A type of petrified wood that is found in Louisiana is called "petrified palm wood". Petrified Palm wood is a group of fossil woods that contain prominent rod-like structures within the regular grain of the silicified wood. Depending upon the angle at which they are cut by fracture, these rod-like structures show up as spots, tapering rods, or continuous lines. The rod-like structures are sclerenchyma bundles that comprise part of the woody tissues that gave the wood its vertical strength (Blackwell 1984).
Petrified palm wood is a favorite of rock collectors because it is replaced by silica and exhibits well-defined rod-like structures and variety of colors. As a result, it exhibits a wide range of colors and designs when cut that can be incorporated into jewelry and other ornamental items. Because it is composed of silica, it is hard enough to polish and withstand the wear and tear of normal use. The popularity of palm wood with rock collectors is documented in a number of articles, i.e. McMackin (1984), Thomas (1986), and Zeitner, (1988).
The Louisiana Legislature designated "petrified palm wood" as the state fossil in Act No. 362 (Senate Bill No. 155) of the 1976 session. The governor of Louisiana approved this act on July 31, 1976. This act does not specify a specific species or genera of fossil plant as palm wood and there are a number of genera that are considered palm wood. However, the petrified palm wood found in Louisiana consists entirely of the petrified wood of the genus Palmoxylon. From Louisiana, Berry (1916) records the presence of three species of Palmoxylon from Louisiana, P. microxylon, P. cellulosum, and P. lacunosum. Another species of Palmoxylon, P. texense, is reported from Texas and three species of Palmoxylon, P. remotum, P. mississippense, and P. ovatum, are reported from Mississippi and could also occur in Louisiana (Berry 1916). These species of Palmoxylon would also be considered palm wood.
At this time, it is unknown why petrified palm wood was chosen as the state fossil. However, Pope (1988, p. 181) notes:
"It is interesting to note that in 1976, while the state legislature was considering the naming of the state fossil, one of the legislators nominated Senator Egdar Mouton of Lafayette for that honor. After the Senator declined in deference to "age, rather than beauty," the (Miocene) petrified wood was declared the winner by acclamation."
At the time, that Pope (1988) was written, the Catahoula Formation was considered to be of Miocene age. Currently, the Catahoula Formation is thought to be older. The older, Oligocene age assignment is still somewhat controversial.
Within Louisiana, the occurrence of petrified palm wood is primarily restricted to the Oligocene age Catahoula Formation. Within its outcrop belt, the Catahoula Formation consists almost entirely of sediments deposited within broad, low-lying coastal plains during the Oligocene (Paine and Meyerhoff 1968). At this time, the shoreline lay within southern Louisiana. The abundance of palm wood in the Catahoula Formation clearly indicates that Louisiana had a tropical climate during the Oligocene (Berry 1916). The source of the silica within the Catahoula Formation needed to form petrified wood is hypothesized to have been volcanic ash blown in from volcanic calderas in either West Texas or central Mexico.
It is not really known who was the first person to discover palm wood in Louisiana. As artifacts form Paleo-Indian sites within Louisiana indicate, the prehistoric Native Americans clearly knew about palm wood and used it to manufacture stone tools from it. Berry (1916, p. 235) notes that palm wood was collected by Mr. L. C. Johnson in Rapides Parish in 1885. Knowlton (1888) used this and other material that he collected to make the first published scientific descriptions of palm wood from Louisiana. Since then, the only published study of palm wood from Louisiana has been Berry (1916) although a few much more recent studies of palm wood, i.e. Blackwell (1984), Blackwell et al. (1983), and Dockery (1987) in Mississippi have been made and published.
Berry, Edward Wilber, 1916, The Flora of the Catahoula Sandstone. U.S. Geological Survey Professional Paper no. 98, pp. 227-251.
Blackwell, Will H., 1984, Palmoxylon from Bayou Pierre, Copiah/ Claiborne County line, southwestern Mississippi. American Journal of Botany. vol. 71, no. 5, Part 2, pp. 113.
Blackwell, Will H., Powell, Martha J., and Dukes, George H., 1983, Fossil wood from Bayou Pierre and White Oak Creek, southwest-central Mississippi. Mississippi Geology. vol. vol. 4, no. 2, pp. 1-6.
Dockery, David T. III, 1987, Petrified palm "wood" from Thompson Creek, Yazoo County, Mississippi. Mississippi Geology. vol. 8, no. 2, pp. 10-11.
Knowlton, Frank Hall, 1888, Description of two species of "Palmoxylon" from Louisiana. Proceedings of the United States National Museum, no. ?, pp. 89-91.
McMackin, C. E., 1984, Petrified wood from east to west; some we've liked best. Lapidary-Journal. vol. 37, no. 11, p. 1582-1588.
Paine, W. W., and Meyerhoff, A. A., 1968, Catahoula Formation of western Louisiana and thin-section criteria for fluvitale depositional environment. Journal of Sedimentary Petrology. vol. 38, no. 1, pp. 92-113.
Pope, David E., 1988, History of the Louisiana Geological Survey. in Arthur A. Socolow, ed., The State Geological Surveys: A History. American Association of State Geologists, 499 pp.
Thomas, L. H., 1986, Elusive in Louisiana. Lapidary Journal. vol. 40, no. 3, p. 54-56
Zeitner, June Culp, 1988, Louisiana's agatized palm. Lapidary Journal. vol. 42. no. 4, p. 43-46.
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