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Distributary channels
These diverge from the
main river channel and
distribute the water and
sediment over the delta
top forming the topset
beds.
The channel will be lens
shaped and will be filled
with medium or coarse
sandstone.
Channel sands have
cross bedding due to
high energy currents.…read more

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Delta Sediments
Topset beds occur at the top on the cross-section (A).
These deposits get finer as the delta deposits sediment
into the sea as the energy drops.
At the front slope of the delta there are finer sandstones
with cross-lamination, these are Foreset beds (B).
Where the delta front levels out onto the seabed the
sediment is finer still, siltstones or shales or marine
limestones and these are the Bottomset beds (C).…read more

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Swamps
In between the distributary
channels are swamps and
slightly elevated areas with
trees/vegetation.
The swamps are stagnant
water and are therefore
anaerobic.
This means that the
vegetation does not break
down and so peat can
accumulate.
The peat will form coal
when burial and
lithification take place.…read more

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Cyclothems
These are a repeated sequence
of sedimentary rocks.
The most common kind of
cyclothem occurs where deltas
advance (prograde) and retreat
(retrograde) repeatedly.
Why would deltas do this:
Sea level changes.
Changes in the sediment
supply.
Isostasy giving changes in
the land level.…read more

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Cyclothems
The coal forms from the vegetation
that grew on the delta top.
The seat earth (fine sand with roots) is
the soil in which the plants grew.
The cross bedded sandstone formed in
the distributary channels on the delta
top.
The foreset sandstones form on the
delta front
Shales and limestones form offshore
as bottom set beds.…read more

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