CEMENTATION HISTORY OF THE CORBIN SANDSTONE MEMBER OF THE GRUNDY FORMATION (LOWER PENNSYLVANIAN) IN EAST-CENTRAL KENTUCKY

The Corbin Sandstone is member of the Pennsylvanian age Grundy Formation in eastern Kentucky. It is a buff to reddish colored, medium- to fine-grained, quartzarenite to sublitharenite. Samples collected from the Corbin Sandstone can vary from very hard and well indurated to extremely friable and poorly indurated. To understand these differences, we statistically compared the texture, mineralogy and petrography of well-cemented/indurated samples against those which were poorly cemented and very friable.

Eighty eight samples were collected from nine localities across east-central Kentucky. For each sample grain size and degree of induration was determined and thin-sections were cut and point-counted. Samples were also examined using x-ray diffraction and the SEM to determine the type of cement and the relationship of the cement to framework grains.

It was found that the degree of induration of the Corbin Sandstone depended upon the original texture of the rock, and the amount and type of cement present. Well-indurated samples had smaller grain sizes, were more poorly sorted, with lower initial porosities and a higher percentage of hematite cement. Poorly indurated samples had larger grain sizes, were better sorted, with higher initial porosities and a greater percentage of clay cement(primarily kaolinite). Evidence from thin-sections and Scanning Electron Microscopy suggested that cement precipitation occurred in the following sequence: (1) formation of quartz overgrowths on detrital grains, (2) precipitation of hematitic cements, and (3) precipitation of clay cements in the remaining pore spaces. Since clay mineral precipitation was the last stage, the well-indurated samples with fewer and smaller pore spaces were already infilled before any appreciable amount of clay cement could precipitate. The poorly indurated samples had more interstitial pore space that could accommodate the final phase of clay precipitation.