Lake Sediment Flashcards
How is the water in lakes layered? what is the proper name for this?
It is layered by salinity and temperature. They are anoxic cold conditions at the bottom, oxic at the top with higher temps.
Density stratification
What causes lake levels to fluctuate?
seasonal effects (snow melt etc), climate change, tectonic breaches
What type of salinity can lakes be stratified by?
At the top they have normal salinity where organisms as happy to live, at the bottom it is hypersaline which is toxic for organisms to live there.
what can you generate in anoxic environments?
Oil shales, organic matter is preserved in anoxic conditions which can create source rocks for petroleum
discuss the difference between river and marine deltas
river deltas are smaller scale than marine deltas otherwise the lake would be filled with sediment, it is hard to tell the difference between a marine and river delta.
What is the only way that carbonates can accumulate in a lake environment?
By turning off the supply of clastic sediment as it swamps carbonate production,
How would a succession with interbedded carbonate and mud layers be created?
By turning on and off the clastic sediments, when the clastics are turned off or diverted they create carbonates.
Lake carbonates precipitating from water create what?
Algal Oncoliths
how are oncoliths formed? where in the lake do these form?
When lake carbonates are precipitating from water. Form as lake margin sediments on the lake margin.
where is coarser sediment deposited on a lake?
At lake margins
are all lakes stratified?
No
If you have evidence of volcanic ash in a lake what does it tell you?
That airbourne dust was falling into the lake, may be situated close to a volcano but may be very far away as ash gets carried a fair distance
P > E tells you what?
That precipitation > evaporation so there is excess water. P/E >1. overfilled lake.
P < E tells you what?
Precipitation is less than evaporation, not enough water to fill the lake. Potentially arid environment. P/E < 1 Under filled lake which affects the sediment character.
Are overbalanced lakes ever saline?
They tend not to be
