Data report: clast counts and petrography of gravels from Site C0007, IODP Expedition 316, Nankai Trough

Abstract

Gravel beds drilled during Integrated Ocean Drilling Program Expedition 316 at Site C0007 in the eastern Nankai Trough, ~100 km offshore from the Kii Peninsula of Honshu, southwest Japan, have been investigated using 26 samples from two horizons (Cores 316-C0007C-17H and 316-C0007D-12R). The gravel from Core 316-C0007C-17H is from a 1.7 m thick layer, whereas the gravel from Core 316-C0007D-12R is from a layer 4.55 m thick. The upper parts of both layers are normally graded. The gravel is clast-supported, polymictic, of granule to pebble size, moderately to poorly sorted, and with subrounded to angular fragments. Clast types are similar from both cores with abundant fine-grained sedimentary clasts that are well cemented, and many clasts contain small quartz veins indicative of a source with a very low metamorphic grade. The main sedimentary clast types are chert of various colors (black, gray, light yellow-brown, clear, and rare red and purple), siltstone, and sandstone. Other clast types are vein quartz and igneous clasts of mainly intermediate volcanic composition, minor plutonic rock fragments, and minor metamorphic rock fragments. Intraformational soft mud fragments occur in most samples.