Textural and Mineralogical Characteristics of Tills of Northeastern and North-Central Ohio

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ABSTRACT. Textural and mineralogical parameters of over 3400 till samples are summarized to provide a database for scientists and engineers working with fractured tills in Ohio. Matrix textures (% <2.0 mm), carbonate contents (% <0.074 mm), and diffraction intensity ratios (illite/chlorite + kaolinite) were commonly measured. Texturally, most tills become sandier and less clay rich as they are traced onto the Allegheny Plateau. The overall distribution of mean textures of the Illinoian tills is similar to that of the Late Wisconsinan tills. Incorporation of local clastic bedrock on the plateau or changes in mode of deposition may be the reason for increased sand content. Carbonate contents of tills are generally larger in the Lake and Till plains provinces, and carbonate contents decline along transects from the Till Plains to the Allegheny Plateau. Exceptions to this trend are caused by the release of far-traveled carbonates from the englacial load of glaciers during formation of end moraines. Similarly the lithology of the sand fraction (1.0-2.0 mm) reflects the underlying bedrock, but proportions of igneous and metamorphic rock fragments increase within end moraines where englacial load is released. Diffraction intensity ratios decrease onto the plateau because of the entrainment of Pennsylvanian-age shales containing kaolinite. Numerous factors such as glacier dynamics, topography of the underlying bedrock, bedrock lithology, amount of bedrock exposure, and dilution by older glacial deposits affect the texture and composition of tills. Future research should examine the possible relation of texture and mineralogy to joint width.


Author Institution: Dept. of Geology, University of Akron, Akron, OH



The Ohio Journal of Science, v106, n2 (April, 2006), 9-16.