GEOLOGY 101: EXAM 2
67 Cards in this Set
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What is weathering and erosion, how do they differ?
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Weathering is the process by which rocks are broken down at the Earth’s surface.
Erosion is the process that moves pieces of rock or weathering products and deposits them elsewhere.
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What factors control the rate of weathering?
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Rock properties
Climate
Soil and vegetation
Length of exposure
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high rainfall hot temperatures leads to?
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Fast weathering
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Hydrolysis
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Water reacts chemically with minerals and breaks them down
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Dissolution
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Chemical weathering during which minerals dissolve into water
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Oxidation
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Transforms iron bearing minerals into a rusty brown mixture of iron-oxide and iron-hydroxide minerals
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Jointing
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Rocks buried deep in the earth rise closer to the earths surface and cause the rock to break and change shapes
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Frost wedging
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When water is trapped in a joint it forces a joint open and forces it go grow
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Salt wedging
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Dissolved salt in groundwater precipitates and grows as crystals in open pore spaces in rocks
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Root wedging
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As roots grow they can push joints open
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Thermal Expansion
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When the outer layer of a rock heats up and then cools down causing the outer part of the rock to break off in sheet like pieces
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Animal attack
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Animals push open cracks and move rock fragments
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Granite would be affected by what type of chemical weathering?
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Hydrolysis
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What are factors that affect soil forming processes?
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Climate, substrate composition, slope steepness, wetness, time, vegetation type
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Physical Weathering
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Breaks rocks into smaller pieces
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Chemical weathering
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Converts minerals and rocks into altered solids, solutions and precipitates
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Type of chemical erosion that would affect Iron
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Oxidation
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Type of chemical erosion that would affect limestone
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Dissolution
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What is sediment and where does it come from?
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Mineral and rock fragments of the parent rock
Solid products of chemical alteration – clay minerals and iron oxides
Ions dissolved in rainwater and soil water
Comes from weathering
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Three types of sedimentary rocks
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Biochemical and organic
Clastic
Chemical
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How are clastic sedimentary rocks formed?
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Composed of pre-existing rocks
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How are biochemical sedimentary rocks formed?
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Comprised of the remains of organisms
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How are chemical sedimentary rocks formed?
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Composed of minerals precipitating out of solution
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Types of sedimentary structures
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Cross-bedding (wind or water) indicates direction of current
Graded-bedding (indicates waning of current)
Ripple marks (formed by waves or currents)
Desiccation mudcracks (exposed to wet dry cycles)
Bioturbation (burrow marks left in sediments by animals)
Tracks and trails
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Sedimentary Environments
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Glacial environments
Mountain stream environments (Conglomerate)
Alluvial-fan environments (conglomerate)
Sand-dune environments
River environments (sandstone, shale)
Lake environments
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Evaporites
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Salts form as water evaporates from a shallow basin
ex great salt lake
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Lithification
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Hardening of soft sediments into rock with compaction and cementation
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Diagenesis
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The chemical and physical changes that transform sediments into rock
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Factors controlling metamorphism
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Temperature (minerals convert to new higher temperature minerals), pressure, fluids (hot water can transport ions), diffusion (movement of atoms due to heat form new minerals), recrystallization (crystals grow larger and change shape)
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Two types of metamorphic rocks
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Foliated
Non-foliated
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Crystal size and foliation increase
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as metamorphism increases
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Foliated definition
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Refers to parallell surfaces and/or layers
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Foliation occurs with
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High pressure
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Mudstone goes to what
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Shale, slate, phyllite, schist, gneiss and gets coarser
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Index minerals
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Used in metamorphic rocks as indicators of peak pressure and temperature
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How can index minerals be used to constrain the temperature and pressure conditions of metamorphism
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The first appearance of a mineral defines an index zone that identifies the minimum peak temperature and pressure obtained
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High grade vs low grade metamorphism
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High grade = higher temperature and pressure
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Main types of metamorphism: Contact metamorphism
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Heat rising from igneous intrusions - low-high temperatures, low pressure
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Main types of metamorphism: regional metamorphism
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Caused by deep burial or tectonic forces that increase pressure and temperature over broad regions, most common, low-high pressure, low high temperature
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Hydrothermal metamorphism
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high temperatures, low pressures
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Burial metamorphism
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low temperatures, low pressures
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Deformation (fault metamorphism)
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very low temperatures, high pressure (san andreas fault)
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Absolute dating
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determining events actual time
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Relative dating
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putting rocks/events in proper order done by
looking at the physical relationships between the rock units based on their stratigraphy.
Stratigraphy- The description, correlation, and classification of strata in sedimentary rocks.
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Superposition
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Each layer of sedimentary rock must be younger than the one below it
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Inclusion
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rock containing inclusion is younger than inclusion
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Angular uncomformity
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Different directions formed when layers undergo folding, erosion produces a flat surface and sea level rises and new layers of sediment accumulate
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Nonconformity
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Sedimentary rocks in contact with igneous or metamorphic rocks (non similar rock types in contact with each other).
Forms when a pluton intrudes, erosion cuts down into the crystalline rock, new sedimentary layers accumulate above the erosion surface
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Disconformity
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Rocks above and below disconformity are parallel
Forms: layers of sediment accumulate, sea level drops and erosion surface forms, sea level then rises
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What is an index fossil?
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Unique and easy to identify, lived for a short period of time, widely distributed
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Eons
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Precambrian: >543 million years ago
Phanerozoic: 543 million and below
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Eras
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Paleozoic: 251-543 mya
Mesozoic: 65 - 251 mya
Cenozoic: 65 and below
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Hypothesized Event That made the dinosaurs go extinct
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Crater around Central America
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Types of strain: Elastic deformation
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temporary strain, goes back to form when tension is released
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Types of strain: Plastic deformation
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permanent strain, folds and bends (folds)
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Types of strain: brittle failure
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permanent strain, cracks or fractures (faults)
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Hinge
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Line along which curvature is greatest
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Limbs
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Side of fold that display less curvature
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Axial Surface
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Imaginary plane that divides the fold in half
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Anticline
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Upfold - a shaped. oldest on inside. Fold arrows point away from each other
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Syncline
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Down fold - u shaped. oldest on outside divergent boundary. Fold areas point toward each other
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Plunging fold
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beds not parallel they converge, zig zag shape
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Domes
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Special type of anticlines. no fold axis bends dip from central point. look like circles on map view. Upside down bowl. Oldest formation on surface
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Basins
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Special type of cynclines. no fold axis bends dip from central point. look like circles on map view. Looks like a bowl. Youngest formation on surface.
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Monocline
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Stair-step like fold
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Anticline
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Convex upward arch
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Syncline
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Concave upward trough
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GEOLOGY 101: EXAM 2