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Fujii

Which Layer Is K-Pg Boundary?

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Fujii
jpc

The K/T boundary is not easy to see, at least in the Hell Creek Fm, which is wht your two pix are. It is NOT an obvious layer. I don't know about marine rocks in DK, NZ, IT and others.

You have to take samples of rock everywhere between the highest dinosaur bone you can find, and the lowest Paleocene mammals. Then look for an abnormally high amount of iridium in it. It is a lot of work done by specialists. This is why there are only a few documented sites (in terrestrial deposits). I think both of the photos you found are of generalized shots of the Hell Creek Fm... "Where the boundary has been found". Meaning that they could not find a photo of the boundary and stuck these Hell Creek pix in there.

Does that make sense?

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jpc

Additionally, I have stood at the boundary in Wyoming, with these very same specialists who did the work, and it is still not obvious. One factor is that is is only about a cm thick and in the Lance and Hell Creek Fm's, every time it rains and when snow melts, the top layers of mudstone just melt away a bit, so the actual surface shown in your pix is "blurry" with last week's rain made mud, so at this scale the 1 cm thick layer will not show up.

Does that make sense?

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Missourian

It's possible the iridium layer is not present at the location. Some of the Cretaceous beds could have eroded away before the Paleocene sediment was deposited.

Edited by Missourian

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Troodon

On the web page that you

Thank you very much for answering. The first picture is shown in wikipedia as representative photo of K-Pg boundary, but no arrow indicated the layer. http://en.wikipedia.org/wiki/CretaceousPaleogene_boundary

I hope this will be improved.

On that web page they do mark the layer on a picture lower in the page. On the image you asked about my guess is that the layer is at the junction between the light and dark area. I say that because I found the attached image on the web which is identical to the one you were asking about just flipped.

post-10935-0-21024900-1424093563_thumb.jpg

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Fujii

Thank you for indicating the boundary, it is highly informative to non-experts.

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