Travel around Pittsburgh to find Fossil Ferns!
Road Cuts around the Pittsburgh Area: Ambridge, Pennsylvania
Coal Forest and marine environment
~ 299 - 300 Million Years Old
Upper Pennsylvanian, Westphalian D to Stephanian A
Conemaugh Group: Glenshaw Formation: Mahoning Shale and Brush Creek Marine Zone
Fellow fossil hunters collecting at the Mahoning fossil fern layer near Ambridge, PA
A Calamites stem fragment from the Mahoning formation near Pittsburgh.
This is a large fossil plate of a bunch of Carboniferous plants. It looks like part of some kind of tree and some tree fern frond pieces. It shattered when it fell from the layer.
Geology and Paleontology of the Fossil sites near Pittsburgh, PA
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 Appalachian mountains, running north and south near the center of Pangea.
The new Appalachian Mountains were some of the largest mountains of all time, and were probably as tall as the
present day Himalayas. East of these Appalachian Mountains, which ended in central Pennsylvania,
were large flood deltas, or flood plains. These large alluvial flood plains extended the
entire way to the west coast of Pangea.
Image from the USGS (Public Domain) showing the United States in the Carboniferous Time period. Notice, the giant Appalachian mountains running along the east coast and the swamps covering much of Pennsylvania.
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.
This is figure 3 from (Gastaldo, et al. 2004). It shows the reconstruction (based on 17 samplings) of an actual fossilized coal forest preserved above the Blue Creek Coal in Alabama.
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 the Carboniferous, similar to today, the Earth experienced Ice Age Glaciation events. When Glaciers advanced in Pangea, the
sea levels would drop. During interglacial periods (similar to today), sea levels would rise. The sea level rise and fall, called
transgression and regression cycles continued for millions of years during the carboniferous.
Every time the Panthalassic ocean (which was almost like the Pacific Ocean, but on a larger scale) on the west coast of Pangea flooded the lowland deltas, a marine environment was created where there once was a tropical coal forest. The forest was buried, compressed, and eventually turned into a coal layer.
These sea level fluctuations can be seen in the rock units as a layering pattern of coal and marine limestone. This pattern can clearly be seen in the Stratigraphic Column below in the next section.
Diagram of a transgression and regression cycle - Periodic glaciation events in Pangea would cause a constant sea level fluctuation. This occurs today. During the Ice Age, over 10,000 years ago, the sea levels were very low. Today, we are in an interglacial event, and the sea levels are high.
The roadcut next to the Ambridge Woodlawn bridge contains part of a transgression / regression cycle. The first level (at road level) has the preserved remains of one of the Pennsylvanian coal swamps. They are in shale from the Mahoning coal. Above the remains of this coal swamp, is a marine environment, the Brush Creek Marine Zone.
The Mahoning shale 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 as 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. Ancient fish also lived here, like placoderms and primitive forms of sharks and occasionally their small teeth are found around this area (although I know of no one actually finding one at this particular site).
Paleozoic Fossil Plants
By: by Bruce L. Stinchcomb, 2013
The author gives a picture of what the first forests in the Devonian was like, to the great coal forests in the Carboniferous. It is written for the general fossil collector in mind and has almost 700 color photos of fossil plants from the Paleozoic, many from the Carboniferous time period. These pictures include stems and seeds, not just the leaves. It's a nice resource if you collect plant fossils from the Carboniferous.
Stratigraphic Column of the Conemaugh group near Pittsburgh, PA
The diagram below shows a general stratigraphic column of the Conemaugh group. The lower half is the Glenshaw Formation.
The roadcuts around Ambridge contain the lower part of he Glenshaw Formation, from the Brush Creek Limestone to the Mahoning Limestone.
The BLUE bars are limestones formed in marine environments, the BLACK bars are coal beds formed from coal forests, and the YELLOW sections are channel sandstones when sand filled in river channels.
By glancing at the colors, one can clearly see the marine transgression / regression cycles that make up this formation.
This is a generalized column, in reality there are many other rock layers, including the red beds and paleosols.
Stratigraphy of the Conemaugh Group. The Ambridge site exposes the Brush Creek Limestone down to the Mahoning Limestone. This diagram is from The University of Pittsburgh Department of Geology and Planetary Science. The complete column is available at their Pittsburgh Area Geologic Sites webpage
Fossil Collecting Location near Pittsburgh
This road cut, and many others in the Pittsburgh area are on/near busy roads. Please use
common sense when collecting at road cuts. Also, make sure you have permission
first before collecting on any private property.
Do not to fossil collect along a busy road or a road with a narrow shoulder.
Do not park your car along a busy road or a road with a narrow shoulder.
Do not fossil collect at a tall road cut, or collect at the base of a tall road cut, the rocks fall all the time!
The author and host of this site bear no responsibility for injury sustained by those who visit the sites listed herein.
Google Map of the Ambridge Roadcut
The road cut is located on the side of Route 51 across from the Ambridge Woodlawn Bridge on the west side
of the Ohio river. It is clearly visible when crossing the bridge.
Most of the roadcut is not accessible because the cut is very high and therefore too dangerous to collect at. Also there is no parking space at the actual road cut.
If you want to fossil collect at this location, you need to go to either the southernmost section or the northernmost section. This is where the Jersey barriers end and the shoulder widens. At these places, the cliff is not nearly as high or steep, and there is room for parking about 1/8 - 1/4 mile down the road from the end of the cut on both the north and south ends.
Pittsburgh is full of roadcuts. Most of these roadcuts around Pittsburgh contain part of the Conemaugh Group.
This means many of these cuts have either Carboniferous plant or marine fossils.
The location listed above is just one of many. Search around and explore. You can find many safe locations to collect fossils all around the greater Pittsburgh area.
Fossil Collecting Tools and Tips For This Site:
The following is a list of recommended equipment to bring with you when fossil hunt in shale for Ferns:
A good rock hammer and a few thin chisels are a must.
A good rock hammer is a must. For fossil hunting in Shale I prefer the ones with the chisel edge, like the ones below.
Estwing E3-20BLC Rock Pick Chisel Edge, 20-Ounce
Estwing make quality products. This is a great rock hammer, and will last you years. However, it you don't want to pay around $30 for a rock hammer, there are cheaper ones that still hold up ok. This Valley Soft Touch is pretty good for under $20: Rock Hammer / Chisel Edged Valley Soft-Touch 20 Oz
An array of chisels is also important. Chisels for splitting shale should be thin, flat, and wide. I also love hand guards, so you don't destroy your hand every fossil trip. I can't remember life without hand guards!
Stanley 2-3/4-Inch FatMax Masons Chisel with Hand Guard This is a nice wide, flat chisel designed to split hard stone, concrete, and brick. It's great for shale! The hand guard will save your hand. Plus the yellow color makes it next to impossible to lose!
Titan 17005 Stainless Steel Prybar and Scraper Set - 2 Piece These thin scrapers, or small flatbars, are great for teasing up thin shale layers without breaking them. Anything thin enough for scraping and yet strong enough for chiseling goes striaght into my fossil tool kit!
Long prybars, a couple feet in length, are convienant for separating large slabs. I can't find any good ones on amazon, but I'm sure your local
hardware store has them.
This should go without saying... Anytime you hit a rock with ANYTHING, you should be wearing protective glasses. One tiny rock fragment
can make one go blind if eye protection isn't worn!
Other collecting items should include aluminum to wrap the fragil fossils in, glue for quick onsite repairs, and insect repellent. There is allot of vegetation at the road cuts, and ticks can be a problem.
If you're alone, make sure someone knows where you are or have a cell phone with reception.
Use common sense while in the field. Road cuts, by definition are along the side of a road.
Don't collect right next to a busy road. Make sure there's plenty of room between the road cut and the road!
Also, road cuts are large cliffs. Stuff falls all the time. Stay away from steep or unstable looking cuts. Don't climb the cuts, and stay away from the base of the cuts. Collecting at the tullus slopes usually provides enough rock to look through.
I often see collectors who look like they are hiking the Appalachian trail for 6 months.
Don't overdo it. You want to have fun while collecting. You don't want to have to carry
30 pounds of MRE's, 2 tents, a kitchen table, 3 changes of clothes, a rubber ducky, etc...
Idealy, you want to pack light and come home heavy with fossils.
If you plan on collecting plant or marine fossils from around Pittsburgh, this section will aid you in fossil identification.
Since there are two distinct type of fossils found in the Glenshaw Formation here, it is broken into two pages, the Fossil Plants and the Marine Zone fossils.
A Guide to Pennsylvanian (Carboniferous) Age Plant Fossils of Southwest Virginia
by Thomas F. McLoughlin, 2013
Yes, I know it says Western Virginia, but the Coal forests in Western Virginia was the same forest in Western Pennsylvania. It was one giant forest that ran down the ancient delta.
This book is chulk full of illustrations, 280 to be exact, many of which are in color. These illustrations makes identifying almost any carboniferous plant fossil a simple task. If you collect fossil ferns from the Carboniferous, this well organized book will serve as your identification guide.
This book is a classic! Although some of the fossil hunting site listed in this book no longer exist, it shows what fossils can
be found in the same area. What makes this book a classic is Jasper Burns incredible sketches of the locations and the fossils
found at each location. It is a very descriptive and useful guide book. Even after all these years,
I still find myself referencing it!
Included are numerous Carboniferous plant sites in Virginia, West Virginia, Pennsylvania, and Maryland.
Gastaldo, Robert A.; Stevanovic-Walls, Ivana M.; Ware, William N.; and Greb, Stephen F. (2004) Community heterogeneity of Early Pennsylvanian peat mires. Geology 32, 693–696. (doi:10.1130/G20515.1)