Late Cenozoic Ice-Rafting Records from Leg 145 Sites in the North Pacific: Late Miocene Onset, Late Pliocene Intensification, and Pliocene—Pleistocene Events

Abstract

Ice-rafted debris (IRD) in marine sediments provides a valuable direct indicator of the presence of glacial ice at sea level on surrounding continents, and is therefore a useful tool in paleoclimatic studies. The location of sites drilled during Ocean Drilling Program Leg 145, combined with the length, stratigraphic integrity, and good age control of the sediments recovered, provides an opportunity to examine the Late Cenozoic record of North Pacific ice rafting at locations within a few hundred kilometers of potential IRD sources. Ice-rafting records for Sites 881, 883, and 887 have been determined, with temporal resolution ranging from one sample per 10 k.y. to one sample per 50 k.y. The mass accumulation rate (MAR) of IRD in the coarse sand-sized fraction of each sample has been calculated from the abundance of coarse sand (wt%), the IRD abundance within the coarse sand fraction (vol%), shipboard measurements of sediment dry-bulk density, and average sedimentation rates constrained by shipboard paleomagnetic and biostratigraphic data. The oldest occurrences of IRD in Leg 145 cores are at least late Miocene in age, and variations in IRD MARs prior to 2.6 Ma are consistent with interpretations of an older episode of tidewater glaciation (~6 to ~4.2 Ma) and a mid-Pliocene warm interval (-4.2 to-3.0-3.5 Ma) recorded in the Yakataga Formation of coastal Alaska.