Sedimentary Rocks Chapter 3 Section 3. Sedimentary sedimentum Latin for ‘settling’ Rock formed from compressed or cemented layers (DEPOSITS) of sediment.
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Sedimentary Rocks
Chapter 3 Section 3
SEDIMENTARY ROCKS
• Sedimentary sedimentum Latin for ‘settling’• Rock formed from compressed or cemented layers
(DEPOSITS) of sediment.• Sometimes fossils accumulate and are
compacted/cemented together. • Contain fragments of older rocks from weathering.
Canyonlands Nat. Park, Utah
SEDIMENTARY FORMATION WITHIN ROCK CYCLE
Formation of Sedimentary Rocks1. Weathering, Erosion, and Deposition• Weathering= breaks rocks into sediments; first step in formation of sedimentary rocks (mechanical and chemical)• Erosion= water, wind, ice, gravity move weathered sediments• Deposition= when agents of erosion (listed above) lose energy sediments stop moving deposition
• Deposited according to size—largest first
2. Compaction and Cementation• After sediments deposited become lithified (turned to rock)
• Compaction= squeezes, or compacts, sediments; caused by weight of sediments
• Cementation= dissolved minerals are deposited in the tiny spaces among the sediments
Sandstone grains are cemented
Conglomerate rounded pebbles cemented together
Classifying Sedimentary Rocks• Classified into two main groups according to the
way they form:1. Clastic: made of weathered bits of rocks and
minerals• Most common minerals found in clastic = clay
(most abundant product) of chemical weathering and quartz (durable and resistant to chemical weathering• Grouped according to size of sediments:• Conglomerate = larger pebbles• Sandstone = sand sized grains• Shale = most common sed. rock; fine grained
Breccia: quartz; clastic
Classifying Sedimentary Rocks2. Chemical/Biochemical: form when dissolved minerals
precipitate (deposit in solid form) from water solutions• Precipitation generally occurs when H2O evaporates or boils off
leaving solid product.• Limestone = calcite and aragonite; clear, shallow marine waters accumulation of shell coral, algal and fecal debris or CaCO3 from water• Coquina=type of limestone biochemical – sediments of shells and skeletal remains settle
• Rock salt = halite (mineral form of NaCl); evaporation• Rock Gypsum = evaporation in shallow sea basins or salt lakes gypsum precipitates
Coquina
Rock Salt
Features
• Unique features of sedimentary rocks that are clues to how, when, and where they formed.• Layers law of superposition• Ripple marks: beach or stream bed• Fossils
Classification of Major Sedimentary
Rocks
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