Earth Systems 3209

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

2. Unit 3: Topic 4.4 Clastic Sedimentary Environments Focus on . . . • identifying different clastic sedimentary rocks and relating the rocks to the environment in which they form.

3. Clastic Sedimentary Rocks • Consist of solid particles which results when physical weathering breaks down rocks. The weathered products include pebbles, sand, silt and clay. • These rocks usually form in water environments such as: rivers, lakes, oceans, but can also form in deserts. • Geologist mainly use particle size to distinguish between clastic sedimentary rocks, as seen in the table below:

4. Clastic Sedimentary Rocks • Examples of clastic sedimentary rocks include: • Conglomerate • Consist of poorly sorted rounded gravel size particles. • Form in shoreline and river environments where mixtures of sediments are deposited. • The rounded rock fragments suggest that the sediment was transported great distances. This allowed angular edges to be eroded to produce rounded fragments.

5. Clastic Sedimentary Rocks • Examples of clastic sedimentary rocks include: • 2) Breccia • Consist of poorly sorted, angular gravel size particles. • Form in shoreline and river environments where mixtures of sediments are deposited. • The angular rock particles suggest that the sediment was not transported far from the place where it originated. Thus angular fragments.

6. Clastic Sedimentary Rocks • Examples of clastic sedimentary rocks include: • 3) Sandstone • Consist of well sorted sandsize particles. • Form in shoreline environments (deltas) where sand is deposited. • Second most abundant sedimentary rock • Sand size sediment is a result of erosion due to wind, water, and ice acting on rock fragments over a long period of time.

7. Clastic Sedimentary Rocks • Examples of clastic sedimentary rocks include: • 4) Shale (Siltstone) • Consist of fine clay and silt sized particles compacted to form thin layers. • Form in quiet (slow moving) water environments; • - deep ocean & continental slope • - lakes • floodplains (siltstone) • Commonly contain organic materialwithin the original clay or mud whichform fossils.

8. Clastic Sedimentary Rock Environments Summary

9. Example 1: When a river slows, which sediment is the first to settle? silt b) sand c) clay d) pebbles Over long periods of time deposits of silt and clay compact to form which sedimentary rock? basalt b) conglomerate c) shale d) limestone

10. Example 2: Which is a clastic sedimentary rock? (A) breccia (B) gypsum (C) rock salt (D) travertine The diagram to the right demonstrates which sedimentary rock? (A) breccia (B) conglomerate (C) sandstone (D) shale

11. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: With reference to the diagram, explain why the two different sedimentary rocks developed in the areas indicated.

12. Solutions . . . Question: With reference to the diagram, explain why the twodifferent sedimentary rocks developed in the areasindicated. It is evident from the diagram that the current direction is from left to right. Velocity of the current decreases with progression from left to right. It is this decrease in the velocity of the current that causes the sediment particles to be horizontally sorted. The coarse/large sediment particles are deposited first, closest to the shoreline, and are lithified to form the sedimentary rock called conglomerate. The fine/small sediment particles are deposited furthest from the shoreline and are lithified to form the sedimentary rock called shale.

13. Summary . . . Overview of Points covered: • Clastic Sedimentary rocks include; • Conglomerate • Breccia • Sandstone • Siltstone • Shale • Clastic Sedimentary environments include; • Fluvial (Rivers) • Lagoonal • Beaches • Deep Marine (Ocean) • Shallow Marine