Maars on Mars?

"Pedro Rosa" skrev i en meddelelse
om...

Well it seems that people are making a little confusion. The original
poster talked about Bonneville in Gusev. Not the Meridiani, which is
right on the other side of the planet. Besides some seem to have
caught the wave and start searching Maars everywhere. And people say
we, the pro-biologists, are fanatic...

I'm mixing things up, sorry.

Carsten

In article ,
says...
Hi Doug

The possible low relief of the maar volcanoes may make them less
distinct in
the Mars landscape - and perhaps more vulnerable to erosion as they do
not
consist of the same rough debris as the meteoritic craters.

Yep -- even the "hollows" at Gusev have noticeable sets of blocks around
their perimeters, making it fairly obvious that they started life as
small meteoric craters that have since become infilled by sediments.

Now, whether the sediments are aeolian or aquatic in nature is another
matter -- but I'd lay better odds on aeolian than aquatic.

Why? Because of the appearance of the rock or the lack of other 'normal'
traces of water, or?

Mostly, I tend towards believing the aeolian theory because this looks
like a landscape that hasn't had anything acting on it except wind for a
LONG time. And because we haven't seen anything except basalts and
other likely magma-generated rocks in the area. If there was a lake in
Gusev, it looks rather like basaltic lava flows came afterward.

At any rate, while there might have been water at some point on top of
the rocks littering the floor of Gusev, there doesn't seem to be a lot
of evidence for that in what we've been able to see thus far...

Doug

"Doug..." skrev i en meddelelse
...

snip

Why? Because of the appearance of the rock or the lack of other 'normal'
traces of water, or?

Mostly, I tend towards believing the aeolian theory because this looks
like a landscape that hasn't had anything acting on it except wind for a
LONG time.

Right, but this applies to the present surface, not nessecarily to the
structure in the outcrop.

And because we haven't seen anything except basalts and
other likely magma-generated rocks in the area. If there was a lake in
Gusev, it looks rather like basaltic lava flows came afterward.

Whatever below: the rock on top is ejecta and has come later.
But basically, you look at the surroundings and not at the rock.

Carsten

In article ,
says...

"Doug..." skrev i en meddelelse
...

snip

Why? Because of the appearance of the rock or the lack of other 'normal'
traces of water, or?

Mostly, I tend towards believing the aeolian theory because this looks
like a landscape that hasn't had anything acting on it except wind for a
LONG time.

Right, but this applies to the present surface, not nessecarily to the
structure in the outcrop.

True -- but I thought we were talking about Gusev. That's what I was
talking about when I mentioned the "hollows" and said that I thought
they were small impact craters that had been filled in over the aeons,
either by water-laden or aeolian sedimentation, leaning towards aeolian.

I don't have much in the way of solid theory (or even flimsy theory) in
terms of the Meridiani plains -- how they were laid down, and how they
got so flat... because we've only seen them from a distance, we haven't
gotten out ONTO them yet. But we haven't seen anything at Meridiani
like the "hollows" that we see at Gusev, at least nothing that looks
like them from Opportunity's vantage point in its crater.

And because we haven't seen anything except basalts and
other likely magma-generated rocks in the area. If there was a lake in
Gusev, it looks rather like basaltic lava flows came afterward.

Whatever below: the rock on top is ejecta and has come later.
But basically, you look at the surroundings and not at the rock.

The rock on top at Gusev *near Bonneville* is certainly ejecta, but the
rocks that litter the ground farther away from the crater may *not* be
ejecta. It may well have gotten there via an entirely different
transport mechanism. We really don't know. We have to cover more
ground, farther away from small craters, to get a clue as to the
transport mechanism for the rocks on the ground at Gusev. And I remind
you, the Spirit science team said early on that "the surroundings" argue
against the current surface having ever been a lake bottom, as it's too
irregular, not flat enough. Meridiani looks more like a lake or sea
floor than Gusev does. And Meridiani's rocks tell that story far more
convincingly than Gusev's do.

So, as of now, it's Meridiani that looks more like it used to be a lake
bottom or sea floor, while Gusev looks nothing like what we'd expect a
lake bottom to look like... which is why I'm more leaning toward aeolian
processes as explanations for what we see at Gusev. At Meridiani, I'd
give aquatic processes better odds. But it's probably too early to tell
either way. Let's wait for more data before we dig ourselves into holes
that will be hard to climb out of later, shall we?

Doug

"Pedro Rosa" wrote in message
om...
Well it seems that people are making a little confusion. The original
poster talked about Bonneville in Gusev. Not the Meridiani, which is
right on the other side of the planet. Besides some seem to have
caught the wave and start searching Maars everywhere. And people say
we, the pro-biologists, are fanatic...

Bonnevile is the most typical of a typical impact crater. Remains of
the rims can still be seen. There is a lot of ejecta debris srrounding
the place. However this is still not a point to distinguish an impact
crater from a Maar. The most important is the morphology of the
debris. They present signs of shock metamorphism. The surfaces are
glassy, there are clear stripes or traces of stripes in them. Some
show brittleness. Besides, some rocks have a cone shaped figure. Over
the rocks, on some places, one can see holes, incrustations and
features with a very specifical morphology of a directed mechanical
deformation (is it quartz?). These are the typical signals of shock
metamorphism. Now shock metamorphism is something non-existent on
Maars. Shock metamorphism is a pre-ejection phase caused by the shock
waves of the bolid entering in hypervelocity into the ground. The
ejecta usually shows minimal traces of it, the most clear ones can be
found underground. On the surface, under erosion, these traces usually
wipe out, so it is usual to see people confunding Maars and impact
craters. However, in Bonneville, they are still there, probably due to
a less aggressive atmosphere.

Anyway it seems that Bonneville appeared after the water went out of
Gusev. Water is too attained to attack surfaces that resulted from
shock metamorphism, as they present a very reactive structure.

I'll ask pitty for some messing I may have made here, but I studied
craters in Russian. Besides it has been years since I read them.

Would fossils survive the "Shock Metamorphism" process?
Ralph Nesbitt

Doug... wrote in message ...
In article ,
says...

"Doug..." skrev i en meddelelse
...

snip

Why? Because of the appearance of the rock or the lack of other 'normal'
traces of water, or?

Mostly, I tend towards believing the aeolian theory because this looks
like a landscape that hasn't had anything acting on it except wind for a
LONG time.

Right, but this applies to the present surface, not nessecarily to the
structure in the outcrop.

True -- but I thought we were talking about Gusev. That's what I was
talking about when I mentioned the "hollows" and said that I thought
they were small impact craters that had been filled in over the aeons,
either by water-laden or aeolian sedimentation, leaning towards aeolian.

I don't have much in the way of solid theory (or even flimsy theory) in
terms of the Meridiani plains -- how they were laid down, and how they
got so flat... because we've only seen them from a distance, we haven't
gotten out ONTO them yet. But we haven't seen anything at Meridiani
like the "hollows" that we see at Gusev, at least nothing that looks
like them from Opportunity's vantage point in its crater.

And because we haven't seen anything except basalts and
other likely magma-generated rocks in the area. If there was a lake in
Gusev, it looks rather like basaltic lava flows came afterward.

Whatever below: the rock on top is ejecta and has come later.
But basically, you look at the surroundings and not at the rock.

The rock on top at Gusev *near Bonneville* is certainly ejecta, but the
rocks that litter the ground farther away from the crater may *not* be
ejecta. It may well have gotten there via an entirely different
transport mechanism. We really don't know. We have to cover more
ground, farther away from small craters, to get a clue as to the
transport mechanism for the rocks on the ground at Gusev. And I remind
you, the Spirit science team said early on that "the surroundings" argue
against the current surface having ever been a lake bottom, as it's too
irregular, not flat enough. Meridiani looks more like a lake or sea
floor than Gusev does. And Meridiani's rocks tell that story far more
convincingly than Gusev's do.

So, as of now, it's Meridiani that looks more like it used to be a lake
bottom or sea floor, while Gusev looks nothing like what we'd expect a
lake bottom to look like... which is why I'm more leaning toward aeolian
processes as explanations for what we see at Gusev. At Meridiani, I'd
give aquatic processes better odds. But it's probably too early to tell
either way. Let's wait for more data before we dig ourselves into holes
that will be hard to climb out of later, shall we?

Doug


It's the Martian coverup you know? They changed places. They picked up
Meridiani and changed it to Gusev and vice-versa... So Gusev is
Meridiani and Meridiani is Gusev... So Spirit is Opportunity and
Opportunity is Spirit but NASA does not have a hint about it, so
Opportunity is Spirit and Spirit is Opportunity... A cause of the the
effects of the Black Hollow generated from the dark inners of the
Fussy Face... And a pretty good joke to our tendency to draw theories
300 kilometers from above...

Now seriously. Frankly, this is really a side effect of we people
trying to pop-up theories based on a 0.0001% knowledge of Mars. As I
told before, Bonneville rocks present some good signs of shock
metamorphism. But also such features have a tendency to disappear ASAP
in chemically active environments. So, either Bonneville was made a
lot later or we are not getting with the real nature of Gusev. But
Gusev, from above, presents a clear sign of sedimentation processes
and water flow! How can you fit both things? Simply. It is too early
to make fast conclusions and draw theories with the nose well above
your head. Mars is a question mark. A big question mark that has
been bothering us since early times. It is a excellent testbed for
many of our hypotesis and theories. But it is always a place that
reminds - don't believe in anything for sure, as on the next corner
there's an Easter Bunny with lots of easter eggs popping around... And
you can't guess what surprise will come on the next egg.

"Ralph Nesbitt" wrote in message m...

Would fossils survive the "Shock Metamorphism" process?
Ralph Nesbitt

On sedimentary rocks, probably. In more preserved rocks, metamorphism
would concentrate only on the border of the rock, particularly on
those belonging to the ejecta blanket. Underground, metamorphism would
possess a wider effect and a longer process of stabilization. However,
we know that metamorphic rocks may preserve minimal traces of fossils.
But shock metamorphism could make a mess of all that.

But what we have there are basalts.. That thing over there looks
everything as a typical 100% rock solid basalt bed with minimal traces
on the presence of water. The unique event I ever saw of a fossil on
basalt was in my childhood. Well, I am seeing already a few geologists
rising their eyeborws on this. Yes, I saw a fossil on basalt. A unique
amphibeous from Devonian right over a 100% basalt rock. How could be
that? That's where the trick was, and the disappointement also. The
damn thing seems to have glued to the rock under a layer of sediment
over-saturated with iron. The sediment was nearly 1cm thick and the
thing looked more as a piece of rust rather than a fossil. A little
later, knowing a little bit more of paleontology, I noted that the
thing was in fact a real 100% fossil. I studied it and again forgot
about it. Then I came into a book where this #$@$@ amphibeous thing
was considered an ancestor of reptiles, rarely found as a fossil.
Really I tried to take it outta there, but the rusty sediment and that
piece of volcanic trash were a problem with two ends, either the
fossil turned to rust or I risk breaking my hammer on the basalt. A
little bit later the place was wiped out for one more of our
ultra-modern urbanizations called "concrete-jungles". Pitty...

In article ,
says...

snip

Now seriously. Frankly, this is really a side effect of we people
trying to pop-up theories based on a 0.0001% knowledge of Mars. As I
told before, Bonneville rocks present some good signs of shock
metamorphism. But also such features have a tendency to disappear ASAP
in chemically active environments. So, either Bonneville was made a
lot later or we are not getting with the real nature of Gusev. But
Gusev, from above, presents a clear sign of sedimentation processes
and water flow! How can you fit both things? Simply. It is too early
to make fast conclusions and draw theories with the nose well above
your head. Mars is a question mark. A big question mark that has
been bothering us since early times. It is a excellent testbed for
many of our hypotesis and theories. But it is always a place that
reminds - don't believe in anything for sure, as on the next corner
there's an Easter Bunny with lots of easter eggs popping around... And
you can't guess what surprise will come on the next egg.

I totally agree. Of course, this is the place to pull out one's crazy
theories and flap them about a bit... but it's also the place to walk
away from one's crazy theories when they're pretty well chopped to bits
by people who are a little more well-informed. (As I've done on many,
many occasions.)

All in all, I just think it's a marvelous adventure.

Doug

"Doug..." skrev i en meddelelse
...

snip

At Meridiani, I'd
give aquatic processes better odds. But it's probably too early to tell
either way.

I may have mixed observations. Aquatic processes should be at Meridiani
Planum.
... Since a new dynamic sedimentation process has become a reality (to me
atleast, Type II dark streaks), I find good reason to put aside any aquatic
consideration until the structural consequences for this type of
sedimentation has been elaborated on. It seems an obvious candidate
mechanism behind the solid outcrop.

Carsten

"Carsten Troelsgaard" wrote in message ...
"Doug..." skrev i en meddelelse
...

snip

At Meridiani, I'd
give aquatic processes better odds. But it's probably too early to tell
either way.

I may have mixed observations. Aquatic processes should be at Meridiani
Planum.
... Since a new dynamic sedimentation process has become a reality (to me
atleast, Type II dark streaks), I find good reason to put aside any aquatic
consideration until the structural consequences for this type of
sedimentation has been elaborated on. It seems an obvious candidate
mechanism behind the solid outcrop.

Carsten

Maybe...
Try to find data on petrified dunes with signs of subsequent
erosion... I have no time to search now but I think I have seen things
similar to a piece of that outcrop over there...