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Slide 1

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Deltas and Coal
All coal was once living
matter- plants.
The Coal Measures in the
Carboniferous formed
from large equatorial
During that period the
conditions were perfect
for the formation of coal.
Anaerobic conditions
Slow subsidence…read more

Slide 2

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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
The channel will be lens
shaped and will be filled
with medium or coarse
Channel sands have
cross bedding due to
high energy currents.…read more

Slide 3

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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

Slide 4

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

Slide 5

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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
Isostasy giving changes in
the land level.…read more

Slide 6

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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
The foreset sandstones form on the
delta front
Shales and limestones form offshore
as bottom set beds.…read more

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