WEBVTT

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(Chime)

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Hi guys,

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the objective of this video is to look at

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the bedding structures that form
when sediment is deposited.

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These bedding structures all form 
in different environments.

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And these environments,
which create the bedding

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structures will be discussed.

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Firstly,
we will talk about the horizontal beds,

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or strata,
that the sediment is laid down in.

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Sedimentary rock is stratified,
which means that it has layers.

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These layers have formed because 
sediment is laid down in

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horizontal layers called strata.

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Between each layer of strata,
we have bedding planes.

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And these bedding planes form because 
the region has experienced

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a change in depositional 
environment or material.

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We can see here in this photo
that we have had one

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type of sediment laid down.

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And then,
a change in depositional environment

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has caused a different type of sediment
to be laid down on top,

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in between which is a bedding plane.

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We know that the strata towards
the bottom of a series is older

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than the strata at the top.

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And this happens because the sediment 
is laid in this way.

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Bedforms are formations that occur due to 
the movement of wind and water.

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Bedforms are created when water or wind,
flows over loose sediment.

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And the shape and the texture of the 
bedform depends on the

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velocity of the flowing wind or water,
and the size of the sediment.

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One type of bedform is ripples.

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Ripples occur to due the flow of water.

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Asymetrical ripples occur when water is
just flowing in one direction.

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As we can see here.

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Symetrical ripples will occur 
when the waves oscillate back and forth.

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As we can see here.

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These bedforms can be preserved in
the sedimentary rock,

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because new sediment 
can be deposited on top.

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And the formation will remain the same
and will be lithified in this shape.

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Another type of bedform are dunes.

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Dunes form with the same formation 
process as the asymetrical ripples

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when they form due to water.

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However,
dunes form due to the action of wind.

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Cross Bedding is another type of 
bedform.

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Cross bedding forms in the process of 
making ripples or dunes.

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Whether that be with water or wind.

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Cross bedding forms because we have
a pile up of sediment along the top

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of the slip face.

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This pile up is being pushed

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towards the edge of the slip face,

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and soon will slip down the face.

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This slip face will then slowly move
downstream as more and more

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sediment comes along.

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Any additional sediment will continue
to form cross bedded layers

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in the environment where ripples and 
dunes are being formed.

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Another type of bed form are
graded beds.

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Graded beds form when the
strata of the sediment becomes

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more fine towards the top of the strata.

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This graded pattern is often repeated
in a formation.

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As we can see here.

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Graded beds form due to a sudden period
of high energy movement of the sediment.

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For example,
as we are actually discussed in the

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previous video,
graded beds will form when we have

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turbidite cones;
when sediment avalanches over

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the edge of a continental shelf.

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So,
when the sediment avalanches over

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the edge of the continental shelf,
these turbidite cones

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are created down here.

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When the sediment is in the turbidite cone
the heavy sediment will settle out first.

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The medium size material will settle next,
and the fine silt material will remain

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suspended in the currents of the water,
and will finally settle out on top.

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This is what creates our graded beds.

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The last thing we will discuss in this 
video are bed-surface markings.

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Bed surface markings occur due to 
alterations on the surface of the Earth.

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Mudcracks form when the surface of the 
Earth dries out.

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Mudcracks can be preserved in the 
sedimentary layers when they are covered

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by sediment.

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These mudcracks indicate that we have had
alternating wet and dry conditions

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in the past.

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Fossils are another type of bed surface 
marking.

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Where fossils can be preserved within the 
layers of sediment,

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and they are an evidence of past life.

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In summary,
sediment is laid down in horizontal beds.

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We know these sedimentary layers can
preserve past environments,

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such as the flow of wind and water over
loose sediment.

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This flow of wind and water can create
bedforms;

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such as ripples, dunes and crossbedding.

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And bed surface markings such as,
mudcracks and fossils can also form

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and indicate the environment in which
the sediment was laid down in.