Trapped solar wind noble gases and exposure age of Luna 16 lunar fines

He, Ne, Ar, Kr and Xe concentrations and isotopic abundances were measured in three bulk grain size fractions prepared from sample L-16-19, No. 120 (C level, 20–22 cm depth) returned by the Luna 16 mission. The expected anticorrelation between the concentrations of trapped solar wind noble gases and grain size is observed. Elemental abundances of solar wind trapped noble gases are similar to those previously found in corresponding grain size fractions of the Apollo 11 and 12 fines. The trapped ratio ${}^4\text{He}{}^{20}\text{Ne}$ varies in the soils from different lunar maria due to diffusion losses. A rough correlation of ${}^4\text{He}{}^{20}\text{Ne}$ with the proportion of ilmenite in these samples is apparent. The elemental and isotopic ratios of the surface correlated noble gases in Luna 16 resemble those previously found in Apollo fines. Based on ²¹Ne, ⁷⁸Kr and ¹²⁶Xe a cosmic ray exposure age of 360 my was determined. This age is similar to those obtained for the soils from other lunar maria.     

The carbon and nitrogen isotopic composition of ureilites: Implications for their genesis

Fourteen ureilites were analyzed for stable C isotopic composition using stepped combustion. The δ¹³C values over the temperature range 500 to 1000°C are fairly constant for any particular meteorite although there are differences between samples. The similarity in combustion temperatures of pure diamond (600–1000δC) and pure graphite (600–800°C) makes it difficult to ascertain the relative proportions of either component within each sample. However, the constant δ¹³C values observed over the range 500 to 1000°C strongly suggests that ureilite diamond and graphite have the same isotopic composition. This would seem to confirm that the diamond in ureilites formed from the graphite during a process, presumably an impact event, which did not fractionate C isotopes.There is a variation in C isotopic composition of graphite/diamond intergrowths among ureilites, which is not continuous—the samples fall into two groups, with δ¹³C values clustered around ?10%. and ?2%. PDB. These groups are also distinguishable on the basis of the Fe content of their olivines, which may reflect the existence of more than one ureilite parent body. The brecciated ureilite North Haig has a δ¹³C value of ?6.5%. and it is thus possible that this sample contains components from mixed parent materials.Nitrogen abundance and stable isotope measurements were made on five samples using stepped combustion analysis. Nitrogen concentrations range from 25 to 150 ppm and $\text{C}\text{N}$ ratios are substantially less than for carbonaceous chondrites. Variation in N isotopic composition is wide and there is evidence of different ratios in diamond/graphite, silicate and metal.     

Hydrogen and carbon isotopes of petroleum and related organic matter

$\text{D}\text{H}$ and ${}^{13}\text{C}{}^{12}\text{C}$ ratios were measured for 114 petroleum samples and for several samples of related organic matter. δD of crude oil ranges from ?85 to ?181‰, except for one distillate (?250‰) from the Kenai gas field; δ¹³C of crude oil ranges from ?23.3 to ?32.5‰, Variation in δD and δ¹³C values of compound-grouped fractions of a crude oil is small, 3 and 1.1%., respectively, and the difference in δD and δ¹³C between oil and coeval wax is slight. Gas fractions are 53–70 and 22.6–23.2‰ depleted in D and ¹³C, respectively, relative to the coexisting oil fractions.The δD and δ¹³C values of the crude oils appear to be largely determined by the isotopic compositions of their organic precursors. The contribution of terrestrial organic debris to the organic precursors of most marine crude oils may be significant.     

Petrography and stable isotope ratios from Archaean stromatolites,Mushandike Formation,Zimbabwe

The Mushandike Sanctuary, near Masvingo (Fort Victoria), Zimbabwe, contains well-preserved, but metamorphosed stromatolitic limestones of Archaean age. Despite the metamorphism, textural preservation is excellent to a scale as fine as c. 100–200μ. Cores recovered from the stromatolites have $\text{δ}{}^{18}\text{O = ?15‰}$ (PDB), approximately, and δ¹³C = 0.0 to 0.5‰ (PDB), in less weathered samples. The results are consistent with a metamorphic history involving volatile loss at 200°C or less, from an original source rock which may have been isotopically similar to the Cheshire stromatolites, Belingwe.     

The geochemistry of the stable isotopes of silicon

One hundred thirty two new measurements of the relative abundances of the stable isotopes of silicon in terrestrial materials are presented. The total variation of ^δ30Si found is 6.2%., centered on the mean of terrestrial mafic and ultramafic igneous rocks, δ³⁰Si = ?0.4%.. Igneous rocks show limited (1.1%.) variation; coexisting minerals exhibit small, systematic silicon isotopic fractionations that are roughly $\text{1}\text{3}$ the magnitude of concomitant oxygen isotopic fractionations at 1150°C. In both igneous minerals and rocks, δ³⁰Si shows a positive correlation with silicon content, as does δ¹⁸O. Opal from both sponge spicules and sinters is light, with $\text{}\text{?}\text{gd}{}^{30}\text{Si}\text{= ?2.3}$ and ?1.4%., respectively. Large ^δ30Si values of both positive and negative sign are reported for the first time from clay minerals (?2.3 to +1.8%.), opaline phytoliths (?1.4 to +2.8%.), and authigenic quartz (+ 1.4%.). All highly fractionated samples were precipitated from solution at low temperatures; however, aqueous silicon is not measurably fractionated relative to quartz at equilibrium. A kinetic isotope fractionation of ≈3.5%. is postulated to occur during the low temperature precipitation of opal and, possibly, poorly ordered phyllosilicates, with the silicate phase being enriched in ²⁸Si. This fractionation, coupled with a Rayleigh precipitation model, is capable of explaining most non-magmatic δ³⁰Si variations. Chert ^δ30Si values are largely inherited, but the primary opal ^δ30Si values can be modified by isotopic equilibration of silicate silicon and dissolved silicon during the transformation of opal into quartz.     

Annual periodicity of the 18O16O and 13C12C ratios in the coral Montastrea annularis

The isotopic ratios ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ show an annual periodicity in the coral Montastrea annularis from Bermuda, Jamaica and Barbados. The abundances of ¹⁸O and ¹³C are positively correlated in the Jamaica and Barbados samples, but inversely related in the Bermuda sample. Annual high density growth bands are formed during the season of warmest water temperature at all 3 sites and are enriched in ¹⁶O. M. Annularis has a constant displacement from oxygen isotopic equilibrium and accurately records seasonal temperature variations via the temperature-dependent aragonite-water fractionation factor. Light intensity, through the activity of the coral's endosymbiotic algae, regulates the depth-dependent and seasonal variations in the skeletal carbon isotopic composition.     

Solar-system abundances of the elements

A new abundance table has been compiled, based on a critical review of all C1 chondrite analyses up to mid-1982. Where C1 data were inaccurate or lacking, data for other meteorite classes were used, but with allowance for fractionation among classes. In a number of cases, interelement ratios from meteorites or lunar and terrestrial rocks as well as solar wind were used to check and constrain abundances. A few elements were interpolated (Ar, Kr, Xe, Hg) or estimated from astronomical data (H, C, N, O, He, Ne).For most elements, the new abundances differ by less than 20% from those of Cameron (1982a). In 14 cases, the change is between 20 and 50% (He, Ne, Be, Br, Nb, Te, I, Xe, La, Gd, Tb, Yb, Ta and Pb) and in 5 others, it exceeds 50% (B, P, Mo, W, Hg). Some important interelement ratios ($\text{Na}\text{K}$, $\text{Se}\text{Te}$, $\text{Rb}\text{Sr}$, $\text{Kr}\text{Xe}$, $\text{La}\text{W}$, $\text{Th}\text{U}$, $\text{Pb}\text{U}$, etc.) are significantly affected by these changes.Three tests were carried out, to see how closely C1 chondrites approximate primordial solar system abundances. (1) A plot of solar vs Cl abundances shows only 7 discrepancies by more than twice the nominal error of the solar abundance: Ga, Ge, Nb, Ag, Lu, W and Os. Most or all apparently reflect errors in the solar data or f-values. (2) The major cosmochemical groups (refractories, siderophiles, volatiles, etc.) show no significant fractionation between the Sun and C1's, except possibly for a slight enrichment of volatiles in Cl's. (3) Abundances of odd-A nuclides between A = 65 and 209 show an almost perfectly smooth trend, with elemental abundances conforming to the slope defined by isotopic abundances. There is no evidence for systematic fractionation of the major cosmochemical groups from each other. Small irregularities (10–15%) show up in the Ag-Cd-In and Sm-Eu regions; the former may be due to a ~ 15% error in the Ag abundance and the latter, to a 10–20% fractionation of Eu during condensation, to contamination of C1 chondrites with interplanetary dust during regolith exposure, or to a change from s-process to r-process dominance.It appears that the new set of abundances is accurate to at least 10%, as irregularities of 5–10% are readily detectable. Accordingly, Cl chondrites seem to match primordial solar-system matter to ? 10%, with only four exceptions. Br and I are definitely and B is possibly fractionated by hydrothermal alteration, whereas Eu seems to be enriched by nebular condensation or regolith contamination.     

Total nitrogen in lunar soils,breccias and rocks

The total nitrogen contents of a number of lunar samples from Apollo 16 and 17 missions are reported. Solar wind is the main source for the observed excess nitrogen in most fines. Total nitrogen in the soils is found to be proportional to the solar wind rare gases Ar³⁶ and Xe¹³². Linear correlations are also noted between the agglutinate contents of the soils and their carbon and nitrogen contents. Seventeen soils (Apollo 15, 16 and 17) have been sieved and nitrogen has been measured in various grain size fractions. An inverse correlation between the mean grain diameter and the nitrogen contents is seen, showing that a large fraction of the solar wind nitrogen is surface correlated. An apparent volume component, due to the presence of agglutinates, is found in most soils.     

Carbon and nitrogen pools in Padanian soils (Italy): Origin and dynamics of soil organic matter

Carbon and nitrogen elemental (C-N, wt%) and isotopic (δ¹³C-δ¹⁵N, ‰) investigation has been carried out on alluvial and deltaic soils from the Padanian plain (northern Italy), an area interested by intensive agricultural activities, to refine previous inferences on depositional facies, pedogenetic processes and anthropogenic influences. Soil analysis, carried out by EA-IRMS, have been focused on inorganic and organic fractions properly speciated by a thermally-based method, whereas further insights on the organic matter constituents have been obtained by sequential fractionation. The bulk EA-IRMS analyses reveal a remarkable compositional heterogeneity of the investigated soils (TC 0.89 to 11.93?wt%, TN 0.01 to 0.78?wt%, δ¹³C_TC -1.2 to -28.2‰, δ¹⁵N -1.2 to 10.0‰) that has to be explained as an integration between inorganic and organic pools. The latter have been subdivided in Non-Extractable Organic Matter (NEOM, δ¹³C -16.3 to -28.6‰) and in extractable fractions as Fulvic (FA, δ¹³C -24.7 to -27.5‰, δ¹⁵N 0.6 to 5.7‰) and Humic (HA, δ¹³C -24.6 to -27.0‰, δ¹⁵N 1.0 to 9.7‰) Acids, which have been used to infer soil dynamics and Soil Organic Matter (SOM) stability processes. Results indicate that SOM at depth of 100?cm was generally affected by microbial reworking, with the exception of clayey and peaty deposits in which biological activity seems inhibited. Peaty and clayey soils display an organic fraction loss of ca. 20% toward the surface, suggesting deterioration possibly induced by intensive agricultural activities. These latter may be the cause of the ubiquitous losses of organic fraction throughout the investigated area over the last seventy years, evaluated by the comparison with historical data on corresponding topsoils. The obtained insights are very important because these soils are carbon (and nitrogen) sinks that are vulnerable and can be degraded, loosing agricultural productivity and potentially contributing to greenhouse gases fluxes.     

Carbon,nitrogen and sulfur in lunar fines 15012 and 15013: abundances,distributions and isotopic compositions

Lunar fines 15012,16 and 15013,3 were analyzed by stepwise pyrolysis and acid hydrolysis as well as complete combustion in oxygen to determine carbon, nitrogen and sulfur. In addition, hydrogen was analysed during pyrolysis as well as during hydrolysis. In the former case, it was released by mineral grains to which it was adsorbed or from cavities within which it had been captured. Hydrogen released during hydrolysis had largely resulted from dissolution of metallic iron.By comparison of the distribution frequencies of C, N, S, H₂ and Fe with ⁴He, considered to have arisen from solar wind contribution, it is concluded that nitrogen and hydrogen have largely a solar origin. Carbon has a significant solar contribution, and metallic iron may have resulted from solar wind interaction with ferrous minerals on the lunar surface. Sulfur probably has a predominantly lunar origin. There is no direct evidence for meteoritic contribution to these samples.Solar wind interaction also has a marked effect on the stable isotope distribution of ¹³C/¹²C, ¹⁵N/¹⁴N, and ³⁴S/³²S. In all cases, the heavy isotope was most enriched in the smallest grain-size fraction. During stepwise pyrolysis, CH₄, CO₂, CO and N₂ were obtained at different temperatures and displayed different isotopic ratios. The carbon fraction most enriched in ¹³C, was CH₄ liberated at 600–800°C with $\text{δ}{}^{13}\text{C = +45.7\%.}$. Between 400 and 600°C, N₂ was liberated with (δ¹⁵N ≈ +119% and at 600–800°C, N₂ was liberated with $\text{δ}{}^{15}\text{N = +75\%.}$ relative to terrestrial atmospheric nitrogen.     

Isotopic constraints on growth conditions of multiphase calcite–pyrite–barite concretions in Carboniferous mudstones

Carbonate concretions in the Lower Carboniferous Caton Shale Formation contain diagenetic pyrite, calcite and barite in the concretion matrix or in different generations of septarian fissures. Pyrite was formed by sulphate reduction throughout the sediment before concretionary growth, then continued to form mainly in the concretion centres. The septarian calcites show a continuous isotopic trend from δ¹³C=?28·7‰ PDB and δ¹⁸O=?1·6‰ PDB through to δ¹³C=?6·9‰ PDB and δ¹⁸O=?14·6‰ PDB. This trend arises from (1) a carbonate source initially from sulphate reduction, to which was added increasing contributions of methanogenic carbonate; and (2) burial/temperature effects or the addition of isotopically light oxygen from meteoric water. The concretionary matrix carbonates must have at least partially predated the earliest septarian cements, and thus used the same carbonate sources. Consequently, their isotopic composition (δ¹³C=?12·0 to ?10·1‰ PDB and δ¹⁸O=?5·7 to ?5·6‰ PDB) can only result from mixing a carbonate cement derived from sulphate reduction with cements containing increasing proportions of carbonate from methanogenesis and, directly or indirectly, also from skeletal carbonate. Concretionary growth was therefore pervasive, with cements being added progressively throughout the concretion body during growth. The concretions contain barite in the concretion matrix and in septarian fissures. Barite in the earlier matrix phase has an isotopic composition (δ³⁴S=+24·8‰ CDT and δ¹⁸O=+16·4‰ SMOW), indicating formation from near‐surface, sulphate‐depleted porewaters. Barites in the later septarian phase have unusual isotopic compositions (δ³⁴S=+6 to +11‰ CDT and δ¹⁸O=+8 to +11‰ SMOW), which require the late addition of isotopically light sulphate to the porewaters, either from anoxic sulphide oxidation (using ferric iron) or from sulphate dissolved in meteoric water. Carbon isotope and biomarker data indicate that oil trapped within septarian fissures was derived from the maturation of kerogen in the enclosing sediments.     

Isotopic fractionation between coexisting organic carbon—carbonate pairs in Precambrian sediments

δ¹³C_org and δ¹³C_carb values of 58 coexisting organic carbon-carbonate pairs covering the whole Precambrian have yielded means of ?24.7 ± 6.0%. [PDB] and +0.9 ± 2.7%. [PDB], respectively. Accordingly, isotopic fractionation between inorganic and organic carbon in Precambrian sediments is about the same as in geologically younger rocks (Δδ ? 25%.), a slight increase displayed by the Early Precambrian pairs (Δδ ? 28%.) being probably biassed by an over-representation in this age group of samples from one single locality (nevertheless, this value still lies within the range permitted for a possible deviation). It is reasonable to assume, therefore, that the overall isotope fractionation factor governing biological fixation of inorganic carbon has been virtually constant since some 3.3 × 10⁹ yr ago.     

Controls, variation, and a record of climate change in detailed stable isotope record in a single bryozoan skeleton

The long-lived (about 20 yr) bryozoan Adeonellopsis sp. from Doubtful Sound, New Zealand, precipitates aragonite in isotopic equilibrium with seawater, exerting no metabolic or kinetic effects. Oxygen isotope ratios (δ¹⁸O) in 61 subsamples (along three branches of a single unaltered colony) range from −0.09 to +0.68‰ PDB (mean = +0.36‰ PDB). Carbon isotope ratios (δ¹³C) range from +0.84 to +2.18‰ PDB (mean = +1.69‰ PDB). Typical of cool-water carbonates, δ¹⁸O-derived water temperatures range from 14.2 to 17.5 °C. Adeonellopsis has a minimum temperature growth threshold of 14 °C, recording only a partial record of environmental variation. By correlating seawater temperatures derived from δ¹⁸O with the Southern Oscillation Index, however, we were able to detect major events such as the 1983 El Niño. Interannual climatic variation can be recorded in skeletal carbonate isotopes. The range of within-colony isotopic variability found in this study (0.77‰ in δ¹⁸O and 1.34 in δ¹³C) means that among-colony variation must be treated cautiously. Temperate bryozoan isotopes have been tested in less than 2% of described extant species — this highly variable phylum is not yet fully understood.     

Light element geochemistry of the Apollo 12 site

Analytical techniques of improved sensitivity have revealed details of the concentrations and isotopic compositions of light elements for a comprehensive suite of samples from the Apollo 12 regolith. These samples show a wide spread in maturity, although maximum contents observed for solar wind elements are less than observed at other sites, possibly reflecting relative recency of craters at the Apollo 12 site. Isotopic composition of nitrogen is consistent with the idea that ¹⁵N/¹⁴N in the solar wind has increased with time, at least a major part of this increase having occurred in the past 3.1 Gyr. Sulfur isotope systematics support a model in which sulfur is both added to the regolith, by meteoritic influx and lost, by an isotopically selective process. Most soils from this site are heavily contaminated with terrestrial carbon.     

The carbon isotopic composition of diamonds: relationship to diamond shape,color, occurrence and vapor composition

Three hundred and thirty new ¹³C analyses of diamonds are presented, indicating, in conjunction with earlier published work, a range of about 30%. in the carbon isotopic composition of diamonds. The frequency distribution of diamond δ¹³C analyses shows a very pronounced mode at ?5 to ?6%.vs PDB, a large negative skewness, and a sharp boundary at about ?1%.. Analyses of diamonds from the Premier and Dan Carl mines, South Africa, demonstrate that: (1) differences in ¹³C content that can be related to diamond color and shape are smaller than 1%.; (2) the mean ¹³C content of kimberlite carbonates is 1–2%. lower than that of associated diamonds; (3) significant differences in ¹³C content exist between the mean isotopic compositions of diamonds from these two pipes; (4) the variability in δ¹³C differs from one mine to the other.Computations were carried out evaluating the effect on the ¹³C content of diamonds of: (i) various precipitation processes; (ii) the abundance of the species H₂, H₂O, CH₄, CO, CO₂ and O₂ in the vapor; (iii) the initial isotopic composition variability of the source carbon; (iv) variations of the carbon isotope effects resulting from changes in pressure and temperature and (v) reservoir effects (Rayleigh fractionation). Fifty-eight genetic models were investigated for compatibility with the ¹³C distribution in diamonds and associated carbonate. The modeling does not permit an unambiguous answer to the question whether or not a vapor participated in diamond formation, although the presence of methane during diamond formation is compatible with the carbon isotopic composition data, possible oxygen fugacities in the mantle and with the composition of gases liberated from diamonds. In all probability carbon isotope effects in the diamond formation process were small, and the very large range in δ¹³C observed was inherited from the source carbon.     

Solar and cosmogenic argon in dated lunar impact spherules

We have studied lunar impact spherules from the Apollo 12 and Apollo 14 landing sites, examining the isotopic composition of argon released by stepwise heating. Elsewhere, we reported the formation ages of these spherules, determined by the ⁴⁰Ar/³⁹Ar isochron method. Here, we discuss solar and cosmogenic argon from the same spherules, separating these two components by correlating their partial releases with the releases of calcium-derived ³⁷Ar on a “cosmochron” diagram. We use the abundances of cosmogenic argon to derive a cosmic ray exposure age for each spherule, and demonstrate that single scoops of lunar soil contain spherules which have experienced very different histories of exposure and burial. The solar argon is seen to be separated into isotopically lighter and heavier fractions, which presumably were implanted to different depths in the spherules. The abundance of the isotopically heavy solar argon is too great to explain as a minor constituent of the solar particle flux, such as the suprathermal tail of the solar wind. The fact that the spherules have been individually dated allows us to look for possible variations in the solar wind as a function of time, over the history of the Solar System. However, the isotopic composition and fluence of solar argon preserved in the lunar spherules appear to be independent of formation age. We believe that most of the spherules are saturated with solar argon, having reached a condition in which implantation by the solar wind is offset by losses from solar-wind sputtering and diffusion.     

Etude pedogenetique et isotopique des neoformations de calcite dans un sol sur craie: Caracteristiques et origines

Cryoturbated facies are found at the boundary between soil horizons and Cretaceous chalk. Several types of secondary calcite appear in soil horizons: orange coloured and rounded (partially dissolved) nodules, deeply coloured angular aggregates, transparent isolated rhombs and polycrystalline nodules, needles. The carbon and oxygen isotope compositions of these calcites are correlated: δ¹³C = 4.9δ¹⁸O_PDB + 15.9End members of this correlation are the orange rounded nodules (δ¹³C ? + 8%., $\text{δ}{}^{18}\text{O ? ?1.5‰}$) and the transparent angular polycrystalline nodules (δ¹³C ? ?13; δ¹⁸O ? ?6).Partially dissolved nodules have formed under periglacial climatic conditions. Crystallisation would have occurred under the following (equilibrium) environmental conditions: δ¹⁸O_SMOW (soil solution) ?7, δ¹³C (gaseousCO₂) ? ?5.2, t ? ?2°C. Soil solution was enriched in ¹⁸O by evaporation and atmospheric CO₂ was enriched in ¹³C as compared to present day. Transparent polycrystalline nodules are compatible with present day environmental conditions: δ¹⁸O (soil solution) ranging from ?9 to ?4 and δ¹³C (soil CO₂) ranging from ?24.5 to ?23. These nodules crystallize between May and October at soil temperatures ranging from 10 to 25°C, from evaporated soil solutions. Angular coloured aggregates may form under present day winter conditions for temperatures between 0 and 10°C. However they may also result from present accretion of fragments of periglacial nodules.All recent secondary calcite results from CO₂ degassing and evaporation of soil solutions. Degassing is controlled by the gradient of CO₂ partial pressure within the soil profile. During winter this gradient is low and the resulting calcite precipitation is not significant. During summer a large difference in pCO₂ appears between the root zone and deep soil horizons. The degassing accounts for an increase of about 2‰ in δ¹³C of the total dissolved inorganic carbon and of the related solid carbonate. Evaporation is the main driving force for secondary calcite precipitation.     

Carbon and hydrogen isotope variation of plant biomarkers in a plant-soil system

Stable carbon (δ¹³C) and hydrogen (δD) isotopic compositions of n-alkanes, anteiso-alkanes, n-alkanoic acids, n-alkanols, phytol and sterols in raw leaves of Acer argutum and Acer carpinifolium, their fallen leaves, mold and soils from a natural Acer forest were measured in order to: (1) understand isotopic variation of the plant biomarkers in a plant-soil system and (2) evaluate which biomarker is the most effective recorder of soil vegetation. Long-chain (> C₂₄) n-alkanes, n-alkanoic acids and n-alkanols are gradually enriched in ¹³C up to 12.9‰ (average of 4.3‰) and depleted in D up to 94‰ (average of 55‰) from raw leaves to soils. However, anteiso-alkanes, phytol and sterols show little variation in both δ¹³C (< ± 1‰) and δD (< ± 2‰) from raw leaves to soils. These isotope signatures in a plant-soil system indicate that isoprenoid plant biomarkers such as sterols in soils faithfully preserve the isotopic compositions of dominant higher plants growing on the soils without a diagenetic effect upon the isotopic compositions. In contrast, long-chain n-alkyl molecules in soils undergo specific isotopic modification during biodegradation associated with early diagenesis and/or a significant contribution from heterotrophic reworking.     

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.