Initial 143Nd/144Nd ratios of clastic sedimentary rocks in the Ordovician Taconic and Sevier foreland basins increase with decreasing stratigraphic age. This shift in isotopic composition reflects an increased influx of juvenile sediment to both basins. For the Taconic basin, geologic and isotopic data are consistent with the juvenile sediment being derived from uplifted Grenville crust, upthrust as part of the Taconic allochthons, sediment derived from the Bronson Hill arc, or a combination of both. For the Sevier foreland basin, there are few geologic constraints on source regions, but the similar shift in isotopic ratios with time suggests a similar increase in the influence of juvenile sources such as exotic terranes. Sevier basin sedimentary rocks have higher ϵNd values than those within the Taconic basin, thus juvenile source areas were of greater importance to Sevier basin sediments.