Conglomeratic intrusions

Okay....this is another long post....maybe too long, but oh well.

A former fellow student (now professor), me, and our adviser have a paper out this month characterizing some very unique sedimentary features in Cretaceous strata of southern Chile: conglomeratic injectites.
Clastic intrusions, now termed injectites, have been recognized for a long time. In some cases, they resemble igneous intrusions (dikes, sills, etc.) with respect to their geometric relationship to the surrounding rock.

What are injectites?
They represent the violent remobilization of typically coarse sediment like sand due to over-pressurization. The best visual I can give you is imagine that you could press down on a jelly donut that was somehow sealed along the sides. That is, the jelly does not squeeze out of the side when you put pressure on it from above (overburden). Now imagine some plane of weakness in the fabric of the donut above the jelly layer. The overburden pressure will force the jelly into that plane of weakness and upward. If the movement of the jelly is of sufficient magnitude it will bust its way through the donut, creating its own path, and perhaps erupting at the surface of the donut.

Coarse sediment (usually sand) that is deposited in deep-marine settings is a mixture of sediment and water and it takes a while for the deposit to slowly de-water. If the sediment accumulation rate is high enough -- that is, if these water-laden deposits get buried relatively quickly by more sediment this layer becomes the "jelly". The increasing overburden pressure combined with some sort of trigger (seismicity? a threshold?) creates a situation for this large-scale injection to occur.

What's cool about our study (at least we think its cool) is that we have (1) a great outcrop example of this phenomenon where the features are explicitly exposed and (2) the injected material is very coarse -- cobble-sized material.

Now, we'll be the first to admit that this paper is not high science. We literally came across these features and spent a few days mapping them out and characterizing them. There's only so much time in a field season and we had other tasks to accomplish. So, this paper is very descriptive in that way...that is, we did not take it to the level of really figuring out how these things work. The mechanics of clastic injection is not well understood.

Because injectites are associated with thick piles of sediment they are being found by oil companies exploring for hydrocarbons in the subsurface. In fact, one hypothesized mechanism for contributing to over-pressurization is gas charging. Believe it or not, there is an entire book about the occurrence of clastic injectites and their relationship to petroleum systems. This paper is in that book. We were happy that the editors really wanted this stuff in there since we weren't sure where else it would ever get published. Take it when you can get it!


Okay...enough set up....here we go.

The figure above is the location information. I've said in the past that I would put together a post about the general geology of the area i've been working in Patagonia....I still mean to do that....someday. As always, click on the image to get a higher resolution view. The study area, Cerro Benitez, is in the center of the satellite image at right. These Cretaceous strata are part of the Magallanes foreland basin and now nicely exposed in the foothills of the southernmost Andes.

The photos above show some of the close-up characteristics of these conglomeratic deposits. Notable are the near vertical groove-like features in F and G. By themselves, however, these small-scale features are not very telling.


This next set of photographs (above) takes a step back and shows the conglomerate bodies in their full glory. The one shown in A and then enlarged in B is particularly nice (note circled person [me] for scale in each). When we first came across these features we thought the juxtaposition of the conglomerate against the shale had to be a fault contact. It's not...we mapped the entire area. Then we thought these were some kind of channelized deposits, but the geometries were just not working out. When we spent a few days mapping out the multiple bodies and their relationship, an interesting picture emerged.


The last day of characterizing the injection complex, we hiked to the other side of the lake and climbed up a mountain to take the photograph above. We felt we needed a view zoomed out even more....it took a day to get this photo....not the first time we spent a day to get a photograph down there. In the corresponding drawing below the photo, the yellow is the "regular" conglomerate bodies (referred to as stratified conglomerate) and the dark brown denotes the injected conglomerate. The cool part about this outcrop is that the old glacial lake created a flat terrace (shown in lighter gray) between two more vertical slices of the stratigraphy (shown in the dark gray). So, it's sort of a "chair" display if you can visualize it. This little bit of three-dimensionality helped immensely in mapping out the different bodies.


The schematic cartoon above (or, as the first author Steve likes to call it, the geophantasmogram) attempts to summarize the outcrop and how we've mapped it. Again, note the "chair" set up. The injectites emanate from the side of the channel-fill deposits, which is a pattern seen in injectites in the subsurface over and over again. Also, note the left complex on the diagram bifurcate and then head up through the strata until they terminate. The photos above with me for scale is the right branch of that bifurcating complex. The very ends of those injectite bodies lack conglomerate and are instead only sand reflecting a "fining-away" trend. That is, the "flow" of material had to come to a stop at some point, and the brief slowing down before stopping was enough to sort the material being carried.


The last thing I want to touch on is the scale of this injectite complex compared to other known and well-studied examples from the subsurface. The figure above (which is the bottom half of the geophantasmogram) shows the cross-sectional outline of the injectite complex we characterized with some that have been mapped using seismic-reflection data in the North Sea. Firstly, notice the "winged" appearance of nearly all of these examples. Secondly, the bottom line is -- our complex, as big as it seemed, is a tiny little sucker. For example, note the small rectangle on one of the little nubs in D. That rectangle represents the size of the complex we characterized. These North Sea injectite complexes are friggin' HUGE! It kind of blows my mind.
Anyway, i'm gonna cut myself off....this post is already ridiculously long. If you'd like to know more about the nitty gritty, please feel free to comment below or e-mail me at romansbrian AT gmail.

Why is this lady so against conserving energy?

Click here to read a short interview on CNN.com with a woman named Trilby Lundberg. She is the publisher of the Lundberg Survey, a survey of United States gasoline prices quoted regularly by news outlets and others.

The beginning of the question-and-answer report has some interesting insight and remarks about the complexity behind what determines the actual price at the pump. And then she says a few things regarding the outlook for fuel costs in the near term future (next 5-10 years) and the role of alternative fuels.

This is all fine and good. There's a few things I would quibble with and maybe disagree with, but no big whoop.

But then, the questioning turns to the notion of energy conservation. I'm just gonna clip the whole part here, as it is worth reading.

Q: As far as conservation, what are the trends you are seeing?

A: I'm hoping that consumers will see through the rhetoric about consuming less, demanding less, as faulty. It is not a given that consuming less will be good for our economy or for our personal freedom. It is not even established for our environment that we [should] deprive ourselves of gasoline for our personal mobility as well our commerce. And to suppose that it is good to do that, and pretend that we have consensus and put our heads together to deprive ourselves of this great product that makes the country go around, commercially and individually, I think is flawed. I'm hoping consumers and voters will see through that and be able to ignore some of the most extreme suggestions.

She then, of course, goes on a little diatribe about the great hoax of global warming. But, I don't want to focus on that here. What really floors me is this attitude that conserving energy means depriving ourselves of it. This is so illogical and I just don't understand it. Yes, I agree...it is a product that makes the country (and the world for that matter) go round. Shouldn't that be reason #1 to conserve it?! Why are some people so anti-conservation? I simply do not get it. We can be a nation of economic prosperity and continued high quality of life AND be much more energy efficient. It's not all or nothing....that's the biggest bunch of malarkey.

Whatever happened to the idea of a "penny saved is a penny earned"? The generation of Americans who actually lived through the Great Depression and had to conserve are all but gone.

And then there's this gem at the end.

...taking into account the many, many millions of people around the world that envy our way of life, it would seem more humanitarian to wish them the kind of plentiful petroleum products and vehicles ... that we enjoy ... to lift themselves out of [a] backward, poor way of life

Right.
Wake up to the 21st century, lady.

End of Suburbia

I recently watched the documentary End of Suburbia and, inspired by Thermochronic's comments on gasoline prices, I figured it was a good time to post my thoughts about the film.

This documentary is essentially about Peak Oil, which is the notion that we are very close to producing half of the Earth's oil reserves (if we haven't already). What this means is that once we hit that peak, production will decline. Couple this decline in supply with an increase in demand over the next half-century and we have a recipe for global disaster...so say the most adamant peak oil theorists.

I'm not going to spend time on this post discussing peak oil as such. If you don't know much about peak oil, it behooves you to learn a bit about it before watching End of Suburbia. There are differing viewpoints from petroleum geologists as well as economists regarding the validity of global oil production being described by a bell curve, but let's save that for another time. So, for the rest of this post, i'm going to focus on the film.

This film discusses the theory, evidence, and implications of peak oil within the context of the American suburbs. This is what I like about this film. The information and commentary regarding this issue are woven into a narrative about the origin, rise, and predicted demise of the suburban landscape. Instead of a boring encyclopedic presentation of what peak oil is and what it means, the creators of End of Suburbia asks a key question: Is suburban living sustainable? The subtitle of the film is Oil Depletion and the Collapse of the American Dream so you can probably guess what they think the prospects are.

The American suburbs evolved from the combination of post-WWII prosperity and the rise of the affordable automobile. That is, everyone can have a car. Why? Because cars are relatively cheap? That's part of it for sure, but more important in this equation -- cheap and abundant fuel to run the cars. They do a great job in the film of emphasizing the underlying issue of peak oil: it's not about running out of oil in an absolute sense...it's about running out of cheap oil. It is an economic as well as geologic issue.


So, fast forward from the prosperous and enthusiastically pro-capitalism 1950s to the turn of the century. We now have a situation where many people drive over 100 miles a day to commute from their unnecessarily large (and poorly constructed) home in the suburbs to their place of work and back. The original suburbs of the 1950s/1960s feel like the inner city compared to these 'exurbs' that are far out on the fringes of a metropolitan area, the so-called suburban sprawl. These areas are designed around the automobile. This is the only way to get around. You know these places...we all do, that's where you can find Target, Chili's, Best Buy, and all the other mega-stores. Try being a pedestrian in this environment and you certainly risk your life.

So, now as Americans are feeling the effects of more expensive fuel it is getting more difficult to sustain this lifestyle. The film does a great job of painting a rather bleek picture of the future of this kind of life. Like most documentaries, End of Suburbia includes a combination of narration that presents the information and interview clips with various people for additional information and commentary.

The last part of End of Suburbia takes a turn from the thesis of a doomed civilization to more optimistic thoughts. They discuss the ideas of people returning to urban settings, sometimes referred to as 'new urbanism', where most of what residents need for everyday life is within walking distance (or at least a much shorter trip on public transportation or car). The filmmakers also touch on the idea of buying locally grown and produced goods to cut down on the ridiculous distances the stuff we buy and consume is transported (why do I need an apple from New Zealand in California?).

Personally, I loved this film. I was raised in American suburbia and didn't think about what it actually was and how it was set up until recently...that is what I knew. For me, these kinds of films (or books, essays, websites, etc.) are important for my own education and awareness.

Call me a pessimist, but I tend to think that it takes significant events to produce significant change. Will we need to experience a Great Depression II to collectively change our ways? I hope it doesn't come to that, but I fear it will. The best-case scenario in my opinion would be continued high fuel prices to wake the public up to the realities of our energy situation. I have set up my own lifestyle to anticipate the future higher gasoline prices (i.e, buying a high-MPG car, having only one car for two of us, taking the commuter train as much as possible, living in a neighborhood where we can walk to the market, taking the bus when we can, etc.).

Check out the trailer to End of Suburbia and then rent it.