Ramblings about what I encounter within the realm of the geosciences, as well as the occasional rant about nonsense.

15 March 2008

Back from Hiatus

Well, my laptop bit the dust (in a truly spectacularly soul-crushing way). I learned a few things from the experience: 1. Always back-up not only your thesis in multiple locations, but your grade book as well (fortunately I was able to recover all my necessary information), 2. Laptops will always die when you are too busy to allow for the inconvenience, and 3. The department laptop runs Windows 98! and as such, cannot use USB drives easily. This calamity (to me at least) coinciding with Spring Break and interviewing grad schools led me to think (again) about extinctions while I was on my somewhat forced hiatus.

Speaking of a hiatus, I recently read this article on the potential of a depositional hiatus to mimic the appearance of a catastrophic (in this usage I mean rapid [by rapid, I have no idea how fast that actually would be. But faster than gradual, which again I have no idea how fast that would be]) extinction event.

Norman MacLeod and Gerta Keller (of Chicuxlub is too early fame) got this article published back in 1991. This is basically a study that applies the Signor-Lipps effect on real-world data, rather than on the initial "thought" experiment (Signor and Lipps didn't really have an experiment so much as just no data, but they had plenty of reasoning skills. Hence why I am dubbing it a thought experiment). MacLeod and Keller have decided to use deposition in the oceans spanning the end Cretaceous (end-K) event. They are examining the appearance and extinction of the foraminifera that have been used in deep-marine settings to infer a cataclysmic extinction event in the marine realm which coincides (approximately) with the demise of the dinosaurs.

Their findings are quite interesting. Basically when you have more constant deposition, the extinction of index forams that supposedly mark the end-K event continue much further into the Tertiary. They are using the Haq curve from Haq et al. 1987. Which states that the lowstands ends just before the end-K event and a sea-level rise was beginning. This would cause a hiatus in deep-sea sedimentation. And while I find this a good application of Signor-Lipps, I am always cautious of global sea-level curves (but that may just be me).

It is also interesting to note that when we discussed this as a part of our journal club, we spent most of the time trying to understand figure 2. Near as we could figure, they used time on the x-axis (by using rock as a measure of time, there are problems with this idea) and the amount of time an individual taxa has existed on the y-axis. We were not at all convinced of this interpretation, but after turning the diagram over in our heads for almost the entire club meeting, we moved on. I am curious what anyone else can make of it.

MacLeod, Norman, and Keller, Gerta, Hiatus distributions and mass extinctions at the Cretaceous/Tertiary boundary: Geology, 1991 19:497-501 (via geoscienceworld.org subscription required)

Haq, B.U., Hardenbol, J., and Vail, P.R., 1987 Chronology of fluctuating sea levels since the Trassic: Science v. 235, p.1156-1166.
(subscription required)

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All the Latin on this page is from my vague recollections from High School. There are mistakes in the text. I just was trying to get the point across

Between Los Alamos,NM and White Rock, NM

Between Los Alamos,NM and White Rock, NM
The photo of the travertine spring was taken in the small opening in the center of the image.

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