Secondary Sedimentary Structures

Secondary Sedimentary Structures

Bedding plane structures

Another class of sedimentary structures form on the interface between beds, usually on the exposed surface of a recently deposited bed before it is buried. These features are useful because they indicate current direction and post-depositional deformation of the sediment.

Sole marks are formed by currents acting on sediment.

• Flute casts: Elongate teardrop shaped depressions that taper upstream. Caused by the scouring action of turbulent flow, common in turbidity currents.
• Tool mark: Indention of the cohesive mud bottom by a "tool," and object dragged across sediment by current (right).

Mud cracks Indicate subaerial exposure. Recent 

Rain drop prints 

Geopetal structures indicate the top of beds, and these can be found as:

• Scoured tops of ripple crests yielding truncated cross-bedding. (Recent.) (Ancient.)
• Graded bedding
• Infilling of fossils or vugs (right).
• sole marks

Soft Sediment Deformation

Soft sediment deformation structures result from movement of sediment after deposition but prior to cementation. Sometimes this is due to the application of some sort of external load (e.g. soft sediment faulting) but are usually due to a density instability between different sediments layers. The most common are load structures, irregular bulbous features formed when a denser material has sunk into a less dense material (right). In some cases, denser material pinches off to form pseudonodules (a.k.a. ball and pillow structures). 

Tongue like protuberances of mud into overlying soft sediment are known as flame structures. 

Finally, deformation of soft sediment leads to convolute bedding, suggesting intense structural deformation.