Science & Technology

Cretaceous Volcanic Ash Linked with Shale Gas and Oil Fields

An infinite volcanic flare-up on the finish of the dinosaurs’ reign kicked off a series of occasions that led to the formation of the U.S. shale oil and fuel fields from Texas to Montana. Rice College geologists mentioned older shale fuel fields, just like the Marcellus in Pennsylvania and Ohio, might have fashioned from related volcanic flare-ups a whole lot of hundreds of thousands of years earlier. Picture courtesy of Wikimedia Commons

Nutrient-rich ash from an infinite flare-up of volcanic eruptions towards the tip of the dinosaurs’ reign kicked off a series of occasions that led to the formation of shale fuel and oil fields from Texas to Montana.

That’s the conclusion of a brand new research by Rice College geologists that seems this week in Nature Publishing’s on-line journal Scientific Reviews.

“One of many issues about these shale deposits is that they happen in sure durations in Earth’s historical past, and a type of is the Cretaceous time, which is across the time of the dinosaurs,” mentioned research lead creator Cin-Ty Lee, professor and chair of Rice’s Division of Earth, Environmental and Planetary Sciences. “This was about 90 million to 100 million years in the past, which is about the identical time as an enormous flare-up of arc volcanoes alongside what’s as we speak the Pacific rim of the Western United States.”

Advances in horizontal drilling and hydraulic fracturing over the previous 20 years led to a U.S. power growth in “unconventionals,” a class that features the shale fuel and “tight” oil present in shale fields just like the Cretaceous Eagle Ford and Mowry and older ones just like the Barnett and Bakken.

A) Extent of continental magmatic arcs (purple strains) above ocean-continent subduction zones within the Cretaceous map taken from Cao et al. Location of discipline web site DR11 proven by star. (B) Size of continental arcs (black line, left vertical axis) and detrital U/Pb zircon ages (purple line, proper vertical axis) by time compiled from the literature. Continental arc size is predicated on compilation of granitoid plutonic belts by time and doesn’t essentially correspond with complete subduction size. Scientific Reviews, quantity 8, Article quantity: 4197 (2018) doi:10.1038/s41598-018-22576-3

“A lot of these pure fuel and oil are in tiny, tiny pores that vary from a number of millionths of a meter in diameter to a couple thousandths of a meter,” Lee mentioned. “The deposits are in slender bands that may solely be accessed with horizontal drilling, and the oil and fuel are locked in these little pockets and are solely obtainable with methods like hydraulic fracturing.”

Lee mentioned that there have at all times been hints of a connection between historic volcanic eruptions and unconventional shale hydrocarbons. Throughout discipline journeys out to West Texas, he and Rice college students seen a whole lot of ash layers in uncovered rock that dated to the Cretaceous interval when a lot of western North America lay beneath a shallow ocean.

One in every of these journeys occurred in 2014 whereas Lee and Rice colleagues additionally have been finding out how a flare-up of Cretaceous-era arc volcanoes alongside the U.S. Pacific rim had impacted Earth’s local weather by enhanced volcanic manufacturing of carbon dioxide.

“We had seen ash layers earlier than, however at this web site we may see there have been loads of them, and that bought us pondering,” Lee mentioned. Lee, graduate pupil Hehe Jiang and Rice undergraduates Elli Ronay, Jackson Stiles and Matthew Neal determined to research the ash beds in collaboration with Daniel Minisini, a colleague at Shell Oil who had been doing intensive work on quantifying the precise variety of ash beds.

Oxygen-depleted “useless zones” typically type within the northern Gulf of Mexico because of nutrient-rich runoff from the Mississippi and Atchafalaya rivers, that are seen right here as tan and greenish-brown plumes seen from the Worldwide House Station in 2012. Nutrient-rich volcanic ash might have fed related useless zones that produced shale oil and fuel fields from Texas to Montana. (Picture courtesy of NASA/GSFC/Aqua MODIS)

“It’s nearly steady,” Lee mentioned. “There’s an ash layer at the very least each 10,000 years.”

Lee mentioned the workforce decided that ash had come from a whole lot of eruptions that spanned some 10 million years. The layers had been transported a number of hundred miles east of their volcanic supply in California. The ash was deposited on the seafloor after being blown by plumes that rose miles into the ambiance and drifted over the ocean. Lee and college students analyzed samples of the ash beds within the geochemical amenities at Rice.

“Their chemical composition didn’t look something like it could have after they left the volcano,” he mentioned. “A lot of the unique phosphorus, iron and silica have been lacking.”

That dropped at thoughts the oceanic “useless zones” that always type as we speak close to the mouths of rivers. Overfertilization of farms pumps giant volumes of phosphorus down these rivers. When that hits the ocean, phytoplankton gobble up the vitamins and multiply so rapidly they draw all of the obtainable oxygen from the water, leaving a “useless” area void of fish and different organisms.

Lee suspected the Cretaceous ash plumes may need induced the same impact. To nail down whether or not the ash may have provided sufficient vitamins, Lee and his workforce used hint parts like zirconium and titanium to match ash layers to their volcanic sources. By evaluating rock samples from these sources with the depleted ash, the workforce was in a position to calculate how a lot phosphorus, iron and silica have been lacking.

“Usually, you don’t get any deposition of natural matter on the backside of the water column as a result of different residing issues will eat it earlier than it sinks to the underside,” Lee mentioned. “We discovered the quantity of phosphorus coming into the ocean from this volcanic ash was about 10 instances greater than all of the phosphorus coming into all of the world’s oceans as we speak. That may have been sufficient to feed an oxygen-depleted useless zone the place carbon could possibly be exported all the way in which right down to the sediment.”

The mixture of the ashfall and oceanic useless zone concentrated sufficient carbon to type hydrocarbons.

“To generate a hydrocarbon deposit of financial worth, you need to focus it,” Lee mentioned. “On this case, it bought concentrated as a result of the ashes drove that organic productiveness, and that’s the place the natural carbon bought funneled in.”

Lee mentioned shale fuel and tight oil deposits aren’t discovered within the ash layers however look like related with them. As a result of the layers are so skinny, they don’t present up on seismic scans that power corporations use to search for unconventionals. The invention that a whole lot of intently spaced ash layers could possibly be a tell-tale signal of unconventionals would possibly permit business geologists to search for bulk properties of ash layers that will present up on scans, Lee mentioned.

“There are also implications for the character of marine environments,” he mentioned. “Right this moment, phosphorus can also be a limiting nutrient for the oceans, however the enter of the phosphorus and iron into the ocean from these volcanoes has main paleoenvironmental and ecological penalties.”

Whereas the revealed research appeared particularly on the Cretaceous and North America, Lee mentioned arc volcano flare-ups at different instances and areas on Earth can also be liable for different hydrocarbon-rich shale deposits.

“I think they might,” he mentioned. “The Vaca Muerta discipline in Argentina is identical age and was behind the identical arc as what we have been finding out. The rock document will get extra incomplete as you go additional again in time, however by way of different U.S. shales, the Marcellus in Pennsylvania was laid down greater than 400 million years in the past within the Ordovician, and it’s additionally related with ashes.”

The analysis was funded by the Nationwide Science Basis, the Guggenheim Basis and the Geological Society of America.

Publication: Cin-Ty A. Lee, et al., “Volcanic ash as a driver of enhanced natural carbon burial within the Cretaceous,” Scientific Reviews, quantity 8, Article quantity: 4197 (2018) doi:10.1038/s41598-018-22576-3

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