FUNDAMENTALS OF EARTH SCIENCE I

Sedimentary rocks

FALL SEMESTER 2018

Marginal Sea
Back-Arc Basin

Ocean Basin

Continental
volcanic arc

Accretionary prism
Mid-oceanridgeLake

SUBDUCTION

Hot spot

COLLISION

Volcanic
island Arc
Marginal searidge

SUBDUCTION
Water column

Sediments + sedimentary rocks

Sediments
Ocean crust

Lithospheric mantle→ ~90% Earth surface
Asthenospheric mantle

Continental crust What are sediments?
Sediments areExamples of sedimentary rocks

1. Solid particles•••

Rocks/minerals
Ex.: Quartz sandHard parts of organisms (biominerals)
Ex.: Foraminiferal sand (CaCO3)
Organic material
Ex.: Plant debris (peat)

Sandstone

Foraminiferal
limestone
Coal

2. Dissolved chemicals••

Abiotic precipitation
Ex.: Na+, K+, Cl-

Evaporite: NaCl, KCl

Biotic precipitation
Ex.: Corals (CaCO3)

Reef limestoneQuartz sandSandstone

1 mm
www.microimaging.ca

Foraminiferalsand

www.pitt.edu

Foraminiferal
limestone

Wikipedia

Peat

Coal

Coral reef(CaCO3)

Reef
limestone

Wikipedia Formation of sediments and sedimentary rocks
1. Weathering
Destruction of rocks andproduction of sediments(source area)

Rain

2. Erosion

Wind1

Surface processes
2

Mobilization and removalof sediments fromsource area

3. Transport
Sediments are moved tothe site of deposition

3

4. Deposition“sink area”

4

5. Burial
5

Processes transforming
sediments into sedimentaryrocks (diagenesis) Weathering processes
1. Physical weathering◼
◼

Mechanical weathering by wind (1), water (2) and ice (3, 4)
Biophysical weathering e.g. root wedging (5)(1) Weathering by wind
Moroccan desert pavement

Mars

F. BoulvainNASA(2) Weathering by waves

Pat Gowen (www.bbc.co.uk)(4) Frost wedging

Ice(3) Weathering by glaciersCollege Fjord

Kimberly Vardeman(5) Root wedging

Understanding Earth2. Chemical weathering◼

◼

Dissolution of minerals (mainly CaCO3) by mildly acidic water (1)Biotic mineral dissolution e.g. microbes, lichen, clionid sponge (2,3)(1) Weathering/dissolution ofcarbonates (karst, e.g. caves)

Carsten Peter, National Geographic

Weathering/dissolution of silicates
Body of granite rounded by weathering anderosion

VietnamUSGS(2) Boreholes of clionid spongeMark A. Wilson(Dep. of Geology, College of Wooster)(3) Boreholes of bivalve

Biolib1 CO2 removed from the atmosphere

CO2 + H2O

Weathering of calcium carbonate

Production of carbonic acid

Ca2+ + 2 HCO3+ 1 CO2 added
Ca2+ to the atmosphere

CaCO3+ H2CO3 + H2OCalcite
Weathering of Ca carbonate

CaCO3 + 1 CO2 + H2O

Calcification in the ocean

NO NET REMOVAL OF ATMOSPHERIC CO2
2 CO2 removed from the atmosphere2 CO2 + 2 H2O
2 KAlSi3O8 + 2 H2CO3 + H2OFeldspar
Weathering of feldspar

Weathering of silicates

Production of carbonic acid

Al2Si2O5(OH)4 + 4 SiO2 + 2 K+ + 2 HCO3+ 1 CO added
Clay mineral
Ca2+ to the2 atmosphere
Calcification in the ocean

CaCO3 + 1 CO2 + H2O
NET REMOVAL OF ATMOSPHERIC CO2 !!!

Carbonate-silicate cycle on Earth
Stabilizing effect on long-term climate
Time scale: millions of years

Increased rate ofsilicate weathering
1Hot, wetclimate

2

Silicate rocks

SILICATE WEATHERINGCaSiO3 + 2CO2 + H2O → Ca2+ + 2HCO3- + SiO2 (1)Cooling
3More CO2
consumed byreaction (1)Carried by streams, rivers to ocean

Calcification
CaCO3 + H2O + CO2
NET REMOVAL OFCO2 FROM THE
ATMOSPHERE

Stabilizing mechanism(buffer)
NEGATIVE FEEDBACK MECHANISM

NB: abiotic precipitation of CaCO3 can also
take place
Process returning CO2 into atmosphere iscarbonate metamorphism (CO2 released
through volcanism) CaCO3 + SiO2 → CaSiO3 + CO2

Link between long-term climate and silicate weathering
Beginning of the collision between India and Eurasia 50-40 Myr ago
Himalaya formation

Increased weathering
Atm. CO2 drops
CoolingLong-term cooling4KAlSi3O8 + 4H+ + 2H2O → 4K+ + Al4Si4O10(OH)8 + 8SiO2
Orthoclase

Hydrolysis of granite

Kaolinite

QuartzRemobilized and transported by rainwater and deposited in depressions

Kaolin quarry (Japan)
NB: Kaolinite is primarily used in the paper industry (paper coating)

http://www.eacrh.net/ojs/index.p
hp/crossroads/article/view/14/Vo
l3_Seyock_html

 Erosion and transport“As soon as a rock particle (loosened by one of the two weathering processes)
moves, we call it erosion or mass wasting. Mass wasting is simply movement
down slope due to gravity. Rock falls, slumps, and debris flows are all examplesof mass wasting. We call it erosion if the rock particle is moved by someflowing agent such as air, water or ice.”
From USGS

1.

Wind

2.

Water

3.

Ice

4.

Gravity (mass wasting)

Erosion by ~1. Wind

2. WaterIdaho (USA)Great Sand Dunes National Park (Colorado, USA)

Walter Meayers Edwards, National Geographic

Michael Melford, National Geographic

1 cm

Whirlwind (dust devil) on Mars

NASAAncient fluvial deposit
on MarsNASA3. Ice

4. Gravity

Glacier in British Columbia (Canada)

Debris cone (Spitzberg, Norway)

Chenuet (1993)
Sarah Leen, NationalGeographic

Glacial grooves formed during the last glaciation (Kelleys Island, Ohio)
Wikipedia

Martian avalancheNASA Sediment deposition
1. Water/wind
As wind/water current decreases, it can no longer keep the largest particles
suspended.
The stronger the current, the larger the particles it can carry:

Strong currents (>50 cm/s): carry gravels (>2 mm) and smaller particles
Moderately strong currents (20-50 cm/s): carry sand grains (62.5 µm-2 mm) andsmaller particles
Weak currents (<20 cm/s): carry silt and clay particles (mud; <62.5 µm)2. Ice
Sediments are deposited as ice melts and retreats.

3. Gravity
Deposition is controlled by topography (slope steepness) and the nature ofsediments (size, shape)

For consolidated clay and fine silt: effectof cohesive forces between particles

Fine sand easiest to erode

EROSION

TRANSPORTDEPOSITION

CLAYSILTHJÜLSTROM DIAGRAM
Deduced experimentally(for sediments transported by water)

SAND

GRAVEL(simplified)Beach gravels and sandEstuary mud flats

http://gravelbeach.blogspot.com/2016/10/mulranny-beach.html

https://geologicalintroduction.baffl.co.uk/?attachment_id=453

Glacial erratic

Glacial striation

Wikipedia

Robert Siegel (Stanford Uni.)

Glacial till (moraine) – coarse unsorted sediment
Glacial valley

in fine-grained (clay) matrix

Wikipedia (Mick Knapton)

USGS Burial and diagenesis: sedimentary rock formation⚫

⚫

Burial: process by which sediments are buried under new layers ofsediments → increase in temperature and pressure
Diagenesis: set of physical and chemical changes affecting sediments
after they are buried.

Diagenetic processes leading to lithification:⚫

Compaction (due to burial)⚫

Cementation

Decrease in porosity (% of rock’s volume
consisting of open space / pores)

Transformation of soft sediments into
hard sedimentary rocks= Lithification

Understanding Earth 6th Ed.

 Properties of sediments and sedimentary rocks• Grain size

→ Influenced by wind/water velocity

Unconsolidated
sediment
Sedimentaryrock• Sortingor shale(Shale breaks along stratification planes, mudstone does not)Good sorting indicates a transport
agent of constant strength
Poor sorting indicates a transport
agent of variable strength• Grain morphology
The degree of abrasion (roundness) depends on the distance of transport.

 Sedimentary basins and sedimentary environments⚫

Sediments tend to accumulate in depressions.

⚫

Large depressions are formed by subsidence.
Subsidence is the process by which a broad area of the crust sinks (subsides)
relative to the surrounding crust. It is mainly due to tectonic deformation of
the lithosphere (stretching) and accentuated by the weight of sediments.

⚫

Regions characterized by thick accumulations of sediments andsedimentary rocks are called sedimentary basins.

Sedimentary Basin

Extension

SubsidenceExtension

LithosphereEast African Rift

USGS

Rift basin(created ascontinental
lithosphere isstretchedand breaks
up)

Ocean basin

Thermalsubsidencebasin(created as thetwo plates arepulled apart andnew oceanic
lithosphere isproduced)(created as
thelithospherecools andcontracts)
Understanding Earth 6th Ed.

Sedimentary environments

Understanding Earth 6th Ed.

Continental environments

Deserts

RiversShoreline environments

DeltasTidal flats

Marine environments

Coral reefs

Deep sea Examples of sedimentary structures
1. Ripple marks

Understanding Earth 6th Ed.

From Stow (2005)

Stratification plane: separation between twobeds (originally horizontal if sediments weredeposited as flat-lying layers or inclined if they
were deposited on a slope)

2. Bedding

BED8Stratification plane
FORMATION B

TIME

BED7

BED6

Massive limestone

BED5
Lamination (mm-scale)

BED4

Laminae
BED3
BED2

FORMATION A

Mudstone
Bioclastic limestone

BED1

Grain sizewww.edupic.net

3. Bioturbation (disturbance of soils and sediments by animals or plants)
Small burrow(Paleozoic, Belgium)

Large burrows in volcanic tuff(Holocene, Japan)

10 cm

 Reconstruction of past sea level and environmental changes
SEDIMENTARYSTRUCTURES

LOG

FOSSILS

Plants

Siltstone
Fine sandstone

Floodplain

Plants

Coal

Swamp

Roots, paleosoil
Small-scale
ripples
Megaripples
Planar strati.
Low-angle
cross strati.

LITHOLOGYDEPOSITIONALENVIRONMENT
Fluvial(Continental)

CoastalShells

Sandstone

Beach

ShellsShale

Open-marine

Sandstone

Beach

ShellsMarineCoastalPlants

Coal

Swamp

Plants

Siltstone
Fine sandstone

Floodplain

Roots, paleosoil
Crossstratification

Fluvial(Continental)

After Marshak (2008)

Data interpretation
1 Initial stage

Floodplain

SwampBeach

3 Transgression (continued)

Open-marine
2 Transgression

Landward migrationof shoreline

4 Regression

Seaward migrationof shoreline

Data
After Marshak (2008)

Transgression = sea level rises and shoreline moves landward
Regression = sea level falls and shoreline moves seaward Types of sedimentary rocks
1. Siliciclastic sedimentary rocks•

Derived from accumulation of mineral fragments and/or lithic (rock)fragments composed mainly of silicate minerals

2. Biochemical sedimentary rocks•

Derived from precipitation (direct or indirect) of a mineral by organisms(most commonly CaCO3 or SiO2)

3. Chemical sedimentary rocks•

Derived from abiotic precipitation of minerals in a saline pond, lake orembayment undergoing intense evaporation (→ EVAPORITES)

4. Organic sedimentary rocks⚫

Derived from accumulation and preservation of organic matter1. Siliciclastic sedimentary rocks⚫

CLASSIFICATION BASED ON GRAIN SIZE:COARSE-GRAINED
Conglomerate⚫

MEDIUM-GRAINED
Sandstone

FINE-GRAINEDShale

CLASSIFICATION BASED ON GRAIN COMPOSITION

Example: sandstones
Lithic sandstone

ArkoseQuartz areniteGraywacke

Rich in rock fragments

Feldspar-rich

Pure quartz

Space between sandgrains filled with mud2. Biochemical sedimentary rocks
A Direct precipitation of CaCO3 by corals, mollusks, foraminifera, diatoms= LIMESTONES
SiO2 by diatoms, radiolarians

Bioclastic limestones
Accumulation of shell debris

Reef limestones
Encrust.
coralsEncrust.
algae

Foraminifers

http://petrographica.ru/fossils/foto/90.html

O. R. Anderson(serc.carleton.edu)

CHERT = siliceous sedimentary rock (composed of silica)

RadiolarianRadiolarite (Japan)

200 µmwww.radiolaria.orgLike foraminifers and radiolarians,
diatoms are single-celled organisms.
However, diatoms can sometimes
Diatoms form colonies of attachedindividuals.
Photo: Sarah SpauldingB Indirect precipitation of CaCO3 induced by photosynthetic activity of microbes
(1)

(2)

3.4-billion years stromatolite
Strelley Pool Chert (Australia)(3)

Photosynthesis:
6H2O + 6CO2 + sunlight → C6H12O6 + 6O2(4)

Calcification

Ca2+ + 2HCO3- ↔ CaCO3 + CO2 + H2O(1) Modern stromatolites at Shark Bay, Australia (P. Harrison, Wiki.) (3) Fossil stromatolite (K. McNamara, www.geolsoc.org.uk)(2) Modern stromatolite (http://phys.org)(4) Fossil stromatolite (Alwood et al. 2006, Nature)3. Chemical sedimentary rocks
EVAPORITES

Calcite-aragonite
GypsumAnhydrite
HaliteSylviteBorates
Nitrates

CaCO3
CaSO4.2H20
CaSO4
NaCl
KCl
Ex: Na2B4O7·5H2O
Ex: KNO3

Messinian (~5.5 Ma) evaporite composed of gypsum
Source: F. Boulvain (University of Liege)

4. Organic sedimentary rocks
Note that biochemical and organic sedimentary rocks can be called biologicalsedimentary rocks
PeatLignite

CoalAnthracite

Burial (increasing P and T)◼

Problems of preservation:

Another example: oil shale

1. RECYCLING (organic matter in water column consumed by organisms)
2. OXIDATION (bacterial and abiotic decay of organic matter)
C6H12O6 + 6O2 → 6CO2 + 6H2O◼

Conditions of preservation:
1. HIGH ACCUMULATION RATE (e.g. plant debris, micro-organisms)
2. ANOXIA or LOW [O2] (e.g. restricted water circulation)

Coal mine (Carboniferous, Graissessac, France)

F. Boulvain (ULg)

Different origin of coal and oil

Biogenic
CH4

Thermogenic CH4

Craig et al. (2011)

Craig et al. (2011)