Earth’s Largest River Delta Was the Size of Alaska

The Triassic Snadd delta between Norway and Russia lasted millions of years and was likely a biodiversity hotspot

Snadd Delta
A bit of the ancient delta off the coast of Svalbard. Tore Grane Klausen

It seems like everything was bigger in the Triassic period. The dinosaurs, of course, were colossal, the volcanic eruptions were massive and even the land area was supersized across the vast supercontinent Pangaea. Now researchers have found another superlative to add to the list. The largest river delta to ever exist on Earth was formed during the Triassic.

Michael Marshall at New Scientist reports that the massive delta floodplain was ten times the size of the Amazon and Ganges deltas, the current largest delta floodplains on the planet. It dates to 227 to 237 million years ago, around the time when the first mammals and dinosaurs evolved.

Researchers identified the delta in the Barents Sea between the north of Norway and Russia by examining core samples drilled by energy exploration companies and examining seismic data. The delta was so large, if it were around today, at roughly 637,100 square miles, it easily covers Alaska with mileage to spare.

So what created such a massive delta? The flood plain was likely formed by sediments carried from mountains created when continents collided during the formation of Pangaea. Those events, called the Variscan Orogeny and Uralian Orogeny created the mountains of Spain, Portugal, Ireland and Great Britain as well as the Ural Mountans, which extend through west central Russia. “The drainage for the Triassic deltas could have been twice that of what feeds Mississippi today,” Tore Grane Klausen of the University of Bergen and lead author of the study in the journal Geology tells Jonathan Carey at Atlas Obscura via email.

The delta wasn’t just a flash in the Triassic pan. The team estimates that it grew over the course of 2 to 5 million years, which lines up with the idea that the Triassic had a pretty steady warm climate in which sea level did not change much. Most of the deltas currently found on Earth appeared in the last 10,000 years.

Marshall at New Scientist reports that during the Triassic, areas near the equator were likely too hot and dry to support much biodiversity. River deltas, like this one, however, were probably cradles of life, just as they are today. The area was likely covered in lush vegetation and full of labyrinthodonts, an amphibian forerunner of many land animals. It's possible the earliest dinos and mammals also skittered across the delta's sediments.

The fossils found at the site seem to bear this out. “Everywhere you look, you can pick up these sandstone samples with imprints of ferns,” Klausen tells Marshall.

So what’s the name of this magnificent geographical wonder? The researchers suggest calling the area the Snadd Delta after the rock formation in which it was found, though we think the better name for it might be Amazon Prime.

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