This week’s discussion paper :
Angiolini, L., Gaetani, M., Muttoni, G., Stephenson, M.H., Zanchi, A., 2007. Tethyan oceanic currents and climate gradients 300 m.y. ago. Geology, 35(12), 1071-1074.
Angiolini et al. (2007) are using many of the principles that we discussed on Tuesday, related to paleogeography, to attempt to explain the fossil assemblages that the authors have found in Iran. Let us know what you think of the paper. Below are a few questions to guide your discussion.
- Given that the paleomagnetic discussion in Angiolini (2007) contains jargon that we may not all understand, how solid do you feel that the paleogeographic reconstruction is? What issues might arise from this?
- It is easy to get lost in the weeds with terminology presented in this week’s paper. Without worrying too much about brachiopods and statistics what is the study of the fossil record trying to show in this particular study? How convincing is the authors’ story?
As always, if there is something that totally blows you away, or leaves you more confused than you ever thought possible, feel free to post your thoughts and questions, so that we may be able to address these things in discussion on Thursday.
I personally have a hard time understanding the concept of paleomagnetism.
ReplyDeleteFig. 2 seems to be the main result with Fig 3 somehow a statistical representation. Fig 2 with a little better map construction might be very insightful, but as it is I am not getting much out of it.
The article was difficult for me to digest in the first read, but going through it again a little slower and attempting to understand the abstract after reading the article helped a lot.
At first I thought the Tethyan was a time period and the article was attempting to reconstruct all the ocean currents to understand all climate gradients 300 m.y. ago. After rereading it I understand the focus of the paper a little better, but am still pretty confused about the findings especially related to climate gradients.
I agree figure 2 is kind of a hard thing to read, but I think all it is trying to show are the bioprovences, the glaciers to the south, and the temperature (in relation to currents and organism). All it says to me is that there are many cold living organisms and cold currents to the south of the 30 degree S. mark, and some worm living organisms and warm current just to the north of the 30 degree S. mark. It seems this way because it is stated in the article that some of their supporting evidence is the diversity of the fossil record of the organisms.
DeleteAlyse: I found some mention of facies, braciopods, etc. in an article Devonian/Lower Carboniferous stratigraphy, facies, patterns and paleaography of Iran Part II Northern and Central Iran by Jobst Wendt, Bernd Kaufmann, Zdzislaw Belka, Noor Farsan, & Alireza Karimi Bavandpur. Acta Geologica Polonica, Vol. 55 (2005), No. 1, pp. 31-97.
Deletehttp://www.uni-graz.at/bernd.kaufmann/Wendt_Iran%202.pdf
Man, I agree the map could use some labels.
ReplyDeleteAlso, I have some questions that are maybe pretty basic but I couldn't find the answer to them:
Why do plates change direction? Only when a pressure underneath a big continent builds up enough to break it up? Also, is a major breakup the only time that new plate boundaries form?
When a craton becomes stable, does the plate stop moving? does the oceanic crust underneath keep slipping from under the continental crust? (otherwise mountains would just continue to rise indefinitely, or orogens be produced around it indefinitely, right?)
I'm not sure about all of your questions, but in EPS105 I learned that the crust spreading is constantly going on and that mountains are constantly being built. A good example of mountain building in response to subduction as a result of crust spreading is the Cascade range in California and Oregon. Mt. Hood in California is a place where subducted crust is rising as magma into an active volcano range. Mountains don't appear to get higher most of the time because weathering happens more quickly on minerals that have formed at high temperatures and pressures because of the atmosphere and oxidation at the surface which causes them to stay about the same height and freeboard. Freeboard is a complicated theory that says there is thicker crust under continents than under the ocean because of density. Hope that helps some!
Delete-Jayda Patterson
Good questions that makes me better appreciate the complexity of climate every hour I read about it...
DeleteJayda Patterson
ReplyDeleteI think I understood how the researchers determined the probable locations of prehistoric life and magnetic shifts in relation to each other to determine where the current continents were in relation to each other 300 M.Y.A. It appears that the research team took the evidence of the magnetic lines in combination with the fossil evidence and put the continents and landforms together to create a single land mass kind of like a jigsaw puzzle. The following seemed strange to me : “This Tethyan surface current system and the associated narrow zonal barrier show similarities to recent glacial climate patterns.” (Angiolini et. al. 2007.pp1071) because it seems only to suggest that there were two polar ice caps at the north and south poles in the paper, not that there was one single super continent. The laws of physics dictate that matter is neither created nor destroyed and that two objects cannot occupy the same space. It is obvious that the ocean crust is new spread covering thin layers of rising mantle. Any new crust must be replacing old crust which is evidenced by subduction of the Nazca Plate, Pacific Plate, etc. Because of pressure and increasing continental crust thickness as freeboard increases the density goes up over time and when it hits a critical mass it sinks into the less dense mantle and re-melts as pressure is let off. If there were a thick ultramafic continent it is probable it would have subducted completely by now because the density would have been immense compared to today's much less dense and more felsic continents. Primary crustal formations would be gone now simply because the density would be too great on today’s earth. It seems plausible to think there should have been two or more massive continents, which have subducted. It seems like only two or more continents would cause the two polar ice caps (common to all planets in our solar system starting from at least earth and continuing as a pattern in rocky bodies as far out as the moons of Jupiter) to create a weather pattern like what is experienced on earth today as opposed to a constant storm or something. Is that the case or could it be possible to have similar weather patterns no matter how many continents there were and how far the ice sheets extended?
Thanks,
Jayda Patterson
Angolini et al. Tethyan oceanic currents and climate gradients 300 m.y. ago . Geology, December 2007; v. 35; no. 12; p. 1071.1/24/2012;8:45PM. http://ereserves.unm.edu/eres/coursepage.aspx?cid=10733&page=docs
The article itself was actually very insightful to me. I personally liked their methodology. Jayda mentioned in her statement all the details of what the scientist did, so I will not get into the procedure, but I really liked that they took the time to explain where there was potential variability in their data. It seemed like a complete idea that was tested to the best of the scientists’ ability, and it was done in a logical way. I don’t know a whole lot about paleomagnetism, but it seems to me that the predictions about the difference in climate could hold water. The experiment, if nothing more, gives a foundation for future advancement on the question at hand.
ReplyDeleteOverall, I thought the author’s story was pretty convincing. I mean in looking at brachiopods it gives a strong sense in how the climate was during a certain period of time. Also using brachiopods helps to re-create the overall position of continents because they usually indicate a shallow marine environment. Therefore, we can infer that these fossils would have been along coastal regions of the continents. Then if you add in climate sensitivity as another factor we can understand how paleogeography may have been. I felt like the authors made complete sense in the reconstruction of the paleogeography. I mean it provides evidence that the theory of plate tectonics should no longer be theory but rather a fact of geology.
ReplyDeleteIn science the term "theory" does not reference what a theory would mean in normal conversation, that would be "Hypothesis". A theory in scientific terminology is essentially very similar to a fact, it is a hypothesis that has proven so bulletproof that it has been accepted as a scientific reality. See also theories of gravity and evolution.
DeleteAlyse: I also was struck by the use of "theory," but after reading your post I went back to find it, and failed. Perhaps the subject paper "Tethyan ocean currents..." is a validation of the use of "integrated paleobiogeographical-paleomagnetic approach for modeling the past on a global scale.
DeleteI don’t know if this forum was meant for this, but here is a breakdown of what I got out of the article, and if I am mistaken please correct me.
ReplyDeleteThe point: to figure out the general climate at 300mya, specifically explaining the stark different in fossilized biota found in Northern Iran and places at only a slightly higher southern latitude like central Afghanistan.
Conclusion: a very small belt of warmth existed around the equator at the time, along with an ocean gyre circulating from equator down to just above central Afghanistan. Warmth ended at the edge of the gyre, thus the stark difference in temperature just below the gyre.
Methods:
1. A map of Pangea was constructed from paleomagnetic data and previous studies (irving 1977)
2. 10 geographic operational units (OGUs) (basically geographic regions?) were determined in the Gondwanan Realm. These area were separated into groups determined by the similarity/difference of biota fossils found in them.
a. How: 71 species of brachiopods were found in various OGUs. Brachiopods species found in only one OGU or in all OGUs were removed (because they were irrelevant to finding similarities between OGUs).
b. Statistical methods were used to plot a graph showing those OGUs with the highest percentage of similarity (?)
3. Since biota found in Iran was most similar to those found in the (equatorial?) regions of the Urals and Yukon, similar climate was inferred.
4. Recent analogs of climate patterns led the authors to conclude that a warm current existed there, as it explains the found data.
Questions:
Why use a scatterplot as the chosen representation of OGU similarities in species found?
Couldn’t leaving out all data from Laurasia (particularly species found there) be detrimental? Wouldn’t comparing the Ural-Yukon-North Iran species to those is similar northern latitudes be useful? Or is it unnecessary?
How does one determine whether a fossil (brachiopods in particular, little bivalve guys similar to clams) once lived in warm or cold climates? I understand how that would work for plants, but plant data was not what was used…
Alyse: Danika I found your review very helpful; unfortunately I have no answers to your questions. Hopefully, we will have a biology lecture to give us a foundation about this facet.
DeleteThis article was pretty difficult at first glance but I now understand their methodology and it seems solid. I did have one simple question and it might be because I'm somewhat new to the field of geology but they mentioned a Pangea B and I was assuming that meant there may be another version of Pangea?
ReplyDeleteRebecca Camden
I'm sure theres a whole slew of Pangea models floating around the scientific community, but I'll look around and see if I can't scare up a list of them somewhere.
DeleteSo I know its not exactly pristine science, but the best thing I could find on this subject was a wikipedia list of past supercontinents. Its possible that at some point a few of them were listed as Pangaea A/B/etc. Another possibility is that Pangaea A/B might be referring to the past Pangaea and the predicted future Pangaea labelled "Pangaea Ultima". This was all I could find on the subject in a few minutes of searching.
DeleteList of supercontinents here: http://en.wikipedia.org/wiki/List_of_supercontinents#Prehistoricals
I like the tenacity Connor. And Rebecca I think you are on to something... The fact that there is a B anything must mean that there is an A? (there is!) and that tells us what about the certainty of their reconstruction?
DeleteGood question. I was wondering about this too. Rebecca, I think you're right - there seem to be different competing reconstructions of Pangea paleogeography. I didn't find much of an authoritative source, but check this out for a visual and explanation. Scroll down for the different A/B representations.
Deletehttp://www.brynmawr.edu/geology/Research/Tectonics.htm
This weeks reading was viciously complex at parts where it delved into complex methodology, I had to just avoid focusing on the precise terminology/calculations in order to keep my head above water on this one.
ReplyDeleteHowever, I did like that they used a wide variety of sources for their data, using multiple sites and varied methods of data collection to get their results. It was a refreshing change from last week, when I was dubious about the less diverse sources of data from computer modelling.
Anyone see my question re: magma composition? I don't see it here... I posted last night - did it get deleted? I was wondering whether there is a functional difference (at least for our purposes) between the mentioned magmas in the paleomagnetism text: andesitic, granitic, basaltic. Are these important distinctions to make?
ReplyDeleteAlyse: I haven't seen any question on magma composition. I believe, but do not know, the distinctions between magmas are of particular interest to corporations seeking oil, uranium, rare metals....:)
ReplyDelete