An ancient river channel system incised on the Precambrian–Cambrian unconformity beneath Jackson County, Ohio

Abstract

We analyzed a migrated three-dimensional (3-D) seismic reflection data set collected from Jackson County, Ohio, using volume-based voxel visualization technology. Adjusting the opacities of voxels in a time slab centered on the Precambrian reflector revealed a drainage channel system incised on the Ohio Precambrian surface, approximately 1460 m (4800 ft) below sea level. Formation sculpting of the Precambrian surface produced an image of 100-m (330-ft)-wide tributaries on the Precambrian unconformity joining to produce a 400-m (1320-ft)-wide channel roughly parallel to the subsurface trend of the Grenville front beneath Ohio. Broadening and splitting of the zero-phase seismic wavelet that defines the Precambrian reflector reveals the channels. The seismic signature is caused by thin-bed interference effects caused by reflections at the boundary between the channel fill with the overlying Mount Simon Formation and the boundary with the underlying Precambrian surface. The seismic images, therefore, locate a new lithologic unit in the Ohio subsurface. The channels are older than the overlying Mount Simon Formation and so must be at of least Middle Cambrian age. The channel morphology indicates flow in the direction of the Rome trough, approximately 60 km (37 mi) to the south, likely transporting sediment to that basin. Given the tiny volume of Ohio sampled by 3-D seismic methods, such buried channels must be common on the Precambrian surface.