SIOUX  FALLS

 

Extensive outcrops of pinkish, Paleoproterozoic-aged quartzites are present at Falls Park along the Big Sioux River in the city of Sioux Falls, southeastern South Dakota, USA.  The quartzites here have nicely water-worn, sculpted surfaces with good, fluvially abraded polish in places.  These rocks are part of the Sioux Quartzite (upper Paleoproterozoic, 1.65-1.70 Ga).  Despite being subjected to regional metamorhpism, this unit's original sedimentary features, such as horizontal stratification and ripple marks, are still preserved.

 

Sioux Quartzite (1.65-1.70 Ga) along the Big Sioux River at Sioux Falls, southeastern South Dakota, USA.

 


 

Sioux Quartzite (1.65-1.70 Ga) along the Big Sioux River at Sioux Falls, southeastern South Dakota, USA.

 


 

Sioux Quartzite (1.65-1.70 Ga) along the Big Sioux River at Sioux Falls, southeastern South Dakota, USA.

 


 

Sioux Quartzite (1.65-1.70 Ga) along the Big Sioux River at Sioux Falls, southeastern South Dakota, USA.

 


 

Water-worn & sculpted surface of the Sioux Quartzite (1.65-1.70 Ga) along the Big Sioux River at Sioux Falls, southeastern South Dakota, USA.

 


 

Ripple marks in the Sioux Quartzite (1.65-1.70 Ga) along the Big Sioux River at Sioux Falls, southeastern South Dakota, USA.  Lens cap for scale.

 


 

Polish on an eroded surface of Sioux Quartzite (1.65-1.70 Ga).  The polish is the result of fluvial abrasion from the Big Sioux River.

 


 

Percussion marks (arcuate cracks) in the Sioux Quartzite (1.65-1.70 Ga).  These features formed as a result of clast impacts during energetic flow in the Big Sioux River.  Ant for scale.

 


 

The Sioux Quartzite is a famous erosion-resistant unit in America's midcontinent.  It has formed a long-lived paleotopographic high since Precambrian times, the Sioux tectonic core.  This high is part of a NE-SW trending series of paleotopographic highs & depressions known as the Transcontinental Arch, which extends from Arizona to Minnesota (see Carlson, 1999, Transcontinental Arch - a pattern formed by rejuvenation of local features across central North America.  Tectonophysics 305: 225-233).

 


 

Home page