Data report: grain size distribution of unconsolidated sands offshore Shimokita Peninsula, Japan (IODP Site C0020)

Abstract

We report particle size analyses measured from 28 unconsolidated sand samples recovered during Integrated Ocean Drilling Program Expedition 337 from Hole C0020A. These samples span from 1277 to 2002 meters below seafloor (mbsf) across two lithostratigraphic units that record a transition from a nearshore estuarine/ intertidal to an offshore hemipelagic paleoenvironment. Most recovered lithologies, including coarse-grained lithologies, are semiconsolidated to consolidated; however, some intervals of sand are unconsolidated and suitable for particle size analysis. Bulk sand samples were measured using a laser diffraction particle size analyzer. All samples fall within the range of sand to silty sand, with silty sand more abundant deeper than 1925 mbsf. Samples contain 49%-97% sand, 3%-42% silt, and 0%-13% clay. Median grain diameter ranges from 55 to 405 µm. Clay and silt content in these sands reach a minimum at ~1500 mbsf and then increase below 1925 mbsf in a coal-bearing unit containing shale, siltstone, sandstone, and unconsolidated sand. The recovered sediment sequence revealed a transition from offshore marine to nearshore/terrestrial environments that was described in four lithostratigraphic units (Figure F1) (see the "Site C0020" chapter [Expedition 337 Scientists, 2013b]) that span the late Oligocene to early Pleistocene (Phillips et al., 2016). Unit I (647-1256.5 mbsf; no core recovery) is composed of a hemi-Chapter contents