sedimentary rocks
DESCRIPTION
Sedimentary Rocks. Chapter 6. What Are Sediments?. Loose particulate material In order of decreasing size. Sources of Sediments. 1. From weathering & erosion 2. From chemical precipitation. What Happens to Sediments. 1. transported by: Water. Ice. Wind. Gravity. - PowerPoint PPT PresentationTRANSCRIPT
What Happens to Sediments1. transported by:
– Water.– Ice.– Wind.– Gravity.
• Most sediment is buried and converted to sedimentary rock.
2. Deposited by• Rivers• Wind• Glaciers• Other water
• When the transportation vector has run out of energy, the sediments are deposited (dropped).
What Happens to Sediments
Principle of Original Horizontality Most sedimentary layers of rock are deposited in a horizontal
position, with older rocks laid down first
Lithification Sediment becomes sedimentary rock
through lithification, which involves: • Compaction • Cementation • Recrystallization (of carbonate sediment) • Ex: sand
Remember that SiO2 is released into groundwater from the chemical weathering of quartz and feldspars.
3 Classes of Sedimentary RockClastic - fragments of
rock debris produced by physical weathering. Ex. Sand & clay.
Chemical - sediment precipitates from solution in water. Ex. Calcium carbonate & salt.
Biogenic (organic) - sediment composed of the fossilized remains. Ex. Coal, oil, & natural gas.
Clastic Sedimentary Rock• From the weathering of
other rocks – broken texture– Clasts (larger pieces, such
as sand or gravel) – Matrix (mud or fine-grained
sediment surrounding the clasts)
– Cement (the glue that holds it all together), such as:
• calcite • iron oxide • silica
Sand Clastic RocksDifferent Sandstones based on
dominate grains
• quartz grains = quartz sandstone
• feldspar grains = arkose
• sand-sized rock fragment grains = graywacke
Clay Clastic Rocks• Grains less than 1/256 mm
(smooth) • Shale (if fissile – splits) • Kaolinite (if massive)
also called Claystone
• Note: Mud is technically a mixture of silt and clay. (Mudstone)
Chemical Sedimentary RocksChemicals removed from seawater and made into
rocks by chemical processes, or with help of biological processes (such as shell growth).
3 types– Evaporites– Carbonates – Siliceous
Chemical EvaporitesFrom the evaporation of
water (usually seawater). • Rock salt - composed of
halite (NaCl). • Rock gypsum -
composed of gypsum (CaSO4.2H20)
• Travertine - composed of calcium carbonate (CaCO3), and therefore, also technically a carbonate rock
Chemical Carbonates• Formed through both chemical & biochemical processes. • Include the limestones (many types)• Two minerals are dominant:
– Calcite (CaCO3) – Dolomite (CaMg(CO3)2)
Chemical SiliceousDominated by silica (SiO2). • From diatoms, radiolarians,
or sponges.
• Diatomite - looks like chalk, but doesn’t fizz in acid. Made of diatoms. Also referred to as Diatomaceous Earth.
• Chert - Massive and hard, microcrystalline quartz. May be dark or light in color. Often replaces limestone. Does not fizz in acid.
Biogenic (Organic) Sedimentary Rocks Coals • organic matter (plants).• Increasing depth of burial
(temperature and pressure): – Peat (porous, brownish
plant fragments)– Lignite (crumbly and
black) – Bituminous (dull to shiny
and black; sooty; layers may be visible)
– Anthracite (extremely shiny and black; low density; not sooty
Formations from Sediments• Large enough to be recognized.• Ex.- haystack rock, sand dunes, delicate arch,
balanced rock
Sedimentary Environments (Sinks) Places where sediments accumulate and
sedimentary rocks form
3 Major Groups1. Continental 2. Marine3. Transitional
Terrestrial Environments• Aluvial Fan• Braided
stream • Lakes • Rivers• Levees• Swamps • Deserts• Glacial
Marine EnvironmentsSeas & oceans• Continental shelf • Continental slope and
rise (deep sea fans) • Abyssal plain • Reefs