End of Early Proterozoic Sioux Quartzite Post Penokean

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End of Early Proterozoic Sioux Quartzite (Post
Penokean)

• Bedrock exposed mainly in NE SW Minnesota
• Rocks include quartz sandstones, basalt lava
  flows and associated gabbro intrusions (mafic
  rocks of mid-continent rift), and post volcanic
  sandstones
• Quartz sandstones sit atop low relief erosion
  surface (unconformity) formed by a long period of
  erosion of the Penokean mountains - deposited
  1.76-1.63 Ga
• Rifting of the continental crust 1.2-1.1 Ga
  formed a narrow basin in which basalt lava flows
  and mafic intrusions were formeed
• Sediments of Keweenawan Group filled the basin
  following the lava flows and mafic intrusions

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Cross Section of Late Proterozoic Rocks in MN and
their Relationship to Underlying and Overlying
Rocks
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Late Proterozoic Sioux Quartzite

• Pure quartz sand produced by several hundred
  million year erosion of Early Proterozoic rocks
• Deposited sometime between 1.76 and 1.63 Ga
• 5,000 feet thick in SW Minnesota and adjacent
  South Dakota
• Nopeming Fm (25 thick) in Duluth area, and
  Puckwunge Fm(200 thick) in NE Minnesota
• Lower 2/3 deposited in rivers, upper 1/3 in
  shallow sea
• Used for decorative stone (see the facing of the
  Choate Building in downtown Winona) and
  aggregate. The clay in the formation is used by
  Native Americans for crafting of pipes

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Problems Interpreting Age and Origin of Sioux
Quartzite

• No fossils - organisms with hard parts had not
  yet evolved - so marine vs river deposition is
  difficult to interpret
• Without fossils, correlation with other similar
  rocks such as the Baraboo Quartzite in Wisconsin
  is difficult
• Reconstruction of environment based on
  sedimentary structures is possible, but more
  equivocal
• Radiometric dating of sandstones gives age of
  original source rock from which the grains were
  weathered, not the age of formation of the
  deposit
• Cross cutting relationships with igneous rocks
  give a range of age that is greater than all of
  the Paleozoic, Mesozoic, and Cenozoic Eras

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Sioux Quartzite at Blue Mounds State Park,
Luverne, MN
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Sioux Quartzite Exposure in Sioux Falls
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Sioux Quartzite at Split Rock Creek
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Basal Conglomerate Sioux Quartzite, New Ulm, MN
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Basal Conglomerate near New Ulm
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Ripple Marks on Bedding Surface of Sioux
Quartzite, Pipestone National Monument

• Ripple Marks indicate transport of sand grains
  on the bed of a sand dune, river, or shallow sea

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Ripple Marks in Sioux Quartzite, Blue Mound State
Park, MN
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Trough Cross Bedding, Sioux Quartzite, Blue
Mounds State Park, MN

• Trough Cross Bedding often indicates higher
  energy transport of sand or gravel, and in
  rivers, it forms in channels instead of bars or
  floodplains

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Trough Cross Bedding, Blue Mounds State Park, MN
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Trough Cross Bedding in Sioux Quartzite,
Pipestone National Mounument
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Cross Bedding in the Sioux Quartzite, Pipestone
National Monument
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Planar Cross Bedding in Sioux Quartzite,
Pipestone National Monument
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Rose Diagrams of Cross Bedding Orientations
Suggest River Deposition
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Vertical Profile of Sioux Quartzite
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Meandering River - Point Bars Located on Inside
Bends
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Point Bars on Rio Socopo, Venezuela

• Point bars located on inside bends where
  velocity is lowered

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Constraints on Age of Sioux Quartzite

• rhyolite in Sioux Quartzite dated at 1.47 Ga
• rhyolite beneath Baraboo Quartzite dated at 1.76
  Ga
• lava flows above sandstones dated at 1.1 Ga
• therefore, sandstones are somewhere between 1.76
  and 1.1 Ga
• most recent studies suggest an age between 1750
  and 1630 Ma

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Similar Quartzites of Same Age?
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Sheet Sandstone or Isolated Sand Bodies?

• If these sandstones are equivalent in age,
  perhaps they are part of a regionally extensive
  sheet that was later eroded, resulting in the
  scattered remnants of similar quartzites
• A sheet-like geometry may suggest a shallow
  marine environment of deposition
• Isolated channel-like bodies may suggest
  deposition in river systems
• How can we tell without fossils to correlate?
• Perhaps similarities in composition, texture
  and sedimentary structures, as well as a common
  direction of transport, is indicative of
  correlation

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Tectonic Setting of the Baraboo Quartzite

• Note derivation of the Baraboo sediment from
  erosion of the Penokean Mountains to the North of
  the Baraboo Basin

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Reconstruction of Sioux Paleogeography
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Quartz Overgrowths in Sioux Quartzite
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Two Generations of Quartz Overgrowths Indicates
Recycling
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George Catlins Painting of Quarries near
Pipestone, Minnesota
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Origin of Clays that Make Up the Catlinite

• Deposition of mud from suspension in quiet water
  on floodplain of river system or in lagoon behind
  barrier island in shallow sea
• Mud interbedded with sands of channel and point
  bars or sands of shallow sea
• Burial compaction and changes under low heat and
  pressure produces the clay

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Catlinite Layer in Sioux Quartzite, Pipestone
National Monument, MN

• Note how the Sioux was stripped from this area,
  down to the Catlinite layer, which was then
  quarried

Catlinite layer
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Catlinite Pipe and Bear Claw Amulet
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Quarries in Sioux Quartzite near Sioux Falls, SD
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Sioux Quartzite as a Building Stone
Calumet Hotel and Pipestone Historic District,
1888 to 1898
Rock County Courthouse, Luverne, 1888
Choate Building, Winona, MN, 1888, decorative
borders