Weve discovered a massive dinosaur-era river delta under the sea

https://www.newscientist.com/article/2197767-weve-discovered-a-massive-dinosaur-era-river-delta-under-the-sea/

The Amazon Delta

The Amazon delta was a tenth the size of a recently discovered dinosaur-era delta

Planet Observer/Universal Images Group via Getty Images

A vast floodplain 10 times the size of the Amazon delta existed during the early days of the dinosaur era. It is the largest known delta from Earth’s history and may have been a crucial habitat.

During the Triassic period when dinosaurs first appeared, all of Earth’s continents were joined together in a supercontinent called Pangaea.

Part of northern Pangaea is preserved under the Barents Sea between Norway and Russia. So Tore Grane Klausen, whilst at the University of Bergen in Norway, and his colleagues took data from drilling wells in the Barents Sea and combined it with seismic data to map the rock layers.

Advertisement

The team found preserved sediments from a delta that existed 237 to 227 million years ago. A delta is a wide, flat plain of muddy sediment that forms when a river meets a larger water body, like a lake or ocean.

The remains spanned the entire Barents Sea and were 10 times the size of largest modern deltas in the Amazon and the Ganges. This equates to 1.65 million square kilometres, or about 1 per cent of the total modern land area.

The team has not named the delta, but has informally called it the Snadd Delta because they found it in rocks called the Snadd Formation.

Delta plain dinosaur stomp

A delta forms when rivers carry sediments downstream then dump them by the coast. The accumulated sediments form vast, fertile plains that can support huge numbers of plants and animals.

The ancient delta lay on the north coast of Pangaea. It was fed by multiple rivers flowing north from a mountain range, which supplied huge volumes of sediment. In turn, intense monsoon rains formed the rivers.

The animals that would have lived in the delta have not been studied in detail, but they included amphibians called labyrinthodonts that often lived in wetlands. The plant life included lots of ferns and some conifers.

“Everywhere you look, you can pick up these sandstone samples with imprints of ferns,” says Klausen. Just off the coast, crocodile-like pliosaurs and dolphin-like ichthyosaurs ruled the seas.

Much of the rest of Pangaea was less hospitable. The regions close to the equator spent much of the Triassic as extremely hot and dry deserts, so the delta may have been a major centre of biodiversity.

The delta was also long-lived, steadily growing for periods of 2 to 5 million years at a time. This suggests sea level did not change much, in line with the established idea that the Triassic had a steady “greenhouse” climate with little or no ice at the poles.

Journal reference: Geology, DOI: 10.1130/G45507.1

More on these topics: