Transcript Sedimentary Rocks - White Plains Public Schools

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.
http://www.classzone.com/books/earth_science/terc/content
/investigations/es0602/es0602page02.cfm?chapter_no=inv
estigation
TYPES OF SEDIMENTARY ROCKS
Clastic rocks
•
•
•
•
•
Conglomerates
Breccia
Sandstones
Siltstones
Shale/mudstones
Evaporitic rocks
These rocks are formed
due to evaporation of saline
water (sea water)
eg. Gypsum, Halite
(rock salt)
Chemical & Organic rocks
Carbonate rocks
Form basically from
CaCO3 (Calcite) – both
by chemical leaching and
by organic source
(biochemical) eg. Fossil
Limestone;
Dolostone (MgCO3)
Organic rocks
Form due to
decomposition of
organic remains
under temperature
and pressure eg.
Coal/Lignite etc.
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.
solidify
Clastic rocks
• Clastic rocks are classified on the
basis of the grain size: conglomerate,
sandstone, shale etc.
GRAIN SIZE
Gravel
< 256 - 2 mm
Sand
2- 0.062 mm
Boulder: >256mm
Cobble: 64-256 mm
Pebble: 4-64 mm
Granule: 2-4mm
Fine gravel
Silt
0.062 - 0.0004 mm
Clay
<0.0004 mm
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.
Halite
Gypsum
CaSO4.2H20
(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.
Non- Clastic 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
-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.
Chalk
• 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.
• 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