Dating Porewater in Rock Samples from Fresh Drilling Cores: Depth Profiles of Sstable Isotopes, Noble Gass and Chloride in Hydraulically Impermeable Geological Formations
New methods have been developed and applied for dating porewater in hydraulically impermeable rock core samples (no groundwater mass flow) by means of stable isotopes, dissolved noble gases and NaCl. Vertical profiles of deltaD and radiogenic ~4He are preseted for a claystone aquitard in the Gorleben area and for claystones and cap rock in the Morsleben area (both in northern Germany). Isotope and noble gas data for conventional groudwater samples pumped from the inflow of fracture water into the borehole fit very well in the obtained porewater profiles. In mosleben these profiles show the occurrence of Holocene porewaters down to 100 m depth. In the depth range 100-300 m, isotopically depleted palaeowaters of the last glacial period were found. In the claystones underneath and in the cap rock formation, waters show noble gas ages increasing with depth up to 100 million years.
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