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.

Geology 12 Geology 12

PresentsPresents

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 – Cemented

• Rock sandstone shale

Sedimentary RocksSedimentary 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

RoundingRounding

• 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 gravelWater & wind are excellent sorters, ice is poor

SortingSorting

• Gravel Sand Silt Clayfacies facies facies facies

high lowriver

Energy

gravel lake/oceandelta

beach

sandsilt clay

sorted

• Pore space = porosity = voids between particles

• Clay 80% sand 20% mixture 5%

Well sorted

PorosityPorosity

• 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

FissileFissile

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

<1/256 mm clay claystone

shale

• 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 Rock Name

Varies calcite CaCO3 limestone/Lst

Varies dolomite CaMgCO3 dolostone

Crystalline gypsum CaSO4 rock gypsum

Crystalline halite NaCl rock salt

carbonate

• 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 Dolostone

• CaCO3 CaMgCO3

HCl Test! Barely fizzesFizz!!!

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.

Very salty water

evaporation

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. BiochemicalTexture Composition Rock Name

Clastic- calcite CaCO3 limestone/Lst

crystalline chalk: microscopic

coquina: shells

Fine quartz chert

Fine- carbon C coal

crumbly

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 chertJasper = 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 Lab 6.1 Do WS 6.1Do WS 6.1

Go to Lab 6.1

Go to 6.2 Notes