Petrified Wood

The Yegua Formation, dating to the Eocene epoch, is renowned for its diverse assemblage of petrified wood specimens, reflecting the rich and varied flora that once thrived in what is now Texas. Fossilized remains from this formation provide valuable insights into the region's paleobotanical history.

Diversity of Petrified Wood:

The Yegua Formation's petrified wood collection includes a variety of species, notably:

• Conifers: Represented by the family Podocarpaceae, these conifers are significant as they are currently predominantly found in the Southern Hemisphere.

• Hardwoods: The formation boasts a rich diversity of tropical hardwoods, including:

  • Leguminosae: Families such as acacia and mimosa.

  • Juglandaceae: Tropical hickories.

  • Apocynaceae: Dogbane family.

  • Elaeocarpaceae: A family of flowering plants.

  • Palmae: Palms, indicating the presence of tropical environments during the Eocene.

• Mennegoxylon jonesii: Commonly known as "snakewood," this extinct genus is distinguished by its unique wood pattern resembling snake scales. Specimens have been predominantly discovered in areas such as College Station, Texas.

Significance:

The petrified wood from the Yegua Formation offers a window into the Eocene's tropical ecosystems, highlighting the climatic conditions and biodiversity of the period. The preservation of these specimens allows for detailed studies of ancient plant life, contributing to our understanding of evolutionary histories and paleoecological dynamics.

Petrified wood from the Yegua Formation formed through a process called permineralization, which preserved the microscopic structures of ancient trees in remarkable detail. This transformation took place over millions of years as mineral-rich water slowly replaced the organic material within the buried wood.

Stages of Petrification in the Yegua Formation

1. Burial in Sediments
   During the Eocene epoch, fallen trees and woody debris were buried in the floodplains, river deltas, and coastal environments of what is now Texas. The Yegua Formation, consisting of clays, silts, and sands, provided an ideal setting for preservation by preventing rapid decay through oxygen deprivation.

2. Mineral Infiltration
   Groundwater rich in dissolved minerals, particularly silica (SiO₂) from volcanic ash or other sources, seeped into the buried wood. The minerals gradually infiltrated the porous cell walls, filling voids left by decaying organic material.

3. Silicification and Crystal Growth
   Over thousands to millions of years, silica crystallized in the wood’s cellular structure, forming minerals such as chalcedony, jasper, and opal. This process preserved fine details, including growth rings, cellular structures, and even microscopic features of the original plant tissue.

4. Coloration from Mineral Impurities
   The petrified wood of the Yegua Formation exhibits a range of colors due to the presence of various mineral impurities:

   • Iron oxides → Red, orange, or yellow hues

   • Manganese oxides → Black or deep brown tones

   • Carbon compounds → Dark or grayish shades

5. Exposure Through Erosion
   Over time, geological processes such as erosion exposed these petrified logs and wood fragments at the surface, allowing modern-day discoveries in regions like College Station, Brenham, and other parts of Texas.