Understanding the role of gypsum in the global Sr cycle using stable-Sr isotopes
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Isotopes of strontium
Stable strontium isotope,one of the non-traditional stable isotopes,has been focused on in isotope geochemistry since last ten years and has become one of the exciting frontier sciences in geo-scientific studies.Strontium has four stable isotopes:84Sr,86Sr,87Sr and 88Sr.TIMS or MC-ICP-MS can be employed to measure stable strontium isotopes,and the ratios are expressed as δ88/86Sr.Variations in δ88/86Sr in nature range from-1.73‰ to 0.66‰.The factors affecting strontium fractionation are indistinct,and more work needs to be done on the fractionation mechanism for further understanding.At present the applications of stable strontium isotope geochemistry are presented as follows:(1) Paleoceanographic temperaure reconstruction based on δ88/86Sr of cold-water corals;(2) combining radiogenic strontium and stable strontium fractionation to study geochemical cycling in the ocean;(3) paleodietary research with stable strontium in bones.
Isotopes of strontium
Radiogenic nuclide
Isotope Geochemistry
Isotopic signature
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Carbonatite
Isotopes of strontium
Table (database)
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A detailed record of the strontium-87 to strontium-86 ratio in seawater during the last 100 million years was determined by measuring this ratio in 137 well-preserved and well-dated fossil foraminifera samples. Sample preservation was evaluated from scanning electron microscopy studies, measured strontium-calcium ratios, and pore water strontium isotope ratios. The evolution of the strontium isotopic ratio in seawater offers a means to evaluate long-term changes in the global strontium isotope mass balance. Results show that the marine strontium isotope composition can be used for correlating and dating well-preserved authigenic marine sediments throughout much of the Cenozoic to a precision of ±1 million years. The strontium-87 to strontium-86 ratio in seawater increased sharply across the Cretaceous/Tertiary boundary, but this feature is not readily explained as strontium input from a bolide impact on land.
Isotopes of strontium
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A succession of different lithofacies including fifteen units, from a to n , have been distinguished in the gypsum section of the Nida area. Geochemical data show distinct variation of the Sr content in gypsum, between 0.03 and 3.13% (average 0.30% Sr). In gypsum lithofacies, a high Sr concentration averaging 0.5% was found in selenitic gypsum and in gypsorudites. The vertical distribution of strontium throughout the section is not uniform. The average strontium content increases in the middle section and reaches as much as 0.92% Sr in unit h . South of the Holy Cross Mts. the horizontal distribution of strontium in gypsum and coeval carbonates is characterized by higher concentration in the northernmost part of the area (Staszow region). Variability of the strontium content throughout the cyclic sequences reflects the evolution of brines during the gypsum formation. The results suggest important diagenesis of the gypsum deposits which allowed the migration of strontium and subsequent crystallization of celestite.
Isotopes of strontium
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The isotopic ratio of strontium-87 to strontium-86 shows no detectable variation in present-day ocean water but changes slowly over millions of years. The strontium contained in carbonate shells of marine organisms records the ratio of strontium-87 to strontium-86 of the oceans at the time that the shells form. Sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium-87 to strontium-86 with a resolution that is similar to that of other techniques used in age correlation. This method may prove valuable for many geological, paleontological, paleooceanographic, and geochemical problems.
Isotopes of strontium
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Nineteen pore-water samples from the late Miocene and younger marine formations were analyzed for strontium contents and isotopic compositions. All samples have /sup 87/Sr//sup 86/Sr ratios lower than the late Miocene seawater value (0.7090). The strontium values in many of these waters reflect silicate rather than carbonate reactions. In general, the strontium contents and isotopic ratios of the pore waters are related to the depth and location of the oil fields. The strontium contents as a whole show a tendency to increase with depth, although /sup 87/Sr//sup 86/Sr ratios have no simple depth relationship. The strontium contents and isotopic compositions of the pore waters fall into five groups related to geographic locations. This suggests localized evolution of pore waters in a given area and limited movement of these subsurface waters.
Isotopes of strontium
San Joaquin
Strontium-90
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