Page 5 - SEG - First issue

Academic Articles

1- clastic sediments

Large sediments roll due to the river moving it along
it's bed ( bed load ) and when the river connects with
the lake it's speed drops and it then drops the bigger
sediments and then finer sediments which have been
suspended till now settle to the bottom ( clays and
silts ). the bottom of a lake will have mainly clays and
silts when surveying away from the shore or the river
mouth . big sediments will reveal their own origin
from nearby source and will show current and wave
directions that lead them where they have been
deposited . volcanic ash may deposit and like the ash
from the Pleistocene epoch it could be used as a
stratigraphic marker . varve deposits are an annual
deposit that indicates the change of seasonal change
, it contains coarse grains and finer grains that alter
between each other . varves are common especially
when the water comes from ice sheets and glaciers
.organic matter comes from plants, Bactria , small
insects and algae which thrives of nitrogen and
phosphorus and other neutrons .
2- chemical deposits

In the lake compose of mainly calcium, sodium, and
magnesium carbonates and dolomite, gypsum, halite, and
sulfate salts. calcium carbonate precipitates as calcite or
aragonite while the lake is saturated with calcium and
bicarbonate ions. algae can also generate the right
conditions for calcium carbonate to precipitate like raise the
ph of the water from 7 to 9 which makes it alkaline.
dolomite is found in very alkaline water where calcium
carbonate and magnesium carbonate combine. also in
saline lakes gypsum occurs with the presence of sulfate,
calcium, and hydrogen sulfide with certain concentrations.
lakes with high concentration of sodium sulfate are called
bitter lakes and lakes that contain high concentrations of
sodium carbonate are called alkali lakes . magnesium salts
can be found in the same sediment as the sodium salts.
lakes could have other salts precipitating like borates,
nitrates, and potash also a small portion of borax is found in
various lakes through out the world
Lakes characteristics according to The gradual thickening of sediments might
put the lake under the danger of extinction.
geological sediments :

1- sediments become more fine toward the center of the lake
2- lakes tend to have Low energy, poor oxygenation: bottom sediment generally poorly disturbed so lamina are
present and commonly made of shale
3- excellent preservation of fossils due to low energy and low disturbance
4- edges of lakes have bigger sediments, bi-directional ripple marks and mud cracks
5- lake shale may get disrupted by bigger sediments (storm deposits (tempestites ))

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