A 12-million-year archive
The Charyn Canyon, stretching 154 kilometers along its namesake river, cuts through a thick sequence of Cenozoic sedimentary rocks. The steep canyon walls, which reach heights of 150 to 300 meters, expose a geological record dating back approximately 12 million years. This natural archive consists primarily of red sandstone, a sedimentary rock formed from compacted sand and minerals. The layers are not uniform; they include a mix of lacustrine (lake) clays and marls, interbedded with alluvial (river-deposited) sand, gravel, and large boulders.
The story of the canyon begins in the Neogene period when this area was a vast intermontane basin. Rivers flowing from the Tian Shan mountains deposited enormous quantities of sediment, which gradually filled the depression. The reddish color of the sandstone indicates the presence of iron oxides, a result of the sediment being exposed to the atmosphere during deposition. The entire 80-meter-thick sedimentary sequence provides a nearly continuous record of climate and geological activity over the last five million years. The Charyn River began carving the canyon we see today much more recently, sculpting the soft sedimentary rock over the last million years.
Volcanic fingerprints
Embedded within the red-orange sedimentary layers are distinct, paler bands of tephra, or volcanic ash. These ash layers are important chronological markers. Each layer represents a specific, powerful volcanic eruption from somewhere in Central Asia. The unique geochemical signature of the ash in a particular layer acts like a fingerprint, allowing geologists to correlate it with a known eruption event. This technique, called tephrochronology, provides precise date markers within the rock sequence.
These ash layers punctuate a fossil record. The sediments contain the remains of ancient fauna that roamed the plains and river valleys millions of years ago. Discoveries include ancient elephants, primitive horses, rhinos, antelopes, and even the shells of ostriches. The combination of precisely dated ash layers and the fossils found between them allows for a detailed reconstruction of the paleoenvironment and how it changed over time in response to shifts in climate and regional volcanic activity. The oldest layers at the very bottom of the canyon are volcanic lava rocks, a foundation upon which the subsequent millions of years of sediment were deposited.