* Formation: Sedimentary rocks form from the accumulation and cementation of sediments, like sand, mud, and organic matter. This process usually happens at the Earth's surface, in environments like rivers, lakes, oceans, or deserts.
* Exposure: Erosion and tectonic activity can bring sedimentary layers that formed deep underground to the surface over millions of years. This is why we find ancient sedimentary rocks, like those containing fossils, exposed in mountains and canyons.
* Burial: New layers of sediment can bury older layers, creating a sequence of sedimentary rocks that can extend far below the surface. These buried layers can be incredibly thick, forming sedimentary basins.
* Fossil Fuel Formation: Many important sedimentary rocks, like those containing oil and natural gas, form deep underground within these basins.
So, while the initial formation of sedimentary rocks usually happens at the surface, their location and depth can change significantly over geologic time.
