Abstract Extraction of soluble minerals, whether by natural or man-induced processes, can result in localized land-surface subsidence. The subsidence is caused by partial or total collapse of underground cavities resulting from dissolution of salt or other soluble evaporites. In many cases, subsidence is ultimately related to the strength limit of the overlying rocks that form the unsupported roof above the cavity. Downwarping results where strength of roof spans are exceeded. In other cases, collapse of the undermined roof causes stoping of the overburden rocks. If sufficient underground space is available for the loosely packed rock debris to collect, the void can migrate to the surface and produce surface subsidence, or in the extreme, catastrophic surface collapse. Another mechanism is subsurface erosion of susceptible layers (sandstone, silt, loess) overlying salt cavities. Ground water can erode and transport the loose material down subsidence-induced and natural cracks, or drill holes into the salt cavity. The voids formed in the higher eroded beds can then cause surface subsidence.

The purpose of this study is to reconstruct the geologic history of a sinkhole collapse basin that formed during late Pleistocene time in Meade County, Kansas; to determine the nature of the vertebrate faunas that lived in and around this basin during Illinoian glacial, Sangamon interglacial, and Wisconsin glacial times; and to reconstruct, on the basis of the fossils, some of the local environments and climatic conditions that existed in the southern High Plains during late Pleistocene time. Small fossils were recovered from the sedimentary deposits by washing and screening large quantities of matrix. Most of these fossils were identified by comparing them with Recent skeletal remains of the same species. Remains of larger, extinct mammals also were found. Mapping of the geology was facilitated by the use of aerial photographs, topographic maps, and Brunton compass. The basin under study is called the Butler Spring Basin and is located in southern Meade County, Kansas, about 1 mile north of the Cimarron River. It is approximately 1 mile in diameter and is believed to have formed when subsurface solution of salt and anhydrite from Permian beds caused the collapse of overlying beds of Pleistocene age. Studies of fossils preserved in the sediments filling the basin have demonstrated the presence of four superimposed vertebrate faunas. Associated with some of these faunas are mollusks, freshwater ostracods, and pollen. The oldest fauna occurs in stream deposits of the ancestral Cimarron River which lie topographically below the High Plains surface and which represent a period of downcutting during late Pleistocene time. Younger faunas occur in a series of overlying silts and sands of sinkhole origin. On the basis of stratigraphic position, faunal composition, and associated floral (pollen) evidence, the faunas are assigned to the third (Illinoian) and fourth (Wisconsin) glacials and the intervening third (Sangamon) interglacial. The Adams local fauna (Illinoian) contains fragmentary remains of large mammals taken from sands and gravels of the ancestral Cimarron River. In the Butler Spring local fauna (late Illinoian), the occurrence of Sorex cinereus , masked shrew; Citellus richardsoni , Richardson ground squirrel; and Microtus pennsylvanicus , meadow vole, whose present ranges do not extend as far south as Meade County, Kansas, suggests summers that were cooler and more moist than those in the area today. The Cragin Quarry local fauna (Sangamon) occurs in sediments which overlie the Butler Spring local fauna. It includes a large and diverse mammalian assemblage; many of the species are upland prairie forms. The remains of the tortoises Gopherus and Geochelone indicate a warm, interglacial climate. A massive caliche immediately above the faunal zone suggests a period of prolonged weathering and aridity—perhaps during middle Sangamon time. The Robert local fauna (late Wisconsin) consists of microvertebrates collected from a 1-foot, dark-gray to black silt or soil zone just below the surface in the immediate vicinity of Butler Spring. Most of the mammals are characteristic of marshy conditions or moist, low meadows. A radiocarbon date of 11,000 ± 390 years B.P. was obtained by dating shells of Succinea ovalis Say. Several of the mammalian species represented in the fauna are not found as far south as Meade County, Kansas, at the present time. Eleven of the extant species may be found living today in northeastern South Dakota. From a study of temperature and effective precipitation in both areas, it appears that the Robert local fauna lived in Meade County, Kansas, during the late Wisconsin glacial in a climate which had cooler summers and more effective moisture than occur in the area today, and that this climate is probably similar to that of northeastern South Dakota today.