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Typically, hemipelagic sediment is transported to the continental slope in suspension from river mouths but can be transported by the wind. The rate of deposition of hemipelagic sediment is higher than pelagic sediment but still quite slow. Ordinarily hemipelagic sediments accumulate too rapidly to react chemically with seawater. In most cases, individual grains thus retain characteristics imparted to them in the area where they formed.
Composition
Hemipelagic sediments can be made of a diverse range of elements or mineral types. The composition of Hemipelagic sediment directly depends on the composition of the adjacent land mass and geologic events such as volcanism that influence sediment input into the ocean. Hemipelagic sediments are mainly terrigenous but can also have biological oozes from marine organisms like Radiolarians or Diatoms. Radiolarians are a species of zooplankton that produce silica tests, or shells and Diatoms are photosynthetic organisms that live in the sunlit region of the ocean. Both organisms are visible in the sedimentary rock record. For example, in the Galice Formation in Oregon the hemipelagic sequence was composed of slaty radiolarian argillite with radiolarian chert present as well. The argillite in the Galice Formation was composed of radiolarians, terrigenous and tuffaceous detritus, and hydrothermal sediment.
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