Discovered: The Largest River Delta Ever on Planet Earth

River delta at the Irrawady
© lavizzara/

Written by Lisha Pace

Published: October 2, 2022

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Have you ever wondered what the world was like during the Triassic period, way before the Jurassic period when T-Rex roamed the Earth? The discovery of a 1.65 million square kilometer river delta plain might give you an answer.

In a 2018 study published in the journal Geology, scientists discovered the Triassic Boreal Ocean Delta near the Barents Sea, off the northern coasts of Norway and Russia.

The Triassic Boreal Ocean Delta is the largest river delta known to have formed on the Earth’s surface. It is even larger than the Ganges River Delta, which would make up only 1/10th of the Triassic Boreal Ocean Delta’s size. If the Triassic Boreal Ocean Delta existed today, it would be equal to 1% of the earth’s current landmass since it appeared to cover the entire basin of the Barents Sea.

How Old and Big Was the Triassic Boreal Ocean Delta?

Scientists believed that the Triassic Boreal Ocean Delta formed during the end of the Permian period and the beginning of the Triassic period. At that time, the supercontinent Pangaea was still present, and it was there that this river delta plain was formed. This period was probably 200 million years before even the famous dinosaurs of the Jurassic and Cretaceous periods roamed the land.

The Triassic Boreal Ocean Delta is the biggest one formed on the earth’s surface. Tore Grane Klausen, the study’s lead author, said that the drainage for the Triassic deltas would have been twice the size of the deltas that lead to the Mississippi today. It was also 10 times larger than the Amazon delta.

With over 600,000 square miles, the Triassic Boreal Ocean Delta was 10 times more than the size of the Ganges-Brahmaputra Delta, the modern-day largest river delta. It was also more than 62 times the size of the Nile River Delta, which is only 9,650 square miles.

In comparison, this river delta is almost as big as Alaska. Researchers believe there could be bigger ones, but they got lost due to geological processes over the years. But as of now, based on the existing scientific discoveries, the Triassic Boreal Ocean Delta is the biggest the world has ever seen.

The Role of the Triassic Boreal Ocean Delta in the Resurgence of Species

Scientists date the delta to be around 200 to 230 million years old based on the Zircon found in the deltaic sediments. During this time, dinosaurs were only starting to emerge in the middle of the Triassic period. The world itself came off the most devastating mass extinction ever recorded in Earth’s history—the Permian-Triassic Extinction, which some referred to as “the Great Dying.” This phenomenon wiped out more than 90% of the land and ocean species after several volcanic eruptions.

The delta is said to be the perfect site for the resurgence of species after the Great Dying. Paleontologists believed that terrestrial and marine life rebounded and evolved post this extinction period.

The Formation of the Triassic Boreal Ocean Delta

Several phenomena are thought to have created the massive delta. The plain was likely formed by sediments coming from mountains, which resulted from the formation of the supercontinent, Pangaea. Then, continents collided to create the formation of the land where mammals and reptiles roamed.

These events, called Variscan Orogeny and Uralian Orogeny, were what formed modern-day land and rock formations. The mountains of Great Britain, Portugal, Spain, and Ireland were formed as a result of these events. Even the Ural Mountains were a creation of these collisions.

How Did the Delta Grow So Massively?

The Triassic period had a warm climate, which means that sea levels rarely changed. Over time—around two to five million years—the delta grew to the size scientists discovered.

During the Triassic period, there was very little biodiversity in areas near the equator. These areas were probably too hot and dry that only a few species remained. But with the help of river deltas, these areas became cradles of life, just as river deltas are now. Early mammals and dinosaurs likely stayed near the delta since they tend to be rife with many forms of life, including prey.

Scientists have suggested that the Triassic Boreal Ocean Delta may have been full of lush vegetation, flora, and fauna. It is thought to have been similar to the ecosystems in river deltas today. It likely had deltaic wetlands, ferns, and gingkophytes. Experts also believed there were labyrinthodonts, pliosaurus, and ichthyosaurs in the seas surrounding the delta.

Why Humans Are Fascinated with Deltas

Humans have always been drawn to deltas because they are fertile and full of life. They are also always rich in water. Deltas are used for their agricultural potential. They have supported large-scale agriculture since ancient civilizations. Because of this, the Nile Delta played a huge role in Ancient Egypt.

But, the very reason river deltas are so fascinating to humans is also the reason why they are challenging to study. Humans tend to alter the characteristics of the places they inhabit. They change the flow of rivers, thereby changing the sedimentary structure that covers the delta’s features. Once covered, it becomes difficult for scientists to study the natural growth and evolution of the deltas.

The Triassic Boreal Ocean Delta was possible because of a unique geographical setting. Unlike the modern delta, the ancient delta only had 400 meters of basin. Modern deltas are emptied into several kilometers of the basin from the edge of the continental shelf. This stops the growth of modern deltas. However, the Triassic Boreal Ocean Delta was the opposite.

For about one million years, the Triassic Boreal Ocean Delta grew uninterrupted. It collected large supplies of sediments from monsoon rains. Researchers are open to the idea that the ancient delta might have even been bigger than initially thought. After all, they have never seen the edge of it. Discoveries of deposits in eastern Greenland and Canada support the possibility that the Triassic Boreal Ocean Delta was far from being 1.65 million square kilometers.

How the Discovery Came to Be

Like many discoveries, the Triassic Boreal Ocean Delta was purely accidental. Scientists were researching another topic when they found evidence of what looked like an ancient river delta. Researchers always believed there was a massive river delta plain from millions of years ago, but they didn’t know where to look.

To get an accurate representation of the Triassic Boreal Ocean Delta, researchers had to examine well logs, rock samples, and seismic histories. The data collected showed a massive geological and hydrological feature.

They also used seismic reflectors, which are akin to sonars. These enabled scientists to look at the different rock layers in the subsurface. There was a distinct seismic signature on the sediment deposits left on the delta’s channels. The researchers compared this data to the data from the delta deposits from Svalbard, Norway. Despite the great distance, the samples showed they were of the same age.

The Impact of the Triassic Boreal Ocean Delta on the Period

If the presumed dates are accurate, it is possible that the Triassic Boreal Ocean Delta was born out of the Great Dying or, at least, it was the only survivor of that massive extinction. To many, this meant that the ancient delta witnessed the resurgence of life on earth. It is widely believed that the Great Dying almost wiped out the entire species on water and land, but the impact was supposedly more massive on land. The ancient delta could hold clues to prove or disprove these assumptions.

The discovery of the river delta also meant that dinosaurs could have roamed that part of the Earth. Enormous herbivore dinosaurs could have made the river delta plain their habitat because of the rich fauna. More research needs to be done since there is a possibility that the delta might also house dinosaur fossils.

What is the largest Delta in the World Today?

The Ganges Delta, in the south Asia area of Bangladesh and India, is the largest delta in the world today. The delta plain, about 350-km wide along the Bay of Bengal, is formed by the confluence of the rivers Ganges, the Brahmaputra and Meghna.

Triassic Boreal Ocean Delta, in Summary

Age200 to 230 million years
LocationNear the Barents Sea, off the northern coasts of Norway and Russia.
SizeOver 600,000 square miles
FormationVariscan Orogeny and Uralian Orogeny, formation of continents
ImpactContributed to the great resurgence of life after the great dying extinction event

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About the Author

After a career of working to provide opportunities for local communities to experience and create art, I am enjoying having time to write about two of my favorite things - nature and animals. Half of my life is spent outdoors, usually with my husband and sweet little fourteen year old dog. We love to take walks by the lake and take photos of the animals we meet including: otters, ospreys, Canadian geese, ducks and nesting bald eagles. I also enjoy reading, discovering books to add to my library, collecting and playing vinyl, and listening to my son's music.

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