APOD: Siccar Point on Mars (2022 Aug 31)

[APOD Robot]

Siccar Point on Mars

Explanation: What created this unusual hill on Mars? No one is sure. A good outlook to survey the surrounding area, Siccar Point stands out from its surroundings in Gale Crater. The unusual mound was visited by the robotic Curiosity rover exploring Mars late last year. Siccar Point not only has a distinctive shape, it has dark rocks above lighter rocks. The apparent much younger age of the dark rocks indicates a time-break in the usual geological ordering of rock layers -- by a process yet unknown. The Martian hill is named for Siccar Point on Earth, a place in Scotland itself distinctive as a junction between two different rock layers. Curiosity continues to explore Gale crater on Mars, looking for clues of ancient life. Simultaneously, 2300 kilometers away, its sister rover Perseverance explores Jezero crater, there assisted by the flight-capable scout Ingenuity.

<< Previous APOD

This Day in APOD

Next APOD >>

[FLPhotoCatcher]

Are those dark rocks the few boulders on the very top?

And does anyone know what the darkish dust is composed of, that is seen over most of Mars? It seems to be fine-grained. I propose that it could be made of dead and/or dried microbes. Most likely not, of course.

[Ann]

Are those dark rocks the few boulders on the very top?

And does anyone know what the darkish dust is composed of, that is seen over most of Mars? It seems to be fine-grained. I propose that it could be made of dead and/or dried microbes. Most likely not, of course.

Wikipedia wrote:
Many locations on Mars have sand dunes. (...) Many dunes are black because they are derived from the dark volcanic rock basalt.

Dark dunes (probably basalt) which form a dark spot in Noachis. Picture from Mars Global Surveyor.

---

Perhaps the dark rocks are made of basalt, too?

Ann

[VictorBorun]

I am confused.
(An eroded outcrop at Siccar Point showing sloping red sandstone above vertical greywacke was sketched by Sir James Hall in 1788)

Siccar Point, Scotland was rather about an upper layer upon a different base than about a thin layer of pebbles

[MarkBour]

The caption here indicates a time break. Not a stranger situation, like a time disordering, which would be truly unsettling (bad pun) -- just a time break. I'm no geologist, but this must happen a lot, right? All you need is for something to erode away a structure's top layers, and then much later, when conditions change, the next layers to be deposited on it. And then there would be a time-jump forward, in the geologic strata.

So, perhaps they are not saying that this is really strange, just that they don't know what may have caused the sequence. If I'm guessing correctly, then glaciers would commonly do this on Earth. But on Mars, it sounds like an interesting problem ... maybe an interesting clue.

[Chris Peterson]

The caption here indicates a time break. Not a stranger situation, like a time disordering, which would be truly unsettling (bad pun) -- just a time break. I'm no geologist, but this must happen a lot, right? All you need is for something to erode away a structure's top layers, and then much later, when conditions change, the next layers to be deposited on it. And then there would be a time-jump forward, in the geologic strata.

So, perhaps they are not saying that this is really strange, just that they don't know what may have caused the sequence. If I'm guessing correctly, then glaciers would commonly do this on Earth. But on Mars, it sounds like an interesting problem ... maybe an interesting clue.

In geology, that kind of boundary is called an unconformity, with the missing period called a hiatus. They are most commonly caused by waters retreating, which of course stops the process of sedimentation and allows for erosion, followed by the return of water and renewed sedimentation. But there are other causes, as well.

[orin stepanek]

Interesting; that if you let go with your imagination; it almost looks
like some of the outcrops could be buildings!
https://cdn.britannica.com/40/230840-05 ... g-mutt.jpg
Beautiful dog; I couldn't transfer!

[johnnydeep]

"...it has dark rocks above lighter rocks. The apparent much younger age of the dark rocks indicates a time-break in the usual geological ordering of rock layers"

So what's the problem that is supposedly visible here? Young rocks on top of old rocks would be what's normally expected, no? And if the dark rocks are are indeed younger, then what should be normal. All I see here is a light sprinkling of dark powder and small rocks on top of lighter rocks. What am I missing?

[Chris Peterson]

"...it has dark rocks above lighter rocks. The apparent much younger age of the dark rocks indicates a time-break in the usual geological ordering of rock layers"

So what's the problem that is supposedly visible here? Young rocks on top of old rocks would be what's normally expected, no? And if the dark rocks are are indeed younger, then what should be normal. All I see here is a light sprinkling of dark powder and small rocks on top of lighter rocks. What am I missing?

The point is that there's apparently a discontinuity. A gap between old and new deposition.

[johnnydeep]

"...it has dark rocks above lighter rocks. The apparent much younger age of the dark rocks indicates a time-break in the usual geological ordering of rock layers"

So what's the problem that is supposedly visible here? Young rocks on top of old rocks would be what's normally expected, no? And if the dark rocks are are indeed younger, then what should be normal. All I see here is a light sprinkling of dark powder and small rocks on top of lighter rocks. What am I missing?

The point is that there's apparently a discontinuity. A gap between old and new deposition.

Where's the gap? Between what and what? I'm only seeing a sprinkling of dark debris on top of light debris. Is that in itself the problem?

[JohnD]

"Curiosity continues to explore Gale crater on Mars, looking for clues of ancient life. Simultaneously, 2300 kilometers away, its sister rover Perseverance explores Jezero crater"
Surely "daughter" rover? Perseverance is another generation, even if it has the family look!
John

[Chris Peterson]

"...it has dark rocks above lighter rocks. The apparent much younger age of the dark rocks indicates a time-break in the usual geological ordering of rock layers"

So what's the problem that is supposedly visible here? Young rocks on top of old rocks would be what's normally expected, no? And if the dark rocks are are indeed younger, then what should be normal. All I see here is a light sprinkling of dark powder and small rocks on top of lighter rocks. What am I missing?

The point is that there's apparently a discontinuity. A gap between old and new deposition.

Where's the gap? Between what and what? I'm only seeing a sprinkling of dark debris on top of light debris. Is that in itself the problem?

My guess is that they're talking about that dark capstone-looking zone at the top, but it could be elsewhere and not terribly apparent in this particular image. I wouldn't call this a "problem", though.

[BillBixby]

I feel some of you may have missed the 2:54 minute dialogue animation at the Gale Crater link, https://www.jpl.nasa.gov/videos/a-guide-to-gale-crater. Worth watching as it seems to address some of the issues being discussed.

[johnnydeep]

The point is that there's apparently a discontinuity. A gap between old and new deposition.

Where's the gap? Between what and what? I'm only seeing a sprinkling of dark debris on top of light debris. Is that in itself the problem?

My guess is that they're talking about that dark capstone-looking zone at the top, but it could be elsewhere and not terribly apparent in this particular image. I wouldn't call this a "problem", though.

"Dark capstone zone on top" + "dark rocks younger" still seems like it makes sense to me. Oh well.

[Chris Peterson]

Where's the gap? Between what and what? I'm only seeing a sprinkling of dark debris on top of light debris. Is that in itself the problem?

My guess is that they're talking about that dark capstone-looking zone at the top, but it could be elsewhere and not terribly apparent in this particular image. I wouldn't call this a "problem", though.

"Dark capstone zone on top" + "dark rocks younger" still seems like it makes sense to me. Oh well.

There's no suggestion that the issue is about being younger. It's about a gap between the older and younger. It's about the fact that the dating is not continuous, but is punctuated.

[johnnydeep]

I feel some of you may have missed the 2:54 minute dialogue animation at the Gale Crater link, https://www.jpl.nasa.gov/videos/a-guide-to-gale-crater. Worth watching as it seems to address some of the issues being discussed.

I had watched that video before. Still not helping me understand the descriptions used in this APOD though. I guess I need to go back to Geology School.

[johnnydeep]

My guess is that they're talking about that dark capstone-looking zone at the top, but it could be elsewhere and not terribly apparent in this particular image. I wouldn't call this a "problem", though.

"Dark capstone zone on top" + "dark rocks younger" still seems like it makes sense to me. Oh well.

There's no suggestion that the issue is about being younger. It's about a gap between the older and younger. It's about the fact that the dating is not continuous, but is punctuated.

You said that before, but " The apparent much younger age of the dark rocks indicates a time-break" indicates the "younger" is somehow implying a time-break, which I still don't understand. I see no discontinuities or punctuated features in this image, just some mostly lighter underlying rock layers with some dark debris on top. If the dark stuff is indeed younger, all would appear to be normal. But I think I've beaten this horse to death enough already

[Chris Peterson]

"Dark capstone zone on top" + "dark rocks younger" still seems like it makes sense to me. Oh well.

There's no suggestion that the issue is about being younger. It's about a gap between the older and younger. It's about the fact that the dating is not continuous, but is punctuated.

You said that before, but " The apparent much younger age of the dark rocks indicates a time-break" indicates the "younger" is somehow implying a time-break, which I still don't understand. I see no discontinuities or punctuated features in this image, just some mostly lighter underlying rock layers with some dark debris on top. If the dark stuff is indeed younger, all would appear to be normal. But I think I've beaten this horse to death enough already :-)

I guess I don't see what you're having a problem with here. If that top layer is much younger than the light layer immediately underneath, it represents a geological unconformity, which is always interesting because it marks some kind of past climatic change, as between a wet and dry period. The (possibly capstone) unconformity I'm seeing looks like a lot more than a bit of dark debris, but a zone at least a few meters thick.
_

[johnnydeep]

There's no suggestion that the issue is about being younger. It's about a gap between the older and younger. It's about the fact that the dating is not continuous, but is punctuated.

You said that before, but " The apparent much younger age of the dark rocks indicates a time-break" indicates the "younger" is somehow implying a time-break, which I still don't understand. I see no discontinuities or punctuated features in this image, just some mostly lighter underlying rock layers with some dark debris on top. If the dark stuff is indeed younger, all would appear to be normal. But I think I've beaten this horse to death enough already

I guess I don't see what you're having a problem with here. If that top layer is much younger than the light layer immediately underneath, it represents a geological unconformity, which is always interesting because it marks some kind of past climatic change, as between a wet and dry period. The (possibly capstone) unconformity I'm seeing looks like a lot more than a bit of dark debris, but a zone at least a few meters thick.
_
SiccarPoint_CuriosityGill_1080_unconformity.jpg

Thanks - by Jove I think I've got it! It's not the fact that a younger layer is above an older layer (which is normal), but the seemingly abrupt change from the old to the new layer that is the notable thing. That requires some drastic environmental change, such as a flood, or meteorite impact, or geologic upheaval. (And yes, I suppose the dark rock on top IS more than just some "debris" as I was characterizing it.)

[gvann]

These pictures from Mars are always beautiful. But they should include an indication of their scale. I am trying to figure out how tall this hill is. Is it as tall as a person? Is it just a few inches? or would a person standing on top of it look like a minuscule ant? Without any scale reference, it's difficult to figure out what we are looking at.

[Sa Ji Tario]

It reminds me of San Marino and, as always, the stratified rocks as if they were multiple terrestrial sedimentary layers of the same thickness that occurred at the same geological time but the appearance tells me that they are layers of dust and dry sand compressed by aeons like charcoal briquettes (or medicine pills).
Sunlight comes from the upper right corner from approximately "2:00 p.m."
The situation of the place would be the consequence of multiple regular deposits with some lateral detachment of some slope of different material that settled before the next periodic batch. The whole seems to have the consistency of compressed cocoa.-

[johnnydeep]

These pictures from Mars are always beautiful. But they should include an indication of their scale. I am trying to figure out how tall this hill is. Is it as tall as a person? Is it just a few inches? or would a person standing on top of it look like a minuscule ant? Without any scale reference, it's difficult to figure out what we are looking at.

Point taken. Your post made me look for a reference that indicates the scale, but I have yet to find one! Here's my wild guess:

Blue six foot human standing close to the base of Siccar Point

[Chris Peterson]

These pictures from Mars are always beautiful. But they should include an indication of their scale. I am trying to figure out how tall this hill is. Is it as tall as a person? Is it just a few inches? or would a person standing on top of it look like a minuscule ant? Without any scale reference, it's difficult to figure out what we are looking at.

The dark colored, erosion resistant material at the top forms the Siccar Point group strata, probably consisting of aeolian sandstone (that is, sedimentation produced by wind carried material). It covers around 20 km², but is largely only visible from orbit. Only one tiny bit is visible from the surface, as we see in this APOD image. At this location, the formation varies between 1 and 3 meters thick. That suggests we're looking at approximately 15 meter cliff faces above another 20 or 30 meters of steeply sloped rock.

[bystander]

...
rover Perseverance explores Jezero crater ...

The Geology at Jezero Crater is Even More
Complex Than Scientists Were Expecting
Universe Today | 2022 Aug 31

[jack.priebe@yahoo.com]

At the top of the photo and on the left side of "Siccar Point", where it seems a giant took a big bite out of the rock, If you zoom in on this section there seems to be a floating rock. Floating rock?, UFO? oh wait UAP? Or is this an artifact of the composite picture compilation or...a Martian aircraft!