The science and industry of the Permian Hutchinson Salt

The 120-m-thick Hutchinson Salt Member of the Permian Wellington Formation of central Kansas supports multiple industries. Composed of bedded halite, gypsum/anhydrite, and minor siliciclastic mudstone, it was deposited by shallow saline waters in a warm, dry climate. Underground salt mines access the purest horizon, producing salt that is distributed through the United States and Canada. The vast space left by mining supports a prosperous commercial storage enterprise and a popular underground tourist attraction. Vertical solution-mined caverns host the nation’s primary midcontinent liquid petroleum gas storage industry. This fi eld trip will explore the origin and use of the Hutchinson Salt in core samples and subsurface outcrops while meeting in an underground salt cavern, and above ground at a solution-mined storage cavern. Schulmeister, M.K., Andeskie, A.S., and Benison, K.C., 2019, The science and industry of the Permian Hutchinson Salt, in Schulmeister, M.K., and Aber, J.S., eds., Exploring Extreme and Unusual Geology in the Stable Midcontinent: Field Excursions for the 2019 GSA South-Central, North-Central, and Rocky Mountain Sections Joint Meeting: Geological Society of America Field Guide 52, p. 25–35, https://doi.org/10.1130/2019.0052(02). © 2019 The Geological Society of America. All rights reserved. For permission to copy, contact editing@geosociety.org. INTRODUCTION The Hutchinson Salt, underlying an area of ~96,000 km (37,000 mi) mainly in central and south-central Kansas, is considered a saline giant (Walters, 1978; Fig. 1). It attains a thickness of up to 122 m in Kansas and is composed of ~60%–80% halite (Kulstad, 1959; Walters, 1978). Although this bedded halite deposit is one of the Earth’s most famous salt deposits, it has been the subject of limited study. In particular, its depositional environment and the brines’ chemistry have not been clearly established. In addition to its scientifi c relevance, the deposit has a rich and evolving history as an economic resource. This fi eld guide focuses on the Hutchinson Salt in the Hutchinson, Kansas, area. The objectives of this fi eld trip and guide are to provide an overview of the Hutchinson Salt’s industrial uses, as well as to describe the past and current studies about its sedimentology, diagenesis, and depositional environment. The History of Salt Mining in Central Kansas The use of salt marshes and springs by Native Americans and early travelers is reported in central Kansas prior to the arrival of European settlers (Sawin and Buchanan, 2002). Natural salt licks that formed from evaporated shallow pools attracted bison, deer, antelope, and elk. In turn, early hunters would use the salt to preserve meat. In 1875, rock salt was discovered in Hutchinson by local entrepreneurs, who attempted to pump the brine to a regional processing plant, evaporate it, and sell the salt to U.S. markets (Vincent, 1915). The brine was not pure enough to evaporate for use as table salt, however, and their endeavors failed. In 1887, a real estate developer drilled in search of oil on land he had purchased in South Hutchinson. His test wells revealed salt instead of hydrocarbons. Solution mining salt plants were immediately developed in Lyons, Kingman, and Kanopolis, Kansas. Underground mining of rock salt began in 1923, when the Carey 26 Schulmeister et al. Salt Mine (now the Hutchinson Salt Mine) was established. Salt mining has contributed signifi cantly to the history and economic vitality of the city of Hutchinson. The morning fi eld-trip stops highlight the geologic origin of the salt deposit in the Hutchinson Salt Mine, as well its mining history and additional use as an underground storage facility and museum. Liquid Petroleum Storage in the Hutchinson Salt Given its impermeable, non-reactive nature, annealing properties, and compressive strength similar to that of concrete, the Hutchinson Salt is well suited for the storage of liquid petroleum gas (LPG). Under pressure, salt behaves plastically, causing cracks or fi ssures to heal themselves. Halite forms an impermeable layer that will not leak or allow entry of extraneous fl uids. The solution mining process used to produce salt brine has been utilized since the 1950s to create storage caverns in the lower part of the Hutchinson Salt Member for liquefi ed hydrocarbons. Although hydrocarbons are stored in caverns at other locations in the United States, Kansas has more storage caverns than any other state. In 2013, there were nine active LPG storage facilities in Kansas, operating 382 active storage caverns with a total storage capacity of ~73 million barrels (Kansas Department of Health and Environment, 2013). The signifi cant storage capacity and a central distribution hub in the Hutchinson region have established the region as one of several large national centers for LPG transmission. The afternoon fi eld-trip stop features one such facility, the Enterprise Products Hutchinson Underground Storage facility in South Hutchinson.