Atarque Sandstone facts for kids

The Atarque Sandstone is a special type of rock layer found in New Mexico, United States. It's like a big, flat stack of sandy rocks that was formed a very long time ago. Scientists study this formation to learn about Earth's past, especially about the late Cretaceous period. This was a time when dinosaurs roamed the Earth, and much of North America was covered by a large inland sea.

What is the Atarque Sandstone?

The Atarque Sandstone is mostly made of very fine to fine-grained sandstone. Sandstone is a type of rock made from tiny grains of sand cemented together. This rock layer can be up to 100 feet (30 m) thick.

The layers of rock in the Atarque Sandstone are mostly flat and thick. They also show a feature called crossbedding. This means the layers inside the rock are tilted at an angle. This tilting happens when sand is deposited by moving water or wind.

This sandstone layer is found between other rock formations. It mixes with the Rio Salado Tongue, which is part of the Mancos Shale below it. Above the Atarque Sandstone, you might find the Carthage Member of the Tres Hermanos Formation or the Moreno Hill Formation.

Scientists believe the Atarque Sandstone formed during the early to middle Turonian Age. This was a specific time period within the late Cretaceous period.

How it Formed

The Atarque Sandstone is thought to have formed along an ancient coastline. It was created as a "coastal barrier sandstone." Imagine a long sandbar or beach that separated a shallow sea from the land.

This happened during a time when the Western Interior Seaway was shrinking. The Western Interior Seaway was a huge inland sea that once covered much of central North America. When the sea pulled back, or "regressed," it left behind these sandy deposits that eventually turned into the Atarque Sandstone.

Fossils Found Here

The Atarque Sandstone is important because it contains fossils. These fossils give us clues about the ancient life that existed when the rock formed.

• Pelecypods: These are a type of shellfish, like clams or oysters. Their fossilized shells are found in the sandstone.
• Plesiosaur vertebra: A vertebra is a bone from the spine. Finding a plesiosaur vertebra means that these large, marine reptiles lived in the waters where the sandstone was forming. Plesiosaurs were long-necked, ocean-dwelling creatures.
• Ammonite Spathites rioensis: Ammonites were ancient sea creatures with spiral shells, similar to modern-day nautiluses. The Spathites rioensis fossil is special because it helps scientists figure out the exact age of the rock layer. This specific ammonite is known to have lived during the middle Turonian Age.

How We Learned About It

The Atarque Sandstone was first described in 1947 by a scientist named W.S. Pike. He called it the Atarque Member of the Mesaverde Formation. He studied the lowest 127 feet (39 m) of the Mesaverde in the San Juan Basin.

Later, in 1983, other scientists, S.C. Hook and his team, looked at the rock layers again. They made some changes to how the Cretaceous rocks in the San Juan and Zuni basins were classified. They decided that Pike's Atarque Member, along with some other rock beds, should be part of the Tres Hermanos Formation. They renamed the Atarque Member as the lower sandstone beds of the Tres Hermanos Formation.

At the same time, another group of scientists, M.W. McLellan and his team, decided that the Atarque should be considered its own separate formation. They officially named it the Atarque Sandstone. This happened in the Salt Lake coal field, which is in west-central New Mexico.