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Silicification Processes of the Goderdzi Petrified Forest: Insights from Mineralogical Studies

Mirian Makadze1, Avtandil Okrostsvaridze2, George E. Mustoe3

  • Affiliations: 1Faculty of Exact and Natural Sciences, Tbilisi State University, Tbilisi, Georgia; 2Institute of Earth Sciences, Ilia State University. 0162 Tbilisi, Georgia; 3Geology Department, Western Washington University, Bellingham, WA 98225, USA

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 40

  • Programme No: 3.8.24

  • Theme 3 > Session 8

Abstract

The Goderdzi Petrified Forest, of the Late Cenozoic Samtskhe-Javakheti volcanic highland, located near the Goderdzi Pass in southern Georgia. It is a remarkable site featuring petrified trees preserved within the tuffaceous sediments of the Upper Miocene--Lower Pliocene volcanogenic Goderdzi Formation. This fossil flora is distinguished by its exceptional preservation and diverse species composition. Goderdzi fossil trees first studied in the early 20th century and approximately 200 species have been identified.    Recent research has identified 11 new subtropical species, with no boreal representatives. The petrified wood exhibits diverse silica mineralization, including amorphous opal (opal-A), opal-CT, and quartz. Many samples display a mixture of opal-A and opal-CT, the latter being a weakly crystalline form of opal containing cristobalite and tridymite interlayers. The transformation of opal-A to opal-CT is thought to occur through silica dissolution and reprecipitation, though opal-CT may also form directly as a primary precipitate. The petrification process begins with the deposition of amorphous silica in cell walls, followed by the infilling of cell interiors (lumens) and large conductive vessels. The final silica forms---opal-A, opal-CT, chalcedony, or quartz---depend on factors such as silica concentration, temperature, wood permeability, and episodic silica-rich groundwater infiltration. The dominance of opal-A, a less stable silica form typically associated with young deposits, aligns with the Pliocene age of these fossils. XRD patterns analyses reveal a range of silicification histories, including specimens dominated by mixtures of opal-A and opal-CT, as well as quartz-rich samples. These findings suggest a multi-stage silicification process influenced by volcanogenic host rocks.