Welcome to Earth Science 2017-2018

Sedimentary Rocks Chapter 6

EES News and Notes Let’s start previewing with a self-guided reading of the opening part of the chapter. After that, we’ll move forward through the first section of notes. Remember: everything is cumulative! Be sure to consider igneous rock formation as we learn about sedimentary rocks!

Weathering and Erosion How do rocks break down?

Weathering and Erosion Weathering takes place when physical and chemical processes break rock down into smaller pieces. What forces most contribute to weathering?

Sediments Simply put, sediments are small pieces of rock that are moved and deposited by water, wind, glaciers and gravity! ‘Gluing’ rocks together makes sedimentary rocks!

Weathering Chemical weathering occurs when the minerals in a rock are dissolved or otherwise chemically changed. Physical weathering occurs when rock fragments break off of the solid rock along fractures or grain boundaries.

Erosion Erosion is simply the removal and transport of sediment. Main agents of erosion: Wind Moving water Gravity Glaciers

Erosion After broken down by weathering, rock bits are carried away by erosion. Eroded material is almost always carried downhill. Eventually, gravity pulls things downhill.

Deposition Takes place when transported sediments are deposited on the ground or sink to the bottom of a body of water. When deposited, the largest grains will settle on the bottom. Why is this?

Energy of Transporting Agents Fast-moving water can transport larger particles better than slow moving water. Think of creek beds. Sand dunes are usually finer particles. Why? Glacial deposits are usually a mix of big and small particles. Why?

Lithification Sediments drop in low-lying areas (valleys and ocean basins) As more layers build up, the lower layers are subject to intense pressure and increasing temperature Lithification is the physical and chemical processes that transform sediments into sedimentary rocks!

Compaction Beginning step of lithification. Weight of top layers of sediment forces grains closer together, causing physical changes. Mud is 60% water; flattens as pressurized. Sand is highly composed of quartz, maintaining open spaces between grains.

Cementation Cementation occurs when mineral growth glues sediment grains together into solid rock. Occurs when new mineral grows between sediment grains as dissolved minerals precipitate out of groundwater. EX: CaCO₃ or Fe₂O₃ fuses layers of sediment together

Bedding Horizontal layering that is the main attraction of sedimentary rocks. Can be only a few mm to several meters thick! Type of bedding depends on transportation of materials and type of material in the bedding.

Graded Bedding Bedding in which the particle sizes become progressively finer and lighter toward the top layers. Usually in marine sedimentary rocks caused by underwater landslides. Heaviest/largest sediment settles first.

Cross-Bedding Inclined layers of sediment are deposited across a horizontal surface. With lithification, the cross-beds are preserved in rock. Can be seen on beaches or migrating sand dunes.

Ripple Marks Ripple marks occur when sediment is moved into small ridges by wind or wave action or by a river current. Back and forth motion of waves create symmetrical ripples. One direction currents (rivers or streams) produce asymmetrical ripples.

Types of sedimentary Rocks All sedimentary rocks are classified by their MODE of formation— (that is, how they formed).