Sedimentary Rocks Flashcards by Elle Kinsman

Sedimentology =

Processes that weather, erode, transport and deposit sediments or depositional environments

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Sedimentary petrology =

Characteristics and origins of sedimentary rocks

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Stratigraphy =

Complex distribution of sedimentary rock record in space and time

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Weathering =

A combination of processes by which pre existing rocks physically disintegrate and chemically decompose to form soils/loose classy/dissolved components

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Slowest weathering

Quartz
Clay
Muscovite
K feldspar
Biotite

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Fastest weathering

Halite
Calcite
Olivine
Plagioclase
Pyroxene
Amphibole

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Components of a sedimentary rock

1) grains/clasts
2) matrix (mud/micrite)
3) cement (silica/sparite)

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Maturity, indications:

Low amounts of clay
Well sorted (grain size not variable)
Well rounded

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Immature-submature; locations

Fluvial overbank

Alluvial fab

Marine turbidite fans

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Submature-mature; locations

Fluvial channel sands

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Mature-super mature; locations

Aeolian dunes

Beach sands

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Transporting agent =

Mechanisms responsible for movement from where it is weathered to where it is deposited

Rolling/sliding/saltation/suspension

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Diagenesis =

All changes (NOT METAMORPHIC) in texture, composition and physical properties that occur in sedimentary rocks after they are deposited

compaction
recrystallisation
cementation

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Conglomerate/breccia classification

ORTHOCONGLOMERATES
- matrix <15%
- grain supported
Can be OLIGOMICT (single mineral) or POLYMICT (multiple minerals)

PARACONGLOMERATES

matrix >15%
matrix supported

Gravel/sand/mud triangles

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Sandstone classification

Quartz arenites

Arkoses (feldspar)

Lithic arenites (lithics)

Wackes

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Quartz arenites - location

Shallow marine

Wind blown dune deposits

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Arkoses location

Alluvial fan
Delta deposited
Desert arkose
(MINERALOGICALLY IMMATURE, TEXTURALLY SUPERMATURE)

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Lithic arenites location

Alluvial deposits
Orogenic clastic wedges
Turbidites

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Wackes location

Sediment gravity flows

Submarine fan complexes

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Different types of carbonates (triangle)

Ca ARAGONITE

Mg MAGNESITE

Fe SIDERITE

DOLOMITE = mixture

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Controls on carbonate deposition

Temperature

Pressure

Agitation
- CO2 absorbed from atmosphere = increases deposition

Organic activity

Sediment masking/clogging
- slow terrigenous accumulation rates = increases deposition

Light

CCD

Limestone components

1) grains - ALLOCHEMS

ORTHOCHEMS

2) matrix
- micrite

3) cement
- sparite

Calcite vs aragonite seas

Calcite

early palaeozoic and mid to late Mesozoic
warm, shallow marine

Aragonite

mid palaeozoic and early Mesozoic and cenozoic
cool marine

Non skeletal grains

1) Coated = ooids/peloids
2) aggregates
3) clasts
4) non carbonate grains

Skeletal grains

Foraminifers Corals Bryozoans Brachiopods (clear fragment in middle) Mollusks Echinoderms Ostracods

Friable =

Tendency of a solid substance to break into smaller pieces under duress or contact, especially by rubbing Opposite = INDURATE

Glauconite

Shallow marine material Easily weathered Presence suggests little transport before deposition and slow rates of accumulation

When do cements form?

During diagenesis

Limestone classification: MUDSTONE

<10% grains Mud supported

Limestone classification WACKESTONE

>10% grains Mud supported

Limestone classification PACKSTONE

Contains mud | Grain supported

Limestone classification GRAIN STONE

Lacks mud | Grain supported

Limestone classification BOUNDSTONE

Original components bound together during deposition

Limestone classification CRYSTALLINE CARBONATE

Depositional texture not recognisable

Stages of cementation

First stage = drusy (needle like crystals radiating away from grains) Second = blocky filling void (Can have bladed in between)

What does the presence of mud (matrix) indicate? Carbonate vs Siliclastic

Carbonate: - prolific algae growth Siliclastic: - settling from suspension

Effect of periodic exposure? Carbonates vs siliclastics

Carbonates: - intensive diagenesis, especially cementation and recrystallisation Siliclastic: - relatively unaffected

Pelagic sediments

1) pelagic rain and marine snow 2) calcareous ooze 3) siliceous ooze

Pelagic sediments =

Mixture of non biogenic (clay), siliceous biogenic (radiolarians/diatoms) and calcareous biogenic (nannofossils) sediments that are organic matter rich

Pelagic rain and marine snow

Mostly fecal pellets Accelerated sinking - week or two rather than years

Calcareous ooze; depends on...

1) production rate of calcareous organisms in overlying water - surface water depleted in CO2 due to photosynthesis (PRIMARY PRODUCTIVITY) but increases as O2 decreases due to respiration 2) dilution by other types of particles 3) CCD (accumulates above) Covers 48% of ocean floor Undergoes small scale cycles

Ooze =

Deep sea sediment with more than 30% biogenic material Accumulates slowly (1-6cm/ky)

Calcareous ooze small scale cycles:

1) carbonate litho/micro facies 2) nodular/non 3) bioturbated/non 4) carbonate rich/poor 5) carbonate/clay 6) carbonate/chert CYCLICITY IN CORES FOLLOWING MILANKOVITCH CYCLES (precession)

Siliceous ooze

CHERT Negative correlation with calcareous 14% deep sea floor surface covered by siliceous ooze

Red clay

Aeolian origin

Glacial sediments

DROPSTONES Highly laminated mud sediments interspersed with horizons of very coarse material Heinrich events - cyclically with glaciation/deglaciation

Varve =

Thin pair of clay/silt layers with contrasting colour/texture which represent a deposit in a single year in a lake

Non laminated mudstone vs laminated mudstone

Siltstone/ laminated siltstone Mudstone/mudshale Claystone/clayshale

Black shale

>1% TOC

Oil shale

>20% TOC

Coal

>50% TOC N.B. Terrestrial