A forest turned to stone
In the dry, sandy landscape of central Myanmar's Sagaing Region, massive stone logs lie scattered across the ground. Some of these silicified trunks are over 30 meters long and more than a meter in diameter. These are the remains of a vast tropical forest that grew here during the Late Miocene epoch, approximately 20 million years ago. The trees are preserved within a geological layer known as the Irrawaddy Formation, a thick sequence of river-deposited sediments.
The process that transformed this forest is called permineralization. Gigantic trees were rapidly buried by sand and silt from overflowing rivers, which cut off oxygen and prevented decomposition. Over millions of years, groundwater rich in dissolved silica percolated through the buried logs. Molecule by molecule, the original organic wood tissue was replaced by minerals, primarily quartz. This process was so precise that it preserved the wood's anatomical structure in three dimensions, right down to the cellular level. This allows paleobotanists to study the tissue under a microscope as if it were modern wood.
Echoes of a Miocene ecosystem
The remarkable preservation allows for precise identification of the ancient trees. The most common species found is Dipterocarpoxylon burmense, an extinct relative of modern dipterocarps. Dipterocarps are large hardwood trees that still dominate the rainforests of Southeast Asia today, indicating that this type of ecosystem has existed in the region for millions of years. Other fossilized plants, including a type of palm wood called Palmoxylon, have also been identified.
The Irrawaddy Formation contains many fossilized plants; it is a well-documented source of vertebrate fossils. Paleontologists have uncovered the remains of ancient mammals and reptiles alongside the petrified trees. These include early elephants (Stegolophodon), horses (Hipparion), rhinoceroses, and long-snouted crocodiles (Gavialis). This collection of fossils shows the complete ecosystem—a warm and wet environment with dense forests and large river systems, drastically different from the semi-arid conditions found in the region today.