Mongol-Okhotsk Ocean

The Mongol-Okhotsk Ocean, also called the Khangai-Khantey Ocean, was a large, triangle-shaped ancient ocean that existed from the Paleozoic to the Mesozoic time periods. Its rocks can still be found today in a special area called the Mongol-Okhotsk suture zone, which stretches from Mongolia to the Sea of Okhotsk.

This ocean began to form during the early to middle Paleozoic era within a region known as the Central Asian Orogenic Belt. Over millions of years, it started to close up, beginning in the Late Triassic period. This closing happened in a way that bent the western Mongolian landmasses and created a curved shape called the Tuva-Mongol Orocline.

Finally, the ocean closed quickly in a scissor-like motion. This led to a major event where the Erguna Block crashed into the Siberian Craton during the Late Jurassic and Early Cretaceous periods, changing the shape of the Earth’s surface forever.

Sequence of events

When the supercontinent Pangea formed in the mid- to late-Paleozoic, the huge Panthalassa ocean covered most of Earth. Smaller oceans included the Tethys, the Mongol-Okhotsk Ocean, and bits of the early Pacific Ocean. Studies from 1987 to 2010 suggest that the floor of the Mongol-Okhotsk Ocean moved under the land areas of Mongolia in the Late Jurassic or Early Cretaceous.

Later, during the early part of the age of dinosaurs, the Solonker Ocean closed, bringing together huge land masses called Amuria and the North China Block. Amuria then moved and joined with the Siberian Craton, leaving behind a line of rocks called the Mongol-Okhotsk suture zone. Scientists are still trying to figure out why this line of rocks stops suddenly near Kazakhstan. They study these rocks to learn more about Earth's past. Some of the rocks in this zone, like those in the Adaatsag area, are very old — about 325 million years!