FOSSILGUY.COM

Guide To The Mahantango Formation: A Fossilized Devonian Coral Reef

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

---

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).

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.

Reference:
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.

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 eleven 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.

Here are 4 Mahantango Locations to get you started:

1. Pennsylvania - Danville:

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 at the Fossil Pit, there is even a big sign that says "Montour Fossil Pit". The preserve is open from sunrise to sunset - no pets allowed.

2. Pennsylvania - Swatara St. Park:

Swatara 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 fossil collect at the fossil pit.

3. West Virginia - Wardensville:

A few large road cuts on Route 55 starting around 2 miles east of Wardensville, West Virginia. The Gray shells contain fossils while the Black shales are relatively barren. Different layers will have different types and amounts of fossils.
There is one large pulloff at one of the roadcuts and a few areas with a very wide shoulder to park.

4. West Virginia - Delray:

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. Different layers will have different types and amounts of fossils.

---

Sample of Fossils Found in the Mahantango Formation:

There are many different types of fossils found in the Magantango. This is just a sample of the more common fossils one can find. Click on any of the images below to go to the Magantango Fossil Identification Page.

TRILOBITES
Basidechenella
Dipleura
Eldredgeops
Greenops

BRACHIOPODS
Athyris
Devonochonetes
Mucrospirifer
Protoleptostrophia
Tropidoleptus

BIVALVES
Goniophora
Leiopteria
Modiomorpha
Orthonota

CORAL
Pleurodictyum
Trachypora

GASTROPODS
Bembexia
Crenistriella
Tropododiscus

CEPHALOPODS
Agoniatites

CRINOIDS
Fragments

---

Recommended Trilobite and Fossil Hunting Books:

Recommended Equipment for splitting shale and mudstones