Appalachian basin architecture during Middle Ordovician time was dominated by a Black River ramp to the northwest flanked by the central Appalachian basin along its southeast margin, with the deeper Sevier basin still farther to the east and southeast. The ramp margin, which marked the western edge of the central Appalachian basin, was in the approximate location of the western edge of the Rome trough. Black River carbonate rocks were deposited on this broad, stable, shallow-water ramp as empiric seas transgressed much of what is now the Appalachian region, while thick, shaley carbonates were being deposited within the trough-influenced foredeep and clastic sediments were being deposited in the Sevier basin. The elongate, north-northeast-trending depocenter that developed during early Black River time would continue to exist and even expand throughout the remainder of the Ordovician Period.