Unit: 3 Earth’s Materials Earth Systems 3209 Unit: 3 Earth’s Materials Reference: Chapters 2, 3, 6, 7; Appendix A & B

Formation of Sedimentary Rocks Unit 3: Topic 4.1 Formation of Sedimentary Rocks Focus on . . . outlining and explaining how sedimentary rocks form.

Formation of Sedimentary Rocks Sedimentary rocks account for approximately 5% of the crust. Regardless of this low percentage, approximately 75% of all rocks exposed at the surface is sedimentary rock. Stages leading to the formation of sedimentary rocks include: Erosion and weathering Transportation Deposition Lithification Text Reference: Pages 158-159

1) Weathering and Erosion In reference to the Rock Cycle, the origin of sedimentary rocks begins with the processes of weathering and erosion. Pre-existing rocks can be broken down both mechanically or chemically to produce sediment. Mechanical weathering occurs when a material is broken into smaller pieces which still retain the characteristics of the original material. Example: freeze – thaw action. Water freezing cracks fragments of rock

1) Weathering and Erosion In reference to the Rock Cycle, the origin of sedimentary rocks begins with the processes of weathering and erosion. Pre-existing rocks can be broken down both mechanically or chemically to produce sediment. Chemical Weathering happens when a material is altered by chemical action and a new material is produced which is chemically different than the original material. Examples: Oxidation reactions - Iron rusting Decomposition of limestone (statues and headstones)

2) Transportation of Sediment Erosional agents (such as, water, wind, and ice,) influenced by gravity, transport the sediment to new locations where it is deposited. Sediment is broken down during the transport phase. This process is called Abrasion. Three main agents tend to transport the sediment, these agents include: Water (rivers and groundwater) Ice (glaciers) Wind

3) Deposition of Sediment Eventually the sediment is deposited in lakes, river valleys, seas, and more frequently the oceans. In dry areas of the world, sediment (sand and silt) can accumulate in areas called deserts. Sediment size will decrease the farther it travels into a lake or ocean. This is referred to as Sorting.

Transportation of Clastic Sediments Size Sorting Coarse-grained Medium-grained Fine-grained Fast Slow Moderate Size Distribution Sorting sandstone shale conglomerate

4) Lithification of Sediment Following deposition, sediment may become lithified, which means turned to solid rock. Sediment is commonly lithified by two processes: Compaction: when the sediment size is small (silt and clay), the weight from the layers of sediment above can compact the lower layers forming solid sedimentary rock. Compaction Silt and Clay Sand Lime (Calcite) Round Pebbles Shale Sandstone Limestone Conglomerate

4) Lithification of Sediment Following deposition, sediment may become lithified, which means turned to solid rock. Sediment is commonly lithified by two processes: Cementation: Over long period of time mineral matter dissolved in groundwater pass through pore spaces and cement (stick) sediment particles together to form solid sedimentary rock. Sediment Particles Cement (in Red) Water with dissolved minerals, (calcite or silica) pass through pore spaces

Example 1: Which processes are responsible for the lithification of sediments? cementation and compaction faulting and folding (C) compression and tension (D) weathering and erosion Which of the following is most likely to have formed farthest from the shoreline? pebble conglomerate quartz sandstone shell limestone silty shale

Example 2: Which letter in the diagram below indicates where sediments is formed? A B (C) C (D) D

Your Turn . . . Take the time and complete the following questions . . . (Solutions to follow) Question: Which is the correct sequence in the formation of sedimentary rock? compaction - deposition - weathering - cementation – erosion deposition - erosion - cementation - weathering – compaction erosion - weathering - deposition - cementation – compaction weathering - erosion - deposition - compaction - cementation

Solutions . . . Question: Which is the correct sequence in the formation of sedimentary rock? compaction - deposition - weathering - cementation – erosion deposition - erosion - cementation - weathering – compaction erosion – cementation – compaction - weathering – deposition weathering - erosion - deposition - compaction - cementation

Summary . . . Overview of Points covered: Four stages leading to the formation of Sedimentary rock include: Weathering and Erosion Transportation Deposition Lithification