GEO Unit 2
Sedimentary rocks are derived through = weathering and erosion of pre-existing rocks.
Sedimentary rocks form by = transport and accumulation of fragmental materials (sediments) or dissolved products, from a source region to a site of deposition
Materials that make up Sedimentary Rocks = biogenic or inorganic
What % of rocks are sedimentary = 75%
Types of Sedimentary Rocks = Clastic, Biochemical, Organic, Chemical
Clastic = loose rock fragments (clasts) cemented together
Clastic Criteria: particle size and maturity
Biochemical = cemented shells of organisms
Organic = carbon-rich remains of once-living organisms
Chemical = minerals that crystallize directly from water
Chemical Criteria = mineral composition
Depositional environments = locations where sediment accumulates.
Mechanical weathering = a reduction of size—larger particles becoming smaller particles
Causes of Mechanical weathering = abrasion by flowing ice/water/wind, pressure changes (exfoliation), frost wedging, wetting/drying, roots/burrows
Chemical weathering = Reaction between minerals and water to form new minerals and/or dissolved ions
Wind Erosion = wind carved rocks
Water Erosion = Grand Canyon
Ice Erosion = Ice carves the rock
Exfoliation = looks like rock is sliding down
Jointing = pushed together
Causes of Chemical Weathering = Carbon dioxide dissolves in water
to make a weak acid (carbonic), Attacks & dissolves rocks, Carbonate is especially vulnerable
Gruss = weathered granite
Causes of physical weathering = works with chemical to accelerate weathering by increasing surface area
At high temp and pressure = low stability at the surface
Lithification = transforms loose sediment into solid rock: burial increases pressure, squeezes out air and water, and compacts grains.
Minerals (often quartz or calcite) precipitate from groundwater into pore spaces. This cement glues the loose sediments together.
In terms of composition, the most mature contain = Clay minerals (weathering of feldspar), Quartz (resistant to weathering)
Presence of unstable minerals (mafics, feldspars) indicates = immaturity
Larger grain size = closer to source
Angularity = the degree of edge or corner smoothness
Sphericity = the degree to which the shape of a clast approaches that of a sphere.
Angularity = how far the sediment was transported
angular and non-spherical = not transported very far.
Sorting = a measure of the uniformity of grain sizes in a sediment population.
Degree of sorting = increases with transport distance.
Sediment maturity = the degree to which the sediment evolved (from initial weathering event).
Mature sediments = well-sorted and well-rounded.
Chemical sediments originate by = direct precipitation of dissolved ions.
Evaporite chemical sediments precipitate = reverse order of their solubility (calcite first, then gypsum, then halite) as the concentration of dissolved ions in seawater becomes highly concentrated through intense evaporation and loss of water vapor.
Biochemical sediments = composed of the undissolved remains of organisms and minerals that were precipitated by biological processes.
Calcite and quartz = the most common minerals in biochemical sedimentary rocks.
Limestone = 10% of all sedimentary rocks, calcite, marine organisms
Coal = formed by organic matter, pressure and temp over time, has no minerals
Precipitates = form as solubility of dissolved ions in solution changes (pH or pressure change)
Stratified = layered sedimentary deposits
Offshore – fine grained
Beach – sandstone well sorted
Inland wetland = coal
Transgression = coastline migrates upward and sea level rises
Regression = coastline migrates seaward and sea level falls
Internal energy: the heat within the Earth.
External energy: energy coming to Earth from the Sun.
Gravitational energy: the downward pull on material at higher elevation.
Mass Wasting = downslope motion of earth's materials by gravity
Mass movement (slow to fast) = creep, slumping, lahars/mudflow, debris flow, rockfall/slide
Creep = slow downhill movement of regolith (expansion, contraction, moving grains)
Slumping = sliding of regolith as coherent blocks (head scarp, bulging toe)
Mudflow = H2O-rich movement with fine sediment
Debris Flow = H2O-rich movement with large rocks
Lahar = volcanic mud debris flow
Landslide = movement down a non vertical slope
Rockslide = slide of only rocks
Debris slide = slide of mostly regolith
Rockfall = vertical freefall
Submarine slumps = coherent blocks break and slip
submarine debris flows = moving material breaks apart
turbidity currents = sediment moves as a turbulent cloud
Downslope forces = gravity
resisting forces = material strength ( cohesion, friction)
steeper slopes = larger forces
Angle of repose is due to = particle size shape and surface roughness
angle of repose for fine sand = 35°
angle of repose for coarse sand = 40°
a angular Pebbles = 45°
Weak subsurface layers can = initiate motion
types of failure surfaces = saturated sand or clay layers joints parallel to the surface weak sedimentary bedding metamorphic foliation
Examples of failure triggers = deepening the slope beyond the angle of repose or adding weight to the top of a slope or removing support
Metamorphic rocks = rocks that have recrystallized as a result of exposure to intense heat and or pressure
Protoliths = undergo changes in texture and mineralogy due to variations in temperature, pressure, tectonic stress, and the amount of reactive water
Foliation = planar fabric that cuts through the Rock, alignment of platy minerals (i.e., micas), or creation of alternating light/dark bands.
Ingredients of metamorphism = elevated temperature and pressure differential stress water
Metamorphism occurs between = 250° C and 850° C
Vein quarts = Indicates hydrothermal fluid action
Differential stress = a common result of tectonic forces. Mountain building creates horizontal compression (push); rifting creates horizontal extension (pull). There are two different kinds of differential stress: normal and shear.
Plastic deformation = mechanism for creating preferred orientation in metamorphic rocks the grains change shape internally without breaking or dissolving
Compressive stress = flattens grains into alignment
Shear stress = flattens and rotates grains into a preferred orientation.
Recrystallization = the minerals change size and shape through dissolution and growth of crystals. The composition of the minerals does not change, however. Example: limestone → marble
Neocrystallization = describes the formation of new (metamorphic) minerals from old (those that were in the protolith). Protolith minerals become unstable and undergo chemical reactions that recycle elements to form a new mineral assemblage. An example is the formation of garnet mica schist from a shale protolith.
Solid-state differentiation = chemical reactions segregate light and dark layers to create compositional banding.
Foliation = rocks have been subjected to differential stress and they have a significant component of platy minerals. It gives the rock a streaked or striped appearance and sometimes provides weakness along which the rock will break.
Thermal metamorphism = heating by a plutonic intrusion
burial metamorphism = deep burial in a basin
Dynamic metamorphism = shearing in a fault Zone
regional metamorphism = pressure and temperature change due to orogenesis
hydrothermal metamorphism = alternation by hot water leaching
subduction metamorphism = high pressure and low temperature alteration
shock metamorphism = extreme High pressure from a bolide impact
Metamorphic grade = is a measure of the intensity of T and P conditions that lead to alteration.
Metamorphic zones = index minerals indicate the metamorphic grade of a rock and make useful maps
During radioactive decay = the number of protons in the atom changes, and one element transforms into another.
Parent isotopes decay into = daughter isotopes.
Once an atoms decays, it can = not change back.
half-life = the time it takes for half of unstable nuclei to decay
Closure Temperature = processes that can “reset” an isotopic clock.
A radiometric date on the dike = a minimum age for the shale and a maximum age for the sandstone.
Where do Earthquakes occur = margins of tectonic plates
Earthquake: an event of ground shaking caused by slip along a fault within the Earth. Associated with a release of energy.
fault: a fracture in earth's crust that is the locus of relative ground movement or rupture
Focus: point of first fault rupture, at depth in crust
Epicenter: point on land surface directly above focus
elastic rebound theory = The buildup of stress on rocks leads to elastic deformation. When the strength of the rock is exceeded the rock ruptures with slip along faults – this releases elastic energy
Most earthquakes occur in narrow zones around the globe = seismic belts
Convergent-plate boundaries = shallow, intermediate, and deep earthquakes.
Earthquakes are rare below = 660 km as the mantle becomes too ductile.
Deep quakes are found at = subduction zones and are confined to downgoing slabs of lithosphere.
Continental rifts = tension and stretching creates normal faults.
Continental lithosphere = compresses along thrust faults. Earthquakes can be very large. Orogenic uplift creates landslide hazards.
Around _____ of earthquakes are not near modern plate boundaries = 5%
Humans can cause earthquakes, mainly due to = changes in groundwater. This is called induced seismicity. Groundwater pressure can push apart faults, thereby reducing the friction on the fault, causing it to slip
Severity of Shaking Depends on: Magnitude of the earthquake,Distance from hypocenter, The nature of the substrate at your location, The frequency of the seismic waves
High frequency waves = do most damage but do not travel very far
The Modified Mercalli Intensity scale = a subjective determination that assigns Roman numerals to differing degrees of damage. Damage intensity decreases with distance from the epicenter.
Intensity = by the severity of damage observed in the field
Magnitude = is a measurement of size based on the maximum amplitude of seismograph waves.
Richter scale (ML)—best for local measurements (near the epicenter), A logarithmic scale based on the maximum amplitude of ground motion, recorded on a standard seismograph, correcting for the distance to the source
Surface-wave scale (MS)—based on R-wave motion, best for shallow quakes
Body-wave scale (mb)—based on P-wave measurements on deeper quakes
Moment magnitude scale (MW)—the best measure. Based on characteristics of different seismic waves and the area and displacement of fault slip.
Can we predict Earthquakes = They CAN be predicted in the long term (tens to thousands of years). They CANNOT be predicted in the short term (hours and weeks).
Seismology = Study of vibrations (elastic waves) that propagate through the Earth – gives info on medium (rock) through which the waves propagate as well as info about the source that created the waves
Seismic Wave = During an earthquake, seismic waves radiate away from the source in all directions
Wave front: boundary between the rock through which a wave has passed and the rock through which it has not passed.
Seismic ray: changing position of an imaginary point on a wave front.
P-waves = travel by compressing and expanding the material parallel to the wave-travel direction. fastest seismic waves, and they travel through solids, liquids, and gases.
S-waves = travel by moving material back and forth, perpendicular to the wave-travel direction. slower than P-waves, and they travel only through solids, never liquids or gases.
L-waves (Love waves) = S-waves that intersect the land surface. They move the ground back and forth like a writhing snake.
R-waves (Rayleigh waves) = P-waves that intersect the land surface. They cause the ground to ripple up and down like water.
Seismographs = instruments that record ground motion. A weighted pen on a spring traces movement of the frame. Vertical motion is recorded as up-and-down movement; horizontal motion is recorded as back-and-forth motion.
Seismogram = the data recorded by a seismograph. It depicts earthquake wave behavior, particularly the arrival times of the different waves, which are used to determine the distance to the epicenter.
Finding Epicenter = One station gives infinite possible epicentral locations, Two stations give two possible locations, Three stations give one location
The ____ will depend on the stiffness of the rock and its density = velocity of waves
Reflection: bounce off the boundary
Refraction: bending as it passes through the boundary
far away stations received waves = travel through the mantle (more rigid, higher velocity
the Moho = crust mantle boundary
Low velocity zone (LVZ) = occurs beneath oceanic crust from 100 – 200 km.
Below LVZ = under oceans, and throughout mantle under continents, seismic-wave velocity increases with depth.
Upper mantle – above 660 km
Lower mantle – below 660 km
Transition zone – 410 – 660 km
Orogenesis = applies force to rocks, causing deformation (bending, breaking, shortening, stretching, and shearing).
Strain = Change in shape via deformation, creates geological structures
Folds = bends in layered rock that form by shearing and or by slow plastic flow.
Joints = fractures that have no offset.
Undeformed (unstrained) rocks display = horizontal beds, spherical sand grains, no folds or faults.
Deformed (strained) rocks show = tilted beds, metamorphic alteration, folding, and faulting.
Deformation = include displacement, rotation, and distortion. Displacement is a change in location.
Rotation = a change in spatial orientation
Distortion = change in shape
Ductile = higher P and T conditions
Brittle = shallow crust rocks break by fracturing, brittle
Deformation behavior depends on = temperature, pressure, deformation rate, mineralogical composition
Compression = takes place when an object is squeezed. Deformation shortens and thickens the material. Horizontal compression drives plate-tectonic collision and orogenesis.
Tension = occurs when the ends of an object are pulled apart, which stretches and thins the material. Horizontal tension drives crustal rifting.
Shear = develops when surfaces slide past one another. Stress neither thickens nor thins the crust.
Pressure = occurs when an object feels the same stress on all sides.
Faults are classified by their = geometry (vertical, horizontal, or dipping) and relative motion.
Footwall = block below the fault
Handing wall = block above the fault
normal fault = the hanging wall moves down relative to the footwall. It most often results from extension (pull-apart or stretching).
reverse fault = the hanging wall moves up relative to the footwall. It usually results from compression (squeezing or shortening).
thrust fault = act to shorten and thicken mountain belts.
Strike-slip faults = often near vertical, hence, there are no hanging-wall or footwall blocks, occur along the boundaries of plates that are sliding past each other.
Horizontal - compression causes rocks to buckle.
Shear - causes rocks to smear out.