Lacustrine Environments

1. Lacustrine Environments Alpine Lake, Switzerland

2. Lacustrine Environments Composicion:siliciclastic, carbonate, or evaporite Texture:well sorted;lake center—silt and clay; lake edges— coarser sediments of sand and gravel

3. Structures:lake center—plane laminations (sometimes annual layers called varves); lake edge—wave ripples or climbing ripples (can look like an ocean beach but with small waves and no tidal effect)

4. Geometry of deposit: deep or shallow bowl Map view Profile view: gl/de = clay and silt from a glacial lake; ct/st = glacial silt (loess); sg = sand and gravel (lake edge); grey color = sediments deposited prior to the last glacial maximum

5. Lateral variations: rivers and deltas, glacial deposits (e.g., till), dunes Torres del Paine National Park, Chile

6. 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

7. 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)

8. Paleo-shorelines of Lake Lahontan Paleo-shorelines of Lake Sarmiento in Torres del Paine, Chile

9. Biology: freshwater fossils, especially gastropods, bivalves, ostracodes, diatoms; it is also possible to preserve leaves and other plant parts in the lake mud Chemical processes: common sediment colors of grey, blue-grey, or green because of reducing environment in lake center In some lakes, carbonates 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)

10. Playas: form in arid climates, where there is ephemeral water in shallow lakes (below: playa in Death Valley, California; notice mud cracks)

12. Processes of deposition?

13. Processes of deposition: deposition from suspension (fine sediments in lake center); traction flows (coarser sediments at lake edge—processes associated with small waves and deltas that form where sediments enter lake) 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 (flows from land during storms) In large, deep lakes it is possible to have turbidity flows like those that form in the deep ocean (but the fossil types are different)

14. 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

15. Example of a lake during a wet period

16. Example of a lake during a dry period

17. Depositional setting: highly variable environments. Open type—water can enter and leave the lake. Closed type—no exit for lake water Crater Lake, Oregon

18. The most distinctive characteristics: laminated mud with freshwater fossils