The isotopic composition of carbon in the Alberta oil sand

The carbon isotopic ratios obtained from Athabasca bitumen, asphaltene and maltene have the same value $\text{δ}{}^{13}\text{C}\text{= ?29.6}\text{per ml}$. The corresponding values in the Cold Lake deposits are ?30.6, ?30.0 and ?31.6 per ml. The ratios determined for methane collected from the oil sand and its fractions are about 15 per ml lower than the above values. It appears that the Athabasca and Cold Lake Reservoirs have similar histories.     

Hydrogen,oxygen and carbon isotopic evidence for the origin of rodingites in serpentinized ultramafic rocks

$\text{D}\text{H}$, ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ analyses were made of 14 whole rock and 28 mineral samples of rodingites associated dominantly with lizardite-chrysotile serpentinites from the West Coast of the U.S.A., New Zealand, and the Northern Appalachian Mtns. The δD values of the rodingite minerals are in three groupings: 5 monomineralic veins of pectolite, ?281 to ?429; 8 monomineralic veins of xonotlite, ?112 to ?135; all other minerals, including hydrogarnet, idocrase, prehnite, actinolite, nephrite, and chlorite, ?34 to ?80. Most calcites in rodingites have δ¹⁸O (+9.3 to +14.4) and (δ¹³C (?6.7 to +0.9) values similar to calcites in other Franciscan rocks, but distinct from the very low temperature calcite veins in serpentinites. The $\text{D}\text{H}$ data, combined with δ¹⁸O values of xonotlite (+5.7 to +10.9) and pectolite (+8.9 to +12.4) suggest formation from meteoric-type waters at low temperatures; the $\text{D}\text{H}$ depletion of pectolite, however, is anomalous. Rodingite whole rock values range from δ¹⁸O = +4.1 to +11.5 and δD = ?50 to ?86; one sample containing minor amounts of lizardite-chrysotile serpentinite has δD = ?92, outside this range. However, most rodingites of basaltic or gabbroic parentage are more restricted in δ¹⁸O (+4.1 to +8.6). Such a wide range in δ¹⁸O is consistent with the idea that most rodingites form over a relatively broad range of hydrothermal temperatures. Hydrogen isotopic data for most rodingite minerals (except xonotlite and pectolite) and for whole rocks are suggestive of non-meteoric waters. These $\text{D}\text{H}$ data overlap those observed for veins of hydrous minerals found in Franciscan igneous rocks studied by Margaritz and Taylor (1976, Geochim. Cosmochim. Acta40, 215–234), possibly suggesting evolved D-enriched, connate type metamorphic waters generated during high P, low T Franciscan-type metamorphism at temperatures (250–500°C) comparable to estimates based on mineral stabilities. Such an interpretation is supported by the ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ data for calcite in rodingites.The isotope data appear to contradict some of the conclusions derived from geologic and petrologic studies that indicate concomitant metasomatism and serpentinization of their presently observed host rock. These data appear most consistent with the interpretation that most rodingite minerals, with the exception of late-stage veins of xonotlite and possibly pectolite, may involve metasomatism in association with antigorite serpentinization of ultramafic rock. Subsequent upward tectonic transport in many instances may result in incorporation of the rodingites into their presently observed lizarditechrysotile host rock during or subsequent to pervasive shallow level serpentinization by meteoric waters.     

Stable sulfur and nitrogen isotopic compositions of crude oil fractions from Southern Germany

Eleven samples of crude oil from the Molasse Basin of Southern Germany were fractionated and their contents of sulfur and nitrogen as well as the stable isotope compositions of these elements (${}^{34}\text{S}{}^{32}\text{S}$ and ${}^{15}\text{N}{}^{14}\text{N}$, resp.) investigated.According to the δ³⁴S determinations, all crude oils from the Tertiary base of the Western and Eastern Molasse belong to one oil family and differ significantly from the Triassic and Liassic oils in the Western Molasse.An enrichment of ³⁴S was observed with increasing polarity of crude oil fractions. The isotope distributions of sulfur in the polar constituents of the biodegraded oils from the sandstones of Ampfing, however, approach a homogeneous distribution.The nitrogen isotope distribution is rather uniform in Southern German oils. A regional differentiation can be recognized, although the overall isotopic variation is small. The δ¹⁵N values of the crudes and asphaltenes do not correlate.     

The isotopic composition of titanium in the Allende and Leoville meteorites

We describe the analytical techniques developed for the precise measurement of the titanium isotope abundances using a TiO⁺ ion beam. Terrestrial, lunar, and bulk meteorite samples yield identical results. Using a normalization to ${}^{46}\text{Ti}{}^{48}\text{Ti}$ for mass dependent isotope fractionation, we obtain the normal Ti composition: ${}^{46}\text{Ti}{}^{48}\text{Ti}\text{= 0.108548}$; ${}^{47}\text{Ti}{}^{48}\text{Ti}\text{= 0.099315 ± 0.000005}$; ${}^{49}\text{Ti}{}^{48}\text{Ti}\text{= 0.074463 ± 0.000004}$; ${}^{50}\text{Ti}{}^{48}\text{Ti}\text{= 0.072418 ± 0.000004}$ (2σ grand mean), taking ${}^{18}\text{O}{}^{16}\text{O}\text{= 0.002045}$ and ${}^{17}\text{O}{}^{16}\text{O}\text{= 0.00037}$. Measurements on thirteen coarse-grained and fine-grained Ca-Al-Ti-rich inclusions from the Allende and Leoville meteorites show the presence of widespread, significant, nonlinear isotope anomalies in the Ti isotopes which were not used for normalization. The data require the addition of at least three exotic components. The distinct correlation of non-linear effects for the most neutron-rich isotopes of Ca and Ti and the absence of substantial effects at ⁴⁶Ca in the FUN samples EK-1-4-1 and C-1 indicate that the effects reflect neutron-rich equilibrium or quasi-equilibrium nucleosynthetic processes in the outer layers of a supernova core. The results on Ca and Ti in conjunction with the isotopic effects on other elements (Mg, Sr, Ba, Nd, Sm) show that the samples represent mixtures of different nucleosynthetic components from distinctive processes (‘e’, ‘r’, ‘p’) which do not appear to be related to processes in the same stellar sites.     

Experimental paleotemperature equation for planktonic foraminifera

Small live individuals of Globigerinoides sacculifer which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14° to 30°C) and water isotopic composition, and a correction was made to account for the isotopic composition of the original skeleton using control groups.Comparison of. the actual growth temperatures with the calculated temperature based on paleotemperature equations for inorganic CaCO₃ indicate that the foraminifera precipitate their CaCO₃ in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with Craig's (1965) equation yields: $\text{t = ?0.07 + 1.01}\text{t}\text{?}\text{(r= 0.95)}$ where t is the actual growth temperature and $\text{t}\text{?}$ Is the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate, is equally applicable for the planktonic foraminifer G. sacculifer.Second order regression of the culture temperature and the delta difference (δ¹⁸Oc ? δ¹⁸Ow) yield a correlation coefficient of r = 0.95: $\text{t}\text{?}\text{= 17.0 ? 4.52(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow) + 0.03(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow)}{}^2$$\text{t}\text{?}\text{, δ}{}^{18}\text{Oc}$ and δ¹⁸Ow are the estimated temperature, the isotopic composition of the shell carbonate and the sea water respectively.A possible cause for nonequilibnum isotopic compositions reported earlier for living planktonic foraminifera is the improper combustion of the organic matter.     

Two notes on the isotopic constitution of carbon in minerals

Measurements of the $\text{C}{}^{12}\text{C}{}^{13}$ ratio on two generations of calcite and the matrix from a single specimen are given and discussed. This ratio has also been determined for four examples of graphite and limestone occurring together. The formation of the graphite is briefly discussed in relation to the $\text{C}{}^{12}\text{C}{}^{13}$ ratios.     

O18O16 of feldspars in carbonate rocks

Six authigenic feldspars and three detrital feldspars in limestones and dolostones of Eocene to Preeambrian ages were analyzed for their $\text{O}{}^{18}\text{O}{}^{16}$ content. The difference in δO¹⁸ between the authigenic feldspars (δO¹⁸range = + 18.2 to + 24.7%.) and carbonate host rocks, both limestones and dolostones, was found to be ?0.5 to ?1.4%. Detrital feldspars (δO¹⁸ = + 11.2, + 22.5 and + 17.0%.) exhibit Δ^feldspar_carbonate values of ?12.0, ?2.4 and ?1.6‰, respectively, and appear to have undergone increased isotopic exchange as a function of decreased grain size under solid-state conditions.     

Neodymium isotopic composition of Quaternary island arc lavas from Indonesia

${}^{143}\text{Nd}{}^{144}\text{Nd}$ ratios measured in Quaternary lavas from Java and the Banda arc of Indonesia range from 0.51242 to 0.51280 and exhibit an inverse correlation with ${}^{87}\text{Sr}{}^{86}\text{Sr}$. Isotopically, the Indonesian samples resemble Andean rather than island arc lavas. The samples from Java plot either within, or adjacent to the mantle array, towards higher ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios. Samples from the Banda arc and the anomalous calc-alkaline volcano Papandajan are characterized by relatively low ${}^{143}\text{Nd}{}^{144}\text{Nd}$ and high ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios. These characteristics are consistent with the interpretation that subducted terrigenous material was involved in the genesis of these lavas. Furthermore the Banda arc samples appear to lie on a mixing line between isotopic compositions characteristic of the mantle and upper continental crust. A high-K trachyte from the alkaline volcano Muriah, Java, has isotopic characteristics of the mantle (${}^{143}\text{Nd}{}^{144}\text{Nd}\text{= 0.51270}$, ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.70424}$), which implies that the extreme enrichment in large-ion-lithophile elements in its source must have occurred only shortly before its formation. The inferred ${}^{143}\text{Nd}{}^{144}\text{Nd}$ ratio of the unmodified mantle beneath Java and the Banda arc is lower than that observed in mid-ocean ridge basalt, which may have important implications for a better understanding of the geochemical structure of the mantle.     

87Sr/86Sr composition of seawater during the Phanerozoic

${}^{87}\text{Sr}{}^{86}\text{Sr}$ measurements of 108 sedimentary carbonate rocks have been used to trace variations in the strontium isotopic composition of seawater during the Phanerozoic. The lowest ⁸⁷Sr/⁸⁶Sr observed for any suite of carbonates is taken as the best approximation to the value in well-mixed contemporary seawater. Our data support the existence of low ${}^{87}\text{Sr}{}^{86}\text{Sr}$ in the Cretaceous and Late Jurassic but they do not support further structure beyond a general trend through the Phanerozoic, which may correlate with the continental denudation rate.     

The isotopic composition and concentration of Ag in iron meteorites and the origin of exotic silver

The isotopic composition of Ag and the concentration of Ag and Pd have been determined in Canyon Diablo (IA), Grant (IIIB), Hoba, Santa Clara, Tlacotepec and Warburton Range (IVB), Piñon and Deep Springs (anom.). Troilite from Grant and Santa Clara have also been analyzed. All of these meteorites, with the exception of Canyon Diablo, give ${}^{107}\text{Ag}{}^{109}\text{Ag}$ in the metal phase that is greater than the terrestrial value with the enrichments of ¹⁰⁷Ag ranging from ~2% to 212%. These data show that Ag of anomalous isotopic composition is common to all IVB and anomalous meteorites. The results on Grant suggest that the anomalies may be widespread including more common meteorite groups. There is a general correlation of ${}^{107}\text{Ag}{}^{109}\text{Ag}$ with $\text{Pd}\text{Ag}$ except for the data from FeS of Santa Clara. It is concluded that the excess ¹⁰⁷Ag is the result of decay of ¹⁰⁷Pd, a nuclide that is extinct at present with an abundance of ${}^{107}\text{Pd}{}^{108}\text{Pd}$ of about 3 × 10^?5. The troilite in Grant exhibits normal ${}^{107}\text{Ag}{}^{109}\text{Ag}$ to within errors, a high Ag concentration and a low ratio of ${}^{108}\text{Pd}{}^{109}\text{Ag}$ ~0.17. Grant metal has ${}^{107}\text{Ag}{}^{109}\text{Ag}$ that is ~2% greater than normal and a high ratio of ${}^{108}\text{Pd}{}^{109}\text{Ag}$ ~ 10³. The data from Grant appear to represent a ¹⁰⁷Pd-¹⁰⁷Ag isochron and indicate that the cooling rate at elevated temperatures was sufficiently rapid to preserve substantial isotopic differences between metal and troilite. Troilite in Santa Clara was found to contain Ag with a very high ${}^{107}\text{Ag}{}^{109}\text{Ag}$ ratio (108% above normal), an Ag concentration only a factor of three above the metal and a high value of ${}^{108}\text{Pd}{}^{109}\text{Ag}$ ~1.3 × 10⁴. The troilite has a higher ${}^{107}\text{Ag}{}^{109}\text{Ag}$ than the metal. These data are not compatible with a simple model of in situ decay and subsequent local Ag redistribution between metal and troilite during cooling. These data suggest that Ag in Santa Clara and possibly other IVB meteorites is made up of almost pure ¹⁰⁷Ag produced from ¹⁰⁷Pd decay and ¹⁰⁹Ag produced by nuclear reactions with only a small amount of “normal” Ag. This indicates an intense energetic particle bombardment history in the early solar system (~10²⁰ p/m²) which occurred after the formation of small planetary bodies. We infer that a T-Tauri activity by the early sun contributed to some late stage “nucleosynthesis” and the heating of a dust cloud. In addition, implications on the early thermal evolution of iron meteorites are presented based on ¹⁰⁷Pd decay and models of the cooling history.     

Strontium isotopic composition of some brines from the Precambrian Shield of Canada

Twenty-four groundwater samples from seven operating mines at Sudbury, Yellow-knife and Thompson (Ontario, North West Territories and Manitoba, resp.), all from depths greater than 1 km and ranging in total dissolved solids (TDS) from 1900 to 250,000 mg l^?1, were measured for their ${}^{87}\text{Sr}{}^{86}\text{Ar}$ values. Each geographic location gives a limited range in values and each location is distinct from the others. This is interpreted as the result of extensive water-rock interaction on a local scale. For most of the time, these brines were isolated and only recently have been exposed to surface water as a result of the mining operations. The extent of the isolation is shown by the contrasting isotopic values of two “pockets” of water (0.711 vs. 0.716) located on opposite sides of the same fault system on the North Range at Sudbury. The exchange at all sites probably has continued until the present, as indicated by the close agreement between water and present-day${}^{87}\text{Sr}{}^{86}\text{Sr}$ whole-rock values. If so, it suggests that there is no single age for such brines, but it may be possible to date stages in the water's evolution by determining the age of secondary minerals that equilibrated with the water.     

A strontium isotopic study of Smackover brines and associated solids,southern Arkansas

The isotopic composition of Sr has been measured in brine samples from the Upper Jurassic Smackover Formation in southern Arkansas; ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios range from 0.7071 to 0.7101. With one exception, the 32 Smackover brines contain Sr which is significantly more radiogenic than the Sr in Late Jurassic sea water, indicating sizable Sr contributions from detrital sources. Isotopic analyses of core samples from rock units associated with the brines and regional stratigraphic relationships suggest that the radiogenic Sr was released from detrital minerals in Bossier shale to interstitial fluids expelled from the underlying Louann Salt in the North Louisiana salt basin. These fluids migrated through the Bossier Formation updip to the South Arkansas shelf, where they entered the upper Smackover carbonate grainstone. The radiogenic fluids mixed with Sr-rich interstitial marine waters that had the isotopic composition of Late Jurassic sea water; mixing in variable proportions resulted in the random distribution pattern of variable ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios that is observed in Smackover brines within the 5000 km² study area. Isotopic analyses of nonskeletal carbonate grains and coexisting coarse calcspar cement from the upper Smackover grainstone imply that the grains were diagenetically stabilized in the presence of interstitial marine waters, whereas the calcspar cement is a relatively late diagenetic phase precipitated after the arrival of radiogenic fluids.     

Isotopic abundances of water of crystallization of gypsum from the Miocene evaporite formation,Carpathian Foredeep,Poland

For sulfates of Miocene evaporites in the Carpathian Foredeep, the waters of crystallization of gypsum (w.c.g.) have $\text{δD = ?38 to ?113\%.}$ and $\text{δ}{}^{18}\text{O = 0 to ?11\%.}$ (SMOW). The $\text{δ}{}^{34}\text{S}$ and $\text{δ}{}^{18}\text{O}$ values of the sulfates are uniform and consistent with a marine origin. It is proposed that the original w.c.g. was equilibrated with marine water. Subsequently, it re-equilibrated towards very isotopically light water (δD ～ ?100%., δ¹⁸O ～ ?14%) during a glacial or postglacial period and is now trending towards current waters circulating through the deposits (δD ～ ?50%., δ¹⁸ ～ ?7%). The extent of reequilibration increased with decreasing crystal size.     

Correction of ground-water chemistry and carbon isotopic composition for effects of CO2 outgassing

Direct measurements on water samples from several CO₂-charged warm springs are significantly higher than values calculated from field pH and alkalinity (and other constituents). In addition, calcite saturation indices calculated from field pH and solution composition indicated supersaturation in samples which, on the basis of hydrogeologic concepts, should be near saturation or undersaturated. We attribute these discrepancies to uncertainties in field pH, resulting from CO₂ outgassing during pH measurement. Because samples for direct measurement can be taken with minimal disturbance to the water chemistry, we have used the measured to back calculate an estimate of the field pH and the carbon isotopic composition of the water before outgassing. By reconstructing water chemistry in this way, we find generally consistent grouping of $\text{δ}{}^{13}\text{C}$, pH, and degree of calcite saturation in samples taken from the same source at different times, an observation which we expect based on our understanding of the hydrogeology and geochemistry of the ground-water systems. This suggests that for very careful geochemical work, particularly on ground-waters much above ambient temperature, measurements may provide more information on the system and a better estimate of its state of saturation with respect to carbonate minerals than can field measurements of pH.     

The isotopic composition of silver and lead in two iron meteorites: Cape York and Grant

Silver in the metal phases of Cape York (IIIA) and Grant (IIIB) has been determined after an extensive surface cleaning process. The ${}^{107}\text{Ag}{}^{109}\text{Ag}$ was found to be enriched over that found in terrestrial Ag by ~7%. to 19%., demonstrating the presence of excess ¹⁰⁷Ag (¹⁰⁷Ag¹) in this class of meteorites. An effort was made to find schreibersite with a distinctive ¹⁰⁸Pd/¹⁰⁹Ag ratio in order to establish a three-point isochron, but the results are not markedly different from those obtained for the bulk metal. The Ag isotopic ratio of sulfides from the same meteorites were nearly normal in composition. These results demonstrate correlations of ${}^{107}\text{Ag}{}^{109}\text{Ag}$ with ${}^{108}\text{Pd}{}^{109}\text{Ag}$ between coexisting phases of two iron meteorites that are associated with planetary differentiation processes. The ratios ${}^{107}\text{Ag}{}^1{}^{108}\text{Pd}$ were found to be 1.7 × 10^?5 and 1.2 × 10^?5 for Cape York and Grant, respectively. These observations are in support of the widespread presence of ¹⁰⁷Pd in the early solar system. The difference in isotopic composition between metal and sulfide phases demonstrates that silver diffusion was small (over 6.5 × 10⁶ y) indicating a cooling rate much greater than 150°C/my for meteorites which have been attributed to small planetary cores. Uranium determinations were carried out on the metal phases and concentrations of ~ $\text{1 × 10}{}^{12}$ g U/g and 2 × 10^?10g U/g were found for Cape York and Grant, respectively. The Pb in these meteorites was determined using the improved cleaning procedures and chemical separations with low blank levels. The results confirm the presence of variable proportions of radiogenic Pb in both the metal and sulfide phases of iron meteorites. No simple explanation for the presence of radiogenic lead is apparent; while terrestrial contamination may appear to be the obvious explanation, it is possible that this effect could result from relatively recent metamorphism in the meteorite parent body.     

Total individual ion activity coefficients of calcium and carbonate in seawater at 25°C and 35%. salinity,and implications to the agreement between apparent and thermodynamic constants of calcite and aragonite

We have calculated the total individual ion activity coefficients of carbonate and calcium, and , in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of and are $\text{0.038 ± 0.002}$ and $\text{0.173 ± 0.010}$, respectively. These values of and are independent of liquid junction errors and internally consistent with the value . By defining and on a common scale (), the product is independent of the assigned value of and may be determined directly from thermodynamic measurements in seawater. Using the value and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of stable Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978, Deep-Sea Research25, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data.     

Aragonite from deep sea ultramafic rocks

Aragonite mineralization was observed in serpentinized peridotites from the Romanche and Vema Fracture Zones in the Atlantic and the Owen Fracture Zone in the Indian Ocean, either in veins or as radial aggregates in cavities within the serpentinites. Evidence of incipient dissolution of the aragonite crystals was observed in one case. The aragonites tend to have lower Mg content (< 0.03%) and higher Sr content (> 0.95%) relative to other marine aragonites. Their ${}^{18}\text{O}{}^{16}\text{O}$, ${}^{13}\text{C}{}^{12}\text{C}$ and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ isotopic ratios suggest the aragonite was deposited at ocean floor temperatures from solutions derived from sea water circulating in fissures and fractures within the ultramafic rocks. The ${}^{18}\text{O}{}^{16}\text{O}$ ratios of the serpentines indicate serpentinization occurred at higher temperatures, probably deeper in the crust. Low-T reactions between circulating seawater and Mg-silicates (primarily serpentine and pyroxenes) caused high pH and enrichment of Mg and Ca in the solution, conditions favoring carbonate precipitation. Aragonite was formed rather than calcite presumably because the high Mg²⁺ concentration in the solution inhibited calcite precipitation. The high Sr content of the aragonites is probably related, at least in part, to their low temperature of formation. Opaque mineral grains containing over 8% NiO and over 40% MnO were observed concentrated along the margins of some of the aragonite veins, suggesting that Ni is one of the elements mobilized during reactions between ultramafic rocks and circulating seawater.     

Source rock-crude oil correlation by isotopic type-curves

An isotopic type-curve has been defined based on the ${}^{13}\text{C}{}^{12}\text{C}$ ratios of the saturated, aromatic, heterocomponent (NOSs), and asphaltene fractions of crude oils. These fractions show ¹³C enrichments with increasing polarity or polarizability. This systematic pattern can be used to estimate the ${}^{13}\text{C}{}^{12}\text{C}$ ratio of the kerogen from which the oil had been generated. Genetically associated source rock oil pairs have been used to show that the difference between the measured and the estimated δ-values of kerogen is about ?0.5%., and between the δ-values of the kerogen and the asphaltene fraction is approximately +0.6%.     

Sm-Nd in marine carbonates and phosphates: Implications for Nd isotopes in seawater and crustal ages

This study explores the possibility of establishing Nd isotopic variations in seawater over geologic time. Calcite, aragonite and apatite are examined as possible phases recording seawater values of ?_Nd. Modern, biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have Nd concentrations of from 0.2 to 70 ppb, showing that primary marine CaCO₃ contains little REE and that Nd/Ca is not greatly enhanced relative to seawater during carbonate precipitation. Very young marine limestone and dolomite containing no continental detritus have ~200 ppb Nd. All the carbonates are LREE enriched ($\text{?0.16 ≤f}{}^{\mathrm{<mtext>Sm</mtext><mtext>Nd</mtext>}}\text{≤?0.45}$). Modern and very young Atlantic and Pacific carbonates have ?_Nd in the range of shallow Atlantic and Pacific seawater respectively, implying that they derive their REE from local seawater. The Nd in well preserved carbonate fossils is ≤4 × 10⁴ ppb, much greater than in their modern counterparts but like the high values found for carbonates in other studies. We believe the high REE contents (at the 500 ppb level) in some detritusfree carbonates are due to REE-rich Fe-hydroxide in/on the carbonate. In favorable cases, such material may record seawater ?_Nd values, however introduction of extraneous REE may obscure the original isotopic composition of pure CaCO₃ because of its very low intrinsic primary REE abundance.Modern biogenic apatite is also shown to have very low REE content (<150 ppb Nd) but appears to quickly scavenge REE from seawater. Inorganically precipitated apatite from phosphorites has high concentrations of seawater-derived REE. Young phosphorite apatite from the Atlantic and Pacific oceans has ?_Nd in the range of the seawater from these oceans. Older apatite samples of similar age from different localities bordering common oceans record similar values of ?_Nd(T). Sedimentary apatite has ?_Sr(T) values in good agreement with the curves for ${}^{87}\text{Sr}{}^{86}\text{Sr}$ of seawater as a function of time. Individual conodonts from a single formation yield the same ?_Sr(T) and ?_Nd(T). Other workers have shown that sedimentary apatite preserves seawater REE patterns. These characteristics suggest that sedimentary apatite can be used to determine ?_Nd(T) in ancient seawater. The seawater values so inferred range between ?1.7 and ?8.9 over the last 700 my and lie in the range of modern seawater, showing no evidence for drastic changes. High values of seawater ?_Nd(T) in the Triassic and latest Precambrian may correlate with the breakup of large continental landmasses. The initial ?_Nd(T) =?15.0 of a 2 AE old phosphorite implies the presence of ~ 1.5 AE old continental crust at 2 AE ago. The approach outlined here can be used to constrain the age of the exposed crust as a function of time.     

Strontium isotopic composition of several oilfield brines from Kansas and Colorado

The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of several oilfield brines associated with Paleozoic dolomites, cherty dolomites and sandstones from Kansas and Colorado range from 0.7113 to 0.7341. Two brines in the Mississippian dolomites from Colorado were found to contain the most radiogenic strontium. The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of brines in a small oilfield in eastern Kansas are constant, and the ratios may suggest that in this field there may be only one oil pool. The isotopic composition of strontium in subsurface waters could be useful in determining hydrologic continuity among reservoirs and for obtaining additional information on the origin and migration of these fluids.