.These observations suggest that skeletal chemistry (SrCa and δ 13C) is primarily controlled by rate of mantle metabolic activity and secondarily modified by variation in seawater salinity. Because metabolic activity in the mantle at the site of carbonate precipitation varies with shell curvature, the composition of calcite secreted along lateral margins is influenced to a greater extent by metabolic activity than calcite secreted coevally at the central margin of the shell. Hence, the chemistry of calcite secreted at the ventral margin is precipitated in near-equilibrium with seawater and allows accurate estimation of seawater SrCa ratios and carbon isotopic composition. In contrast, shell precipitation along lateral margins is dominantly controlled by metabolic activity, and calcite chemistry is not in equilibrium with ambient seawater. In this context, we present a biomineralization model where variations in skeletal SrCa and δ 13C values are explained in the context of mantle metabolic activity and seawater salinity.

Effects of salinity and ontogenetic movements on strontium:calcium ratios in the otoliths of the Japanese eel, Anguilla japonica Temminck and Schlegel

To study the mechanism of Sr incorporation into otoliths of the Japanese eel, Anguilla japonica, a total of 100 elvers collected from an estuary were reared in the laboratory at salinities of 0, 10, 25 and 35%. for approximately seven months. The elvers grew from 56 mm TL to 100–300 mm TL. Twenty elvers were randomly selected and the Ca and Sr concentrations of their otoliths were analyzed from the primordium to the edge, using an electron microprobe equipped with a four-channel wavelength-dispersive spectrometer. Sr Ca ratios in the otoliths of eels reared in various salinities were much lower than the ratio of 15 × 10 −3 observed in elvers about one month before they arrived at the estuary. The irreversibility of Sr Ca ratios at 35%. salinity in this experiment indicated that the drastic change of the Sr Ca ratios in otoliths of elvers was not due to the reduction of salinity in the coastal waters, but more likely to the development from leptocephalus to glass eel. The mean Sr Ca ratios in the new increments of the otoliths of eels during the rearing period were highly correlated with salinity ( S), [ Sr Ca ] × 10 3 = 3.797 + 0.14S ( n = 20, r = 0.77), which can be used to predict elver movements and habitat utilization rates.

High resolution windows into early Holocene climate: [formula omitted] coral records from the Huon Peninsula

High-precision measurements of Sr Ca ratios are reported for Porites corals from the uplifted Holocene coral terraces at Huon Peninsula, Papua New Guinea. The early Holocene Porites have UTh mass spectrometric ages of 8920 ± 60 yr and 7370 ± 50 yr, and δ 234U(t) values of 145 ± 2, similar to modern seawater. The Sr Ca coral records provide 5–6 year high resolution (near weekly) time windows into early Holocene sea surface temperatures. Seasonal temperature fluctuations are generally in the range of ± 1°C, with occasional excursions of ± 2°C, which may indicate the more frequent recurrence of very strong ENSO (El Niño-Southern Oscillation) events. Mean annual Sr Ca temperatures of 24.2 ± 1.1°C and 22.9 ± 0.8°C have been obtained, which are ∼ 2–3°C cooler than that exhibited by a modern Porites. These results indicate that, during the early Holocene, the equatorial western Pacific ocean was at least several degrees cooler than present-day temperatures. This is consistent with late glacial coral records from the Caribbean that indicate lower (∼ 6°C) sea surface temperatures for the equatorial oceans. The Huon Peninsula corals also indicate that SSTs were several degrees cooler than those in the Caribbean during the early Holocene. Thus, although the northern hemisphere summer radiation maximum occurred at ∼ 10 ka, there appears to have been a significant lag in the response of the equatorial western Pacific ocean to this warming. Cooler early Holocene sea surface temperatures in the western Pacific may have been due to changing patterns of ocean-atmosphere circulation, resulting from the exposure of large areas of continental shelf in the southeast Asia region, a consequence of lower glacial sea levels. It is likely that ocean temperatures in the Huon Peninsula were influenced by the opening at ∼ 7 ka of the Torres Strait, that now separates New Guinea from the Australian mainland.

Can otolith microchemistry chart patterns of migration and habitat utilization in anadromous fishes?

Seasonal and ontogenetic patterns in estuarine and coastal migrations of anadromous fish species have important consequences to their survival, growth, recruitment, and reproduction. We tested the hypothesis that otolith (sagitta) microchemistry can document the environmental history of individual fish across an estuarine salinity gradient. Juvenile striped bass, Morone saxatilis (Walbaum), (80 days posthatch) were reared for 3 wk in aquaria at two temperatures and six salinities. The ratio of strontium/calcium ( Sr Ca ) deposited in the sagittal otoliths of reared juveniles was positively related to salinity. Temperature and growth rate had relatively minor, but significant effects on the Sr Ca ratio. In a second experiment, juveniles (80 days posthatch) were exposed to increasing salinity (0 ppt to 25 ppt) and then decreasing salinity (25 ppt to 0 ppt) over a 20-wk period. Electron microprobe examination of the otoliths from these juveniles showed a gradual rise and decline in Sr Ca during the experimental period which corresponded directly with experimental changes in salinity. Field data on subadult and adult striped bass corroborated the laboratory analyses and indicated a logistic relationship between ambient salinity and otolith Sr Ca ratio. Verification studies support the use of otolith microchemistry to measure migratory schedules and habitat utilization patterns in anadromous striped bass populations.

Calcium, magnesium and strontium concentrations in the calcite sclerites of Mediterranean gorgonians (Coelenterata: Octocorallia)

The mineralogical analysis of the sclerites of four Mediterranean gorgonians revealed magnesium calcite as the only calcium carbonate polymorph. The Mg Ca ratio (0·064–0·098) and the Sr Ca ratio (0·0014–0·0025) in the sclerites of the investigated species were the lowest ever reported in octocoral calcite. Calcium concentrations generally did not vary with water depth or colony region, whereas there was a high intraspecific variation of Mg Ca and Sr Ca ratios related to water depth and colony region. This variation of the Mg Ca and Sr Ca ratios in the sclerites cannot be explained by the chemical composition of the seawater, as the Mg Ca and Sr Ca ratios of seawater were constant over the depths and seasons investigated (4·0 ± 0·04 and 0·0084 ± 0·00015). The comparison with inorganic precipitated calcite revealed a biological enrichment of Mg and a discrimination against Sr in octocoral calcite. Our data do not support the hypothesis that the Mg concentration is influenced by the growth rate. According to our data on Mg concentrations in gorgonian sclerites and ambient water temperature, the relationship between Mg content in octocorals and ambient water temperature derived by Chave 1954 should probably be revised. A positive correlation between Mg and Sr values in octocoral calcite (including data from literature) intimates that Mg is an important factor influencing the incorporation of Sr into the calcium carbonate matrix. No correlation between Sr concentration and temperature was found, however, growth rate is discussed as a potential factor influencing Sr concentrations.

Formula omitted] ratios of modern marine calcite: Empirical indicators of ocean chemistry and precipitation rate

Holocene biotic and abiotic marine calcite have a similar range of Mg contents (0 to 22 and 4 to 21 mol% MgCO 3, respectively), yet biotic calcite has Sr 2+ concentrations that are consistently 1250 ppm higher than those of abiotic calcite. As in laboratory experiments, a positive linear relation is observed between D Sr and calcite Mg content. This produces two distinct linear trends on a plot of Sr 2+ vs. Mg 2+ concentrations. Principal axes of variation for both trends have similar slopes, yet distinctly different Sr 2+ concentration intercepts. (Biotic: y = 0.024 x + 1298, r 2 = 0.70; Abiotic: y = 0.027 x + 47, r 2 = 0.77). The similar slopes of these trends reflect the constancy of Mg Ca and Sr Ca ratios of modern seawater. Equations describing the dependence of D Sr on calcite Mg content are derived from both trends (Biotic: D Sr = 3.16 x 10 t-6 (ppm Mg) + 0.169; Abiotic: D Sr = 3.52 x 10 −6 (ppm Mg) + 0.0062). Characterization of Sr-Mg trends for Holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater Mg Ca and Sr Ca ratios. The relatively high Sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms. Calcites precipitated from seawater in laboratory experiments have D sr values that are similar to those of biotic marine calcite, suggesting that both precipitate at approximately the same rate. Our estimates of surface area-normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded, pH-stat experiments. We conclude that the D Sr values for biotic and experimental marine calcite are kinetically controlled, whereas the lower precipitation rates of abiotic marine calcite yield D Sr values that approximate equilibrium conditions. Experimentally derived equations describing the relation between D Sr and calcite precipitation rate indicate that the offset in Sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates. However, observations of naturally occurring marine cements suggest that the five-order-of-magnitude offset best represents natural system processes.

Fluorine mobility during early diagenesis of carbonate sediment: An indicator of mineral transformations

The abundant occurrence of calcium carbonate minerals in marine sediment, their well-documented dissolution or precipitation during diagenesis, and their high F content suggest that carbonate mineral diagenesis may be an important influence on F behavior in marine sediment. To test this hypothesis, we have examined the geochemistry of F in shallow carbonate mud bank sediment of Florida Bay, USA.The F content of biogenic calcium carbonate in Florida Bay varies with mineralogy, positively correlates with the Mg content of calcite, and occurs in similar abundance to Sr (high-Mg calcite: FSr = 2.4 mol/mol; aragonite: 0.53–0.79 mol/mol; low-Mg calcite: 0.22 mol/mol). Models of porewater distributions, direct solute flux measurements, and reaction rate estimates over the upper 0–16 cm of sediment from Bob Allen Key Bank predict net fluxes out of the sediment of 170 μmol F/m2/d, 230 μmol Sr/m2/d, and 5.6 mmol Ca/m2/d. The net solute flux ratio of FSr (0.71 mol/mol) is consistent with dissolution of aragonite or high-Mg calcite, but FCa and SrCa ratios (28 mmol/mol and 40 mmol/mol, respectively) are 3–10 × that of biogenic carbonate sources. Selective dissolution of a high F and Sr content phase or, more likely (based on dissolution experiments), concurrent dissolution and reprecipitation of phases with different F and Sr contents account for this discrepancy. The loss of F, Sr, and Ca to fluorapatite precipitation, as predicted from a stoichiometric model of phosphate release, can be added to the transport-reaction model predicted net fluxes. A resulting, more complete mass balance model incorporating both carbonate mineral reactions and fluorapatite formation yields total release estimates of F, Sr, and Ca of 770 μmol, 332 μmol, and 53 mmol/m2/d, respectively. Calcium carbonate minerals apparently undergo transformation whereby 34 mmol high-Mg calcite/m2/d and 19 mmol aragonite/m2/d dissolve, and 46 mmol low-Mg calcite/m2/d precipitates (ignoring other cations besides Ca). If no fluorapatite formation occurs, the required fluxes are that 23 mmol aragonite/m2/d dissolves and 3.4 mmol high-Mg calcite/ m2/d and 14 mmol low-Mg calcite/m2/d precipitate. Net loss of CaCO3 from the deposit by dissolution is ~6–7 mmol/m2/d (3% of the accumulation flux). The magnitude of these fluxes could cause significant mineralogical and chemical changes on rapid time scales in nearshore carbonate sediment. Fluorine is probably mobile in other carbonate deposits undergoing diagenetic alteration on short and longer time scales and is a powerful additional constraint on the rates and nature of carbonate mineral diagenesis.

Intertidal barnacles—Assessment of their use as paleo-environment indicators using Mg, Sr, [formula omitted] and [formula omitted] variations

Composite shell samples of the intertidal barnacle Tetraclita serrata Darwin from eight localities around the coast of southern Africa have been analyzed for major- and minor-element contents and carbon- and oxygen-isotope ratios. These data have been used to evaluate the temperature scales that have been developed for barnacles using MgCO 3 contents and oxygen-isotope fractionations. The temperatures of seawater calculated from the δ 18O-values were found to be within ± 1†C of the average annual surface temperature computed for the sampling sites of the barnacles and to be more reliable than temperature estimates made from MgCO 3 contents. Detailed investigation of the MgCO 3 distribution in sections of the barnacle shells showed irregular variations of this component in the profile and, in particular, a marked increase in the MgCO 3 content towards the outer rim of the shells. This is attributed to dissolution and precipitation effects occuring on the outer surfaces of the shells during their alternate exposure and submergence in the intertidal zone. The carbon-isotope values show a poor negative correlation with average annual surface temperature and the relationship is not sufficiently good to be used as a paleothermometer. The Sr contents of the samples of T. serrata were found to be constant from all sample locations on the southern African coast. Similar contents have been reported in the literature for intertidal barnacles in other parts of the world. The average Sr Ca ratio of all intertidal barnacles is ∼ 8.3 · 10 −3 The consistency of this ratio suggests that Sr contents of unaltered barnacle shells preserved in sediments can be used for estimating Sr contents of the paleo-oceans.

Li, Sr, Mg, and Na in foraminiferal calcite shells from laboratory culture, sediment traps, and sediment cores

Constant-temperature laboratory culture experiments of the planktonic foraminiferal species Globigerinoides sacculifer (Brady) suggest that the ratios of Li and Sr to Ca in the shells are a function of these ratios in the culture solutions. Mg Ca and Na Ca in the shells did not vary with changes of these ratios in the culture solution. These are the first direct determinations of the relationship between foraminiferal shell chemistry and solution composition. The possibility of temperature dependence for the minor elemental composition of foraminiferal shells was also investigated in the laboratory and by analysis of several planktonic and one benthic foraminiferal species from sediment trap and sediment core samples. The Sr Ca , Mg Ca , and Na Ca ratios in the natural samples roughly correlate with calcification temperature, whereas differences in the Li/Ca ratios are small and not systematically related to temperature. However, laboratory culture experiments at 20°C and 30°C showed no variation in the Li Ca , Sr Ca , Mg Ca , and Na Ca ratios with calcification temperature for the planktonic foraminifera G. sacculifer and Orbulina universa. Therefore, observed differences in the Sr Ca , Mg Ca , and Na Ca ratios for the sediment trap and core foraminiferal samples cannot be ascribed to direct effects of calcification temperature, but may be due to some other environmental factor which is correlated with temperature.

Weaning patterns are reflected in strontium-calcium ratios of juvenile skeletons

As human milk is exceptionally low in strontium-calcium ( Sr Ca ) ratios, but solid foods are relatively high, it should be possible to examine the pattern of dietary supplementation and the age of weaning in prehistoric groups by reference to the Sr Ca ratios of juvenile skeletons. The data are presented that support this rationale, along with an investigation of the Sr/Ca values of juvenile and adult skeletons from a medieval Arab graveyard. The Sr Ca data from these skeletons are shown to coincide with the age-curves expected in theory, suggesting that new palaeodemographic information is indeed obtainable from Sr Ca studies. However, until further research is conducted, the technique provides a functional estimate of weaning patterns that is only suitable for comparative purposes. Additional research should clarify the relationship of functional to actual estimates of dietary supplementation and weaning.

Formula omitted] and [formula omitted] ratios, interstitial water chemistry and diagenesis in deep-sea carbonate sediments of the Ontong Java Plateau

Interstitial waters and sediments from DSDP sites 288 and 289 contain information on the chemistry and diagenesis of carbonate in deep-sea sediments and on the role of volcanic matter alteration processes. Sr Ca ratios are species dependent in unaltered foraminifera from site 289 and atom ratios (1.2–1.6 × 10 −3) exceed those predicted by distribution coefficent data (~0.4 × 10 −3). During diagenesis Sr Ca ratios of carbonates decrease and reach the theoretical distribution at a depth which is identical to the depth of Sr isotopic equilibration, where 87Sr 86Sr ratios of interstitial waters and carbonates converge. Mg Ca ratios in the carbonates do not increase with depth as found in some other DSDP sites, possibly because of diagenetic re-equilibration with interstitial waters showing decreasing Mg 2+/Ca 2+ ratios with depth due to Ca input and Mg removal by alteration of volcanic matter. Interstitial 18O 16O ratios increase with depth at site 289 to δ 18 O = 0.67%. (SMOW), reflecting carbonate recrystallization at elevated temperatures ( $ ̆ = 20°C), the first recorded evidence of this effect in interstitial waters. Interstitial Sr 2+ concentrations reach high levels, up to 1 mM, chiefly because of carbonate recrystallization. However, 87Sr 86Sr ratios decrease from 0.7092 to less than 0.7078, lower than for contemporaneous sea water, showing that there is a volcanic input of strontium at depth. This volcanic component is recorded in the Sr isotopic composition of recrystallized calcites. Isotopic compositions of the unrecrystallized calcites suggests that the rate of increase of the 87Sr 86Sr ratio of sea water with time has been faster since 3 my ago than in the preceding 13 my.

Strontium-calcium ratios in Cenozoic planktonic foraminifera

The Sr Ca ratio and other parameters have been measured in fossil planktonic foraminifera from the Atlantic and Pacific Ocean basins in order to evaluate the Sr Ca ratio of seawater during the last 75 million years. Results on well-preserved samples indicate that the ratio has increased to its present value by 10–15% during the Cenozoic, and that minima occurred between 55-45 Ma and 10-5 Ma, when the ratio was 15–25% less than at present. The long-term increase may reflect either decreasing deposition of aragonite with a high Sr Ca ratio in shallow seas, or decreasing seafloor spreading rates and consequently decreasing hydrothermal supply of Ca during the Cenozoic. Other geologic evidence suggests that the Eocene minimum (near 50 Ma) may have resulted from increased aragonite sedimentation, while the Late Miocene minimum (between 10-5 Ma) may have been caused by an increased rate of seawater-basalt exchange when seafloor spreading rates increased on the East Pacific Rise near 10 Ma.

Formula omitted] and [formula omitted] ratios in polygenetic carbonate allochems from a Michigan marl lake

Rapid accumulation of CaCO 3 is occurring in Littlefield Lake, a marl lake located in central Michigan. The sediment, which is 95% CaCO 3, primarily consists of eight different genetic groups of carbonate allochems. These include calcite muds, sands, algal oncoids and Chara encrustations, as well as the dominant aragonitic gastropods Valvota tricarinota. Gyraulus deflectus and Amnicola integra. and the dominant aragonitic pelecypod Sphaerium partumeium. Samples of each of these groups were analyzed for Ca, Sr and Mg. Molar Mg Ca ratios are primarily controlled by allochem mineralogy, with calcitic forms having Mg Ca ratios 5–10 times larger than aragonitic (shelled) forms. The Sr Ca ratios are primarily controlled by biochemical fractionation, and are significantly lower than Sr Ca ratios of inorganically precipitated aragonite from other settings. Partition coefficients were determined for both Sr and Mg for each carbonate allochem group and, based on comparisons with results reported by other workers, the partition coefficients determined here are generally considered ‘typical’ or representative values for biogeneous freshwater carbonates. An analysis of variance of the data indicates that most genera and species of carbonate-secreting organisms in marl lakes have highly characteristic Sr Ca and Mg Ca ratios. These ratios can potentially serve as geochemical tracers in future investigations of lacustrine carbonate diagenesis. Both Sr and Mg are influenced by grain size and/or surface area, probably due to the presence of these elements in non-lattice-held (exchangeable) positions.

Behaviour of strontium in subsurface calcium chloride brines: Southern Israel and Dead Sea rift valley

Calcium chloride brines are, as a rule, relatively rich in strontium, but the enrichment is usually limited and is found to be related to the concentration of calcium. The limiting mechanisms were evaluated as a model which comprises simple interactions between minerals and solutions. Based on the known ranges of strontium concentration in minerals, mineral solubilities and partition coefficients of strontium (both poorly known in certain cases), six fields of Sr Ca molar ratios were defined in terms of participating minerals and processes: (a) 0.38−1.56 × 10 − 3 by dolomitization of calcite; (b) 1.5−2.2 × 10 − 2 due to dolomitization of aragonite; (c) 0.4−1.4 × 10 − 2 as a result of solution-reprecipitation of calcite; (d)0.12−0.20 through transformation of aragonite to calcite; (e)0.10−0.60 through equilibrium of the pair calcite-strontianite; and (f)0.01−0.08 by equilibrium with gypsum and celestite. The model was applied to the analysis of two groups of brines from southern Israel which are originated in the coastal plain (group C) and in the rift valley (group R). The low Mg Ca ratios of both water groups point to dolomitization as the main subsurface modifying process. Sr Ca ratios of brines belonging to group C are consistent with dolomitization of aragonitic surface sediments at the beginning of their evolution. Brines of group R bear evidence to a similar pathway at the beginning of their evolution, but most of them were further affected by interaction with limestone.

Use of Sr-Ca ratios in hair for monitoring.

Consideration has been given to the measurement of Sr/Ca ratios in hair as an indication of body burdens and exposures. Experiments were done in rats using both double tracer techniques and measurements of stable strontium and calcium. Two findings emphasize the difficulties that must be overcome if such measurements are to be useful: (a) The values of ORhair/diet and presumably of ORhair/bone were markedly affected by the washing of the hair and (b) discrepant results were obtained in comparisons of double tracer values and those from stable Sr and Ca analysis. The latter observation has also been reported by other laboratories and is as yet unexplained.

On the interpretation of trends in element ratios in differentiated igneous rocks, with particular reference to strontium and calcium

A detailed consideration of the partition of Sr and Ca between coexisting solid and liquid phases shows that the increase in the Sr Ca ratio with differentiation cannot be interpreted in terms of plagioclase, the major Sr-bearing phase alone. In contradistinction to the normally expressed view, Sr enters plagioclase more readily than Ca and the observed rise in Sr Ca in successive plagioclases reflects the changing liquid composition which, in turn, is controlled by the crystallization of pyroxenes in addition to plagioclases. The conclusions are of general applicability to trace element studies.

Genesis of migmatites from the palmer region of south Australia

Migmatites of the veined gneiss type are associated with granites and granitic gneisses within the highest grade region of an Early Palaeozoic metamorphic terrain around Palmer on the eastern flank of the Mount Lofty ranges, South Australia. The four main hypotheses previously proposed for the genesis of the granitic portions of migmatites, viz., bodily injection of granitic magma, metasomatism, partial melting and metamorphic differentiation are discussed in the light of new chemical data. Structural and stratigraphic interpretations of the region indicate that migmatites were formed from quartzofeldspathic rocks without disturbance of the structural style. Bulk analyses of three selected migmatites are compared with six analyses of lower-grade quartzofeldspathic schists collected from an equivalent stratigraphic horizon 10 km from the migmatites. Differences in major element chemistry can be explained in terms of variation in proportions of the constituent minerals. Critical trace-element ratios are similar, and it is suggested that there is no necessity to introduce material from adjacent igneous intrusions or from unknown sources. Four granitic veins from the migmatites are richer in potassium than the associated large bodies of granitic rocks (twelve analyses). The veins also have high K Rb ratios (average 454) compared with these other granitic rocks in which the K Rb ratios are normal (average 229). Abnormally high K Rb , Ba K , Ba Sr , Sr Ca and Ba Rb ratios, all of which have been shown to decrease with fractionation, are the reverse of those expected if the granitic portions were produced by regional metasomatism since “emanations” coming either from granitic magmas or from any other source should be highly fractionated. Metamorphic temperature estimates are such that partial melting cannot be discounted. A plot of the normative percentages of quartz, albite and orthoclase onto the synthetic granite system show that the granitic veins are rich in potassium compared with the “ternary minimum” composition. The normative Ab An ratios are too high to explain this as a projection of a quaternary minimum in the tetrahedron Q, Ab, Or, An as suggested by Von Platen (1965). Partial melting would also require an abnormally equilibrium high water pressure (greater than 10 kbar) and could not explain the presence of “dents du cheval”. Three new analyses of biotite from the Palmer migmatites are compared with two from an associated intrusive granite and two from an associated granitic gneiss. The three migmatite biotites are identical in major and minor element composition: the mole % annite is constant and similar to the mole % annite in the granitic gneiss but different from the values for biotites of the intrusive granite. From this data it is suggested that the f H 2O - f O 2 - T conditions within the migmatite zone were constant. Four complete analyses of potassium feldspars separated from the migmatites show no differences in major element concentrations from the twelve potassium feldspars separated from the rocks of the major granitic bodies, but minor elements in both potassium feldspar and biotite reflect the minor element variations in the total rocks. The distribution of Ba Rb in coexisting biotite and potassium feldspar from seven rocks of the migmatite zone is close to theoretical predictions, indicating that these minerals are in equilibrium even in the migmatites in which this feldspar is virtually confined to the granitic veins and biotite concentrated in the selvedges. Barium and strontium are preferentially enriched in the potassium feldspar relative to biotite, whereas Rb is concentrated in biotite relative to potassium feldspar so that by concentration of potassium feldspar within the veins and concentration of biotite in the selvedges, the abnormally high K Rb , Ba Rb , Ba K , Sr Ca and Ba Sr can be adequately explained. It is concluded that the granitic portions of the Palmer migmatites were formed in place without introduction of material from granitic magma or any other source. The data is most readily explained by production of granitic veins by metamorphic differentiation.

Paleoecological problems of Mg and Sr in biogenic calcites in light of recent thermodynamic data

Calcitic shells of three species of the ostreid pelecypods, Exogyra cancellata, E. costata (Late Cretaceous) and Crassostrea virginica (Recent) were analyzed for Mg and Sr. Shells of Exogyra contain 0.5–1.5 mole per cent MgCO 3, 0.04–0.13 mole per cent SrCO 3; shells of Crassostrea—1.0–1.6 mole per cent MgCO 3, 0.08–0.09 mole per cent SrCO 3. These calcites are not at equilibrium with the (a Mg ++ ) (a Ca ++ ) ratio as in the Recent sea water. The concentrations of Sr in the skeletons of these species and of Belemnitella americana (Late Cretaceous) can, at least in part, be accounted for by Nernst's distribution equilibria with respect to the Sr Ca ratio as in the Recent seas. A combined record of Mg and Sr, treated as an incomplete ternary free energy surface, may accentuate differences between geographically distinct populations. Interpretation of such differences is at present impeded by a lack of exact knowledge of the genetic and environmental effects on the skeletal chemistry. Approximate calculation of the activity coefficients of the components in magnesian calcites at 25°C is given in the Appendix.