Unit 8.3-Sedimentary Rocks

Clastic
1. Clastic Sedimentary Rocks are formed when sediments are laid down by wind and water,gravity & ice, and then compacted and cemented.
2. They contain broken pieces of rocks. These pieces are known as clasts
3. They may have layers like stacks of pages in a book because the sediments build up one on top of another as they are deposited.
4. These may contain rock fossils
Chemical
1. When minerals dissolved in groundwater crystalline within the sediments or when the water evaporates
2. Chemical sedimentary rocks are quite soft.
3. This helps to distinguish them from much harder igneous rocks
Biogenic
1. Formed when dead plants or matter accumulate
2. And then cemented together
3. These sediments are mostly from organisms but they are may be small amounts of sediments from weathered rock
4. Coal is a type of biogenic rock.
Relative age of Rock Strata
1. Relative age is not the actual age of the rock but only indictaeds whether a rock is older or younger than another rock.
2. Be found over a widespread area
3. Have lived in a narrow period of time in the past
4. have been abundant with lots of organisms

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