How do Sedimentary Rocks Form? By J. Piccirillo

For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away by wind and water (ice included).

These little bits of our earth are washed downstream by ( E…. )where they settle to the bottom of the rivers, lakes, and oceans.

Layer after layer of eroded earth sediments have been deposited and buried on top of each other.

These layers are pressed down ( ) more and more through time, until the bottom layers slowly turn into rock.

While compacting, these sediments are also glued ( ) together by dissolved minerals oozing from the sediments

Eventually all the weight of Sediment squeezes all or most of the water out.

Later on through many years of Earth moving upward or seas retreating or evaporating the compacted sediment turns into Hard Rock when exposed above the earth’s surface.

/investigations/es0602/es0602page02.cfm?chapter_no=inv estigation

Conglomerates Breccia Sandstones Siltstones Shale/mudstones TYPES OF SEDIMENTARY ROCKS Clastic rocksChemical & Organic rocks Evaporitic rocks These rocks are formed due to evaporation of saline water (sea water) eg. Gypsum, Halite (rock salt) Carbonate rocks Form basically from CaCO 3 (Calcite) – both by chemical leaching and by organic source (biochemical) eg. Fossil Limestone; Dolostone (MgCO 3 ) Organic rocks Form due to decomposition of organic remains under temperature and pressure eg. Coal/Lignite etc.

Formed from broken rock fragments weathered and eroded by river, glacier, wind and sea waves. These clastic sediments are found deposited on floodplains, beaches, in desert and on the sea floors. CLASTIC ROCKS Clastic rockssolidify Clastic rocks are classified on the basis of the grain size: conglomerate, sandstone, shale etc.

GRAIN SIZE Gravel < mm Sand mm Clay < mm Silt mm Boulder: >256mm Cobble: mm Pebble: 4-64 mm Granule: 2-4mm Fine gravel

Non- Clastic or Chemical or Crystalline EVAPORITIC ROCKS These rocks are formed within the depositional basin from chemical substances dissolved in the seawater or lake water. Gypsum Halite (NaCl) CaSO 4.2H 2 0

Economic importance of Evaporites SALT: other then daily use of salt for cooking, it is used For production of Paper, Soap Detergents Antiseptics As chemical for dyeing etc. GYPSUM: is used for plaster and in manufacturing construction materials.

Limestone: It is a non-clastic rock formed either chemically or due to precipitation of calcite (CaCO 3 ) from organisms usually (shell). These remains will result in formation of a limestone. Limestones formed by chemical precipitation are usually fine grained, whereas, in case of organic limestone the grain size vary depending upon the type of organism responsible for the formation -Chalk: which is made up of foraminefera is very fine grained -Fossiliferous Limestone: which medium to coarse grained, as it is formed out of cementation of Shells. Non- Clastic CARBONATE ROCKS

used as a building stone and in the manufacture of lime, carbon dioxide, and cement. Massive and compact lst. Are competent to support CE-structure However, if it occur in huge thickness then it is not advisable, because of its typical CAVING character. Chalk

Let’s look at some sedimentary rocks with your teacher using the ESRT.

Conglomerate (has large and small grains mixed)

Conglomerate

Sandstone Varieties

Fossil Sandstone

(from clay) shows some layering Shale

Limestone - chemical variety..from precipitated calcite out of seawater.. deposited on the bottom beds of evaporated seas and lakes and from sea animal shells

Rock Gypsum (looks like cake and flakes)

Halite (rock Salt..looks crystally)

Fossil Limestone ….organic variety…Bioclastic

Fossil Limestone