Sedimentary Rocks
Deposited on or Near Surface of Earth by
Mechanical or Chemical Processes
What Rocks Tell Us
Rock Type
Igneous
Sedimentary
How Classified
Composition
Texture
Chemical
Composition
Grain Size
Composition
Metamorphic
Mineral Makeup
Texture
What it Tells Us
Tectonic Setting
Cooling History
Surface
Environment
Energy of
Environment
Original Rock Type
Temperature,
Pressure
Degree of Change
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
Depositional environments in ancient sediments are
recognized using a combination of sedimentary facies,
sedimentary structures and fossils
Environmental Clues in
Sedimentary Rocks
•
•
•
•
•
Grain Size - Power of Transport Medium
Grading - Often Due to Floods
Rounding
Transport, Reworking
Sorting
Cross-bedding - Wind, Wave or Current
Action
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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 Rocks
Clastic Rocks
• Made of Fragmentary
Material
• Deposited by
– Water (Most
Common)
– Wind
– Glacial Action
– Gravity
Biochemical
Sedimentary Rocks
• Evaporation
• Precipitation
• Biogenic Sediments
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)
• Terrigenous
sedimentary rocks
are classified
according to their
texture (grain size):
Gravel:
Grain size greater than 2 mm
1. If rounded clasts = conglomerate
2. If angular clasts = breccia
•Sandstones
•Conglomerates
Rounded fragments
•Breccia
Angular fragments
CLASTIC ROCKS
• 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.
(mudstone)
solidify
Clastic rocks
• Clastic rocks are classified on the basis of the grain
size: conglomerate, sandstone, shale etc.
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
Rock Type
Sediment
Grain Size
Shale
Clay
less than 0.001 mm
Siltstone
Silt
.001-0.1 mm
Sandstone
Sand
.01-1 mm
Conglomerate Gravel
1mm +
Sedimentary rocks made of silt- and clay-sized
particles are collectively called mudrocks, and are
the most abundant sedimentary rocks.
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
GRADED BEDDING
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
Ripple marks
Mud cracks
Biogenic structures
Foot prints
Diagenesis
Compaction
+
Cementing
Quartz
Calcite
Iron Oxide
Clay
Glauconite
Feldspar
Alteration
• Limestone - Dolomite
• Plagioclase – Albite
Recrystallization
• Limestone
Diagenesis is any chemical, physical,
or biological change undergone by a
sediment after its initial deposition and
during and after its lithification.
Cementation
Clastic particles ranging from siltsize to boulder-size may be
deposited on the sea floor. As
they are buried, ion-laden sea
water may deposit minerals in
the pore spaces between the
grains, thus effectively
cementing them together. By
this process the sediments
become rocks such as
siltstone, sandstone and
conglomerate.
Compaction
Clastic 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.
TYPES OF SEDIMENTARY ROCKS
Clastic rocks
•
•
•
•
Chemical & Organic rocks
Sandstones
Conglomerates
Breccia
Shale/mudstones
Evaporites rocks
These rocks are formed
due to evaporation of saline
water (sea water)
eg. Gypsum, Halit
(rock salt)
Carbonate rocks
Organic rocks
Form basically from
CaCO3 – both by
chemical leaching and
by organic source
(biochemical)
eg.
Limestone; dolomite
Form due to
decomposition of
organic remains
under temperature
and pressure eg.
Coal/Lignite etc.
Chemical Sediments
Evaporites -Water
Soluble
• Halite
• Gypsum
• Calcite
Precipitates
Example: Ca(sol'n) +
SO4 (Sol'n) = CaSO4
• Gypsum
• Limestone
• Iron Formations
Alteration After
Deposition
• Dolomite
Biogenic Sediments
• Limestone - Shells,
Reefs, Etc.
Organic Remains
• Coal
• Petroleum
EVAPORITIC ROCKS
These rocks are formed within the a depositional basin
from chemical substances dissolved in the seawater or
lake water.
Gypsum
CaSO4.2H20
Halite
(NaCl)
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
–Chalk: which is made up of foraminefera is very fine grained
Non-Clastic
Sedimentary
Particles I
Broken fragments of
calcite, mostly from
algae. Shallow sub
tidal sediments from
the Yucatan,
Holocene.
Chalk
Largest fragments are about 1 mm in length.
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 almost
100 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 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 Seams, Utah
• Delta, continental environments
• Carbonized Woody Material
• Often fossilized trees, leaves
present
Coal Formation
Plant Fragments Are Often
Visible in Coal
Characteristics and names of some common clastic sedimentary rocks.
Particle Size
Rock Name
Rock Characteristics
mud
(see below)
Shale
smooth feel, layered appearance
mud
(mud sized particles:
< 0.063 mm)
Mudstone
smooth feel, massive to layer
silt
(silt sized particles:
0.063 - 0.004 mm)
Siltstone
slightly gritty feel, may have
layered appearance
sand
(sand-sized particles:
0.0625-2.0 mm)
Sandstone
granules, pebbles,
cobbles, boulders
(granule to boulder
sized particles:
2 mm - > 256 mm)
Conglomerate
large rounded fragments composed of older rock
materials
granules, pebbles,
cobbles, boulders
(granule to boulder sized
particles:
2 mm - > 256 mm)
Breccia
large angular fragments composed of
older rock materials
rough gritty feel, constituent grains clearly visible,
including quartz, feldspar, other minerals, and rock
fragments.
Characteristics of common non-clastic sedimentary rocks that will not react with dilute HCl.
Grain size
very fine
grained:
can't see
constituent
particles with
naked eye
variable grain
size
Rock Name
Rock Characteristics
Chert
hard, scratches glass,
typically white, green, or
red; tends to have
conchoidal fracture
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
Chalk
Pure white, powdery, light-weight, will write on
sidewalks or walls
variable in grain size
Limestone
dense and soft, with a crystalline
or dull (earthy) luster
medium grained, particles
commonly visible with naked
eye
Coquina
fragments of fossils, usually
shells of invertebrates
Fossil Limestone
dense and soft, may be
crystalline or dull, with visible fossils, such as
snail or
clam shells or other taxa
variable in grain size
Sedimentary Rock
Review Of Sedimentary Processes
This 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
Mesa
• Flat-topped hill capped
with hard rock
Cuesta
• Gently-tilted layer of
hard rock: Door
Peninsula
• The gentle upper slope,
on top of the layer is
called the dip slope
Hogback
• A sharp ridge of hard
rock, edge of a steeplydipping layer
Mesas, Utah
Grandfather Bluff, Wisconsin
Cuestas, Wyoming
A Hogback, Wyoming
Flatirons, Boulder, Colorado
Garden of the Gods, Colorado