Wanderlust World Wanderlust World When a turbidity current—a fast-moving, sediment-laden underwater flow—races down a continental slope and spreads across the abyssal plain, it leaves behind a distinctive deposit called a turbidite. These deposits are the primary building blocks of deep-sea fans and submarine fans, and they provide geologists with a readable record of past catastrophic sediment transport events.
In 1962, Arnold Bouma described the idealized vertical sequence of sedimentary structures in a single turbidite bed. Not all divisions are always present.
| Division | Lithology & Structure | Flow Process |
|---|---|---|
| Ta (Basal) | Massive, coarse sand/pebbles; graded bedding; sole marks (flutes, grooves) | High-concentration, turbulent flow; rapid deposition from suspension + traction |
| Tb | Parallel-laminated sand; current ripples rare | Upper flow regime plane bed; lower concentration |
| Tc | Current-rippled sand; climbing ripples common | Lower flow regime; decelerating flow |
| Td | Parallel-laminated silt/fine sand; delicate laminae | Suspension settling; very low velocity |
| Te (Top) | Massive mud/clay; bioturbation common; gradational top | Final suspension fallout; background pelagic sedimentation resumes |
Turbidites are the deep sea's sedimentary alphabet—each bed a sentence, each sequence a chapter in the story of continental margin evolution.