Agate Fossil Beds National Monument

Agate Fossil Beds National Monument is a fossil deposit in the Northwest of the U.S. state of Nebraska, which is designated as a National Monument since 1997 and is managed by the National Park Service.

The area is located in the valley of the Niobrara River. The cliffs along the river are natural outcrops of sedimentary rocks leading fossils from the Miocene.

Named the reserve is named after the English word for the mineral agate Agate, because in a horizon of this rock sequence agates occur.

Description

The National Monument preserves a portion of the Great Plains, the Great Plains, which was not affected by its location at about 1400 m above the sea of ​​glaciation in the last ice age.

As before, about 70 to 40 million years ago the Rocky Mountains were raised in the course of lara mix orogeny, rivers and streams transported the debris of the young mountain range to the east, and pitched him into the local flood plain as sand and Feinklastika from. Thin layers of volcanic ash from the then active volcanic areas in present-day Nevada and Oregon also attended the deposition, they are turned into sedimentary rock sequence as low mighty tuff horizons. The oldest open-minded rocks of this sequence in the Agate area date from the Oligocene and are about 34 million years old. However, almost everywhere they are covered by rocks from the Miocene and therefore do not rule out.

In the early Miocene, about 25 million years ago, the rivers in the region changed its course and dug deep valleys in the young and little- 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 slightly harder than the surrounding rocks.

Before about 21 million years, on this ground a savanna vegetation. In shallow river valleys and lakes herds lived on large mammals such as Chalicotherien, Menoceras ( a pigs large rhinoceros), Entelodonten, Amphicyoniden, Stenomylus ( a dwarf - camel ), but also horses Palaeocastor ( a fully terrestrial ancestor of beaver ) and pocket gophers. A massive drought is the cause that many animals of different species died in a few places. Probably represent the present-day localities with mass deposits of fossils former water holes where the corpses were covered by dried mud and embedded in such a way.

About one million years later, the same process took place again, so that in today's sanctuary there are two fossil-rich horizons with an age of 21 and 20 million years. They are separated by a thin white ash layer. This contains quartz in the form of chalcedony. There are also deposits of agate, of which the English name Agate was eponymous for a farm in the area and finally to the National Monument.

In the last five million years ago found throughout the Great Plains instead of a raise, the meandering rivers changed their courses to several times today. The Niobrara River cut at several points in the hard rock units of the Miocene, and laid them free.

The National Monument

The fossilized bones in the cliffs along the river were already known to the Indians. To 1878, the Homesteader James H. Cook made ​​the first white fossil finds in the area. He and his son Harold recognized the importance and called experts in the prairie. 1904, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, the first scientific excavation by, in the following year, a team from the University of Nebraska. The two neighboring hills where they discovered undisturbed bearing layers, since hot Carnegie and University Hill. 1905 met scientists at the Amherst college. They found in the following years, the first fully preserved Stenomylus skeletons. From 1910, the American Museum of Natural History dug twenty-year in the area. The national monument was formally recognized in 1965 in order to preserve the fossils identified as significant deposits permanently.

At this time, however, land was still privately owned. Only after the former Homestead of the Cook family, where the most valuable discoveries were made, could be acquired by the Federal Government, there were 1997 dedication of the National Monument. Of the 12.4 km ², which were originally designated as a protected area, around 11 km ² are in federal ownership since then and are currently used by the National Monument. The rest belongs to two private farms and should be acquired if possible in the future.

In the museum the visitor center are out of fossils and information on the geology of the area and approximately 500 exhibits the culture of the Lakota Indians issued, which were collected by several generations of Cooks.

The National Monument is secluded and according to area how to count number of visitors to the small objects of the National Park Service. Visitors can explore the prairie and the river on short walks while also rising to the cliffs above the river, in which store the fossils. There are two picnic areas, but neither overnight nor catering facilities.