Nd and Sr isotopic signatures of fine-grained clastic sediments: A case study of western Pacific marginal basins

Stratigraphic isotopic fluctuations within the Shikoku Basin are sharp, spanning five ɛNd units, and roughly synchronous across the topographically complex basin floor. Fluctuations in the isotopic signature are used to correlate drill holes across over 5400 km2 of basin floor. The isotopic signature of fine-grained sediments reflects the average isotopic composition of the entire source region, and stratigraphic fluctuations in the isotopic signature record variations in the relative importance of isotopically distinct crustal domains through time. Isotopic variations are synchronous across the Shikoku Basin, and are interpreted to reflect episodic basin margin volcanism superimposed on a background of hemipelagic sedimentation with a strong eolian component. Fluctuations in the isotopic signature of basinal strata ultimately result from geologic events on the basin margins and paleoclimatic influences, and may therefore be useful in reconstruction of basin evolution.