Purse Beach, located along the Potomac River on Maryland’s western side, is a great place to find fossil shark teeth. Purse Beach is the former Purse State Recreation Area, which was absorbed into Nanjemoy Wildlife Management Area. The WMA consists of a number of parcels of land on the east side the Potomac River as well as along State Route 224. The Nanjemoy WMA has a wide range of recreational opportunities, such as bird watching, fishing and hunting.
Shark Teeth Fossilization
Fossilized teeth of sharks are easily identifiable. Sharks’ internal skeleton is cartilage, which disappears quickly after burial. The teeth and dermal-ossicles (the tiny, hard protrusions that look like sandpaper on shark skin) are the main exceptions. The central vertebrate is also calcified, and can be fossilized. Cartilage breaks down more quickly than shark teeth because it does not mineralize. The most common fossils are shark teeth, but other fossils such as dermal ossicles or vertebrates can also be found. The dermal-ossicles can be difficult to identify because they are so small.
Permineralization is the process by which shark teeth fossilize. Other organisms, such as crab fossils found on Florida beaches, can also undergo permineralization. It occurs when minerals in water fill the empty spaces of an organic tissue or organism. Sharks that lose a tooth, or die, sink to the bottom. They may also be covered with sediment. Sharks or teeth that aren’t buried will dissolve, for example, those that sink to a rocky base or settle in rapidly moving water. The buried material creates an anaerobic environment that is oxygen-deficient and preserves shark teeth or other hard parts.
The sediments accumulate over time and the pressure of the sediments forces water containing dissolved minerals to enter the tooth. Eventually the minerals crystallize. The tooth is almost completely replaced by calcium, phosphorus, iron and silica. Later, the buried sediments will be eroded by tectonic force and exposed to the fossils and shark teeth. Mineralization takes a long time. The age of fossil shark teeth can range from 75 million years to 10000 years. To determine the age, you need to know the geologic formation where the fossil was found. The fossil shark tooth is also blackened or dark greyed by the permineralization procedure, making it easier to identify in the sands of the beach.
The Fossil Rich Aquia Form
Aquia Formation contains fossils such as shark teeth, and is found at Purse. The Aquia Formation consists of silty glauconitic, clayey sands. Some areas are rich in fossilized invertebrate remains. The Aquia Formation is a sedimentary rock that was formed during the Paleocene Epoch. This was between 59 and 55.5 million years back. The Aquia Formation in Maryland is older than sediments found at Calvert Cliffs, a shark tooth-collecting area along the eastern shore of the Chesapeake. Calvert Cliff fossils belong to the Chesapeake Group and were formed during the Miocene Epoch (23- 5 million years ago). The fossils of the Calvert Cliffs were deposited much more recently than those found in the Purse Area.
The Aquia Formation in Maryland’s southwest is most visible along the Potomac along the cliffs and along the streams that have cut through the formation. The cliffs on the Potomac are unstable, and they are continually eroding. The exposed sections have more shark teeth and Paleocene-era fossils.
Purse Area Beaches
Purse is a remote area, but all the roads leading to it are paved. State Route 224 is also known as Riverside Road and bisects Nanjemoy WMA. Signage indicating the parking lot is located in the Nanjemoy WMA is prominently displayed at trailhead. Parking is available on the side of the road to the south of the park. These areas have limited parking, and on busy days collectors could be forced to walk for up to a quarter of a mile in order to reach the trailhead.
The path to the beach from the parking is flat and clearly marked. Collectors will not be lost if continue walking westward. There are no nearby restaurants or restrooms because the area is so remote. Bring plenty of water and a lunch. You should be prepared as those who leave their parking spot will lose it quickly and miss the opportunity to spend time on the beach.
Purse beach advantages
It is difficult to find space for a lunch break or to relax if it is crowded. It gets narrower when the tide is high. It is most popular on the weekends, like most beaches. However, people do come during the week.
Purse Beach is also a great place for fossil hunters and other visitors. The beach faces West, so there is sun until dark. It is quite a contrast from the beaches of the Calvert Cliffs in the eastern part of Maryland which face east. After the sun sets, the eastern Maryland collecting sites become much colder and darker.
Find shark teeth
On the beach, and near the water, you can find fossilized ray dental plates and shark teeth. Some collectors use small trowels or shovels to dig in the beach gravel, then use screens to check for shark’s teeth. For screening, a colander made of metal or a similar screen is ideal. But it’s important that the holes be sized properly. The larger holes will allow some smaller teeth to pass through them, while the smaller holes will prevent the sand from being screened. In general, the holes should have a minimum diameter of one quarter inch. Some collectors create their own screens by using wood and wire screens from the local hardware store.
Collectors can find shark teeth, and other fossils by scanning the waterline. The low tide is the best time to collect, and you can find tide tables easily online. Shark teeth, fossils and other traces of life can be found on the beach because the sand and sand particles are constantly being reworked. Shark teeth and rays plates are dark and easy to spot in the brown sand. Black shark teeth with sharply angled shapes stand out in the brown sand. The rectangular ray dental plates are black and also have a rectangular form.
Purse Beach is home to many shark teeth, ray plates and other small rays. Some of these are as small as a quarter-inch. The larger teeth can be found in the same area as smaller teeth. The largest teeth can reach up to an inch in size. Purse’s teeth are generally pointed and curved in comparison to other shark teeth sites that have large triangle-shaped tooth shapes. The teeth in Purse are very narrow and sharp, and are believed to be from Scapanorhynchus. This is an extinct shark genus that is similar to the living goblin.
The best way to avoid injury is by wearing shoes when walking on the sand. The beach is a place where broken glass can be found, but small sharp pieces of driftwood are the greatest danger to barefooted people. The beach is usually open and accessible from the trail. It is best to avoid the water if you are carrying a camera or phone. Some of the water can be more than your waist depth and it is possible to trip or slip.
Turritella Fossils – A Bonus
There are small cliffs north of the trail, where it meets the beach. The rocks in this area are covered with fossils. Many of them are turritellas which are tightly coiled snails in a cone-shaped shape. Some of the casts of fossils are still intact, even though most of them are crumbling and weathered. The fine mud has preserved some of the interior spaces of the turritella. The mud remained intact even after the original shells were eroded. These casts are like a negative of the original animal’s shell.
Turritella, a medium-sized genus of sea snails. The shells are coiled and resemble an elongated conical shape. The name comes from the Latin “turritus” which means turreted or towered. The Latin diminutive suffix “-ella” means small. Turritellas are found in all parts of the world and can range from the Cretaceous up to modern times. Turritella Agate is a stunning specimen.
Turritella fossils can be found in a variety of places
The Potomac River has a small point south of the trail. Just south of this swampy area, which drains into the river, is a small point on the Potomac. The cliffs get steeper to the south of the swampy areas, and there are many fallen trees that block the beach path. On the shore, sections of the cliffs are collapsed. It is difficult to get into this area, as you will need to climb over fallen trees and wade in the water.
This area contains huge outcrops from the Aquia Formation. In some sections the rock is entirely made up of fossils. The fossils can be easily seen because they are usually white, against a brown-to black matrix of sandstone. Turritellas and bivalves are abundant in the outcrops. Many of these fossils are solid, but are also found in loose pieces near the large boulders and outcrops. The fossils in the large blocks that fell from the cliffs can be found on the matrix of the fallen blocks. Illegal to dig into the cliffs as it increases erosion, and can be hazardous in areas with overhangs. In this area, large rocks are also found with distinct turritella castings. Although shark teeth are present on the beach near cliffs, it is hard to find them in this area because of the rocks.
How to find GPS coordinates and purse
Purse, located in Charles County’s southwest corner, can be reached via State Route 224. This route roughly follows the Potomac River. State Route is also called Riverside Road. The parking area is marked with a sign that says “Nanjemoy Wildlife Management Area.”
These are the key GPS coordinates that Google Earth provides:
• Parking area at trailhead: 38°25’56.33”N, 77°15’6.28”W
• Beach area at end of trail: 38°25’54.69”N, 77°15’23.34”W
• Southern outcrops with turritella fossils: 38°25’24.81”N, 77°15’40.00”W
Purse can be accessed throughout the year depending on the weather. Winter can be a problem with snow and ice, while thunderstorms pose a danger, particularly during unsettling weather conditions in spring and summer. Purse offers a great opportunity for families and experienced collectors to collect shark teeth and fossils of turritella.
This story about fossil shark teeth previously appeared in Rock & Gem magazine. Subscribe by clicking here. Story & Photos by Robert Beard.
The post Fossil Shark Teeth at Purse Beach first appeared on Rock & Gem Magazine.