Computer Science
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001gecoa..65.4087k&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 65, Issue 22, pp.4087-4101
Computer Science
10
Scientific paper
The paper presents the isotopic (B, Sr, O, H) and chemical composition of solid salts, brines, groundwater, and surface water in the vicinity of a Permian salt dome in Northern Germany (diapir of Gorleben-Rambow) being considered for disposal of high level radioactive waste. The site is situated in the NW European Basin that is dominated by intensive diapirism of Permian salt and overprinted by glacial erosion/sedimentation. The local hydrogeology comprises an upper aquifer system of heterogeneous Pleistocene sediments and a lower aquifer system of Tertiary clastics tectonically disturbed by diapirism. There is a clear chemical and isotopic evolution with TDS, that generally increases with depth up to 328 g · l -1 . The chemistry and isotope ratios of the saline groundwater can be explained by a two end-member mixing system. The Na-Cl brine end-member is derived from evaporite dissolution as indicated by major ion chemistry, Cl/Br ratios, Sr and B isotopes. It is mixed with fresh-brackish groundwater dominated by water-silicate interaction. This low salinity end-member (TDS from 0.3-10 g · l -1 ) shows radiogenic 87 Sr/ 86 Sr ratios ranging from 0.70910 to 0.71030 and low 11 B values between 7.4 and 16.5 vs. NBS951. Two halite samples and a borate sample from the unaltered parts of the diapir show 87 Sr/ 86 Sr ratios from 0.70696 to 0.70868 and 11 B values of 20.8 and 27.7 . Brine (TDS from 100-328 g/l) Sr isotope ratios, ranging from 0.70758 to 0.70788, lie in the uppermost range of late Permian ocean waters and are within the range of halite. The 11 B values of the brines vary between 25.1 to 33.5 , which is close to the range of solid salt but well below those of evaporating present-day sea water. B isotope composition is thus compatible with salt dissolution rather than with residual evaporite brines. The chemistry and isotope characteristics of the brine end-member derived from halite dissolution are not significantly modified by subsequent interaction with the siliciclastic aquifer material. Most highly saline groundwaters show cold climate O and H isotopic signatures with 18 O values ranging from -10.5 to -9 . A limited group of four rather deep-seated brines (>200 m) plots in the range of Holocene signatures with 18 O > -9 close to those of the shallow groundwater which is interpreted as an indication of rapid groundwater circulation from the surface and ongoing salt dissolution.
Casanova Jordi
Guerrot Catherine
Klinge H.
Kloppmann Wolfram
Négrel Ph.
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