Re: stratigraphy in my backyard

<[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Again, an amateur request for help.
>
> Can someone steer me in the right direction to determine the age of a
layer
> of limestone in a creek-cut hillside in my backyard?
>
> Being in Cincinnati, I know I am near (but not too near) the Cincinnati
Arch
> of Ordovician layers.  I don't know the fossils very well.  This
particular
> formation is about 15-20 cm thick and lies between much thicker layers of
> soft clayey shale of medium gray with very few fossils.  This is in a
> drainage area to the Little Miami River maybe ten miles north of its mouth
> on the Ohio.  I am thinking it is much less old than 450 MYA...but how
much?
>
>
> I am guessing that for most of the period while this rock was laid down
was
> turbid and muddy: the clayey shale.  There was a period of clear water
with
> a prolific marine environment: the high density of shell debris and other
> fossils in the limestone.  Am I close?
>
> The coolest thing, though, is that the under-surface of a large rock I
> pulled out of its position in the cut has these great casts of indented
> trails made by some crawling thing ...how long ago?  So, I am thinking
that
> these trails occurred at the transition from a muddy swamp or something to
a
> clear water environment at that time.
>
> What is the best approach to solve this puzzle?  I suppose I could lug the
> rock down to the Univ of Cincinnati Geology Department...what would they
ask
> me regarding the original location? anything else I should tell them?
>
> Thanks very much for understanding my enthusiasm and for looking past the
> lack of training!

You most likely have found a limestone ledge within the Eden Shale, which is
very widespread in your area.  Give a specific locality, and I may be able
to narrow it down for you.