ABSTRACT

Fossil turbidites have been recognized and described from many areas all over the world. A model, comprised of a fixed succession of sedimentary structures was established a decade ago and seems to be usable although some changes have been suggested.

Turbidites are generally assumed to be deposited by turbidity currents but the presence of these currents in the marine realm has not been definitely established. Submarine canyons presumably are the major, if not only, important transport route for moving "shallow" water material to "deeper" basins. Questions arise about the origin of turbidity currents when studying canyons in which gradual filling followed by sudden emptying has occurred. The material in the canyon head moves downward slowly, comparable to glaciers. Besides this slow sliding, traction currents and debris flow have been suggested. Where turbidity currents start and whether or not they absorb the slow moving canyon fill is a question that cannot as yet be answered. Another problem is the relationship between fluxoturbidites or gravitates and turbidites, as well as the terms proximal and distal turbidites.

When comparing recent turbidites with ancient ones a number of discrepancies appear, most of which can be eliminated by considering the influence of primary consolidation on sedimentary structures.

Studies indicate that the use of electrical logging and seismic records do not allow detailed interpretation of deposits such as turbidites. The resolution of the records is not fine enough, although their application for basin analyses and overall trends is necessary.

Recently a new genetic term, contourites, was introduced for sediments redeposited by contour currents. Recent and ancient contourites are compared to turbidites and although minor differences exist, none of them are indicative. A combination of parameters may allow a distinction between the two types and it is possible that both can be found in the same area.