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Sedimentary Rocks . Deposited on or Near Surface of Earth by Mechanical or Chemical Processes. What Rocks Tell Us . Types of Sedimentary Rock. Clastic (terrigenous or detrital) Conglomerate or Breccia Sandstone Siltstone Shale Chemical/biochemical Evaporites

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Sedimentary Rocks

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sedimentary rocks

Sedimentary Rocks

Deposited on or Near Surface of Earth by Mechanical or Chemical Processes

types of sedimentary rock
Types of Sedimentary Rock
  • Clastic (terrigenous or detrital)
    • Conglomerate or Breccia
    • Sandstone
    • Siltstone
    • Shale
  • Chemical/biochemical
    • Evaporites
    • Carbonate sedimentary rocks (limestones and dolostone)
    • Siliceous sedimentary rocks
  • Organic (coals)
    • Other - ironstones
sedimentary rocks are the principal repository for information about the earth s past environment
Sedimentary Rocks are the Principal Repository for Information About the Earth’s Past Environment

Depositional environments in ancient sediments are recognized using a combination of sedimentary facies, sedimentary structures and fossils

environmental clues in sedimentary rocks
Environmental Clues in Sedimentary Rocks
  • Grain Size - Power of Transport Medium
  • Grading - Often Due to Floods
  • Rounding
  • Sorting
  • Cross-bedding - Wind, Wave or Current Action


Transport, Reworking

environmental clues in sedimentary rocks6
Environmental Clues in Sedimentary Rocks
  • Fossils
    • Salt Water - Corals, Echinoderms
    • Fresh Water - Insects, Amphibians
    • Terrestrial - Leaves, Land Animals
  • Color And Chemistry
    • Red Beds - Often Terrestrial
    • Black Shale - Oxygen Poor, Often Deep Water
    • Evaporites – Arid Climates
sedimentary rocks8
Clastic Rocks

Made of Fragmentary Material

Deposited by

Water (Most Common)


Glacial Action


Biochemical Sedimentary Rocks



Biogenic Sediments

Sedimentary Rocks
clasts larger pieces such as sand or gravel
Clasts (larger pieces, such as sand or gravel)
  • Clasts and matrix (labelled),and iron oxide cement (reddish brown color)
terrigenous also called detrital or clastic

Gravel: Grain size greater than 2 mm

  • If rounded clasts = conglomerate
  • If angular clasts = breccia
Terrigenous (also called detrital or clastic)
  • Terrigenous sedimentary rocks are classified according to their texture (grain size):


Grain size greater than 2 mm

1. If rounded clasts = conglomerate

2. If angular clasts = breccia



  • Conglomerates
  • Breccia

Rounded fragments

Angular fragments



  • 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 rocks are classified on the basis of the grain size: conglomerate, sandstone, shale etc.
clastic rocks
Clastic Rocks

Classified by:

  • Grain Size
  • Grain Composition
  • Texture

Degree of roundness helps in knowing the

distance of transportation (method of erosion)

  • Angular clasts- short distance transport from the source
  • Rounded clasts- long distance transport
sediment sizes and clastic rock types
Sediment Sizes and Clastic Rock Types

Sedimentary rocks made of silt- and clay-sized particles are collectively called mudrocks, and are the most abundant sedimentary rocks.

bedding or stratification
Bedding or Stratification
  • Almost Always Present in Sedimentary Rocks
  • Originally Horizontal
  • Tilting by Earth Forces Later
  • Variations in Conditions of Deposition
  • Size of Beds (Thickness)
    • Usually 1-100 Cm
    • Can Range From Microscopic to 50m


Fine gravelly lithounit

Medium-coarse sandy

lithounit (cross stratified)


Laminated layers of fine silt and clay

Cross-stratified sst. Paleo-flow from right to left

mud cracks
Mud cracks

Biogenic structures

Foot prints


Limestone - Dolomite

Plagioclase – Albite



  • Compaction
  • +
  • Cementing
  • Quartz
  • Calcite
  • Iron Oxide
  • Clay
  • Glauconite
  • Feldspar

Diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification.


CementationClastic particles ranging from silt-size to boulder-size may be deposited on the sea floor.  As they are buried, ion-laden sea water may deposit minerals in the porespaces between the grains, thus effectivelycementing them together.  By this process the sediments become rocks such as siltstone, sandstone and conglomerate.

CompactionClastic particles smaller than silt, such as mud are deposited on the sea floor.  As they are buried, the weight of overlying sediments presses downward on the mud particles and compacts them, resulting in the formation of rocks such as claystone,mudstone or shale.



Clastic rocks

Chemical & Organic rocks

  • Sandstones
  • Conglomerates
  • Breccia
  • Shale/mudstones

Carbonate rocks

Organic rocks

Form due to decomposition of organic remains under temperature and pressure eg. Coal/Lignite etc.

Form basically from CaCO3 – both by chemical leaching and by organic source (biochemical) eg. Limestone; dolomite

Evaporites rocks

These rocks are formed

due to evaporation of saline water (sea water)

eg. Gypsum, Halit

(rock salt)

chemical sediments
Evaporites -Water Soluble





Example: Ca(sol'n) + SO4 (Sol'n) = CaSO4



Iron Formations

Alteration After Deposition


Biogenic Sediments

Limestone - Shells, Reefs, Etc.

Organic Remains



Chemical Sediments



These rocks are formed within the a depositional basin from chemical substances dissolved in the seawater or lake water.




economic importance of evaporites
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.
biogenic sediments
Biogenic Sediments
  • Chalk: which is made up of foraminefera is very fine grained

Non-Clastic Sedimentary Particles IBroken fragments of calcite,   mostly from algae.Shallow  sub tidal sediments from the Yucatan, Holocene.  


Largest fragments are about  1 mm in length.

biogenic sediments28
Biogenic Sediments

Non-Clastic Sedimentary Particles Broken shell fragments of calcite frombivalve molluscs.  These shell fragments accumulated on a beach and are cemented together. 

This rock  is almost100 percent shell fragments,and is therefore called a coquina.Largest fragments about 2 cm in length.

carbonate rocks
  • Limestone: It is a non-clastic rock formed either chemically or due to precipitation of calcite (CaCO3) 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
    • Fossiliferous Limestone: which medium to coarse grained, as it is formed out of cementation of Shells.
coals organic remains
COALS: Organic Remains
  • Coals are carbon-rich rocks that are composed of the altered remains of woody plant debris.
  • The two principal types of coals are:
    • lignite (brown coal): composed
    • of loosely bound (friable) organic
    • detritus, including some clearly
    • recognizable plant remains
    • bituminous coal: highly compacted
    • black coal composed of
    • recrystallized carbon
coal formation
Coal Formation
  • Delta, continental environments
  • Carbonized Woody Material
  • Often fossilized trees, leaves present

Characteristics and names of some common clastic sedimentary rocks.

Particle Size

Rock Name

Rock Characteristics

mud(see below)


smooth feel, layered appearance

  mud (mud sized particles: < 0.063 mm)


 smooth feel, massive to layer

silt(silt sized particles:0.063 - 0.004 mm)


slightly gritty feel, may have layered appearance

sand(sand-sized particles:0.0625-2.0 mm)


rough gritty feel, constituent grains clearly visible, including quartz, feldspar, other minerals, and rock fragments.

 granules, pebbles, cobbles, boulders (granule to bouldersized particles:2 mm - > 256 mm)


large rounded fragments composed of older rock materials

granules, pebbles, cobbles, boulders (granule to boulder sized particles:2 mm - > 256 mm)


large angularfragments composed of older rock materials


Characteristics of common non-clastic sedimentary rocks that will not react with dilute HCl.

Grain size

Rock Name

Rock Characteristics

very fine grained:can't see constituent particles with naked eye


  hard, scratches glass, typically white, green, or red; tends to haveconchoidal fracture

 variable grain size

Rock Gypsum

 soft, can be scratched with fingernail; may be translucent or opaque


Characteristics of common non-clastic sedimentary rocks that will react with dilute HCl.

Grain Size

Rock Name

Rock Characteristics

very fine grained, can't make out particles with naked eye


Pure white, powdery, light-weight, will write on sidewalks or walls 

variable in grain size


 dense and soft, with a crystalline or dull (earthy) luster

medium grained, particles commonly visible with naked eye


fragments of fossils, usually shells of invertebrates

variable in grain size

Fossil Limestone

dense and soft, may be crystalline or dull, with visible fossils, such as snail or clam shells or other taxa 

sedimentary rock
Sedimentary Rock

Review Of  Sedimentary ProcessesThis chart is a review of the various steps  involved in the formation of sedimentary rocks that have been discussed above.

landforms associated with sedimentary rocks
Landforms Associated with Sedimentary Rocks


  • Flat-topped hill capped with hard rock


  • Gently-tilted layer of hard rock: Door Peninsula
  • The gentle upper slope, on top of the layer is called the dip slope


  • A sharp ridge of hard rock, edge of a steeply-dipping layer