5.2 Lacustrine environments. Hydrological regimes of lakes. - презентация

1 5.2 Lacustrine environments

2 Hydrological regimes of lakes

3 A hydrologically open lake basin Supplied from a river (foreground) with outflow to the sea in the distance

4 Lacustrine environments Clastic lakes have coarser deposits in shallower water and finer deposits in the deeper lake

5 Lacustrine (lake) environments Lake delta and shoreline deposits

6 Thermal stratification in a freshwater lake

7 A sedimentary log of clastic freshwater lake deposits Shallow lake deposits. Beach and/or lake delta sands Shallow lake deposits. Muds and wave- rippled sands Deeper lake deposits. Laminated dark shales and thin turbiditic sands and silts. 10s metres

8 Thin-bedded clastic freshwater lake deposits

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10 Thin-bedded clastic freshwater lake deposits, including wave ripple lamination

11 Fine-grained freshwater lake deposits

12 Lacustrine environments – distinctive features Lake level of hydrologically closed lakes can vary with climate – lake margin can dry out

13 Lacustrine environments – distinctive features Lake level of hydrologically closed lakes can vary with climate – lake margin can dry out

14 Sedimentary structures formed by desiccation Mudcracks form by mud drying out: desiccation cracks

15 Sedimentary structures formed by desiccation Mudcracks preserved in ancient dry lake deposits

16 Erosion of desiccated mudrocks produces clasts of mud: mudclasts Sedimentary structures formed by desiccation

17 Lake sedimentation patterns Lakes do not have strong currents – water mass is stable Epiliminion – warm, buoyant, oygenated water Hypolimnion – cold, denser water, anoxic conditions - separated by a thermocline

18 Lake sedimentation patterns Stratification of the lake waters results in anoxia of the deep lake floor Organic-rich deposits preserved, no lake-floor fauna