Wilson County, Southeastern Kansas, U.S.A. Its geologic environment, cyclic sedimentation, basic intrusive rocks, and mineral and petroleum resources.

Wilson County is situated in the southern part of the Midcontinent region of the United States. The Nemaha Ridge lies to the west, the Bourbon Arch to the north, the Ozark Dome to the east, and the Amarillo-Wichita-Arbuckle complex to the south. Extensive field mapping was done in order to determine the geologic characteristics of the strata and to delineate the limits of deposits of limestone (for cement, lime, and road aggregrate), of clay (for brick, tile, and other building materials, and as a mixer in the rock-wool industry), and of coal (for heating purposes); this study and an associated study of bore-hole data from thousands of wells drilled for oil and gas have provided new insight into many fascinating aspects of Kansas geology. The Precambrian basement, encountered at depths below 355 m, includes granite, syenite, schist and gneiss. Through the Paleozoic there was extensive sedimentation ranging from varied coarse detritus from surrounding areas of orogenic uplift to Pennsylvanian epicontinental carbonates containing deltaic and channel filling clastics from the east, south, and west. Five unconformities were recognized below the Pennsylvanian which can be seen throughout the area as cyclic sequences of limestone, sandstone and shale. Six major cyclic units can be recognized over several hundred square kilometers with persistent sedimentary and biological features. They are attributable to Milankovitch-type cycles invoked to explain the nature of glacial deposits of Northern Europe. The great variety and abundance of marine plants and invertebrates reflect the changing geological environment. The mound lithofacies is dominantly a calcilutite with phylloid algae, the channel and rim lithofacies are calcarenites with echinoderm debris and brachiopods respectively. The area contains only two contrasting structural features of interest. The Fredonia Dome is a short complex anticlinal feature which is important for oil and gas production. The Silver City Dome is attributed to intrusion by several Cretaceous sills of lamproite encountered in boreholes; a very micaceous yellowish clay represents the lamproite at the outcrop. The youngest strata encountered are Tertiary and Quaternary gravels containing abundant chert pebbles derived from chert-rich limestones to the northwest; the gravels were deposited by vigorous migrating streams and rivers.