sedimentary rocks chapter 6. materials that make up sediments weathered rocks organic material...
TRANSCRIPT
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SEDIMENTARY ROCKS
CHAPTER 6
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Materials that make up sediments
• Weathered Rocks
• Organic Material
• Mineral Fragments
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Ways sedimentary rocks can form
• Compaction and cementation of sediments
• Evaporation of a solution
• Precipitate from a solution
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Kinds of sedimentary rocks1) 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
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Fragments
• Round Fragments = CONGLOMERATE
• Angular Fragments = BRECCIA– (pronounced Brechia) – (“cc” is “ch” like Gucci)
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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.
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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.
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– Contains the cemented (lithified) remains of once living things
– Sometimes contain fossils– Ex) coal
2) Organic
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3) Chemical
• Form by precipitation or evaporation of a solution
• Often contain crystals or appear “dried up”
• Ex) rock salt
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4) Bioclastic
• Composed of broken shell fragments and similar remains of living organisms
• Ex) limestone
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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.
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Stratification and Fossils
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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.
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Ripple Marks and Mud Cracks
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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.
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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.