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Part 8
PRECIPITATION OF TRAVERTINE
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• Carbon dioxide (CO2) is dissolved in groundwater
  percolating through limestone, forming a weak
  carbonic acid (H2CO3 ). This weak acid reacts
  with the limestone to form soluble calcium acid
  carbonate, CaH2(CO3). When this mixture spills
  over the small falls it is aerated and loses some
  of the dissolved carbon dioxide (CO2) to the dry
  atmosphere, causing the precipitation of
  insoluble carbonate (CaCO3) and water (H2O).

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• Precipitation of travertine at Travertine Rock in
  Holocene Lake Cahuilla, in the Salton Trough of
  the Colorado Desert of southeastern California.
  Lake Cahuilla was periodically filled with fresh
  water by the Colorado River between 700 and 1700
  AD.

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• Carbonate bathtub ring exposed along the
  shoreline of Lake Mead immediately behind Hoover
  Dam. This ring was initially deposited during a
  3-month period in Aug-Oct 1941

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• Lake Powell was formed behind the Glen Canyon Dam
  in southern Utah beginning in 1963. It can store
  up to 27 million ac-ft of water, making it the
  second largest man-made lake in the USA. Note
  the carbonate bleach line on the orange Navajo
  Sandstone.

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• Limnology studies in Lake Powell found that
  travertine deposition was stimulated by presence
  of algae in the warmer lake water, within 30 feet
  of the lake surface.

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• The limnology studies in Lake Powell also
  discovered fresh water diatoms in the warmer
  surface waters stimulated carbonate deposition
  and that lake salinity increased with depth.

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Conclusions-Lake Powell Studies

• Salinity increases with depth
• Temperature decreases with depth, then increases
  near density current interface because of
  anaerobic digestion of organics
• Dissolved Oxygen Content is replenished at depth
  during winter months
• Silica is extracted from the lake water by
  diatoms
• Photosynthesis in surface waters produces high pH
  conditions and precipitation of calcite
• Calcite precipitation appears to be controlled by
  pH, temperature, and surface area of calcite
  nuclei

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• Marble Canyon is a deeply incised gorge lying
  between Lees Ferry and the Grand Canyon, carved
  by the Colorado River.

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• River view of Marble Canyon just downstream of
  House Rock Rapid (RM 17). Note what appear to be
  carbonate bathtub rings high on cliffs (arrow).

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• Cross section of Marble Canyon near River Mile
  15, showing projected level of deepest lake
  possibly impounded by lava dams, around el. 4125
  ft. This coincides with the level of the bathtub
  rings shown in the previous image. These
  reservoirs would have been short-lived, from
  10,000 to possibly 30,000 years.

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Lava Dams in Grand Canyon

• During the late Pleistocene a series of lava
  flows built upon each other to periodically dam
  the Colorado River between River Miles 179
  (Toroweap, above right) and 183 (Whitmore Wash,
  above left).

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• Extensive deposits of travertine blanket the
  slopes of the Grand Canyons Inner Gorge between
  River Miles

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Vertical distribution of travertine

• The travertine deposits lie between elevations of
  1840 and 3440 feet, and 30 to 1655 feet above the
  Colorado River.
• There is no apparent correlation with bedrock
  geology the travertine being deposited on
  sandstone, shale, limestone, and dolomite.
• This suggests that lake chemistry may be dominant
  deposition mechanism, as opposed to percolation
  through limestone.

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Frequency Analysis-Travertine Deposits

• Frequency analyses suggests that the travertine
  deposits in the Grand Canyon were likely
  deposited in lakes of varying elevations, in
  particular, those sequences between elevations
  2350-2480 and 3320-3480 feet.

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• The largest of the hypothetical Pleistocene
  impoundments was Prospect Lake, which eventually
  rose to an elevation around 4125 feet, creating a
  series of lakes extending several hundred miles
  upstream, beyond present day Moab, Utah

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River Mile 157
River Mile 57
Lava Dam
River Mile 116

• Detail view of Pleistocene Prospect Lake in the
  Grand Canyon. It filled the Grand Canyon to an
  average depth of about 1500 feet.