The Sr-isotope record of late quaternary hydrologic changes around Lake Frome, South Australia
The Sr-isotope ratios ( 87 Sr/ 86 Sr) of modern brines and salts from the Lake Frome closed-basin are remarkably consistent (0.71126±0.00005 to 0.71206±0.00006). However, gypsum deposited from lake brines during the late Quaternary show a much greater variation (0.71032 ± 0.00007 to 0.71219±0.00010)...
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| Published in: | Australian journal of earth sciences 1994-02, Vol.41 (1), p.37-45 |
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| Main Authors: | , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | The Sr-isotope ratios (
87
Sr/
86
Sr) of modern brines and salts from the Lake Frome closed-basin are remarkably consistent (0.71126±0.00005 to 0.71206±0.00006). However, gypsum deposited from lake brines during the late Quaternary show a much greater variation (0.71032 ± 0.00007 to 0.71219±0.00010). This variation is due to the changing sources of water and Sr to the Lake Frome basin. The present isotope ratio of the Lake Frome brines and the modern halite crust is similar to the isotopic composition of groundwater from the shallow (Willawortina Formation) aquifer of the adjacent Lake Frome Plains (0.71171±0.00004 to 0.71223±0.00004), reflecting the contemporary importance of this source of Sr and water. Isotope ratios of preserved gypsum deposits greater than those presently observed reflect either an increased importance of the moderate depth (Namba Formation) aquifer (0.71468±0.00004 to 0.71554±0.00007) or a generally increased residence time of groundwater entering the basin at times in the past. Sr-isotope ratios lower than the present brine and modern salts are interpreted to result either from an increased flux of marine Sr (∼ 0.7092) via aerosols or an increased flux of less radiogenic Sr from the deep Jurassic aquifer of the Great Artesian Basin (≤0.7118). On the basis of the Sr-isotopic composition of the preserved gypsum, periods of high rainfall ('wet') were identified at 3-6 Ka, 12-15 Ka, and > 17 Ka and dry periods at ∼ 10 and ∼ 17 Ka. These results, which are fairly consistent with previous palaeoclimatic inferences, indicate that variations in Sr-isotope ratios of dated authigenic sediments from closed-basin lakes may be used for palaeoenvironmental reconstruction. |
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| ISSN: | 0812-0099 1440-0952 |