Paleozoic: Lower Mid Cambrian Rocks in Georgia

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PaleozoicLower Mid Cambrian Rocks in Georgia

• Ryan Perry

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Paleogeography N. America in the Paleozoic
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Early Cambrian
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Earliest Rox in GA

• The oldest rocks in Georgia are found in the
  Piedmont and Blue Ridge provinces and are
  Proterozoic in age (1 to 1.3 billion years old).
• Sediment -gt SedRox- gtMetamorphism.
• Early CambrianGrenville mountains eroded
• Streams stransport seds to sea, covering GA in
  sediments.
• Metamorphosed gneiss, marble, metaconglomerate,
  phyllite, quartzite, schist, and slate found in
  the Blue Ridge and Piedmont.

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Paleozoic Cambrian Period (542 - 490 MA)

• Principle rock typessandstones, dolostones, and
  shales.
• -Early beaches.
• Limestones and other carbonates were deposited
  later in the Cambrian in warm, shallow seas.

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Early Cambrian

• The Valley and Ridge Physiographic Province is
  characterized by a sequence of folded and
  faulted, northeast-trending Paleozoic sedimentary
  rocks that form a series of alternating valleys
  and ridges that extend from Alabama and Georgia
  to New York.

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Early Cambrian

• Weisner Quartzite/Chilhowee Formation
• Chilhowee comes from the Cherokee word,
  Tsu'lunwe'I, but noone remembers what it means!
• Maybe Kingfisher??

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Origin of the Chilhowee

• Erosion of the proto-Appalachian Mountains during
  the Lower Cambrian Period.
• 1.2 billion years ago Grenville orogeny initial
  uplif of the proto-Appalachians.
• Erosion during this time created sediments.
• Eroded into Iapetus Ocean.

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Chilhowee Quartzite

• Quartzite derived from sandstone
• Sedimentary origin orthoquartzite
• Percolating fluid dissolved silica silica
  cementation of quartz grains.
• High P and T the silica grains recrystallize so
  that the original sedimentary structure is
  obliterated.

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Chilhowee Quartzite
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Chilhowee Quartzite
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Chilhowee Formation

• Phyllite, Shale, Mudstone
• Shallow Marine Fossils
• Skolithos ichnofacies
• Obvious evidence of metamorphism!

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Where can we see the Chilhowee?

• Blue Ridge Province, NW Georgia -- earliest
  evidence of Pre- Cambrian life!
• Shenandoah Natl Park Sky Line Drive, Brown
  Mountain

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Cambrian Carbonates

• Shady Dolomite first carbonate sequence in
  Georgia, Lower Cambrian
• Shallow, warm, aragonitic sea

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Shady Dolomite

• Along the boundary between the Valley and Ridge
  province and Blue Ridge province from Alabama to
  Pennsylvania.
• 1,000 feet thick at most places and consist of
  gray to light-gray medium- to thick-bedded
  crystalline dolomite

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Shady Dolomite

• local lenses of limestone and shale
• Andundant shallow marine fossils
• Biostratigraphic correlations with other units of
  same time period
• Maximum thickness at 1800 ft in SW. Virginia

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Shady Dolomite
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Shady Dolomite

• Mostly found in S. Tennessee
• Outcrops contact between Chilhowee and Shady

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Shady Dolomite
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Shady Dolomite

• Manganese deposits
• Iron-oxides
• Rich in ochre, and ferruginous minerals
• Mined in pits

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Middle Cambrian
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Rome Formation

• fine-grained, interbedded sandstone, siltstone,
  and shale which are interbedded.
• Lower Formation heavily bedded sandstones with
  interbedded fine-grained silt stones
• Upper Formation thinly bedded, shaly siltstones,
  fine- grained sandstones, shales, and few
  dolomites

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Rome Formation

• sandstone is its principle constituent and varies
  in color from red to green
• Similar beds of the same time of deposition and
  composition are observed in Alabama, Tennessee,
  and Virginia

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Rome Formation
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Rome Formation
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Rome Formation
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Rome Formation

• There are three belts of the formation which
  display out crops.
• The westernmost belt extends from Villanow
  northeast to Tennessee
• Central belt Resaca and Dalton.
• Cartersville to Crandall and passes beneath the
  rocks of Cohutta Mountain

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Rome Formation

• thickness of the formation varies between 500 to
  1,000 feet
• overall thickness, however, is difficult to
  estimate due to the abundant faulting and folding
  in the region.

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Boundary Between Rome and Conasauga

• Difficult to distinguish
• lenticular lime stone and dolomite interbedded
  with thick deposits of shale, rust-colored
  sandstone within the uppermost portion of the
  Rome Formation
• fossil assemblages within shales of the Lower
  Conasauga Formation (Biostratigraphy).

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Conasauga Formation

• named for the Conasauga River in Georgia by C.W.
  Hayes.
• consists of shales in varied states of
  weathering.
• yellow, grey, and pink coloration.
• The more stable, unweathered portions are
  typically pale green in color

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Conasauga Formation

• Many outcrops of pale, highly fissile shale are
  visible at road cuts along the western portion of
  the formation

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Conasauga Formation
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Conasauga Formation
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Honaker Formation

• northeastern Tennessee is about 2,000 feet thick
• thinbedded to massive dolomite and magnesian
  limestone and some interbedded limestone and
  shale.
• The lower part of the formation contains abundant
  chert

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Honaker Formation

• Magnesian limestone beds of variable composition
  are most abundant they generally contain 90
  percent carbonate, of which the MgCO3 content
  ranges from 7 to 38 percent and averages slightly
  more than 10 percent

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Rogersville Formation

• Earliest evidence of land plants
• Polynological analyses

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Rogersville Formation
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Rogersville Formation

• Estuarian environment
• Shallow Marine
• Fossil spores and pollen