Chap 4-GEOLOGY PROF EDY

8/2/2019 Chap 4-GEOLOGY PROF EDY

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Luxembourg


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EaES 350-6 44


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CHAP 3.4 Sedimentary rocksq Sedimentary rocks composed of sediment(derived by weathering process, erodedfrom weathering site, transportedelsewhere & deposited as a loose

aggregate of particles) .q Sediments accumulate at earths surface contain evidence of past events, e.g

environment of particles deposited,mechanisms involved in transported &fossils to study geologic past.q Sedimentary rock important in economic


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Formation Sedimentary rocks

Sedimentary rocks are formed of the overburden pressure asparticles ofsediment are deposited out of air, ice, wind, or waterflows carrying the particles in suspension.

As sediment deposition builds up, the overburden pressuresqueezes the sediment into layered solids in a process known aslithification and the original connate fluids are expelled.

Sedimentary rocks are laid down in

layers called beds or strata. Each new layer is laid down horizontally

over older ones in a process

called superposition.
http://en.wikipedia.org/wiki/Overburden_pressurehttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Settlinghttp://en.wikipedia.org/wiki/Suspension_(chemistry)http://en.wikipedia.org/wiki/Lithificationhttp://en.wikipedia.org/wiki/Connate_fluidshttp://en.wikipedia.org/wiki/Superpositionhttp://en.wikipedia.org/wiki/Superpositionhttp://en.wikipedia.org/wiki/Connate_fluidshttp://en.wikipedia.org/wiki/Lithificationhttp://en.wikipedia.org/wiki/Suspension_(chemistry)http://en.wikipedia.org/wiki/Settlinghttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Overburden_pressure


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What is diagenesis?

any chemical, physical, or biologicalchange undergone by a sediment after its

initial deposition and during and after itslithification

exclusive of surface alteration (weathering)and metamorphism
http://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Lithificationhttp://en.wikipedia.org/wiki/Metamorphismhttp://en.wikipedia.org/wiki/Metamorphismhttp://en.wikipedia.org/wiki/Lithificationhttp://en.wikipedia.org/wiki/Sediment


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CHAP 3.4 - Lithificationq Lithification transforming sedimentsedimentary rocks, involved of compactionand/or cementation.q Compaction : from weight of ove rlayingsediment reduce pore spaces & volume.q Cementation : consists of chemicallyprecipitated minerals in pore spaces thatbind the particles. E .g calcium carbonate

(CaCO3), silicon dioxide (SiO2).


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COMPACTION

From weight of overlaying sediment compresses the deepersediments.

Reduce pore spaces

Reduce volume.

Compaction occurs as the weight of accumulating sediment forces therock and mineral grains together. This reduces pore space and eliminatessomeof the contained water


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Cementation

Cementation is a result of water circulating throughthe pore spaces of a sediment.

If that water carries in it dissolved substances that

then precipitate out during circulation, thosesubstances left behind in the sediments can act ascementing agents.

Calcium carbonate is one of the most commoncements because it is found abundantly in seawater.


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CAHP 3.4 Types of sedimentary rocksq Materials accumulating as sediment have 2principle sources:

1. Detrital sedimentary rocks.2. Chemical sedimentary rocks.

q Detrital rock: made up of solid particlesfrom parent material by mechanical &chemical weathering.- All have clastic texture.- Particle size : primary basis to

distinguish the rock & relate to energy of


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Figure 2: L ithification of detrital sedim ents.


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SHALE Consist of silt and clay,shale covers over half of

sedimentary rocks Particles is the smallest among other type of

DSR

Deposition occurs as a result of gradual settlingfrom nonturbulent conditions. e.g lake,lagoons

Deposition occurred in an oxygen-poorenvironment like swamp,where organic materialsdo not oxidize


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SANDSTONE

After shale,sandstone is most abundantsedimentary rock (20 %)

Sorting is degree of similarity in particle sizein a sedimentary rock

Well sorted all grains in sandstone areabout same size

Poorly sorted rock contains mixed largeand small particles

Poor sorting usually result when particles aretransported for a short time and distance andquickly deposited


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Shapes of sandstone can also determine the history of sandstone If the transportation is long,the grains lose their sharp edges and become

more rounded. Its because they collide with other grains often enough. If the transportation is short,the grains tend to be more angular Length of trasportation also influence its mineral composition Long trasportation caused gradual destruction of weaker minerals.

e.g feldspar Usually quartz mineral survive the long trip.Thats because the mineral is

very durable Quartz sandstone sandstone that have many quartz mineral Arkrose sandstone contain feldspar,quartz and mica

- poorly sorted and angular


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CONGLOMERATE OR BRECCIA

Large enough to be identified as rocktypes

Poorly sorted because contain sand ormud between the grains

If the large particles is angular rather than

rounded, it is calledBreccia Breccia indicate that they did not travel

far before they were deposited

Particles size reveal the strength of thecurrents that carried them

Degree of rounding indicate how far theparticles travelled


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CAHP 3.4 Detrital sedimentary rocksq Current: the stronger current, the largerparticle size carried.

- e.g gravel moved by swiftly flowingrivers, landslide & glaciers.q Less energy to transport sand commonfeature as windblown dunes, river deposits

& beaches.q Silt & clay settle very slow associated

with quite water such as lake, lagoon &


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CHAP 3.4 Sediment transport & depositionq Sorting refer to particle size distribution

in sedimentary deposit .- Well sorted : all particle about in samesize.- Poorly sorted : wide range of particlesize.

q Rounding process of abrasion that sizeparticles & sharp corner.q Sorting & rounding important aspect in

decipher the history of a deposit .


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Figure 1 : Depositional environm ents.

FIG 5.18A - 130


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Table 2: Environment of depositi on for detrital rocks.


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Conglom erates


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Sandstone


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Shale


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CHAP 3.4 Chemical sedimentary rocks

q Chemical s.r. : Derive from material that iscarried in solution does not remaindissolved in water, some is precipitate toform chemical sediments.

q Chemical processes responsible for theorigin, as when minerals form frominorganic chemical reaction/chemicalactivities of organisms.

q Texture: crystalline (gypsum) & clastic


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Limestone

10% of all sedimentary rock Most abundant Composed of calcite (CaCO3) Form by biochemical processes Varies type because form under variety of condition Having 3 types: skeletal limestone, oolitic limestone,microcrystalline limestone


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Dolostone Composed of the mineral dolomite (CaMg(CO3)2calcium magnesium carbonate From by direct precipitation from seawater Brownish yellow or light gray Form from biochemical rocks Most is ancient rock React with acid only


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Chert Very compact and hard rock made of microcrystallinesilica (SiO2) Hard, dense and typically break like glass Usually white or shades of gray, tan, green, or red

Found in 2 situation- irregularly shape nodules inlimestone or as rock layer Flint- dark colour Jasper- red cause of iron oxide


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Evaporates Rock form from evaporation of seawater or salinelake example gypsum (CaSO4.2H2O) have crystalline texture


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ORGANIC

SEDIMENTARYROCK


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Decay of plants and animal. Accumulation and

lithification of plants andanimals (shell)

Swamp region, sea.


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Australia Great Barrier Reef


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Limestone


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Chalk


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Siliceous rock

Composed of silicon dioxide,

(SiO2). Chemical precipitates.

Chert


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Chert

Very fine-grained quartz.

Jasper Agate


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Chert


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Jasper


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Agate


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Carbonaceous rock

Coal Fossil fuel

Combustible Swamp ecosystem

Exp: lignite


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Coal Form from the compaction of plant material

that has not completely decayed is a fossil fuel made more-or-less entirely of organic matterwhich is not crystalline Compose by carbon and sulfur biochemical rock brown or black Light weight

Larger source of fuel


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Shale


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CHEMICAL SEDIMENTARY ROCKS

Rock Type Composed of Texture

Carbonate

Limestone

Dolostone

Calcite (CaCO3)

Dolomite [CaMg(CO3)2]

Varies

Varies

Evaporite

Rock gypsum

Rock salt

Gypsum (CaSO4.2H2O)

Halite (NaCl)

Crystalline

Crystalline

Cherts Silica (SiO2 ) Crystalline

Coal Carbon from altered land plants -


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CHAP 3.4 Sedimentary structures

1. Graded bedding:- show upward decrease in grain size.- form by turbidity current deposition

(underwater flow sediment / water withgreater density than sediment).- current flow downslope reaches flatsea/lakefloor begins deposit large particlefolloed by smaller ones.


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Figure 3: Graded- bedding


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2. Cross-bedding:- layers are arranged at an angle to thesurface deposited.- found : sand dunes, along shorelines.- cross-bed are inclined downward samedirection of current flow (wind/water).


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Figure 4: Cross-bedding


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3. Ripple-marks:- small wave of sand that develop onsurface on sediment layer.- current ripple marks :

- asymmetrical in cross section, gentleslope at one side & steep slope at otherside.- current flowing in 1 direction.- wave-formed ripple marks:- symmetrical cross section.- generated by to-and-from motion ofwaves.


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Figure 4 : Ripple m arks


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4. Mud cracks:- form when clay rich sediment dries &shrink develop intersecting features.- indicate sediment deposited inenvironment where periodic drying tookplace, e.g river floodplain, near lakeshore &muddy deposits exposed along seacoast at

low tide.


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Figure 5: Mud cracks

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Chap 4-GEOLOGY PROF EDY