CL-ISOTOPIC SIGNATURES OF GROUNDWATERS, PORE WATERS AND CALCITE FLUID INCLUSIONS: CONSTRAINTS ON FLUID ORIGIN AND TRANSPORT IN A MARL SEQUENCE
The Na-Cl groundwaters have chlorine isotopic signatures in the range of +0.2 to +0.9 per mil, relative to Standard Mean Oceanic Chloride. The delta 37Cl signatures of pore waters determined from rock matrix leaching fall within the same range (+0.2 to +0.8 per mil). A mixed 1st and 2nd generation, and a 3rd generation vein calcite have delta 37Cl signatures of +0.4 per mil, which is within the range of values measured for both the Na-Cl waters and the rock matrix leachates. The similar, positive signatures are consistent with a common origin for the fluids. A Na-HCO3-Cl groundwater, which is thought to be transitional between the Na-Cl waters and the overlying Na-HCO3-type waters, has a delta 37Cl signature of -0.4 per mil, suggesting that upward diffusion of chloride from the Na-Cl waters has occurred. Given sufficient time, diffusion will shift the chlorine isotopic signature in the center of the sequence towards more positive values compared to the fluid inclusions, as observed for the Na-Cl waters and rock leachates.