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That is to say, elongated and commonly flattened pebbles and cobbles in gravelly sediment are deposited so that they overlap one another like roofing shingles.Imbricate bedding forms where high-velocity currents move over a streambed or where strong currents and waves break over a gradually sloping beach, thereby forming beach shingle.In addition to sedimentary structures that are normally associated with bedding planes, there are other such structures that result from deformation during or shortly after sedimentation but before induration of the sediment into rock.These are nontectonic features—i.e., they are not bends and folds brought about by metamorphism or other such causes.The suite (repeated sequence) of sedimentary structures in any single stratigraphic unit is another attribute by which that unit may be physically differentiated from others in the region.Stratification (or bedding) is expressed by rock layers (units) of a general tabular or lenticular form that differ in rock type or other characteristics from the material with which they are interstratified (sometimes stated as interbedded, or interlayered).Other sedimentary structures are stratigraphic “top and bottom” indicators.
It is commonly associated with submarine density currents.).
They conventionally are subdivided into categories based on mode of genesis.
Structures that are produced at the same time as the sedimentary rock in which they occur are called primary sedimentary structures.
They are termed casts, because they are fillings of depressions that formed on the surface of the underlying mud.
They originate (1) by unequal loading upon the soft and plastic wet mud, (2) by the action of currents across the upper mud surface, or (3) by the activities of organisms on this surface.