Bigach
Key facts
- Country
- Kazakhstan
- Diameter
- 8 km
- Age
- about 5 ± 3 million years
- Location
- 48.57° N, 82.02° E
A shallow round basin about 8 km across in the steppe of eastern Kazakhstan, near the Chinese border.
Bigach is an impact structure about 8 km across in the steppe of East Kazakhstan, not far from the border with China.
What it hit. The impactor struck a sequence of folded Palaeozoic volcanic and sedimentary rocks, partly covered by younger Cenozoic sediments.
Proof of impact. Soviet geologists studied the structure in the 1970s and 1980s. They found breccias and impact melt rocks with shock features in their minerals, including planar deformation features in quartz, which confirmed an impact.
Age. Argon dating of the melt rock gives an age of about 5 million years, in the late Miocene or Pliocene, with an uncertainty of about 3 million years.
Why it matters. Bigach is one of several young impact structures in Kazakhstan. Because it is young, it still preserves its basin shape. The impactor is unknown.
Did you know?
Bigach is about 5 million years old.
Rock melted by the impact has been found there.
It lies near the border with China.