Whew! A busy start to a semester, what with seminars and teaching and paper work and writing and oh yeah GSA isn't that far off so gotta get that talk done (well, started, actually). In amongst all this bullshit that you've got to put up with in schoolin', it's sometimes hard to keep sight of the reason why you got yourself into the mess that is grad school in the first place, you know?
There's a series of Op-Eds at The New York Times website, ostensibly for incoming freshmen, about how to get the most out of your college experience. All of them are written by big-wig academic types with hugely famous reputations, and some of the advice is a mixed bag (and some is hilariously predictable, given the writer, fer' instance: Harold Bloom thinks people should read the classics. Who'd a thought!?!). Anyway, there is kind of a neat one by Nancy Hopkins, on the excitement of Your Chosen Field, which is pretty good, I think.
Now get back to work!
Monday, September 14, 2009
Monday, September 7, 2009
Mud as Sand!
Mud is, as we all know, an important component in the sedimentary rock record, and in some successions, completely dominates the record. The picture below is from around Grand Junction, Colorado, USA, and shows a thick package of the Mancos Shale, deposited in the Western Interior Cretaceous Seaway. I don’t care who you are or where you’re from, that’s a lot of mud!
Anyway, mudrocks (encompassing silt- and clay-sized grain populations) occur across the depositional landscape, from floodplains to abyssal plains, and are easily the third-best grain size out there (the others, sand- and gravel-sized particles, are tied for first in the “best grain-size” category). And that grain-size holy trinity (mud, sand, gravel) represents the methodological hydrodynamic triumvirate that most sed/strat types deploy (almost casually) in the field: mud is deposited in low energy conditions, sand takes some energy to shift around, and gravels need quite the push to get moving through a system.
There has been some recent, ahem, erosion, of that venerable concept of quiet-water suspension fall-out of mud, however; recent work, both field-based and experimental, are beginning to show that muds may be a little more complicated than just the “fine-grained, laminated, organic rich --- 50 meters thick” nonsense that gets slapped down in your field book.
Schieber and Southard, 2009 pulled off a rather nice, simple flume experiment using mud (in the 10 – 20 micron range) in both fresh and saltwater. They were able, through careful use of time-lapse photography, observations on ripples that became attached to the flume wall, and by quickly draining the slurry from the flume, to capture a variety of ripple formsets made entirely out of mud! The data repository for the paper has some slick movies of the mud ripples forming and migrating, as well. The picture below is their Figure 1, on pg. 484. That there’s a ripple, a-yup.
Anyway, the neat-o thing about this ripple is the kind of sediment transport these muds are experiencing. It was possible, for example, that the muddy ripples just looked like sandy ripples, but were being deposited as fine-grained, turbid slurries, which would still be a fairly low energy condition for ripple formation, right? However, Shieber and Southard 2009 have shown that, in fact, the muds rapidly flocculate into silt and sand-sized particles, which are then transported at comparable velocities to regular ol’ sand and silt grains.
Of course, the implications are pretty obvious: previously interpreted quiet-water offshore muds, for example, might not be as quiet-water as we thought. And, post-depositional burial and compaction might result in the general obliteration of these ripple cross-laminations and bedforms from the record, and the superficial appearance of horizontally laminated mudrock. That really changes your interpretation of hydrodynamics, sedimentation rate, and how the mudrocks fit into whatever lithofacies association scheme you’ve cooked up for your rocks.
Wright and Marriott, 2007, came to the same general conclusions regarding mudrock in the Lower Old Red Sandstone (South Wales, UK). These mudrocks generally lack the stereotypical “fine-scale laminations” of most mudrocks; because of this, the assumption has been that these muddy units have been altered by soil formation. However, Wright and Marriott 2007 point out that these mudrocks are often interbedded with gravel-lens that have sharp contact (above and below) with the mudrock, that there are sharp truncations that separate mudrock from other mudrock, and that there are some faint, large scale architectural components associated with these mudrocks, reminiscent of accretion packages in fluvial macroforms. The picture below sums up, diagrammatically, their own field-based evidence for these interesting mud associations; it’s Wright and Marriott’s Figure 3, on pg. 95.
Wright and Marriott (2007) point out that this is sort of a big deal. The interpretation of muddy deposits as relatively continuous, flat-lying overbank deposits with lots of pedogenesis is FUNDAMENTALLY different from the interpretation of mudrock deposited as sand-sized aggregates within a channel complex. Hydrodynamics, Time, and Sedimentation Rate…there are big differences between these two models. And, from a practical side, if I’m depositing mud-rich plugs in an active channel as macroforms, that is going to really change fluid migration paths for hydrocarbons within the ostensibly permeable and porous channel complex sandstones.
Anyway, kind of a neat thing to think about, next time your haulin’ ass over the mudrocks to get up there at the obviously more interesting sandstones. Maybe these fine-grained bedload phases are more common than we realize?
WORKS CITED
Schieber, J., and Southard, J.B., 2009, Bedload transport of mud by floccule ripples – direct observation of ripple migration processes and their implications: Geology, v. 37, p. 483-486.
Wright, J.P., and Marriott, S.B., 2007, The dangers of taking mud for granted: lessons from Lower Old Red Sandstone dryland river systems of South Wales: Sedimentary Geology, v. 195, . 91-100
Anyway, mudrocks (encompassing silt- and clay-sized grain populations) occur across the depositional landscape, from floodplains to abyssal plains, and are easily the third-best grain size out there (the others, sand- and gravel-sized particles, are tied for first in the “best grain-size” category). And that grain-size holy trinity (mud, sand, gravel) represents the methodological hydrodynamic triumvirate that most sed/strat types deploy (almost casually) in the field: mud is deposited in low energy conditions, sand takes some energy to shift around, and gravels need quite the push to get moving through a system.
There has been some recent, ahem, erosion, of that venerable concept of quiet-water suspension fall-out of mud, however; recent work, both field-based and experimental, are beginning to show that muds may be a little more complicated than just the “fine-grained, laminated, organic rich --- 50 meters thick” nonsense that gets slapped down in your field book.
Schieber and Southard, 2009 pulled off a rather nice, simple flume experiment using mud (in the 10 – 20 micron range) in both fresh and saltwater. They were able, through careful use of time-lapse photography, observations on ripples that became attached to the flume wall, and by quickly draining the slurry from the flume, to capture a variety of ripple formsets made entirely out of mud! The data repository for the paper has some slick movies of the mud ripples forming and migrating, as well. The picture below is their Figure 1, on pg. 484. That there’s a ripple, a-yup.
Anyway, the neat-o thing about this ripple is the kind of sediment transport these muds are experiencing. It was possible, for example, that the muddy ripples just looked like sandy ripples, but were being deposited as fine-grained, turbid slurries, which would still be a fairly low energy condition for ripple formation, right? However, Shieber and Southard 2009 have shown that, in fact, the muds rapidly flocculate into silt and sand-sized particles, which are then transported at comparable velocities to regular ol’ sand and silt grains.
Of course, the implications are pretty obvious: previously interpreted quiet-water offshore muds, for example, might not be as quiet-water as we thought. And, post-depositional burial and compaction might result in the general obliteration of these ripple cross-laminations and bedforms from the record, and the superficial appearance of horizontally laminated mudrock. That really changes your interpretation of hydrodynamics, sedimentation rate, and how the mudrocks fit into whatever lithofacies association scheme you’ve cooked up for your rocks.
Wright and Marriott, 2007, came to the same general conclusions regarding mudrock in the Lower Old Red Sandstone (South Wales, UK). These mudrocks generally lack the stereotypical “fine-scale laminations” of most mudrocks; because of this, the assumption has been that these muddy units have been altered by soil formation. However, Wright and Marriott 2007 point out that these mudrocks are often interbedded with gravel-lens that have sharp contact (above and below) with the mudrock, that there are sharp truncations that separate mudrock from other mudrock, and that there are some faint, large scale architectural components associated with these mudrocks, reminiscent of accretion packages in fluvial macroforms. The picture below sums up, diagrammatically, their own field-based evidence for these interesting mud associations; it’s Wright and Marriott’s Figure 3, on pg. 95.
Wright and Marriott (2007) point out that this is sort of a big deal. The interpretation of muddy deposits as relatively continuous, flat-lying overbank deposits with lots of pedogenesis is FUNDAMENTALLY different from the interpretation of mudrock deposited as sand-sized aggregates within a channel complex. Hydrodynamics, Time, and Sedimentation Rate…there are big differences between these two models. And, from a practical side, if I’m depositing mud-rich plugs in an active channel as macroforms, that is going to really change fluid migration paths for hydrocarbons within the ostensibly permeable and porous channel complex sandstones.
Anyway, kind of a neat thing to think about, next time your haulin’ ass over the mudrocks to get up there at the obviously more interesting sandstones. Maybe these fine-grained bedload phases are more common than we realize?
WORKS CITED
Schieber, J., and Southard, J.B., 2009, Bedload transport of mud by floccule ripples – direct observation of ripple migration processes and their implications: Geology, v. 37, p. 483-486.
Wright, J.P., and Marriott, S.B., 2007, The dangers of taking mud for granted: lessons from Lower Old Red Sandstone dryland river systems of South Wales: Sedimentary Geology, v. 195, . 91-100
Tuesday, September 1, 2009
SedPortal
Well, sadly, I'm back from the field...however, having to deal with the dismal, post-field depression is somewhat mollified by the soothing, minty balm that is the geoblogonetosphere. ANYWAY, just thought I'd point out a recent (?) addition to that august electron-based sed/strat portion of the web that I (and a few others) reside in. Boyan Vakarelov is a lecturer in Sed/Strat at the University of Adelaide, and also runs the website SedPortal, which has some nifty stuff. Welcome to the HiveMind, Boyan!
Wednesday, August 19, 2009
Nifty stuff from the Utah Geological Survey
Hup! Just a quick post about this thing that I recently found. The Utah Geological Survey has made up some of them there KMZ files that the Google Earth Folks are so hyped-up about, letting you drape a 3-D geological map over the terrain around St. George, Utah. Pretty spiffy, really. They also have a virtual field trip that makes use of the crazy 3-D map, which is a pretty neat thing. All in all, a pretty cool use of the ol' Google Earth.
Anyway, back to work!
Anyway, back to work!
Tuesday, August 11, 2009
Might as well post a picture, while I'm at it...
Since I'm in town, using that there internets to do my patented "Last Minute Abstract Submittal" to GSA, I thought I'd slap up a picture of some nifty soft-sed deformation. Here you go (in the words of the Prophet, "Click it, and it shall be Bigger"):
This picture is from some Cretaceous deltaic stuff exposed on the Rock Springs Arch, a little east of that shining beacon of metropolitanism, Rock Springs Wyoming. A picture of this very outcrop is in the "Roadside Geology of Wyoming", making it famous, I guess. That same book probably also tells you the name of the unit it's in, which escapes me now (I THINK it's Mesaverde Group, but I can't get any finer scale than that).
Anyway, you can see the nice folding going on in these slippery, mudrock and sandstone prodelta interbeds. If you look REALLY close, near the core of the fold, there's a little red stripe of something...that's my rockhammer for scale. The metal post on the right is a Speed Limit Sign, which is maybe 6 or so feet tall? So it's a good sizes feature. If you're every heading out on I-80, this outcrop is right on the westward-side of the interstate, a few miles before you get to Rock Springs proper. Take a look!
This picture is from some Cretaceous deltaic stuff exposed on the Rock Springs Arch, a little east of that shining beacon of metropolitanism, Rock Springs Wyoming. A picture of this very outcrop is in the "Roadside Geology of Wyoming", making it famous, I guess. That same book probably also tells you the name of the unit it's in, which escapes me now (I THINK it's Mesaverde Group, but I can't get any finer scale than that).
Anyway, you can see the nice folding going on in these slippery, mudrock and sandstone prodelta interbeds. If you look REALLY close, near the core of the fold, there's a little red stripe of something...that's my rockhammer for scale. The metal post on the right is a Speed Limit Sign, which is maybe 6 or so feet tall? So it's a good sizes feature. If you're every heading out on I-80, this outcrop is right on the westward-side of the interstate, a few miles before you get to Rock Springs proper. Take a look!
Thursday, July 30, 2009
Field Pictures
Gotta get a post in before July vanishes! I've been out fieldin' it up in Wyoming since mid-June or so, which has resulted in a SHOCKING lack of updates; luckily for me, the geoblogosphere gets pretty quiet come the summertime, which I choose to interpret as evidence for Milankovitch cyclicity as an allogenic forcer on the internet. THERE IS NO OTHER VIABLE INTERPRETATION.
Anyway, thought I'd just post up a quick few pictures of the pretty scenery out West; maybe at the end of the field season I'll put some sed/strat specific pictures up, but these ones below are more of your "Gosh-golly-geewilikers! Purty!" type of pictures.
This first picture (below) shows the Green River Formation (Eocene); the yellowish-tan stuff at the base of the cliff is the Tipton, while the white-colored interval (shot through with some pretty rad brown sandstone) are the Wilkins Peak Member (that's my baby). The river in the background is the Green, making the Flaming Gorge Recreation Area behind a dam.
This next picture is Exhibit #34591 in the continuing series "Rocks That Have Been Shaped Into Rude And Amusing Shapes"; its a pinnacle made up of the volcaniclastic-rich deltas of the Sand Butte Bed, which marks the fillin' in of Eocene Lake Gosiute. On the topo maps of the area, this feature is referred to as "South Chimney Butte"; the Locals have another name for it.
This picture is of the Green River Formation, expressed on the EASTERN side of the Rock Springs Arch, sort of near(ish) to the town of Wamsutter. The red-n-green funtime strata are alluvial and fluvial strata of the Cathedral Bluffs Member (equivalent to the Wilkins Peak on the West flank of the Arch), while the lakey lookin' white tannish/whitish stuff in the Laney Member of the Green River Fm.
Finally, here's a picture of a Hawk that was yelling at me for a good couple of hours. I must have been taking paleocurrents in it's living room, since there was a huge nest not to far away from where this picture was taken.
All right, back to the Field!
Anyway, thought I'd just post up a quick few pictures of the pretty scenery out West; maybe at the end of the field season I'll put some sed/strat specific pictures up, but these ones below are more of your "Gosh-golly-geewilikers! Purty!" type of pictures.
This first picture (below) shows the Green River Formation (Eocene); the yellowish-tan stuff at the base of the cliff is the Tipton, while the white-colored interval (shot through with some pretty rad brown sandstone) are the Wilkins Peak Member (that's my baby). The river in the background is the Green, making the Flaming Gorge Recreation Area behind a dam.
This next picture is Exhibit #34591 in the continuing series "Rocks That Have Been Shaped Into Rude And Amusing Shapes"; its a pinnacle made up of the volcaniclastic-rich deltas of the Sand Butte Bed, which marks the fillin' in of Eocene Lake Gosiute. On the topo maps of the area, this feature is referred to as "South Chimney Butte"; the Locals have another name for it.
This picture is of the Green River Formation, expressed on the EASTERN side of the Rock Springs Arch, sort of near(ish) to the town of Wamsutter. The red-n-green funtime strata are alluvial and fluvial strata of the Cathedral Bluffs Member (equivalent to the Wilkins Peak on the West flank of the Arch), while the lakey lookin' white tannish/whitish stuff in the Laney Member of the Green River Fm.
Finally, here's a picture of a Hawk that was yelling at me for a good couple of hours. I must have been taking paleocurrents in it's living room, since there was a huge nest not to far away from where this picture was taken.
All right, back to the Field!
Tuesday, June 9, 2009
Summer Reading Meme
Contagion once again sweeps the geoblogs, this time in the form of a Summer Reading Meme; the original infection spread quickly from Suvrat to Brian, and currently threatens the whole of the Developed World. NOW DO YOU SEE THE DANGER OF THE ANTI-VACCINATION CROWD!?!
Anyway, I've obviously succumbed to the hellish meme-fever myself, 'cause here's my summer readin' list:
Beyond the Hundredth Meridian: John Wesley Powell and the Second Opening of the West, by Wallace Stegner, followed closely by:
A River Running West: The Life of John Wesley Powell, by Donald Worster; I'm still on my Powell kick from LAST summer out in the Green River, and these two books are pretty much the definitive scholarly examinations of Powell's life, career, and his subsequent impact.
Bigfoot: The Life And Times of A Legend by Joshua Blu Buhs; I wrote about this one here, and from what I've heard, it's gonna be a pretty rad book, examining the myth of Bigfoot, the people who "study" it, and the role that the Big Hairy Ape plays in gender-class-race dynamics. Neato!
The Black Lizard Big Book of Pulps, edited by Otto Penzler: I've always loved the pulpy goodness of 20's, 30's and 40's magazine fiction, and this collection has 1100+ pages of Detective fiction from the pulps!
Now go wash your hands and drink some Orange Juice, lest ye be infected by the Meme!
Anyway, I've obviously succumbed to the hellish meme-fever myself, 'cause here's my summer readin' list:
Beyond the Hundredth Meridian: John Wesley Powell and the Second Opening of the West, by Wallace Stegner, followed closely by:
A River Running West: The Life of John Wesley Powell, by Donald Worster; I'm still on my Powell kick from LAST summer out in the Green River, and these two books are pretty much the definitive scholarly examinations of Powell's life, career, and his subsequent impact.
Bigfoot: The Life And Times of A Legend by Joshua Blu Buhs; I wrote about this one here, and from what I've heard, it's gonna be a pretty rad book, examining the myth of Bigfoot, the people who "study" it, and the role that the Big Hairy Ape plays in gender-class-race dynamics. Neato!
The Black Lizard Big Book of Pulps, edited by Otto Penzler: I've always loved the pulpy goodness of 20's, 30's and 40's magazine fiction, and this collection has 1100+ pages of Detective fiction from the pulps!
Now go wash your hands and drink some Orange Juice, lest ye be infected by the Meme!
Sunday, June 7, 2009
More Damn Tafoni!
Michael has put up yet more Tafoni pictures, obviously still stinging from my earlier usurpation of the whole tafoni pictures thing. As such, I shall respond with yet more images of these artsy weathering pits in sandstones! The picture below is from the Ordovician St. Peters Sandstone, in Governor Dodge State Park, Wisconsin, where I was on a little camping jaunt earlier in the week.
Anyway, you might notice that Michael's pictures from the Santa Cruz Mtns are much better than my picture above; this is undoubtedly due to the fact that 1) His Rocks Are Better Than These Scrappy Ord. Ss from Humid Wisconsin; and 2) He Is A Better Photographer Than I Am. Both of these are rather unfair advantages, frankly, and Michael should be ashamed of himself for exploiting them so mercilessly like that.
Anyway, you might notice that Michael's pictures from the Santa Cruz Mtns are much better than my picture above; this is undoubtedly due to the fact that 1) His Rocks Are Better Than These Scrappy Ord. Ss from Humid Wisconsin; and 2) He Is A Better Photographer Than I Am. Both of these are rather unfair advantages, frankly, and Michael should be ashamed of himself for exploiting them so mercilessly like that.
Monday, June 1, 2009
A life-sized Whale, in the comfort of your own Home
Check this out! It's a life-sized whale, put up on your computer screen; you can click and drag all over the critter, and get a sense (sort of) of just how big it is. Those with access to really nifty huge computer screens will have the best views, of course, but still, kind of neat!
The whale is a part of the Whale and Dolphin Conservation Society, and is part of a campaign to get people thinking about Cetacean conservation. It's kind of neat use of visual media, don't you think?
The whale is a part of the Whale and Dolphin Conservation Society, and is part of a campaign to get people thinking about Cetacean conservation. It's kind of neat use of visual media, don't you think?
Earthquakes and the Wrath of God!!!!!!!!!!
It's not just our crazy, US, Christian-flavored fundies that have wacked-out ideas! The recent seismicity in Saudia Arabia has inspired some End-O-The-World, Koranic musings from the Saudi Gazette. Go here to read about the Wrath-o-Allah! My favorite quote, of course:
Their argument about earthquakes being the result of natural geological activity holds no more ground than a claim that this published article on paper or website is a result from the functioning of a machine (printer or computer) without any effort of a human brain behind it that has made it make sense.Just kind of nice to see other folks getting in on the geo-madness, you know?
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