PETRIFIED WOODS OF NORTHERN BELIZE by Jean H. Cornec, Geologist, July 2010
Belize is home to scientifically intriguing, and potentially commercially valuable, petrified wood resources. Petrified wood fragments have been reported in the areas of Duck Run, Spanish Lookout, San Marcos, Iguana Creek, Buena Vista and Valley of Peace in the Cayo District and in an area west of San Felipe in the Orange Walk District. They are associated with sediments of the Red Bank group, a geological unit defined by G. Flores in 1952, which is comprised of clays, sands and chert. The known areal extent of Red Bank surface outcrops is illustrated by red shading in figure 1.
Petrified wood is a type of fossil where all the organic materials have been replaced with minerals, most often quartz, while retaining the original structure of the wood. The petrification process occurs below the surface when root stumps, tree trunks and branches become rapidly buried under falling volcanic ashes. The wood is preserved from the normal rotting process due to lack of oxygen as it is suddenly isolated from atmospheric conditions. Water percolating through the ashes deposits minerals in the plant’s cells while the lignin and cellulose slowly decay away. The major fossilization process starts with a molecule by molecule exchange of the organic plant by inorganic materials. Therefore morphological characteristics of the tree trunks such as the annual rings, bark, as well as patterns and fabric of the internal structure of the wood, can sometimes be preserved in excellent condition. Elements such as manganese and iron oxides present in the water and volcanic ashes during the petrification process give the Belizean petrified woods a variety of color ranges (black, red, brown, yellow, white, grey). Most of the Belize petrified woods are fragments of stumps and trunks which can measure up to 3-4 feet in length and weight up to 100 pounds. A 5-foot long branch still encased in situ within green-red clays was recently found by the author near San Felipe (Figure 2a).
These fossilized plants represent the remnants of a sub-tropical or tropical forest that existed in Belize some 15-20 million years ago. Large mammals were roaming the forest as evidenced by a fossilized mastodon tooth found in Calla Creek and a giant ground sloth femur uncovered on the bank of the Belize River near Santa Familia. Salt water lagoons were also present as evidenced by gypsum outcrops in Buena Vista, north of Iguana Creek, in San Marcos and Spanish Lookout, and in Buena Vista near Calla Creek. Fossilized ray and shark teeth indicative of coastal waters have been found on the bank of the Belize River near Bermudian Landing, including that of Carcharodon megalodon, a now extinct, gigantic shark that grew up to a maximum length of 80 feet with a body mass of more than 100 metric tons. The formation of petrified wood is likely related to intense large-scale explosive volcanic activity in El Salvador, Guatemala and Mexico during Miocene times. The bentonitic clays in which these fossils are found have a chemical composition compatible with a Central America volcanic source. The extremely large volcanic eruptions responsible for the ash resulted in ejected material with column heights in excess of 40 kilometers, and spread out to giant mushroom-shaped plumes reaching stratospheric elevations where wind flows from west to east , i.e., in the opposite direction of the lower level trade winds (S. Carey & H. Sigurdsson, 1999). Despite the fact that a systematic study of Belize petrified woods has not yet been undertaken, the fossils likely belong to higher plant groups: Angiosperm (flowering plants/palm trees) and Gymnosperm (conifers). Some fragments are beautifully colored with a well-preserved wood structure. Since they can be easily cut and polished, or tumbled, they can be incorporated into jewelry or other ornamental items and provide the tourism industry with a new local source of handicraft souvenirs.