Last Update: 10/25/04
Location:
Ambridge, PA: Twin road cuts
Coal Forest and marine environment
~ 299 - 300 Million Years Old
Upper Pennsylvanian, Westphalian D to Stephanian A
Conemaugh Group: Mahoning Formation and Brush Creek Marine Zone
This site is CLOSED
PenDOT has widened route 51 and removed these road cuts.
read the "access site" section toward the bottom of this page for more info.
"The Fern Level, The First Level"
Fern packed shale
"The Fern Level"
Here is Amy for scale
"The Marine Zone, The Second Level"
Shell packed shale
The black oily shale is almost entirely buried under the dense vegetation.
This is why it is strongly advised to collect in the fall, or early spring.
"Lookie what I found"
Here is Amy pulling a Calamites stem from the shale.
View our fossils found at Ambridge, PA
View a Stratiographic column and corresponding
geologic time units of the Upper Pennsylvanian.
About the Site
In the United States, the Carboniferous period (360 -280 Million Years ago) is divided in
the Mississippian (360 - 320) and Pennsylvanian (320 - 280) periods.
During the middle Pennsylvanian period, the supercontinent Pangea, meaning "all land",
had formed along with the Appellation mountains, running north and south near the center
of Pangea. These new Appellation mountains were some of the largest mountains of all
time, and were probably as tall as the present day Himalayas. East of these Appellation
mountains, which ended in central Pennsylvania, were large flood deltas, or flood plains.
These large aluvial flood plains extended the entire way to the west coast of Pangea.
Around this time, Pennsylvania was approximately located 5 degrees south of the equator,
in a tropical
rain forest type climate with very little seasonal fluctuation. Also, at this time,
the Earth had much higher concentrations of carbon dioxide in the atmosphere. This was
very conducive to the growth of plants. Hence, in these flood deltas, large, swampy forests
grew. However, the plants in these forests were far different than plants of the present
day. Flowering plants, or deciduous plants of any kind had not yet evolved. Instead,
there were very large, simple, fernlike plants, such as Calamities (a giant horse tail),
Lycopods (which grew up
to 100 feet) seed ferns and herbaceous ferns (that grew up to 50 feet). However, at the end
of the Pennsylvanian, most of these strange plants became extinct, and deciduous plants
eventually evolved. Much of these forested areas became buried and now
create the carboniferous coal beds
that are mined today throughout the eastern United States and Europe. Because of this,
these swampy forests are often called coal swamps and coal forests.
In these forests, new insect life also flourished, such as dragonflies, mayflies, millipedes,
scorpions, and spiders. However, these were not normal insects, they were giant man eating
creatures. Well, the may not have been man eating, however some dragonflies had wingspans
of 2.5 feet, cockroaches were a whopping 4 inches, and flies needed extra large fly swatters.
Unfortunately, these fragile insects did not readily survive fossilization in the coal swamps,
and only rarely can be found as fossils.
A unique feature of this period was the development of the amniotic egg for reproduction.
This basically means animals could now lay eggs on land. So, very primitive reptiles, such
as Hylonomus and Anthracosaurs evolved. Also, around this time,
large amphibians existed. Fossilized jaw fragments from these amphibians can occasionally
be found in outcrops around the Ambridge area.
During this time, sea levels were in constant fluctuation. This resulted in
the Panthalassic ocean (which was almost like the pacific ocean, but on a larger scale)
on the west coast of Pangea to flood these deltas, creating a marine environment where the
tropical forest environment was.
During the times of these marine environments, many invertebrate creatures thrived.
However, Trilobites did not thrive, they were scarce and would become extinct by the
end of the Permian. Also, Armored Placeoderms became extinct, and were replaced by more
modern fish.
The roadcut next to the Ambridge Woodlawn bridge contains two levels. Each level contains
distinctly different fossils. The first level, the Mahoning formation, has the preserved
remains of one of these coal swamps. Above the remains of the coal swamp, is a marine
environment, the Brush Creek Marine Zone. This marine zone was formed from one of the
sea level fluctuations, when the sea invaded this place.
The Mahoning formation is composed of the very thin gray to green shale. This finely
grained, thin shale is packed full
of mainly carbon films of well-preserved middle Pennsylvanian plants,
such at Neuropteris, Pecopteris, and Calamites.
The Brush Creek Marine Zone is composed of black, oily shales and limestones. These
shales contain numerous gastropods, and straight shelled nautaloids. Also, ancient
forms of sharks lived here,
and occasionally their small teeth are found around this area (although I know of no one
actually finding one at this particular site).
Access site:
As of October 2004, PennDOT was in the process of removing this road cut in order to
prevent rock slides onto Route 51.
A small section of road cut on the fern level was still accessable, but has now
been removed.
The twin road cuts were once directly opposite the Ambridge Woodlawn Bridge at the west side of
the Ohio River. The cuts were clearly visible when crossing the bridge.
When crossing the bridge,
turn left (south) onto Route 51.
The first level was the fern level, and the second level (the black shale) was the marine zone.
Recomended Equipment:
A rock hammer and a nice wide, thin chissel. The ferns are smooshed in very thin and fragile
shale. A wide, thin chissel will work best at splitting the shale (take your time).
Safety Goggles
Lots of water, and bug spray.
Long pants, the place is FILLED with poison ivy.
Other Recommendations
The fossils plants are clustered in certain layers in the shale. Once you find one
of these layers, slow down and work carefully so you don't hack the plant fossils to pieces.
If your trying to get big slabs, don't just dig into the hillside,
work from the top of a pre-existing outcropping, and carefully and slowly excavate.
Carefully work your way down, slowly removing the thin slabs (Take your time!).
Watch were you step! Perfect specimens can be found in the debris at the base
of the hill (where you walk).
Whatever you do, don't touch the carbon films. They will easily smear when touched.
If there is dirt on the shale, wait till you get home before trying to clean it.
If you want to collect at the Brush Creek Marine zone, but do not want to climb up the
nearly vertical hill, look for Brush Creek debris at the fern level (chunks of black rock).
There are many chunks of Brush Creek debris that has fallen to the fern level.
Collecting in mid-late summer is not recommended. The dense vegetation hides almost
everything and makes it almost impossible to move around on the second level.
Recommended Books:
Fossil Collecting in the Mid-Atlantic States
by Jasper Burns
Copyright 1991
The Johns Hopkins University Press
Baltimore
ISBN 0-8018-4145-3
This is site # 38 in this book
Fossil Collecting in Pennsylvania
General Geology Report 40
by D. Hoskins, J. Inners, J. Harper
Pennsylvania Geological Survey
This is site # 3 in this book
This book was online in PDF format at the fossil section of the
Pennsylvania Geologic Survey
website. However, many of the fossil places in this book
have been developed over, making the publication obsolete. Therefore, they
removed the publication. Email me if you want more info about this publication.
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