CHAPTER 3 SEDIMENTARY ROCKS - Mvn.net€¦ · 3 • A. How Clastic Rocks Form • 1. weathering of existing rocks • 2. rock sediment is transported and deposited • 3. rock sediment

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• CHAPTER 3

• SEDIMENTARY ROCKS

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• A. Sedimentary Rocks- most of the surface is covered by sedimentary rocks. (however, most of the crust is made of igneousrocks)

• 1. three main kinds of sedimentary rock

• a. clastic-formed from fragments of other rocks.

• 1) examples; shale, sandstone, and conglomerate

• b. chemical- formed from mineral grains that fall out of a solution (precipitate) by evaporation or by chemical action.

• 1) examples; rock salt, gypsum and some limestones

• c. organic- formed from the remains of plants and animals.

• 1) examples; coal, some limestones made of shell fragments

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• A. How Clastic Rocks Form

• 1. weathering of existing rocks

• 2. rock sediment is transported and deposited

• 3. rock sediment is bound together

• 1) natural cement in the form of dissolved minerals

• a) ocean water, lake water and groundwater contain dissolved minerals

• b) silica, lime and iron-oxide cement types

• 2) pressure can cause fine sediments to bind together

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• A. Sorting of Sediments

• 1. when a river flows into a lake or ocean, it slowsdown when it meets the larger body of water. It can no longer carry the sediments it has picked up and they start to fall out on the bottom of the lake or ocean. The first sediments to drop out are the larger particles, (pebbles and gravel). Next, smaller sands drop out and finally the last to drop out would be the finestparticles, the silts and clays.

• a. pebbles and gravels become conglomerates

• b. sands become sandstones

• c. silts and clay form shale

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• A. Conglomerate, Sandstone, and Shale

• 1. conglomerate is the coarsest of the clastic rocks, composed of pebbles and gravels

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• 2. sandstone is made of grains of sand (quartz), it may contain up to 30% air spaces and is referred to as porous (filled with small holes) in which case it may be permeable (water may pass through it).

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• 3. shale is composed of clays and silts. Spaces in shale are so tiny that water cannot pass through the rock (impermeable).

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• A. Sedimentary Rocks of Chemical Origin

• 1. water contains dissolved minerals.

• 2. chemical sedimentation occurs when evaporationor chemical precipitation occurs.

• 3. limestones, rock salt, and rock gypsum

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• A. Sedimentary Rocks of Organic Origin

• 1. organic sediments come from the remains of animals and plants

• a. important examples; chalk, coal and limestone

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• b. Coquina—shell sediment (lime shells)

• 1) acid test is positive.

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• A. Sedimentary Features: Stratification

• 1. stratification-is described as visible layering

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2. cross-bedding-bedding plane

that is not horizontal

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• A. Fossils in Sedimentary Rocks

• 1. fossil- the remains, impressions, or any other evidence of plants and animals preserved in rock

• a. plants and animals die and are buried

• b. soft body parts decay

• c. hard parts may be replaced by other minerals dissolved in water

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• A. Ripple Marks and Mud Cracks

• 1. ripple marks-are formed by the action of the winds, streams, waves or currents on sand

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• 2. mud cracks-develop when wet clay dries and contracts leaving cracks. These cracks are later filled with a different material.

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• A. Nodules, Concretions, Geodes

• 1. lumps found in some rock deposits are called nodules

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• 2. round masses may be called concretions

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3. hollow sphere of rock may be lines with crystals or calcite are called geodes.

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