Monday, February 2, 2009

Standardizing Sequence Stratigraphy - Are We Still Talking About This?

I'm sure everyone, at some point in their career, develops a bit of a stereotypical view of certain kinds of geologists. You know what I mean; you had a geophysics prof once who was ridiculously quiet and nerdy, or you took a class from a structural geologist who was a white-hot ball of rage. And now, everytime you meet a geophysicist or a structural geologists, you've always got this little niggling suspision that they are they're going to act the exact same way. Part of this might be reinforced by the literature, too; take a look at papers about the Heart Mountain Thrust, and tell me that structural folks don't seem a little...on edge.

I suspect that people might develop a similarly unflattering view of stratigraphers. Specifically, they might decide that we are a bunch of contrarians who can't seem to agree on anything. I mean, we tend to argue about the same things (like eustasy) over and over and over again, with little apparent progress. And frankly, I blame sequence stratigraphy. Ever since AAPG Memoir 26, the sed/strat literature has been rife with arguments, nomenclature, arguments about nomenclature, and discussion on the nomenclature of arguments.

Anyway, just in case anyone was getting worried that things might be quieting down, Octavian Catuneanu and twenty-five others recently published an article titled: "Towards the standardization of sequence stratigraphy" in the journal Earth-Science Reviews! Thank Goodness! Things were getting to quiet around here!

This paper seems to be the summation, in a peer-reviewed venue, of a running gun-battle that Catuneanu et al. have been having with Ashton Embry and others. This terminological war has been documented on the USC Sequence Strat website here, and makes for some entertaining and enlightening (for a variety of reasons, not all scientific) reading, though I suspect beer would help to get you through it all.

Fundamentally, the argument of Catuneanu et al. (2009) is this: sequence stratigraphy has become a very important part of modern sed/strat life. As such, there should be some sort of accepted, formalized rules regarding its deployment and use, thereby allowing us to more effectively communicate our chronostratigraphic work to one another. Importantly, Catuneanu et al. (2009) advocate the formalization of a seq strat framework "sufficiently flexible [to] accommodate the range of likely expressions" of sequence straigraphically important units and bounding surfaces (Catuneanu et al., 2009, p. 1).

A lofty goal, and maybe even an important one. It is true that there exists considerable confusion in the seq. strat literature about what constitutes a "Sequence", and how best to define AND interpret it. However, I have some questions regarding Catuneanu et al.'s approach.

Catuneanu et al. (2009) recognize two facets of the sequence stratigraphic paradigmm, which they identify as "model-independant" verus "model-dependant" aspects. I think the nomenclature here is a little confusing, however. What Catuneanu et al. (2009) mean (I think) by model-independant and -dependant is in regards to INDIVIDUAL uses of sequence stratigraphy. In otherwords, model-independant aspects of the sequence stratigraphic paradigm are those things that everyone agrees on. Model-dependant aspects vary between different practioners. I've reproduced Catuneanu et al's Figure 10 (from Page 8) below, where this dichotomy is illistrated:

Take a gander at that figure, paying particular attention to the "basic concepts" section of the Model-Independant box. I think this is where we are going to get ourselves into trouble; this is the fly in the ointment, the monkey in the wrench, of so many stratigraphic discussions. What is it, you ask?


Briefly, baselevel is a theoretical, undulating surface that defines relative aggradation or degradation across an earth-surface profile.

OR it is the graded profile of a river.

OR it is sea level.

Brian has an excellent summary of Wheeler's baselevel concept , which you should all go read if you havn't already (the fact I'm linking to it sort of gives away my bias as to what I think baselevel is). Anyway, the baselevel concept is probably one of the most contentious issues in stratigraphy (probably needlessly, but there you go...), and the way it is discussed by Catuneanu et al. (2009) is frankly a little schitzophrenic.

The salient point of the argument about baselevel boils down to the fundamental question of whether baselevel controls sedimentation or erosion by modelating equilibrium surfaces, or whether baselevel is the result of modulations in equilibrium forces dictated by the changing conditions of sediment supply and transport energy. Simplicitically, these can be defined as "geomorphic baselevel" for the former, and "stratigraphic baselevel" for the latter.

Catuneanu et al (2009) start of promisingly enough, citing Wheeler, Barrell, and Cross and Lessinger papers, and discussing the way baselevel plays an important role in the chronostratigraphic paradigm. But in the same sections, they discuss baselevel in terms of sea level fluctuations, and how baselevel for some river systems should be replaced with the graded river concept, effectively conflating geomorphic baselevel with stratigraphic baselevel without neccessusarily distinguishing the two.

The discussion is not purely academic, either. The baselevel concept has a fundamental role in underpinning correlation strategies, and very different ways of looking at strata come from the different ways people use the concept of baselevel. Especially in the nonmarine realm, there are fundamentally important ramifications for interpeting stratigraphy or modeling forcing functions in the rock record that rest soley on how baselevel is used. It's a big deal, folks!

And the fact that Catuneanu et al. (2009) place "baselevel" in the "everybody agrees on it" bin in Figure 10 (above), makes me question whether the time is ripe for a standardized sequence stratigraphy. There still are basic questions about the "How" and "Why" strata are preserved that have yet to be answered, and the answers will have very important implications for the way we do chronostratigraphy. Baselevel stands out, because it is such a contentious issue already, but there are other fundamentals of stratigraphy that still need to be resolved before we start talking about standardization. We have a lot of arguing ahead of us. Which is good! Really it is!

Just be patient with us, is all I ask.


Catuneanu, O., et al., 2009, Towards the standardization of sequence stratigraphy: Earth-Science Reviews, v. 92, p. 1-33.


Callan Bentley said...

"White hot ball of rage"??!!

Why dagnabit, that's the most infuriating thing I ever heard! You stratigraphers have no idea what we structural geologists have to go through, and how ridiculously messed up our rocks are! Grrr! (throws eraser)

-- Mr. Structural Geologist :)

Mathias said...

During the Latinamerican Geological Congress in Lima, Peru, last year Catuneanu gave an interesting presentation exactly about this matter. He already announced that a paper was to be published about the standardisation of seqstrat. This is it. I didn't read it, yet, beyond the abstract and looking at the nice diagrams. So I am unable to actually comment it. From my personal experience so far with seqstrat I would greatly appreciate if an agreement on the standardisation would finally be reached. It's a tool for me, nothing more, that sometimes helps with stuff like I write about in my SeqStrat & Industrial Minerals series. I'm not a stratigrapher neither involved in the developments. But as said. It is a tool and as with other important tools like screw-drivers, nails, power-plugs it would be extremely useful to know other people use the same tool as I do - and not just a similiar tool with the identical name. Because then, like you said, we'll get into trouble.

Silver Fox said...

Perhaps sequence stratigraphy is a bit like a scientific revolution (ala Kuhn) in the strat/sed world - in which case, like plate tectonics, it will just take a bit of time.

Callan, I didn't know you were a structural geologist. Stop throwing those erasers! ;)

Eric said...

Callan - c'mon now. You've met the structural geologist at Montana State U...tell me that's not an accurate description :)

Callan Bentley said...

Now, the individual to whom you refer is a HILARIOUS white hot ball of rage, and that's TOTALLY who popped to mind when I read that line. It's a perfect description of said individual -- and it keeps it might entertaining hanging around with him. He's a character!

Anonymous said...

Great post ... I'm glad to see Catuneanu's paper is out ... he's been giving this talk for a few years now.

I don't think a true "standardization" is achievable ... at least in terms of a standardized application. Those desiring an easy "cookbook" of how to apply seq strat should not think of it as such. It is a conceptual framework for approaching stratigraphy ... not necessarily a plug-and-chug workflow. In some cases it can be relatively straightforward, but in other cases, it creates more questions than answers (which is good from a scientific perspective).

That said ... I do welcome discussions within the community to attempt standardization because it makes us think about the concepts, re-test them w/ new data, re-evaluate them w/in the context of more recent ideas, and so on.

Finally, stratigraphy is awesome.

saxifraga said...

Interesting post. I downloaded and printed the article last week, but haven't gotten around to read it yet. Now I'll probably be more aware of the controversial parts. I agree with BrianR in that I don't think it will be possible to reach a one-size-fits-all system for sequence stratigraphy. I think it is a framework for developing ideas as much as a tool. Although, I do encourage development of a common terminology, I actually think more would be gained by doing new innovative studies of rocks than by battling over sequence stratigraphic definitions.

220mya said...

For the non-stratigrapher, sequence strat can be very frustrating given the proliferation of terms that don't necessarily have the same meaning to everyone. In that respect, I would welcome standardization of at least the nomenclature.

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