Multi-Proxy Evidence for Environmental Change During the Last Two Glacial-Interglacial Cycles from Core BL00-1, Bear Lake, Utah-Idaho

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Multi-Proxy Evidence for Environmental Change
During the Last Two Glacial-Interglacial Cycles
from Core BL00-1, Bear Lake, Utah-Idaho
2

• Darrell Kaufman
• R. Scott Anderson
• Jordon Bright
• Steven Colman
• Walter Dean
• Richard Forester
• Chip Heil, Jr
• Katrina Moser
• Marith Reheis
• Joseph Rosenbaum
• Kathleen Simmons

(Northern Arizona U) (Northern Arizona
U) (Northern Arizona U) (U Minnesota) (US
Geological Survey) (US Geological Survey) (U
Rhode Island) (U Utah) (US Geological Survey) (US
Geological Survey) (US Geological Survey)
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Bear Lake

• NE Basin and Range
• Within the Bonneville drainage basin

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Setting
Uinta Mountains

• Bear River enters Bear Lake valley 13 km north of
  lake
• Local inflow primarily (95) from Bear River
  Range and subsurface
• Glaciated headwaters
• Uintas
• Bear River Range

SLC
Bear River
N
5
Inflow/outflow

• Lake nearly balanced hydrologically
• Bear River diverted into Bear Lake via canals ca.
  1912 AD
• Affords a whole-lake experiment to understand a
  major hydrologic shift

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Bear Lake

• TDS (1912 AD) 1060 mg L-1
• TDS (2000 AD) 550 mg L-1
• Mesosaline / alkaline
• Surface area 280 km2
• Maximum depth 63 m
• Bear River Range
• - Paleozoic limestone dolomite
• Bear Lake Plateau
• - Mesozoic limestone sandstone
• - Mantled by Tertiary Wasatch Fm

Bear River Range
Bear Lake Plateau
10 km
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Coring

• Gravity cores in 1996 by U Minnesota USGS
• GLAD800 drilling in 2000 by USGS (U Minnesota
  DOSECC)

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Seismics
Colman et al.

• Sediment wedge thickens toward basin-bounding
  fault
• gt250 m of well-layered sediment
• BL00-1 55 m water depth two adjacent cores

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Lithology

• 120 m long

Marl Aragonitic Silty clay Tephra
massive gray silty clay with variable CaCO3
contents ranging from calcareous silty clay to
marl

• 120 m long

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Chronology

• MS correlations with 14C age in BL96-2
• U/Th age on aragonite
• 128 ka
• Tentative magnetic excursions
• Laschamp (41 ka)
• Blake (121 ka)
• 7? (236 ka)
• Correlations with Devils Hole ?18O
• Peak isotope stages

Depth (m)
tuned model
Colman et al.
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Carbonate mineralogy
1
5e
7c
7e
7a
5c
5a
CaCO3 ()
Dean et al.

• 50 cm sample spacing
• Aragonite precipitated prior to historic
  diversion
• High-Mg calcite precipitated following diversion
• Aragonite inferred to form in closed-basin lake
  (e.g., Holocene)
• Rapid accumulation of magnesium in lake water
  poisons calcite lattice and forces aragonite
  precipitation

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Allogenic input

• Quartz dominates stream-sediment input
• Calcite and dolomite influence bulk carbonate
  composition
• Qtz/dolo deceases over aragonite-rich intervals

Quartz
Dolomite
CaCO3
Abundance ()
Abundance ()
Age (ka)
Dean et al.
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Oxygen isotopes
Candona Cytherissa
Bulk-sediment CaCO3
?18O ( PDB)
?18O ( PDB)
Bright et al.

• 30 cm sample spacing 90 ostracode samples
• Enriched ?18O coincides with major aragonite
  zones
• Bulk sediment ?18O is otherwise relatively
  uniform
• Higher variability in ostracode ?18O

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Oxygen carbon isotopes
11
()

• Candona ?18O nearly always higher than enclosing
  bulk sediment
• More uniform bulk-sediment ?18O reflects
  allogenic influence
• O and C isotopes correlate strongly in aragonite
  intervals

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Sr isotopes
pre-diversion lake
87Sr/86Sr
Simmons et al.
Simmons et al.

• 1.3 m sample spacing
• Bear River water dominates Sr budget
• 87Sr/86Sr lt 0.710 over most of core implies
  presence of Bear River water during the past 250
  ka
• 87Sr/86Sr of CaCO3 rocks 0.7093 0.0002 (n
  18)

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Lake hydrologic status Peak interglaciation

• Lake retracted into closed basin
• Aragonite precipitated
• Low detritial mineral component
• High ?18O
• Strongly covariant O C isotopes
• High 87Sr/86Sr
• Occurred during OIS 1, 5e, and 7a
• Low effective moisture
• High desert shrub and juniper

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Lake hydrologic status Glaciation

• Lake transgressed, captured Bear R
• Filled to northern threshold
• Carbonate content influenced by allogenic
  component
• Low ?18O
• Weakly covariant O C isotopes
• Low 87Sr/86Sr
• Cytherissa lacustris associated with
  polar/sub-polar air masses
• High pine, spruce sagebrush

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Lake hydrologic status

• Intermediate
• Bear River and Bear Lake connected via wetlands
• Influence of Bear River buffered
• Variable influence on sediment deposited at the
  core site

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Conclusions

• Multi-proxy data document millennial-scale
  fluctuations in hydrology and environment during
  last 250 ka
• Fluctuations reflect variations in water and
  sediment discharged from the glaciated headwaters
  and processes that influence sediment delivery to
  the core site, including lake-level changes
• Most pronounced change resulted from
  re-arrangements of drainage, controlled by both
  climatic and non-climatic factors