Araucarioxylon arizonicum
Araucarioxylon is the obsolete name of various kinds of extinct conifer family Araucariaceae the. The individual species are present as fragments of stems and branches and are only distinguishable under the microscope. In the Petrified Forest National Park of the fragments occurring there, petrified wood are called Araucarioxylon arizonicum up to 90 %.
Under this designation, the fossils are the state fossil of Arizona. The petrified wood of these trees is due to the diversity of colors that have some copies, called "Rainbow Woods".
Taxonomy
The genus Araucarioxylon was erected in 1870 by G. Kraus, and Knowlton introduced in 1889 following Araucarioxylon arizonicum as a new species on. All fragments found in the Petrified Forest and its surroundings petrified wood with the "typical" appearance of Araucarioxylon were assigned in the wake of this kind. In this way, the image of a conifer, the vegetation of a tropical plane of the prehistoric Arizona, which was at that time in the north- western part of the supercontinent Pangaea formed.
The membership of these fragments to a single species but has been doubted in the early 20th century. Later investigations revealed that it is indeed not a single but several species can only be distinguished under the microscope. Thus, based, for example, the first description of Knowlton in 1889 on three root pieces from the area of the Petrified Forest. Savidge 2007 Araucarioxylon considered as an invalid name ( nomen superfluum ), since this was derived arbitrarily from other, already existing name. In addition, the kind built on this name included obviously different ways. For this reason he ordered to three different genera from the detected differences in microscopic examinations of the structure of these syntypes.
So far the following Morphotaxa have been rewritten:
- Pullisilvaxylon daughertii
- Pullisilvaxylon arizonicum
- Chinleoxylon knowltonii
- Silicisilvaxylon imprimicrystallus
- Crystalloxylon imprimicrystallus
- Crystalloxylon secundacrystallus
- Arboramosa semicircumtrachea
- Protocupressinoxylon arizonica
- Ginkgoxylpropinquus hewardii
- Protopiceoxylon novum
Description
The petrified logs are usually long and have a diameter of up to three meters, so that tree heights of up to 60 m are assumed. The similar at first glance root surfaces have branch scars, which are not arranged as a vortex, but distributed irregularly over the trunk. Some of the specimens show traces of bark, which does not resemble the modern Araucaria heterophylla. The branch and stem fragments often have holes of insects and remnants of sticks of prehistoric insects which modern bees were compared.
The plant fossils are present as fragments of stems and branches that have black, red to purple, yellow and green colors rare. Black colors indicate an appreciable amount of organic carbon. The red and yellow colors are produced by large iron oxide particles, the yellow and the red by limonite by hematite. The purple glow of some petrified wood pieces goes back to very small beads of hematite, which are distributed in the quartz matrix. The rarely occurring green colors are attributed to chromium.
The strains are almost always found together in probably geschwemmten groups, only in some cases they seem to be preserved in normal growth position. Along with " Araucarioxylon arizonicum " occur Woodworthia arizonica, Dadoxylon chaneyi, Lyssoxylon grigsbyi, Charmorgia dijolli and Schilderia adam anica that can be distinguished with the naked eye from this part.
Dissemination
The previously Araucarioxylon arizonicum ascribed petrified trunks occur in the Chinle Formation of Late Triassic, which spans the Carnian and Norian stages. Your rocks were deposited in rivers and lakes or come flooding levels. Often the fossils in the lower part ( Shinarump Members ) of the Chinle Formation, striking mainly in southeastern Utah. Also common are they in Sonsela member that is open in the southern half of the Petrified Forest. Even younger deposits are located in the upper part of the Chinle Formation, such as Wolverine Petrified Forest ( southeastern Utah) and in the northern part of the Petrified Forest. Other deposits are located in New Mexico.