Tuesday, April 1, 2008

Precambrian fossil!

I've been waiting and waiting to tell someone about this, and today seemed an appropriate day.(Edit: Note post date. ;) )

I've been working in metamorphosed Precambrian (well, Paleoproterozoic, to be precise) sediments. Their exact age is thought to be around 1.7 billion years, but that's estimated from detrital zircons. They are cut by a 1.4 billion year old granite, though, so we've got a minimum age, as well.

Now, these rocks are conglomerates, made mostly of pebbles of quartzite, vein quartz, and banded iron formation, so they were deposited someplace where water was moving fast. I didn't expect to see subtle features preserved, let alone this:



Can't see it? Well, it's usually hard to recognize fossils in rocks metamorphosed to andalusite grade. Here, let me outline it for you:



A Precambrian rabbit.

J.B.S. Haldane is rolling in his grave.

8 comments:

Ole said...

In your first image I thought I recognised a fish - one like this
http://customsholidays.suite101.com/article.cfm/the_april_fish

Kim said...

I had never heard of the April Fish tradition before! (And the conglomerate could be a good geologic ink blot test.)

Joey said...

You got me! I recognized it immediately as the Uncompaghre (sp?), and thought "What? There's no fossils in there!"

Kim said...

It's actually the Vallecito Conglomerate - but it's recently been proposed to be the base of the Uncompaghre, and in a few years, the same name might be applied to both of them.

Silver Fox said...

That's a good one. :D

andrew said...

! ! !

Elli said...

:)

Jennie said...

cute. I didn't read this on April Fool's day so it took me a second to get the joke.