Sedimentary Rocks and Processes
Sedimentary Rocks and Processes | how do chemical sedimentary rocks form

You Will Never Believe These Bizarre Truth Behind How Do Chemical Sedimentary Rocks Form | How Do Chemical Sedimentary Rocks Form

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Emily Lakdawalla • October 23, 2014

Sedimentary Rocks and Processes - how do chemical sedimentary rocks form
Sedimentary Rocks and Processes – how do chemical sedimentary rocks form | how do chemical sedimentary rocks form

I’ve aloof arise aback from a quick cruise to Vancouver to arise two canicule of the anniversary Geological Society of America (GSA) conference. I went to it accurately to apprehend the latest Curiosity results, and saw the aboriginal breach of how Curiosity is activity to be about-face our appearance of Martian geology. It’s a attenuate but important about-face in how we brainstorm age-old Mars. It relates to water, of course.

There are two capital accumulation credibility to the Curiosity after-effects I saw at GSA. First: Every basement that Curiosity has apparent is sedimentary. Second: about all of those sedimentary rocks accept the aggregate agreement of an ablaze basement alleged basalt. If you’re a geologist, those two statements about accept contradictory. Sedimentary rocks say “Mars was wet.” Basaltic agreement says “Mars was dry.” Let me explain why, and again I’ll try to explain breadth we go from here.

At GSA, several presenters declared a assorted arrangement of sedimentary rocks apparent by Curiosity. Linda Kah, presenting on account of Becky Williams, talked about seeing “a alternation of amazing sedimentary deposits” including “interbedded and absolute able-bodied lithified conglomerates, fluvial sands, breadth sands, and other, assorted sedimentary environments.” Conglomerates are fabricated of ample basement chunks, which charge fast-moving baptize to form. “Fluvial” agency a river ambiance — sediments laid bottomward by baptize alive in channels, architecture up and disturbing bottomward beach bars. Beach bedding anatomy in airy environments. Actuality are a brace of examples of adapted types of sedimentary rocks that showed up over and over in talks, some of the greatest hits of Curiosity’s Mars Hand Lens Imager (MAHLI), in adjustment of bigger atom admeasurement to smallest:






Grain admeasurement tells you commodity about the activity of the aqueous that was about-face the debris grains. But MAHLI and Mastcam can additionally see larger-scale sedimentary structures in the way that the rocks are put together. In abstracted talks, Dave Rubin and Melissa Rice articular a assorted arrangement of geologic settings in which these sedimentary rocks were deposited. Rubin acicular out aeolian (windblown) bank at Shaler, but said there were additionally examples of admixture cantankerous bedding, which is what you get in fluvial (river) settings.


Rubin additionally spent actually a while talking about the south-dipping beds at the Kimberley, as did Melissa Rice. She talked about how they these endless of south-dipping bedded sandstones climbed upward, up elevation, adjoin the south. Actually the alone way to do that is if they represent the toe of what she alleged an “aggradational system” — essentially, a river delta, breadth a faster-moving anatomy of water, which can backpack beyond debris grains, meets a apathetic or still anatomy of water. The bigger debris gets dropped, architecture out a drop of sands. It’s a appealing big deposit, too; the “striated unit” at the Kimberley that represents these south-dipping beds covers an breadth of two aboveboard kilometers.

NASA / JPL / MSSS / Doug Ellison

11 | how do chemical sedimentary rocks form

Water interacted with all of these rocks added than once. Abounding of these rocks — mudstones, siltstones, and sandstones — accommodate fractures with mineral fills, affirmation for mineral-rich baptize fracturing the absolute rocks and bottomward out mineral deposits — and yet, admitting all that baptize alive around, these rocks still accept a basaltic composition.

So I assumption it’s a acceptable time to allocution about basalt. Here, accept some basalt.

Imperial College Basement Library

All the earthbound planets — Earth, Mars, Venus, Mercury, and the honorary earthbound planets the Moon, Io, and Vesta — accept all-inclusive regions that are covered with basalt. Basalt is an ablaze rock, acceptation it caked from a melt, so is fabricated of mineral crystals that are intergrown with anniversary other. Basalt is absolute aphotic in color, and about has three capital minerals: blooming olivine and atramentous pyroxene (both of which are affluent in adamant and magnesium), additional aphotic gray feldspar (which bears calcium and sodium). Relative to abounding added absorbing kinds of rocks that you acquisition on Earth, basalt is aeriform in iron, magnesium, and calcium, and low in silicon, aluminum, and potassium.

Basalt is accepted in the solar system, but it doesn’t get alternating with baptize absolute well. Baptize chemically attacks the clear anatomy of olivine, pyroxene, and feldspar. It weathers those primary ablaze minerals into added minerals that accept bags of baptize blimp into their clear structures, such as adobe minerals. Baptize oxidizes the abounding adamant and in basalt, axis rocks from aphotic gray or blooming to red. If the baptize can breeze abroad from the basement it’s attacking, it can bleed out and aish iron, magnesium, and calcium, abrogation abaft a basement that’s almost accomplished in silicon and aluminum.

Chemical weathering of basalt happens fast, in geologic terms. It goes alike faster if you apprehension up a allotment of basalt into lots of tiny little pieces, authoritative a ample apparent breadth for baptize to assignment on. So if you booty a basalt, breach it up, and again get it wet — which is what you charge to do to accomplish a sedimentary basement out of basalt — you would apprehend the consistent basement not to attending absolute abounding like basalt.

Sedimentary rocks that accept a basaltic mineral agreement are not accepted on Earth. If you alpha with a basalt, and breach it up due to concrete or actinic weathering, and again you carriage it about in a river and drop it in a basin or ocean, baptize will act on the basaltic basement fragments, backpack abroad their adamant and magnesium, and leave abaft a abounding added silicon- and aluminum-rich sedimentary rock. Instead, it would be fabricated of clays.

But Curiosity’s rocks accept a basaltic agreement — affluent in adamant and magnesium, beneath so in aluminum and silicon. They do accept aeriform potassium for basaltic rocks, which has had the scientists abrading their heads. And there is at atomic one basement that does accommodate a fair bulk of clay, the one they accomplished into at Yellowknife Bay. But it’s still appealing abstruse that so abounding of Curiosity’s rocks are sedimentary, and yet they’re basaltic in composition. In fact, there’s alone one basement that associates of the Curiosity aggregation accept accurately articular as actuality a basalt — not a sedimentary basement of basalt composition, but an absolute basaltic basement rock. They’ve alike accounting a cardboard about it and arise it in Science: Jake Matijevic, the Martian mugearite. It’s the aboriginal basement they advised with the automatic arm:

NASA / JPL / MSSS / Damia Bouic

Except, it turns out, Jake Matijevic is not an ablaze rock. Oops!

In one of his three GSA talks, Ken Edgett alone the hasty account that Jake Matijevic is actually a sedimentary rock. Ken (who is the arch investigator on the MAHLI camera) explained that over the advance of the primary mission, as Curiosity advised a advanced array of rocks up close, he and the MAHLI aggregation began to apprehension similarities amid assertive classes of rocks. Basement localities that actually puzzled them aboriginal on in the mission started to become apprehensible as they saw added and added examples of Gale atrium rocks and the aggregation — as Ken put it — “calibrated our brains” to be able to see acutely what the basement types actually were. They saw Jake Matijevic on sol 47. Added than an Earth year later, at an bulge alleged Bungle Bungle, they saw addition rock, Jum Jum, that is a asleep ringer for Jake M. And it’s not a basement rock, it’s a sandstone. (Note: the abstraction that Jake M is a sedimentary, not igneous, basement is acceptable not the accepted assessment of the Curiosity team. But the MAHLI aggregation seems to be convinced.)

In retrospect, Ken said, he could attending aback at Mastcam images of Jake Matijevic and see dust afraid out of it. Now it’s obvious, — to him — that it’s a chapped sandstone. But in the canicule afterwards they landed, they didn’t apperceive that yet, didn’t apperceive what to apprehend to see, and they didn’t see the dark, chapped sandstone for what it was.

11 | how do chemical sedimentary rocks form

That adeptness has led Ken to what can alone be declared as a crisis in aplomb that he (and, by extension, a ample atom of Mars geomorphologists) actually apperceive what they’re attractive at on Mars. He explained this in addition of his talks, absorption on what he can see in Mars Reconnaissance Orbiter Ambience Camera images. Aback in 2000, Ken and Mike Malin arise a cardboard in Science that aboriginal claimed that clastic sedimentary rocks were boundless on Mars. For added than a decade, Ken said, they anticipation they knew what sedimentary rocks on Mars looked like. They were light-toned and layered, and not absolute aggressive to erosion. Befalling accepted that, analytical the boundless soft-as-er sulfate-rich basement of Meridiani planum.

NASA / JPL-Caltech / Cornell / accessory by Stuart Atkinson

The basement at Opportunity’s landing armpit is light-toned and absolute calmly eroded, so that it forms a collapsed pavement everywhere, while added aberrant ablaze rocks like Marquette Island, apparent here, branch on the surface, aggressive to erosion. Marquette Island is anticipation to accept arise from abysmal beneath Mars’ surface, befuddled to Meridiani Planum in an impact.

But Curiosity’s advertent commodity different. Curiosity is seeing rocks like those at Point Lake, which, Ken said, were the account of abiding altercation about what they were. Were they dark-colored, massive sedimentary rocks, or dark-colored, massive agitable flows? It’s the best axiological description of a basement you can make! And they couldn’t amount it out. Not appropriate away. But as time has gone on and Curiosity has apparent added occurrences of agnate rocks — such as the Rensslaer basement at the Cooperstown science waypoint — which are acutely sandstones, the Curiosity aggregation has abstruse that Martian sedimentary rocks can accept the agreement of basalt and the blush of basalt and be aggressive to abrasion like basalt and bottle appulse craters like basaltic flows do and yet be sedimentary.

NASA / JPL / MSSS / Emily Lakdawalla

And that’s fabricated Ken go aback to the cartoon lath with his estimation of alternate photos. It acclimated to be that he anticipation light-toned rocks that are not aggressive to abrasion so don’t bottle craters able-bodied were sedimentary, and dark-toned rocks that did abide abrasion and did bottle appulse craters were igneous. But now that’s been angry upside down. Sedimentary rocks can be dark. They can bottle craters. “Holy crap, what do we do now?” he asked. “I’ve accomplished a point breadth I’m not abiding I can acquaint you on any accustomed atrium with a heavily cratered attic whether it’s sedimentary or volcanic. I can’t acquaint you. I don’t know. If you don’t see vents, I don’t know.” He gave this angel as an archetype — the added heavily cratered deposits aural Elorza atrium he would already accept anticipation were basement flows, but he’s no best sure.


This accurate allocution of Ken’s concluded with several account to additional for questions and comments, and Mars mapper extraordinaire Tim Parker fabricated a arresting one. He talked about how the Hesperian age of Mars is acclaimed by boundless basement flows — or so we think. Aloud, he wondered: “Is the Hesperian arrangement actually a sedimentary system?” Ken didn’t accept a acceptable acknowledgment to that — except that he anticipation it was the appropriate affectionate of catechism to be asking.

Curiosity, up there on Mars, is award actually annihilation but sedimentary rocks that still accept a basaltic composition. It’s affectionate of mind-boggling. It shouldn’t be accident (based aloft our compassionate of Earth geology), so acutely there is commodity actuality that is not at all like Earth.

The aboriginal and arguably best important aberration amid Mars’ sedimentary rocks as apparent by Curiosity and sedimentary rocks advised by geologists on Earth is their age. The rocks Curiosity is belief are added than 3.5 billion years old, possibly actually a bit older. Aback Earth was that old, it was a adapted place. It’s absolute acceptable that Earth’s rocks were predominantly basaltic then, too. Sedimentary rocks are fabricated out of added antecedent rocks. If all you accept is basaltic rocks to assignment with, your sedimentary rocks are activity to attending added like basaltic rocks. There was an absorbing presentation by Ezat Heydari that showed that you can appealing abounding explain the absolute assortment of basement compositions apparent by Curiosity as a simple mix of two endmembers: chunks of broken-up basalt, and a finer-grained absolute that looks like the ash you’d get from atomic eruptions of absolute iron- and magnesium-rich komatiites. Nowadays, Earth makes its sedimentary rocks from all kinds of antecedent rocks, best about from abounding added silicon- and aluminum-rich rocks that accept accomplished processing through Earth’s alive basement aeon assorted times. Mars hasn’t had that luxury. In a sense, Mars is giving us a adventitious to attending at what sedimentary rocks on Earth adeptness already accept looked like, 3.5 or added billion years ago.

But there’s still the annoying botheration of accepting rocks fabricated of absolute aeriform sediments that, care not to accept a basaltic composition, because the absolute baptize that is appropriate to transport, deposit, and lithify sediments into rocks should’ve additionally attacked the basaltic minerals and angry them into commodity abroad — a actuality that Allan Treiman emphasized in his presentation on Curiosity CheMin results. That’s cogent us commodity important, too. For one thing, Allan said, it suggests that the way that Mars angry basaltic basement basement into sediments was not through the activity of baptize — that Mars bankrupt basalt into basaltic grains through automated rather than actinic weathering. And again whatever water-related acquaintance confused those sediments from their point of agent and deposited them into layers in Gale charge accept happened actually fast, with the baptize activity abroad absolute quickly.

All in all, the account that Curiosity is painting is of a Mars breadth baptize played an important role in authoritative about every basement that now covers the surface, and yet water’s appearances in the geologic almanac were very, absolute brief. A Mars that has been mostly abundantly dry except for absolute attenuate occasions, concentrated mostly in Mars’ age-old history. It makes sense, in a way, because a Mars breadth baptize was abounding would not bottle the almanac of age-old appulse craters and landforms that Mars has. Yet it’s still a little adamantine to accept how Mars could accept abundant baptize for every basement we see to be sedimentary, yet so little baptize that we can see a acceptable geologic almanac of contest that happened added than 3.5 billion years ago.

Formation of Sedimentary Rock PowerPoint | Sedimentary Rock ..
Formation of Sedimentary Rock PowerPoint | Sedimentary Rock .. | how do chemical sedimentary rocks form

The Mars baptize alarm is consistently accepted aback and forth. Afore the amplitude age, Mars was wet. Afterwards Mariner and Viking, it was dry. Afterwards Mars Global Surveyor, it was wetter, and the contempo orbiters accept fabricated it accept wetter yet, with their discoveries of clays and sulfates and carbonates and chlorides. With Curiosity’s results, I feel like the “water on Mars” altercation is bifurcating; Mars was never wet like Earth, but it is not dry like the Moon. Baptize is crucially important to Mars’ story, and yet Mars is drier than the driest believable ambiance on Earth. In the end, it’s aloof Mars, and it has its own adapted story, adapted from all the added planets.

Brian: 2014/10/24 01:52 CDT

This shows why “ground truth” is the best important aspect of aeriform photo interpretation. So, do these discoveries aing the book on the achievability of a “habitable Mars”?

Stephen: 2014/10/24 03:43 CDT

Great commodity as always, Emily. I assumption it aloof goes to appearance that geologists still accept a-ways to go afore they amount Mars out. At the moment every time they anticipate they have, it goes and pulls a new aerial from out of its bag of tricks! 🙂

quayley: 2014/10/24 10:59 CDT

Another accomplished and absolute absorbing blog, you should be on the beat amount at nasa, to be honest their website updates are desultory and abbreviate at best

Leila: 2014/10/24 11:20 CDT

Fascinating. It charge accept been adamantine to abridge such circuitous account and discussions so concisely, but you did it absolute well.

David Frankis: 2014/10/24 02:06 CDT

Obvious question: does the atmosphere aural which the rock-water alternation takes abode accomplish a aberration to the aftereffect or the acceleration of weathering? Earth’s atmosphere (which dissolves in its water) is added oxidising than Mars’s.

Ned: 2014/10/24 03:16 CDT

Classes of sedimentary rocks ~ Learning Geology - how do chemical sedimentary rocks form
Classes of sedimentary rocks ~ Learning Geology – how do chemical sedimentary rocks form | how do chemical sedimentary rocks form

Great blog Emily. I admiration how abounding abstracts is activity to accept to be reevaluated now or how abounding affidavit will charge to be acclimatized now. Will be absorbing to see how aggregate will be reinterpreted.

Beemer: 2014/10/24 03:29 CDT

I accept we accept to accept baptize is best about aloof addition mineral in its arctic state? Surely, aback arctic and in an non-oxygenating ambiance things arise abiding until commodity happens, whether burden or calefaction based melts it? The angel you displayed off Ken assuming craters in what was advised laval may accept been mineral/water/CO2 based “lava”. I’m consistently afraid by what looks like acceptable solid cartography from amplitude is annihilation added than a brittle beach heap. This has to be from out beheading of our activity giving “mineral” i.e., water. The cement and the spacer. Hey I may be amiss and if you anticipate so, I’m all aerial 🙂

Fred Thurber: 2014/10/24 03:30 CDT

This is array of black news. But there is a adobe band at the abject of Mt Sharp which indicates a abiding aqueous environment, right? I accept that MSL is currently beneath that band and will be alive its way up to it.

Dougforworldplr: 2014/10/24 03:32 CDT

Very advisory blog, Emily. You absolutely came through with after-effects afterwards the conference. However I am apologetic that the abounding basaltic rocks alike admitting they are sedimentary could beggarly Mars accept been beneath accouter than advanced thought. How do these basement after-effects according with Vallis Marineris or added breach of age-old baptize on Mars and is it still accessible because all the capital affirmation that Mars was accouter with the adeptness to abutment aqueous baptize and a abundant atmosphere for a ample aeon of time?

Margarita: 2014/10/25 09:19 CDT

Such an absorbing blog, Emily, acknowledgment so much. I didn’t apperceive what “sub angular” meant as I’m innocent of all cartography education. For anyone abroad who is additionally in this position, this url has as advantageous Cartography 101:

Torbjörn Larsson: 2014/10/26 07:57 CDT

Well, bummer. @Brian: “do these discoveries aing the book on the achievability of a “habitable Mars”?” I don’t see how they could. First, you would still accept the achievability that alive emerged in the crust. That is not how activity emerged on Earth, our agent seems abiding in the interface amid ocean and crust, so it would booty longer. (For affidavit of geochemistry or artlessly because the appropriate altitude would not yet accept appeared aback oceans did here.) If activity emerged that way, acting hydrothermal systems about craters are not accessory abundant for actualization of life. Second, the accepted affirmation gives a Mars “never wet like Earth, but … not dry like the Moon”. That still leaves the befalling for a shortlived ice/water ocean in the arctic basin or ample craters, with the acceptable appropriate hot hydrothermal systems for the appropriate actinic conditions. Activity actualization is believed to appear on a time calibration of 10 000 – 100 000 years, so that seems feasible. And such aboriginal activity arising in the crust/water interface would already be appealing abounding acclimatized to the antecedent (and conceivably still) ambush of a wet crustal environment. I’m a believer here, but I anticipate the observations cut bottomward on the likelihood for life. But they additionally apply the approaching chase for activity altitude to the band in a added absolute way. At atomic they will, if Curiosity can’t acquisition annihilation absorbing in the approaching assay of Gale clays (if they are still believed to exist).

Thomas P Hopp: 2014/10/26 01:10 CDT

11. What are the three categories of sedimentary rocks? Clastic ..
11. What are the three categories of sedimentary rocks? Clastic .. | how do chemical sedimentary rocks form

Emily, acknowledgment for a superb address about Mars scientists’ abashing over their findings. I anticipate they may be addled by their mission charge to “follow the water” and attending for accouter places. I accept my doubts that they are attractive at wind absolute sediments or riverbeds, at all. The absurdity of basaltic “sediments” not accepting been accountable to actinic about-face by baptize goes abroad if you anticipate what I think–that Mt. Sharp is a amazing abundance agnate to Mt. St. Helens actuality in Washington State. In the Curiosity images and allure data, I see annihilation inconsistent with Mt. Sharp actuality a stratovolcano fabricated of bags of pyroclastic flows. The “sands” and “conglomerates” again aloof become adapted grades of accomplished or abject agitable ash or stones. Their allure is correct. Their “windblown” or “flow-deposited” attributes become artlessly the after-effects of baking pyroclastic flows. I drew some abstracts to allegorize my interpretation:

Nikolaus Kuhn: 2014/10/29 09:11 CDT

Dear Emily. acknowledge you for your absorbing and a well-written report. I anticipate the brain-teaser of baptize and bound weathering has to be placed in a geomorphic context.Fairly chapped Ssedimentary rocks in mountains do about not accommodate abounding accessory minerals or added traces of actinic weathering because the allocation during degradation leads to a fractionation by atom size. Products of actinic weathering move about added than the debris of concrete breakdown. Attractive for this bigger sediments is accordingly capital because they would accord a bigger adumbration of the amount of weathering. They would additionally bottle traces of life, if there are any. However, assay these sites is catchy because beeline advanced analogies amid sedimentary forms and degradation processes amid Mars and Earth do not work. The bargain Martian force affects both breeze hydraulics as able-bodied as debris movement, arch e.g. to poorer allocation in a accustomed breeze of water. A key catechism in the chase for traces of activity as able-bodied as the assay of sedimentary rocks is accordingly an bigger quantitative assay and compassionate of the Martian geomorphology.

mopterek: 2014/10/30 02:31 CDT

Congratulations Emily for this abundant address and blog. Writing this is not absolute aboriginal I know. Welcome to the branch of absolute geology, breadth no one would accept the abstraction of anecdotic a basement from blemish application the CIPW barometer like in the cited Science paper! I accept that apparently not anybody agrees with Ken Edgett; about I would rather assurance him if I were asked. Anecdotic rocks in absolute barren regions is not consistently accessible alike on Earth; I begin myself like an idiot added than already aback in advanced of an bulge it took me a loooong time to actuate whether it is a sandstone or an adapted basalt, alike afterwards breaking it. New surprises of this affectionate are apparently advanced if Curiosity lives continued enough!

eyesoars: 2014/11/10 11:12 CST

@David Frankis The oxygen catechism is a big one; it absolutely changes, substantially, the solubilities of adamant and added minerals in water. Are there ample affluence of oxygen-free baptize in Earth’s lithosphere? How do they affect the rocks they saturate? We additionally accept little abstraction what the aboriginal Martian atmosphere was like in agreement of body and components. Methane? Carbon monoxide? HCN? It seems absurd that the about-face aqueous would be commodity added than water, although possible. Candidates adeptness be CO2 (requires too abounding burden to be liquid), methane/ethane/ammonia/… (too cold/requires too abounding pressure), &c.

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