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Guide to Fossil Hunting in the Mahantango Formation


Guide to Fossil Hunting in the Mahantango Formation

Devonian Mahantango

Guide To The Mahantango Formation: A Fossilized Devonian Coral Reef

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

A large Dipleura trilobite found in the Mahantango Formation of Central PA.

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

A grammysioidea bivalve from the Mahantango

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).

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.

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 roadside exposure of the fossil bearing Magantango 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 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.

Trilobite Fossils TRILOBITES

Brachiopod Fossils BRACHIOPODS

Bivalve Fossils BIVALVES

Coral Fossils CORAL

Gastropod Fossils GASTROPODS

Cephalopod Fossils CEPHALOPODS

Crinoid Fossils CRINOIDS

Recommended Trilobite and Fossil Hunting Books:

The Trilobite Collector's Guide
Andy Secher, 2024

This book by Andy Secher, a leading trilobite collector, offers a captivating journey into the world of these ancient arthropods. With over 400 stunning photos, entertaining top-ten lists, invaluable collecting tips, and ways to spot a fake trilobite, it's a must-have for fossil enthusiasts!

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

An excellent guide for identifying North American trilobites, featuring meticulous line drawings and concise information on classification, geologic range, and distribution. Ideal for enthusiasts seeking detailed insights and accurate identification of these ancient arthropods.

101 American Fossil Sites You've Gotta See
Albert B Dickas, 2018

This is a great updated fossil sites book with at least one fossil site in each state. Each site is broken into 2 pages. One has detailed information, such as directions, GPS coordinates, formation information, etc... The other is dedicated to images of the site and the fossils found there. It also gives information on fossil 'viewing' sites such as dinosaur trackways, museums, and active excavations.
Plus, my fossil photos are peppered throughout this book!

Recommended Equipment for splitting shale and mudstones

INCLY Amazon Store: Rock Hounding Gear

INCLY provides budget-friendly rock hounding gear, ranging from the widely favored (4.6/5 stars) 15-piece Geology kit featured in the image to compact 4 and 5-piece sets. These tools are ideal for fossil and mineral collecting, particularly in harder matrixes and shale.

Rock Pick - 28 oz Geological Hammer with Pointed Tip & Shock Reduction Grip - 11.4 Inch

I bought this as a replacement rock hammer. The color makes it stick out so you don't lose it in the field! It's a little heavier than your average hammer, making it easier to break rock. It also has a nice grip and for under $20, it's a great deal!

TOOLEAGUE Heavy Duty Masonry Chisel,8 inches Brick Chisel with Hand Protection(1Pc)
Albert B Dickas, 2018

I learned years ago to only use chisels with hand guards! The bright color makes also makes it hard to lose when you set it down. This is a nice wide chisel ideal for splitting thin shale.

Trilobite Fossils:

Trilobite fossils are some of the most beautiful and collectible fossils in the world! There are countless species and countless colors of trilobites. They make beautiful display pieces and conversation pieces. Common ones make very affordable for gifts to fossil and paleontology enthusiasts. Fossil Era has a huge selection of top quality trilobites from many states and many countries. It's fun just to browse through the inventory and look at all the different types!

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