Sand Trends and Paleoslope in Illinois Basin and Mississippi Embayment1

Abstract

Relationships between major sand body trends and facies distributions of the Cretaceous Gulfian Series in the Mississippi embayment and the Mississippian Chesterian Series in the Illinois basin have been investigated. This study indicates that trends of major sand bodies in these two depositional basins are intrinsically related to their paleoslopes, depositional strikes, and basin axes. Major sand bodies in the Gulfian and Chesterian Series have southwesterly trends that parallel the respective paleoslopes and basin axes, and that are normal to depositional strikes. Studies of directional properties enhance the predictability of these trends. An impressive similarity exists between the sediments in the Gulfian Series of the Mississippi embayment and the Chesterian Series of the Illinois basin. Both basins were open-ended to the south and sediments were introduced longitudinally at the northeastern end; the paleoslopes were to the southwest and parallel with the basin axes; the depositional strikes were east-west, normal to the basin axes; sediment transport directions were to the southwest; and the depositional patterns are those of deltaic deposition in the north, becoming increasingly marine to the south. Based on the parallelism exhibited by these features, a depositional model has been developed for this type of sedimentation in an intracratonic basin. Within the model, trends of major sand bodies are oriented parallel to the basin axis, paleoslope, and sediment transport direction, are normal to the depositional strike, and are the result of a deltaic pattern of sedimentation.