#Fossil Melting Pot
2 messages in this thread
One of my favorite fossil hunting sites (Simi Valley, CA) consists of an arroyo
with Quaternary alluvium, which is surrounded by three formations contributing
the majority of the fossils. The formations are of Late Cretaceous, Paleocene,
and Eocene. I know how to recognize which formations the fossils are from when
I find them because I've collected them at their sources. However, in the
arroyo, they often occur together where they've washed down.
What I want to know is, if the alluvium were to become a fossil site in the
distant future, and all these different aged fossils became part of the same
deposition layer, how easy is it to identify them as being of different origin?
Also, assuming the future paleontologist is on the ball and recognizes the
difference between them, how difficult is it to determine their respective ages
at this point?
This must be a very common phenomenon. Is this relevant to the purported
"Cenozoic" dinosaurs from Canada that I've heard about?
Anyone??
-Rande
Hi, Rande–
While it must be common for fossils to be washed away from their home stratum,
it will be less common for them to get built into a new rock – the odds are
they will be destroyed by weathering first.
If one can see how they fit into the parent rock, one will often be able to
tell there is a risk of anachronisms. These washed-down fossils of yours, if
incorporated in a new rock, would likely be in a conglomerate where one has to
suspect such things of fossils found _within_ the conglomerated units. Even if
it winds up in a uniform smoothly-bedded rock, the particular rock the fossil
arrived in will be an oddball, a section with different angling of layers and
different kinds of sediment.
I was assuming above that the fossil is still embedded in a piece of its home
rock; if not, it is more vulnerable to the weathering I spoke of.
The other fossils at the site taken together may tell a consistent story or a
discordant one (as they would at your arroyo), which would have a bearing on
interpreting any one fossil.
Your arroyo seems likely to appear as some sort of projection at the boundary
of whatever layer it winds up in. I suspect paleontologists are more
comfortable with specimens from the body of a formation than some extension.
Without knowing the exact point in the formation the fossil was found in,
suddenly there would be a lot less to go on, and the fossil would lose a lot of
its value as a source of information. There may still be radioactive dating or
some such, but that will often not be possible.
–Doug