A sedimentary basin is a region of the crust that sinks over millions of years, so that sediments pile up in it, often several kilometres thick.
Earth and Space Sciences · Glossary
What is Sedimentary basin?
A sedimentary basin is a region of the Earth’s surface where the crust has subsided for a long time, a few million to a few hundred million years, and where the space so created has been filled with sediment, hundreds of metres to many kilometres thick.