The contrasting geochemical behaviours of iodine and bromine in recent sediments from the Namibian shelf     

N.B. Price  S.E. Calvert 《Geochimica et cosmochimica acta》1977,41(12):1769-1775

The vertical distribution of iodine, bromine and organic carbon has been examined in sediment cores from a range of environments on the Namibian shelf. The relationship between Br and C org. is linear, and that between I and C org. is variable, for all surface sediments; I/C org. ratios show a decrease of about one order of magnitude between the outer shelf oxidising sediments ($\text{250 × 10}{}^{\mathrm{?4}}$) and the organic-rich inner shelf sediments ($\text{20 × 10}{}^{\mathrm{?4}}$). The contrasting behaviour of the halogens in surface sediments is explained by differences in the amount of halogen absorbed by living organisms within the euphotic zone and on seston on the seabed. It is suggested that sorption by seston occurs only in oxidising sediment where free O₂ is available. Hence, iodine is sorbed by seston in the outer shelf environment, but is not sorbed by the reducing sediments of the inner shelf. Here the iodine in the sediment represents only that taken up by plankton. On the outer shelf, 50–80% of the total iodine in the organic matter is sorbed by seston. The principal site of Br uptake is not known.The distribution of C org. in subsurface sediments broadly reflects that found at the surface, although there is a slight decrease with depth in the outer shelf cores due to dilution by terrigenous materials. In the inner shelf cores, there is no change in the relationship of iodine and bromine to organic carbon at depth. Those from the mid shelf, and especially the outer shelf, on the other hand, show decreases in both I/C org. and Br/C org. ratios, reaching values at about 70 cm depth that are similar to those in surface reduced sediments from the inner shelf. Over this depth interval I/C org. ratios decrease by a factor of five while Br/C org. ratios show a two fold decrease. These changes in the ratios at depth imply that diagenesis within the reducing cores is negligible compared with that of oxidised sediments. The implications of diagenesis with regard to halogen recycling in sediments are briefly discussed.  相似文献   

A review of various factors influencing the stable carbon isotope ratio of organic lake sediments by the change from glacial to post-glacial environmental conditions     

Sören Håkansson 《Quaternary Science Reviews》1985,4(2):135-146

A survey is made of various factors influencing the ${}^{13}\text{C}{}^{12}\text{C}$ ratio of the organic component in lake sediments, focusing on the behaviour at the change from glacial to post-glacial environmental conditions.Increase in the ¹³C content of the organic sediment is caused by increase in temperature and the corresponding decrease of the supply of molecular CO₂ in the water of the lakes. An increase in the rate of organic production in the lakes may also, perhaps, cause a corresponding ¹³C increase. An increase of the fermentation of organic mud in the lakes may also have an effect in the same direction.Decrease in the ¹³C content of the organic sediment is caused by the change of the relative amounts of production of plankton and submersed macrophytes in the lakes from mainly submersed macrophytes to mainly plankton. A decrease towards almost complete absence of bicarbonate and CO₂ originating from carbonate rocks will also lead to a ¹³C decrease in the organic sediments. The same effect has the change of the terrestrial vegetation cover from almost complete absence to complete cover. A possible decrease of the ¹³C content in the atmospheric CO₂ has an effect in the same direction.  相似文献   

Biogenic hydrocarbon gases and sulfate reduction in the Orca Basin brine     

Denis A Wiesenburg  James M Brooks  Bernie B Bernard 《Geochimica et cosmochimica acta》1985,49(10):2069-2080

The composition of light hydrocarbon gases in the Orca Basin, an anoxic, hypersaline intraslope depression on the continental slope of the northern Gulf of Mexico, indicates that both methane and ethane are biogenic in nature with a $\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{)}$ ratio of 730 and a δ¹³C of methane of ?73%. relative to the PDB standard. The concentrations of methane (750 mM) and ethane (1300 mM) in the Orca Basin brine are higher than any other marine anoxic basin. These high levels result not from high rates of productivity, but from the long residence time of the brine in the basin, due to its high stability toward mixing with overlying seawater ($\text{Δσ}{}_1\text{ΔZ}\text{=}\text{3.2}\text{m}$). Both methane and ethane show well mixed distributions in the brine. These distributions probably result from convective mixing of the isohaline brine pool due to normal heat flow from the basin sediments. Methane and ethane maxima above the pycnocline at the brine/seawater interface reflect in situ production and/or consumption in the aerobic water column. Concurrent maxima in suspended particulate material distributions in this region suggest methane may be produced there in anaerobic microenvironments associated with the suspended matter. Reduced rates of anaerobic decomposition (including sulfate reduction) in the brine sediments are inferred from preserved Sargassum fronds in the sediments, vertical sulfate profiles in most cores, and the sediment organic carbon content which is two to three times higher in sediments below the high salinity brine than in the normal Gulf sediments nearby.  相似文献   

Thorium and radium isotopic relationships in manganese nodules and sediments at MANOP Site S     

Willard S Moore 《Geochimica et cosmochimica acta》1984,48(5):987-992

Relationships among Th and Ra isotopes in nodule, sediment and water phases at MANOP Site S establish the most likely source for Th in the nodules, the frequency of nodule turning, and the similarity of micro and macro nodules. Manganese nodules and bottom waters have ${}^{230}\text{Th}{}^{232}\text{Th}$ activity ratios considerably higher than other phases at this site suggesting that sea water is the likely source of Th for the nodules. Similar ${}^{230}\text{Th}{}^{232}\text{Th}$ activity ratios in nodule tops and bottoms and in certain cases departure from expected ${}^{226}\text{Ra}{}^{230}\text{Th}$ activity ratios in nodule tops and bottoms indicate that the nodules rotate every one to ten thousand years. The micro nodules have diffusion coefficients of Ra similar to macro nodule bottoms. I suggest that they may act as a carrier phase for transporting metals through oxic sediments to nodules.  相似文献   

The extent of oxygen isotope exchange between clay minerals and sea water     

Hsueh-Wen Yeh  Samuel M. Savin 《Geochimica et cosmochimica acta》1976,40(7):743-748

The extent of oxygen isotopic exchange between detrital clay minerals and sea water was investigated by analyzing $\text{O}{}^{18}\text{O}{}^{16}$ ratios of separated fine-grained size fractions of deep-sea sediments from three North Pacific ocean cores. Isotopic results were interpreted according to models based on the assumption that the extent of isotopic exchange should increase with decreasing particle size and increasing time of exchange between the sediment and sea water. The data indicate that information concerning the provenance and mode of formation of detrital clay minerals can be obtained from the $\text{O}{}^{18}\text{O}{}^{16}$ ratios of the coarser-than-0.1 μm fraction of deep-sea sediments younger than several million years and the finer-than-0.1 μm fraction of deep-sea sediments younger than several tens of thousands of years. Furthermore, if the extent of chemical reaction between detrital clays and sea water is similar to the extent of oxygen isotopic exchange, such reaction may be important in regulating the chemistry of sea water.  相似文献   

Plutonium and americium in anoxic marine sediments: Evidence against remobitization     

R. Carpenter  T.M. Beasley 《Geochimica et cosmochimica acta》1981,45(10):1917-1930

^{239 + 240}Pu activities of 100–450dpm/kg are found down to 15–18 cm in anoxic Saanich Inlet sediments, with a subsurface maximum in undisturbed deposits. Integrated ^{239 + 240}Pu inventories which overlap delivery estimates are present both in two cores of anoxic sediments from Saanich Inlet and in one core of oxic sediments 65 km away in Dabob Bay, Washington. ${}^{241}\text{Am}{}^{\mathrm{239\; +\; 240}}\text{Pu}$ ratios in Saanich Inlet sediments overlap ratios in unfractionated midnorthern latitude fallout, in oxic sediments from the Washington continental shelf, and in anoxic sediments from two basins off southern California and Mexico. The ${}^{\mathrm{239\; +\; 240}}\text{Pu}{}^{137}\text{Cs}$ ratios in three intervals of Saanich Inlet sediments are also in agreement with ratios previously reported for oxic coastal marine sediments. The Pu inventories, the $\text{Am}\text{Pu}$ and $\text{Pu}\text{Cs}$ ratios, and the Saanich Inlet Dabob Bay comparison all argue that Pu is not rapidly remobilized in anoxic sediments.The subsurface ^{239 + 240}Pu activity maximum is not in agreement with the historical record of peak Pu fallout in 1963–1964 unless our ²¹⁰Pb-derived sedimentation rates are incorrectly high. However, they are in good agreement with previous ²¹⁰Pb and varve chronologies in Saanich Inlet, and also give reasonable dates for times when ^{239 + 240}Pu and SNAP-9A supplied ²³⁸Pu first appear in the sediments. We conclude they properly date the maximum in sedimentary ^{239 + 240}Pu activity at 1970–1973, and seek explanations for the 7–10yr time lag after peak fallout.^{239 + 240}Pu inventories in one core from the eastern basin of the Cariaco Trench and in two cores from Golfo Dulce. an anoxic basin off the Pacific coast of Costa Rica, are also in reasonable agreement with fallout delivery to these latitudes when excess ²¹⁰Pb inventories and fluxes are used to verify recovery of at least a major fraction of the most recently deposited sediments.  相似文献   

Light hydrocarbons in Red Sea brines and sediments     

Roger A. Burke  James M. Brooks  William M. Sackett 《Geochimica et cosmochimica acta》1981,45(5):627-634

Light hydrocarbon (C₁-C₃) concentrations in the water from four Red Sea brine basins (Atlantis II, Suakin, Nereus and Valdivia Deeps) and in sediment pore waters from two of these areas (Atlantis II and Suakin Deeps) are reported. The hydrocarbon gases in the Suakin Deep brine (T = ~ 25°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 85‰}$, $\text{CH}{}_4\text{=}\text{~ 71}\text{1}$) are apparently of biogenic origin as evidenced by $\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3$) ratios of ~ 1000. Methane concentrations (6–8 μl/l) in Suakin Deep sediments are nearly equal to those in the brine, suggesting sedimentary interstitial waters may be the source of the brine and associated methane.The Atlantis II Deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources. The upper brine (T = ~ 50°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 73‰}$, CH₄ = ~ 155 μl/l) gas seems to be of biogenic origin [$\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{) = ~1100}$], whereas the lower brine (T = ~ 61°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 155‰}$, CH₄ = ~ 120μl/l) gas is apparently of thermogenic origin [$\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{) = ~ 50}$]. The thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine, whereas the biogenic gas is produced in situ or at the seawater-brine interface. Methane concentrations in Atlantis II interstitial waters underlying the lower brine are about one half brine concentrations; this difference possibly reflects the known temporal variations of hydrothermal activity in the basin.  相似文献   

The geochemistry of fallout plutonium in the North Atlantic: II. 240Pu239Pu ratios and their significance     

《Geochimica et cosmochimica acta》1987,51(10):2623-2637

  相似文献   

Carbon and oxygen isotopes in epigenetic hydrothermal rocks from Hamam-el-Farun,Sinai     

Mordechai Magaritz  Arie Issar 《Chemical Geology》1973,12(2):137-146

Rock samples from an Eocene cliff above the thermal spring of Hamam-el-Farun (west coast of Sinai) show various degrees of dolomitization and calcitization ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ ratios indicate that dolomite and secondary calcite precipitated from hot brines.  相似文献   

I-Xe studies of individual Allende chondrules     

T.D. Swindle  M.W. Caffee  C.M. Hohenberg  M.M. Lindstrom 《Geochimica et cosmochimica acta》1983,47(12):2157-2177

Iodine-xenon studies have been performed on nine Allende chondrules and a sample of oxidized Allende matrix material. The chondrules are all very rich in radiogenic xenon relative to trapped xenon, making it possible to determine a relatively precise model initial iodine composition for each temperature extraction. These model compositions show a total range in variation of about 20 percent, spanning the compositions seen in Bjurbole chondrules. One of the chondrules (chondrule 6) gives a well-defined isochron, with an apparent age .53 ±. 15 m.y. later than Bjurbole whole rock. The rest of the chondrules show a pattern of increasing apparent antiquity with increasing extraction temperature, which could be interpreted as relatively slow cooling (100–200°C/m.y.). Alternatively, poorly-defined plateaus in composition can be seen, perhaps indicative of a few phases with distinct initial iodine compositions (but also temperature-ordered), as has been previously suggested for Allende inclusions. Possible consequences of these interpretations are discussed. Elemental abundances were determined for some elements several months after the irradiation by INAA, and suggest that all the chondrules except chondrule 6 might be pyroxene- or mesostasis-rich. The oxidized matrix sample gives a well-defined isochron with an initial ${}^{129}\text{I}{}^{127}$I ratio higher than any plateaus seen in the chondrules, suggesting that, if this sample is representative of matrix, the matrix pre-dates the chondrules. The initial ${}^{244}\text{Pu}{}^{238}\text{U}$ ratios of the Allende chondrules and 10 Bjurbole chondrules irradiated earlier appear to be consistent with. 004–.007 values quoted for unfractionated material in the early solar nebula.  相似文献   

The geochemical significance in early sedimentation of geolipids obtained by saponification of lacustrine sediments     

Mitsugu Nishimura 《Geochimica et cosmochimica acta》1977,41(12):1817-1823

Significant quantities of solvent-inextractable geolipids, obtained by saponification of solvent extracted sediments, were found in various sedimentary samples including soils, river inlet sediment and lake sediments from Lake Suwa.The carbon isotopic composition ($\text{δ}{}^{13}\text{C}$) of extractable and inextractable geolipids from the same sediment sample were similar. Moreover, the carbon number distributions of sterols in the two geolipid fractions from the same sediment were also similar.Whereas the ratios of both lipids and sterols to total organic carbon for the extractable geolipids in the lake sediments decreased with depth, the former ratio for inextractable giolipids tends to increase with depth and the latter remains fairly constant. On the other hand, the stanol to stenol ratio of the extractable fraction increased with depth but that of the inextractable fraction was lower than that of the extractable fraction and was fairly constant irrespective of sediment depth.The transformation of extractable sterols into inextractable ones was not observed during incubation for 1200 days of sterols with Suwa sediments.Thus, the following conclusions were made: (1) the extractable and inextractable geolipids have similar origins, (2) some constituents of the latter may be protected from chemical or microbiological degradation and transformation in the sediments, and (3) the transformation of some constituents of the former into the inextractable ones virtually does not occur after incorporation into Suwa sediments.These results suggest that some constituents of the inextractable geolipid fraction may provide fundamental information on early diagenetic alteration of geolipids in lake sediments and on the relatively recent paleoenvironment.  相似文献   

Coupling among the terrestrial sulfur,carbon and oxygen cycles: numerical modeling based on revised Phanerozoic carbon isotope record     

Manfred Schidlowski  Christian E Junge 《Geochimica et cosmochimica acta》1981,45(4):589-594

Numerical modeling of the terrestrial oxygen budget based on the revised δ¹³C_carb record by Veizeret al. (1980) has shown that total photosynthetic oxygen has varied between ±7% and ±10% of its average reservoir size (～3.2 × 10²² g) during the last 800 myr as a result of oscillations of the sedimentary reservoir of organic carbon. Calculated curves of oxygen evolution display a distinct minimum in the Early Paleozoic framed by two maxima in the Latest Proterozoic and the Mesozoic. The sympathetic relationship observed between the curves of total oxygen evolution and respective functions for the partial reservoir of sulfate-bound oxygen suggests that the O₂ required for an additional conversion of sulfide to sulfate was most probably provided by excess burial of organic carbon, the results of the modeling thus adding credence to current interpretations proposed for the negative correlation between the secular ${}^{13}\text{C}{}^{12}\text{C}$ and ${}^{34}\text{S}{}^{32}\text{S}$ trends.  相似文献   

Mg,Ca and $\text{O}{}^{18}\text{O}{}^{16}$ exchange in the sediment-pore water system,hole 149, DSDP     

Edward A. Perry  J.M. Gieskes  J.R. Lawrence 《Geochimica et cosmochimica acta》1976,40(4):413-423

The diagenesis and geochemical evolution of deep-sea sediments are controlled by the interaction between sediments and their associated pore waters. With increasing depth, the pore water of Hole 149 (DSDP) exhibits a strong depletion in Mg and a corresponding enrichment in Ca, while the alkalinity remains relatively constant. Dissolved SiO₂ is nearly constant in the upper 100 m of sediment, but is highly enriched in the deepest pore waters. The pore waters exhibit a depletion in K with increasing depth, and $\text{O}{}^{18}\text{O}{}^{16}$ pore water ratios also decrease.The sediment section has three zones of sedimentary regimes with increasing depth in the drill hole: an upper 100 m section of detrital clays, a middle section enriched in calc-akalic volcanics which have undergone submarine weathering to a smectite phase, and a lower section of siliceous ooze which still has a diagenetic smectite phase. The quartz-feldspar ratios and $\text{O}{}^{18}\text{O}{}^{16}$ composition of the silicate phases are in agreement with these interpretations.The submarine weathering of volcanics to a smectite can account for the observed pore water gradients. Volcanics release Ca and Mg to the pore waters causing the alkalinity values to increase. Smectite is formed, depletes the pore waters in Mg and O¹⁸ and causes the alkalinity to decrease. The net reaction allows for the observed relationship between pore water Ca and Mg gradients with little net change in alkalinity. Given the abundance of volcanics in many deep-sea sediments, especially in lower sections which often form near ridge crests, the submarine formation of smectite may be an additional oceanic Mg sink which has not yet been fully considered.  相似文献   

Isotope and trace element geochemistry of sediments from the Barbados Ridge-Demerara Plain region,Atlantic Ocean     

William M. White  Bernard Dupré  Philippe Vidal 《Geochimica et cosmochimica acta》1985,49(9):1875-1886

Twenty-four piston core sediment samples and 13 sediments and 3 basalts from DSDP Leg 78 Site 543 were analyzed for Sr, Nd and Pb isotopic compositions. The results show sediment with highly radiogenic Pb${}^{206}\text{Pb}{}^{204}\text{Pb}$ up to 19.8) and rather radiogenic Sr and unradiogenic Nd has been deposited in the region since the Cretaceous. The source of this sediment is probably the Archean Guiana Highland, which is drained by the Orinoco River. Pb and Sr isotopic compositions and sediment thickness decrease and${}^{143}\text{Nd}{}^{144}\text{Nd}$ increases northward due to a decrease in turbiditic component. This decrease is partly due to the damming action of basement ridges. Rare earth concentrations in the sediments are somewhat low, due to the abundance of detrital and biogenic components in the sediment and rapid sedimentation rates. Both positive and negative Ce anomalies occur in the surface sediments, but only positive Ce anomalies occur in the Site 543 sediments. It is unlikely that sediment subducted to the source region of Lesser Antilles arc magmas could be the cause of negative Ce anomalies in those magmas.Isotopic compositions of Site 543 basalts show some effect of contamination by seawater-basalt reaction products and sediments. Beyond this, however, they are typical of “normal” depleted MORB.  相似文献   

Diffusion of ions in sea water and in deep-sea sediments   总被引：3，自引：0，他引：3  

Sandra Gregory 《Geochimica et cosmochimica acta》1974,38(5):703-714

The tracer-diffusion coefficient of ions in water, D_j⁰, and in sea water, $\text{D}{}_{\mathrm{j}}{}^1$, differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective $\text{D}{}_{\mathrm{j}}{}^1$ or D_j⁰ values. The tracer diffusion coefficients of ions in deep-sea sediments, D_j,sed., can be related to $\text{D}{}_{\mathrm{j}}{}^1$ by $\text{D}{}_{\mathrm{j,sed.}}\text{= D}{}_{\mathrm{j}}{}^1\text{·}\text{α}\text{θ}{}^2$, where θ is the tortuosity of the bulk sediment and a a constant close to one.  相似文献   

Hydrogen and carbon isotopes of petroleum and related organic matter     

Hsueh-Wen Yeh  Samuel Epstein 《Geochimica et cosmochimica acta》1981,45(5):753-762

$\text{D}\text{H}$ 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.  相似文献   

Etude systématique des isotopes de l'oxygène,du carbone et du strontium dans les carbonatites     

Françoise Pineau  Marc Javoy  Claude J Allegre 《Geochimica et cosmochimica acta》1973,37(11):2363-2377

${}^{18}\text{O}{}^{16}\text{O}$, ${}^{13}\text{C}{}^{12}\text{C}$ and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios have been measured on the same samples for carbonatite complexes. The results show that besides the ‘carbonatite box’ of Tayloret al. (1967) there exist higher δ¹⁸O and δ¹³C values than can be explained by late magmatic or deuteric processes. These processes correspond to high concentrations of CO₂ and lead to big enrichments in ¹⁸O and ¹³C as well as in some ‘volatile’ elements. Strontium results are consistent with a model of selective contamination of deep-seated material by highly radiogenic strontium. The whole study leads to the opinion that parent magmas of carbonatites differentiated in a crustal environment with or without significant contamination.  相似文献   

Micromanganese nodules in deep-sea sediments: Uranium-isotopic evidence for post-depositional origin     

Robert Immel  J.K. Osmond 《Chemical Geology》1976,18(4):263-272

Micromanganese nodules from three deep-sea cores are found to contain less U than average nodules dredged from the sea floor. The ${}^{234}\text{U}{}^{238}\text{U}$ ratio in these micronodules is higher than any previously reported in deep-sea sediments. We interpret these data to mean that at least some micronodules form well after deposition of the enclosing sediments, in particular where conditions are less oxidizing than average.  相似文献   

Stable isotopic investigations of early development in extant and fossil chambered cephalopods I. Oxygen isotopic composition of eggwater and carbon isotopic composition of siphuncle organic matter in Nautilus     

Kimberley C. Crocker  Michael J. DeNiro  Peter D. Ward 《Geochimica et cosmochimica acta》1985,49(12):2527-2532

Eggwaters from the chambered cephalopod Nautilus are depleted in both ¹⁸O and deuterium relative to ambient seawater. Eggwaters from six other species, including the related chambered cephalopod Sepia, do not show such depletion. These observations indicate that the previously observed step towards more positive $\text{δ}{}^{18}\text{O}$ values in calcium carbonate laid down after Nautilus hatches, relative to carbonate precipitated prior to hatching, can be explained by equilibration of the carbonate with water in the egg before hatching and with seawater after hatching. The presence of an oxygen isotope difference between eggwater and seawater for Nautilus and its absence for Sepia suggest that hatching will be recorded in the $\text{δ}{}^{18}\text{O}$ values of shell carbonates for some but not all extinct and extant chambered cephalopods.The $\text{δ}{}^{13}\text{C}$ values of the organic fraction of the siphuncle in Nautilus do not show any consistent pattern with regard to the time of formation before or after hatching. This observation suggests that the minimum in $\text{δ}{}^{13}\text{C}$ values previously observed for calcium carbonate precipitated after Nautilus hatches is not caused by a change in food sources once the animal becomes free-swimming, as has been suggested.  相似文献   

Systematic variations of sialic and volcanic detritus in piston cores from the Red Sea     

Phillip D. Boger  Gunter Faure 《Geochimica et cosmochimica acta》1976,40(7):731-742

The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios and Sr concentrations of the non-carbonate fractions of sediment from two cores taken in the median valley of the Red Sea indicate that the detrital fractions are mixtures of two components originating from old sialic and young volcanic rocks of the surrounding land areas. The mixing equations were derived from the data and were used to estimate the Sr concentrations of the two components. The volcanogenic detritus has a Sr content between 770 and 800 ppm while the component derived from old sialic rocks contains from 50 to 70 ppm. The volcanic component consists primarily of unweathered particles of alkali basalt and volcanic glass while the sialic component is represented by clay minerals and X-ray amorphous material. Systematic variations of the concentration of volcanogenic detritus were used to define layers of sediment which correlate over a distance of about 200 km separating the two cores. The concentrations of quartz, feldspar, amphibole, illite, kaolinite and chlorite were found to vary systematically with the content of volcanogenic detritus as calculated from the Sr data. The carbonate concentrations of the sediment range from 33 to 87% and appear to increase in a southerly direction. The rate of carbonate deposition increased at times of more efficient input of sediment derived from old sialic rocks. This relationship is explained by the hypothesis that both were influenced indirectly by brief warming trends during the Würm glaciation. The occurrence of sediment layers enriched in sediment derived from old sialic rocks correlates approximately with interstadials of the Würm glaciation in northern Europe. Increased input of volcanogenic detritus occurred around 37,000 and 26,000yr ago and during the past 5000 yr. A plot of ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and ${}^{87}\text{Rb}{}^{86}\text{Sr}$ ratios defines a line on the Rb-Sr isochron diagram yielding a fictitious date of about 230 million yr.  相似文献