How It All Began: The Geology of the Marcellus Shale

The Marcellus sprawls under more than half of Pennsylvania. It stretches for 95,000 square miles and is believed to be the the third largest natural gas field in the world. When you're here or in surrounding states, you see a similar type of shale just about everywhere rock is exposed. But how did it get here? With the help of some sound effects, and a geologist who can really give you a taste of the shale, The Allegheny Front's Jenelle Pifer explores the creation of the Marcellus formation.

Read the transcript »Close the Transcript

Transcript

OPEN: The Marcellus sprawls under more than half of Pennsylvania. It stretches for 95,000 square miles and is believed to be the the third largest natural gas field in the world. When you're here or in surrounding states, you see a similar type of shale just about everywhere rock is exposed. But how did it get here? With the help of some sound effects, and a geologist who can really give you a taste of the shale, The Allegheny Front's Jenelle Pifer explores the creation of the Marcellus formation.

PIFER: Geology professor Charles Jones takes a small path toward Chartiers Creek. Along the way, he's quick to point out things he finds interesting: a hill covered in Garlic Mustard and a meadow that gets packed with praying mantises in the summer.

JONES: I found in the loose rock here a nice little piece of black shale.

PIFER: Shale is nothing more than mud that has been compressed until it turns to stone, a process that takes millions of years. The Marcellus is a black shale--the black coming from marine organic matter compressed inside the mud.

JONES: You can see the very, very fine, thinner-than-millimeter-scale layers in this rock.

PIFER: How would people see black shale and know it's black shale? This rock, in particular, is covered in mud.

JONES: Right. Well, there's a reason geologists carry rock hammers. You look at the shale and you break it open, and if you can't see a granular texture, and it breaks into platy pieces, it's going to be a shale. The shales can either be a silt stone or a clay stone, and if you want to really see if you have a clay stone, what you do is you chew on the rock a little bit. You just take a bite, and you can chew it down and it just turns into a smooth grit. So, this is a clay stone.

PIFER: Of course, you wouldn't be able to do this with most of the Marcellus Shale, because it's still buried thousands of feet below the surface, and has been since it began to form 380 million years ago. To get a sense of some of the sights and sounds of the time takes a bit of imagination.

The United States was flipped on its eastern side. Pittsburgh was south of the tropics--about 30 degrees below the equator. Sea level was high back then. So high that a narrow finger of shallow water, called the Appalachian Seaway, swelled up from the Gulf of Mexico and into Pennsylvania and upstate New York.

JONES: Would have been kind of nice, a place to go boating. It would've had beaches on both sides of this little body of water.

PIFER: Unfortunately, there wasn't anyone around to enjoy it. We're talking almost 200 million years before the first dinosaurs. Most living creatures at that point were fish.

JONES: They were like a freak show of fish by our standards. They were crazy. They had all these different shapes. Most of them had no jaws. They just sort of had this fleshy opening where they could slurp stuff up.

PIFER: So, if you think of the Appalachian Seaway as a big fish tank, Jones says, one that hasn't been cleaned in a while, the Marcellus Shale would have been that fluffy slime that started to build up along the bottom.

JONES: There are little microscopic plankton living in the water column. They photosynthesize; they die. They have a very rapid turnover. They just produce far more mass of dead organic material than do fish or any animals.

PIFER: It's this organic matter that, if heated and compressed, will eventually turn to oil or natural gas.

In Pennsylvania, the Appalachian Seaway reached depths of up to 750 feet. Shallower areas to the south, in present-day Tennessee and Kentucky, restricted these deeper waters from circulating freely with the ocean. As a result, the water along Pennsylvania's sea floor was dark, still and almost completely devoid of oxygen. And this was key, because when the dead plankton landed, they stayed put. And they layered and layered and layered.

This went on for a few million years. Plankton lived; they died; they sank. And then, to quote Jones, "the action really began."

A sliver of land, roughly the size of Japan, slammed into eastern North America and put up a huge chain of mountains. And it wasn't long afterward that Africa smashed into the east coast and raised the Appalachians. When these mountain chains eroded, tons of sediment poured into the basin and buried the mud on the sea floor, until modern-day Pittsburgh was covered in 16,000 feet of sediment.

JONES: This point of maximum burial is when the Marcellus Shale formation would have been subject to the maximum temperature and maximum pressure. It was in this pressure cooker, and the organic matter was getting converted into natural gas. It turns out the shale has lots of little spaces between all those little grains of mud. It's very difficult to go from one space to another, so this shale is porous, but it's not very permeable. So all this gas, as it was forming, some of it was expelled, but a lot of it stayed in the Marcellus, and it's stayed there until today.

For The Allegheny Front, I'm Jenelle Pifer.