GEOL1100: Parsons - Exam 3

Weathering, Erosion, Transport, Deposition, Burial, and Lithification (compaction+cementation)

What is the sediment cycle? (List the steps)

Weathering

Step of the sediment cycle in which raw materials are produced (sediments and solutions)

Erosion

Step of the sediment cycle in which raw materials are removed (composition reflects source)

Transport (more distance means more weathering)

Step of the sediment cycle in which raw materials are moved "downhill" via ice, water,wind, and/or gravity.

Deposition

Step of the sediment cycle where eventually sediments will come to a rest. Seds are "sorted" as they rest in different environments, e.g. sands at beaches vs. muds at the bottom of quiet lakes

burial and lithification

Once disposited, sediment can be buried and compacted by the weight of overlying material. Chemicals in groundwater can coat sedimentary grains with minerals and deposit natural cements that bind adjacent grains.

Abrasion, frost/salt wedging, thermal expansion and contraction, and biological activity

Types of mechanical abrasion

mechanical weathering

physical disintegration of a rock into smaller fragments, each with the same properties as the original. Occurs mainly by temperature and pressure changes.

chemical weathering

weathering that involves the removal of some minerals in solution and the transformation of others into new minerals.

dissolution

Type of chemical weathering where minerals dissolve, leaving no residue; everything enters solution. Works best for evaporites; gysum; halites.

carbonation

Type of chemical weathering where rocks react with carbonic acid (H 2 CO 3 ); Carbonates are especially susceptible

Oxidation

Type of chemical weathering involving degradation of materials due to chemical reactions with oxygen. Usually, iron (Fe) is the thing being oxidized.

Hydrolysis

Type of chemical weathering where minerals are broken down by reacting with water. Happens more readily in an acidic solution. Hydrogen ions (H+) replace ions such potassium (K+), sodium (Na+), and magnesium (Mg2+). With enough time, all of our favorite silicates (except quartz) will be hydrolyzed into clay minerals, like kaolinite.

-Mechanical weathering breaks rock into smaller pieces, increasing the surface area available for chemical weathering

-Chem weathering weakens rock, making it easier to weather mechanically

What happens to a rock's surface area as it becomes increasingly weathered?

-loose or broken unconsolidated rock at the surface resulting from weathering; covers most of earths surface.

-If not transported, becomes soil

-If regolith is picked up and transported, it becomes sediment. transported by the action of wind, water, or ice or by the force of gravity acting on the particles. There are three common types of sediment: clastic, chemical, and biogenic.

What is Regolith and what happens to it?

Karst geography. (Caves, sinkholes, stalactites/stalagmites)

Weathering of carbonates leads to what?

Goldich Dissolution Series

The minerals that crystallize late in Bowen's Reaction Series are the most resistant to chemical weathering, whereas the ones that crystallize early are the most susceptible. Shows why granite is so strong and quartz is immune to both kinds of weathering.

sedimentary rock

A type of rock that forms when particles from other rocks or the remains of plants and animals are pressed and cemented together

compaction

burial increases pressure, squeezes out air and water, and compacts grains

cementation

minerals (often quartz or calcite) precipitate from groundwater into pore spaces. This cement glues the loose sediments together.

Lithification

The process that converts sediments into solid rock by compaction or cementation.

clastic (detrital), chemical, and organic

Types of sedimentary rocks

clastic sedimentary rock

Type of sedimentary rock composed of solid particles (gravel, sand, silt, andclay) cemented together. (ex: sandstone, shale, conglomerate, etc.)

chemical sedimentary rock

Type of sedimentary rock formed from precipitation of material that was once in solution (dissolved) in water (ex: limestone, dolostone, coquina, etc)

organic sedimentary rock

Type of sedimentary rock composed of remains of decayed plants or animals (ex:coal)

clay, silt, sand, gravel (pebbles, cobbles, boulders)(largest)

grain size classification of detrital rocks (reflects energy of the transporting medium)

Water, Wind, Gravity, and Ice (glaciers)

Types of transporting mediums for sedimentary rock

conglomerate (sedimentary rock)

sedimentary rock in which the different larger materials have been cemented together. Varied clast composition reflects a lot of different sources of rock types. transported over longer distances. High energy environment (large pebble grain size).

breccia

A sedimentary rock made with large, angled particles. Little to no transport (based on angular clasts). High energy environments (based on large sediment gravel).

River channel, Alluvial plain, beach-only rarely

Environments of conglomerate formation?

Landslides, Volcanoes, Impact craters, and Glaciers

Environments of breccia formation?

Forms in many environments: beach, river, lake, desert

Environments of sandstone formation?

-composed of mostly quartz

-well sorted and well rounded

Mature sandstone formation?

Quartz sandstone, arkose sandstone (rich in k-feldspar), Graywacke (poorly sorted, many lithic fragments)

Types of sandstone

high: rivers, landslides

low: swamps, lakes, deep ocean

High energy vs. low energy transporting mediums

-distance from the source

-As rocks are carried, especially by water, they become increasingly rounded via abrasion, and are sorted according to clast size

What does Roundedness and sorting reflect?

-low oxygen environment

-In oxygen-rich environments, we expect organic matter to be respired and reconverted into CO

-Otherwise, carbon accumulates, and breaks down abiotically, forming compounds like kerogen and bitumen, which are generally dark in color

(high oxygen usually results in red)

what does dark tint reflect in organic?

Law of Superposition

Sedimentary layers are deposited on top of one another, therefore the youngest strata are on top

Mud cracks

-Indicate drying after deposition

-As it dries, it contracts

-Common in muddy margins of a lake and tidal zones.

-If you find cracks, sediment was exposed to air!

bedding

rock layers bounded by well-defined surfaces

laminae

Extremely thin beds (<1mm)

cross-bedding

Structure in which relatively thin layers are inclined at an angle to the main bedding. Formed by currents of wind or water.

graded bedding

Bedding in which the particle sizes become progressively heavier and coarser toward the bottom layers. Results when a sediment-laden water current (turbidity current) begins to slow down or when sediment of various sizes is dumped into standing water.

ripple marks

Undulations of the sediment surface produced as wind or water moves across sand.

-Symmetric form are produced by waves

-Asymmetric form in unidirectional currents (such as in streams or rivers).

facies

a body of rock with a distinguishing characteristic

sand and silt (near-shore) -> shale -> carbonates (deep sea)

basic facies sequence

Walthers Law

- Regression (sea level fall) vs. transgression (sea level rise)

"The vertical succession of facies reflects lateral changes in environment"

regression

-Results from a sea level fall

-produces a coarsening-upward (shallowing-upward) sequence of sedimentary facies.

-coarser-grained (shallower water) facies overlie finer-grained (deeper water) facies.

transgression

-results from a sea level rise.

-produces a fining-upward (deepening-upward) sequence of sedimentary facies.

-finer-grained(deeper water) facies overlie coarser-grained (shallower water) facies.

fossils

sedimentary rocks are practically the only type of rock that can host ______

-Mineralized hard parts: shells, bones, exoskeletons (usually CaCO3)

-Organic compounds are generally lost

-The trick is RAPID BURIAL

what parts of lifeforms are typically fossilized? what type are lost? what is the trick?

supersaturation

_____ an be a result of constant input or decrease of solvent (water) by evaporation (evaporites)

Evaporites (ex: layered Halite NaCl, Layered Gypsum CaSO4)

Salts & Sulfates precipitated out of evaporating water

Limestone (CaCO3)

-Can precipitate chemically and/or biologically

-around 10% of all sed Rx

-Most abundant chemical sed

-Fizzes when exposed to weak acid

-Found in Ocean, warm-shallow sea, Evaporating lake, and caves

biochemical sedimentary rocks

Tons of organisms build their bodies out of calcium carbonate sourced from the water column. In essence, they're driving the chemical precipitation by taking the Ca2+ and CO32- out of the solution and depositing it as CaCO3 on the seafloor when they die

Marine Limestone, Oolitic Limestone, Fossiliferous Limestone, chalk, coquina,

Types of biochemical sedimentary rocks

Chert (Microcrystalline CO2)

-Forms from the precipitation of silica (originally dissolved from Hydrolysis)

-Made up of amorphous silica (harder than limestone)

-Often found as nodules in limestone

organic sedimentary rocks

consist of the undecayed organic tissue of plants and animals preserved in depositional settings characterized by a lack of free oxygen (ex: coal, oil shale)

chalk

Formed from massive accumulations of the shells of microscopic coccolithophores (haptophyte phytoplankton)

-Most sedimentary rocks will be predominantly silica-based or calcite-based

-Silica (SiO2) is hard and barely soluble

-Calcite (CaCO3) is soft and fairly soluble

calcite vs. silica based

metamorphic rock

A type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions.

Protolith

the original rock from which a metamorphic rock formed. pre-existing rock before metamorphism.

Solid-State Transformation

temperature and pressure, pore fluid, and stress

factors that affect metamorphism

diagenesis

chemical and physical changes that happen to sediment before, during, and after lithification to sedimentary rock

Foliation

-layered texture on rocks due to differential stress

-It forms when stress squeezes the flat or elongated minerals within a rock, so they became aligned.

Protolith:

-Shale (400x magnification)

Low-Grade Metamorphism:

-slate (40x)(microscopic micas)

-phyllite

High-Grade:

-schist (1x)(visible micas)

-gneiss (1x)(visible mafic and felsic mins; gneissic banding)

-migmatite (1x)(if partial melting occurs)

How does foliation change as metamorphic grade increases, crystal size also increases:

non-foliated metamorphic

-Type of metamorphic rocks that lack a planar (oriented) fabric, either because the minerals did not grow under differential stress, or because the minerals that grew during metamorphism are not minerals that have elongated or flat shapes.

-Does not have the necessary minerals or micas to produce the foliation

Limestone -> Marble

Quartz Sandstone -> Quartzite

Hornfels

Types of non-foliated metamorphic rocks

increase in crystal size and increase in coarseness of foliation

What happens as metamorphic grade increases?

low to intermediate grade

Presence of Mica (chlorite, muscovite, biotite) indicates:

intermediate to high grade

Presence of Garnet and Staurolite indicates:

contact metamorphism, Subduction zone metamorphism, Fault metamorphism, and Shock metamorphism

Types of metamorphism processes

kyanite (H P, L T), andalusite (L P, mid T), and sillimanite ( H P, H T)

polymorphs of Aluminosilicate (Al2SiO5)

contact metamorphism

-type of metamorphism that occurs adjacent to igneous intrusions and results from high temperatures, low pressure associated with the igneous intrusion.

-Metamorphism is restricted to the zone surrounding the intrusion, called a contact aureole.

-Different rocks/minerals are formed in the aureole, based on distance from the heat source

-produces hornfels

Regional Metamorphism

-Type of metamorphism that occurs over large areas and generally does not show any relationship to igneous bodies.

-Result from collisions between tectonic plates

Subduction Zone Metamorphism

-Type of metamorphism with high pressure, low temperature.

-Occurs where sediments are carried to great depths by a subducting plate.

-basalt -> blueschist -> eclogite

Fault metamorphism

- metamorphism caused by differential shear stresses at a fault zone

- trying to grind past each other

- localized (not large scale)

- pressure change

-cataclastite (shallower,brittle), Mylonite (deeper, ductile)

Shock Metamorphism

-Type of metamorphism involving very high pressures and fairly high temperatures caused by meteorite impact.

lithostatic stress

a strong confining pressure (acting the same in all directions) due to the weight of the overlying rocks

differential stress

(tension, compression, shearing)

force acting on a surface per unit of area, which may be greater in certain directions than in others

strain (deformation)

The change in shape or volume of a rock due to stress

-brittle (material breaks or cracks)

-ductile (material bends or flows)

Types of deformation

more ductile

How does increasing T affect deformation?

more brittle

How does increasing stress rate affect deformation?

more brittle

How does increasing rock strength affect deformation?

-strength increases from sea level down (upper crust)

-hits the brittle-ductile transition

-as depth increases further, rock strength decreases with increasing temperature (lower crust)

How does increasing depth affect rock strength?

-Faults: Fractures with displacement

-Joints: Fractures without movement

Faults vs. joints

veins

fractures filled with minerals

1. normal fault (tensional stress)

2. reverse fault (compressional stress)

3. strike-slip fault (shear stress)

three types of faults

hanging wall

The block of rock that forms the upper half of a fault.

footwall

The block of rock that forms the lower half of a fault

right lateral strike slip fault

as you face the fault, the opposite side of the fault moves to the right

left lateral strike slip fault

as you face the fault, the opposite side of the fault moves to the left

-Offsets

-Scarps

-Fault rocks like fault breccia

-Slicken Lines

The ways to recognize a fault

fault scarps

long, low cliffs produced by normal or reverse faults

fault slicken lines

series of parallel lines on a fault plane and represent the direction of relative displacement between the two blocks separated by the fault. usually linear pattern on a polished rock surface.

geographic folding

caused by compression stress on a ductile rock

-Anticline (rainbow shape; peak at top)

-Syncline (bowl shaped)

-Monocline(higher level -> curves down -> lower level)

-Chevron (WWW)

The types of folding

Hinge Line (fold axis)

fold geometry: line of maximum curvature on a folded surface