(Chime)
Hi guys,
the objective of this video is to look at
the bedding structures that form when sediment is deposited.
These bedding structures all form in different environments.
And these environments, which create the bedding
structures will be discussed.
Firstly, we will talk about the horizontal beds,
or strata, that the sediment is laid down in.
Sedimentary rock is stratified, which means that it has layers.
These layers have formed because sediment is laid down in
horizontal layers called strata.
Between each layer of strata, we have bedding planes.
And these bedding planes form because the region has experienced
a change in depositional environment or material.
We can see here in this photo that we have had one
type of sediment laid down.
And then, a change in depositional environment
has caused a different type of sediment to be laid down on top,
in between which is a bedding plane.
We know that the strata towards the bottom of a series is older
than the strata at the top.
And this happens because the sediment is laid in this way.
Bedforms are formations that occur due to the movement of wind and water.
Bedforms are created when water or wind, flows over loose sediment.
And the shape and the texture of the bedform depends on the
velocity of the flowing wind or water, and the size of the sediment.
One type of bedform is ripples.
Ripples occur to due the flow of water.
Asymetrical ripples occur when water is just flowing in one direction.
As we can see here.
Symetrical ripples will occur when the waves oscillate back and forth.
As we can see here.
These bedforms can be preserved in the sedimentary rock,
because new sediment can be deposited on top.
And the formation will remain the same and will be lithified in this shape.
Another type of bedform are dunes.
Dunes form with the same formation process as the asymetrical ripples
when they form due to water.
However, dunes form due to the action of wind.
Cross Bedding is another type of bedform.
Cross bedding forms in the process of making ripples or dunes.
Whether that be with water or wind.
Cross bedding forms because we have a pile up of sediment along the top
of the slip face.
This pile up is being pushed
towards the edge of the slip face,
and soon will slip down the face.
This slip face will then slowly move downstream as more and more
sediment comes along.
Any additional sediment will continue to form cross bedded layers
in the environment where ripples and dunes are being formed.
Another type of bed form are graded beds.
Graded beds form when the strata of the sediment becomes
more fine towards the top of the strata.
This graded pattern is often repeated in a formation.
As we can see here.
Graded beds form due to a sudden period of high energy movement of the sediment.
For example, as we are actually discussed in the
previous video, graded beds will form when we have
turbidite cones; when sediment avalanches over
the edge of a continental shelf.
So, when the sediment avalanches over
the edge of the continental shelf, these turbidite cones
are created down here.
When the sediment is in the turbidite cone the heavy sediment will settle out first.
The medium size material will settle next, and the fine silt material will remain
suspended in the currents of the water, and will finally settle out on top.
This is what creates our graded beds.
The last thing we will discuss in this video are bed-surface markings.
Bed surface markings occur due to alterations on the surface of the Earth.
Mudcracks form when the surface of the Earth dries out.
Mudcracks can be preserved in the sedimentary layers when they are covered
by sediment.
These mudcracks indicate that we have had alternating wet and dry conditions
in the past.
Fossils are another type of bed surface marking.
Where fossils can be preserved within the layers of sediment,
and they are an evidence of past life.
In summary, sediment is laid down in horizontal beds.
We know these sedimentary layers can preserve past environments,
such as the flow of wind and water over loose sediment.
This flow of wind and water can create bedforms;
such as ripples, dunes and crossbedding.
And bed surface markings such as, mudcracks and fossils can also form
and indicate the environment in which the sediment was laid down in.