Two Hundred Million Years Ago in New Jersey

Time travel back about two hundred million years ago in your time machine that is sitting in Mine Brook Park (Flemington, NJ). When the dials stop, you would find yourself in a rifting Pangaea amidst volcanic activity that is occurring throughout New Jersey.

Okay, we don't have a time machine, but if you take note of the rock exposures along the Walnut Brook and many other locations in NJ, you can read the story of our state's geologic past.

Pangaea (see map) is a term that comes from Ancient Greek "pan" meaning "entire" and Gaia meaning "Earth" and is used to the supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago before the component continents were separated into their current configuration.

Throughout the history of the planet, Earth's plates have merged together then split and drifted apart. This action is a byproduct of a well-known geologic theory called plate tectonics. This theory states that the Earth's surface is broken up into roughly 20 or so giant pieces of rigid crustal plates that carry the oceans and continents with them as they move slowly around the planet.

It's a topic that hasn't just been for classroom study lately with the earthquakes in Haiti and Chile - and even a few small ones in Somerset County, NJ recently.

In New Jersey, earthquakes are measured with seismographs operated by the Lamont-Doherty Earth Observatory of Columbia University and the Delaware Geological Survey. New Jersey doesn't get many earthquakes, but it does get a few small ones.

Pangaea was cracking apart or "rifting" and as the North American Plate moved westward, separating from what is now Africa, volcanic activity deep in the earth was triggered. The rift would lead to the formation of the Atlantic Ocean.

The magma (molten rock) that erupted on the surface as a lava flow eventually cooled and solidified to form the igneous rock called basalt that is known as the Orange Mountain Basalt.

Along Walnut Brook, you can see the contact points between the basalt and the older red shale of the Passaic Formation. That older red shale is from lake sediment deposits which was covered by the lava flow.


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