Blackwater Draw Formation facts for kids

The Blackwater Draw Formation is a special layer of rock found in the southern High Plains of eastern New Mexico and Texas. Think of it like a very old blanket of sand and dust that settled over a huge area. This formation was laid down a very long time ago, between 1.8 million and 300,000 years ago. This time period is known as the Pleistocene epoch, which is often called the "Ice Age."

What is the Blackwater Draw Formation?

This rock layer is mostly made of very fine, reddish sandstone. This sand was carried by the wind, which scientists call "aeolian" (pronounced ee-OH-lee-an). It sits on top of a hard, resistant layer called "calcrete." This calcrete is like a natural cement layer that formed in the soil. It's part of an older rock unit known as the Ogallala Formation.

The Blackwater Draw Formation can be different thicknesses in different places. At its thickest, it's about 27 meters (89 ft) deep. The sand particles generally get finer as you go northeast. This tells us that the sand likely came from the Pecos River valley, which is to the southwest.

Scientists believe this formation was created by "loess" (pronounced LOH-ess) deposition. Loess is a type of fine, wind-blown dust or silt. It settled down on ancient grasslands. The layers probably didn't form all at once. Instead, they likely built up in stages. More dust would settle during drier times, and then soil would form during wetter periods.

We can tell how old different parts of the formation are by looking at volcanic ash layers within it. For example, the lower part has ash from the Toledo eruption in the Jemez Mountains. This eruption happened about 1.61 million years ago. There's also another ash layer called "Lava Creek B" from about 0.62 million years ago. The very top of the formation has been dated using a method called infrared stimulated luminescence (IRSL). This dating shows it's about 300,000 to 350,000 years old.

What Fossils Are Found Here?

In some parts of the Blackwater Draw Formation, you can find "rhizoliths" (pronounced RY-zoh-liths). These are fossilized roots of plants. They are often found in layers that were once ancient soils, called "paleosols" (pronounced PAY-lee-oh-sols). These rhizoliths show us that small plants, like grasses, once grew in this area.

How Was It Discovered?

The Blackwater Draw Formation was first studied in 1957 by John C. Frye and A. Byron Leonard. They called it the "Cover Sands." Later, in 1976, a scientist named C.C. Reeves, Jr., officially named it the Blackwater Draw Formation.