Florissant Formation facts for kids
Quick facts for kids Florissant FormationStratigraphic range: Eocene |
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Florissant Formation at the Clare fossil quarry in Florissant, Colorado
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| Type | Formation |
| Overlies | Wall Mountain Tuff, Pikes Peak Granite |
| Thickness | 74 m (243 ft) |
| Lithology | |
| Primary | Shale |
| Location | |
| Coordinates | 38°54′50″N 105°17′13″W / 38.914°N 105.287°W |
| Region | Colorado |
| Country |  United States |
| Type section | |
| Named for | Florissant, Colorado |
| Named by | Cross |
| Year defined | 1894 |
| Florissant Fossil Beds National Monument | |
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IUCN Category V (Protected Landscape/Seascape)
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The Pioneer House, showing how the original pioneers of the west lived
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 Florissant Fossil Beds National Monument
Location in Colorado
Florissant Fossil Beds National Monument
Location in the United States
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| Location | Teller County, Colorado, United States |
| Nearest city | Florissant, Colorado |
| Area | 5,998 acres (24.27 km2) |
| Authorized | August 20, 1969 |
| Visitors | 71,763 (in 2017) |
| Governing body | National Park Service |
| Website | Florissant Fossil Beds National Monument |
The Florissant Formation is a special rock layer found near Florissant, Colorado. It's famous for its amazing fossils of insects and plants. These fossils are incredibly well-preserved in layers of mud and shale.
Scientists believe this formation is about 34 million years old, from a time called the Eocene epoch. Back then, this area was a lake. The fossils were preserved thanks to volcanic ash from nearby volcanoes. This ash mixed with tiny lake organisms called diatoms, causing them to multiply rapidly. When these diatoms died and sank, they covered and preserved dead plants and animals.
The Florissant Fossil Beds National Monument is a protected area. It was created to save and study the unique geology and history of this fossil-rich place.
Contents
Discovering the Past: History of Florissant
The name "Florissant" comes from a French word meaning "flowering." In the late 1800s, people started visiting this area. They came to see the wildlife and collect fossils. Sadly, many early collectors took large amounts of petrified wood from the famous Petrified Forest.
During the 1860s and 1870s, geologists began mapping the area. Scientists like Leo Lesquereux studied fossil plants. Samuel Hubbard Scudder looked at fossil insects, and Edward Drinker Cope examined vertebrate fossils. In 1894, Charles Whitman Cross officially named the rock layers the Florissant Lake Beds.
In 1969, after a long legal process, the Florissant Fossil Beds National Monument was created. Today, about 60,000 people visit the park each year. Scientists continue to study the fossils found here. In 2001, the formation was officially renamed the Florissant Formation.
How Florissant Formed: Geology of the Area
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About 34 million years ago, during the late Eocene, this area was a lake surrounded by redwood trees. The oldest rocks here are the Proterozoic-aged Pikes Peak Granite. Above this, there's a gap in the rock record, then the Wall Mountain Tuff. This gap shows a lot of erosion happened when the Rocky Mountains were forming.
The Wall Mountain Tuff formed from a huge volcanic eruption far away. The Florissant Formation itself is made of layers of shale, mudstone, and volcanic ash. These layers tell a story of a changing lake environment.
Scientists have identified six main layers within the Florissant Formation. The shale layers formed in the lake and are full of fossils. The mudstone layers formed in stream environments, not in the lake. Sometimes, giant mudflows called lahars flowed through the valley. These lahars could have blocked the valley, creating new lakes where more shale layers formed.
The Rocky Mountains were uplifted to the west during the Laramide Orogeny. Later, volcanoes began erupting southwest of Florissant. These eruptions covered the area with ash and volcanic debris. This volcanic material was very important for preserving the fossils. The fossil-rich "paper shales" are mixed with thicker layers of volcanic ash.
Most rocks deposited after the Oligocene and before the Ice Age have worn away. Some younger layers contain pieces of the Pikes Peak Granite and volcanic rocks. These were carried by streams. Even some mammoth bones, about 50,000 years old, have been found in these younger layers.
Volcanoes That Shaped Florissant: Thirtynine Mile Volcanic Field
About 25–30 kilometers (15-18 miles) southwest of Florissant, a group of volcanoes erupted regularly. These were like modern volcanoes such as Mount St. Helens. This area is called the Thirtynine Mile volcanic field.
These volcanoes had many types of eruptions, including lava flows and explosive events. Ash from these eruptions settled over the Florissant area. Mudflows (lahars) also flowed down the valleys. This ash created the tuff layers, and the lahars formed the mudstones and conglomerates in the Florissant Formation.
The Florissant lake formed when a lahar dammed up a valley. The lake grew to be as large as 36 square kilometers (14 square miles). There were two main periods when the lake existed. The first lake created the lower shale layer. The second lake created the middle and upper shale layers.
Eventually, the volcanoes became quiet and began to wear away. Over time, they eroded so much that there are no obvious signs of them on the surface today.
Amazing Discoveries: Florissant Fossils
The volcanic material that caused so much change also helped preserve the fossils. As ash fell, water carried it into streams and lahars. These lahars covered the bases of redwood trees, turning their trunks into petrified wood. This happened through a process called permineralization. Minerals from groundwater flowed into the tree trunks, replacing the wood with silica. This process preserved the tree stumps.
Inside the lake, volcanic material was regularly deposited. This material was rich in silica. Tiny organisms called diatoms, which have silica shells, lived in the lake. The extra silica from the ash caused the diatoms to "bloom" or multiply rapidly. At the same time, stress from volcanic events caused many plants and animals to die.
When plants and animals died, their leaves and bodies sank to the bottom of the lake. Large amounts of organic material built up. This process likely happened yearly, creating thin layers of ash and clay. These layers are called "paper shales" because they are so thin (0.1 to 1.0 mm thick). The best-preserved fossils are found in these paper shales. Scientists estimate the lake existed for 2,500 to 5,000 years, based on these annual layers.
Ancient Plants: Paleoflora of Florissant
The Florissant Formation has a huge variety of plant fossils. These range from giant redwoods to tiny pollen grains. The petrified forest is a major attraction, with about 30 preserved stumps. These are some of the largest petrified stumps in the world.
Most of the stumps are from Sequoia affinis, a relative of today's coast redwood. These trees could have been 60 meters (200 feet) tall. They likely died when lahars buried their roots. By studying their tree rings, scientists estimate they were 500–700 years old when they died. Some stumps are also from flowering plants.
The Florissant Formation is also known for its fossilized leaves, fruits, seeds, cones, and flowers. Most leaves come from trees and shrubs. Flowering plants are the most common, but conifers (like sequoias) are also present.
Fossilized Sequoia affinis cones and foliage are different from modern redwoods. The fossil foliage is thinner, and the female cones are smaller. Over 130 species of pollen have been found in the shale beds. These show that many different habitats existed around the lake.
Benthic diatoms are common in the beds. Their silica shells make them easy to fossilize. During volcanic periods, silica from ash caused huge diatom blooms. These blooms helped preserve other fossils. Florissant is important because it has some of the earliest known freshwater diatoms.
Ancient Animals: Fauna of Florissant
Most animal fossils at Florissant are invertebrates (animals without backbones). However, many vertebrates (animals with backbones) have also been found. The large number of species shows that the environment was perfect for many animals. Their excellent preservation gives clues about their ancient environment and behavior.
Invertebrate Life: Insects and More
The invertebrate fossils include arthropods like spiders, millipedes, insects, and ostracods. Also found are mollusks like clams and snails. Spiders and insects are especially important, with over 1,500 species identified.
Many types of Arachnids, mostly spiders, are found at Florissant. There are also possible harvestmen and daddy long-legs. One interesting thing about the spiders is that their legs are often fully extended. This might mean they died in warm or acidic water.
The insects found in the ash-clay beds are very diverse. They include mayflies, dragonflies, damselflies, grasshoppers, crickets, katydids, cockroaches, termites, earwigs, web-spinners, cicadas, snake flies, lacewings, beetles, flies, mosquitoes, butterflies, moths, wasps, bees, and ants. Beetles are the most common, making up about 38% of all insect fossils. These fossils show both aquatic and land insects, giving clues about the ancient ecosystem.
Ostracods likely ate algae at the bottom of the lake. Only one species of ostracod has been described so far. Several freshwater mollusks, including snails, have also been identified. Snails (gastropods) are the most common mollusk found.
Vertebrate Life: Fish, Birds, and Mammals
Vertebrate fossils at Florissant are mostly small, broken bones. However, some complete species have been identified, mainly fish, but also birds and mammals.
Fish found include bowfins, suckers, catfishes, and pirate perches. Most of these lived on the lake bottom, except for the perches. Many could tolerate poor water conditions. Fish fossils are often found in specific shale layers, suggesting better conditions for fish at certain times.
Three types of birds have been found, including a cuckoo. Most of the skeleton was missing, but enough features remained to identify it. There are also examples of rollers and shorebirds.
Mammals are very rare in the shales. Only one small opossum fossil has been found there. In the lower mudstone layers, broken bones of a horse, a brontothere, and an oreodont have been discovered. The ancient horse was small, like a medium-sized dog, with three toes. The brontothere was a huge, elephant-sized animal with horns. The oreodont was an extinct animal similar to modern sheep and pigs. In total, about a dozen different mammal types have been found at Florissant, mostly from teeth.
Surprisingly, no reptiles or amphibians have been found at Florissant. This is unusual, as they would be expected in such an environment. Scientists are still trying to understand why, especially since nearly 40,000 specimens from this site are in museums. Toxic water from volcanic activity could be a reason, but other aquatic animals lived in the lake.
Ancient Weather and Homes: Paleoclimate and Paleohabitats
Fossil plants, especially their leaves, are the best source of information about the ancient climate at Florissant. Plants are more sensitive to climate changes than many animals.
By comparing fossil leaves to modern plants, scientists can guess what the climate was like. For example, by looking at the general appearance of the leaves, the average temperature has been estimated to be around 13°C (55°F). This is much warmer than today's average of 4°C (39°F). Some estimates even suggest 16-18°C (61-64°F). It also seems that seasonal changes were not as extreme as they are today.
Based on the size and features of fossil teeth, the rainfall during the late Eocene was about 50-80 centimeters (20-31 inches) per year. This included a clear dry season. This is much wetter than today's average of 38 cm (15 inches). Most rain likely fell in late spring to early summer, with rare winter snow.
Tree-ring analysis of the redwoods shows that the ancient climate was even better for them than the climate where redwoods grow in California today. The average width of a tree ring (one year of growth) is larger than in modern California redwoods.
Towards the end of the Eocene, global temperatures started to drop. However, the fossil record at Florissant doesn't clearly show this global cooling trend.
Where Life Lived: Paleohabitats of Florissant
The fossilized algae and aquatic flowering plants tell us the lake was shallow and had freshwater. Near the streams and lake shore, there was plenty of moisture, allowing lush plants to grow. However, higher up the hillsides, the plants were adapted to drier conditions.
At the bottom of the valley, large trees like sequoias dominated the landscape. Smaller trees and shrubs grew beneath them. There was a gradual change in habitats from the valley floor up the hillsides, with some overlap.
Insects found in the area also point to different habitats. Some, like dragonflies, lived their whole lives in or near the lake. Bees and butterflies, on the other hand, preferred more open spaces in the surrounding hills and meadows.
How High Was It? Paleoaltitude of Florissant
Early estimates suggested the Florissant area was much lower in elevation during the Eocene, between 300–900 meters (1,000-3,000 feet). This is much lower than its modern elevation of 2,500-2,600 meters (8,200-8,500 feet).
However, more recent studies using fossil plants suggest the elevation was much higher in the Eocene. Estimates range from 1,900 to 4,100 meters (6,200-13,500 feet). This would mean that global climate change, rather than mountain uplift, was the main reason for environmental changes in the area.
The exact elevation of Florissant during the Eocene is still being debated by scientists. While many studies suggest a higher elevation, some evidence still supports the earlier, lower estimates.
Images for kids
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Florissant Formation at the Clare fossil quarry in Florissant, Colorado
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The Pioneer House, showing how the original pioneers of the west lived
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An aerial view of Florissant Fossil Beds National Monument in 2013
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A large petrified stump of Sequoia affinis at Florissant Fossil Beds National Monument
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Florissantia speirii flower, a fossil flower found at Florissant
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A petrified redwood stump showing visible tree rings
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Fossilised leaf preserved in fine detail
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Palaeovespa florissantia, a fossil wasp, is the logo for Florissant Fossil Beds National Monument
