Abstract: Stable Chlorine Isotopes as Indicators of Brine Origin in the Palo Duro Basin, Texas

Christopher J. Eastoe, Austin Long

The Palo Duro basin contains thick beds of Permian halite interlayered with carbonate and clastic rock. Shale is insignificant. Brines occur above, within and below the salt. The ^dgr³⁷Cl range of halite is narrow, with mean 0.22 +/-0.03 per mil (n = 26), compared with modern seawater, 0.0 +/-0.01 per mil (n = 22). The ^dgr³⁷Cl values of brine chloride range from -1.1 to +0.4 per mil. Brine chloride with ^dgr³⁷Cl values overlapping those of halite was probably derived by dissolution of halite. Brine chloride with lower ^dgr³⁷Cl values is from a different source, possibly Permian bittern. Diffusive fractionation of chlorine isotopes is precluded by the lack of shale in the basin. On the basis of the relative sizes of crustal chlorine reservoi s and fluxes, it is unlikely that ^dgr³⁷Cl of seawater varied measurably during the Phanerozoic. Evaporite formation in basins isolated from continual input of seawater may result in salt enriched in ³⁷Cl relative to seawater, leaving bittern depleted in ³⁷Cl.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994