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Sedimentary Rocks. What is a Sedimentary Rock? Sedimentary rock is formed by – deposition and consolidation of sediment and organic material – precipitation.

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Presentation on theme: "Sedimentary Rocks. What is a Sedimentary Rock? Sedimentary rock is formed by – deposition and consolidation of sediment and organic material – precipitation."— Presentation transcript:

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” Erosion: transportation of sediment/ions – streams, wind, glaciers – super-strong hikers… Water is the most efficient natural transporter – ~27 billion tons annually) Direction of transport

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

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7 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

8 Compaction VS. Cementation

9 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

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

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

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

13 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

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

15 Bedding Layering in sedimentary rocks Sediment accumulates layer by layer

16 Cross-Bedding Basically, lithified sand dunes

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

18 Mud Cracks Polygonal cracks formed as mud dries and shrinks Modern mud cracks→ Ancient mud cracks in mudstone→


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