Surface Water Paleotemperatures and Chemical Compositions from Fluid Inclusions in Permian Nippewalla Group Halite
Kathleen Counter Benison
Quantitative climatic data for the Permian have been determined from Nippewalla Group halite. The middle Permian Nippewalla Group of Kansas and Oklahoma consists of several hundred feet of bedded halite, anhydrite and red beds. Study of core and surface samples suggest that this halite was deposited by ephemeral lakes. Fluid inclusions provide evidence for the geochemistry of these Permian saline lake waters, including temperatures, salinities, and chemical compositions.
Primary fluid inclusions are well-preserved in the Nippewalla halite. They are 5- to 30- µm cubic inclusions situated along chevron and cornet growth bands. Most are one phase aqueous inclusions, but some also contain anhydrite "accidental" crystals. Rare two phase liquid-vapor inclusions may have formed by subaqueous outgassing or trapping of air at the water surface.
Fluid inclusion freezing-melting behavior and leachate analyses suggest that Nippewalla halite precipitated from Na-Cl-rich waters with lesser quantities of SO4, Mg, K, Al, and Si. This composition may be a product of long-term weathering.
Surface water paleotemperatures were determined from one phase aqueous fluid inclusions. Homogenization temperatures range from 32 to 46°C in primary fluid inclusions and are consistent (within 3°C) along individual chevrons and cornets. These homogenization temperatures are interpreted to represent maximum surface water temperatures.
These fluid inclusion data are significant in addressing global change problems. Temperatures and chemistries in these Permian lake waters agree with some modern shallow saline lake waters and with Permian climate models. This study suggests that this Permian environment was relatively similar to its modern counterparts.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California