PALEOCLIMATE TRENDS RECORDED IN EPHEMERAL LAKE HALITE DEPOSITS OF THE PERMIAN NIPPEWALLA GROUP OF WESTERN KANSAS

The Permian Nippewalla Group, likely uppermost Leonardian (Kungurian), in the Rebecca Bounds core of western Kansas is composed of redbeds and evaporites that typify the Permian succession of the North American midcontinent. While the majority of the Nippewalla Group in this core is dominated by mud-sandflat and eolian deposits, ephemeral lake evaporites, including bedded halite, are found throughout the Nippewalla at depths of 587-782 m. The bedded halite consists mostly of chevron and cumulate crystals that exhibit dissolution surfaces and pipes as well as desiccation features suggesting multiple episodes of flooding, evapo-concentration, and desiccation. These observations, and previous work, suggest that individual beds represent halite precipitation on time scales on the order of hours to days. In this study, we use the homogenization temperature of artificially nucleated vapor bubbles in primary, unaltered fluid inclusions from crystals in bedded halite to determine the temperature of the parent brine (lake water) during precipitation. Since these lakes were shallow (<50 cm), lake water temperature is a good proxy for air temperature. Although any given halite bed is a record of paleoweather, combining homogenization temperature data from different beds at the formation-scale as well as trends between individual beds allow meaningful paleoclimate reconstructions. In the lowest Nippewalla Group, average temperatures increase from ~26 to ~40°C. This warming trend is associated with a transition from massively bedded gypsum to mud-sandflat and eolian deposits. In the middle Nippewalla Group, average temperatures decrease from ~44 to ~35°C. This cooling trend is associated with a transition from eolian deposits back to predominantly mud-sandflat deposition. In the uppermost Nippewalla Group, average temperatures are consistently between 20 and 33°C and are associated with the recurrence of massive gypsum deposition in the Blaine Formation. The paleotemperatures found in this study agree well with those reported previously for Permian halite from New Mexico, Kansas, and South Dakota. Furthermore, the highest temperatures observed in this study, ~70°C, are from bedded halite within the widespread, eolian Cedar Hills Sandstone, suggesting conditions similar to the modern Lut Desert of Iran.