Sedimentary Rocks Chapter 3 Section 3

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 Rocks 1.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 Rocks 2.Chemical/Biochemical : form when dissolved minerals precipitate (deposit in solid form) from water solutions Precipitation generally occurs when H 2 O evaporates or boils off leaving solid product. Limestone = calcite and aragonite; clear, shallow marine waters accumulation of shell coral, algal and fecal debris or CaCO 3 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