Bursum Formation facts for kids
Quick facts for kids Bursum FormationStratigraphic range: Lower Permian |
|
|---|---|
| Type | Formation |
| Unit of | Madera Group |
| Underlies | Abo Formation |
| Overlies | Atrasado Formation |
| Thickness | 35 m (115 ft) |
| Lithology | |
| Primary | Mudstone, limestone |
| Location | |
| Coordinates | 33°48′46″N 106°28′42″W / 33.812698°N 106.478451°W |
| Region | New Mexico |
| Country |  United States |
| Type section | |
| Named for | Bursum triangulation point |
| Named by | Wilpolt, R.H., MacAlpin, A.J., Bates, R.L., and Vorbe, George |
The Bursum Formation is a special type of rock layer found in New Mexico. Scientists study it because it holds fossils from a very long time ago, during the Early Permian period.
Contents
What is the Bursum Formation made of?
The Bursum Formation is mostly made of mudstone. But it also has a lot of limestone, especially in its lower parts. This rock layer can be more than 100 m (330 ft) thick!
It sits on top of another rock layer called the Atrasado Formation. It also gradually changes into the Abo Formation above it. Think of it as a bridge between two different types of environments. The Bursum Formation shows where ancient seas (like the Madera Group) met dry land (like the Abo Formation).
What is the Red Tanks Member?
A special part of the Bursum Formation is called the . This section is mostly made of colorful shale, mudstone, and siltstone. These rocks formed on land, not in the sea.
However, the Red Tanks Member also has some layers of marine limestone and shale. These layers show times when the sea level rose and covered the land. This happened six times, creating what scientists call "transgressive depositional sequences."
The Red Tanks Member is found at a place called Carrizo Arroyo. Further south, the Bursum Formation generally has more signs of being formed in the sea.
Scientists have noticed that the number of sea level changes in the Bursum Formation is different from other areas. This suggests that the movement of Earth's plates (tectonics) had a bigger effect on this formation than ice ages did.
What kinds of fossils are found in the Bursum Formation?
The Bursum Formation is famous for its fossils. One important fossil found here is a tiny creature called Triticites. It's a type of fusilinid. Finding Triticites helps scientists know that the Bursum Formation is from the Early Permian period.
Other small fossils found here include forams like Bradyina lucida and Eostaffella.
Fossil Hotspots in the Red Tanks Member
The Red Tanks Member has two special places called Lagerstätten. These are spots where many fossils are very well preserved. They are from the early part of the Permian period, called the Asselian age.
The Red Tanks Member also has interesting round oncolites at Cibola Spring. These are small, lumpy rocks that look like tiny balls. They are unusual because they are mostly made of forams, not cyanobacteria (blue-green algae). Scientists think these oncolites formed in a shallow sea, below where sunlight reached, but above where big storms could stir up the water.
How was the Bursum Formation discovered?
The Bursum Formation was first described in 1946 by R.H. Wilpolt and his team. They found it near a place called the Bursum triangulation point in New Mexico.
Later, other scientists studied the formation more closely. M.L. Thompson redefined it to include all Permian rocks that were older than the Abo Formation. He saw these rocks as a link between the sea-formed rocks of the Madera Group and the land-formed Abo Formation.
In 1972, D.A. Myers officially placed the Bursum Formation within the Madera Group. Barry S. Kues agreed with this in 2001, except for one small area. He also connected the Bursum Formation to other similar rock layers, like the Laborcita Formation.
