FINAL (theory) Flashcards
Lithostratigraphic vs
Chronostratigraphic units
Lithostratigraphic: Older rocks under younger rocks
Chronostratigraphic: Uses absolute or relative dating methods to date the rocks.
A delta complex is an example of a…
Clastic wedge
Limestones are especially vulnerable
to what kind of change?
Diagenetic change (chemical
processes that occur post-deposition).
After burial, they can start dissolving allochems and precipitating cement.
What environment are stromatolites found in?
Subtidal environments with high salinity.
What is river avulsion?
The abandonment of one river and the formation of a new one in a different area.
Types of Tides/Tidal Environments
- Flood Tide: Incoming tide (landward direction)
- Ebb Tide: Outgoing tide (seaward direction)
- Slackwater: Period between flood and ebb tide where flow velocity is almost zero
Estuary
BANANA!
An embayed coastline with fluvial AND marine sediment sources.
Tripartite Zonation
Bayhead delta at the head, central basin in the middle, barrier with inlets at the mouth.
Sand –> mud –> sand pattern
Wave- vs Tide- Dominated Estuaries
Wave-Dominated Estuaries
- Higher fluvial energy
- Landward = high fluvial energy, low energy in central basin, near barrier = high marine energy
- Sediment from rivers is trapped in the estuaries and lagoons
Tide-Dominated Estuaries
- Tidal flats can flank the central basin
- Less energy than wave-dominated because flow is “channelized”
- Less defined tripartite facies (because less energy)
Hemipelagic Sediment
Terrigenous mud (delivered by rivers) deposited far from the coast with other pelagic sediment.
Debrites vs Turbidites vs Tempesites
Debrites: Deposits from debris flows
Turbidites: Deposit from turbidity current
Tempesites: Waves & currents from a storm
How does wind move grains?
- Saltation: Key mode of transport; sand-sized grains
- Creep: Grains rolling along the surface under pressure of wind or impacts from saltating grains; larger grains
- Suspension: Smaller grains light enough to be carried by turbulent air, scattered as dust
Progradation vs Retrogradation in cross-section
Progradation = SHALLOWING
- Increasing energy
- Getting coarser
Retrogradation = DEEPENING
- Decreasing energy
- Getting finer
Proximal vs Distal
Proximal = channels
Distal = floodplains
Crevasse Splays
Fan-shaped material formed by breaching a levee during flood. Exhibits the fining upwards of a fan.
What is a floodplain? What are natural levees? What is the whole region called?
Floodplain: The WIDE PLAIN of a river, finer-grained material (silt and clay) deposits dropped from floodwaters.
Natural Levees: Fine sands dropped NEAR to the channel due to a sudden loss of competence.
The whole region is called the “Overbank Region”.
Point bar migration creates…
Chutes (cutoffs) result in…
Scroll bars (inner scroll scars)
Oxbow lakes (C shape river)
What is a channel thalweg?
An imaginary line drawn through the LOWEST points in the channel, which marks the path of FASTEST flow.
Types of Rivers (Classifications)
- Straight - a stick (single-thread)
- Meandering - squiggly (single thread)
- Braided - inter-tangled (multi thread)
- Anastomosing - vegetated islands in between (multi thread)
What controls rates of weathering?
Surface Area: As mechanical weathering breaks rocks into smaller bits, more surface area is exposed to chemical weathering– faster weathering)
Mineral Resistance: Harder minerals with fewer planes of weakness will resist weathering. Note the most physically stable mineral is quartz!
Two Types of Weathering
- Physical Weathering
- Chemical Weathering
They work at the same time and together!
Types of Physical Weathering
- Stress Release (me): Overlying rock erodes to uncover balloon-like pluton that “rebounds” up.
- Volume Changes: Bunch of types…
- Bio Agents: Little animals digging holes, tree roots breaking rocks!
- Abrasion (key): Transported grains (by one method or another) bash against each other, become more rounded, and break down.
Types of Physical Weathering: Volume Changes
A. Insolation: Repeated heating and cooling over daily cycles to break apart rock.
B. Freeze-Thaw: Water seeps into cracks, freezes and expands cracks, melts, and the process repeats until these cracks break the rock apart.
C. Salt: Rock disintegration by salts crystallizing in cracks during salt water evaporation, breaking the rock apart.
D. Wetting/Drying: Clays expand when wet and contract when dry- these cycles lead to cracks.
Types of Chemical Weathering
- Simple Solution: Mineral dissolves completely (ie halite).
- Hydrolysis: Hydrogen ion replaces other positive ions to dissolve ions and solid products (ie k-feldpsar). Clays (ie kaolinite) are main product.
- Redox: Reduction (addition of electrons) and oxidation (removal of electrons) of a substance (ie pyrite).
What indicates provenance?
Grain size and composition indicate:
- composition of source
- transport distance and processes
- local climate
Types of Sedimentary Rocks
- Silici-clastic: Made from clasts (fragments) of older rocks (ie sandstone)
- Carbonaceous: Accumulation of organic debris (ie coal)
- Chemical/Biochemical: Precipitation of minerals from water (ie limestone)
What are the ingredients for our “Carbonate Factory”?
- Water clarity
- Sunlight
- Nutrient levels
- Salinity
What do we use to classify SILICICLASTIC rocks?
Grain size, shape, and sorting.
- Transport distances
- Transport processes
Grain composition.
- Source area
- Transport processes
Rounding and sorting increases with ________________ and ______________________.
Transport DISTANCE and ENERGY of transport (processes).
Reynold’s Number vs Freud’s Number
Reynolds: The ratio of inertial forces to viscous forces.
- High R = turbulent flow
- Low R = laminar flow
Freuds: The ratio of flow inertia to external field.
- High Fr = supercritical
- Low Fr = subcritical
Shields stress & Critical shear stress
Shields Stress: Uses the balance of DRIVING vs RESISTING forces to tell us if a grain will move or not.
Critical Shear Stress: The shear stress at the moment of particle entrainment.
Why is water better at moving sediment than air?
More flow, and more turbulent flow to overcome resisting forces.
Hydraulic Jump
When a flow goes from supercritical to subcritical.
As velocity increases, we move through different bedforms. Explain this.
From LOWEST to highest flow VELOCITY…
LOWER FLOW REGIME
1. Lower plane beds: flat
2. Current ripples: mini dunes
3. Dunes
UPPER FLOW REGIME
4. Upper plane beds: dunes are wiped out
5. Antidunes: dunes in opp direction!
6. Chutes and pools: short-lived and unstable forms
What creates bedding?
- Physical Processes: Changes in sediment transport conditions.
- Chemical Processes: Changes in temp, CO2, ion concentrations.
- Biological Processes: Changes in biota.
- Diagenesis: Post-depositional changes.
How is cross bedding created?
Landform migration.
Upper plane beds generate ___________________________, top surfaces shows ________________________.
Parallel laminations
Parting lineations
What’s the difference between fluvial and tidal flow?
Fluvial: Unimodal
Tidal: Stops and reverses (tides cause flow reversal!)
Bimodal dips of dune and ripple foresets due to tidal/flow reversal is called…
Herringbone Cross-Stratification
Walther’s Law
A vertical succession of facies represents migration LATERALLY ADJACENT depositional environments (unless there is evidence of erosion!)
Gamma ray logs vs Resistivity logs
Gamma Ray Logs: Provide insight into lithology
Resistivity Logs: Provide insight into fluid properties
Conformity:
Disconformity:
Angular Unconformity:
Nonconformity:
Conformity: Surface separates older and younger layers.
Disconformity: Erosion layer of missing time.
Angular Unconformity: Older strata at an angle to flat younger strata.
Nonconformity: Igneous or metamorphic rocks under younger strata.
Sequence Boundary
The unconformity generated during sea level fall.
Coarsening upward is an indication of…
Progradation
Parasequences are always progradational, but they can stack together to create what types of stacking patterns?
- Retrogradational: Long-term accommodation > sedimentation
- Progradational: Long-term accommodation < sedimentation
- Aggradational: Each parasequence is roughly equal
- Degradational: Units are shifted downward to due base-level fall (forced regression)
Parasequence
Shallowing upward cycles bound by flooding surfaces (ie peritdal cycle).
Explain and go through the steps of a Base Level Cycle (systems tract).
- Highstand Systems Tract: Sea level is constant, sediment input = progradation (seaward direction).
- Falling Stage Systems Tract: Sea level falls, coast moves seaward = unconformity (due to base level erosion).
- Lowstand Systems Tract: Rate of sea level fall slows, and then slowly begins to rise again.
- Rising Stage/Transgressive Systems Tract: Sea level rises so accommodation creation is higher than sediment input = forces transgression (landward direction). Capped by Maximum Flooding Surface.
When it reaches the next Highstand, transgression stops and regression resumes.
Gypsum begins to precipitate after seawater has been evaporated down to __% of its original volume.
Halite precipitates from brines reduced to __% its original volume
Gypsum = 20%
Halite = 10%
Explain the growth and different precipitation textures/stages of gypsum.
- Gypsum directly precipitating from seawater forms large SELENITE crystals.
- Gypsum can dehydrate to form ANHYDRITE, and rehydrate to form ALABASTER, fine-grained gypsum.
Nodal textures form when gypsum grows in carbonate or clay sediment:
- If the nodules grow large enough to interfere, it causes CHICKENWIRE TEXTURE.
- If more gypsum is added, the gypsum nodules fold over each other, forming an ENTEROLITHIC TEXTURE.
Iron formation and phosphorite are what? Give examples of importance.
Bioelemental sediments.
Iron formation = Hemoglobin, etc
Phosphorite = DNA and ATP
Highest grade Fe ore is…
Highest grade P ore is…
Pristine iron formation = taconite or DSO
Granular phosphorite = amalgamated storm beds
Ages…
Iron formation =
Phsophorite =
Iron formation = Precambrian
Phsophorite = Phanerozoic
What creates/destroys accommodation?
- Eustasy (changes in global sea-level) due to:
- Global tectonics - e.g. mid-ocean ridge volume
- Climate - ice mass
- Climate - thermal expansion of water - Tectonics
- Subsidence
- Uplift
Base level
Sea level/lake level
A change in accommodation can be driven by a change in…
base level or by subsidence (uplift).
Dating/correlation techniques in stratigraphy
- Biostratigraphy (fossils)
- Absolute dating
- Magnetostratigraphy
- Chemostratigraphy (isotopes)
- Sequence stratigraphy
Continental evaporites form thin deposits in…
Marginal marine evaporates are prevalent in…
Evaporite deposits hundreds of meters thick can form in…
Arid playa-lake settings.
Arid sabkha and salina settings.
Silled, arid marine basins.
Stratigraphy
- The study of larger successions of sedimentary rocks
- The study of how TIME is recorded in rocks
Playa Lakes vs Salinas vs Sabkhas
Playa lakes = salt pans in lake (smaller)
Salinas = arid lagoons and salt pans (larger)
Sabkhas = arid, supratidal mud flats
Coccoliths produce ________.
Chalk
When did the pelagic factor evolve? Any sediment before then must be what?
Jurassic. Any samples older are basically just periplatform (re-sedimented) ooze.
What are the two sources of deepwater carbonate sediment?
- Pelagic Factory: Pelagic rain
- Periplatform: Gravity-driven transport downslope (re-sedimented)
Explain the CCD
Carbonate Compensation Depth is the depth at which carbonate sediment no longer accumulates (the line where rate of accumulation = rate of dissolution).
Increase in CO2 =
Decrease in CO2 =
Cold temps =
Warm temps =
Increase in CO2 = Dissolution (of CaCO3)
Decrease in CO2 = Precipitation (of CaCO3)
Cold temps = Dissolution (of CaCO3)
Warm temps = Precipitation (of CaCO3)
Why does the Pacific (N. Pacific especially) have less calcareous deepwater sediment than the Atlantic?
- The Pacific has more CO2, meaning more acidic water, keeping the CaCO3 DISSOLVED
- Its CCD is deeper
- It’s also a deeper ocean
Pelagic
Near the surface of the ocean
What are the 3 reasons carbonate sediments are found in oceans?
- Solubility differences between carbonate minerals
- Ocean circulation
- Changes in seawater chemistry with depth
Order of Evaporation
- Calcite
- Gypsum
- Halite
- K & Mg salts
Stromatolitic reefs are the norm in…
subtidal environments with elevated salinity.
What does “peritidal” mean?
Within and slightly outside of tidal influence.
How does carbonate mud form?
Direct precipitation or breakdown of skeletal (usually algae) components.
Intraclasts vs Extraclasts
Intraclasts: Fragments of lithic (stoned) sediment transported only a short distance.
Extraclasts: Transported far; foreign to depositional environment.
Big 3 Carbonate Minerals
- Calcite
- Aragonite
- Dolomite
Types of Ooids
- Oolites: 0.25-2 mm
- Pisolites: 2+ mm
- Oncoids: mm to cm
- Oncolites: cm
What are allochems?
Carbonate grains.
A. Skeletal remains
B. Ooids
C. Intraclasts
What are carbonate sediments?
Precipitates from organic material, like the skeletons and shells of organisms.
