Turbidite

This was anomalous because within the deep ocean it had historically been assumed that there was no mechanism by which tractional flow could carry and deposit coarse-grained sediments into the abyssal depths.

Bouma cycles begin with an erosional contact of a coarse lower bed of pebble to granule conglomerate in a sandy matrix, and grade up through coarse then medium plane parallel sandstone; through cross-bedded sandstone; rippled cross-bedded sand/silty sand, and finally laminar siltstone and shale.

This vertical succession of sedimentary structures, bedding, and changing lithology is representative of strong to waning flow regime currents and their corresponding sedimentation.

It is now recognized that the vertical progression of sedimentary structures described by Bouma applies to turbidites deposited by low-density turbidity currents.

As the sand concentration of a flow increases, grain-to-grain collisions within the turbid suspension create dispersive pressures that become important in hindering further settling of grains.

As a consequence, a slightly different set of sedimentary structures develops in turbidites deposited by high-density turbidity currents.

The greater the size or density of the particle relative to the fluid in which it is travelling, the higher the water velocity required to suspend it and transport it.

Lithified accumulations of turbidite deposits may, in time, become hydrocarbon reservoirs and the petroleum industry makes strenuous efforts to predict the location, overall shape, and internal characteristics of these sediment bodies in order to efficiently develop fields as well as explore for new reserves.