Sedimentary Rock Notes
________________ are pieces of solid material that have been deposited on
Earth by wind, water, ice, gravity, or chemical precipitation. The formation
of sedimentary rocks begins when weathering (breaking down) and erosion
(transporting) of rocks to produce sediments. Weathering of existing rocks
(igneous, metamorphic, or sedimentary) creates small fragments called
______________ sediments. The sediment particles range in size from
_______________ to microscopic particles. See Table for particle sizes.
After clastic sediments are transported (eroded) and deposited in a new
location the process of lithification may begin if the conditions are
favorable. The word lithify comes from the greek word lithos meaning
“stone”. The first step of lithification is ________________. The weight of
overlying sediments squeezes grains together forcing out any water or air
present between the grains. Once the sediments are covered and buried deep
enough underground (3-4 km) then the next step called _________________
can start to transform compacted sediments into rock. Cementation occurs
when minerals grow between the grains causing them to become “stuck”
together. As groundwater flows through compacted sediment, minerals such
as calcite or iron oxide ________________ out of the water cementing the
grains together.
There are two major categories of sedimentary rock which are
________________ also known as detrital and ______________________
/biochemical. Overall classification of sedimentary rocks is based on how
they are formed but each category has its own classification scheme.
CLASTIC SEDIMENTARY ROCKS
Clastic sedimentary rocks composed of loose sediments that have been
cemented together are classified by _________________. Grain size ranges
from clay-sized particles which cannot be seen when examining a rock to
coarse-grained pebbles and gravel. The size, shape, and sorting of sediments
within sedimentary rocks provides information about the environmental
conditions at the time the sediments were deposited. When the particles are
____________ it suggests the sediment did not travel far, where if the
particles are _______________ it could mean the particles were transported
over long distances providing the time necessary to weather and round the
grains. Sand-sized grains are indicative of beaches, river channels, deserts
due to the constant transport that is needed to break sediment down to sand.
CHEMICAL SEDIMENTARY ROCKS
Chemical sedimentary rocks are formed by evaporation and precipitation.
When water becomes _______________ with a particular mineral it means
no more of that mineral can be dissolved in the water. When saturation is
reached the mineral begins to crystallize (precipitate out of water) and settle
to the bottom of the water body. This forms chemical sedimentary rocks
called ____________________. These types of chemical rocks are normally
found in __________ regions because little water flows in the area causing
mineral concentrations to become high and crystallization to occur. Calcite,
_________________ and gypsum are the three most common evaporites.
Other types of chemical sedimentary rocks form as a result of
_______________ material sinking to the bottom of the ocean or deep lakes.
Living organisms makes their _______________ out of carbonate dissolved
in the water. After the organisms ______ they sink to the bottom and a
calcite layer forms resulting in the formation of __________________ after
cementation and lithification occur. Limestone is the most common organic
sedimentary rock.
___________________ is another form of organic sedimentary rock that is
formed over a period of time after plant remains accumulate and become
_______________ in swamp environments. Antarctica has ancient coal beds
located under the layers of ice dating back to the ___________________
time period. This provides supporting evidence for scientists that the
continents were once connected together near the ________________.
Name of
Particle
Boulder
Cobble
Pebble
Sand
Silt
Clay
Size Range
Loose
Sediment
>256 mm
Gravel
64 - 256 mm
Gravel
2 - 64 mm
Gravel
1/16 - 2mm
Sand
1/256 - 1/16 mm Silt
<1/256 mm
Clay
Consolidated Rock
Conglomerate or Breccia (depends on
rounding)
Sandstone
Siltstone
Claystone, mudstone, and shale
(http://www.tulane.edu/~sanelson/geol111/sedrx.htm)
Cross Bedding - Sets of beds that are inclined relative to one another. The beds are
inclined in the direction that the wind or water was moving at the time of deposition. Boundaries
between sets of cross beds usually represent an erosional surface. Very common in beach deposits,
sand dunes, and river deposited sediment.
.
Graded Bedding - As current velocity decreases, first the larger or more dense particles
are deposited followed by smaller particles. This results in bedding showing a decrease in grain size
from the bottom of the bed to the top of the bed.