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