Thursday, September 26, 2013

Hunting The Elusive K-T Boundary...

My wife and I are back from our great trip to Wyoming, Montana, South Dakota and Colorado.  Usually when we travel, I let her make most of the decisions on where to go and how long to stay at each stop along the way.   But, this time, it was my trip!  So with some compromises with her, we did many things that she would not normally choose to do.  What we had in my favor, however, was the gorgeous and interesting scenery and other sights of parts of the northern Rockies and the northern plains.

My last two articles (Noreen Firearms and the Yellowstone Supervolcano), while both of interest to me, were not the expected highlight of the trip for me.  What I really wanted to see was the somewhat famous "K-T Boundary", a seldom seen rock outcrop (complete with iridium-rich sediment) that marks the end of the Cretaceous Period (from about 145 to 65 million years ago).  The Cretaceous was the last period of the Mesozoic Era when dinosaurs ruled the Earth (including the famous Tyrannosaurus Rex, as well as the familiar Velociraptors (both the Tyrannosaurus Rex and Velociraptors were in the movie "Jurassic Park"), also living in the Cretaceous was the Triceratops, more information the Cretaceous period and its flora and fauna is here at wikipedia: http://en.wikipedia.org/wiki/Cretaceous_Period.

This article hereafter is divided into two parts, the first part just below (finishing with the map) is slightly technical and explains more about the K-T Boundary and includes snippets and a map from an important paper on the subject.  The second part (after) describes our details (and pictures) of hunting the elusive K-T Boundary in Wyoming and South Dakota.

***

It is pretty well accepted now that the Cretaceous ended with a mass extinction probably caused. at least in part, by the approximately 6 mile diameter meteorite/asteroid that hit the Yucatan Peninsula some 65 million years ago (the "Chicxulub Crater").  There is ample evidence of dust and ash that were blasted into the atmosphere and later to settle all over the world (or at least the Northern Hemisphere).  The most commonly cited evidence is the "K-T Boundary" (Cretacous - Tertiary), but the stratigraphers (geologists who specialize in layers of rocks) now use the term "K-Pg Boundary" (Cretaceous - Paleogene Boundary), but it is still better known as the K-T Boundary.  Here is wikipedia's discussion of the K-T Boundary: http://en.wikipedia.org/wiki/K%E2%80%93Pg_boundary

The fossils before and after the K-T Boundary are completely different!  It is believed that some 25% - 50% of the species of land animals became extinct (different sources have different figures).

The K-T Boundary itself is typically seen (where the dust settled on land) as a this black and white layer (usually between 1 cm and 2.4 cm thick) all over the world where good outcrops exist.  Over 100 such sites have been located, some of which are under the ocean now (but were on land when the impact occurred, the K-T Boundary was found when analyzing offshore drilling cores).  What is special to me is the very high amounts of Iridium (a platinum group metal, second densest metal that exists).  There is between 60 and 1000 times more iridium in the K-T Boundary formation than in most other rocks in the Earth's crust.

Here are the Conclusions from an excellent paper (that states that the authors, among others, were preparing a worlwide database on the K-T Boundary, in 2002): http://we.vub.ac.be/~dglg/Web/Claeys/pdf/Claeys-etal-02.pdf, by Phillipe Claeys, Wolfgang Kiessling and Walter Alvarez (the last a geologist who is famous in this niche), these Conclusions are with a gray background:

CONCLUSIONS

1. There are 101 K-T boundary sites (some representing multiple outcrops), all over the world, that contain ejecta debris.  This represents nearly 30% of all the sites entered in KTbase.  Of the sites that contain latest Maastrichtian and earliest Danian biozones, 15% (i.e., more than 50 sites) have not been investigated for ejecta material.

2. K-T sites formed in shallow-water depositional environments are more commonly considered incomplete in terms of ejecta debris than deeper marine ones.

3. KTbase does not support a global regression at the K-T boundary. The hypothesis of a K-T regression stems in parts from the misinterpretation of impact-related coarse clastic or debris-flow units deposited in the Gulf of Mexico region. These coarse sandy units do not represent a transgressive sequence tract overlying a sequence boundary and are not related to a K-T boundary sea-level change.

4. The Chicxulub impact affected sedimentation within the Gulf of Mexico region and the Atlantic, probably all the way to offshore Portugal. This effect is reflected by the presence of coarse clastic units and/or breccia in deep-water settings and/or by the erosion of Upper Cretaceous sediments from depositional settings usually not prone to unconformities. The precise sedimentological mechanisms are not fully understood: for
example, it is not clear if debris flows are created by the seismic wave or ground shaking or by the tsunami waves generated by the impact. It is also possible that in some places, massive debris flows generated tsunami waves. Most likely all these processes acted together, leading to the chaotic sedimentation and
erosion occurring at or near the K-T boundary in the Gulf of Mexico and the North Atlantic.

5. The positive Ir anomaly has been recorded at 85 sites and appears to have been spread homogeneously all around the globe. Concentration does not vary systematically with distance from the crater. At proximal sites, the Ir concentration is diluted by the high amount of sediment put in suspension in the Gulf of Mexico’s water after the impact.

6. Shocked quartz grains appear more abundant and larger west of the Chicxulub crater, although the absolute size factor may strongly depend on the amount of material available for study. Nevertheless, as proposed by Alvarez et al. (1995) and Bostwick and Kyte (1996), the maximum grain size of quartz grains with planar deformation features seems larger in the Pacific than at sites located at equivalent distances from the crater in Europe.

7. KTbase demonstrates that a significant effort is needed to improve our knowledge of K-T boundary sites in South America, Africa, Australia, and the high latitudes ( 60 ). 

Preliminary examination of the K-T database in terms of the ejecta debris distribution and K-T boundary sedimentation shows that it is probably the most convenient and user-friendly method to compile and sort the huge amount of literature on the subject. Plotting the current data on paleogeographic maps indicates zones where further studies are required. The occurrence of impact debris must also be reported in a clear and quantitative manner (e.g., abundance per cm2 of sediments) before the distribution pattern of impact products can be understood.

The main advantage of the database is to point toward potential trends or characteristics in the data, which can then be investigated further. The information extracted from the database coupled with mathematical models will permit the documentation of the origin, transport, and deposition of ejecta material during cratering events. It is our goal to have the ejecta debris part of the database available through the internet in the near future.

Here is their map of sites that they examined for their database, note worldwide distribution of the ejecta.  The map is of the Earth as of 65 million years ago (note India), the "best" showings of the K-T Boundary are with the symbol of a circle with a dot in the middle:


***

There were three sites (two in Wyoming and one in South Dakota) that I thought we should try to find.  I was able to do a few hours of research (not that much, not enough as it turns out) to get a pretty good idea of locating one or more of these boundaries.  The two in Wyoming have the iridium-rich layer seen all over the world (above map), the one in South Dakota being a "marine" K-T Boundary, that is, a geologic record of a tsunami formed by the impact of the asteroid (65 million years ago, that part of S. Dakota was underwater).

The first one is in the SW Powder River Basin of central Wyoming (some 15 miles east of the Interstate 25 Exit at Kaycee).  I made an inquiry at the general store of Kaycee (a very tiny town) and was directed to see a rancher located near where the boundary is located.  So, I drove over to visit him, unannounced, and found him there at home.  The rancher knew all about it, he had several times hosted visits by geologists from one of the Colorado universities (but apparently not from the U. of Wyoming's unhelpful (to me) Geology Department however, LOL...).  He then told me that he had sold that particular parcel of his ranch to another couple, he gave me their phone numbers.  Ahh, rather than disrupt the lives of more people without having more information, I then asked him if the K-T Boundary was easy to get to (ideally by roadside or a short hike along the Powder River looking for an outcrop).  No, he told me, it was accessible only by a four-wheel-drive...  I thanked him for his time and told him I would not bother the new owners (and, of course, ask people I did not know to give me time and run their truck just for my curiosity...).  So, Strike One, but here is a picture of a bridge over the Powder River very near the actual outcrop of the boundary:


The type of outcrop to look for (Powder River), but not here!


Close, but no cigar...

Our next opportunity came up with a reported K-T Boundary at Badlands National Park, about an hour east of Rapid City, South Dakota.  The price I had to pay my wife was to visit Mt. Rushmore as well, but that was a small price to pay to see (and take a good picture of) the K-T Boundary.  Philip Stofer of the USGS published a paper (he mentioned upfront that it was tentative) on finding the boundary in Badlands.  He provided pictures and evidence in a convincing paper: http://geopubs.wr.usgs.gov/open-file/of01-056/of01-056.pdf.

I took a few pictures that pretty closely match Stofer's, I was looking for his "Disturbed Zone", the evidence of a tsunami affecting the area.  I was quite hopeful as Stofer said that this K-T Boundary was the most easily accessible in the whole world!  Here is a picture, description below:


Stofer's "K-T Boundary" is the slightly pinkish-white set of formations under the two thin white layers and above the bottom yellow ones.

But, the Park's resident paleontologist (a geologist specializing in study of ancient life and their environments), Dr. Rachel Benton wrote me that the "K-T Boundary" at Badlands has been disproven (her email to me, her comments in gray background):

Dear Mr. Mix:

Thank you for your interest in the geology of Badlands National Park.  Unfortunately the existence of the K/T boundary at Badlands National Park has been disproved.  I have attached two abstracts to professional geological societies that provide evidence that the disturbed zone we have in the park is too old and we do not have the early Tertiary rocks in the park.  Phil Stoffer is an author on one of the abstracts.  The authors still believe that the sediments preserved in the park are from some type of impact event but not linked to the K Chixculub or Manson impact.  Please let me know if you have further questions.

Sincerely,

Rachel Benton

Ouch!  Strike Two!  Three strikes and you're out!  (in baseball anyway)

We then went on to see if we could find the third boundary site, this one in the SE Powder River Basin (Wyoming), near Linch Creek and Doggie Creek.  Bruce Bohor wrote a few papers on the K-T Boundary in Wyoming, and found one at Doggie Creek:

http://www.scribd.com/doc/94516429/Bohor-etal-Dinosaurs-Spherules-and-the-Magic-Layer-A-New-K-T-Boundary-Clay-Site-in-Wyoming-Geo15-10-1987-4-pdf

Being zero for two so far, I was not hopeful that we would find a K-T Boundary at Doggie Creek.  The area is remote and as far as I can tell all the land is privately owned ranch land.  I did ask the postmaster at Linch Creek (another very small Wyoming town) for information about Doggie Creek and/or the K-T Boundary.  She did not know about the boundary, but did direct me up the gravel road (Wyoming 272) north of Linch Creek some 15 - 20 miles.  Bohor in one of his papers mentioned such features as a "prominent conical hill", an abandoned Post Office with gully nearby, and other clues.  But, they did not have ubiquitous GPS in those days, so I only had written text to go with, and some was incorrectly spelled, nor were the creeks marked along the remote small bridges.  Nonetheless, I believe that we did indeed find the "prominent conical hill" (the only one in the area that matched that description) as well as the apparently abandoned hamlet.  I went ahead and walked along a couple of creeks, one of which would likely be Doggie Creek.  This first picture shows the "prominent conical hill", so I felt fairly confident that we might find the boundary after all:


OK, so I got busy looking into the nearby gully:


The picture just above is typical of what I saw within some 250 meters of the road.  I did not want to go any further as this land IS privately owned.  The K-T Boundary in this area is supposed to be just above three thin lignite (low quality coal) beds, but I did not see (else, correctly identify) any lignite.  So, while it is very likely I was close again, "close, but no no cigar!"  Strike Three!

So, we were not able to find ANY of the elusive three K-T Boundaries supposedly in the scope of our trip.  I am consoled by three things:

1) the remarkable kindness of the people (scientists and local folks) from there

2) the absolutely beautiful parts of the countryside we went through, truly gorgeous, we saw this at Badlands:



3) the company of the best traveling companion I have ever had, here she is (the photo is a little dark because it was nearly sunset):


***

Soon I will write up the final article of this series of our trip, this one will have commentary and pictures of things that most tourists do NOT see, write about or take photos of.

Why don't you join us on the (mis)adventures of two tourists doing a trip like this...,  differently!

4 comments:

  1. Great stuff; I particularly like the lower end of the rainbow pic, followed by what is doubtless a pic of yr gold at the end of the rainbow, Mrs. Mix. Glad you had fun.

    ReplyDelete
  2. Robt, great stuff brother,and the pic of Mrs. Chen is a good one!,I must ask it seems that there is a sort of golden hue around that pic,and just around that marker and the Mrs.,any idea what caused this anomaly?.
    Sounds like you had a blast,and saw some wondrous places most just get to read about.

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