GEOS 302 Final

Define the difference between "sediments" versus "sedimentary rocks"

sediments are eroded grains/loose material while sedimentary rocks are deposited and compacted sediments

What do you need to have to form sedimentary rocks?

erosion, transport, deposition, lithification

Explain what defines "facies"

body of rock with specified characteristics that reflect the conditions under which it was formed

How do we interpret the depositional environment?

based on physical processes and facies association

Why is the stratigraphic record important?

Becuase it is the fundamental database for understanding the evolution of life, plate tectonics through time and global climate change

List the 6 principles of Stratigraphy/geology

1. superposition
2. original horizontality
3. original lateral continuity
4. uniformitarianism
5. fossil (biotic) succession
6. cross-cutting relationships

Explain Walther's law

facies that are found today in the vertical sequence are the product of a series of depositional environments which lay laterally adjacent to each other

What controls erosion and deposition?

weathering, climate, tectonics, relief, source type and grain size

What controls sedimentology and stratigraphy?

tectonics, sediment supply, eustacy(change in sea level)

What are the different types of sedimentary rocks?

clastic (volcaniclastic, terrigenous clastic, carbonates), non-clastic (carbonates, others, evaporites)

What are the physical properties that describe sedimentary rocks?

textures (size of clasts, shape, orientation, porosity and permeability), composition, sedimentary structure

How do we measure and represent grain size? (mm scale vs. phi scale)

mm scale - clast size, phi scale - -log(2)(diameter), manual measurement or thin-section measurement

What is the boundary in grain size between sandstone and conglomerate?

sandstone .064-2 mm, conglomerate >2mm

How is the size of a grain related to its settling velocity? (Explain Stoke's law with a simple balance of forces and derivation)

(D^2)g(ps-pl)=18(u)V

Why is fabric important?

shows the flow direction

What is porosity?

space between grains

What is and what controls permeability?

rocks ability to tranmit fluids, how a fluid flows through

How do we classify sandstones?

composition (quartz, feldspar, lithics), matrix/cement%, maturity

What is the difference between an arkosic arenite and a lithic arenite?

Arkose arenite has more feldspar while lithic arenite has more lithics

What is maturity (describe the two different kinds)?

Compositional: amount of stable vs unstable minerals, Textural: sorting, matrix content, grain angularity

What is the difference between QFL and QFR?

With a polimineralic grain >.0062mm, QFR would put the grain in rock/lithics (R) but in QFL it would be sorted into QFL based on composition

Why are ternary diagrams important?

Help sort composition of sediment

What is the typical compostion of sandstones from recycled orogens versus the composition of sandstones from stable cratons? (Plot estimated average composition on a QFL diagram).

recycled orogens (high quartz on lithics side), Volcanic arc(bottom-middle on lithics side), Stable cratons(high quartz on feldspar side), block faulted basement (feldspar side)

What are the most common minerals forming carbonate rocks?

calcite, aragonite, dolomite

What are the most common carbonate forming animals and plants?

molluscs, gastropode,cephalopod, crinoids, corals, serpulide, stromatolites, oncoids, ooids

What are the two main classification schemes for carbonates and how do they differ?

Dunham: proportion od carbonate mud(matrix) present vs allochems, Folk: requires a microscope and texture/composition based

What is the difference between a wackestone and a grainstone?

Wackestone is mud supported, grainstone is grain supported

Where do you preferentially despoit carbonates and why (what controls carbonate production)?

carbonate platforms, reef, carbonate ramps, chemistry of the ocean, light, temperature and nutrients

What is the carbonate factory and what are the main controlling factors?

defined as the shallow illuminated seafloor where sediment particles are generate within the sea water from the crystallization of skeletal remains or precipitation out of sea water, light, temperature, climate

What is the CCD and what controls it?

carbonate compensation depth, temperature, pressure, productivity

Define a fluid

material that deforms under shear stress

Which type of flows do you know and how do they differ in terms of their velocity behaviour?

air, water, water+sediment, high viscosity - low velocity

Define shear stress and derive it using balancing of forces for a laminar flow at the boundary bed

shear stress(tau) = F/A exerted parallel to surface, gravity vs friction, t=hpgS

if you increase S, what does (tau) do? If you increase h, what does tau do? If you increase p what does tau do?

high S - high t, high h - high t, high p - high t

Do you expect higher tau to be more or less capable of eroding and transporting sediment than lower tau?

higher tau would erode and transport less sediment

Which relationships does the Reynolds number describe?

ratio between inertial forces/viscous forces Re=(velocityXdepthXdensity)/viscosity

Do you expect flow to be turbulent at low or high velocities?

turbulent - high velocity

If you decrease water depth, do you expect to increase or decrease turbulence?

decrease h, increase turbulence

Which relationships does the Froude number describe?

describes the ratio between inertial/gravity forces Fr=(velocity)/sqrt(gravityXdepth)

What's the condition by which wave propagate upstream?

Fr

What are the relationships between flow regime, Re and Fr numbers?

Re=turbulent vs laminar, Fr = subcritical vs supercritical, flow regime based on velocity

When do sediment start to move (think about forces)?

after overcoming critical shear stress

Explain the lift force (Bernoulli principle)

high V low P to low V high P

What is flow seperation?

Bernoulli principle, change in pressure causes fluid to seperate

What are the forces (moments) related to movement of particles in fluid and how do you analytically balance them?

gravity, drag, lift

What are the relationships between sediment transport, erosion, deposition (shields and hjulstrom diagrams)?

hjulstrom diagram(grain size vs flow velocity), different velocities

Which types of loads do you know?

bedload, sediment load, wash load, suspended load

What other fluids do you know deside water and how do they differ?

air, water, water+sediment, high viscosity - low velocity

What are sediment gravity flows?

occur when grains become separated and dispersed so that cohesiveness and friction are reduced enough for movement to initiate

What is the difference between debris flows and grain flows?

debris flows have large clasts, grain flows have grain size clasts

What is the main force controlling inverse grading in grain flows?

reverse grading is a result of kinetic sieving

Do you expect velocity to be higher in debris flows or turbidity flows?

depends, debris flows have higher viscosity so generally a lower velocity than turbidity flows

What drives turbidity currents?

density contrasts

What is the Bouma sequence?

one bed for one turbidity event

Explain the relationships between the Bouma sequence and flow regime?

Bouma sequence starts with high flow regime and ends in low flow regime

Laminae versus bed

Laminae: layer less than 1cm in bed, bed: depositional unit

What is the difference between primary and secondary structures?

primary: depositional sedimentary structures, secondary: post-depositional, erosional, biogenic structures

How do ripples form?

high velocity, shallow water, fluid flow exceeds the flow strength required for sediment movement

What controls ripples to climb?

ratio between the rate of sediment accumulation and the rate of ripple migration

What is the difference between a 2D and 3D ripple?

2D: low velocity straight crests, 3D: high velocity irregular crests

What is the difference between a dune and an antidune?

antidune: fr>1 higher velocity, dune: lower velocity

Symmetrical versus asymmetrical ripples

symmetrical ripples: waves, asymmetrical ripple: one direction flow

What is the flow regime necessary to form primary current lineations?

upper flow regime

What are the relationships between flow regime and sedimentary structure?

low flow regime: ripples, lower plane bed, dunes, upper flow regime: antidunes, upper plane bed, chute and pool

Planar cross lamination/stratification versus trough-cross lamination/stratification

planar - 2D, trough - 3D

What controls erosion and depostition?

velocity and grain size

What are the relationships between and what controls erosion, transport and deposition?

Erosion: function of climate(water) and slope, Transport: slope, water discharge, type of sediment, Deposition: sedimentation rate, basin size, tectonics, sea level

Chemical weathering vs. physical weathering

Chemical: hydrolysis, oxidation, Physical: freeze-thaw, salt, temperature

What are the main chemical weathering reactions and what are their products?

Hydrolysis: clay minerals, Oxidation: iron/manganese silicate minerals

Explain isostacy and why it is important

body in fluid is pushed up by a force equal to weight of displaced fluid, assumes local compensation(earth composed of free floating pistrons)

Difference between uplift and erosion and their relationships

Uplift: displacement of rocks in opposite direction of gravity, Erosion: material removed from surface, surface uplift = rock uplift-erosion

What are the different branches of stratigraphy?

lithostratigraphy (based of facies), biostratigraphy (based on fossil content), allostratigraphy (based of discontinuity), Chronostratigraphy (based on age), Magnetostratigraphy, Pedostratigraphy (study of soils), Sequence stratigraphy

What is the difference between a Group, Formation and Member?

A group is the highest hiearchy, a formation is a mappable unit, and a member is below a formation

What are strato-types and type locations and why are they important?

Stratoypes is the formal representation of a rock in the field that is represented as a type section

How can you correlate facies? What is facies anaylsis?

Facies analysis: The study and interpretation of the textures, sedimentary structures, fossils and lithologic associations of sedimentary rocks on the scale of an outcrop, well section or small segment of a basin. Correlate facies by looking for the same units in the same order

What is the product of facies analysis?

an understanding of the depositional environments that produced the facies

Explain Walther's Law.

facies that occur in vertical succession occur today in laterally adjacent environments

Transgression vs, regression and relationship with progradational system versus retrogradational system

Regression-sea level fall-progradation-depo environment moves forward. Transgression-sea level rise-retrogradation-depo environment moves backward.

Autocyclic vs. allocyclic

Autocyclic occurs due to within system changes, allocyclic occurs with large scale global events

First and second order cycles

First order:200-400Ma: formation and break up of supercontinents ,Second order: 10-100Ma: formation of new crust and changes in ocean spreading, pole changes

Greenhouse and icehouse stages and Zachos curve

icehouse- permanent polar caps, greenhouse- no ice caps, Zachos curve shows relationship between O16 and O18

Where do you find dry-desert like environments and why? And which type of flow regime is typical of eolian environments?

Dry desert environments are found beween 0-30 degrees latitude due to the trade winds. Eolian environments have upper flow regime

What are typical desert features? (ventifacts, deflation surfaces, desert varnish, etc.)

Desert pavement - pebbles, no sand, looks coated. Deflation - fine grains get swept away. Ventifacts - product of wind erosion on previous features. Desert varnish - clays +Mn oxides from bacteria. Sand grains - frosted, pitted, microfractures

Which type of flow (laminar vs. turbulent) is characteristic of eolian environments and why?

Turbulent due to entrainment of grains

How do you form dunes? Where do you have grain flow? Bagnold equation.

Dunes form with high wind speed. Grain flow occurs when sand grains flow down a slope in a dune.

Grain size vs. bedform wavelength

Shows the eolian bedform sizes. Increasing bedform wavelength: ripple, dune, draa, erg

Grain flow versus grain fall

Grain fall deposits are created by sand grains dropping more or less ballistically from the air. Grain flow layers are created by sand grains flowing down a slope.

What are CTS-climbing translatent strata-how do they form?

CTS: climbing translatent strata - the migration of ripples that leaves behind parallel strata

Know the difference between barchan, transvers, parabolic, star dunes

brachans: cresent shaped, high velocity, low sand supply. transverse - straight dunes, form right angles with flow direction. parabolic: horn points upwind, stabalized by vegetation. star: complex wind convergence. longitudinal: parallel to wind direction

Which type of flow (laminar vs. turbulent) is characteristic of glacial environments and why?

Laminar flow is characteristic of glacial environments due to the high viscosity

What is a tillite (and diamictite)?

Tillite and Diamictite are glacial deposits and are poorly sorted

On a QFL diagram, where would you expect tillites to plot?

Tillites would plot in recycled orogen? but it is mostly based on the source terain

Which types of moraines do you know?

Terminal, Lateral, Medial: a mass of rocks and sediment carried down and deposited by a glacier, typically as ridges at its edges or extremity.

What is an Esker, drumlins, jokulhlaup?

Esker: a long ridge of sediment, typically having a winding course, deposited by meltwater from a retreating glacier or ice sheet. Drumlins: lodgement till deposited beneath ice sheet. Jokulhlaup: Outburst lood deposits, carry large clasts out onto outwash plain, think beds with super-sized fluvial characteristics

What is the typical facies association of a glacial environment (sketch a simplified stratigraphic log), eolian environment versus fluvial for example

facies marine: Laminated muds with ice-rifted sands and gravel as beds and isolated dropstones. Facies continental: Lodgement till (thick deposits at glacial front), Outwash braided stream deposits, glacial-lacustine deposits, Loess

What characterize an alluvial fan?

fan shaped accumulation of coarse sediment that forms in areas with steep gradients

Which facies do you expect to find in the upper vs. lower part of an alluvial fan and why?

courser closer to the source. Conglomerate to sandstone

Which type of depositional processes can act in forming alluvial fans?

Debris flows, sheet floods, stream channel flows

Do you expect flow to be laminar or turbulent close to the apex of an alluvial fan? And what is the character of the deposits near the apex of an alluvial fan?

apex - conglomerates- laminar -more energy

Do you expect the deposits to get more or less organized as you move away from the apex of an alluvial fan and why?

more organized futher away due to decrease in velocity