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Science Forum Index » Geology Forum » stratigraphy in my backyard
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| Guest |
 Posted: Sun Nov 30, 2003 10:17 pm |
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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! |
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| Jo Schaper |
| Posted: Sun Nov 30, 2003 10:41 pm |
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Guest
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jawod@fuse.net wrote:
Quote: 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?
http://www.ohiodnr.com/geosurvey/pdf/geologic.pdf
Generalized Geological Map of Ohio.
If this does not answer your question,
I would call the general number of the Ohio State Geological Survey,
tell them what where you are: (nearest small town, highway intersection
and quadrangle topo map, if you know its name) and ask to be put through
to someone who knows about the area. Chances are someone on staff knows
your area. Then describe the location and the rock to them over the
phone. They can ask appropriate questions in return.
That's part of the reason a state geological survey exists, and hey,
you're paying their salaries! They might have a book on general Ohio
geology you can purchase, and presumably a more detailed geological map.
Quote:
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?
I have no idea about the Univ of Cincinnati, but many geology professors
have study sites elsewhere, and may only have the faintest inklings of
local geology. I think there a good Science Museum in Cincy--my husband
has talked about it and their karst/cave exhibit. They might be able
to help, too.
Quote: Thanks very much for understanding my enthusiasm and for looking past the
lack of training!
No problem and happy geo information hunting!
--
Geo Communications Services -- www.geocommunications.net
Jo Schaper's Missouri World -- http://www.missouriworld.net |
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| Paul |
| Posted: Mon Dec 01, 2003 12:48 am |
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Guest
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jawod@fuse.net wrote:
Quote:
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!
Alas, it was once my backyard, too.
Unfortunately, I don't remember it anymore.
You need as localised of a strat column that you can get.
Copy & paste the following into Google:
ohio "stratigraphic column" cincinnati |
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| Edward Hennessey |
| Posted: Mon Dec 01, 2003 1:26 am |
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Dear Jawod:
<jawod@fuse.net> wrote in message
news:3fcab2c6$0$62210$a0465688@nnrp.fuse.net...
Quote: 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.
Your thinking is obviously systematic. I think you can do the required
sleuthing on
your own if that is a prospect which interests you. I would use a search
engine to
check for geological maps on line along with information on the paleontology
of the
area.
Derived from your own writing, some terms you may want to mix in the search
would
be +geology +"geological map" +paleontology +fossils +Cincinnati
+"Cincinnati Arch" +"*** Ohio,
etcetera. The asterisks would equal the sectional compass area of Ohio you
are in.
Quote: I don't know the fossils very well.
Shimer and Shrock are famous for their work "Index Fossils of North
America".
See your search engine, library or Amazon at
www.amazon.com/exec/obidos/tg/detail/-/026219001X?v=glance
for more details. An index fossil is generally a species which existed for
only a
small interval of geological time but occurs across an ample geographical
area. Index
fossils are accordingly great indicators of the age of the host rock,
assuming they have
not been reworked (redeposited) into sediments of a later time period.
Quote: 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?
The Ordovician Richmond Formation is plentiful in your area and sounds very
close to
what you describe. You will find a good bit on it online.
Quote: 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?
High energy deposition or turbidity is usually associated with a lot of
broken fossils.
Is that what you see? Taphonomy is the study of conditions and processes
relating to
fossilization---another search word for your pursuit.
Quote: 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.
I'd have to see the specimen to join in your verdict. Carefully examine both
sides
of any broken rock face to make sure there are no hard fossil structures in
one making imprints in another. Fossil impressions are called trace fossils
or ichnofossils. There are a number of different trilobite impressions made
by digging, walking, nesting, etcetera and there are known occurences of
these in similar sediments from your area. Try looking at Google or Dogpile
for images of cruziana(trilobite trackways) and rusophycus (trilobite
resting places) to start. Here is a starter page on ichnology:
http://www.geo.arizona.edu/geo3xx/geo308_fall2002/backup/cha3.html
Quote: 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!
I think you will have little trouble effectively pursuing this if you take a
little time. The
web is replete with sources for you. The U of C is heavily involved with
area paleontology. It
is the consensus choice in your area for institutional resources. There is
also an amateur fossil
club with a good reputation in the vicinity called the "Dry Dredgers". A
number of knowledgeable
folk belong who would be of aid to your quest.
Jo made other fine suggestions for you to consider.
Good luck and regards,
Edward Hennessey
nohalozzyzxnohalo.noyahoo.com minus no,no,no. |
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| George |
| Posted: Mon Dec 01, 2003 4:20 am |
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Guest
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<jawod@fuse.net> wrote in message
news:3fcab2c6$0$62210$a0465688@nnrp.fuse.net...
Quote: 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. |
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