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Sedimentary Rocks

Sedimentary rocks are formed at or near the Earth's surface through processes like weathering, erosion, deposition, burial, and lithification. These rocks are characterized by their layered structure (strata) and can contain fossils and other features such as ripple marks and concretions. Sediments, carried by wind, water, and gravity, accumulate in sedimentary basins, undergoing compaction and cementation to transform into rock. Key types of sedimentary rocks include clastic, chemical, and organic formations like limestone and coal.

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Sedimentary Rocks

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  1. Sedimentary Rocks • Sedimentary rock is formed by erosion • Sediments are moved from one place to another • Sediments are deposited in layers, with the older ones • on the bottom • The layers become compacted and cemented together http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

  2. Sedimentary Rock • Sedimentary Rocks are formed at or near the Earth’s surface • No heat and pressure involved • Strata – layers of rock • Stratification – the process in which sedimentary rocks are arranged in layers

  3. Sediments -pieces of material left by: *wind *ice *chemical precipitation *water *gravity Step 1: WEATHERING Chemical- minerals are chemically broken down

  4. * Physical – minerals remain chemically unchanged

  5. Step 2: EROSION * transporting weathered materials to another location * Wind, water, gravity and glaciers transport

  6. Step 3: DEPOSITION * sediments are deposited and sorted

  7. Step 4: BURIAL * deposited into depressions called “sedimentary basins” * the deeper it gets, the more pressure on it til…… 2 ROCK BURIAL

  8. Step 5 : LITHIFICATION (FYI – lithos: Greek for stone) * physical and chemical process that changes it to sedimentary rock 1st Compaction 2ndCementation & Solidification new minerals precipitate more of the same type around existing ones crystallize around existing ones

  9. FEATURES OF SEDIMENTARY ROCKS BEDDING – *horizontal layers *if sorted, graded bedding CROSS-BEDDING - *inclined layers move forward like sand dunes

  10. RIPPLE MARKS * when sediment is moved into small ridges by wind or wave action * back & forth waves yield symmetrical waves * currents, (like in rivers) asymmetrical waves Sand dune – ripple marks from wind

  11. Asymmetrical ripple marks

  12. FOSSILS *animals die, buried, lithified * some plants replaced by other minerals * shells, bones, etc. could leave impressions

  13. CONCRETIONS * lumps of fine grained silica * called chert *also called nodules CHERT

  14. MUD CRACKS *wet clay dries and contracts * cracks later fill with sediment

  15. TYPES OF SEDIMENTARY ROCKS CLASTIC formed by lithifications Coarse Medium Fine gravel sand silt & mud some rocks sandstone siltstone conlglomerates mudstone POROSITY * percent of open space between grains of sand *good reservoirs for oil, natural gas, and H2O * permeable if water can pass through

  16. Porous Rock

  17. 2. CHEMICAL a. rocks formed by evaporation - called evaporites ex: calcite, halite & gypsum S DEAD SEA SALT CALCITE

  18. b. organic sedimentary rock -formed from the remains of living things - most abundant is limestone (mostly calcite) CaCO3 from shells if shells are high in silica, they form siliceous ooze - Coal – from remains of plant material…almost entirely carbon Siliceous ooze CALCAREOUS OOZE

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