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Sedimentary Rocks

Sedimentary Rocks. What is a Sedimentary Rock?. Sedimentary rock is formed by deposition and consolidation of sediment and organic material precipitation of minerals from solution. Where does sediment come from?. Weathering is the process that reduces solid rock to rubble Two types

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Sedimentary Rocks

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  1. Sedimentary Rocks

  2. What is a Sedimentary Rock? • Sedimentary rock is formed by • deposition and consolidation of sediment and organic material • precipitation of minerals from solution

  3. Where does sediment come from? • Weathering is the process that reduces solid rock to rubble • Two types • Physical: solid rock to rubble without changing chemical composition • Chemical: altering or dissolving minerals in a rock

  4. Moving Rocks “Au Naturel” Direction of transport • Erosion: transportation of sediment/ions • streams, wind, glaciers • super-strong hikers… • Water is the most efficient natural transporter • ~27 billion tons annually)

  5. Grain Size and Distance • It’s the size that counts… • Sediment far removed from its place of origin • Small and round • Sediment close to source • Larger and angular

  6. Lithification • Sediment is deposited in low spots • Transportation continues—new sediment buries older sediment • Buried sediment is compacted (loss of empty space) • Cementation—filling in spaces

  7. Compaction VS. Cementation

  8. Types of Sed. Rocks • Clastic • formed from compacted sediment • Organic • formed from lithified plant/animal remains • Chemical • formed from direct precipitation of ions from solution • Bioclastic • formed from broken shell fragments

  9. Clastic Sed. Rocks →Increasing Grain Size → Shale siltstone conglomerate sandstone

  10. Organic Sed. Rocks • Coal • Buried and compressed dead things From this To this …in a matter of eons

  11. Chemical Sed. Rocks • Water evaporates leaving behind mineral deposits (evaporite deposits) Death Valley, CA Great Salt Lake, UT

  12. Bioclastic Sed. Rocks • Seawater contains dissolved ions • Critters use these ions to make their shells • When they die, their shells fall to the ocean floor where lithification can take place coquina

  13. Sedimentary Structures • Features that develop in sediment during or shortly after deposition • Most common types • Bedding • Cross-bedding • Ripple marks • Mud cracks

  14. Bedding • Layering in sedimentary rocks • Sediment accumulates layer by layer

  15. Cross-Bedding • Basically, lithified sand dunes

  16. Ripple Marks • Small, parallel ridges and troughs • Created by wave and wind action Modern ripples on a sand dune Ancient ripples preserved in sandstone→

  17. Mud Cracks • Polygonal cracks formed as mud dries and shrinks Modern mud cracks→ Ancient mud cracks in mudstone→

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