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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.

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Sedimentary rocks

Sedimentary Rocks

Chapter 3 Section 3

Sedimentary rocks1

  • Sedimentary  sedimentum Latin for ‘settling’

  • Rock formed from compressedorcementedlayers (DEPOSITS) of sediment.

  • Sometimes fossils accumulate and are compacted/cemented together.

  • Contain fragments of older rocks from weathering.

Canyonlands Nat. Park, Utah

Formation of sedimentary rocks
Formation of Sedimentary Rocks

  • Weathering, Erosion, and Deposition

    • Weathering= breaks rocks into sediments; first step in

      formation of sedimentary rocks (mechanical and


    • 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

  • 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

  • Conglomerate rounded pebbles cemented together

    • Sandstone

    • grains are

    • cemented

    Classifying sedimentary rocks
    Classifying Sedimentary Rocks

    Breccia: quartz; clastic

    • Classified into two main groups according to the way they form:

      • 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

    Classifying sedimentary rocks1
    Classifying Sedimentary Rocks

    • 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


    Rock Salt


    • 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