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Bear Lake, UTID Core BL001E

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Title: Bear Lake, UTID Core BL001E

1
Bear Lake, UT/IDCore BL00-1E

3
Bear Lake Geography(see next slide)

Bear River Range to west
10,000 max. elevation
127 cm of water per year, of which 80 falls
as snow
Bear Lake Plateau to east
7,700 max. elevation
no precipitation gauges, but 3 at Bear Lake
receive 30 cm of water per year
- evaporation at Bear Lake is estimated to be
56 cm per year (calculated from data in Amayreh,
1995).
Bear River drains Uinta Mts ( 13,528 max.
elevation)
enters Bear Lake Valley _at_ Dingle, roughly 13 km
north of Bear Lake
Original channel flowed northwest, past Bear Lake
Bear River was diverted into Bear Lake via canals
1912 A.D.
Amayreh, J., 1995. Lake evaporation
a model study. PhD dissertation. Utah State
University, Logan, UT. 178 pp.

4
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5
Bear Lake Geology

Bear River Range
primarily Paleozoic limestones and dolomites
Bear Lake Plateau
primarily Mesozoic limestone and sandstone with
mantling of Tertiary Wasatch Formation
Large potential for detrital carbonate in lake
sediments
Geology generalized from
Dover, 1995. Geologic map of the Logan 30 x 60
Quadrangle, Cache and Rich Counties, Utah, and
Lincoln and Uinta Counties, Wyoming. US
Geological Survey, Miscellaneous Investigation
Series, map I-2210.
Oreil, S. S., and Platt, L. B., 1980. Geologic
map of the Preston 1 x 2 quadrangle,
southeastern Idaho and western Wyoming. US
Geological Survey, Miscellaneous Investigation
Series, map I-1127.

7
courtesy Steve Colman, L.L.O./U. Min.
8
BL00-1E core stratigraphy and chronology

120 m long
three major aragonite-rich sections
one 14C MS correlation with BL96-2
three tentative magnetic excursions
Laschamp (41 ka , 26.5 m)
Blake (121 ka, 64.3 m)
7b (236 ka, 114.1 m)
one U/Th age on aragonite
128 ka, 64 m
four tephras (not used in chronology)
Arco 1
Hegben Narrows
Summer Lake JJ
Summer Lake NN
Note oxidized, hematite rich zone 10-18 m. No
hematite in Bear Lake drainages, but hematite is
found in Bear River sediments.

9
Significance of Aragonite in Bear Lake sediments

West-side water accounts for 95-99 of modern
lake solute budget
92-98 of west-side solutes is calcium, magnesium
and bicarbonate
Carbonate precipitation removes calcium and
bicarbonate
Rapid accumulation of magnesium in lake waters,
poisoning of calcite lattice
Forces aragonite precipitation
Aragonite only forms if Bear Lake is
topographically closed and isolated from Bear
River. Isolation can probably only be maintained
during warm, dry climates, typically
interglacials. Aragonite will not form if Bear
Lake and Bear River are connected, even during
interglacials.
Modern lake is precipitating high-Mg calcite
rather than aragonite, due to the Bear River
being diverted into the lake.

10
BL00-1E XRD
11
Oxygen isotopes in BL bulk sediment and the
ostracode Candona

Enriched isotopes coincide with major aragonite
zones 0-10, 60-68, 100-105 m.
Bulk sediment record is relatively invariant
10-40 m and 70-100 m, probably due to a large
portion of detrital carbonate in the bulk
sediments.
Much higher variability in the ostracode record.

12
Strontium isotope ratios and Sr around BL

13
Strontium isotopes in BL00-1E bulk sediment

Horizontal line pre-diversion lake Sr isotope
ratio of 0.7102
Sr isotope ratio 0.7100 during aragonite
intervals 0-10, 55, 60-69, and 101-103 m.
Majority of core has Sr isotope ratios implying presence of Bear River water. Bear River
and Bear Lake were connected.
High Sr isotope ratios at 10-18 m correlate to
quartz-rich, hematite-rich zone probably
leaching of radiogenic Sr from those sediments
during analysis.

14
Oxygen Isotope Stages in Bear Lake?
15
Bear Lake vs. other climate records

16
Conclusions

The three largest aragonite zones (separation of
Bear Lake from Bear River) appear to coincide
with peak interglacials (OIS 1, 5e, 7a). The
fourth, smaller aragonite zone ( 55 m) occurred
sometime after OIS 5e, but still within OIS 5.
Sr isotope ratios core suggest that Bear Lake and Bear River have
been connected for most of the last 250 ka.
The Bear River was mainly connected to the lake,
but its influence on the sediments deposited at
the core site varied through time.
Bear Lake experienced significant fluctuations in
its hydrologic balance, as shown by the ostracode
oxygen isotope record, due to climatic change and
lake-river interactions.
Because it is influenced by catchment-scale
processes, the Bear Lake oxygen isotope record
differs from globally integrated records from
deep marine deposits.
Sediment deposited in Bear Lake is strongly
influenced by variable production of endogenic
carbonate within the lake, by fluctuating input
of fluvial and glacial-fluvial material from its
headwaters, and by periodic retraction of the
lake into a topographically closed basin.