Deposits of turbidity currents are characterized by alternating layers of sandstone and shale, in which a unit layer is defined as the sandstone together with its overlying shale.

Studies of turbidites of different ages, and from many different localities in Europe, make it clear that turbidites are characterized by one sedimentary facies model, which is composed of five specific intervals in a fixed succession. In a complete layer the intervals from bottom to top are: graded interval (20-500 cm), lower interval of parallel lamination (10-200 cm), interval of current ripple lamination (4-100 cm), upper interval of parallel lamination (2-50 cm), and pelitic interval (1-40 cm).

Each turbidite layer in the areas studied shows part or all of this sequence, and everywhere the succession is the same. The completeness of the sequence generally increases with increase in thickness of the unit layer. Incomplete sequences normally are caused by truncation of the upper intervals or omission of the lower intervals. Large differences in grain size between successive turbidite layers occur where the base of a layer is formed by one of the three lower intervals. The lower bedding planes of such layers are most readily exposed by weathering and are more likely to contain sole markings than layers in which the lower three intervals are missing.

An understanding of the origin of each of the five intervals and the reason for their definite succession in turbidite layers is essential to understand the mechanism of deposition by turbidity currents.

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