I am interested in quantitative measurements of porosity and permeability in bedded salt. Most reports assume salt has no porosity, or permeability, which is likely true for deformed salt. But, there published reports of halite "sands" in bedded salt.
Dear Tom,
Knauth and Robert (1991) made direct measurement of the oxygen isotope composition of water of fluid inclusion in halite that formed over Silurian-Permian interval. The values they obtained ranged from about –6 to +6 ‰ and showed a general trend with depth from isotopically light to heavy values, which they interpret as the result of influence of meteoric water. However, I am not convinced that bedded salt rock is permeable for meteoric water. It might be instead that salt rock trapped in fluid inclusions water present in the basin during halite sedimentation, which had simply d18O varying in time.
If you are interesting in measurements of closed porosity of salt rock, it can be determined by the method of positron annihilation - there is a group of physicist in my department doing this.
REFERENCE. Knauth, LP and Robert, SR, 1991. Hydrogen and oxygen isotope history of the Silurian-Permian hydrosphere as determined by direct analysis of fossil water. In: H.P. Taylor, Jr., J.R. O’Neil and I.R. Kaplan (eds.) Stable Isotope Geochemistry: A tribute to Samuel Epstein. The Geochem. Soc., Special Publication No. 3, San Antonio.
In situ measured properties for bedded salt (Permian Salado Formation, New Mexico) are reported by Beauheim and Roberts (2002) (see Hydrology and hydraulic properties of a bedded evaporite formation in Beauheim profile).
O'Neill et al (1986; Applied Geochemistry, v. 1, p. 265-271) made an argument similar to Knauth anf Robert, interpreting evaporative curves of stable isotopes from large fluid inclusions in the Salado as evidence of meteoric penetration into salt to depths of hundreds of m. This argument was brought forward by Hasen and Roedder (2001, Nature, v. 411, p. 155) in a comment on the paper by Vreeland et al. (2000, Nature v. 407, p. 897-900) reporting on isolation of viable bacteria from samples from the Permian Salado Formation. In a reply, Powers et al. (2001, Nature, v. 411, p.155) described the direct and indirect evidence that these rocks have remained unpenetrated by fresh water since approximately the time of deposition. Holt and Powers (2011, GSA Bulletin, v. 123, p. 1513-1523) provided a much lengthier discussion of the evidence for isolation of these rocks at depth since Permian time. The Salado is characterized by desiccating upwards, m-scale depositional cycles with exposures surfaces and synsedimentary dissolution pipes that apparently trapped meteoric water that quickly became halite-saturated and then cemented the pipes as the "brine table" rose and the cycle began again.
Because of the mechanical properties of halite, these bedded deposits display very high internal fluid pressures that will exceed the fluid pressure from the overlying fresh water zones. Although solution may occur around the halite body, an extreme event would be needed to introduce modern meteoric water into a buried salt deposit.
See also Casas and Lowenstein (1989, J. of Sedimentary Petrology, v. 59, p. 724-739) about how porosity becomes occluded in salts.
There are more details, but this will get you started.
Hello! As the specific weight of salt is known, you can easily calculate the total porosity (including the closed porosity) from the bulk density of regularly shaped specimens. If your specimen is not too big, you can also measure the open porosity by a helium pyknometer/porosimeter - helium is a innert gas that does not react with the salt like water does, so it does not change the real porosity.
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