480-million-year-old limestone preserves trilobites in three dimensions with eyes intact. The assemblage shows Korea was once near Australia on the ancient continent Gondwana.
An Ordovician seabed in the mountains
In the hills of Yeongwol County, layers of limestone contain a complete marine ecosystem from 480 million years ago. These rocks are part of the Mungok and Duwibong formations, which formed from carbonate mud on the floor of a shallow, tropical sea during the Early and Middle Ordovician Period. The conditions were perfect for fossilization. Rapid burial in this fine-grained sediment prevented the decay and crushing of organisms, leading to exceptional three-dimensional preservation.
Unlike many fossils that are flattened into two-dimensional impressions, the trilobites of Yeongwol retain their original shape. This allows paleontologists to study their morphology in detail. The most remarkable feature is the preservation of their compound eyes. Trilobite eyes were complex visual systems with lenses made of calcite, the same mineral that forms limestone. The fossils in Yeongwol often have these holochroal eyes—a type with many small, densely packed lenses—fully intact, showing one of Earth's earliest visual systems.
A continental drift puzzle
The types of trilobites found in Yeongwol show the region's paleogeography. The fossil beds contain a mix of pandemic genera like Asaphopsoides and Kayseraspis alongside endemic species. This specific collection of species, or faunal assemblage, is very different from Ordovician fossils found in South China. Instead, it shows a strong similarity to trilobite faunas from the same period discovered in Australia.
This faunal evidence demonstrates that the Sino-Korean Craton, the tectonic plate on which these rocks formed, was not near its present-day neighbors. During the Ordovician, it was attached to the northeastern margin of the supercontinent Gondwana, adjacent to what would become Australia. The trilobites could move freely along this contiguous shallow shelf, creating a shared biological province. The discovery of the index fossil Jujuyaspis in the Mungok Formation helps to precisely date these rocks and firmly establish the beginning of the Ordovician period at this location. The entire region is now recognized as part of the Gangwon Paleozoic National Geopark.
💡Fun Facts
The name "trilobite" means "three-lobed," referring to the three longitudinal lobes that run the length of their exoskeleton.
The fossil beds are protected as part of the Gangwon Paleozoic National Geopark.
Trilobite eyes were made of calcite, the same mineral that makes up the limestone in which they are fossilized.
The trilobite genus *Jujuyaspis*, found here, is used by scientists globally as an index fossil to define the start of the Ordovician Period.
The fossil beds are part of the larger Gangwon Paleozoic National Geopark. A key site in the park, Gossigul Cave, is open 09:00–18:00 (last admission 17:00).
Admission
For Gossigul Cave: Adults 4,000 won / Students 3,000 won.
Accessibility
The fossil beds are natural rock outcrops with varying accessibility. The associated Geopark sites like Gossigul Cave have developed walkways.