U-Th isotope systematics from the Soreq cave, Israel and climatic correlations
Precise 230Th-234U ages were obtained on thirty-one growth laminae in speleothem samples which are self-consistent with the detailed layer stratigraphy. Samples with low 232Th/238U ratios give ages with analytical uncertainties of 40 years at 2 ky and 1000 years at 90 ky. Some growth zones with high...
| Main Authors: | , , , , , |
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| Format: | Journal article |
| Language: | English |
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1998
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| _version_ | 1797094725364219904 |
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| author | Kaufman, A Wasserburg, G Porcelli, D Bar-Matthews, M Ayalon, A Halicz, L |
| author_facet | Kaufman, A Wasserburg, G Porcelli, D Bar-Matthews, M Ayalon, A Halicz, L |
| author_sort | Kaufman, A |
| collection | OXFORD |
| description | Precise 230Th-234U ages were obtained on thirty-one growth laminae in speleothem samples which are self-consistent with the detailed layer stratigraphy. Samples with low 232Th/238U ratios give ages with analytical uncertainties of 40 years at 2 ky and 1000 years at 90 ky. Some growth zones with high but variable 232Th/238U were dated by internal isochrons. This permits the determination of the initial 230Th/232Th assuming equilibrium of 232Th and 238U series in the source of the high 232Th component. This shows initial (230Th/232Th) (in activity units) of from 1.3 to 2.9. The calculated atomic ratios of 232Th/238U for the high 232Th component range from 1.08 to 2.4 which is well below the average crustal value. Speleothem materials with high 232Th/238U are found to exhibit clear correlations of 232Th with Si, Al and Fe, while 238U correlates with Sr and Ba. Analyses of Soreq cave drip waters show that the particulates in the waters have high 232Th concentrations and a 232Th/238U ratio much lower than that found in the high 232Th component in speleothems but with (230Th/232Th) = 1.0 to 2.4. We infer that the trapped high-Th component in speleothems is from particulate matter in water with a large concentration of adsorbed U and not simply from detrital material. The speleothems have only small 234U excess. The initial (234U/238U)0 show a range of 1.02 to 1.14 that was found to correlate with age over the past 25 ky. The youngest samples have values in the same range as the modern drip waters. There appears to be a correlation of (234U/238U)0 with the δ18O values. There is a drop of δ18O in the time interval 20 to 15 ky which then remains relatively constant to recent times. As the high δ18O values have been related to rainfall and associated climatic conditions, we suggest that the 234U/238U in the speleothem reflects the effects of rainfall and soil weathering conditions on drip-water composition and may provide a proxy for climate change. © 1998 Elsevier Science B.V. All rights reserved. |
| first_indexed | 2024-03-07T04:17:58Z |
| format | Journal article |
| id | oxford-uuid:ca09306f-bd14-45bb-947c-62701a6e8f73 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T04:17:58Z |
| publishDate | 1998 |
| record_format | dspace |
| spelling | oxford-uuid:ca09306f-bd14-45bb-947c-62701a6e8f732022-03-27T07:04:27ZU-Th isotope systematics from the Soreq cave, Israel and climatic correlationsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:ca09306f-bd14-45bb-947c-62701a6e8f73EnglishSymplectic Elements at Oxford1998Kaufman, AWasserburg, GPorcelli, DBar-Matthews, MAyalon, AHalicz, LPrecise 230Th-234U ages were obtained on thirty-one growth laminae in speleothem samples which are self-consistent with the detailed layer stratigraphy. Samples with low 232Th/238U ratios give ages with analytical uncertainties of 40 years at 2 ky and 1000 years at 90 ky. Some growth zones with high but variable 232Th/238U were dated by internal isochrons. This permits the determination of the initial 230Th/232Th assuming equilibrium of 232Th and 238U series in the source of the high 232Th component. This shows initial (230Th/232Th) (in activity units) of from 1.3 to 2.9. The calculated atomic ratios of 232Th/238U for the high 232Th component range from 1.08 to 2.4 which is well below the average crustal value. Speleothem materials with high 232Th/238U are found to exhibit clear correlations of 232Th with Si, Al and Fe, while 238U correlates with Sr and Ba. Analyses of Soreq cave drip waters show that the particulates in the waters have high 232Th concentrations and a 232Th/238U ratio much lower than that found in the high 232Th component in speleothems but with (230Th/232Th) = 1.0 to 2.4. We infer that the trapped high-Th component in speleothems is from particulate matter in water with a large concentration of adsorbed U and not simply from detrital material. The speleothems have only small 234U excess. The initial (234U/238U)0 show a range of 1.02 to 1.14 that was found to correlate with age over the past 25 ky. The youngest samples have values in the same range as the modern drip waters. There appears to be a correlation of (234U/238U)0 with the δ18O values. There is a drop of δ18O in the time interval 20 to 15 ky which then remains relatively constant to recent times. As the high δ18O values have been related to rainfall and associated climatic conditions, we suggest that the 234U/238U in the speleothem reflects the effects of rainfall and soil weathering conditions on drip-water composition and may provide a proxy for climate change. © 1998 Elsevier Science B.V. All rights reserved. |
| spellingShingle | Kaufman, A Wasserburg, G Porcelli, D Bar-Matthews, M Ayalon, A Halicz, L U-Th isotope systematics from the Soreq cave, Israel and climatic correlations |
| title | U-Th isotope systematics from the Soreq cave, Israel and climatic correlations |
| title_full | U-Th isotope systematics from the Soreq cave, Israel and climatic correlations |
| title_fullStr | U-Th isotope systematics from the Soreq cave, Israel and climatic correlations |
| title_full_unstemmed | U-Th isotope systematics from the Soreq cave, Israel and climatic correlations |
| title_short | U-Th isotope systematics from the Soreq cave, Israel and climatic correlations |
| title_sort | u th isotope systematics from the soreq cave israel and climatic correlations |
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