Guidebook—Geology of the Kanopolis Lake Area

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Kiowa Formation

The Kiowa Formation is exposed in several places around Kanopolis Lake. The Kiowa is a heterogeneous unit made up of shale, siltstone, sandstone, and coquina limestone ("shell-beds"). The thickness of the Kiowa Formation in Ellsworth County ranges from 110 to 150 feet.

The lower part of the Kiowa Formation is a medium to dark gray, and black, shale that splits easily. Thin sandstone bodies are common throughout the unit, and a persistent, thick, light-colored sandstone occurs at the top. Beds of cone-in-cone, "quartzitic" sandstone, siltstone, and thin limestone are common. Pyrite, marcasite, gypsum crystals, ironstone concretions, lignitized wood fragments and logs, and marine invertebrates (mainly bivalves and gastropods) are found in the shales. Marine molluscs occur in the limestone.

Sandstone is a major component of the Kiowa Formation in the Kanopolis Lake area. The sandstones are very light gray to pale grayish orange, but in places hematitic (iron) stain and cement color it reddish brown. Barite rosettes, ripple marks, and crossbedding can be seen in the sandstones.

These rocks formed from sediments that were deposited in nearshore to coastal environments as the early Cretaceous sea spread northeastward across gentle terrain developed mainly on Permian rocks. The climate was probably warm and humid. The shales were deposited in relatively quiet water where the bottom was only occasionally disturbed by currents and waves. Bottom-dwelling marine life inhabited bays or other places where salinity and current or wave activity were favorable. Stronger currents, waves, or storms destroyed and reworked some of these areas to form the coquina shell-beds.

The abundance of sandstone and associated carbonaceous material in the upper part of the Kiowa Formation is evidence that the seas were starting to recede and marked the beginning of deposition of the overlying, mostly non-marine Dakota Formation.

Cone-in-cone—Cone-in-cone structure forms oval-shaped concretions and discontinuous lenses in the Kiowa Formation in many parts of Ellsworth County. Formation of cone-in-cone is attributed to precipitation and growth of fibrous crystals of calcite soon after the sediments were deposited. A unique set of physical and chemical conditions was essential to the formation of cone structures in the sediment. Decaying organic matter in the sediments underlying the cone-in-cone may have lowered the pH in the sediments sufficiently to cause recrystallization of the calcite. Gravity-induced stresses during compaction of the sediment may have been partly responsible for the near vertical orientation of the calcite fibers and the cone structures. Contortion of the shale beds around the cone-in-cone structures indicates that the cone-in-cone developed before the enclosing sediments were firm and were still quite plastic.

Marcasite—Common in the dark gray shales of the Kiowa, marcasite (iron sulfide) is distinguished from pyrite by its pale bronze color and flat or bladed crystals. Pyrite is darker in color and has cubic crystals.

Gypsum crystals—Weathered shale, slopes are littered with crystals of gypsum (selenite) measuring up to 7 inches in the long dimension. Radial aggregates (sunbursts) of gypsum may also be found. The gypsum (calcium sulfate) is a secondary product derived from the weathering of iron sulfide (mainly marcasite) in the shale.

Clay-Ironstone concretions—Composed mainly of very fine-grained siderite (iron carbonate) and some clay, these concretions occur in thin discontinuous zones parallel to the bedding of the enclosing shale. On weathering, the concretions break into angular fragments.

This guidebook is also available in print form as Kansas Geological Survey, Open-file Report 2003-52, from KGS Publications Sales office, 785-864-3965.

Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey. Text by Jim McCauley, Bob Sawin, Rex Buchanan, and Liz Brosius, Kansas Geological Survey.

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