Isotopes of Oxygen, Carbon, and Strontium Track Changes in Unusual Carbonate Sedimentation in Bear Lake, Utah-Idaho, over the last 25,000 years

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Isotopes of Oxygen, Carbon, and Strontium Track
Changes in Unusual Carbonate Sedimentation in
Bear Lake, Utah-Idaho, over the last 25,000 years

• Walter Dean, USGS, Denver, CO

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GSA Special Paper 450, 2009
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Kullenberg piston coring on Bear Lake, Utah-Idaho
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Water Sampling, Bear Lake Drainages
Bear River Range
Bear Lake Plateau
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Ca and Mg in Bear Lake and drainages
Bear River diversion
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C and O Isotopes in Bear Lake and Drainages
Evaporation!
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Bear Studies
Bear Lake Sediment Trap Studies
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High-Mg Calcite, surface sediment trap
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Aragonite (and diatom), bottom trap
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In the US aragonite usually occurs in saline
prairie lakes

• Aragonite does not form in large, cold, deep,
  oligotrophic, high altitude, north temperate
  lakes fed by snowmelt, and does not form by
  conversion of high-Mg calcite at the bottom of a
  lake!

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SURFACE SEDIMENTS

• 1998 Short Gravity Cores

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BL98-10, 30 m
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O, C, and Sr isotopes in core BL98-10
210 Pb
Pb210
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GLACIAL THROUGH HOLOCENE CHANGES IN CARBONATE
DEPOSITION

• 1996 Kullenberg Piston Cores

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3.5 kHz Seismic Profile
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Glacial-age Red, calcar. clay
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Evaporation!
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Where the correlation between carbon and oxygen
isotopic variation is high (rgt7), the
carbonatesprecipitated from a closed lake.
(M.R. Talbot, 1990)
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Conclusions

• 1. Prior to AD 1912, the primary endogenic
  carbonate mineral forming in a closed
  Bear Lake was aragonite.
• 2. Beginning in1912, part of the flow of Bear
  River was artificially diverted into Bear lake.
  This severely altered the chemistry of the lake,
  particularly the Mg/Ca ratio, so that today, the
  primary endogenic carbonate mineral forming in
  Bear Lake, trapped in sediment traps, is high-Mg
  calcite.
• 3. The predominance of aragonite in surface
  sediments of Bear
• Lake is due to reworked aragonite from water
  depths shallower
• than 30 m that is at least 100 years old.