MINERALOGY AND PROVENANCE OF PINK INCLUSIONS IN THE ILLINOIAN TITUSVILLE TILL, MAHONING COUNTY, EASTERN OHIO

Researchers, who have mapped glacial sediments within the glaciated portion of the Allegheny Plateau, have noted the occurrence of isolated diamicts having a pink color and containing more carbonate minerals than their surrounding gray diamicts. A large continuous exposure in a strip mine near North Lima, Mahoning County, Ohio, provides an opportunity to examine the physical relationship of pink diamicts to gray ones. Pink layers of diamict tend to thicken, thin, bifurcate, and may also surround clasts within gray layers: pink blebs of diamict also occasionally appear within the gray diamicts. The pink layers range from a 2 mm to approximately 80 cm in thickness and extend for more than 20 m laterally. Layers disappear under overburden and reappear at the same elevation 16.5 m away.

The matrix texture (% < 2 mm), carbonate (% < 0.074 mm) and clay mineralogy, and elemental composition of samples of pink and gray diamicts were examined for major differences. More variation was found in the sand fractions of gray samples than in those of pink samples. Pink samples average 31% sand, 43% silt, and 26% clay, whereas gray samples contain 55% sand, 27% silt, and 18% clay; differences are statistically significant at P ≤ 0.05. Pink diamicts have more total carbonate in the medium-sand to silt fractions but contain 6.6% total carbonate compared to 5.2% for gray diamicts. Diffraction intensity ratios (DI) average 1.1 for pink diamicts and 0.9 for gray diamicts; this difference is statistically significant. A 32-element chemical analysis of both the sand and fine fractions shows that composition of pink diamicts differs significantly from that of gray diamicts in 7 of 25 comparisons for the sand fractions and 12 of 25 for the fine fractions. Both sand and fine fractions contained significantly different amounts of Al, Ba, K, Mg, and V.

Geometry and laboratory analyses of diamicts at this site suggest that pink diamicts have a source in the Queenston and Grimsby formations of the Niagara Peninsula. Eroded blocks of these formations may have been transported englacially and smeared out along shear planes in thrust-stacked gray units at the terminus of the Illinoian Titusville glacier.