No, there's a fundamental misconception here.

Rocks on Earth can be several billion years old, but landforms are much more ephemeral. Earth's surface is so dynamic that a specific landscape feature can not last very long. Look at the Appalachian mountains in the US, or the mountains of Scotland or Wales - old rocks, but they are modern landforms, cut by water or ice within the last few million years. Any specific mountain or ridge was carved recently out of older rocks. The Canadian Shield, or any other craton, is made of very old rocks, but the landforms on them are still young.

Mars still has, in places, crater rims and other primary landforms which must be 3.5 billion years old or more. Only at the local scale, with sand dunes, dust drifts, yardangs etc., are we looking at fairly young landforms.

Phil

A really elegant and simple explanation Phil. Another illustrative example would be the Grand Canyon and it's depths which were cut from 5.3-1.2 million years bp, yet the schist that comprises the canyon's lowest levels is about 2 billion years old. (I keep a chunk of it on my desk at work -- makes a great conversation piece)

Damn...I love it. The Uniformitarian versus Catastrophist debate renewed! Although we are straying a bit from the stratigraphy topic, this is probably the place for this discussion. I can agree with all of you in some ways. There are many fundamental processes evident on Mars that are very similar to those which we are very familiar with on Earth, but there are also indications that some unfamiliar processes are also taking place. There are examples of ancient geomorphology that is currently being exhumed on our home planet. I only hope the resumption of new imagery doesn't distract us from this interesting debate.

...Please carry on...

No misconception from my end .

The oldest non exhumed landform I know of is the erosion surface of the Kimberley Pleateau in Western Australia. It, and its drainage, predates the Neoproterozoic glaciation is is at least 750 Ma, and probably older. There are other old landscapes in Australia, the Davenport surface is probably of similar age. There are depositional landscapes that are Neoproterozoic in age, also in WA. Land surfaces that are at least 1.5 Ga appear to be being exhumed from beneath the Gawler Range Volcanics in South Australia.

Even in the regions mentioned, eastern N America and northern Europe, there is evidence of landscapes of considerable antiquity, considerably more than a few million years. They include land surfaces, weathering profiles and drainages that predate the onset of Cainozoic glaciation.

Jon

Sorry, but the Appalachian mountains are not a few million years old. they are more like 1/2 billion years. It is true that they are highly evolved from there original form but ancient none the less.

The rocks of the Appalachians are old, but any individual hill or ridge is a relatively young feature, carved out of the older rock. On a timescale of - let's say - tens of thousands of years, any individual hillside is reshaped by erosion, by gullies, mass wasting, undermining etc. The debris is carried away by rivers, and the cycle continues. So the actual landforms are relatively young, and if you looked at them a million years ago they would look very different.

The same applies to the Australian examples. You may have a regional landscape which in its overall pattern has existed since the Neoproterozoic, but the drainage features are cutting down into it, carrying away debris, reshaping the channels and hillsides etc. The smaller-scale landforms of individual stream banks, hillsides etc. are not Neoproterozoic, only a much larger regional scale landscape can be said to be that.

I think this difference of opinion is really about scale (and/or semantics - what's a landform?). Let me give another planetary example. Look at the lunar maria and highlands at 1 km resolution (earth-based telescopes), and you see heavily cratered landscapes in the highlands and lightly cratered plains - it's obvious the highlands are much older. But now look at the Taurus-Littrow valley with the resolution of Apollo panoramic camera images, about 1 m. The highland massifs look smoother, with fewer craters than the plains. They are older, but less cratered, because at that scale we're seeing mass wasting effects. Craters form on the hillsides but get erased by mass wasting, so the surface actually exposed to view is younger.

Phil

Not strictly true. There are even small-scale landforms that are very old in Western Australia. There are glacial pavements and U-shaped valleys from the Carboniferous/Permian glaciation in Pilbarra. And there are relict river valleys in the southwest from the time before Australia separated from Antarctica (they are truncated at the south coast, their upper courses having been left behind in Antarctica).

Even older landforms can be exposed by denudation. There are ordovician eskers in Sahara and on the Fennoscandian shield where I live there are large areas where late Precambrian landforms ("det subkambriska peneplanet") are being exhumed.

So while it is true that the landforms and surficial deposits here on Earth are usually quite young, particularly in rugged terrain, this is far from always the case, and to determine the age of landforms in a particular area is far from simple.

tty

Phil,

Ok, so individual land forms are relitively young. But the Appalachians are not. And the same can be said for the features on Mars. Victoria crater and the Columbia hills are highly evolved from their original shape. The Appalachians were uplifted about 1/2 billion years ago. And they still persist today in a very significant way. There are no landform on mars that are 10 times older than the Appalachians (Mars is only 4.5Gyrs old). There is a difference in time scale but they are in the same league.

Although the oldest rocks in the Appalachians are as old as 1/2 billion years, the youngest involved in the orogeny are 1/4 billion. And the Appalachians have changed markedly over their history. The original mountain belt stretched from the British Isles through New England to Alabama and curved around through Mississippi and Lousiana ending in Arkansas. At the time of the mountain's formation, Europe and Africa were just off the East Coast. At their tallest, they were higher and more rugged than the Rocky Mountains, at their lowest, they were eroded to a flat plain extending from Pennsylvania to Alabama. Currently the southern portion lies under Cretaceous sediments in the Mississippi Embayment. The current Appalachian landforms are recent in comparision.

--Bill

To merge this original point with the Appalachain discussion, if we were to hypothecize an Earth as dry and devoid of erosional processes as Mars, only the cratons might preserve several-billion year old craters, while the lowlands in the dry Atlantic basin of course would not. So by this reckoning yes, the 1/2 or 1/4 billion year old (and much taller) Appalachains would in fact be relatively young compared to the 3 billion year old craters on the arid Canadian Shield, despite the fact that they're not orders of magnitude different in age.

Scale (or should that be size?) does matter. Which features of the landscape in question is also important. Small scale features are more likely to be young than larger ones. In mesa landscapes the surface defined by mesa tops will be much older elements than the intervening lowlands which in their turn will be older than the mesa sides. Landscapes are also tiered in their structure. In my work we recognise six scales, each separated by a factors of 10-1000 of landscape analysis and mapping.

In the case of the Kimbereley plateau the main drainage pattern is throught to predate the Neoproterozoic glaciation. Obviously small gullies will be much younger. As a later poster as pointed out, in the Australian landscape antiquity is the norm, father than the rule. However ancient (pre Neogene) landscape features are much more common that often realised, as shown by the examples of tty. Cliff Ollier's book "Ancient landscapes" repays study in this regard.

All these comments are as true for martian landscapes as terrestrial ones. The smallest scale landforms (or if you prefer geomorphic elements) are likely to be quite young and even ephemeral. the larger scale features are more likely to be ancient. Take Meridiani Planum, what is the age of that landscape? Is it the age of the sediments, the age since the present surface was exhumed, the age of the dune deposits on the surface? the time since the detailed aeolian fretting on exposed bedrock surfaces formed? each will give you a different (and correct) answer, depends which answer to relevant to the question you are asking and which scale you are asking it.

Jon

Fair enough, folks... though personally I would say an exhumed landform - as a landform, not a geological entity - is only as old as the date it was exhumed. But really, here, we are mostly agreeing apart from some semantic differences and maybe a few exceptions. I wasn't talking about the Appalachian mountain range, I was talking about individual slopes and gullies, the landform at a more human scale rather than a continental scale. My perspective is that of a human observer in the landscape, but watching that landscape evolve over millions of years. Almost everywhere that landscape will have evolved in this way so that its components are ephemeral even if the general form stays the same. (Am I to assume these incredibly ancient rivers have no sediment load? That their valleys haven't changed in hundreds of millions of years? If they have experienced only downcutting, with a similar planform to that they had the Cambrian, they have still cut down, making a new surface.)

Still, in general denudation rates on Mars are much lower than on Earth and extremely old landforms are going to be more common there.

Phil

The Appalachians, while the rocks are much older, are much newer in their current form, rpducts of erosion. Phil is right.

Here are three L257 Pancams of Cape St Mary and the unnamed Bay between C. Verde (A1) and C. St Mary (A2). This is a good view of the rubble pile of the ejecta blanket and the in-place strata underlying the ejecta. There are a number of boulders visible on the ejecta plain and I don't see any indication of them on the MRO imagery.

My initial thoughts on C. St Mary, aka The Beacon, is that it is a local thickening of the ejecta so it stands a few meters higher above the plain and the Beacon itself is an accumulation of light-toned dust that has collected behind the wind shadow of the peak of the rubble pile.

--Bill

Hmmm, how big would that rock in the background of the left image be? The rock near the top left.
Image from above post

A lot smaller than it looks! AlgorimancerPG gives around 30-32 metres distance to that rock, which means it's only around 12 or 15 cm wide! That explains why we can't see it on the MRO image.

Basically in this direction the apparent horizon is very close due to curvature of the ground outside of the beacon, which means things are much closer than they may appear.

Doesn't this image of Red Cliffs at North Cape of Prince Edward Island in Canada ring a bell? Another exhumed crater? Even the "beacon" is there
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It depends at what scale of landscape element you are looking at.

The rocks of the Appalacians are for the most part (ignoring some crystalline basment blocks) Palaeozoic, deformed in the Devonian with the closure of the Iapetus ocean. The Appalachians themselves were uplifted progressively from the Jurassic through to the Paleogene with deposition along the margins. Regional dip decreases with time.

The uplifted surface was essentially a plain, on its margins it is buried by the Jurassic sediments and across the Appalachians it is defined by concordant ridge tops. This surface is thus Jurassic or older. The uplift is traversed and dissected by antecedent drainage, which thus is also Jurassic or older. Some workers have suggested as old as Permian. Mondern valley floors contain Latest Cretaceous to paleocene sediments, indicating that much of the relief was developed by this time.

So while individual small scale features such as gullies, surfical deposits and soils may well be geologically young, the broad scale landscape elements - antecedent drainage, the upwarp, regional surfaces, large scale relief features, and valley floor sedimentsare Palaeogene and Mesozoic, or perhaps even older in some cases.

Jon

Pavel: Yes, it does. Although not a crater, it is a nice, earthly example of the regularly-spaced erosion we observe on Earth and Mars. The regular spacing of Victoria's capes and bays has been discussed here previously. While there seem to be some simple explanations for such features when they are structurally controlled, they are not always so simply explained in homogenous material. I am not suggesting that this article about beaches is an explanation of the capes and bays of Victoria, but only that some of the dynamic processes may be relevant. I actually prefer a fracture (structural) related origin for the capes and bays at this point, but it would be so much easier to interpret if we could send one of us to Mars.

12-15cm!! That's tiny compared to what I was imagining.
A valuable lesson in not always believing what you see. Cheers for the info

Images from today's Exploratorium but look old to me... never mind, some lovely detail on the cliffside...

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Thanks for working out the heights etc guys, very very useful.

Here are a few more stratigraphic L257 Pancam images of Cape St.Mary assembled from data dribbling through the pipeline. A few dozen more of these and we'll be able to start understanding what is/has happening/happened here.

--Bill

And a few "close-in" Pancams of the surface of Cape Verde:

--Bill

And L257's of Duck Bay:

--Bill

I wanted to save this thread from falling off onto the second page. For a while now we have had views of Cape Verde from both sides. I was kind of hoping that seeing a promontory from both sides would give us that eureka moment, where we could nicely visualize the internal geometry of the thing. I'm still not seeing it.
Click to view attachment

It would be interesting to identify in the MRO image of Cape Verde how far around the cape Opportunity was able to see from each side. Do the images meet?

No. For that to be the case we would have to be seeing the St. Mary vantage point to the right of the end of Cape Verde in the first image.

The weathering is drastically different on the windward (east) side which makes the comparison difficult.

Looks like two different promontories, doesn't it?

Interesting how the part that juts out the most, perhaps the MOST exposed to any weathering elements is a bit blocky, and yet just a short distance away what looks to be the same rock type is worn completely smooth? While there's probably a zone between the smooth and not smooth that one might label "transitional", this certainly provides evidence that the the bulk of the erosional smoothing may not be from wind action.

Just eyeballing the two rover panoramas, I concluded that the two lines of sight almost intersected at the same tip of the cape, but slightly fell short. That was a good suggestion regarding looking at it from the HiRise perspective. We have two route maps from Phil and James that show essentially the same positions for the rover when the images were captured. From the orbiter images it you can see that the lines of sight pretty much intersect very close to the tip of the cape on both maps. Any differences are mostly due to my errors drawing the lines. At the distances involved here, the visual resolution of the rovers is better than HiRise. You would have to guess that those positions were intentionally chosen.

MarkL: It sure does look like there is a different style of weathering/erosion on the opposing sides. Other effects, like solar illumination may also be at play. We have some pancams coming down that will give us a better view. As more of this crater's rim is imaged in detail, we will have more observations to play with. Who would ever have guessed, early in these missions, how wildly successful these engineering masterpieces would become.
Click to view attachment

But as viewed from the Duck Bay position, there is a 10 to 20 meter section near the tip of the outcrop that lies parallel to the line of sight, and thus is practically unseen.

True enough, but it was the profiles of the silhouettes that I was trying to match. The silhouettes don't quite match. Of course, it is obvious from the Duck Bay view that even from the very tip of CSM, the Duck Bay line of sight will be beyond the reach of Opportunity from CSM. We are forced to extrapolate, and that is where some fun starts...

There's a fascinating new HiRISE image entitled "Victoria Crater Warm-up Image" just released, showing low-angle illumination crater rim and floor, but not immediately recognisable as "our" Victoria

http://hiroc.lpl.arizona.edu/images/TRA/TRA_000873_1415/

I just noticed some discussion if it here in the MRO 2005 area...

http://www.unmannedspaceflight.com/index.p...=3502&st=15

Perhaps it is a misleading title meaning it was taken somewhere else, as a test prior to the Victoria colour shots we saw?

The title makes sense - it was used to warm up the instrument before the critical Victoria observation.

Doug

If you play with the contrast there's a lot of fine detail in the 'warm-up' image's dark shadow area.

Phil

The image is near 38 degrees south latitude, so definitely nowhere near Meridiani.

Given that MRO moves south-to-north on the lit side of the planet, and that 38 degrees would something like 15 minutes, it makes a lot of sense.

Doug

Moved posts about the strange feature to a new thread - Not really about Victoria's Stratigraphy is it.

James: I disagree with your comment that the discussion was "not really about Victoria's stratigraphy." In it's broad definition stratigraphy is the study of layers sequentially deposited over time. As small as this feature is, it sure does look like a layer that contains clues to the sequence of events that took place here. Before you accuse me of splitting hairs, I'd go on to say that we don't yet know whether it is a very recent layer deposited by the rover, or a record of a previous event.

Going beyond the strict definition of the topic, this thread has sort of become one place where those interested in detailed geology could discuss geology at length with less concern about boring people and interfering with the more popular discussions without creating a lot of short-lived topics. That said, you are the moderator, and I don't really have a problem discussing this in another topic.

define:stratigraphy

Hehe, I tried to choose the most generic one of the bunch.

Where have you been lately? I thought we'd see more of you after you retired. Please don't tell me it is not all it is cracked up to be.

Oh, Lawdy me, what has we got here? 2007Pan0001
2007MI0002
It's float not stratum, but I insist on a full RAT/IDD. This is not your father's Mars rock!
I'm sorely tempted to use the S-word, but I won't until we've had a deeper look.
2007 is getting off to an interesting start!

... and the "s-word" would be...? Something exciting and geological? An expletive?

It certainly looks interesting and crystaline but that could be the light. As for the S word I,m stumped, sexy sulphate salt?
Roy F

The rock in color (brightness exagerated to see it completely)
Click to view attachment

You just beat me to it Ant...!

Click to view attachment

Oh lordy, a green-tinted rock on Mars... I bet Hoagland's Googling different obscure types and names of lichen right now...

Actually, if you look in the sunlit bit it's more bluish... metallic-looking... thinking this is maybe a heavily-weathered iron meteorite...

... and a red NASA-logo!

Ah yes... that's not quite right... I'll have to re-balance ... that's what you get for rushing!

Such is the joy of L257

Doug

Yes "The joy of L257... "