Chapter 6 Sedimentary Rocks (Part I)
The Archives of Earth History
1 History from Sedimentary Rocks • Sedimentary rocks are rocks that are formed from the compaction and hardening of sediment • They account for about 5% (by volume) of Earth’s outer 10 miles – preserve evidence of surface depositional processes – and many contain fossils – These give clues to the depositional environment
2 Sedimentary Rocks • Sedimentary rocks – preserve evidence of the physical, chemical and biological processes that formed them • Some sedimentary rocks are resources, or contain resources – – – – petroleum natural gas coal phosphorus
3 Turning Sediment into Rocks • Many changes occur to sediment after it is deposited • Diagenesis – all of the chemical, physical, and biological changes that take place after sediments are deposited • Occurs within the upper few kilometers of Earth’s crust Diagenesis Includes Recrystallization – development of more stable minerals from less stable ones Lithification – unconsolidated sediments are transformed into solid sedimentary rock by – Compaction – Cementation by calcite, silica, and iron oxide
4 Types of Sedimentary Rocks • Sediment originates from mechanical and/or chemical weathering • Rock types are based on the source of the material • Detrital rocks – transported sediment as solid particles • Chemical rocks – sediment that was once in solution • Biogenic rocks – remains of once-living organism
5 Composition of Detrital Rocks • Very common minerals in detrital rocks are: – quartz, feldspars, and clay minerals • Detrital rock composition tells – about source rocks, – not transport and deposition • Quartz sand may have been deposited – in a river system – on a beach or – in sand dunes
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