h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

The portion I was studying turned out to be a turbidite sequence, intruded by several plutons and metamorphed by the last orogeny. Some of the team on the other side of the river that divides the forest had the more boring time of it, layer and layer again of lava flow, and suspect terrains.

I don't remember anything about the large-scale structure of the desert. The whole quaternary portion of the desert there has small 30m cones all over it, most of them quite strongly weathered. Most of the strata there was various kinds of shallow sea carbonate deposition. More Crinoids than you can shake a stick at. Most interesting to me were the minerals where a calcium poor intrusion hit the existing rock, especially if a caliche layer was exposed.

One lady at Darwin sold us cold soda she drove far into town for. You'd find the whole team there, sucking down caffeine and sugarwater after a long sweaty day. She also fed the desert hummingbirds, she had maybe thirty jars of sugarwater lined with mesh, and they came in droves. This is what I meant about hummingbird warnings-I had a red backpack and this strongly indicated food to them. They'd buzz up behind me chatter angrily and divebomb attack. If I turned around to defend myself, this nicht gornisht hilfen, because the backpack is what was red, so they'd zoom around behind me again.

Excuse me for being confused, but the first paragraph relates to Washington, correct? So you found a piece of seafloor, probably at or just beyond the continental shelf at the time, or associated with a delta, that was subsequently intruded, metamorphosed and uplifted?

I don't think I've ever seen a turbidite formation actually. I was thinking maybe it would be similar to an alluvial fan or apron only on a bigger scale and probably more extended along the course of the currents. Is that right?

Then the subsequent paragraphs refer to Death Valley? There you found evidence of a reef maybe? Underlying Quaternary spatter or cinder cones? So what's with the caliche? Do you think the superheated fluids around the intrusions assisted in its formation or something else? This seems like a very interesting location. Not that the other one wasn't, but this seems more complex.

Yes, turbidites were in WA, and associated with a delta, found by others to the north from where I was working. Turbidites are strange phenomena. There are steep narrow canyons just off the coast of Western US, but mostly CA. The Japanese current sweeps deposits southward, and they accumulate at the top of the canyon in a semiconsolidated state until (imaginative geologists speculate)earthquake or flood from a nearby associated creek. Then, they crash down in a mass rush of chaotic turbulence. Formations then alternate between periods of quiet, stratified deposition and chaos. THey tend to be made of beach sands that flowed over the accumulating turbidite-to-be and down into the canyon, and typical steep coast deposits, and ripped up chaos in which interesting things that survive the crush get fossilized because they were so suddenly buried. They happen every 20 years ago in some locations. They've been trying to study them as they happen, but instruments so far (last I knew in 1987 or so) haven't survived the events.

Most of the Quaternary portions of the desert near DV are absolutely unstudyable: they've been washed over, faulted, with loose deposits many hundreds of feet thick, and this is seldom easily exposed. The small sputters are notable simply because they are there, they stick out, and decomposed volcanic rock has it's own distinctive morphology in the desert. I didn't really study them-too damn hot to hike there, and 4 wheeler will only get you so far across that looseness. There was only weak evidence that the exposed lagoon-grading into the reef was once covered by this because you could find evidence enough to make a stereogram from folded bits in the 'top'(overturned before intrusion, probably) area of the study. Further north, the whole shebang was covered in a basaltic caprock, but as there was a fault between the area studied, and the expected area based on offset was totally different elevation, there wasn't any surviving evidence it covered the study area (near Darwin). Caliche, it's everywhere, so it's supposed it's modern.

Very interesting. With respect to the turbidites, did you notice anything like the turbidity current structures that have been identified in the Gulf of Mexico? I believe that the strength of those currents has actually been measured and it's rather colossal, given the amount of water involved, from which we infer the existence of the mass transport that causes the currents periodically. I would be surprised if any instrument could survive a submarine landslide so maybe indirect methods will have to do.

Clicked on a "who's online" name, then clicked again on a thread and found an intelligent conversation. Nothing to add really, just let you know this web thing still works.

I don't think I was aware it hadn't been working but thanks just the same.

Any intelligence you might find is due almost entirely to Rita.

I wasn't aware of the mass transport currents in the Gulf. How might I find out about them, do they have an official name I can search with?

Go here to start: http://www.caller2.com/2000/november/02/today/texas_me/8196.html

My memory may have been in error to assign the cause of these things to turbidity currents, but I'm still looking for the source. The above reference isn't it but it does describe the phenomenon pretty well.

Okay, I'm going to go way out on a limb or the edge of the abyss on this one.

These "storms" occur along the bottom of the escarpment of the continental shelf, therefore, in the absence of some magically unknown factor, I'm hypothesizing that the things are due to massive landslides along the shelf, perhaps in some sort of unusual synchronicity where say one slide tends to set off another and another domino fashion while each contributes to the overwall current magnitude.

They are after all evidently transient events and not a constant feature of the deep sea environment. I doubt that one turbidity current could account for them but several occurring in proximity along the rim of the shelf, perhaps responding to longshore accumulations that hit critical mass at approximately the same time, these then taken in aggregate might account for the deep sea events.

Here's another link. Apparently, these things are mostly of news interest in the offshore "oil patch" and the Gulf port communities.

http://www.staugustine.com/stories/110200/nat_1102000032.shtml

I thought that somebody else had proposed before, but I can't find the reference so, if they didn't, I just did. &;D

Fascinating! It would be interesting to see if any formerly puzzled sedimentologists come up with formations that show signs of this kind of weathering. It seems to me that it might have scour effects like glaciers, which could also be thought of as thick masses of flowing water. The other thing it might look like are the coulees of Washington State.

I thing your hypothesis is a good place to work from, and it makes me think of similar processes that might cause New Madrid-style tremors, if they were happening on dry land where there isn't any lubrication. Do any of the really slippy clays like montmorillonites survive in Gulf conditions?

I am exercizing my imagination on how to test the hypothesis over such a large area. One may have to rent a bit of satellite time and some sequenced images from imagesfromspace.com.

The currents that I know about called turbidity currents are much more localized and the chaotic layers of the formation have another order of magnitude in estimated speeds of deposition. Some oceanographers, based on the damage seen to the instruments that got nailed, are now supposing that it might be even two orders of magnitude, and might be similar to the nueee ardent, if you were to look at one happening (and survive). The upper part of the canyon where they form might very well get scoured by the start of the 'land'slip, but this part isn't ever well preserved. The part of a turbidite sequence that you would see would be the payload at the end. It would either be exposed neatly due to sea-level drop, or due to indirect folding due to the imperfect shear as the Pacific Plate scrapes along.

I don't know about the level of The PencilQueen's specialization, but I know she studied clays, so I have asked hir about that, to see if we can get hir to speculate.

I should think, Sea Change, that practically any clay mineral would survive given that it represents the diagenetic end of the weathering of volcanic ashes, feldspars or other relatively unstable igneous minerals. I think the USGS estimates clays represent at least 60 percent of the Continental shelf and 40 percent of the ocean floor.

So my next stretch of the imagination would involve making a conceptual connection between the Lewis Overthrust Belt and maybe what actually happens on the edge of the Shelf. The Belt formations consist predominantly of Precambian shales and mudstones, whole blocks of which have been thrust over younger Cretaceous formations for distances of 30 miles or more.

If that can happen in response, presumably, to isostatic adjustments from the various orogenies that were occurring to the west during the Upper Cretaceous, then I presume something similar happens when silt accumulates on the deltas that overlie the Shelf. Whole slabs might be "squeezed out" from under the accumulations.

I've observed such slabs being squeezed out of exposures of Mancos shale west of Durango, Colorado. These were relatively consolidated because there hasn't been an ocean in the area for 65 million years and they underlie some pretty impressive exposures of Mesa Verde sandstone members, but imagine what might happen to a stack of >> wet << deposits of this type. The point is the displacement of water would be qualitatively different than if the same amount of loose debris, like sand for instance, slid off the edge, would it not?

Or you could perhaps model it by studying the difference between powder snow avalanches and slab-type avalanches, correct? Maybe study the chutes to determine if any telltale signs are left that would help identify the types of avalanches that created the chutes. You could do several transects of new chutes at various elevations to eliminate the acceleration factor or whatnot and then see if the Escarpment showed evidence of similar structures maybe.

I hope this isn't too boring, but I'm sort of brainstorming right now and not really addressing the specific issues you raised directly. Maybe when the scattering in my brain settles down, something consolidated might emerge. &;D

This is the exact opposite of boring. One of the reasons I follow your posts is that it is a delight to hear you speak. Your reasoning patterns show that you have the roots of good well-formed scientific hypothesis formation wired neatly into your brain. Geology is very very young as a science, and such antiuniformitarian concepts as the extinction bolide and continental drift must have seemed wild at the time. I myself am not sufficiently imaginative, which is why I never went for my masters.

I like your general hypothesis. I wasn't aware that isostasis could do this for anything other than plutons, pegmatites, or salt/other anhydrous layers, and this is new information for me. I wasn't contradicting and don't mean to contradict you. You are the real practicing geologist, I edit medical reports for a living. I am practical by nature, and so when I hear someone propose something interesting, I wonder if it is a scientific idea or not: whether it is falsifiable and whether it can succumb to testing. I am also collaborative by nature, and so I was hoping to suck The PencilQueen into the discussion, not in a restrictive way, but to give us more than just our two brains to riff onto.

In California, folks say we don't have the four seasons, but we do: fire, riot, earthquake, and mudslide.

There are some clays that are considered more slippy and unstable than others. In most cities with expansionist plans like LA and San Jose, there is a huge economic incentive to build on the hills, and a lot of them have clay layers that just aren't stable, for more than just earthquake reasons. Clays tend to change from one form to another fairly easily. You'd think a certain mineral would be found in certain areas by following formations, soil compaction tests, sieving samples, trench tests, and studying the land forms, but certain conditions can change them into less dangerous forms. The rich developer then pays your consulting firm handsomely and refers more of her clients to you if you do (one of the very few geology related jobs I have done).

I was thinking about what might be a stabilization effect of the salts in seawater, the warmth of the Gulf and possible heat from decomposition of rich organics that you'd find in the delta and along barrier island lagoons, and possible chemical changes due to a reducing environment, if the strata become sufficiently thick.

The other thing I was thinking is a riff on several ideas that you have suggested earlier. The clathrated methane hydrates that the abyssal Gulf (we now know) has lots of and the report that you kindly linked for me reminded my of. I hypothesize that perhaps the irregularity of these currents might have to do with more subtle shifts of the strata, similar to what you are suggesting. These clathrates are hypothesized to be rather unstable, so this small broad change may be just enough to make 'small' pockets of gas escape their pressure cages. Remote sensing might find evidence of this by checking for small inexplicable plumes in locations that an oberver might select as a likely source for these currents.

Can one study avalanches by dyeing/radioisotope seeding layers of snow as they accumulate and then observing/gas chromatographing the resultant mess?

I hope you're colleague gets involved. As I mentioned before, it's easy for my brain to start scattering and lose any semblance of focus. But I'm glad you enjoy my writing. I should add that I'm still very much a student with a lot to learn and a lot of field experience yet to gain. I have little respect for geologists who think plugging numbers into computer models can substitute for fieldwork.

Consequently, I spend a lot more time in the field than some of my colleagues and enjoy the science a good deal more I think. They may not like to get their hands dirty but I love it. I love playing in the mud and dirt, running my fingers over the rouge colored, iron impregnated bones of beasts bigger than a house or examining with a magnifying glass the small, fragile stems of reeds from a Cretaceous marsh or the ferns of a miocene forest entrapped in a volcanic mudflow. In these ways I can feel as well as think about the experience of the earth.

The reason I became interested in your observations is because, while I've spent most of my really short career in the West where oceans were once ubiquitous, the nearest extant one is 1200 miles away. So I've had very little opportunity to observe the things that happen along the coast firsthand. What I know comes from reading mostly.

One time I was standing on the beach at Seaside, Oregon watching the sunset and getting the distinct impression that I was looking uphill. I didn't get that impression further down the coast. I subsequently read that water tends to pile up in the ocean in some locations because of surges or wind or current patterns. I think I may have observed a gentle pile of water that evening. But I've never been back since to confirm it.

Still, I need to understand the processes as they are applicable to shallow, more or less inland, seaways because that's the sort of record I'm looking at in the regions I study firsthand. I'm sort of in a similar situation to the geologists who studied the copper bearing structures in Cyprus. There was a distinct impression that they were looking at smokestacks, however, since smokestacks had never been observed on the seafloor and there was no known process by which they could have developed, the structures seemed inexplicable.

Then scientists using Alvin, the submersible, discovered the things in action on the East Pacific Rise in the Sea of Cortez, the Black Smokers associated with plate tectonic spread zones. So these were the structures observed in Cyprus in what was apparently an uplifted portion of a old spread zone in the ancient Tethys Sea. In effect, the geologists had predicted the existence of Black Smokers before they were discovered, or an adequate theory for their existence could be formulated.

We often observe things in the geologic record that don't appear to occur much in the contemporary world.

The Yellowstone volcano is an active, resurgent caldera that has erupted for several million years at intervals of 600,000 years, the last eruption occurring 600,000 years ago. Consequently, it's quite possible that it will erupt again in our lifetimes with a force never observed in recorded human history. Mount St. Helens would register as little more than a hiccup in comparison. Volcanics from the last eruption are found as far away as south Texas, which should give you some idea of the magnitude of the event.

From an environmental geology point of view, extensive development around Jackson's Hole is tantamount to mass suicide, but I suppose someone has decided it's worth the risk, just as they've decided that building on a hill of expansive clays is economically feasible, especially if you can convince the consulting geologist that the clay just might be altered to a more stable form due to the salutory or hypothetical effects of saltair, saltwater or whatever.

Around where I live, such clays do heavy damage to foundations and literally lift residential structures off the foundation walls. Screw-jack type pillars are typically built into the houses to compensate for the rise of the basement floor transmitted to the main beam holding up the floor of the house, but most homeowners have no idea what they're for and typically enclose them in walls when the basement is finished. Probably a lot of those clays originated as ash falls from the Yellowstone volcano or other volcanos in closer proximity.

An exposure of the Dakota Sandstone near my principle study area shows the ripple marks typical of a tidal flat. There are iguanodont footprints near by in the same layers and small therapod prints as well. There's also a rather large accretion that probably originated when a portion of cutbank fell in one piece into one of the streams that fed the lagoon or marsh and was rolled around in the sands that had accumulated in littoral zone. It's probably a half a meter in diameter. Have you ever seen such a thing forming along the California coast?

Much of the geology I observe in this area then could probably be related to your area now or to New Zealand or Papua New Guinea, the Olympic Peninsula, the area around Mt. Shasta or similar locations. Some of it can't be related to anything extant in the contemporary world, however.

Who could have imagined whole blocks of crust sliding on partially melted granite leaving huge structural valleys in their wakes? Big Hole in western Montana is such a structural valley. It's at least 14,000 feet deep under all the tertiary and quaternary debris. And who can explain the existence of intrusions in central Montana far away from the Idaho Batholith? That batholith apparently caused the Belt Rocks of the Sapphire and Pioneer ranges to slide east out of the Big Hole and other regions, but it's too faraway to account for the Bear Paws or the Little Rockies or the Crazy Mountains among other little ranges in the region. The Cretaceous and Jurassic strata lie nearly as flat in that region as they were when they were deposited.

What was the earth like when 3.3 billion year old basement rocks in the region were metamorphosed? What was it like when a rift opened up approximately along the current Lewis and Clark fault zone giving rise to mountains that eroded and left huge alluvial deposits to the north that became the Belt Rocks 800 million to a billion years ago. They look something like the Morrison Formation, purple and green shales and mudstones consolidated for 800 million years into bedrock, but without vertebrate fossils of course. There was no life on land then as far we know.

What was it like when the world was tranforming itself into something resembling what we see today during the Upper Cretaceous? The sea advanced and retreated, alternately narrowing and then expanding a piedmont inhabited by duckbills and ceroptids and tyrannosaurs. Flowering plants and the insects that help pollinate them coevolved in this world.

And then, abruptly in geologic time terms, the dinosaurs and something like 75 percent of the life on earth were no more, setting the stage for the huge mammalian adaptive radiation of the Paleocene and later, probably as huge as the dinosaur radiation during the Triassic. Speaking of Triassic, why are so many of those formations redbeds? Was there more oxygen in the atmosphere then? No one knows.

I don't know that any of this relates to remote sensing of gas discharges in coastal sediments, but that's a very pertinent hypothesis, as pertinent as any I've proposed. Speaking of gases, the super heated waters in the Yellowstone magma chamber could easily flash into steam hot enough to melt aluminium. It's these steam explosions that make the volcano so dangerous. The earth is an awesome thing, don't you think?

The avalanche process could be tagged as you suggest, but what would be the point? The snow debris would melt leaving a good deal less than a mess to study. That's why I suggested studying the chutes instead since they tend to persist longer. It would be similar to studying floods. I'm still not sure how relevant such study would be to the study of turbidity current or surge precursors. It was just one of my inane brain storms that probably missed the point entirely, but it was worth throwing out to take a little look I think.

I originally questioned you about the structures you observed to determine if I could identify anything similar around here. I don't think I can because I suspect the continental shelf was at least a few hundred miles west of the Colorado Plateau, probably behind the ancestral Sierra Nevada which probably was a large island similar to the islands along the coast of British Columbia today.

But it's very hard to make sense of it. I think it may be one of the few places on earth, perhaps the only place, where a continent has overridden a spreadzone. This unprecedented event may also account for those inexplicable mountains in central Montana, the Rio Grande Rift, the Basin and Range Province, the Black Hills, and a host of other anomalies of the geologic Wild West.

The PencilQueen is in East Anglia, I'm from LA she's Unitedkingdomese: we've never met.

The California coast hasn't been calm enough for anything like that for a good long while. You might see something like that, buried on the western section of our Central Valley, which was one HUGE lagoon. The most easily visible to geology portion of eastern Central Valley is a very uniform but rapid deposition of alluvium from the relatively young Sierra Nevadas. The lagoon like deposits are a mile thick beneath it.

Almost the entirety of CA coast is cliffs, and then step back a little bit, and another set of cliffs when the ocean level was higher, and step back a little bit of flat land again, and a third set of cliffs due to uplift portion of the much larger sideways slide of the two plates. Our littoral is very very narrow.

If you wanted to see what geologists suppose the upper chute of the avalanche looked like, there are a number of drowned-canyon-and-fjordish-like narrow valleys running from Orange County to San Diego which were presumed to be similar in nature to the now-underwater canyons where turbidites are now happening.

I have more on this, but it is time to leave work. I will post more on this tomorrow.

What the sedimentary layers would look like, would be (going inland in from the ocean) turbidite, thin glaucus fine clay, oxidized clay with shoreline valvular critter fossils, well sorted sand with shark teeth, becoming cleaner towards the 'top', coarser well sorted sand, and then a discontinuity (where the former cliff was)to the turbidite layer from the higher sea level/previous fault-caused uplifting. You might find outwash clay layers and alluvial layers interrupting this sequence, depending on the proximity of the source rock to a creek. The outwash layers would be in a gradually thinning flume with a hook pointing south, as the Japanese Current has been shown to be geologically stable and long term. In any case, creeks are much narrower than turbidite canyons, and the alluvial conglomerations are more uniform and have much less angular clasts, so you can usually trace which chaotic layer is due to what.

Because my arthritis prevents me from going out in the field again, I think of the remote sensing answers first-If you've got a hammer, everything starts looking like a nail.

I am wondering, about the squirted-out clay layers that you have found, what is the time frame involved to cause this dislocation, and how would you estimate it? Catching nature in the act is tricky indeed, especially if the timing of these currents detected are random. You never can tell just how random these currents or their causative events are, because oil explorers have economic incentive and possibly are gagged by their contracts to keep somewhat mum or misleading about the whole thing.

The other half of the of the currents seems not so random. The reports you have shown me they do have a good estimate of the uniformity of the current when it happens, and measured of its speed. This makes me think it would be possible to calculate the size of the event and relative thickness of the discontinuity you are looking for when one is looking in the field, so that you'd know it when you see it.

Has anyone speculated about wandering hot spots in Montana? I make two guesses. Either the source for Yellowstone, gradually leaving it and moving in a curve through the plains, or the intrusions left over from the hot spot as it moved toward Y'stone, where it finally found its 'out' within the orogeny, no longer weighted down by the thick deposits of the plains, finally finding a spot where it could to the surface.

I'm not sure of the time frame. I suspect it's like moving a boulder down a creek. It probably occurs abruptly in coarse increments during storms. It's a desert, after all, so nothing much happens between cloudbursts. When enough of the strata has been squeezed out, it breaks off at the slope line and slides down the slope.

I guess you could index it as it's emerging and maybe get an idea of how fast it goes on average.

What you say about the uniformity of the current is probably correct although a difference of only 1/10th of a naut is probably a considerable percentage of the normal current. Also, we don't know for a fact that the currents arise from single events, so what do we look for? A scar or a bunch of little scars in some sort of proximity.

It's likely to be a problem similar to monitoring earthquakes. If you can triangulate something from the current speed and direction observed from two or three stations, it might at some point show where the thing is likely to have originated. Then you can search that location for something large and unique or small and frequent.

Well, if they build those platforms to 'mine' the clathrates or to pump for oil, we will have some ready made stations to do our measurements from.