Hemipelagic sediment refers to a type of marine sediment that consists of fine-grained biogenic and terrigenous material. It differs from pelagic sediment compositionally, which is composed of primarily biogenic material containing little to no terrigenous material. Rate of deposition of hemipelagic sediment is higher than pelagic sediment but still quite slow. Hemipelagic sediments are deposited on continental shelves and rises, and ordinarily 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.
^ abOchoa, J., Wolak, J., & Gardner, M. H. (2013). Recognition criteria for distinguishing between hemipelagic and pelagic mudrocks in the characterization of deep-water reservoir heterogeneity. AAPG bulletin, 97(10), 1785-1803.