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#21
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Spheres coming from bedrock?
i call that the mirror sindrome
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#22
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Spheres coming from bedrock?
the spluerukes you mention come from forces iam still try to figure ou but are
more Powerful then we would to ube iwas veiwing shot i took scared the----out of me cause i think i know were they came look at faces |
#23
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Spheres coming from bedrock?
Joe Knapp wrote:
"Timothy Demko" wrote http://www.jpl.nasa.gov/mer2004/rove...s/image-1.html suggests that even if it is an ash, it's been transported by some sort of traction currents and is not a simple air fall. Cross beds I take it simply means that the layers are not always parallel--they diverge and converge sometimes? If so, how about this photo of the effect of "volcanic bombs": http://www.geo.hunter.cuny.edu/~cwang/impacts.jpg Wouldn't the layers in that photo be a simple air fall? The presence of cross beds means something more than the beds just not being parallel. The beds in the link you provided would be called deformed beds rather than cross beds. Cross beds formed by the migration of bedforms (ripples, dunes, etc.) and are a primary featu they form during, and are linked to, deposition. These bedforms may be subaerial (eolian) or subaqueous. In deformed beds, the deformation event, in your example the impact of a falling volcanic bomb, happens after the deposition of the beds. It's interesting that last week Squyres said there were three main theories for the origin of the spherules: lapilli, solidified volcanic material, or concretions. He said the lapilli idea was "fading fast" on the logic that they look to be of a different material than the matrix. There has not been a word in the press conferences since about any progress along those lines. However, an interview with Ronald Greeley, Ph.D., Regents Prof. of Geology, Arizona State University Dept. of Geological Sciences, and one of the 7 Chairs of the Science Operations Working Group (SOWG) for Spirit and Opportunity, Tempe, Arizona this Wednesday was a bit surprising. When asked about the spherules, Prof. Greeley said: "The general consensus seems to be centering around two possibilities: "First, that they are what are called 'accretionary lapillae' * that is a volcanic feature that forms in certain kinds of eruptions in which material is added to a small nucleus like a little dust grain and these form these spherule masses." "Secondly, they could be some kind of precipitate * perhaps from water. In additional findings, there are some minerals that have been identified in the infrared that would suggest the presence of water since they form in water. In particular, if this is a volcanic terrain that we are looking at, the presence of these minerals might suggest this was a hydrothermal area." What--lapilli are fading back in and the other two theories (magma & concretions) are gone, to be replaced with "some kind of precipitate"? No, I think he is talking about concretions or nodules. The confusion is in that most people are assuming that the precipitation was happening in a water column or on a lake/sea bed. I think what Greeley means here is that he thinks they formed by prepitation from water in the subsurface (pore waters), and he is leaning towards a hydrothermal origin for the water, and maybe mineralization too. snip AND ALL THIS IS ADDING UP TO A QUESTION ABOUT WHETHER THE PLACE WHERE OPPORTUNITY CAME DOWN ORIGINALLY MIGHT HAVE BEEN HOT MAGMA COMING UP TO THE SURFACE IN SOME KIND OF VOLCANIC ACTIVITY? OR AT LEAST HOT SPRINGS? "Yes. The evidence is sort of pointing towards the presence of a hot environment * hot for some reason and that's under debate right now. Volcanic activity, magma close to the surface, is one possibility." ... THE BIGGEST SURPRISE RIGHT NOW HAS BEEN THE HIGH AMOUNT OF SULFUR IN THE BEDROCK? "That was a surprise, yes. The measurements that have been made there suggest there is a very high percentage of sulfur present in the material and that there are these spherules that have been seen and reported earlier, those are still very curious features." "Such a high percentage of sulfur (in the bedrock) is unusual and this is what leads some folks to consider the volcanic origin (at the Martian bedrock), or at least volcanic processes to be involved. There are some minerals that have been identified in the infrared that would suggest the presence of water since they form in water. In particular, if this is a volcanic terrain that we are looking at, the presence of these minerals might suggest this was a hydrothermal area and sulfur is a component of such environments." If you look through the older Mars literature, the origin of soil minerals (including sulfur minerals) seen at the Viking and Pathfinder sites if often related to something called "palagonitization". This a garbage can term for various geochemical processes involved in the weathering and divitrification of basaltic glass (palagonite is an amorphous to poorly crystalline, almost clay-like substance). Palagonitization does involve hydration and it is common in hydrothermal areas where hot thermal waters are circulating through volcanic and volcaniclastic rocks. If we read between lines then, it would seem that the MER project scientists are leaning towards a palagonitized, volcaniclastic (re-sedimented tuff/ash) origin for the bedrock, and a subsequent diagenetic/hydrothermal alteration origin for the sulfur anomaly and hematite-rich spherules. Note that these processes may all have been related to the same event of series of events. Maybe something like: 1) rise of magma through the mantle and crust of Mars; 2) eruption of vents, tuff rings, and maybe maar volcanoes; 3) melting of permafrost due to higher crustal heat flow and creation of standing water surface water (lakes, ponds, streams); 4) deposition of glass-rich, basaltic tuff in lakes and ponds; 5)reworking of tuff by lacustrine shoreline and fluvial processes; 6) hydrothermal alteration (palagonitization) of tuffs; 7) leaching of iron-rich minerals in reworked tuff and re-precipitation as hematite in spherules/concretions/nodules; 8) heat flow subsides, everything dries out, winds return and erode lake bottom, various impacts; 9) Opportunity lands (bunny comes to investigate); 10) speculation ensues. What will be interesting is to see how the spherules are concentrated in the residual soil above the light-colored bedrock. Comparing the density of spherules in the soil to that in the bedrock may give a good indication of how much of the bedrock has been eroded to create the soil. -- Tim Demko http://www.d.umn.edu/~tdemko |
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Spheres coming from bedrock?
"Timothy Demko" wrote Cross beds I take it simply means that the layers are not always parallel--they diverge and converge sometimes? If so, how about this photo of the effect of "volcanic bombs": http://www.geo.hunter.cuny.edu/~cwang/impacts.jpg Wouldn't the layers in that photo be a simple air fall? The presence of cross beds means something more than the beds just not being parallel. The beds in the link you provided would be called deformed beds rather than cross beds. Cross beds formed by the migration of bedforms (ripples, dunes, etc.) and are a primary featu they form during, and are linked to, deposition. These bedforms may be subaerial (eolian) or subaqueous. In deformed beds, the deformation event, in your example the impact of a falling volcanic bomb, happens after the deposition of the beds. Thanks for clarifying that. I managed to find this short USGS video which helped me to visualize it: http://tinyurl.com/ysoda "Secondly, they could be some kind of precipitate * perhaps from water. In additional findings, there are some minerals that have been identified in the infrared that would suggest the presence of water since they form in water. In particular, if this is a volcanic terrain that we are looking at, the presence of these minerals might suggest this was a hydrothermal area." What--lapilli are fading back in and the other two theories (magma & concretions) are gone, to be replaced with "some kind of precipitate"? No, I think he is talking about concretions or nodules. The confusion is in that most people are assuming that the precipitation was happening in a water column or on a lake/sea bed. I think what Greeley means here is that he thinks they formed by prepitation from water in the subsurface (pore waters), and he is leaning towards a hydrothermal origin for the water, and maybe mineralization too. OK, my misunderstanding as a google-ogist rather than a geologist. When I hear precipitate I think of something falling, like through said column of water. snip AND ALL THIS IS ADDING UP TO A QUESTION ABOUT WHETHER THE PLACE WHERE OPPORTUNITY CAME DOWN ORIGINALLY MIGHT HAVE BEEN HOT MAGMA COMING UP TO THE SURFACE IN SOME KIND OF VOLCANIC ACTIVITY? OR AT LEAST HOT SPRINGS? "Yes. The evidence is sort of pointing towards the presence of a hot environment * hot for some reason and that's under debate right now. Volcanic activity, magma close to the surface, is one possibility." ... THE BIGGEST SURPRISE RIGHT NOW HAS BEEN THE HIGH AMOUNT OF SULFUR IN THE BEDROCK? "That was a surprise, yes. The measurements that have been made there suggest there is a very high percentage of sulfur present in the material and that there are these spherules that have been seen and reported earlier, those are still very curious features." "Such a high percentage of sulfur (in the bedrock) is unusual and this is what leads some folks to consider the volcanic origin (at the Martian bedrock), or at least volcanic processes to be involved. There are some minerals that have been identified in the infrared that would suggest the presence of water since they form in water. In particular, if this is a volcanic terrain that we are looking at, the presence of these minerals might suggest this was a hydrothermal area and sulfur is a component of such environments." If you look through the older Mars literature, the origin of soil minerals (including sulfur minerals) seen at the Viking and Pathfinder sites if often related to something called "palagonitization". This a garbage can term for various geochemical processes involved in the weathering and divitrification of basaltic glass (palagonite is an amorphous to poorly crystalline, almost clay-like substance). Palagonitization does involve hydration and it is common in hydrothermal areas where hot thermal waters are circulating through volcanic and volcaniclastic rocks. If we read between lines then, it would seem that the MER project scientists are leaning towards a palagonitized, volcaniclastic (re-sedimented tuff/ash) origin for the bedrock, and a subsequent diagenetic/hydrothermal alteration origin for the sulfur anomaly and hematite-rich spherules. OK, had to look that up: diagenesis: The physical, chemical or biological alteration of sediments into sedimentary rock at relatively low temperatures and pressures that can result in changes to the rock's original mineralogy and texture. After deposition, sediments are compacted as they are buried beneath successive layers of sediment and cemented by minerals that precipitate from solution. Grains of sediment, rock fragments and fossils can be replaced by other minerals during diagenesis. Note that these processes may all have been related to the same event of series of events. Maybe something like: 1) rise of magma through the mantle and crust of Mars; 2) eruption of vents, tuff rings, and maybe maar volcanoes; 3) melting of permafrost due to higher crustal heat flow and creation of standing water surface water (lakes, ponds, streams); 4) deposition of glass-rich, basaltic tuff in lakes and ponds; 5)reworking of tuff by lacustrine shoreline and fluvial processes; 6) hydrothermal alteration (palagonitization) of tuffs; 7) leaching of iron-rich minerals in reworked tuff and re-precipitation as hematite in spherules/concretions/nodules; 8) heat flow subsides, everything dries out, winds return and erode lake bottom, various impacts; 9) Opportunity lands (bunny comes to investigate); 10) speculation ensues. By george, you may have it... Water not persistent in that scenario though, just a flash in the pan. Joe |
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Spheres coming from bedrock?
Timothy Demko wrote: If you look through the older Mars literature, the origin of soil minerals (including sulfur minerals) seen at the Viking and Pathfinder sites if often related to something called "palagonitization". This a garbage can term for various geochemical processes involved in the weathering and divitrification of basaltic glass (palagonite is an amorphous to poorly crystalline, almost clay-like substance). Palagonitization does involve hydration and it is common in hydrothermal areas where hot thermal waters are circulating through volcanic and volcaniclastic rocks. If we read between lines then, it would seem that the MER project scientists are leaning towards a palagonitized, volcaniclastic (re-sedimented tuff/ash) origin for the bedrock, and a subsequent diagenetic/hydrothermal alteration origin for the sulfur anomaly and hematite-rich spherules. Note that these processes may all have been related to the same event of series of events. Maybe something like: 1) rise of magma through the mantle and crust of Mars; 2) eruption of vents, tuff rings, and maybe maar volcanoes; 3) melting of permafrost due to higher crustal heat flow and creation of standing water surface water (lakes, ponds, streams); 4) deposition of glass-rich, basaltic tuff in lakes and ponds; 5)reworking of tuff by lacustrine shoreline and fluvial processes; 6) hydrothermal alteration (palagonitization) of tuffs; 7) leaching of iron-rich minerals in reworked tuff and re-precipitation as hematite in spherules/concretions/nodules; 8) heat flow subsides, everything dries out, winds return and erode lake bottom, various impacts; 9) Opportunity lands (bunny comes to investigate); 10) speculation ensues. -- Tim Demko http://www.d.umn.edu/~tdemko The description above reads like a textbook description of the formation of the St. Francois Mountains-- in the anorogenic rhyolite-granite terrane of the US Midwest. Hence the reason I posted the photos under the "Earth rock Mars rock" geology thread. Include caldera rise and collapse, and by jove, you've got it. Mars would be expected to be slightly different, assuming that it has always had a high CO2 atmosphere, since atmospheric effects on all this would be different. The analogy to Yellowstone some have drawn is incomplete, since much of the rhyolite there is too recent to have been extensively reworked. Jo |
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Spheres coming from bedrock?
Timothy Demko wrote: If you look through the older Mars literature, the origin of soil minerals (including sulfur minerals) seen at the Viking and Pathfinder sites if often related to something called "palagonitization". This a garbage can term for various geochemical processes involved in the weathering and divitrification of basaltic glass (palagonite is an amorphous to poorly crystalline, almost clay-like substance). Palagonitization does involve hydration and it is common in hydrothermal areas where hot thermal waters are circulating through volcanic and volcaniclastic rocks. If we read between lines then, it would seem that the MER project scientists are leaning towards a palagonitized, volcaniclastic (re-sedimented tuff/ash) origin for the bedrock, and a subsequent diagenetic/hydrothermal alteration origin for the sulfur anomaly and hematite-rich spherules. Note that these processes may all have been related to the same event of series of events. Maybe something like: 1) rise of magma through the mantle and crust of Mars; 2) eruption of vents, tuff rings, and maybe maar volcanoes; 3) melting of permafrost due to higher crustal heat flow and creation of standing water surface water (lakes, ponds, streams); 4) deposition of glass-rich, basaltic tuff in lakes and ponds; 5)reworking of tuff by lacustrine shoreline and fluvial processes; 6) hydrothermal alteration (palagonitization) of tuffs; 7) leaching of iron-rich minerals in reworked tuff and re-precipitation as hematite in spherules/concretions/nodules; 8) heat flow subsides, everything dries out, winds return and erode lake bottom, various impacts; 9) Opportunity lands (bunny comes to investigate); 10) speculation ensues. What will be interesting is to see how the spherules are concentrated in the residual soil above the light-colored bedrock. Comparing the density of spherules in the soil to that in the bedrock may give a good indication of how much of the bedrock has been eroded to create the soil. -- Tim Demko http://www.d.umn.edu/~tdemko The description above reads like a textbook description of the formation of the St. Francois Mountains-- in the anorogenic rhyolite-granite terrane of the US Midwest. Hence the reason I posted the photos under the "Earth rock Mars rock" geology thread. Include caldera rise and collapse, and by jove, you've got it. Mars would be expected to be slightly different, assuming that it has always had a high CO2 atmosphere, since atmospheric effects on all this would be different. The analogy to Yellowstone some have drawn is incomplete, since much of the rhyolite there is too recent to have been extensively reworked. Jo |
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Spheres coming from bedrock?
"Greg Crinklaw" wrote Joe Knapp wrote: http://www.earthfiles.com/news/news....tegory=Science Joe I was with you right up to that point. This web site is not a reliable source of information. The reporter in question is a nutter who thinks crop circles are made by visiting aliens. That is an ad hominem fallacy. I was not recommending the web site per se. The interviewed source is on the MER team (Dr. Greeley). It's interesting that MER personnel (Greeley, Grove and others) are talking to and emailing these reporters that you shun. Puritans, a very dogmatic people, couldn't go to sleep at night worrying that somewhere, somebody was having fun. Mars Puritans can't sleep at night thinking that somewhere, someone might be having an idea about Mars outside the envelope of the latest JPL press release. The horror! Better that your nemesis should not be the people with off-beat ideas about space, but the people who don't care one whit about space exploration on way or the other. It seems JPL is giving "earthfiles.com" the time of day at least, and not with supercilious condescension. Without nutty ideas based on almost total speculation, the pages of Mars history would be blank. Or it would be a pamphlet. Joe |
#28
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Spheres coming from bedrock?
"Joe Knapp" wrote in message .com... "Timothy Demko" wrote Cross beds I take it simply means that the layers are not always parallel--they diverge and converge sometimes? If so, how about this photo of the effect of "volcanic bombs": http://www.geo.hunter.cuny.edu/~cwang/impacts.jpg Wouldn't the layers in that photo be a simple air fall? The presence of cross beds means something more than the beds just not being parallel. The beds in the link you provided would be called deformed beds rather than cross beds. Cross beds formed by the migration of bedforms (ripples, dunes, etc.) and are a primary featu they form during, and are linked to, deposition. These bedforms may be subaerial (eolian) or subaqueous. In deformed beds, the deformation event, in your example the impact of a falling volcanic bomb, happens after the deposition of the beds. Thanks for clarifying that. I managed to find this short USGS video which helped me to visualize it: http://tinyurl.com/ysoda "Secondly, they could be some kind of precipitate * perhaps from water. In additional findings, there are some minerals that have been identified in the infrared that would suggest the presence of water since they form in water. In particular, if this is a volcanic terrain that we are looking at, the presence of these minerals might suggest this was a hydrothermal area." What--lapilli are fading back in and the other two theories (magma & concretions) are gone, to be replaced with "some kind of precipitate"? No, I think he is talking about concretions or nodules. The confusion is in that most people are assuming that the precipitation was happening in a water column or on a lake/sea bed. I think what Greeley means here is that he thinks they formed by prepitation from water in the subsurface (pore waters), and he is leaning towards a hydrothermal origin for the water, and maybe mineralization too. OK, my misunderstanding as a google-ogist rather than a geologist. When I hear precipitate I think of something falling, like through said column of water. snip AND ALL THIS IS ADDING UP TO A QUESTION ABOUT WHETHER THE PLACE WHERE OPPORTUNITY CAME DOWN ORIGINALLY MIGHT HAVE BEEN HOT MAGMA COMING UP TO THE SURFACE IN SOME KIND OF VOLCANIC ACTIVITY? OR AT LEAST HOT SPRINGS? "Yes. The evidence is sort of pointing towards the presence of a hot environment * hot for some reason and that's under debate right now. Volcanic activity, magma close to the surface, is one possibility." ... THE BIGGEST SURPRISE RIGHT NOW HAS BEEN THE HIGH AMOUNT OF SULFUR IN THE BEDROCK? "That was a surprise, yes. The measurements that have been made there suggest there is a very high percentage of sulfur present in the material and that there are these spherules that have been seen and reported earlier, those are still very curious features." "Such a high percentage of sulfur (in the bedrock) is unusual and this is what leads some folks to consider the volcanic origin (at the Martian bedrock), or at least volcanic processes to be involved. There are some minerals that have been identified in the infrared that would suggest the presence of water since they form in water. In particular, if this is a volcanic terrain that we are looking at, the presence of these minerals might suggest this was a hydrothermal area and sulfur is a component of such environments." If you look through the older Mars literature, the origin of soil minerals (including sulfur minerals) seen at the Viking and Pathfinder sites if often related to something called "palagonitization". This a garbage can term for various geochemical processes involved in the weathering and divitrification of basaltic glass (palagonite is an amorphous to poorly crystalline, almost clay-like substance). Palagonitization does involve hydration and it is common in hydrothermal areas where hot thermal waters are circulating through volcanic and volcaniclastic rocks. If we read between lines then, it would seem that the MER project scientists are leaning towards a palagonitized, volcaniclastic (re-sedimented tuff/ash) origin for the bedrock, and a subsequent diagenetic/hydrothermal alteration origin for the sulfur anomaly and hematite-rich spherules. OK, had to look that up: diagenesis: The physical, chemical or biological alteration of sediments into sedimentary rock at relatively low temperatures and pressures that can result in changes to the rock's original mineralogy and texture. After deposition, sediments are compacted as they are buried beneath successive layers of sediment and cemented by minerals that precipitate from solution. Grains of sediment, rock fragments and fossils can be replaced by other minerals during diagenesis. Note that these processes may all have been related to the same event of series of events. Maybe something like: 1) rise of magma through the mantle and crust of Mars; 2) eruption of vents, tuff rings, and maybe maar volcanoes; 3) melting of permafrost due to higher crustal heat flow and creation of standing water surface water (lakes, ponds, streams); 4) deposition of glass-rich, basaltic tuff in lakes and ponds; 5)reworking of tuff by lacustrine shoreline and fluvial processes; 6) hydrothermal alteration (palagonitization) of tuffs; 7) leaching of iron-rich minerals in reworked tuff and re-precipitation as hematite in spherules/concretions/nodules; 8) heat flow subsides, everything dries out, winds return and erode lake bottom, various impacts; 9) Opportunity lands (bunny comes to investigate); 10) speculation ensues. By george, you may have it... Water not persistent in that scenario though, just a flash in the pan. Joe One of the problems with this scenario (and it is a good one) is that we have yet to see any clay beds, which you would expect to see in a lacustrine deposit. even if the clay beds had worn away, there should still be clay in the soil. Unfortunately for that scenario, the microscpic images taken so far of the trench at the opportunity site appear to indicate a sandy soil. |
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Spheres coming from bedrock?
"Joe Knapp" wrote in message .com... "Greg Crinklaw" wrote Joe Knapp wrote: http://www.earthfiles.com/news/news....tegory=Science Joe I was with you right up to that point. This web site is not a reliable source of information. The reporter in question is a nutter who thinks crop circles are made by visiting aliens. That is an ad hominem fallacy. I was not recommending the web site per se. The interviewed source is on the MER team (Dr. Greeley). It's interesting that MER personnel (Greeley, Grove and others) are talking to and emailing these reporters that you shun. Puritans, a very dogmatic people, couldn't go to sleep at night worrying that somewhere, somebody was having fun. Mars Puritans can't sleep at night thinking that somewhere, someone might be having an idea about Mars outside the envelope of the latest JPL press release. The horror! Better that your nemesis should not be the people with off-beat ideas about space, but the people who don't care one whit about space exploration on way or the other. It seems JPL is giving "earthfiles.com" the time of day at least, and not with supercilious condescension. Without nutty ideas based on almost total speculation, the pages of Mars history would be blank. Or it would be a pamphlet. Joe I don't know about anyone else, but despite their enthusiasm (and mind you, I see nothing wrong with mixing it up with the ideas), I don't know if people who espouse the wonders of crops circles are necessarily who I want sitting behind me at a Congressional budget meeting when the decision is made on funding for the next space mission. |
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Spheres coming from bedrock?
George wrote:
"Joe Knapp" wrote in message .com... "Timothy Demko" wrote Note that these processes may all have been related to the same event of series of events. Maybe something like: 1) rise of magma through the mantle and crust of Mars; 2) eruption of vents, tuff rings, and maybe maar volcanoes; 3) melting of permafrost due to higher crustal heat flow and creation of standing water surface water (lakes, ponds, streams); 4) deposition of glass-rich, basaltic tuff in lakes and ponds; 5)reworking of tuff by lacustrine shoreline and fluvial processes; 6) hydrothermal alteration (palagonitization) of tuffs; 7) leaching of iron-rich minerals in reworked tuff and re-precipitation as hematite in spherules/concretions/nodules; 8) heat flow subsides, everything dries out, winds return and erode lake bottom, various impacts; 9) Opportunity lands (bunny comes to investigate); 10) speculation ensues. By george, you may have it... Water not persistent in that scenario though, just a flash in the pan. Joe One of the problems with this scenario (and it is a good one) is that we have yet to see any clay beds, which you would expect to see in a lacustrine deposit. even if the clay beds had worn away, there should still be clay in the soil. Unfortunately for that scenario, the microscpic images taken so far of the trench at the opportunity site appear to indicate a sandy soil. Well, a couple of things to keep in mind: 1) The trench was dug in the crater where Opportunity ended up. The impact that created this crater happened at step #8 in my scenario above...after the volcanic and lacustrine/fluvial events. The impact event excavated through the residual soil and spherule-bearing bedrock. I would expect the trench that Opportunity just made within the crater to have been made through materials that have accumulated since the impact (eolian and mass-wasting from the crater rim). 2) Trenches to come, especially outside the inner/lower part of the crater, and completely outside the crater on the plains, may yet encounter clay-sized material. However, my view is that much of this material will be lag from wind-eroded bedrock (spherules etc.) and eolian material from elsewhere. The key boundary will be at the very top of the bedrock, although this, too, may end up being a saprolitic or soil "C" horizon type of boundary. 3) Clay-rich lake deposits need a source of the clay (most of it in terrestrial lakes is detrital and comes in as suspended load material in feeder streams, with a minor, but variable, input from airborne dust). The martian systems may have been much different...less chemical weathering and therefore less detrital clay...more relative input of airborne dust...etc. 4) Finally, the very fine-grained nature of the light-colored bedrock may suggest that at least some of it was originally was clay-sized material. It may have been altered, cemeneted, leached, etc. since its original deposition. However, I do submit that some of it was originally sand-sized material because of the presence of cross beds. It's hard to get clay-sized material to make constructional bedforms because the grains are sticky and don't like to move after they've been deposited. You can get ripple-forms, gutters, and other forms, in clayey materials, but they are due to fluid stressing and deformation rather than transport (you would not produce cross beds). -- Tim Demko http://umn.edu/home/tdemko |
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