High-Resolution Stratigraphy with Strontium Isotopes
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Abstract:
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.Keywords:
Isotopes of strontium
Carbonatite
Isotopes of strontium
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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.
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Abstract In archaeology, strontium isotope analysis is developing into an efficient scientific technique for tracing the movement of prehistoric humans and animals. Determining the local bioavailable 87 Sr/ 86 Sr ratio range is the key to distinguishing whether the human or animal is indigenous to the local area. It has been shown that the 87 Sr/ 86 Sr ratio in the enamel of pigs can be an excellent sample to determine the range of local strontium isotope ratio at the site. However, pigs may not be all local at the site, and there is no special study on whether pigs’ different ages and tooth types impact the local strontium isotope characteristics. In this paper, the tooth enamel of 19 pigs from the Zaoshugounao site for strontium isotope ratio ( 87 Sr/ 86 Sr) by multicollector–inductively coupled plasma mass spectrometry. There were no significant differences in 87 Sr/ 86 Sr ratios of local pigs at different months and different molar types, which did not affect the determination of the local strontium isotope standard. Based on the local strontium isotope ratio range (0.711056–0.711476), we found that five pigs were non‐local. The Jing and Wei river basins (in Guanzhong basin) and northern Shaanxi are likely sources of non‐pigs.
Isotopes of strontium
Isotope Analysis
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From a sector within an extended Tertiary basin 21 groundwater samples as well as 3 rock samples of a Zechslein diapir were analysed for 87Sr/86Sr-ralio. As a tendency the isotope ratio of the dissolved strontium is decreasing with increasing depth and strontium content. Furthermore, strontium content and salinity are correlated. With two exceptions the isotope data are in the range between about 0.7080 and 0.7100. Significant differences in the strontium isotope composition were found between the Zechstein salts and the typical groundwaters. This shows, that the Zechstein diapir can not be the source of the higher salinity in parts of the groundwater system. The results are discussed.
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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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