Shale Oil Deposits Caused By Volcanic Ash From The Time Of The Dinosaurs

When large pulses of phosphorus enter the Gulf Of Mexico, large dead zones occur as phytoplankton consume all the oxygen. A similar process after volcanic eruptions could have produced shale oil and gas. NASA/GSFC/Aqua Modis 

The term “fossil fuel” for oil and gas has never been more appropriate. Oil and gas deposits of the central United States are the result of volcanic eruptions towards the end of the dinosaurs' reign. The work is the strongest confirmation yet of volcanic involvement in the creation of these types of rocks in many locations.

Much of the world's oil and gas is trapped in sedimentary rocks known as shale. Rather than being pooled in large basins like other deposits, shale fluids are held in tiny pores, micrometers to millimeters across within the rock. To extract economic amounts of fuel from these shales requires the hydraulic fracturing, or fracking, that technological advances only recently made economically viable. Consequently, across much of the world, long-ignored shale oil and gas have suddenly become both an economic boom and an environmental curse.

While some have raced to exploit these deposits, others have sought to understand them. Professor Cin-Ty Lee of Rice University had seen hints of a connection to volcanic eruptions, but found nothing conclusive until he came across hundreds of layers of ash in West Texas' Cretaceous rocks. This area, along with territory as far north as Montana, was once the floor of a shallow ocean. "We had seen ash layers before, but at this site we could see there were a lot of them, and that got us thinking,” Lee said. “It's almost continuous. There's an ash layer at least every 10,000 years.” Over a period of 10 million years, that adds up.

A 13-meter (40-feet) high outcrop of the Eagle Ford Shale. Ash layers have an orange color. Lee et. al/Scientific Reports

The ash was traced back to volcanoes in what's now California, part of a huge Pacific rim arc that erupted 90-100 million years ago. However, Lee noticed something strange about the ash layers. "Their chemical composition didn't look anything like it would have when they left the volcano," he said. In fact, three-quarters of the silicon, iron, and phosphorus the volcanoes would have emitted in the ash had been leached out.

What was left reminded Lee of what happens when farms apply too much phosphorus as fertilizer, with the excess running into lakes or oceans. Phytoplankton gobble the precious nutrient up in huge blooms, taking oxygen with it, leaving the waters uninhabitable to anything else. "We found the amount of phosphorus entering the ocean from this volcanic ash was about 10 times more than all the phosphorus entering all the world's oceans today,” Lee said.

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