1. adj. [Geology]

Pertaining to the depositional environment of the deepest area of the ocean basins, the abyss. The depositional energy is low, the abyssal plain is flat and nearly horizontal, and fine-grained sediments are deposited slowly by waning turbidity currents or from suspension in the water. The water is thousands of meters deep, so the water is cold and sunlight is minimal.

See: abyss,  bathyal,  benthic,  depositional energy,  littoral,  neritic,  turbidite,  turbidity current