1. Walter Dean, USGS, Denver, CO
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

2. GSA Special Paper 450, 2009

4. Kullenberg piston coring on Bear Lake, Utah-Idaho

5. Water Sampling, Bear Lake Drainages
River
Range
Bear
Lake
Plateau

6. Ca and Mg in Bear Lake and drainages
Bear River
diversion

7. C and O Isotopes in Bear Lake and Drainages
Evaporation!

8. Bear Lake Sediment Trap
Studies
Bear Studies

11. High-Mg Calcite, surface sediment trap

12. Aragonite (and diatom), bottom trap

13. 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!

14. SURFACE SEDIMENTS
1998 Short Gravity Cores

16. BL98-10, 30 m

17. O, C, and Sr isotopes in core BL98-10
210 Pb
Pb210

18. GLACIAL THROUGH HOLOCENE CHANGES IN CARBONATE DEPOSITION
1996 Kullenberg Piston Cores

20. 3.5 kHz Seismic Profile

21. Glacial-age
Red, calcar.
clay

22. Evaporation!

23. Where the correlation between carbon and oxygen isotopic variation is high (r>7), the carbonates…precipitated from a closed lake. (M.R. Talbot, 1990)

24. 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.