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Carbonate Deposition in the Great Salt Lake, Utah

Robert Baskin (1) & Paul Wright (2)University of Utah, Salt Lake City, Utah 84112. [email protected] Sciences, National Museum of Wales, Cardiff, UK ([email protected])
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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50 kms


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Carozzis1962 sediment map

based on Eardley 1938

Because it is the largest

lacustrine carbonate systemtoday

Because it is a natural

laboratory for understanding

carbonate deposition in a

dryland rift setting

Because there has been no

integrated study of the

sedimentary system

Why study it?


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4

Great Salt Lake- Key Facts

Area: 4400km2present

Drainage: Three ephemeral rivers fromwestern side; main rivers on the east.

Water Depth: 4.45m average (10mmaximum)

Climate: Arid to Semi-arid

Wave Base: Approx 4m

Chemocline: intermittent, affected byNorth Arm flow

Lake Type: Hypersaline-Saline (13-25%salinity)

Setting: Intracontinental rift

Fauna: Brine shrimp, brine fly larvae.

Sediments: extensive microbialites, ooliticsands. Halite precipitation in the NorthArm.

2003


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The current deposystem is very young and it is unclear how this

might be preserved to enter the stratigraphic record

In broad terms it fits well with the big picture model forcarbonate deposition in an arid rift setting, but with critical and

subtle tectonic controls on sediment production and distribution

We can develop some simple facies models but shoreline

diversity still not fully assessed

Most of the lake is currently within wave base

The specific hydrology of this shallow lake favours carbonateproduction over very large areas, with limited terrigenous

dilution and carbonate production related to groundwater inflow

(cf many other carbonate lakes).


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Structure

Various sources


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Closed basin hydrological model

From Renaut R & Gierlowski-Kordesch 2010, Facies Models 4,ed. By N P James & R W Dalrymple, Geoscience Canada

The Great Salt Lake

receives:-

66% from runoff

31% from direct

precipitation.

3% recharge from

groundwater


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Major catchments and river

inflows (Baskin et al 2002)

Terrigenous sedimentation is largelylocalised in the northwest allowing

carbonates to dominate most of the

lake


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From Harris P M et al. 2012 Bull. AAPG, 97, 27-

60

270m fall in 4kyrdue to breaching and

climate change

The current deposystem is

young!


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Modified from Harris P M et al. 2012 Bull. AAPG, 97, 27-60


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How well does the GSL today correspond to this model?

How well does the GSL today correspond to this model?

Dryland rift carbonate model

Hanging wall ramp margin


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500m

Shore line deposition: Bridger Bay = oolitic and

microbial (reflective) shorelines

Microbial mounds

Oolitic shore

Prevailing

wind


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Rippled ooliticsand flat

intraclasts

Oolite dunes

Oolitic

nebkha

Intraclast zone

Oolitic bars

Littoral-supralittoral facies


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Importance ofstable substrates

Oolitic shore

Microbial

mounds


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Pop-corn faciesaragonitic crusts shed off microbialites

pop corn berm


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PROGRADATIONAL WALTHERIAN

Supralittoralfacies aeolian oolitic sands, rooted,

larger dunes rarely preserved

platy intraclast rudstones

planar laminated oolitic, intraclasticgrainstones

small scale cross-bedding in ooliticgrainstones

microbial bioherms locally developed,partially truncated

popcornaragonite & ooid grainstones,peloidal

wave rippled oolitic grainstone -packstone

laminated, organic-richaragonite muds

Eulittoralfacies

Sub-littoralfacies

Profundalfacies

Based on southern arm of GSL

0

4m

Possible stratigraphic product

Analogue

Upper Triassic, SW England; Milroy & Wright 2002


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Restriction in the North Arm shows the fate of the carbonate

system when the lake begins to dry out -


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NON-WALTHERIAN,

lake evaporates

will be reducedin thickness dueto evaporation

tepees, truncated,brecciated bioherms

injected muds,selenite

displacive evaporitein saline mud flatfacies; dolomite?

dry mud flat facies

,

Based on northern arm of GSL


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Supralittoralfacies aeolian oolitic sands, rooted,

larger dunes rarely preserved

platy intraclast rudstones

planar laminated oolitic, intraclasticgrainstones

small scale cross-bedding in ooliticgrainstones

microbial bioherms locally developed,partially truncated

popcornaragonite & ooid grainstones,peloidal

wave rippled oolitic grainstone -packstone

laminated, organic-rich

aragonite muds

Eulittoralfacies

Sub-

littoralfacies

Profundalfacies

Based on southern arm of GSL

0

4m

Difficult to assess

Sub-littoral Zone


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Except when the lake dries out - 1964

Edge of rift

Perhaps 1000 km2of

stromatolites/microb

ial mounds in lake.

Sid d CHIRP l btl i t hi


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Side scan sonar and CHIRP surveys reveal subtle microtopographic

control by small faults on bioherm distribution and sediment

accumulation


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VE=70

The bioherm clusters extend

in dip direction of >400m

and much further in strike

direction - given typical

average outcrop constraints

it is highly unlikely thisrelationship to small faults

would be detected

Microbialite bioherm

fault

Sediment covered trough


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Stromatolitic Thrombolitic


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Arid rift carbonate model

Pyramid Lake10% groundwater fed.but 66% of Cacomes from thermal waters

Mono Lake

Carbonate production focussed

around Ca-rich vents producingsub-lacustrine mounds


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Larger buildups around faults occur but are not common andhave not been studied

from Colman et al.

2002

Colman et al. 2002


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Model Based on Current Great Salt Lake


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Aragonitic oolitic sand, bison hoof prints and snow


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The current deposystem is very young and it is unclear how this might be

preserved to enter the stratigraphic record

In broad terms it fits well with the big picture model for carbonate deposition

in an arid rift setting, but with critical and subtle tectonic controls on

sediment production and distribution

We can develop some simple facies models but shoreline diversity still notfully assessed

Most of the lake is currently within wave base

The specific hydrology of this shallow lake favours carbonate production oververy large areas, with limited terrigenous dilution and carbonate production

related to groundwater inflow (cf many other carbonate lakes).

Conclusions


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Moody and withdrawn, the lake unites a haunting loveliness to a raw

desolateness. Dale L Morgan, 1947: The Great Salt Lake

Thanks to BG Group for supporting RBs research

s21 01 baskin-wright

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