Chemistry and Mineralogy of < 2μm Size Fraction of Non-Marine Cyclothems, Dunkard Group, Upper Pennsylvanian-Lower Permian, in Ohio, U.S.A

The acid insoluble < 2μm size fraction of 22 sandstones, 36 shales and 15 limestones from the largest exposed section of the Dunkard sediments was analysed by X-ray diffraction for the clay minerals and by spectrographic methods for trace elements. After verification of the precision and accuracy in the data, the results were statistically processed.

Vermiculite, kaolinite, illite, chlorite and mixed layer lattice minerals are the principal clay minerals identified. Montmorillonite was identified only in two samples out of 75 and corrensite in a single sample. The clay mineralogy appears to have been diagenetically altered particularly in sandstones. The migration and incorporation of trace elements into the clay minerals differ with the lithological type being deposited irrespective of the clay mineralogy. Ni and Cr seem to be present in vermiculite. Fe in the < 2 μm fraction of sandstones seems to have been dispersed by more than one process. The K/Rb, Ga/Ti ratios have distinct ranges for each of the lithologies.

Compared with crustal abundance values (Taylor, 1964), the average Dunkard rock has higher K, Rb, Mn, Ga, Y, Ni, Sc and Cr, and lower Ti, Fe, V, Zr, Cu, Co and Sr values.