GEOLOGIC SETTING OF COAL BALLS IN IOWA

Iowa was formerly a significant source of coal balls: masses of mineralized peat that preserve plant material in microscopic anatomical detail. The earliest geologic observations (1894) and the first illustrations of fossil plants from American coal balls were made here. Coal mining began around 1840 and became a major industry in Iowa with the advent of railroads following the Civil War, peaking during the first decade of the 20^th century. More than 220 mines operated in the city of Des Moines. Underground extraction concentrated in upper Atokan and lower Desmoinesian coal beds that locally exceeded 2 m thick and in one case approached 5 m thick. However, these seams were notoriously lenticular and difficult to correlate. Younger Desmoinesian coals are regionally extensive but seldom thicker than 1 m. Gleaning geological information from paleobotanical publications on Iowa coal balls requires much detective work. Some do not even correctly report the name of the mine. Nearly all collections were made by third parties such as mine workers or gathered from waste piles at mine tipples, where potentially more than one coal seam was collected. A few collections were made by paleobotanists from in situ coal in surface mines during the middle 20^th century. Online and published sources were searched to identify all localities where coal balls were collected. Borehole data, including continuous core records, from the Iowa Geological Survey enabled pinning down identity of coal beds. Cores drilled at Buxton and Lovilia actually penetrated coal balls. Sketches and descriptions of coal balls appear in comprehensive reports published by the Iowa Geological Survey during the late 19^th and early 20^th centuries. Little can be gleaned about geologic setting or origin of these petrifactions beyond the fact that host coal beds are overlain by marine shale and limestone. With the demise of the Iowa coal industry in 1995 the outlook for further collection and research is practically nil.