<p><strong>Vredefort</strong></p>

<p>No extraterrestrial iridium anomaly: <a href="http://adsabs.harvard.edu/full/1989LPSC...19..733F" rel="nofollow noreferrer">http://adsabs.harvard.edu/full/1989LPSC...19..733F</a> </p>

<p>I'm not sure I fully agree with them, because there is quite a lot of Ir there and their threshold of 200 pg/g seems somewhat arbitrary to me. They claim the Ir was derived from local rocks, but that's a hell lot of iridium!</p>

<p><strong>Sudbury</strong></p>

<p>There is an an iridium anomaly. Read all about it <a href="http://www.nature.com/nature/journal/v429/n6991/full/nature02577.html" rel="nofollow noreferrer">here (paywalled)</a> and <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.2010.01057.x/full" rel="nofollow noreferrer">here (open access)</a>.</p>

<blockquote>
  <p>but the KT boundary is the only one commonly mentioned…why?</p>
</blockquote>

<p>Because it's the first one found, a nice story of serendipity, because it's the last really big one, and the one that killed the dinosaurs. Everything you need to make a good story - even though it's not unique.</p>

<p>Iridium (and other PGE) anomalies and pretty much common feature of impacts. <a href="http://www.sciencedirect.com/science/article/pii/S167498711730049X" rel="nofollow noreferrer">This paper</a> shows attempts to link mass extinction events with impacts. This is a controversial issue, because you can also link massive volcanic events with mass extinctions, not only impact. But that's not for now - they do show iridium anomalies for all impacts. <a href="http://www.sciencedirect.com/science/article/pii/S0012821X04000627" rel="nofollow noreferrer">That's another paper</a> showing iridium anomalies for impacts, much older this time.</p>

CC BY-SA 3.0
2017-07-23T01:50:44.097Z
This is further complicated by the theory that large impacts can also trigger or even create large volcanic events.
John
CC BY-SA 3.0
2017-07-22T06:55:50.203Z
2017-07-22T06:55:50.203Z
Gimelist
<p>Chicxulub crater is the third largest crater on earth, which is said to have produced the KT boundary.   What is the sediment layer produced by the 1st and 2nd largest craters?</p>

<p>Also, there many craters before and after Chicxulub was created, but the KT boundary is the only one commonly mentioned…why? </p>

CC BY-SA 3.0
2017-07-17T17:05:41.797Z
The sediment layer produced by the _largest_ impact is [the Moon](http://en.wikipedia.org/wiki/Giant-impact_hypothesis)..
Spencer
CC BY-SA 3.0
2017-07-21T17:49:50.543Z
Perhaps true, but that crater doesn't exist...
Inetquestion
<earth-history><meteorite><natural-disasters><impacts>
Sediment boundarys produced by largest meteors? Vredefort, Sudbury and Chicxulub
Inetquestion
# Sediment boundarys produced by largest meteors? Vredefort, Sudbury and Chicxulub

(Asked by: username_0 on 2017-07-16)

Chicxulub crater is the third largest crater on earth, which is said to have produced the KT boundary. What is the sediment layer produced by the 1st and 2nd largest craters?

Also, there many craters before and after Chicxulub was created, but the KT boundary is the only one commonly mentioned…why?

**Tags:** earth-history, meteorite, natural-disasters, impacts

> **Comments:**
> **username_1**: The sediment layer produced by the _largest_ impact is [the Moon](http://en.wikipedia.org/wiki/Giant-impact_hypothesis)..  
> **username_0**: Perhaps true, but that crater doesn't exist...  

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## 1 answers

### Answer by username_2 on 2017-07-22. Score: 1 | Accepted answer

**Vredefort**

No extraterrestrial iridium anomaly: <http://adsabs.harvard.edu/full/1989LPSC...19..733F>

I'm not sure I fully agree with them, because there is quite a lot of Ir there and their threshold of 200 pg/g seems somewhat arbitrary to me. They claim the Ir was derived from local rocks, but that's a hell lot of iridium!

**Sudbury**

There is an an iridium anomaly. Read all about it [here (paywalled)](http://www.nature.com/nature/journal/v429/n6991/full/nature02577.html) and [here (open access)](http://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.2010.01057.x/full).

> but the KT boundary is the only one commonly mentioned…why?

Because it's the first one found, a nice story of serendipity, because it's the last really big one, and the one that killed the dinosaurs. Everything you need to make a good story - even though it's not unique.

Iridium (and other PGE) anomalies and pretty much common feature of impacts. [This paper](http://www.sciencedirect.com/science/article/pii/S167498711730049X) shows attempts to link mass extinction events with impacts. This is a controversial issue, because you can also link massive volcanic events with mass extinctions, not only impact. But that's not for now - they do show iridium anomalies for all impacts. [That's another paper](http://www.sciencedirect.com/science/article/pii/S0012821X04000627) showing iridium anomalies for impacts, much older this time.

> **Comments:**
> **username_3**: This is further complicated by the theory that large impacts can also trigger or even create large volcanic events.  

---

