so up until now all of the rocks that
we've been targeting for our thermo
chronology and geochronology sample have
been igneous and metamorphic rocks and
that's usually what people target
sedimentary sequences have a lot of
potential but they they always have a
few difficulties associated with them
they can be really powerful for you
because what they're often preserving
our rocks that are no longer where they
used to be so for instance we're
standing here on an outcrop of the
Humboldt formation looking at a
conglomerated layer and all of the rocks
that we see here used to be on top of a
mountain somewhere and got eroded down
so if we hiked all the way up to sample
these we wouldn't find them this is
where they are so the the complication
was set with using sedimentary rocks for
geo or thermal chronology comes in with
how you interpret and analyze the data
typically when we're gonna analyze and
interpret thermo chronology from a
particular sample we're going to be
looking at data from multiple individual
crystals or a little pile of crystals
that we put together and analyze
together in an igneous and metamorphic
rocks that works well because when you
sample a big chunk of igneous or
metamorphic rock you know that that has
been a big chunk of rock that's been
together and shared a common history for
millions and millions of years but in
sedimentary rocks you can't assume that
sometimes if you're looking at sand
stones or shales the material that is
being fed into the basin where the
sedimentary rock is accumulating could
come from an enormous drainage basin
hundreds and hundreds of square miles in
some instances so if I wanted to pick
out five or six individual crystals and
analyze them and interpret them
I couldn't assume that they've actually
shared their whole lifespan together or
even a large part of their life span
they could be representing completely
different thermal histories that are not
related to each other at all they just
happen to end up living in the same
place now what is exciting for us then
is when we find samples like this so
like I said this is part of the Humboldt
formation it's a Miocene to  younger
conglomerate and what we have preserved
in here as you can see here is an
enormous chunk, a big honkin chunk of
some sort of grano diorite, granitic
rock I'm not entirely sure where it's
from right now but I know if I
sample this big clast that all of the
minerals inside here have all shared the
same thermal history and even though
this is might be different from this
clast and this clast and this clast and
all the other ones around here
everything in this clast has shared the
same thermal history which means that I
can actually use all of the tools
available to me in thermo chronology and
reconstruct fairly detailed thermal
histories of this one particular part of
the rock
