Mudcracks

 

Dessication (shinkage) cracks that form in non-marine mudstones as they dry out in the sun, and are later filled in by sediment. Mudcracks cut across bedding in cross-sectional view, and form polygonal patterns in map view. Multiple episodes of dessication, infilling and re-wetting may be displayed as in the Tulare core below from the Maxwell 860 well. Sub-aqueous shinkage cracks can also form, and are known as syneresis cracks. These form in limey sediments during contraction of the clay minerals in response to salinity changes in the overlying water column. However, syneresis cracks tend be much more discontinous and irregular than most mudcracks.

 

Examples of Ancient Mudcracks

Mudcracks in outcrop
Eocene Matilija Fm (non-marine)
Matilija Springs Road
California Transverse Ranges
South Margin San Joaquin Valley

Mudcracks in outcrop
Piru Gorge Sandstone Member
Miocene Ridge Route Formation
Templin Highway, Transverse Ranges
South Margin San Joaquin Valley

Mudcracks in core.
The cracks are filled with soil.
Pleistocene Tulare Fm (non-marine)
EXF 376T well
Midway-Sunset oil field
San Joaquin Valley

Mudcracks in core
Shown in cross-section w/ multiple
episodes of wetting and shrinkage.
Pleistocene Tulare Fm (non-marine)
Maxwell 860 well
Midway-Sunset oil field
San Joaquin Valley

More to Come

Mudcracks in outcrop
Fisher Springs Sandstone Member
Miocene Ridge Route Formation
Templin Highway, Transverse Ranges
South Margin San Joaquin Valley

Mudcracks in outcrop
Paleozoic Maroon Fm (non-marine)
Maroon Peak area
Colorado Rockies
 

Mudcracks in Paleozoic redbeds
Glacier National Park, Montana
(Photo from National Park Service)
 
 

 

Examples of Modern Mudcracks

More to Come

Modern mud cracks in a sump pond
(polygons about 12 inches across)
Near Tule Elk Reserve State Park
Central San Joaquin Valley
 

Modern mud cracks in a quarry pond
(polygons about 8 inches across)
Twisselman Ranch, Temblor Range
West Margin San Joaquin Valley
 

More to Come