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.
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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 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) |
More to Come |
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 |
Examples of Modern Mudcracks
Modern bird tracks on top of a bed of dried river mud with mud cracks Kern River flood plain (Bike Path) Bakersfield, Calif. |
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 |