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TitleGeochemistry, geology, and isotopic (Sr, S, and B) composition of evaporites in the Lake St. Martin impact structure: New constraints on the age of melt rock formation
AuthorLeybourne, M I; Denison, R E; Cousens, B L; Bezys, R K; Gregoire, D C; Boyle, D R; Dobrzanski, E
SourceGeochemistry, Geophysics, Geosystems (G3) vol. 8, no. 3, Q03001, 2007, 22 pages, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20070468
Mediaon-line; digital
File formatpdf
NTS62O/09; 62O/10; 62O/15; 62O/16
AreaLake St. Martin; Interlake Region; Gypsumville
Lat/Long WENS -99.0000 -98.0000 52.0000 51.5000
Subjectsextraterrestrial geology; geochemistry; isotope geochemistry; isotopes; isotopic studies; isotope ratios; strontium strontium ratios; boron geochemistry; boron; sulphur; sulphur geochemistry; sulphur isotope ratios; evaporites; anhydrite; gypsum; carbonates; red beds; gneisses; meteorite craters; craters; lithology; whole rock analyses; whole rock geochemistry; groundwater geochemistry; Mesozoic; Jurassic; Triassic
Illustrationssketch maps; plots
Released2007 03 03
AbstractWe report new Sr, S, and B isotopic data for evaporites (gypsum, anhydrite), carbonates, melt rocks, gneisses, and groundwaters recovered in and around the Lake St. Martin (LSM) impact structure, Interlake Region, Manitoba, Canada. The LSM meteorite impacted Devonian to Ordovician carbonates and sandstones of the eastern Williston Basin, resulting in partial melting of underlying Superior Province (?2.5 Ga) gneisses of the Canadian Shield. Overlying the LSM melt rocks are red beds and evaporites (anhydrite/gypsum/glauberite) previously inferred to have been deposited during the Jurassic. The 87Sr/86Sr (lowest values cluster at 0.70836) and d34SCDT (+23.7 ± 0.9 per thousand) of the evaporites, combined with B isotope compositions of associated groundwaters (d11BNBS951 = +25 to +28 per thousand), are consistent with evaporite deposition within the impact structure near the edge of an ocean-connected salina. The establishment of a marine origin for the evaporites offers a method of age assignment using the secular variation of S and Sr isotopes in seawater. Comparison of Sr and S isotope results with the seawater curves precludes Jurassic deposition for the evaporites or correlation with Watrous and Amaranth formation evaporites, previously considered correlative with those at LSM. The lowest Sr and mean of S isotope values from the LSM evaporites are similar to seawater in the latest Devonian, consistent with conodonts recovered from carbonate breccia overlying melt rocks, and we suggest this as an alternative age of the evaporites. Data presented here preclude a Jurassic age for the evaporites and therefore for the impact event.

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