Buried Pre-Cambrian Hills in Northeastern Barton County, Central Kansas

Abstract

Six buried pre-Cambrian hills in the Kraft-Prusa, Beaver, and Bloomer oil fields are defined by 952 tests drilled within the 160 square miles mapped. These flat-topped hills were quartzite monadnocks on a Cambrian peneplain eroded across pre-Cambrian quartzite, schist, granite, syenite, granite-gneiss, and pegmatite. During the deposition of 220 feet of lower Cambro-Ordovician Arbuckle beds these monadnocks were islands. On their slopes sediments were deposited with 2° to 5° initial dips. They were buried under 340 feet of upper Cambro-Ordovician dolomites, under 40 feet of Ordovician Simpson shale, and probably also under 650 feet of younger pre-Pennsylvanian strata. Erosion culminating in an early Pennsylvanian peneplain exhumed five of the hills. Slight uplif followed. The paleo-outcrop belt of the truncated Cambro-Ordovician dolomites became a youthful karst plain pitted by sinkholes. Solution valleys to 1½ miles in width fringed each resurrected pre-Cambrian hill at the dolomite-quartzite contact. These solution valleys and sinkholes are partly filled with untransported leached residuum (chert, clay, sand) of the Cambro-Ordovician beds and with transported residuum-derived material deposited in them either as non-marine or marine Pennsylvanian conglomerate. In late Des Moines time the pre-Cambrian hills became diminishing islands in a transgressing sea. Limestones of the Missouri series were deposited on their summits. They are now buried under 3,300 feet of Pennsylvanian, Permian, and Cretaceous rocks. Oil is produced from Pennsylvan an limestones, shore-line sands of the Pennsylvanian marine conglomerate, Cambro-Ordovician dolomite, Cambro-Ordovician residual sand, and pre-Cambrian quartzite. The data obtained in this 4-year sample study were summarized graphically by plotting the height of the hills above the average ground surface, or their depth of burial below it, as ordinates and geologic times as abscissas. The resulting curve summarizes quantitatively the vertical movements experienced by the six quartzite hills from late pre-Cambrian time to the present.