Glacial Till Features

Okay, so this is the difference between uh, glacial till,

which is unstratified,

and non-glacial till.

So, hopefully you can see that this uh, gravel here

is well-stratified.

There are a lot of sedimentary features here.

Um, you can see graded bedding.

You can also see cross bedding.

Maybe I can just sort of zoom in on that.

So there's cross bedding right there.

Very coarse uh, cross bedding.

However, the stratification or the horizontal layering,

the general horizontal here,

indicates that this is not glacial gravel.

Even though it's approximately the correct size

and sorting distribution.

The presence of sedimentary features

as well as uh, the stratification,

that's the horizontal layering,

indicated as not glacial gravel.

Okay. I'll try and show you glacial gravel a little later.

So this is uh, glacial till.

It is gravel that is deposited by a glacier.

Um, and the identifying characteristics of it

is well-rounded clasts,

however they're not really really well-rounded.

They are definitely rounded to some extent.

Um, oftentimes there are striations on each individual clast,

maybe I can show you that later.

Um, those are scratches that are produced

when gravel bounces or scrapes against

other pieces of gravel or the bedrock.

And the other identifying characteristic

is that the gravel itself is unstratified.

There is no layering, no horizontal stratification.

Um, and there really are no sedimentary features here,

other than the lack of sedimentary features,

which indicates that it was deposited by a glacier.

Now hopefully you'll be able to see,

if it'll focus on that,

the scratches on the surface of this clast.

Those parallel scratches are glacial striations,

which are present on a clast.

It's stuck in there pretty hard. Argghh.

It won't come out.

And in addition to the lack of uh, sedimentary features,

um, one of the characteristics that you always look for

is a very very poor degree of sorting

in terms of clast size.

And so, maybe I can zoom in on that a little bit.

You've got clasts of all different, uh, sizes.

Very poorly distributed.

I suppose even down to these sizes,

which have fallen down from the cliff face, I suppose,

the gravel face anyways.

Very poor sorting.

Okay. Since we're talking about till,

I thought I'd show you what happens when till, um,

becomes a rock, when it comes consolidated or indurated.

This is called tillite, which is uh,

the rock, I suppose, from glacial till, a conglomerate.

This one is very old.

It is on the side of the Trans Canada, here. [cars going by]

As you can tell by the traffic.

And it is south of Wawa in Ontario, Canada.

[traffic in background]

This particular crop has been highly metamorphosed,

so these in the Canadian shield.

Um, so strongly metamorphosed.

And this tillite is uh, weathering very rapidly

as a result of the intense metamorphism,

which has caused cracks and fractures

which increase surface area, of course,

and cause weathering to accelerate.

[traffic in background]

Now realize I'm looking at a shadow here,

but hopefully you can see that the clasts are well-rounded.

Very poorly sorted, in terms of size distribution.

And are not layered. They are unstratified.

I just thought you might want to see what's on the other side of the road.

That is Lake Superior,

about an hour south of Wawa, Ontario.

Pretty big lake, eh? Kind of looks like the ocean.

You can't see the other side of Lake Superior,

even though we're way the heck up on the roadside.

There you can see down to the beach.

Alright, that's it. Bye for now.