6 - Sedimentary Petrology

Sedimentary Rocks

Sedimentary Rocks

formed at low temperature and pressure compared to other types of rocks

Sedimentary Petrology

study concerned especially with the composition, characteristics, and origins of sedimentary rock

Weathering

Erosion

Transport

Deposition

Diagenesis

5 Sedimentary processes

Weathering

The physical breakdown and chemical alteration of rocks at or near the Earth's surface

Exposure of rocks

The first step before weathering

disintegration

the physical breakdown of rocks

decomposition

the chemical alteration of rocks

Mechanical and Chemical Weathering

two types of weathering

Physical Weathering

processes that break the solid rock into pieces and may separate the different minerals without involving any chemical reactions.

Freeze-thaw action

Temperature change

Salt dome intrusion

Root wedging

Wetting and drying

Organic activity

Unloading

7 most important agents of physical weathering

increase

Mechanical weathering leads to a/an (increase ; decrease) in surface area

Frost wedging / Freeze-thaw action

the expansion force of water as it freezes is sufficient to split any mineral or rock

9%

How much does water expand when it freezes?

Heating and cooling / temperature change

Differences in temperature in a rock give rise to differential expansion and contraction

Wetting and drying

The disruption of soil results in the swelling and contracting of soil particles.

Organisms / Organic activity

action of organisms including plants and animals, reduces the size of rocks and minerals

Unloading

the removal of thick layers of sediments overlying deeply buried rocks by erosion or uplift

Wetting and drying

What agent of mechanical weathering produces mud cracks

Chemical weathering

involve changes to the minerals that make up a rock

Solution

Hydrolysis

Oxidation

examples of chemical weathering

Source Composition

Climate

Topographic Relief

factors controlling weathering

kaya mo yan

How does topographic relief affect weathering

Through the chemical weathering of feldspar by hydrolysis wherein acid rain reacts with feldspar that produces a solution forming kaolinite

How does feldspar turns into kaolinite

Chlorite

What mineral results from the weathering of Olivine, Pyroxene, and Amphibole

Illite

Altered mineral of muscovite

Montmorillonite

A clay mineral that results from alteration of biotite

Because quartz is a very stable mineral as it is in the end of the Goldich Stability Series, however it can still be weathered mechanically

Why can't quartz be chemically weathered?

Dissolution

the dissolving of a solid in a liquid

Hydration

combination of a solid mineral or element with water

Oxidation and reduction

used in mineral weathering, is both the chemical combination of oxygen with a compound and the change in oxidation number of some chemical element

Reduction

the chemical process in which electrons are gained

Ion-exchange

involves the transfer of charged atoms of Ca, Mg, Na, and K between waters rich in one of the ions and a mineral rich in another

kaya mo na yan

Explain the Goldich Stability Series

Erosion

the removal of material by mobile agents such as water wind ice or man

Landslides or mass movements

Mass wasting

Tectonics

Scouring

Sand blasting

Wave actions

Examples of erosion

Air

Water

Ice

Gravity

Transport media

Water

Most effective transport media in desert

Air

Most common transport media in desert

Rolling

The clasts move by rolling along at the bottom of the air or water flow without losing contact with the bed surface

Saltation

the particles move in a series of jumps, periodically leaving the bed surface and carried short distances within the body of the fluid before returning to the bed again

Suspension

turbulence within the flow produces sufficient upward motion to keep particles in the moving fluid more-or-less continually

bedload

particles being carried by rolling and saltation

suspended load

the material in suspension

Laminar flows

all molecules within the fluid move parallel to each other in the direction of transport

Turbulent flows

molecules in the fluid move in all directions but with a net movement in the transport direction

eddies

the current of water in turbulent flow

Reynolds number

dimensionless quantity that indicates the extent to which a flow is laminar or turbulent

Clastic and Non-clastic

2 main types of Sedimentary rock

Volcaniclastic sediments

Products of volcanic eruptions or the result of the breakdown of volcanic rocks

Tuff and Ignimbrite

examples of volcaniclastic rock

Ignimbrite is welded and more compacted than tuff

Difference of tuff and ignimbrite

Terrigenous clastic material

This is a material that is made up of particles or clasts derived from pre-existing rocks.

Sandstones and conglomerates

They make up 20-25% of sedimentary rocks in the stratigraphic record

Mudrocks

They are 60% of all sedimentary rocks in the stratigraphic record

Shale

most abundant sedimentary rock

Carbonates

They constitute 10-15% of the sedimentary rocks in the stratigraphic record

Limestone

any sedimentary rock containing over 50% CaCO3

invertebrates

Principal source of CaCO3

Evaporites

deposits formed by the precipitation of salts out of water due to evaporation

Sedimentary ironstone

Phosphate sediments

Organic deposits (coal and oil shales)

Chert

Other sediments and sedimentary rocks that make up 5% of the stratigraphic record

Gravel, Sand, Mud, Clay

Based on Uden-Wentworth scale, sediments are classified into this 4 naturally occurring groups

Lutite

Other name of mudstone

Rudite

Other name of conglomerate

Arenite

Other name of sandstone

Agglomerate

A conglomerate made of volcanic materials such as blocks and bombs

Mudrocks

The collective term for sedimentary rocks made of silt- and clay-sized particles

Megaclast

conglomerates in a conglomerate

Conglomerate

consolidated grains of rounded gravel sized particles

Cobble Conglomerate

The term used for conglomerate with particles ranging 64-256mm in diameter

Breccia

Consolidated grains of angular gravel sized particles

Breccio-conglomerate

mixtures of rounded and angular clasts

Extraformational and Intraformational

2 main types of conglomerate and breccia

Orthoconglomerate and Paraconglomerate

2 types of extraformational conglomerate

Orthoconglomerate

clast supported conglomerate

Paraconglomerate

matrix supported conglomerate

Till / Tillite

debris deposited directly by melting ice in a glacier

Tilloid

non-glacial till-like deposit, deposited by mass movement (olistostrome or grainflows)

Oligomict and Petromict

2 types of conglomerate based on the composition of clasts

Open and close framework

2 types of orthoconglomerate based on the presence of matrix

Open framework

suggests an efficient sorting mechanism that caused selective removal of finer grained sediment. no matrix between clasts

Close framework

suggests that the transporting agents was less able to selectively remove the finer fractions or was varying in competence. spaces between clasts are filled with matrix

Oligomict

more than 90% of the framework clasts consist of fragments of only a few varieties of resistant rocks and minerals (e.g. metaquartzite, vein quartz, chert)

Petromict

also known as polymict. clasts of many different composition of metastable and unstable rocks are abundant e.g. basalt slate and limestone

it can reflect climate and topography that promote chemical decomposition and physical disintegration of all but the most resistant components

What implies oligomict orthoconglomerate

near shore marine setting

typical depositional environment of oligomict orthoconglomerate

They are mainly alluvium eroded from high-relief areas

What is a petromic

Deposits of debris flow or water flow where gravel sized clasts were not abundant in comparison to the finer grain sizes

Where are we most likely to find paraconglomerate

Laminated and Unlaminated matrix

2 types of paraconglomerate based on internal organization of their matrix

laminated pebbly (or cobbly, or bouldery} mudrock

Paraconglomerates containing a matrix of delicately laminated mudrocks in which coarser framework grains float

Unlaminated

Paraconglomerates in which the matrix is disorganized

Diamictite

A rudite composed of poorly sorted, mud to gravel-size sediment, commonly with angular clasts.

Intraformational conglomerate

composed of clasts of the same material as the matrix and is formed as a result of reworking of lithified sediment soon after deposition

Extraformational conglomerate

A conglomerate in which clasts are exotic (i.e., derived from outside the depositional basin).

No, extraformational have clasts that are normally very well rounded and well sorted, as they are derived from a distant source

On normal conditions, can a breccia be extraformational

Resistant lithologies

those which are less susceptible to physical and chemical breakdown, have a higher chance of being preserved as a clast in a conglomerate.

minerals present, and the ease with which they are chemically or physically broken down in the environment

Factors controlling the resistance of a rock type

availability, mechanical and chemical stability

The abundance of a particular mineral in a sedimentary rock is dependent on its -???-

Quartz

The only mineral grain that are likely to survive in an environment with low relief and humid climate

high relief

an area where some unstable grains will always be liberated for erosion and later deposition, even if weathering is extreme

Labile grains

unstable grains