Sources of Basal Pennsylvanian Sediments in the Eastern Interior Basin 1. Cross-Bedding

Abstract

The long distance separating the basal Pennsylvanian sediirents of the Eastern Interior Basin from possible major source areas combines with mineralogic maturity to make solution of the source-area problem difficult. Our approach toward its solution utilizes both regional cross-bedding mapping and petrology. Statistical analysis provided measures of reliability for estimates of regional cross-bedding directions, estimated the variability arising from levels of subsampling, and made possible significant economies in field sampling. Over 1,000 miles of linear basal Pennsylvanian outcrop in the Eastern Interior Basin, northwestern portions of the Appalachian Basin, and Michigan Basin were examined in 41 days. Over 950 measurements of cross-bedding in 340 outcrops were obtained. The parallelism of local and regional cross-bedding directions to orientation of the subaerially formed channels of the Mississippian-Pennsylvanian unconforrr ity, directions of regional stratigraphic overlap, and regional quartz-pebble distribution indicate that, measured over wide areas, cross-bedding direction reflects the regional slope from the source area. Based on this hypothesis, the basal Pennsylvanian sediments of the Eastern Interior Basin had a minor source area to the northwest, in the direction of the Transcontinental Arch, and a major source area to the northeast. Northeasterly source directions are also indicated for the basal Pennsylvanian sediments of the Michigan Basin and adjacent portions of the Appalachian Basin. Hence, excluding the western shelf area of the Eastern Interior Basin, the craton in the north-central states had a regional slope to the south-southwest. This portion of the craton had source areas in the middle and northern Appalachians and the southeastern Canadian Shield.