Pi Phis Pass Geology Test # 2

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Sedimentary Rocks:
Detrital

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Composed of solid particles (sediments) derived from weathering

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Sedimentary Rocks:
Chemical

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Formed by the precipitation of dissolved substances.
Organic - if organisms are what extracted the dissolved substances.
Inorganic - if no organisms were involved
Ex. evaporation

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Characteristic of Detrital Rocks:
Texture

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Size - particles size, shows the amount of energy present in the environment of deposition.
Shape - degree of rounding, shows distance or time involved in transport of particles.
Sorting - similarity in particle size. Transport agents sort particles. Wind is a good sorting agent b/c it can only carry a few sizes. Glaciers are a bad sorting agents b/c any size particle can be moved by it.

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Characteristic of Detrital Rocks:
Mineral Composition

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Substantial weathering and long transport lead to destruction of less stable minerals. - Quartz & hematite are very stable.

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Types of Detrital Rocks

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Shale, sandstone, conglomerate.

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Chemical Rock Types

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Coal:organic
Limestone:inorganic, organic
Dolostone: inorganic, organic
Chert: inorganic, organic
Rock gypsum: inorganic
Rock salt: inorganic

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Organic Sedimentary Rocks

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Coal - consists of organic carbon from the remains of plants that died and accumulated.

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Lithification

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Process made up of compaction - sediment accumulated and being compressed deeper into the earth - and Cementation - the crystallization of minerals among the individual particles.
Common Cements: Calcite, Silica, Iron oxide.

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Sedimentary Environments:
Terrestrial (Continent)

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Lake, flood plain, river, swamp, dune.

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Sedimentary Environments:
Transitional (shoreline)

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Lagoon, beach, delta

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Sedimentary Environments:
Marine

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Shelf, Deep water

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Sedimentary Structures

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Form during or after deposition, before lithification, provides clues about the environment of deposition.

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Sedimentary Structures:
Cross Bedding

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Layers of sediments are deposited at an angle to horizontal.
Ex. sand dunes, river deltas

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Sedimentary Structures:
Graded Bedding

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Particles within a single layer range from coarse at the bottom to fine at the top. Characteristic of rapid deposition in water with different sizes of particles.

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Sedimentary Structures:
Ripple Marks

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Small waves of sand develop on surface of sediment layer by action of moving water or air.
Asymmetrical - current was moving in one direction
Symmetrical - oscillation, current was moving in both directions.

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Sedimentary Structures:
Mud Cracks

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formed when sediment is alternately wet and dry. Most common in shallow lakes, desert basins, and tidal flats.

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Metamorphic Rocks

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Transformation of pre-existing rocks by elevated pressure, temp, hot and chemically active fluids
Pressure and heat that drive metamorphism are consequences of internal heat of earth, weight of overlying rocks, pressures at plate boundaries.
Temps: 200 - 800 C
Pressures: 5000, 40,000 atm

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Changes during metamorphism

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Mineralogical - (chemical) existing minerals and ions in water recombine to form new minerals.

Textural: re-alignment of mineral grains (foliation)

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Principle Settings for Metamorphism: Regional

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Along boundaries of colliding plates of earth (Convergent boundaries)
-most common

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Principle Settings for Metamorphism: Local (contact)

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Around a mass of magma, must have contact with magma.

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Principle Settings for Metamorphism: Cataclastic

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Along fault zones where blocks of rock grind past one another.

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Principle Settings for Metamorphism: Hydrothermal

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seawater percolates through fractures in basalt at ridge flanks, the increased temp. causes chemical reactions between seawater and rocks.

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Principle Settings for Metamorphism: Burial

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Heat and pressure exerted by overlying sediments. This is how coal is formed.

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Foliated Meta. Rocks

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Foliation - a parallel alignment of minerals caused by structural deformation.
(from low to high grade)
slate, phyllite, schist, gneiss.

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Non-foliated Meta. Rocks

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Marble, Quartzite
Parent rocks composed mostly of a single mineral (quartz or calcite) often produce non-foliated meta. rocks.

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Texture of Metamorphic Rocks:
Slaty Cleavage

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Has closely spaced, flat, parallel layers.

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Texture of Metamorphic Rocks:
Phyllic texture

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Has a green or gray silky sheen.

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Texture of Metamorphic Rocks:
Schistosity

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Has threads of mica - similar to slaty cleavage but the minerals are larger and the rock appears coarsed grained.

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Texture of Metamorphic Rocks:
Gneissic Banding

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Has alternating layers of different mineral composition.

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Mechanical Weathering:

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Disintegration into smaller pieces, each retaining the chem. characteristics of the original material.

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Mechanical Weathering:
Frost Wedging

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Water freezes in cracks then expands, exerts outward force. Most common in climates where temps. fluctuate between above and below freezing.

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Mechanical Weathering:
Mineral Crystallization

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Minerals crystallizing from solutions in cracks (calcite, gypsum, halite) Crystals can grow so big they break the rock.

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Mechanical Weathering:
Thermal Expansion

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Heat causes the rocks to expand, and then the cold causes them to contract. Most common in rocks from the desert.

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Mechanical Weathering:
Expansion from Unloading

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When large masses of igneous rock are exposed by erosion concentric slabs begin to break loose - the reduction in pressure it was causes the exfoliation.

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Chemical Weathering:

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Chem. transformation of rock into one or more new compounds
-Water is a key agent.

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Chemical Weathering:
Hydrolysis

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H2O dissociates in to H+ and OH-
H+ attacks and replaces other positive ion in crystal lattice

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Chemical Weathering:
Dissolution

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Water is a polar molecule, dissolves certain minerals (ex. halite)
Most minerals are insoluble in pure water, but small amount of acid increases the corrosive force.

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Chemical Weathering:
Oxidation

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Rusting - Oxygen combines with iron to form iron oxide.
Decomposes ferromagnesian silicate minerals
Water is required to release iron via dissolution, which then combines the oxygen w/ the atmosphere

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Factors that control type, and rate of weathering

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-Rock type
-Climate
- warm,moist favors chemical weathering
-Topography
- effects how much of the rock is exposed to weathering.
- determines amt of precipitation
- determines amt, type of vegetation.

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Soil

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-loose mantle on rock or sediment, formed by weathering.
-relied on for food
-combination of mineral and organic matter (humus), water, air.

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Factors Controlling Soil Formation: Climate

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-hot, wet: thick layer of chemically weathered soil.

-cold, dry: thin layer of mechanically weathered soil.

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Factors Controlling Soil Formation: Parent Material

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-bedrock or unconsolidated sediment
-residual soils form on bedrock
-transported soils form on unconsolidated sediment
-affects soil fertility, stability.

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Factors Controlling Soil Formation: Time

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-avg. 1000s years for soil to form.

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Factors Controlling Soil Formation: Plants, Animals

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-furnish organic matter to soil which releases nutrients
-decaying organic matter forms organic acids which hasten weathering
-organic matter has good water retention.
-worms mix soil, aiding in the passage of water and air.

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Factors Controlling Soil Formation: Slope

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-influences amt of erosion and water content
-steep slopes = poorly developed soil

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Soil Profile

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O: organic matter (humus), bio. activity
A: mineral matter
E: leaching, eluviation (The downward movement of suspended material within soil when rainfall exceeds evaporation)
B: zone accumulation of the material removed from E.
C: partially altered rock debris

-much water: soluble material like caco3 leached from soil, less soluble iron oxides and clay accum.
-little water: calcium carbonate accum. in B horizon, less clay accum. b/c there is less chemical weathering

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Soil Erosion

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-natural process
-accelerated by farming, logging, construction, that remove vegetation, also causes sediment pollution.

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Mass Wasting

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downslope movement of rock or soil under influence of gravity.

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Classifications of Mass Wasting:
Rock

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-Rockfall
-Rockslide
- esp. when sloping strata or fractures parallel sloping land surface
-Rock Avalanche
-composed of large mass of rocky material moving at high velocity. Over 100 mi/hr

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Classifications of Mass Wasting:
Unconsolidated

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-Creep: gradual downhill movement of soil
-Earth flow: vegetated mass of soil oozes downhill
-humid climates
-Debris/mudflow: rapidly flowing masses of mud, soil, rock, or water
-arid climates
-Slump: mass slides among curved surface.

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How to prevent mass wasting:

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Active measures: rockbolts, retaining walls, steel or wooden piles, fluid removal, ground cover, grading, mass removal

Passive measures: divert water, land use planning.

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Hydrologic Cycle

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continuous circulation of earth's water supply between reservoirs, powered by the sun

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What are the key processes of the hydrologic cycle?

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Precipitation, evaporation, transpiration, infiltration, runoff, groundwater flow, sublimation

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Laminar water flow

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slow moving, smooth channel, particles flow in straight paths parallel to channel, little mixing

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Turbulent water flow

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high velocity, irregular channel, chaotic flow, high mixing, most common in streams

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Suspended stream load

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all materials are in suspension

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Beded stream load

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material carried along bottom

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What are the 3 types of stream loads?

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Suspended, Bed, and Dissolved

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Velocity determines...

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the ability to erode and transport materials

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If velocity increases then...

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suspended load and bed load increases

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Bend

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faster at the outside of the meander

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Velocity is determined by...?

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Slope (gradient), shape, and roughness of channel

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As the gradient increases...

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the velocity increases

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Channel shape determines

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frictional drag, wide and shallow is inefficient, semicircular is efficient

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Channel roughness- smooth channel means...

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=efficient flow

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Stream Discharge (Q)

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discharge- velocity times cross sectional area

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What are the effects of Urbanization?

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(+) Magnitude & frequency of flooding, (-) lag time between rain and flood, engineers try to mitigate flooding with channelization, levees, and dams

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Base Level

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elevation at which a stream enters a larger body of water

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Deposition

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rising base level

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Downcutting (erosion)

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falling base level

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Dendritic drainage network

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most common, underlying flat rocks

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Rectangular drainage networks

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right angle bends/joints and faults

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Radial Drainage Networks

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domes/volcanoes

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Trellis Drainage Networks

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alternating bands of resistant and less resistant rocks