The Virtual Petrified Wood Museum.  Dedicated to the Exhibition and Educational Study of Permineralized Plant Material
Home Button
Science Button
Students Button
Fossils Button
Time Button
Tectonics Button
Taxonomy Button
Anatomy Button
Links Button
Contact Button
Bibliography Button
Paleozoic Drop Down Menu
Mesozoic Drop Down Menu
Cenozoic Drop Down Menu
Zimbabwe, Africa

Introduction

West of Gokwe in Zimbabwe, Africa a 30km wide Triassic aged forest is exposed to the surface (Dernbach, 1996, p. 88). Specimens of Araucarioxylon, Woodworthia, and Rhexoxylon can be found (Daniels and Dayvault, 2006, p. 119). Popular among collectors are the specimens with a green coloration. This green coloration is created by the presence of chromium compounds (Daniels and Dayvault, 2006, p. 175).

Araucarioxylon is the wood of a conifer that is represented in many of the forests of the Triassic and Jurassic (Tidwell, 1998, p. 206). Fossil wood assigned to this genus is though to be related to members of the Araucariaceae family. The genus is derived from the name of a tribe indigenous to the Andes of South America. The Incas used arauco to describe any tribe that remained unconquered (Dernbach, 1992, p. 14). Present day well known araucaria are cultivated in the Southern Hemisphere. These include the Norfolk Island Pine (Araucaria heterophylla), Araucaria bidwilli, and Araucaria brasiliensis.

When looking at a cross-section of araucaria with a 10x loupe one can clearly see the trachieds that make up the xylem. One can also note the absence of resin canals. Dadoxylon may also be an araucaria fossil wood. Traditionally, araucaria from the Paleozoic was refered to as Dadoxylon, while araucaria-like wood from the Mesozoic was assigned the genus Araucarioxylon (Derbach, 1992, p. 127). Most collectors of these fossil woods consider them to be different species regardless of the time period assigned. The collector identifies Dadoxylon with pith that has distinct serrations formed by the primary xylem centers of growth (Dernbach and Tidwell, 2002, p. 129). In some specimens the pith can exhibit a star-shaped pattern.

Woodworthia is the wood of an araucarioid with numerous leaf and shoot traces, which can be seen both in cross-section and on the outer surface of well-preserved specimens.

Rhexoxylon, in cross-section, would remind one of Pentoxylon or Hermanophyton. Rhexoxylon has similar wedges of secondary xylem, which surrounds pith that contains anomalous growth and Rhomboidal-shaped leaf bases on the outer surface of the stem. The wedges of xylem are very interesting in that they have growth centers that produced wood towards the inside pith as well as to the outside (Dernbach and Tidwell, 2002, p.199). Rhexoxylon may represent an arborescent seed fern.

 


Bibliography:


Daniels, F.J. and Dayvault, R.D. 2006. Ancient Forests: A Closer Look at Fossil Wood. Western Colorado Publishing Company: Canada.

Dernbach, U. and Tidwell, W.D. 2002. Secrets of Petrified Plants: Fascination from Millions of Years. D’ORO: Germany.

Dernbach, U. 1996. Petrified Forests: The World’s 31 Most Beautiful Petrified Forests. D’ORO: Germany.

Dernbach, U. 1992. Araucaria. D’ORO: Germany

Tidwell, W.D. 1998. Common Fossil Plants of Western North America. [2nd Edition]. Smithsonian Institution Press: Washington, pgs 214-215.


©Copyright 2008 by Mike Viney| Website Use |