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Glacial Till Features

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    Okay, so this is the difference between uh, glacial till,
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    which is unstratified,
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    and non-glacial till.
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    So, hopefully you can see that this uh, gravel here
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    is well-stratified.
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    There are a lot of sedimentary features here.
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    Um, you can see graded bedding.
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    You can also see cross bedding.
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    Maybe I can just sort of zoom in on that.
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    So there's cross bedding right there.
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    Very coarse uh, cross bedding.
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    However, the stratification or the horizontal layering,
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    the general horizontal here,
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    indicates that this is not glacial gravel.
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    Even though it's approximately the correct size
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    and sorting distribution.
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    The presence of sedimentary features
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    as well as uh, the stratification,
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    that's the horizontal layering,
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    indicated as not glacial gravel.
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    Okay. I'll try and show you glacial gravel a little later.
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    So this is uh, glacial till.
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    It is gravel that is deposited by a glacier.
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    Um, and the identifying characteristics of it
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    is well-rounded clasts,
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    however they're not really really well-rounded.
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    They are definitely rounded to some extent.
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    Um, oftentimes there are striations on each individual clast,
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    maybe I can show you that later.
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    Um, those are scratches that are produced
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    when gravel bounces or scrapes against
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    other pieces of gravel or the bedrock.
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    And the other identifying characteristic
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    is that the gravel itself is unstratified.
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    There is no layering, no horizontal stratification.
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    Um, and there really are no sedimentary features here,
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    other than the lack of sedimentary features,
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    which indicates that it was deposited by a glacier.
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    Now hopefully you'll be able to see,
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    if it'll focus on that,
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    the scratches on the surface of this clast.
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    Those parallel scratches are glacial striations,
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    which are present on a clast.
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    It's stuck in there pretty hard. Argghh.
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    It won't come out.
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    And in addition to the lack of uh, sedimentary features,
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    um, one of the characteristics that you always look for
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    is a very very poor degree of sorting
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    in terms of clast size.
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    And so, maybe I can zoom in on that a little bit.
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    You've got clasts of all different, uh, sizes.
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    Very poorly distributed.
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    I suppose even down to these sizes,
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    which have fallen down from the cliff face, I suppose,
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    the gravel face anyways.
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    Very poor sorting.
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    Okay. Since we're talking about till,
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    I thought I'd show you what happens when till, um,
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    becomes a rock, when it comes consolidated or indurated.
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    This is called tillite, which is uh,
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    the rock, I suppose, from glacial till, a conglomerate.
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    This one is very old.
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    It is on the side of the Trans Canada, here. [cars going by]
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    As you can tell by the traffic.
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    And it is south of Wawa in Ontario, Canada.
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    [traffic in background]
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    This particular crop has been highly metamorphosed,
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    so these in the Canadian shield.
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    Um, so strongly metamorphosed.
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    And this tillite is uh, weathering very rapidly
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    as a result of the intense metamorphism,
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    which has caused cracks and fractures
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    which increase surface area, of course,
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    and cause weathering to accelerate.
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    [traffic in background]
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    Now realize I'm looking at a shadow here,
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    but hopefully you can see that the clasts are well-rounded.
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    Very poorly sorted, in terms of size distribution.
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    And are not layered. They are unstratified.
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    I just thought you might want to see what's on the other side of the road.
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    That is Lake Superior,
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    about an hour south of Wawa, Ontario.
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    Pretty big lake, eh? Kind of looks like the ocean.
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    You can't see the other side of Lake Superior,
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    even though we're way the heck up on the roadside.
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    There you can see down to the beach.
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    Alright, that's it. Bye for now.
Title:
Glacial Till Features
Description:

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Video Language:
English
Duration:
05:29
odscaptioning edited English subtitles for Glacial Till Features Feb 21, 2025, 6:39 PM
odscaptioning edited English subtitles for Glacial Till Features Feb 21, 2025, 6:18 PM
odscaptioning edited English subtitles for Glacial Till Features Feb 21, 2025, 6:16 PM
odscaptioning edited English subtitles for Glacial Till Features Feb 21, 2025, 4:34 PM

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