Geology 12
Presents
Sedimentary Rocks
• 95% of the Earth’s volume is igneous and
metamorphic rocks but 75% of the Earth’s
surface is covered by sediments or
sedimentary rocks.
• Derived from pre-existing rocks:
– 1. detrital/clastic rocks: mineral grains or rock
fragments (mechanical or biological
weathering)
– 2. chemical: dissolved & precipitated minerals
(chemical weathering).
• Ex: granite:
Quartz + Fs + Biotite
• Weathering: Mech/bio
quartz sand
clays
• Transport
–
River, wind, ice
• Deposition
–
Beach delta ocean
• lithification
–
• Rock
Cemented
sandstone
shale
Sedimentary Rocks
• Ex: granite: Qtz + Ca plag’ Fs + Biotite
• Weathering: Chem’
calcium
• Transport
–
solution in river
• Deposition
–
ocean
• lithification
–
precipitation
• Rock
limestone
Terminology
• Precipitation: opposite of dissolve:
aqueous to solid
• lithification: materials are compacted
and/or cemented together to form rock.
• Rounded: angular fragments become
rounded (& smaller) through abrasion as
they are transported
Rounding
• Deposition: ice, wind, or water
deposit/drop sediment in river bed,
moraine, lake, beach, ocean, etc.
• Facies: a distinct sediment or rock type
• Sorting: process by which particles are
separated according to size (& density)
– Clay with clay
– Sand with sand
– Gravel with gravel
Water & wind are excellent sorters, ice is poor
Sorting
high
river
gravel
Energy
beach
sand
low
delta
silt
lake/ocean
clay
sorted
• Gravel
facies
Sand
facies
Silt
facies
Clay
facies
• Pore space = porosity = voids between
particles
• Clay 80%
sand 20%
Well sorted
mixture 5%
Porosity
• Compaction: weight of overlying sediment
compresses sediments, forces water out
and “glues”/lithifies mud siltstone & shale
• Cementation: weathered silica, calcite and
iron oxides dissolved in water precipitate
in pore spaces to cement/lithify particles
together.
• Friable: rock is easily crumbled (like dry
cake)
• Fissile: rock breaks easily along closely
spaced parallel lines
– Like cleavage in rock
Fissile
Sedimentary Rocks
• 1. Detrital/Clastic
• 2. Chemical
• 3. Biochemical
• 1. Detrital/Clastic
– Detritus = solid particles or pre-existing rocks
– Clastic = composed of rock fragments
Sediment size description rock name
• Gravel >2mm rounded conglomerate
gravel
angular
breccia
gravel
• Sand 1/16 – 2mm (mostly Qtz) sandstone
• Mud <1/16 mm
silt
siltstone
silt & clay mudstone
shale
1
< /256 mm
clay
claystone
• Sandstone = Sst: sandy
– Red sandstone:
• with lots of K Fs (pink Fs) = arkose sst
• Siltstone: gritty with wet mud smell
• Shale: greasy with wet mud smell
Siltstone
• 2. Chemical: originate from substances
taken from solution from chemical
weathering
• These chemicals are extracted from lake
or ocean water via:
– i) precipitation (Ex; drying lake bed)
– Ii) organisms (coral reef) BUT this is a
biochemical rock!
Death Valley Salt Flats
Dead Sea
Texture
Composition
Varies
calcite CaCO3
Varies
Rock Name
limestone/Lst
carbonate
dolomite CaMgCO3 dolostone
Crystalline gypsum CaSO4
Crystalline halite
NaCl
rock gypsum
rock salt
• Travertine: Lst that precipitates out of
hotsprings but is rare
• Lst: most is biochemical
• Dolostone: forms from Lst that is altered
in: i) very saline lagoons
– ii) where Lst has been uplifted above the
water table and fresh water with Mg leeches
through replacing the Ca
• Lst
• CaCO3
Fizz!!!
Dolostone
CaMgCO3
HCl Test!
Barely fizzes
Travertine Terraces in Turkey
• Evaporites: (rock gypsum and rock salt)
precipitate from land-locked lakes and
seas where the evaporation raises the
salinity to the saturation point.
evaporation
Very salty water
Gypsum & halite crystals
• Rock gypsum: white-pink-grey, massive or
tabular crystals, H =2, white streak
• Rock salt = halite: colourless, cubic
crystals, salty taste, H = 2-3
• Silvite = KCl = potash: a fertilizer formed
from evaporation on vast, shallow seas in
Saskatchewan
Gypsum
Gypsum Thin section
• 3. Biochemical
Texture
Composition
Clastic- calcite CaCO3
crystalline
Rock Name
limestone/Lst
chalk: microscopic
coquina: shells
Fine
Finecrumbly
quartz
carbon C
chert
coal
Limestone: accumulation of billions of
skeletons of corals,shellfi`sh,algae, etc.
• Originally as aragonite which alters to
calcite.
• Forms:
– Massive: shells broken and ground into
powder before lithification
– Sugary = crystalline
– Coquina (KD)= cemented broken shells
– Chalk = soft, microscopic fossils
• HCl test!
Chert: forms 2 ways:
i) silica rich waters percolate up through
earth replacing the Lst in the form of
nodules, a bulbous mass of chalcedony
(“elephant man”)
ii) organisms (sponges, diatoms) that use
silica for skeletons die; the silica
accumulates on the ocean floor to form
bedded chert (usually grey).
Flint = black chert
Jasper = red chert
Chert thin section
Radiolarians
Radiolarians
Coal: form in the process
i) land plants accumulate in swamps, bogs
low in pH and low in O2 to prevent
bacterial decay of organic matter (OM).
ii) The OM accumulates to form peat.
iii) heat + time drives off the volatiles (H2,
N2 & O2) leaving C to form coal
• Black, H = 1 – 3, SG = 1 (light)
 Do
Lab 6.1
 Do WS 6.1
Go to 6.2 Notes
Go to Lab 6.1