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Lacustrine Environments Alpine Lake, Switzerland
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Where does this word come from?
The word Lacustrine comes from the Latin prefix “Lacustr” and the English suffix “ine”. Lacustr-: marshy lake -ine: resembling in nature.
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Inland body of water that forms in topographic lows on land surfaces.
Definition of Lake: Inland body of water that forms in topographic lows on land surfaces. Geometry of deposit: deep or shallow bowl
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Formation
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Playas: form in arid climates, where there is ephemeral water in shallow lakes (below: playa in Death Valley, California; notice mud cracks)
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Composition: siliciclastic, carbonate, or evaporite
Texture: generally well sorted lake center - silt and clay lake edges - coarser sediments of sand and gravel
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Structures: lake center - planar laminations
lake edge - wave ripples or climbing ripples (can look like an ocean beach but with small waves and no tidal effect)
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Lateral variations: rivers and deltas, glacial deposits (e. g
Lateral variations: rivers and deltas, glacial deposits (e.g., till), dunes Torres del Paine National Park, Chile
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Vertical sequence: coarsening upward (if the lake fills with sediments); interstratified mud from lake center and silt/sand/±gravel from lake edge Lake- Lake- Lake- Sediments of Lake Lahontan, Nevada
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Size of Lake Lahontan 13 ka, shortly after the last glacial maximum (light blue colors are modern remnant lakes (Tahoe and Pyramid) and playas (Carson and Humboldt)
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Biology: freshwater fossils, especially gastropods, bivalves, ostracodes, diatoms; it is also possible to preserve leaves and other plant parts in the lake mud
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Chemical processes: common sediment colors of grey, blue-grey, or green because of reducing environment in lake center In some lakes, carbonates form at the lake edges because of concentration of elements and evaporation In playas, evaporites (gypsum, anhydrite, halite) precipitate from shallow water (during desiccation)
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Processes of deposition?
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Processes of deposition:
Deposition from suspension; traction flows Lakes in regions with large changes between summer and winter can have annual laminations (varves) of clay rich in organics during the summer (anoxia) and of silt in winter In large, deep lakes it is possible to have turbidity flows like those that form in the deep ocean
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Processes of deposition (playas): precipitation of salt from water, processes of wind and ephemeral rivers when the playa desiccates In permanent lakes it is possible to find carbonates precipitated from water or in the form of stromatolites (algal structures) Tufa at the edge of Pyramid Lake, Nevada
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Example of a lake during a wet period
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Example of a lake during a dry period
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Depositional setting: highly variable environments
Depositional setting: highly variable environments. Open type—water can enter and leave the lake. Closed type—no exit for lake water Crater Lake, Oregon
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The most distinctive characteristics: laminated mud with freshwater fossils
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