Petrified Forest National Park

Petrified Forest National Park
	Silicified wood
Location:	Arizona , United States
Next city:	Flagstaff
Surface:	895.93 km²
Founding:	January 1, 1962
Visitors:	644,922 (2018)
Address:	Petrified Forest National Park; 1 Park Road ; Petrified Forest, AZ 86028 ; Tel. (928) 524-6228
	i3 i6

The Petrified Forest National Park is a national park in the United States in northeastern Arizona . The park belongs to the southern Colorado Plateau and the Painted Desert , a desert at around 1,800 m above sea level. It preserves geologically remarkable sedimentary rocks of the Upper Triassic with a multitude of fossils . There are extensive sites of silicified wood in the area , hence the name "Petrified Forest".

On December 8, 1906, some of the sites were placed under protection as a National Monument , in 1932 a part of the Painted Desert was added, and the reserve has since covered an area of around 378 km². The United States Congress designated the area a national park in 1962 . In 1970 a little more than half of the area at that time was placed under the extended protection of a wilderness area . A program has been running since 2004 to expand the park area to 885 km². Neighboring areas of other federal authorities are to be transferred to the national park, private land will be purchased if funds are available. On January 30, 2008, the Petrified Forest National Park was added to the tentative list for nomination for UNESCO World Heritage . In September 2011 around 105 km² of a purchased ranch was added to the park.

overview

In the northern part of the park, which lies above Interstate 40 between Holbrook and Navajo , is the "Painted Desert". This is a dry wasteland, where erosion has created a colorful landscape.

Most of the petrified wood can be seen in the southern part of the national park, here you can also find old rock carvings, so-called petroglyphs . The best known are attached to the "Newspaper Rock". In the nearby, the ruins are one Pueblos from the 11th century , the Puerco Pueblo.

Attractions

Painted Desert - from the northern entrance to the park, the road leads along the edge of the " Painted Desert ". Some viewpoints offer a beautiful view over the highlands.

The tepees - because of their conical shape of teepees of the Plains Indians reminiscent rock formations. The individual rock layers of the Blue Mesa Member are very easy to recognize.

Blue Mesa - a 5 km long road winds through the hilly landscape, there is also a small circular path. The clay layers of the Blue Mesa member visible here, ranging from white to blue-gray in color, gave this part of the landscape its name.

Crystal Forest - here, too, there is a small circular route, about half a kilometer long. There are logs along the circular route, some of which are almost a meter thick. The special thing about the trunks are clear quartz and amethyst crystals that have formed in cavities.

geology

Painted desert with sediments from the Petrified Forest member

Blue Mesa

The «tepees», made up of layers of the Blue Mesa member

Petrified tree trunk

Crystal Forest - cross section of a silicified tree trunk

The dry desert area on the edge of the Colorado Plateau is particularly impressive because of the many colors that this landscape shows. These are particularly noticeable in the "painted desert" and on the "tepees". The layers of rock on top of each other appear as if drawn with a ruler:

their base consists of rock partly colored red by iron oxide ,
the white layer above is made of sandstone ,
This is followed by a bright red colored layer of sedimentary rock interspersed with iron ( silt ),
Finally, the top is made of dark clay , which got its color from the addition of organic carbon.

The progress of erosion can be clearly observed within the park . While the top layer of clay on the “Tepees” has almost been removed, only this is visible in the higher lying area of the “Blue Mesa”.

General overview

The rock layers in the area of the national park belong to the Upper Triassic Chinle Formation , which here mainly consists of fluvial and lacustric deposits. They are generally flat and only dip slightly to the south. In the park, the following shift members are open (from young to old):

On the northern edge of the park, the Chinle Formation is discordantly overlaid by the volcanogenic Bidahochi Formation from the Upper Miocene and Lower Pliocene . This is followed by the Late Pleistocene and Holocene dunes and alluvial deposits.

Stratigraphic description

The approximately 225 to 220 million year old Blue Mesa member consists mainly of brightly colored (gray, blue, purple and green) clay stones with only a few sandstone banks such as the Newspaper Rock Sandstone . It is best approached near the "Tepees".

The approximately 216 million year old Sonsela Sandstone member , often just a Sonsela member , can be divided into three parts:

Flattops-One-Bed , a thick, resistant, slanted sandstone unit.
Jim Camp Wash Beds , blue, gray and purple mudstones, which alternate with numerous gray and white sandstone layers.
Rainbow forest bed , white sandstones and conglomerates of rounded pebbles and boulders. In this position there are silicified tree trunks. It forms the final cover layer at Blue Mesa, Agate Mesa and north of Rainbow Forest.

The Upper Petrified Forest Member , often just Petrified Forest Member , carries red-colored clay stones and brown sandstones. It is well open in the flattops and contains countless petrified tree trunks. In the Painted Desert it is formed as a white and pink unit that contains reclaimed sediments of volcanic origin. The switched-on Black Forest Bed was radiometrically dated to 213 ± 1.7 million years.

The approximately 205 million year old Owl-Rock-Member consists of pink to orange-colored clay stones, which alternate with hard, thin layers of limestone . It also contains gypsum lenses ( selenite ) that were formed when former lakes were evaporated. The Owl-Rock Member is waiting at Chinde Mesa on the north edge of the park.

The approximately 16 to 4 million year old Bidahochi formation follows the owl rock member of the Chinle formation discordantly with a shift gap lasting around 184 million years. In its lower section, it carries fine-grained fluvial and lacustric sediments (silts, clays and sands) - at that time the northeast of Arizona was covered by an extensive network of ephemeral lakes. Then volcanic rocks follow : phreatomagmatic ashes and lava flows. The place of origin of these volcanic entries is mostly local, but can sometimes be traced as far as southwestern Nevada ( Southwest Nevada Volcanic Field ). The subsequent erosion has meanwhile eroded a large part of the Bidahochi Formation, leaving behind some ash cones and maars . In the area of erosion-resistant lava flows (e.g. Pilot Rock and Hopi Buttes ), however, the lake sediments below were preserved. The Hopi-Buttes-Volcanic-Field to the north-west has one of the largest accumulations of maars in the world.

Aeolian and alluvial deposits lay over the volcanic rocks in the late Pleistocene. The oldest dune fields are around 500,000 years old, they are located in the higher parts of the national park and show north-east-south-west orientation. In younger rivers, such as the sandy Lithodendron Wash , there is a younger generation of dunes that are only around 10,000 years old. Recent dunes up to a maximum of 1,000 years old can actually be observed everywhere; they are mostly stabilized by grass growth. The remains of an original proboscis have even been discovered in these Quaternary sediments .

The erosion continues now, so the Little Colorado River and its tributary, the Puerco River , constantly deepen their canyons in the relatively soft Chinle Formation and the associated "Washes" then clear these sediments, including the overlying Bidahochi Formation, more and more out.

History of origin

About 215 million years ago, in the late Triassic period , there was a floodplain with many rivers running through it. Araucarias , tree ferns and conifers formed the vegetation. Crocodile-like reptiles , giant amphibians and also smaller dinosaurs lived in this country. Many fossil finds in the Chinle Formation are evidence of this .

Fallen trees were buried under mud and silt by floods. Burying more debris slowed the natural decay of the wood due to a lack of oxygen . Under the increasingly thick sedimentary cover leaked siliceous groundwater into the tree trunks. Quartz and chalcedony stored in the cavities of the trunks, gradually replacing the cell tissue and thus preserving the wooden structures of the trunks in stone.

The layers continued to sink and were flooded again. More and more layers of material carried by water were deposited on top. Much later onset of tectonic movements in the earth's crust (see Laramian mountain formation ) lifted the land surface, the resulting tensions within the rock layers caused the trunks to break. The erosion caused by wind and water, which now began to intensify, gradually removed the softer layers of the sediments , exposing the petrified tree trunks, which are made of hard quartz substance.

history

colonization

Rock carvings, finds of broken glass and the remains of settlements suggest that people were settled around 2,000 years ago. There is currently no precise information about this, but it is certain that there were several settlement phases. This ranges from early nomadic tribes to the Pueblo culture around 1100 to 1400. From the period after 1400 there is no longer any evidence of human settlement.

The Army Corps of Topographical Engineers land surveyors came to this area in the mid-19th century. With their reports they brought tales of a "painted desert" and stone turned trees back to the east. They were followed by the first settlers and ranchers.

Commercial use

The bright colors and patterns of the various mineral deposits , which come into their own after grinding and polishing, make petrified wood an ideal material for the arts and crafts. For some time the petrified wood was literally dismantled, mainly for the souvenir shop. When it was realized that these deposits were only limited, the first votes came to preserve some of the particularly rich deposits. Today's park protects them and thus preserves future generations an insight into human history and into the geological development of the earth.

Pieces of jewelry (e.g. pendants), animal figures and various decorative objects, but also unprocessed or only polished pieces are available in stores. There are also larger sites outside the park and the material for this comes only from these. No small piece of it may be taken from the park itself. Violations of this prohibition face draconian penalties. When leaving the park you have to expect car controls. Walking away from the path is also strictly prohibited.

Individual evidence

literature

National Park Service: Official Map and Guide
John V. Bezy and Arthur S. Trevena: Guide to Twenty Geological Features at Petrified National Park . Petrified Forest Museum Association, Holbrook, Arizona 1975, L of C No 75-10847.

Web links

Commons : Petrified Forest National Park - Album with pictures, videos and audio files

National Park Service: Petrified Forest National Park (official site; English)
NPS contribution to the geological formations (English)
Mineral Atlas - Petrified Forest, viewing the geology and numerous photos of the formations and fossils

[1] Entry Petrified Forest National Park on the website UNECO

[2] Riggs, NR, Ash, SR, Barth, AP, Gehrels, GE, and Wooden, JL 2003. Isotopic age of the Black Forest Bed, Petrified Forest Member, Chinle Formation, Arizona: An example of dating a continental sandstone. Geological Society of America Bulletin, 115: 315-1323. (PDF; 228 kB)