Surface Markings and Imprints


Mud Cracks Bubble Sand Structure and Other Bubble Cavities
Frost and Ice Cracks Wrinkle Marks
Raindrop Imprints Antiripplets (Adhesion Ripples)
Foam Impressions Swash Marks
Crystal Imprints and Casts Rill Marks
Water Level Marks Drag marks (Wind-blown, solifluction)
Primary Current Lineation  

Mud Cracks

These are cracks formed during the drying out of fine grained mud sediments and are some times known as mud cracks. They indicate that the environment must at one time have been exposed to the air, in order for it to dry out. As the mud layers dry out they contract and the resulting shrinking causes cracks to appear within the top few centimetres of the sediment. This contraction gives an isotropic, horizontal, tensional stress field which diminishes downwards from the surface. Desiccation cracks generally form in polygonal shapes, often six sided, due the fact the contraction causes equally forces from all directions. On slopes steeper than about 5 degrees, the cracks tend to form in rectangular shapes. The sediment then cracks as the sun bakes it causing the edges of the mud to curl upwards giving the mud cracks a concave shape. This in turn causes the vertical cracks, which taper down wards and then become infilled by coarser grained sand's and later sediments which may be either flood deposits or wind blown deposits. These concave shapes and tapering downwards of the cracks can be used as a way up indicators. The resultant  desiccation cracks are preserved in the rock record  as  imprints on the base of sedimentary layers and provide good stratigraphic markers. Often though the beds above have been eroded sufficiently, that the structures can clearly be seen at the surface.

Schematic 3D of Mud Cracks Modern-day Mud Cracks, Death Valley, Nevada
Black Rock Desert, Nevada: Picture from terragalleria.com Modern Mud Cracks
Ancient Mud Cracks Ancient Mud Cracks

Frost and Ice Cracks

 

 


Raindrop Imprints

Marks caused by rain drops falling on un-compacted sediment.

   

 


Foam Impressions

 


Crystal Imprints and Casts

 


Water Level Marks

 


Primary Current Lineation

Primary current lineation (parting lineation): flow direction vertical in photo

Wrinkle Marks

Wrinkle marks are minature, irregular ripple-like features caused by non-erosive shear from water moving over a cohesive surface. they can be found in:

a) shallow-water tidal or beach sediments, probably caused by wind blowing over sediment covered by a thin film of water or

b) in turbidite sequences due to shear without erosion.

 


Antiripplets (Adhesion Ripples)

 


 

Bubble Sand Structure and Other Bubble Cavities

Swash Marks

Rill Marks

Tooth-Shaped Rill Marks

Comb-Shaped Rill Marks

Fringy Rill Marks

Conical Rill Marks

Branching Rill Marks

Meandering Rill Marks

Bifurcating Rill Marks

Rill Marks with Accumulation Tongues


Drag Marks (wind-blown, solifluction)

Drag Marks (Wind-blown over low friction surface), Nevada USA.