turbidite: a standalone construct

Ph. H. Kuenen and Carlo Migliorini's 1950 paper Turbidity currents as a cause of graded bedding established the deposit experimentally, showing that a turbidity current, a dense, sediment-laden underflow that races down a slope beneath clearer water, drops its load as it slows so that coarse grains settle first and finer grains last, leaving a single bed that grades from coarse at the base to fine at the top. Deposits of this kind came to be called turbidites during the 1950s, and Arnold Bouma's 1962 study of flysch, the thick sequences of alternating sandstone and shale found in ancient deep-sea settings, set out the standard descriptive model now called the Bouma sequence: an idealised ordering of five internal divisions, from a graded base through parallel and rippled laminations to a muddy cap, that records the waning of the current. A turbidite is therefore the rock record of a single sediment-gravity-flow event, one event leaving one bed. Because such currents carry sand far out onto the deep-ocean floor, turbidites are the chief way coarse sediment reaches abyssal depths, and stacked turbidite beds build the submarine fans that hold major hydrocarbon reservoirs and preserve a datable history of the earthquakes and floods that triggered the flows.[1][2][3]

Unit

A single graded sedimentary bed recording one turbidity-current event, one of the deposit types of subaqueous sediment density flows

Recovery means

Not applicable

Measured by

Identified in outcrop and core by its sharp erosional base, upward grading from coarse to fine, and internal Bouma divisions, and mapped in the subsurface with seismic reflection and well-log data