Deep-Sea Sediments

Abstract

Deep-sea sediments typically have sedimentation rates less than 30 m/10 years, and rates as low 0.1 m/10 years have been reported. The slow sedimentation rates and unusual sediment compositions reflect the low fluxes of aluminosilicates eroded from continents. The terrigenous material that does deposit is often windblown dust. Other solids produced through biological activity, through hydrothermal leaching of basalts, or even by earth’s bombardment by meteorites can make up large fractions of a deepsea sediment deposit. Not all sediments in the deep ocean are deep-sea sediments depositing slowly. A significant portion of the deep ocean is filled by turbidites, which are gravity flow deposits that typically originate from the continental margins. These sediments will be discussed briefly in section “Turbidites and Hemipelagic Sediment Components” but are really extensions of continental margin sedimentation. Typically, the total sediment accumulation in the deep sea that is on basalt crust is less than 250 m (Fig. 1; Whittaker et al., 2013). For most ocean regions, sediment production is small compared to erosion of mountains and river transport. Because of plate tectonics, there is little time to accumulate a thick sediment pile because the ocean crust is young – the seafloor is totally resurfaced in about 160 million years. Thickest accumulations outside of the turbidite regimes are on older shallower crust or underneath zones of high biological productivity. Sediments are thicker under regions of high productivity because the CaCO3 and SiO2 tests of plankton are a major deep-sea sediment component (section “Biogenic Sediment Components”) and in shallow plateaus because there is better preservation (section “Seafloor Processes Affecting Deep-Sea Sediment Composition: Dissolution, Early Diagenesis, and Sediment Movement”; Berger, 1970).