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Once upon a time, an underwater landslide (turbidity current) buried this particular patch of sea floor.
The landslide deposits (turbidite) is that tall yellow sandy bit.
The landslide deposits (turbidite) is that tall yellow sandy bit.
Turbidity currents are an interesting style of landslide because they’re density-driven flows: a dense fluid (water & sediment) running out under a less-dense fluid (seawater) across solid ground.
They can be fast or slow.
More: gizmodo.com/when-freshwate…
They can be fast or slow.
More: gizmodo.com/when-freshwate…
Stratigraphy is how geoscientists learn the order of events for a landscape. I always think of it like unravelling a murder mystery where your crime scene is rock.
It only has 6 rules, but you won’t need all of them to read these particular rocks.
It only has 6 rules, but you won’t need all of them to read these particular rocks.
1. Everything starts flat.
The pencil indicates we’re looking straight down at the ground, edge-on to history.
@ZaneJobe’s caption tells us “up” is right.
The pencil indicates we’re looking straight down at the ground, edge-on to history.
@ZaneJobe’s caption tells us “up” is right.
2. Big areas of similar rocks in the same layer are probably related, even if they’re interrupted.
This is a small area (thanks, pencil!) with no interruptions, so we can skip this one.
This is a small area (thanks, pencil!) with no interruptions, so we can skip this one.
3. Old stuff is on bottom, young stuff is on top.
The ground (green line) needs to exist before a landslide can run across it.
The ground (green line) needs to exist before a landslide can run across it.
Don’t need the rest:
4. If something happens to a rock, the rock must’ve existed before it happened. We’re big on establishing rocks can’t time-travel.
5. If a rock has pieces of another rock, the pieces come from an older rock.
6. Found fossils? That’s how old your rock is.
4. If something happens to a rock, the rock must’ve existed before it happened. We’re big on establishing rocks can’t time-travel.
5. If a rock has pieces of another rock, the pieces come from an older rock.
6. Found fossils? That’s how old your rock is.
Now it’s your turn:
Look at how the rock is deformed around the turbidite pinchout (where the landslide ends).
Notice it’s not-flat in different ways on either side.
Use Rules 1 & 3 to explain how you could tell which way us up if we hadn’t told you.
Look at how the rock is deformed around the turbidite pinchout (where the landslide ends).
Notice it’s not-flat in different ways on either side.
Use Rules 1 & 3 to explain how you could tell which way us up if we hadn’t told you.
Hint:
Imagine a sandy beach at low tide, or how a lake bottom feels when you wade out. Is it hard or soft? Does it squish between your feet?
If you sand still in the surf line with wee waves crashing against your shins, does sand move above &/or below your feet? How?
Imagine a sandy beach at low tide, or how a lake bottom feels when you wade out. Is it hard or soft? Does it squish between your feet?
If you sand still in the surf line with wee waves crashing against your shins, does sand move above &/or below your feet? How?
