Constraining the timing and provenance of trans-Laurentian transport using Nd and Sm isotopes from Silurian and Devonian marine carbonates

Abstract

We demonstrate trans-Laurentian transport processes during the late Silurian and Late Devonian via a combination of eolian transport, large rivers traversing up to 3000km, and mid-Laurentian epeiric seawater currents using Nd and Sm isotopes from marine limestone successions. Upper Silurian εNd(425Ma) range from −10.94 to −8.27. Upper Devonian εNd(380Ma) range from −12.83 to −6.44. Negative and absent linear correlations for 147Sm/144Nd versus 143Nd/144Nd for upper Silurian and Upper Devonian samples reflect mixing between older (low εNd) and younger (higher εNd) sources. Upper Silurian samples reflect major contributions from an average Acadian source (higher 143Nd/144Nd and εNd) and the Canadian Shield and/or Transcontinental Arch (low 143Nd/144Nd and εNd). Upper Devonian samples also demonstrate mixing between the Acadian and Canadian Shield/Transcontinental Arch, with minor contributions from proximal ophiolites, arc volcanics, and local uplifts. A compilation of Cambrian-Mississippian εNd(t) data from sedimentary rocks across Laurentia illustrate a transition from older (low εNd) to younger (higher εNd) sources was established in mid-Laurentia by the early Silurian and in western Laurentia by the Middle Devonian. These results suggest that transport of weathered continental material to marine basins is more complex than a simple source-to-sink model, involving contributions from multiple sources over thousands of kilometers of transport from the original source to marine basins.