GE0-3112GE0-3112 Sedimentary processes and products Sedimentary processes and products

Lecture 8. LakesLecture 8. Lakes

Geoff CornerGeoff CornerDepartment of GeologyDepartment of GeologyUniversity of TromsøUniversity of Tromsø20062006

Literature:Literature:- Leeder 1999. Ch. 19. Lakes.- Leeder 1999. Ch. 19. Lakes.

ContentsContents

►8.1 Introduction8.1 Introduction►8.2 Lake types8.2 Lake types►8.3 Hydrology8.3 Hydrology►8.4 Sedimentation processes8.4 Sedimentation processes►8.5 Modern lakes8.5 Modern lakes►8.6 Ancient lake deposits8.6 Ancient lake deposits►Further readingFurther reading

Geological importance of Geological importance of lakeslakes

►Sinks for water and sediment on Sinks for water and sediment on continents.continents.

►Presently comprise/contain:Presently comprise/contain: 2% Earth’s area.2% Earth’s area. 0.02% Earth’s water volume.0.02% Earth’s water volume.

►Sediments are climate archives.Sediments are climate archives.►Sediments host hydrocarbons, coal Sediments host hydrocarbons, coal

and uranium. and uranium.

Lake types (origin)Lake types (origin)

►Rift basinsRift basins►Cratonic sagsCratonic sags►VolcanicVolcanic►Glacial Glacial

overdeeped by scouroverdeeped by scour moraine-dammedmoraine-dammed

►OtherOther

Rift basin lakesRift basin lakes

►African rift valleyAfrican rift valley►Lake Baikal, RussiaLake Baikal, Russia►Basin and range, USABasin and range, USA

Volcanic lakesVolcanic lakes►Calderas:Calderas:

Crater Lake, USACrater Lake, USA Mono L, YellowstoneMono L, Yellowstone L. Taupo, NZL. Taupo, NZ

Cratonic basin Cratonic basin lakeslakes

Glacial lakesGlacial lakes

Lake water (density) Lake water (density) stratificationstratification

►Thermal (seasonal)Thermal (seasonal)►Haline (perennial)Haline (perennial)

Maximum gradient

Transition

Less warm

Warm upper

Lake typesLake types► Amictic – permanent ice cover.Amictic – permanent ice cover.► Monomictic – one season free circulation (summer or Monomictic – one season free circulation (summer or

winter).winter).► Dimictic – two seasons of circulation (spring/autumn).Dimictic – two seasons of circulation (spring/autumn).► Oligomictic - circulation rare (stable stratification).Oligomictic - circulation rare (stable stratification).► Polymictic – frequent or continuous circulation.Polymictic – frequent or continuous circulation.► Meromictic – salinity stratified. Meromictic – salinity stratified.

Lake circulationLake circulation

►Thermally driven (seasonal).Thermally driven (seasonal).► Inflow drivenInflow driven►Wind driven (intermittent).Wind driven (intermittent).

ExampleExample

► Inflow and wind-driven circulation, Inflow and wind-driven circulation, Peyto Lake, Canada. Peyto Lake, Canada.

Wind driven circulation and Wind driven circulation and mixingmixing

Hypolimnion

Epilimnion

Mixing

SedimentationSedimentation► Clastic input from riversClastic input from rivers► Wave reworkingWave reworking► Downslope mass-movementDownslope mass-movement► In-situIn-situ biological and chemical production biological and chemical production

Clastic sediment inputClastic sediment input► Points sources via fan and river deltas:Points sources via fan and river deltas:

underflows (turbidity currents)underflows (turbidity currents) interflowsinterflows (overflows)(overflows)

Wind-driven processesWind-driven processes

► Waves along the shoreline.Waves along the shoreline.► Set up water gradient and generate currents.Set up water gradient and generate currents.► Wind relaxation causes surface or internal oscillations Wind relaxation causes surface or internal oscillations

(seiches).(seiches).

Chemical processesChemical processes► Input controlled by weathering and lithology.Input controlled by weathering and lithology.► Ionic salinity dom. by:Ionic salinity dom. by:

cations: Ca, Mg, Na, Kcations: Ca, Mg, Na, K anions: HCOanions: HCO33, CO, CO33, SO, SO44, Cl, Cl

► Carbon cycle dom. by:Carbon cycle dom. by: precipitation of CaC0precipitation of CaC033

fixation of C by organisms.fixation of C by organisms.

► Si fixed by diatoms.Si fixed by diatoms.► Seasonal variations.Seasonal variations.

Marl-lake facies common in temperate dimictic lakes.

Saline lakesSaline lakes► Solutes >5000 ppm (5 Solutes >5000 ppm (5 ‰).‰).► Playa: seasonally exposed evaporitic lake floor.Playa: seasonally exposed evaporitic lake floor.► Lake levels much higher during pluvials. Lake levels much higher during pluvials. ► Examples:Examples:

Death ValleyDeath Valley Dead SeaDead Sea

► Surface and subsurface inflow.Surface and subsurface inflow.► Dom. Na-Ca-Cl-S0Dom. Na-Ca-Cl-S044

Biological processesBiological processes

►Photosynthetic plankton in the Photosynthetic plankton in the epilimnion.epilimnion.

►Diatoms important in nutrient-poor Diatoms important in nutrient-poor (oligotrophic lakes).(oligotrophic lakes).

►Bacterial decay of organic matter uses Bacterial decay of organic matter uses up oxygen up oxygen anoxis at depth in anoxis at depth in chemically stratified lakes.chemically stratified lakes.

►Seasonal oxygen fluctuation give Seasonal oxygen fluctuation give organic-rich/organic-poor laminae. organic-rich/organic-poor laminae.

Organic

Minerogenic

Lake Nakkevatnet, Troms

Meromictic lake lamination

Modern lakes and faciesModern lakes and facies

►Cool dimictic lakesCool dimictic lakes Lake Brienz, SwitzerlandLake Brienz, Switzerland Lake ZurichLake Zurich

►East African rift lakesEast African rift lakes Lake MalawiLake Malawi Lake TanganyikaLake Tanganyika Lake TurkanaLake Turkana

►Lake Baikal rift lakeLake Baikal rift lake►Shallow saline lakesShallow saline lakes

Cool dimictic lakesCool dimictic lakes

►Thermal stratification summer and Thermal stratification summer and winter; overturn in autumn and spring.winter; overturn in autumn and spring.

►Lake Brienz, Swiss AlpsLake Brienz, Swiss Alps 14 km long, 261 m deep.14 km long, 261 m deep. Turbidite sands and varves.Turbidite sands and varves.

►Lake ZurichLake Zurich

Lake BrienzLake Brienz

► Clastic deposition.Clastic deposition.► Deposition in seasonally stratified lake by overflows, interflows and Deposition in seasonally stratified lake by overflows, interflows and

underflows.underflows.► High-density turbidity currents (extreme flood events) High-density turbidity currents (extreme flood events) thick (<1.5 thick (<1.5

m) graded sand beds.m) graded sand beds.► Low-density turbidity currents (seasonal flood events) Low-density turbidity currents (seasonal flood events) thin (cm’s) thin (cm’s)

faintly graded sand.faintly graded sand.► Summer settling of overflow/interflow silt Summer settling of overflow/interflow silt dark part of varve dark part of varve

couplet.couplet.► Winter settling of silt/clay after overturn Winter settling of silt/clay after overturn light part of varve couplet. light part of varve couplet.

Reineck & Singh 1980

Lake ZurichLake Zurich

►Flood dams in 1900 have stopped Flood dams in 1900 have stopped most clastic input.most clastic input.

►Dominant biogenic and chemical Dominant biogenic and chemical deposition.deposition.

►Chemical and biogenic cycles produce Chemical and biogenic cycles produce chalky varves on lake floor.chalky varves on lake floor.

►Cf. to Neogene lacustrine chalks in Cf. to Neogene lacustrine chalks in Black Sea.Black Sea.

East African rift lakesEast African rift lakes

►Half-grabensHalf-grabens►Deep lakes Deep lakes

permanently permanently stratifiedstratified

►Shallow lakes well Shallow lakes well mixedmixed

East African rift lakesEast African rift lakes

Lake TanganyikaLake Tanganyika

► 23000 km23000 km22, 1470 m , 1470 m deep.deep.

► 4 km thick sediments, 1 4 km thick sediments, 1 Myr.Myr.

► Asymmetric basin form.Asymmetric basin form.► Steep slopes: sediment Steep slopes: sediment

bypass and mass flow.bypass and mass flow.► Turbidity currents onto Turbidity currents onto

lake bottom.lake bottom.

L. Tanganyika - faciesL. Tanganyika - facies

Lake MalawiLake Malawi► 45 000 km45 000 km22, 730 m deep., 730 m deep.► 4.5 km thick sediments, 5 Myr.4.5 km thick sediments, 5 Myr.► Slope deposits and turbidites.Slope deposits and turbidites.► Side deltas common.Side deltas common.► S. floor contains hemipelagic muds , diatom oozes and S. floor contains hemipelagic muds , diatom oozes and

Fe-oolites.Fe-oolites.► NB. Variable facies due to major (>150 m) rapdid (NB. Variable facies due to major (>150 m) rapdid (~350 yr) lake ~350 yr) lake

level fluctuations.level fluctuations.

Lake TurkanaLake Turkana► 5000 km5000 km22, 35 m ave. depth., 35 m ave. depth.► Well mixed.Well mixed.► Saline (2.5Saline (2.5‰), alkaline (pH9.2), oxidizing (70-100%).‰), alkaline (pH9.2), oxidizing (70-100%).► Clastic underflows during floods.Clastic underflows during floods.► Deltas and beaches at different levels.Deltas and beaches at different levels.► Little organic sediment.Little organic sediment.► Varve-like muds; some authogenic minerals.Varve-like muds; some authogenic minerals.

Lake BaikalLake Baikal► World’s largest: 23 000 kmWorld’s largest: 23 000 km33, 1640 m deep., 1640 m deep.► Oligotrophic.Oligotrophic.► No dimictic overturn below 500 m.No dimictic overturn below 500 m.► <7 km thick sediments, 15 Myr.<7 km thick sediments, 15 Myr.► Deltas and turbidity currents.Deltas and turbidity currents.► Fe/Mn cement horisons in muds.Fe/Mn cement horisons in muds.► Diatom-rich (>60%) sediments.Diatom-rich (>60%) sediments.► Hot-spring vents.Hot-spring vents.

Shallow saline lakesShallow saline lakes

►Salinas and playasSalinas and playas►Evaporite-clastic couplets.Evaporite-clastic couplets.►Halite, gypsumHalite, gypsum►Sensitive to climate change (lake level Sensitive to climate change (lake level

fluctuationfluctuation

Facies successions in evolving Facies successions in evolving lakeslakes

►Pluvial –interpluvial (100 kyr) Pluvial –interpluvial (100 kyr) fluctuations.fluctuations.

►Short-term fluctuations (e.g. during Short-term fluctuations (e.g. during Holocene) in warm environments. Holocene) in warm environments.

Ancient lake faciesAncient lake facies

► Newark SupergroupNewark Supergroup Transgressive sandsTransgressive sands microlaminated black shalesmicrolaminated black shales Highstand-lowstand 21 kyr cyclesHighstand-lowstand 21 kyr cycles

► Devonian Lake OrcadiaDevonian Lake Orcadia Fluviolacustrine sedimentsFluviolacustrine sediments Carbonate-, organic rich and clastic laminites.Carbonate-, organic rich and clastic laminites. Ripples and subaerial shrinkage cracks.Ripples and subaerial shrinkage cracks.

► Eocene Green River FormationEocene Green River Formation 950 m thick950 m thick World’s largest Trona /NA2CO3) deposit.World’s largest Trona /NA2CO3) deposit. World’s single largest hydrocarbon reserve.World’s single largest hydrocarbon reserve.

► Tertiary lake MadridTertiary lake Madrid pedified mudrockspedified mudrocks

Eocene Green River Eocene Green River FormationFormation

Further readingFurther reading

►Galloway and HobdayGalloway and Hobday►ReadingReading