Transcript CHAPTER 6-3 SEDIMENTARY ROCKS

CHAPTER 6-3
SEDIMENTARY ROCKS
What is sediment?
Loose fragments of rock,
minerals, and organic material
that result from natural
processes (including the
breakdown of rock)
Characteristics of sedimentary
rocks are determined by:
• The source of the sediment
• The way the sediment was moved
• The conditions under which the
sediment was deposited
Processes
• Compaction- the process in which sediment is
squeezed and the size of the pore space
between the sediment particles (porosity) is
decreased by the weight and pressure of
overlying layers
• Cementation- the process in which sediments
are glued together by minerals that are
deposited in water.
Chemical Sedimentary Rocks
• Minerals made up of ions such as Ca, K, and Cl
can dissolve in water.
• This type of rock forms when dissolved
minerals precipitate out of water
• Minerals precipitate due to evaporation (when
water evaporates, the minerals that were
dissolved in the water are left behind
increasing the concentration of the minerals)
• The minerals left behind form rocks called
EVAPORITES.
• Examples are halite (or rock salt) and gypsum.
Organic Sedimentary Rock
• Rock that forms from the remains of living
things
• Examples are coal, coquina and fossiliferous
limestone
• INTERESTING NOTE: Chalk is made up of the
shells of tiny one celled marine organisms that
settle to the ocean floor.
Clastic Sedimentary Rock
• Made up of fragments of rock that are carried
away from their source by water, wind, or ice
• Over time these fragments become cemented
or compacted into solid rock
• They are classified by the size of their
sediments
Clastic continued
• Conglomerate- rock composed of round
fragments from 2 mm to boulders in size
• Breccia- rock composed of sharp angular
fragments
• Sandstone- rock composed of sand grain size
sediment cemented together
• Shale- rock composed of clay sized particles
cemented and compacted together.
Sediments are transported by:
•Water
•Wind
•Ice
•Effects of gravity
Sorting
• The tendency for currents of air or water to
separate sediments according to size
• Well sorted- all grains are roughly the same
size and shape
• Poorly sorted- consists of grains that are many
different sizes.
Angularity
• As sediment is transported from its source to
where it is deposited, it collides with other
sediments and other objects.
• These collisions cause the sediment to change
size and shape.
• When particles first break they are angular and
uneven…..
• As they travel farther from source they become
rounded and smooth.
• The farther it travels the finer the sediment
becomes.
The place in which setting is deposited
is called the DEPOSITIONAL
ENVIRONMENT
Examples are rivers, deltas,
beaches, and oceans
Characteristics of CLASTIC sediments
• Stratification- layering of sedimentary rock
– This occurs when the conditions of sediment
deposition change
• Beds- stratified layers
• Massive beds- beds that have no internal
structures
• Cross-beds- sedimentary rock characterized by
slanting layers
• Graded bedding- when various sizes and shapes
of sediment settle to different layers. (largest on
bottom; smallest grain on top)
• Reverse grading- smallest grains on bottom;
largest on top.
RIPPLE MARKS
Caused by the
action of wind or
water on sand.
Shows that the
sediment was
once part of a
beach or river
bed.
Mud Cracks
Form when
muddy
deposits dry
and shrink
FOSSILS
The remains or
traces of
plants and
animals may
be preserved
in sedimentary
rock
CONCRETIONS
Lumps of rocks
on
sedimentary
rocks that have
a composition
different than
that of the
main rock
body
.
GEODES
Groundwater
sometimes
deposits
dissolved
minerals inside
cavities of
sedimentary
rock where they
crystallize.