Abstract:

Under its own gravitational weight and interaction with the overriding plate, a subducting oceanic plate bends significantly, leading to the formation of a deep trench. Here the subducted plate brings sediments into the mantle depths, constituting an important part of the global cycling of Earth materials. At the extreme environment of the deep ocean trench, the sedimentation processes differ significantly from that in a continental shelf or a shallow water zone. In general, the sediment provenances, environments, and mechanisms are much more complex at ocean trenches. Sediment sources at trenches are linked strongly to trench tectonics including, for example, the formation of accretionary wedges composing of deep sea sediments scraped off the overriding plate; turbidity deposits triggered by trench gravity sliding and seismic events; and volcanic deposits. Meanwhile, trench sediment is also controlled by other sedimentation mechanisms, including biochemical sedimentation and funneling effect. As a result of the funneling effect, trench sediment deposition rate is typically faster and thus thickness is greater than that at abyssal basins. Trench sediment thickness, however, varies significantly both within a trench and between trenches. The differences in the sedimentation mechanism and process affect the properties of trench sediments, including sediment grain-size, mineralogy, and biology. This paper examined intra- and inter-trenches variations in sediment thickness, grain-size, mineral composition, and biological characteristics. Several trench sedimentation mechanisms were examined, including gravity sliding, seismically-induced turbidity deposit, volcanic activity, biochemical sedimentation, and funneling effect. We also discussed the current research focuses in trench sedimentation research and the outlook of future investigations.

Key words: trench, sediment, sediment provenance, sedimentary thickness, sedimentary mechanisms, research progress and outlook