The Glacial/Deglacial History of Sedimentation in Bear Lake (Utah and Idaho)

The Glacial/Deglacial History of Sedimentation in Bear Lake (Utah and Idaho)

Joe Rosenbaum, Walt Dean,and Richard Reynolds science for a changing w orld

Interpretations based largely on changes in provenance of detrital material and the transition from siliciclastic to carbonate sedimentation

• Catchment– Relation of Bear River to Bear Lake– Properties of fluvial materials

• Mineralogy and elemental chemistry• Magnetic properties

• Lake sediment cores– Variations in provenance with age– Glacial history

• Comparisons to other records– Rocky Mountains– Lake Bonneville

science for a changing world

Bear Lake and the Bear River

• Headwaters of the Bear River in the northwestern Uinta Mountains

• Bear River is the largest river in the Great Basin

GreatSaltLake

Wasatch

Range

U inta Mtns.

River

Bea

r

Wyom

ing

IdahoUtah

BearLake

Salt LakeCity


Bear Lake & Bear River

The Bear River did not enter the lake during much of the Holocene, but did during the last glacial period.


Geologic Map

Watershed boundary

Geologic Map of the Bear Riverand Bear Lake Watersheds(after R eheis, in press)

Be ar

Lake

42 30'o

42 30'o

41 30'o

41 00'o

110 30 'o111 30 'o 111 00'o

0 10 20 km

W yom ing

Wyo

min

g

U tah

Uta

hW

yom

ing

Idah

o

UtahIdaho

Evanston

GardenCity

R i

v e

r

Pliocene-Pleistocene surficial deposits

Tertiary alluvial and lacustrine rocks

M esozoic and Upper Paleozoicshale, lim estone, and sandstone

Low er Paleozoic lim estone,, and quartzitedolom ite

Upper Precam brian shale and quartzite(including of the Uinta M ountain G roup)

hem atite-rich rocks

5351

4947

4543

41

3937

35

31

29

27

25

23

21

19

17

15

1311

9

7

1

3

5

33

G lacial till and outwash


Magnetic Properties of Fluvial Sediments

• “Magnetite” content– low in Uinta Mtns. and lower

reaches of the Bear River– high in local Bear Lake

catchment– about the same on east and

west sides of lake• “Magnetite” in the fluvial

sediments is largely from dust– variety of magnetite and

titanomagnetite grains that are derived from igneous rocks that do not exist in the catchment

– fine-silt sized grains (<10 m)

Wyo

min

g

Bear LakeCatchm ent

Bear River(upstream )

Uta

h

10 20 30 40 50

Sam ple Num ber

W E Lower Upper

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2


Magnetic Properties of fluvial sediments

• “Hematite” content– higher in Uinta Mtns. than in

other source areas.– about the same in local Bear

Lake catchment as along lower reaches of the Bear River

Note dilution of material from the headwaters of the Bear River downstream so that under present conditions Uinta Mountain material is a minor component of the river sediments.

Wyo

min

g

Bear LakeCatchm ent

Bear River(upstream )

Uta

h

10 20 30 40 50

Sam ple Num ber

W E Lower Upper

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2


Properties of 3 catchment areas

Al/Ti *Local Bear Lake catchm ent

“Low er” Bear River

Headwaters of the Bear River

M g/CaMS HIRM Dolom iteCalcite

• Local Bear Lake catchment– High dolomite content (Mg/Ca)

& magnetic susceptibility (MS)– Low HIRM

• Headwaters (Uinta Mtns.)– High HIRM and Al/Ti– Low MS

• “Lower” Bear River– Low MS, HIRM, & dolomite

content


Cores• Composite record from

two 4-m-long cores– BL96-2: Largely

carbonate-rich sediments overlying uppermost siliciclastic sediment

– BL96-3: Very thin, incomplete Holocene record overlying more than 3.5 m of siliciclastic sediment

• GLAD800– 120 meters– Last 240,000 years

Utah

GardenCity

Idaho

42 04' No

41 56’ No

111 12’ No

G23

10

30

50


Composite Section and Chronology

• The composite record provides a nearly continuous record for most of the Holocene back to about 32 cal. kyr

• Siliciclastic sedimentation 32 – 17 cal. kyr

• Endogenic calcite or aragonite 14.5 cal. kyr - present

BL96-3

BL96-20

1.0

2.0

3.0

4.0D

epth

(met

ers)

0

1.0

2.0

3.0

4.0

% Calcite0 20 40 60 80

0 20 40 60 80% Calcite

Cal. A ges(kyr)

Cal. A ges(kyr)

5.0 13.015.4

23.7

25.725.7

27.5

31.3

3.2

3.74.86.0 6.67.39.2 9.512.1

14.916.819.322.024.725.126.6


Ages

• 14C ages– AMS ages on pollen

concentrates (pollen + other refractory organic material)

– Pollen is plentiful and well preserved in carbonate sediments

– Pollen is sparse and in poor condition in the siliciclastic sediments

– Ages are in good stratigraphic order and there is no apparent discontinuity

BL96-3

BL96-20

1.0

2.0

3.0

4.0D

epth

(met

ers)

0

1.0

2.0

3.0

4.0

% Calcite0 20 40 60 80

0 20 40 60 80% Calcite

Cal. A ges(kyr)

Cal. A ges(kyr)

5.0 13.015.4

23.7

25.725.7

27.5

31.3

3.2

3.74.86.0 6.67.39.2 9.512.1

14.916.819.322.024.725.126.6


Properties vs age“Hematite”

0 4 8 12

“Magnetite”

0 2 4 6

Mg/Ca (leach)

0.0 0.2 0.4 0.6

10

15

20

25

30

CaCO (%)3

0 40 80

Cal

. Age

kyr

BP

Al/Ti (bulk)

20 25 30 35

Quartz (%)20 40 60 80

I. Quasi-cylical variations in magnetic properties and elemental ratios

II. Decreasing HIRM and Al/Ti

III. Increasing MS and Mg/Ca

IV. Transition to carbonate

V. Constant carbonate (alteration of Fe-oxides)

VI. Aragonite precipitation

Observations


MS vs. HIRM for Zone I

• Strong negative relation between content of material from Uinta Mountains and from the local Bear Lake catchment

0 2 4 60

2

4

6

8

10

from local catchment

from

Uin

ta M

ount

ains

“Magnetite”M S x 10 (m kg )-7 3 -1


Detrital material from the Uinta Mountains is glacial flour:

• High content of material from the Uinta Mountains requires enhanced erosion.

• There was extensive Pinedale-equivalent glaciation in the Uinta Mountains.

• Sediment with high content of Uinta Mountain material is finer-grained.


Properties vs age 2“Hematite”

0 4 8 12

“Magnetite”

0 2 4 6

Mg/Ca (leach)

0.0 0.2 0.4 0.6

10

15

20

25

30

CaCO (%)3

0 40 80

Cal

. Age

kyr

BP

Al/Ti (bulk)

20 25 30 35

Quartz (%)20 40 60 80

Uinta Mtns.Bear Lake

Catchment (BLC)

I. Variations in glacial extent with material from BLC replacing Uinta Mt. Material and vice versa.

III. Increasing input from BLC

IV. Progressive loss of river

II. Decreasing glaciation

V. Little if any input of Bear River sediment

VI. Increasing salinity

Interpretations


Magnetic properties from BL96-3 and

GLAD800

• Unequivocal correlation based on magnetic susceptibility

• Base of BL96-3 just captures the base of the zone with high values of HIRM

GLAD800M S x 10 (volum eSI)-6

0 20 40

8

10

12

14

16

18

20

GLAD800HIRM x 10 (Am )-3 -1

0 4 8 12

0

1

2

3

4Dep

th in

GLA

D80

0 (m

eter

s)

Dep

th in

BL9

6-3

(met

ers)

BL96-3M S x 10 (m kg )-7 3 -1

0 2 4 6

BL96-3HIRM x 10 (Am kg )-4 2 -1

2 6 1 0


Comparison to other records of glacial extent• Upper Klamath

Lake– Millennial-scale

variations– Peak at about 19

to 18 cal. kyr • Rocky Mts.

– Peak at about the same time

– Major deglaciation somewhat later

• Southern Uintas (Laabs) and Wasatch (Lips)

– Cosmogenic ages indicate significantly later deglaciation

0 2 4HIRM

Bear Lake( this study)

NorthwesternUinta M ountains

10

20

30

40

0 50 100Glacier length (% )

(m odified from Porter, 1983;Pierce, 2004)

Cal

enda

r age

1,0

00 y

r B.P

.

RockyM ountains

1965 m odel

1983 m odel

?

?

??

0 40 80

SouthernCascade Range

Flux of g lacial flourUpper Klam ath Lake

(Rosenbaum and Reynolds, 2004)

10

20

30

40


Comparison to Lake Bonneville

• Onset of glaciation at same time as initial growth of Bonneville

• Increase to max. glaciation corresponds to rise following SO

• Deglaciation occurs while Bonneville continues to rise

• River leaves Bear Lake (Zone IV) during fall from Provo shoreline

• Salinity increases (Zone V/VI boundary) during fall from Gilbert (i.e., at end of YD)

IIIIIIIVVVI

1550

1450

1350

1250Lake

Bon

nevi

lleA

djus

ted

elev

atio

n (m

eter

s) B

P

G SSO

10 15 20 25 30 35

Calibrated age (kyr)

0

1

2

3

4

5

U2

U1

U3 modified fromOviatt, 1997


Summary• Bear Lake contains glacial flour from the headwaters

of the Bear River in the Uinta Mountains. The record suggests:– onset of glaciation at 32 cal. kyr– maximum glaciation from 25-24 cal. – deglaciation during later stages of growth of Bonneville and

earlier than indicated by recent dating of moraines in the southern Uinta and Wasatch mountains

• The Bear River abandoned Bear Lake 17-14.5 cal/kyr

• The salinity of Bear Lake increased at the end of the Younger Dryas


Documents

The Glacial/Deglacial History of Sedimentation in Bear Lake (Utah and Idaho)