1.11 Sedimentary Bedding Structures

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.

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 stratafied,
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's
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,
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.