Sedimentary Rocks

1. Sedimentary Rocks Sedimentary rocks form when sediments harden into rocks 3 main kinds clastic, chemical and organic Most of Earth’s crust is covered by sedimentary rocks

2. Three Main Kinds of Sedimentary Rock • Clastic:cemented together fragments of other rocks • Chemical:mineral grains that are removed from a solution by evaporation or chemical action • Organic: remains of plants and animals

3. Clastic Rocks • Clastic sedimentary rocks are made up of weathered rocks that already exist • Rocks are weathered and transported by rivers, winds, waves, and glaciers • Sediments are deposited when the transport system loses energy ie: stream • Ocean water, lake water, and groundwater contain natural cements: silica(SiO2), calcite (CaCO3), and iron oxide(FeO) • These dissolved minerals settle into the spaces between the sand grains or pebbles, binding them together into rock • The pressure of overlying sediments can also make fine sediments stick together

4. Clastic Rocks: Conglomerate • Coarse, large grains • Deposited in high energy system (rough water) • Cemented mixture of rounded pebbles and sand grains • Pebbles can be any durable rock material

5. Clastic rocks: Sandstone • Medium grained • Quartz grains (7 on Moh’s scale of hardness) • Porous (small holes) • Permeable (water can pass through)

6. Clastic rocks: Shale • Fine grained clay minerals • Impermeable • Smooth, soft and easily broken • Found in very low energy environments

7. Sorting of Sediments

8. Chemical Sedimentary Rocks • Dissolved minerals fall out of solution • Evaporation or the combining of dissolved ions to form new minerals. • The most common are limestone, rock salt, and rock gypsum • Limestones are formed from tiny grains of calcite • Rock salt is the natural form of table salt, it is almost pure halite • Rock gypsum occurs in layers and is almost pure gypsum

9. Chemical Sedimentary Rocks Rock Salt Limestone

10. Organic Sedimentary Rocks • Organic sediments come from the remains of plants and animals • The most common are shell limestone and coal • shell limestone is mostly calcite, shell producing animals die and their shells pile up and are cemented together

11. Sedimentary Features: Stratification • Stratification is the arrangement of rocks in visible layers • When there is a change in the type of sediments being laid down, new rock layers are formed • Change results from new source sediments or energy change • The layers are called beds and are separated by bedding planes

12. Sedimentary Features: Cross Bedding • Cross-bedding develops when beds are deposited at an angle: wind on dunes, rivers on deltas or sandbars

13. Fossils in Sedimentary Rocks • Animals and plants that die and are buried, as sediments pile up= fossils • The hard parts may remain as fossils when the sediments turn to rock • Fossils are the remains, impressions, or any other evidence of plants and animals preserved in rock

14. Ripple Marks and Mud Cracks • Many sandstones show ripple marks that are formed by the action of winds, streams, waves or currents on sand. • Mud cracks develop when deposits of wet clay dry and contract • Mud cracks are later filled with different materials, and the clay becomes shale rock.

15. Nodules, Concretions, Geodes • Nodules are lumps of fine-grained silica called chert, solid replacement bodies • Concretions are round masses of mineral precipitation that form around some kind of nucleus • A Geode is a hollow nodule of silica rock, filled with crystals of quartz or calcite Geode Nodule