Sedimentary basin brines waters

Gascoyne M., Purdy A., Fritz P., Ross J. D., Frape S. K., Drimmie R. J., and Betcher R. N. (1989) Evidence for penetration of sedimentary basin brines into an Archean granite of the Canadian shield. In Proc. 6th Int. Symp. Water-Rock Interaction (ed. D. L. Miles). Malvern, UK Balkema, Rotterdam, The Netherlands, pp. 243 -245. 

Figure 3. Histogram of 5 C1 in groundwater and formation water brines from sedimentary basins and oil fields relative to Cl/ Cl in SMOC (vertical dashed line at 0%o). N is the number of analyses, and bracketed numbers identify references as follows [1] Kaufmann et al. 1993 [2] Eggenkamp 1994 [3] Ziegleret al. 2001 [4] Eastoe et al. 2001 [5] Kaufmann 1984 [6] Kaufmann et al. 1984 [7] Kaufmann et al. 1988 [8] Eastoe and Guilbert 1992 [9] Eastoe et al. 1999 [10] Desauliniers et al. 1986 and [11] Eggenkamp et al. 1994.

Land (1987) has reviewed and discussed theories for the formation of saline brines in sedimentary basins. We will summarize his major relevant conclusions here. He points out that theories for deriving most brines from connate seawater, by processes such as shale membrane filtration, or connate evaporitic brines are usually inadequate to explain their composition, volume and distribution, and that most brines must be related, at least in part, to the interaction of subsurface waters with evaporite beds (primarily halite). The commonly observed increase in dissolved solids with depth is probably largely the result of simple "thermo-haline" circulation and density stratification. Also many basins have basal sequences of evaporites in them. Cation concentrations are largely controlled by mineral solubilities, with carbonate and feldspar minerals dominating so that Ca2+ must exceed Mg2+, and Na+ must exceed K+ (Figures 8.8 and 8.9). Land (1987) hypothesizes that in deep basins devolatilization reactions associated with basement metamorphism may also provide an important source of dissolved components. 

A number of descriptive terms, including oilfield brine, basinal brine, basinal water, and formation water, have been used in the literature to describe deep aqueous fluids in sedimentary basins. No satisfactory overall classification system exists, due to the fact that these waters can be assessed by several different criteria. These include the sahnity of the water, the concentration and origin of various dissolved constituents, and the origin of the H2O, which is commonly different from that of the solutes. The following terminology has been extracted mainly from Han or (1987) and from Kharaka and Thordsen (1992). The interested reader should also consult White et al. (1963) and Sheppard (1986). 

There is also field evidence that halite-derived brines can be transported over long distances in sedimentary basins. For example, the chemical compositions of waters from the Houston-Galveston area, Texas, and several other areas in the northern Gulf of Mexico basin indicate dissolution of halite (Kharaka et al., 1985 Macpherson, 1992). However, in a number of these areas, there are no known salt domes within 50 km of the sampled sites. Large-scale fluid advection is probably the main mechanism for the... 

The principal sources of dissolved chloride in the more saline fluids of sedimentary basins include dissolved chloride buried at the time of sediment deposition, chloride derived by refluxing of subaerially evaporated surface brines, chloride derived from subsurface mineral dissolution, principally halite, and marine aerosols. The Cl-Br systematics of sedimentary brines provide useful constraints on interpreting the origin of chloride in these waters (Carpenter, 1978 Kharaka et al., 1987 Kesler et al., 1996). 

Equilibrium fractionation of the Ne/Ar ratio An example. From Equations (20) and (21) and the solubility data presented in Tables 2 and 3, the fractionation of the noble gases between gas and liquid phases can be calculated for a range of Vg/Vi ratios and at temperatures and salinities appropriate to those in an active sedimentary basin. Figure 7a shows the maximum Ne/Ar fractionation in water and gas phases for pure water and a 5M NaCl brine. For pure water, maximum fractionation in the gas phase is 3.4 at 290 K and decreases with increasing temperature, salinity and Vg/Vi. For example, at 290 K and in equilibrium with a 5M NaCl brine, Ne/Ar fractionation in the gas phase has a maximum value of 2.5. 

Wilkinson JJ (2001) Flnid inclnsions in hydrothermal ore deposits. Lithos 55 229-272 Winckler G, Sness E, Wallman K, deLange GJ, Westbrook GK, Bayer R (1997) Excess hehnm and argon of radiogenic origin in Mediterranean brine basins. Earth Planet Sci Lett 15 225-231 Worden RH (1996) Controls on halogen concentrations in sedimentary formation waters. Mineral Mag 60 259-274... 

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