Sedimentary Rocks
Bits and Pieces
Sedimentary rocks form as
sediment is:
lDeposited
lBuried
lCompacted
lCemented
Sedimentary rocks fall
into 3 groups:
Clastic/inorganic
Organic
Chemical
Physical Weathering
 Clastic sediments
are produced when
rock physically
weathers, which
means it breaks
apart.
 Big rocks break
into smaller rocks.
 Weathering is an
extremely slow
process.
There are 6 sizes of clastic
sediments.
 Boulders
 Cobbles
 Pebbles
 Sand
 Silt
 Clay
Particles are collected and
transported by running water.
http://www.youtube.com/
watch?v=fATA1SOLICo
Abrasion
 Sediments
become
smoothed and
rounded as
they bounce
along the
bottom of the
stream and hit
against each
other.
Deposition and Sorting
 A stream loses velocity when entering quiet waters
so its ability to transport sediment decreases.
Particles drop to the bottom. This is deposition.
 Large particles settle first. Other particles settle
according to size. Smallest particles last. This is
sorting.
Burial and Compaction
 As more sediments accumulate, the bottom
ones are buried.
 This increased weight of the top sediments
physically squeezes the lower sediments
together which compacts them.
Heavy Weight
OUCH!
Cementation
 All the waters of the Earth contain dissolved
minerals. These dissolved minerals and
sometimes clay fill up spaces between the
rock fragments and bind them together. This
is cementation.
Stratification
 Sedimentary rocks often form in horizontal layers
called strata.
Fossils
 These layers or strata
often contain fossils.
 Only sedimentary rocks
contain fossils.
Fossil Structures
 Mud cracks
and ripple
marks give
evidence of
environment
at formation.
Organic(Bioclastic)Sediments
 The remains of plants and animals. The two
most common are shells and plant material.
Chemical Sediments
 Chemical sediments form when water
evaporates and the materials dissolved in the
water precipitate (settle).
Bonneville Salt Flats
 Home of
the land
speed
record.
Thrust
SSC –
763 mph
http://www.youtube.com/watch?v=LKQ-xj5C2m8
Yucca Mountain
 Nuclear waste
depository
http://www.youtube.com/watch?v=tbq9a2oyMAo
http://www.youtube.com/watch?v=Q41vzLjwZqM
Characteristics of
Sedimentary Rocks
 Sedimentary rocks are the most common
type of rocks on Earth’s surface.
 Sedimentary rocks usually form underwater.
 Sedimentary rocks may contain fossils.
 Sedimentary rocks often form in layers or
strata.
 Sedimentary rocks are our keys to the past.
Nature’s Palette
Antelope Canyon
Bryce Canyon
Mexican Hat
Clastic Sedimentary
Rocks
 Breccia – angular
 Conglomerate -
rounded
Clastic Sedimentary
Rocks
 Sandstone – can be
various size grains.
Clastic Sedimentary
Rocks
 Siltstone
Clastic Sedimentary
Rocks
 Shale – breaks along
bedded planes.
Bioclastic Sedimentary
Rocks
 Bituminous coal – plant remains = carbon
Bioclastic Sedimentary
Rocks
 Limestone – cemented
shell fragments or
precipitates of biologic
origin = calcite
Chemical Sedimentary
Rocks
 Rock salt - Crystalline
texture composed of
halite.
Chemical Sedimentary
Rocks
 Dolostone –
Crystalline texture
composed of
dolomite.
Fossil
Chemical Sedimentary
Rocks
 Rock Gypsum –
Crystalline texture
composed of gypsum.