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CHAPTER 6. SEDIMENTARY ROCKS. Materials that make up sediments. Weathered Rocks Organic Material Mineral Fragments. Ways sedimentary rocks can form. Compaction and cementation of sediments Evaporation of a solution Precipitate from a solution. Kinds of sedimentary rocks.
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CHAPTER 6 SEDIMENTARY ROCKS
Materials that make up sediments • Weathered Rocks • Organic Material • Mineral Fragments
Ways sedimentary rocks can form • Compaction and cementation of sediments • Evaporation of a solution • Precipitate from a solution
Kinds of sedimentary rocks 1) Clastic/Detrital • Composed of fragments and small pieces of rock (clasts) • sometimes show layering • Make up more than 85% of all sedimentary rocks • Ex) sandstone, siltstone, shale
Fragments • Round Fragments = CONGLOMERATE • Angular Fragments = BRECCIA • (pronounced Brechia) • (“cc” is “ch” like Gucci)
Types of Clasts • The formation of clastic rocks begins with the movement and relocation of fragments. • The majority of these are moved by running water. • Larger pebbles and gravels are often the first to be dropped and settle in shallow water near the shore. • Next to settle are the smaller sands. • Finally, in calm water, the silts and clays.
Formation of Clastic Rocks • Loose sediments become solid rock when sediments become cemented. • Ocean water, lake water, and ground water all contain natural cements in the form of dissolved mineral. • Silica (SiO2), calcite (CaCO3), iron oxide (Fe2O3), and clay minerals. • When minerals fill in the spaces between sand grains, pebbles, or other rock particles, they bind the fragments together through cementation. • The type of cement influences the rock’s color.
2) Organic • Contains the cemented (lithified) remains of once living things • Sometimes contain fossils • Ex) coal
3) Chemical • Form by precipitation or evaporation of a solution • Often contain crystals or appear “dried up” • Ex) rock salt
4) Bioclastic • Composed of broken shell fragments and similar remains of living organisms • Ex) limestone
Features of Sedimentary Rocks • Stratification • The arrangement of visible layers. • The most characteristic feature of sedimentary rocks. • Results from the change in the type of sediment being laid down in one place. • Fossils • The remains, impression, or any other evidence of a plant or animal preserved in rock. • Occurs when a dead organism is buried by sediment that gradually turns into rock. • The soft parts of the organism decay; the hard parts become rock.
Features of Sedimentary Rocks • Ripple Marks • Common feature of sedimentary rocks. • Sand patterns formed by the action of winds, streams, waves, or currents. • Ripple marks are generally preserved in sandstone. • Mud Cracks • Common feature of sedimentary rocks. • Develop when deposits of wet clay dry and contract. • The cracks are filled in with different solutions and fossilize. • Generally form in shale.
Features of Sedimentary Rocks • Nodules • Hard lumps of fine-grained silica • Found in limestone and chalk. • Concretions • Round solid masses of calcium carbonate. • Found in shale. • Both Nodules and Concretions form when minerals in a solution precipitate around a fragment in the clay sediment.
Geodes • Spheres of silica rock. • Generally found in limestones. • Groundwater creates cavities in limestone and minerals in the groundwater concentrates in the cavities to form crystals.
