THE PERMIAN HUTCHINSON SALT MEMBER OF KANSAS: MARINE, CONTINENTAL, OR TRANSITIONAL?

The Permian Hutchinson Salt Member of the Wellington Formation (Sumner Group) of Kansas is well known, but its depositional environment has not been resolved. The Hutchinson Salt overlies alternating marine and continental shales and limestones. Stratigraphically above the Hutchinson Salt are distinctly continental rocks, including paleosols, acid lake evaporites, and eolian siltstones and sandstones. Past studies have described S and Br isotopes, trace element geochemistry, and microfossils in the Hutchinson Salt. However, no unequivocal evidence for marine or nonmarine origin has been recognized. Here, we provide preliminary observations of sedimentological and stratigraphic features from a well-preserved core in an effort to better interpret depositional setting.

This study consists of a detailed measured section of the Hutchinson Salt of the ~100-m-long AEC Hole No. 2 core drilled in Lyons, Kansas. The core is composed of ~85% halite, ~10% gypsum/anhydrite, and 5% ~mud-sized grains. The majority of halite was gray and black with rare zones of reddish coloration and present as bedded halite (~70%) and displacive halite (~30%). Bedded halite units contain chevron crystals composed of primary fluid inclusions. Gypsum efflorescent crusts were observed. Sedimentary structures include discontinuous wavy lamina, rip-up clasts, and mudcracks. Diagenetic features include dissolution features, anhydrite nodules, and sylvite veins. There were no distinct trends moving upsection. No fossils were observed. Chevron halite, efflorescent crusts, and dissolution features indicate shallow brines that experienced evapoconcentration, desiccation, and flooding. Our ongoing studies focus on identification of elemental and mineralogical composition through XRF and XRD analyses, as well as documentation of parent water compositions and temperatures through fluid inclusion homogenization and freezing-melting analyses. Combined sedimentology, stratigraphy, and geochemical data may show that the Hutchinson Salt represents a transition from marine to continental setting for the mid Permian of Kansas.