The Geology of Cheesequake State Park: Eighty million years ago the park lands would have been right on the edge of the late Cretaceous period Atlantic Ocean. Some dinosaurs - likely Dryptosaurs, Hadrosaurs and Deinosuchus (distant relatives of crocodiles) might have been among the first park visitors as the land was just being built up. Clay and silt running down the ancient versions of the Delaware, Hudson and Raritan rivers collected along the shore which stretched in a southwesterly line from eastern Middlesex down to western Salem counties (the lime-green band in the image to the left). This sediment would mix with sand and eventually form (from lowest to highest) the muddy Cheesequake, sandy Magothy, gravelly Merchantville and clayey Woodbury sedimentary rock formations on which the park now sits. The formations are fairly similar being made up primarily of sand except the Woodbury Formation which contains a very pure white clay. It was this clay that was used to create the pottery that became area's first industry. The Woodbury Formation is also excellent for fossil hunting and in 1858 even yielded the skeleton of a Hadrosaurus - the first nearly complete dinosaur skeleton ever discovered. In more modern times, with the glaciers melting at the end of the most recent ice age, new rivers formed and sea levels changed dramatically. Eventually the Raritan bay started to intrude on the current low-lying areas and a salt marsh began to form.
What is a salt marsh? The land known as Cheesequake, a word derived from the native Lenape words "Cheseh-oh-ke" meaning Upland Village, contains an important natural resource - a large tidal marsh and estuary. Tidal marshes are lowlands that are regularly flooded by tides. The Cheesequake marshes are a brackish salt-marsh as sea water from the Raritan Bay mixes with freshwater run-off from the upland forest and developed land. The Cheesequake salt marsh is unique to the region in that the transitional zone from lower marsh to upland forest spans just a few yards in places. The great marshes in southern New Jersey require hundreds of feet to make the same transition. Salt marshes like this one are home to or are critical to the the survival of a surprising number of creatures. Read on to learn why!
How does a salt marsh form? Clay and silt particles drift down from higher land and slowly settle to the bottom. Eventually enough build up to start raising the land above sea-level. This process is called accretion. Marsh Accretion is a three part process involving the deposition of erosion from upland areas into a marsh along with sediment from tidal water which is trapped by grasses and deposited in the marsh. Also peat development by decomposition of marsh grasses builds on the marsh. These processes are in direct competition by RSL (Rising Sea Level) RSL is winning in areas and marsh development is being slowed or stopped in others. This is a major disruption to marsh accretion. The process takes many years. Core samples from the Cheesequake marsh estimate it to be at least 7000 years old! Eventually gentle a slope is created and meandering channels of water begin to form. With little to no direct wave action salt-tolerant grasses to begin to grow. The roots of the plants stabilize the mud while the rest of the plant helps trap more sediment. When a thriving colony of plant-life is established crustaceans and mollusks can move in and things start to change more rapidly. Grasses multiply the rate of accretion while ribbed mussels protect their roots. The tiny fiddler crab constantly aerates the mud by digging burrows throughout the mud-banks. As the marsh matures you will be able to identify the tide level by which plants are visible at any given time. Eel grass does well if it is completely submerged most of the time. Smooth Cord Grass (Spartina Alterniflora) grows right at the water's edge and is flooded at high tide. In areas that are only occasionally submerged you find Salt Hay (Spartina Patens) and the tall tufted Phragmites. This Earthcache guides you over a boardwalk that lies between the lower intertidal marsh and the dryer upper marsh.
Are marshes like this important? Definitely. The meandering streams and channels serve to filter pollutants that wash down from developed areas that would otherwise wash out into the bay or ocean. Wetlands are nurseries to most species of fish in the area. Most commercially harvested fish and shellfish species in the United States are at least partially wetland dependent. The waters are teaming with mummichog and other minnows, glass shrimp and diamondback terrapin turtles. On the water's edge you find various types of snails, ribbed mussels, blue and fiddler crabs. These invite larger animals like racoons and muskrats. Birds are also reliant on the marshes for food and shelter: common ducks and geese but also less common birds like terns, clapper rails, skimmers and egrets. If you are fortunate you may glimpse a Great Blue Heron or an Osprey hunting for fish. Many of these species cannot survive outside this limited environment and as much as half of New Jersey's tidal marshes have been developed over the years. Because of this New Jersey now has laws protecting coastal wetlands from pollution and development.
What dangers do tidal marshes face? We are by far the greatest threat to the marshes and their inhabitants. Hurricanes Irene and Sandy had almost no effect other than moving around the driftwood and broken off reed stalks but pesticides, pollutants and over-harvesting have destroyed several species of fish and the once famous Chingarora oyster. A European variant of phragmites was accidentally introduced and is now crowding out native marsh flora and reducing useful habitats for the indigenous fauna. Attempts at mosquito control in the early 20th century is still evident in aerial views; We cut straight lines across the marshes in order to drain them. The only effect was a decrease in the mosquito ravenous killifish population which resulted in even more mosquitoes. We tried again with pesticides in the mid-century and nearly wiped out the ospreys. Have we learned our lesson?
To log this Earthcache:
From the posted coordinates look out over the marsh. Notice the different types of grasses described above and at the nearby information kiosk.
1) Walk south west along the boardwalk. What is the primary type of grass growing right alongside the walkway?
2) Continue to the Crabbing Bridge. Note the muddy banks. Using what you have learned here, is it closer to high or low tide?
You should notice that this short walk took you from a marsh to the edge of an upland forest. This short of a transitional zone is rare in a salt marsh.
3) On the upland side of the bridge what is the composition of the ground under the thin layer of topsoil? Make a guess as to which Sedimentary Rock Formation you are standing on.
Optional: Describe any wildlife you see. Do you see fiddler crabs or their burrows? Photographs are not required but are most welcome! Follow the Blue Trail to the Perrine Pond waypoint to see an example of how the marsh survives while man-made constructions do not.
This Earthcache has been placed with permission of the park naturalist and park superintendent.