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. 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

River Sorting- Transporting & Depositing HeadwatersMouth Grade = change in elevation/length

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 SiO 2 is released into groundwater from the chemical weathering of quartz and feldspars.

3 Classes of Sedimentary Rock Clastic - 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

Gravel Clastic Rocks If rounded clasts = conglomerate If angular clasts = breccia

Sand Clastic Rocks Different Sandstones based on dominate grains quartz grains = quartz sandstone feldspar grains = arkose sand-sized rock fragment grains = graywacke

Silt Clastic Rocks Siltstone - Grain size 1/256 to 1/16 mm (gritty)

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 Rocks Chemicals 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 Evaporites From 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 Siliceous Dominated 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 Groups 1.Continental 2.Marine 3.Transitional

Terrestrial Environments Aluvial Fan Braided stream Lakes Rivers Levees Swamps Deserts Glacial

Marine Environments Seas & oceans Continental shelf Continental slope and rise (deep sea fans) Abyssal plain Reefs

Transitional Environments between the land and the sea.