Agate Fossil Beds National Monument
| Agate Fossil Beds National Monument | |||
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| Location: | Nebraska , United States | ||
| Specialty: | Site of fossils from the Miocene geological period | ||
| Next city: | Scottsbluff | ||
| Surface: | 12.4 km² | ||
| Founding: | June 14, 1997 | ||
| Visitors: | 13,521 (2006) | ||
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Agate Fossil Beds National Monument is a fossil deposit in the northwest of the US state Nebraska , which has been designated as a National Monument since 1997 and is administered by the National Park Service .
The area lies in the valley of the Niobrara River . The cliffs along the river are natural outcrops of fossil-bearing sedimentary rocks from the Miocene .
Named the reserve after the English word Agate for the mineral agate , because in a horizon of rock strata occur agates.
description
The National Monument preserves part of the Great Plains , the great prairies, which, due to its location at over 1,400 m above sea level, was not affected by glaciation in the last Ice Age .
When about 70 to 40 million years ago the Rocky Mountains were lifted in the course of the Laramian mountain formation , rivers and streams transported the rock debris of the young mountains to the east and deposited it in the flood plains there as sands and fine plastics. Thin layers of volcanic ash from the then active volcanic areas in present-day Nevada and Oregon were also deposited; they are integrated into the sedimentary rock sequence as thin tuff horizons. The oldest exposed rocks of this sequence in the Agate area come from the Oligocene and are around 34 million years old. Almost everywhere, however, they are covered by rocks from the Miocene and therefore do not strike out.
In the early Miocene, about 25 million years ago, the rivers of the region changed their course and dug deep valleys into the young and hardly consolidated sedimentary rocks. The valleys were subsequently refilled with sediments from the Rocky Mountains. Since these had a slightly different composition than before, the solid rock formed from them by diagenesis was somewhat harder than the surrounding rocks.
Savannah vegetation developed on this subsoil about 21 million years ago . Herds of large mammals such as chalicotheria , menoceras (a pig- sized rhinoceros ), entelodonts , amphicyonids , stenomylus (a dwarf camel ), horses, but also palaeocastor (a land-dwelling ancestor of beavers ) and pocket rats lived in flat river valleys and lake landscapes . A massive drought is believed to be the reason why many animals of different species died in a few places. Presumably, the current sites with mass occurrences of fossils represent former water holes at which the carcasses were covered by the drying mud and embedded in this way.
About a million years later, the same process took place again, so that in today's protected area there are two fossil-rich horizons with an age of 21 and 20 million years. They are separated from each other by a thin layer of white ash. This contains quartz in the form of chalcedony . In addition, there are deposits of agate , the English name of which was named Agate for a farm in the area and ultimately for the National Monument.
In the last five million years there has been an uplift in the entire area of the Great Plains , the meandering rivers have changed their courses several times until today. The Niobrara River cut into the hard rock units of the Miocene in several places and exposed them.
The National Monument
The petrified bones in the cliffs by the river were already known to the Indians. Around 1878 homesteader James H. Cook made the first white fossil record in the area. He and his son Harold realized the importance and called experts on the prairie. In 1904 a paleontologist from the Carnegie Museum of Natural History in Pittsburgh carried out the first scientific dig, followed by a team from the University of Nebraska the following year . The two neighboring hills in which they discovered undisturbed bedding layers have since been called Carnegie and University Hill . In 1905 scientists from Amherst College arrived. In the following years they found the first completely preserved stenomyl skeletons. Starting in 1910, the American Museum of Natural History excavated the area for twenty years. The National Monument was formally designated as early as 1965 in order to permanently preserve the fossil sites recognized as significant.
At that time, however, the land was still privately owned. Only after the former homestead of the Cook family, on which the most valuable finds were made, could be acquired by the federal government, the National Monument was dedicated in 1997 . Of the 12.4 km² that were originally designated as a protected area, around 11 km² have since been federally owned and are currently used by the National Monument. The rest belongs to two private farms and, if possible, is to be acquired in the future.
In addition to fossils and information on the geology of the area, around 500 exhibits on the culture of the Lakota Indians, collected by several generations of the Cooks, are on display in the museum of the visitor center .
The National Monument is remote and is one of the National Park Service's small objects in terms of area and number of visitors. Visitors can take short hiking trails to explore the prairie and river, including climbing to the cliffs above the river where the fossils are stored. There are two picnic areas, but there are no places to stay or eat.
