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Guide To The Mahantango Formation: A Slice of a Devonian Coral Reef

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Guide to the Devonian
fossils of the Mahantango Formation

Guide To The Mahantango Formation: A Fossilized Devonian Coral Reef

Central PA, and West Virginia
Middle Devonian, ~387 Million Years Old

Devonian Fossils from the Mahantango siltstones

View of Mahantango Fossil Brachiopods, freshly split from the siltstone.

About The Devonian Mahantango Formation

The Mahantango is a very large middle Devonian formation that runs through many North Eastern states, including Pennsylvania, Marlyand, and West Virginia. It's the major middle Devonian formation in Pennsylvania and is part of the Hamilton Group.

Many oil experts know this formation because it sits directly on top of the Marcellus shale (which is now a household name). The Mahantango is sandwiched between the Marcellus shale on the bottom, and in many places, the Tully limestone on the top. In Western New York, the Mahantango of the Hamilton group is replaced by mainly the Moscow and Ludlowville shale. (Here is a link to the Western New York Fossil Page). The thickness of the Mahantango ranges from 1200 to 2200 feet and is comprised of shale, siltstones, and sandstones arranged in nested coarsening-upward cycles (Harper 1999).

It is an organic fossil bearing sequence of rock that was formed from the shallow Kaskaskia Sea which fluctuated in depth over time. The finer grained sediments come from shallow sea environments, while the coarser grained sediments indicate near shore environments, such as tidal areas, beaches, and deltas. Many of these near shore sediments contain deposits from violent storms. The slow transgression and regression of the sea levels caused these coarsening cycles that created the different subdivisions and layering in the formation. This is common in most marine and delta deposits, including the nearby Brush Creek Formation in Eastern PA.

Fossil sites from the Catskil Delta and Kaskaskia Sea include: Red Hill (Fossils Preserved in Freshwater lakes in the Castskill Delta), Lost River (Needmore Formation), Mahantango Type Locality (Hamilton Group), Western New York Sites (Hamilton Group), Sylvania, Ohio (Silica Formation), and the Clarita Oklahoma (Haragan Formation).

A rough map of the Eastern U.S. in the middle Devonian.  This
shows the shallow Kaskaskia Sea, the Catskill Delta, and the Acadian Mountains.

This is a rough map of the Eastern U.S. during the middle Devonian. It shows the shallow Kaskaskia Sea, the Catskill Delta, and the Acadian Mountains. As the Acadian Mountains eroded, sediments washed into the delta and out into the shallow sea.

The Mahantango was a typical tropical shallow sea environment. It contains a preserved middle Devonian reef system. Fossils of corals, brachiopods, cephalopods, and trilobites are commonly found. The fossil genera are very similar to the Hamilton group fossils of Western New York and the slightly older and very soft fossils from the Needmore formation of Pennsylvania, Virginia, and West Virginia.

A cross section of the Devonian Strata from New York down to Tennessee,
 showing the Hamilton Group; the Marcellus shale, Mahantango, and Needmore Formation

This image shows a cross section of Devonian Strata from New York to Tennessee. Notice, in the North (New York), The Hamilton Group is on top of the Marcellus Shale, and is mainly composed of the Moscow and Ludlowville formations, in Pennsylvania (toward the middle) it is the Mahantango Formation, in West Virginia it is the Needmore Formation.

This image is from the USGS Scientific Investigations Report 2006-5198 by Boughton, Carol J., McCoy, Kurt J. (2006), and is Public Domaion in the U.S.

Harper, J. A., 1999, Chapter 7: Devonian, p. 108-127, in Shultz, C. H., ed., The Geology of Pennsylvania. Pennsylvania Geological Survey, 4th series, Special Publication 1, 888 p.

Fossil Collecting Locations in the Mahantango Formation:

The fossil rich shale and siltstone are very fissile and usually break into many pieces. As a result many of the fossils are very fragile and are often broken when found. Lots of care and glue are often needed when trying to extract intact fossils.

A fossil exposure of the fossil bearing Magantango formation

A roadside exposure of
the Mahantango formation

Since the Mahantango formation is so expansive, there are numerous fossil collecting sites. Most are road cuts and roadside quarries spanning Central Pennsylvania, the Panhandle of West Virginia, North East Maryland, and Northern Virginia.

Jasper Burns lists a dozen Mahantango collecting locations in his " Fossil Collecting in the Mid-Atlantic States " book alone... many of which still exist. This book is also great because it has countless identification diagrams of fossils from the Mahantango and other nearby formations.

A few well known locations include:

1. Pennsylvania: The Montour Fossil Pit in Danville, PA. This is part of the PPL Montour Environmental Preserve. On the preserve is an old borrow pit that digs into the Mahantango formation. Fossil collecting is allowed here, there is even a big sign that says "Montour Fossil Pit". The preserve is open from sunrise to sunset.

2. Pennsylvania: Swarata State Park, the east side of the park has a borrow pit called the "Suedberg Fossil Site." The pit exposes the Mahantango formation. You are allowed to collect in the park.

3. West Virginia: A few large road cuts on Route 55 starting around 2 miles east of Wardensville, West Virginia.

4. West Virginia: Around 1.5 miles south of Delray in West Virginia. The rocks along the road and along the bank of the North River are from the Magantango formation.

Sample of Fossils Found in the Mahantango Formation:

This is a very rough and incomplete list of fossils that can be found. As I fossil collect in the formation more, the list will be added to and revised.

Eventually, these will be linked to a fossil examples page, where you can scroll through the different fossils for identification aid.

Trilobite Fossils TRILOBITES

Brachiopod Fossils BRACHIOPODS
Brachiopod Fossils PELECYPODS

Fossil Coral CORAL

Brachiopod Fossils GASTROPODS

Brachiopod Fossils CEPHALOPODS

Recommended Books for Devonian Fossils:

Fossil Collecting in the Mid-Atlantic States: With Localities, Collecting Tips, and Illustrations of More than 450 Fossil Specimens

This book is a must for West Virginia! It's also a classic!
Out of the 45 fossil collecting sites, 22 are from West Virginia, and another 10 or so are just across the border! Although the book is getting old, many of the sites are roadcuts and are still accessable. Many of these sites are roadcuts that expose the Mahantango Formation.

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!

Fossil Collecting Locations in this book are from Virginia, West Virginia, Pennsylvania, Maryland, and Delaware.

Trilobites: Common Trilobites of North America (A NatureGuide Book)
by Jasper Burns, 2000

I love Jasper Burns. His Fossil Collecting in the Mid-Atlantic book is still one of my favorite fossil books. His drawings are spectacular and the books are well laid out. This book serves as a field guide and identification guide to North American trilobites. If you fossil hunt for trilobites in North America, you should have this book!

Recommended Book on CD:

"Pennsylvania Paleozoic Playground"

This is an illustrated book (on CD) of fossils from Pennsylvania's Paleozoic period. It's a must for those who collect fossils along the mid-atlantic and from the paleozoic periods. It is written by Kerry Matt, who is one of the foremost fossil collectors in Pennsylvania and a personal acquaintance.

The CD book is actually 4 books in one:

Pennsylvania's Paleozoic Playground
Overview of The Paleozoic of Pennsylvania

The Lower Cambrian Explosion of life in my back yard
Cambrian of Pennsylvania

Swatara Gap Pa. Ordovician fossil fauna
In Depth Look at the Swatara Gap

Capturing Calvert
A look at the Calvert Cliffs Fossils from the Chesapeake Bay

It's a great book to use for reference, or it's nice to simply browse through the countless high quality images of fossils. Kerry Matt has found some very rare and world class fossils, which are all shown in this book.

This over 200 page Book is Available on CD and is in word document format (.doc). Each page is a separate descriptive document file, which actually, makes it incredibly easy to find specific fossils and fossil locations.

Cost: $21 + $2 shipping