Harrell Shale facts for kids
Quick facts for kids Harrell FormationStratigraphic range: Middle Devonian-Late Devonian |
|
|---|---|
| Type | sedimentary |
| Sub-units | Burket Shale Member |
| Underlies | Brallier Formation, Sonyea Formation, Trimmers Rock Formation |
| Overlies | Mahantango Formation, Millboro Shale, and Tully Limestone |
| Lithology | |
| Primary | shale, sandstone |
| Location | |
| Region | Appalachian Mountains |
| Country | United States |
| Type section | |
| Named by | Charles Butts, 1918 |
The Harrell Formation is a specific layer of rock found in the eastern United States. It's a type of bedrock unit, which means it's part of the solid rock that makes up the Earth's crust. You can find this rock formation in states like Pennsylvania, Maryland, West Virginia, and Virginia. It formed a very long time ago during a period called the Devonian Period.
Contents
What is the Harrell Formation?
The Harrell Formation was first officially described by a scientist named Charles Butts in 1918. Think of a rock formation as a specific type of rock layer that geologists (scientists who study rocks) can identify and map. It's like a unique chapter in Earth's history book.
What Does the Harrell Formation Look Like?
Scientists Hasson and Dennison described the Harrell Formation in 1978. They said it's mostly a very dark gray shale. Shale is a type of rock made from mud and clay that has been hardened over millions of years. This shale is often thin and breaks into flat pieces. In some places, beneath this dark shale, there's an even darker, grayish-black shale layer called the Burket Member.
What Fossils Are Found in the Harrell Formation?
Fossils are the preserved remains or traces of ancient life. Scientists can learn a lot about Earth's past by studying them. Hasson and Dennison found several interesting fossils in the Harrell Formation. These fossils help us understand what kind of life existed during the Devonian Period.
Here are some of the fossils they reported:
- Bivalves: These are sea creatures with two shells, like modern clams or oysters. Examples found include Buchiola livonae (?), B. retrostriata, Paracardium doris, Pterochaenia fragilis, and Lunlulicardium (?).
- Cephalopods: These are marine animals with a head and tentacles, like modern squids or octopuses. Fossils found include Bactrites aciculum and Probeloceras lutheri.
- Cricoconarida: These are a group of ancient mollusks (like snails or slugs) that had small, cone-shaped shells. An example is Styliolina fissurella.
Where Can You See the Harrell Formation?
The "type locality" is the specific place where a rock formation was first clearly identified and described. For the Harrell Formation, its type locality is at Horrell Station in Blair County, Pennsylvania. This is like its official birthplace for scientific study.
How Old is the Harrell Formation?
Scientists use methods like "relative age dating" to figure out how old rocks are. This means they compare the rock layers to each other to see which ones are older or younger. Based on these studies, the Harrell Formation was formed during the late part of the Devonian Period. The Devonian Period was a time in Earth's history that lasted from about 419 to 359 million years ago. It's often called the "Age of Fishes" because many new types of fish appeared during this time.
