OU geology 1114 exam 2

Professor Sanders class

Physical weathering

Breaks rock into smaller pieces without changing its minerals (frost wedging, root wedging, thermal expansion, abrasion)

Chemical weathering

Changes the minerals themselves (dissolution, oxidation, hydrolysis); sped up by physical weathering exposing more surface area

Parent material

The rock or sediment that weathers to form soil; its composition, grain size, and fractures control soil type and weathering rate

ClORPT

Climate, Organisms, Relief, Parent material, Time: the five factors controlling weathering and soil formation

How caves form

Weak carbonic acid in groundwater dissolves limestone along fractures and bedding planes at or below the water table; later drained passages host stalactites and stalagmites

Karst

Landscape shaped by dissolution of rock (sinkholes, caves, disappearing streams)

Soil

Weathered rock mixed with organic matter, water, and air; supports plants, stores and filters water, cycles nutrients

Soil horizons (top to bottom)

O (organic), A (topsoil), E (leached), B (accumulation of clays and minerals), C (partly weathered parent material)

Slope stability

Balance of driving forces (gravity, water weight) against resisting forces (friction, material strength)

Slope failure

Occurs when driving forces exceed resisting forces; triggered by heavy rain, earthquakes, undercutting, vegetation removal

Types of slope failure

Fall, slide, slump (rotational slide), flow (debris flow, mudflow), creep; also classified by material (rock, debris, earth)

How we study slope failures

Mapping past failures and hazard zones, aerial/satellite/LiDAR imagery, GPS and instruments to measure movement, testing material strength and water content

Sedimentary environments

Continental (rivers, alluvial fans, lakes, deserts, glaciers); transitional (deltas, beaches, tidal flats); marine (shelves, reefs, deep sea)

Clast

A fragment of weathered rock; classified by size: clay, silt, sand, granule, pebble, cobble, boulder

What controls clast size, shape, and sorting

Energy of the transporting medium, transport distance, and source rock; more transport gives smaller, rounder, better-sorted clasts

Lithification

Turning loose sediment into rock through compaction and cementation

Compaction

Burial squeezes sediment grains together and forces out water

Cementation

Minerals (calcite, silica, iron oxide) precipitate in pore spaces and glue grains together

Clastic sedimentary rocks

Made of fragments of preexisting rock (sandstone, shale, conglomerate)

Nonclastic sedimentary rocks

Formed by chemical precipitation or biological activity (limestone, chert, rock salt, coal)

Why sedimentary rocks have beds

Changes in sediment supply or energy over time (floods, storms, sea-level shifts); bedding planes mark each depositional episode

Cross beds

Inclined layers formed by migrating ripples or dunes; point downcurrent

Graded beds

Coarse grains at the bottom fining upward as a current loses energy (e.g., turbidity currents)

Formation of sedimentary rocks (sequence)

Weathering, erosion, transport, deposition, burial, lithification

Stratigraphic section

Vertical column showing rock layers, thickness, and rock type; oldest at the bottom; fining upward suggests deepening water, coarsening upward suggests shallowing

Importance of sedimentary rocks to society

Oil, gas, coal; building materials; aquifers; salt, gypsum, phosphate, iron ore; fossils and Earth history

Metamorphism vs. deformation

Metamorphism changes minerals or texture in the solid state (heat, pressure, fluids); deformation changes shape or position (folds, faults)

Fault

A fracture along which rock has moved

Hanging wall / footwall

Hanging wall is the block above the fault plane; footwall is the block below it

Normal fault

Hanging wall moves down; caused by tension

Reverse / thrust fault

Hanging wall moves up; caused by compression (thrust = low-angle reverse fault)

Strike-slip fault

Blocks slide horizontally past each other (e.g., San Andreas)

Anticline

Arch-shaped fold with the oldest rock in its core

Syncline

Trough-shaped fold with the youngest rock in its core

Fold components

Limbs (sides), hinge (line of maximum curvature), axial plane (divides the fold)

Foliation

Alignment of platy minerals perpendicular to directed pressure (slaty cleavage, schistosity, gneissic banding)

Porphyroblast

Large crystal (e.g., garnet) that grows within a finer-grained metamorphic matrix

Nonfoliated metamorphic rocks

Form by recrystallization without alignment (marble, quartzite)

Metamorphic grade sequence (foliated)

Slate (low), phyllite, schist, gneiss (high); grain size and foliation coarseness increase with grade

Agents of metamorphism

Heat, pressure (confining and differential), and chemically active fluids

Settings of metamorphism

Contact (near intrusions), regional (mountain belts), subduction zones (high pressure, low temperature)

Superposition

In undisturbed layers, older rocks lie below younger rocks

Original horizontality

Sediment is deposited in flat, horizontal layers

Lateral continuity

Layers extend sideways until they thin out or hit a barrier

Cross-cutting relationships

A feature that cuts across rock is younger than the rock it cuts

Inclusions

Fragments within a rock are older than the rock that contains them

Unconformity

Surface representing a gap in the rock record from erosion or no deposition; types: angular unconformity, disconformity, nonconformity

Relative dating

Orders events using geologic principles and fossils without giving numerical ages

Radiometric dating

Uses the ratio of radioactive parent to stable daughter isotopes and the known half-life to find a numerical age; works best on igneous rocks

Eons (oldest to youngest)

Hadean, Archean, Proterozoic, Phanerozoic

Eras of the Phanerozoic

Paleozoic, Mesozoic, Cenozoic

Age of Earth

About 4.5 billion years

Great Oxidation Event

Oxygen built up in the atmosphere about 2.4 billion years ago

Cambrian explosion

Rapid appearance of complex animals about 540 million years ago

End-Permian extinction

Largest mass extinction, about 252 million years ago

K-Pg extinction

About 66 million years ago; ended the dinosaurs and opened the way for mammals to diversify

Weather vs. climate

Weather is short-term atmospheric conditions (hours to days); climate is the long-term average (30+ years)

Why wind occurs

Uneven solar heating creates pressure differences; air flows from high to low pressure

Three-cell circulation model

Hadley (0-30 degrees), Ferrel (30-60), Polar (60-90) cells in each hemisphere; air rises at the equator and 60 degrees, sinks at 30 degrees and the poles

Global wind belts

Trade winds, westerlies, polar easterlies

Coriolis effect

Earth's rotation deflects moving air and water to the right in the Northern Hemisphere and to the left in the Southern

How water transfers heat globally

Ocean currents carry warm water poleward and cold water toward the equator; evaporation moves latent heat that is released on condensation

Surface ocean currents

Driven by wind and the Coriolis effect; form gyres (clockwise in Northern Hemisphere, counterclockwise in Southern); warm currents on western boundaries, cold on eastern

Thermohaline circulation

Deep ocean currents driven by differences in temperature and salinity

Where rainforests form and why

Near the equator where air rises, cools, and drops heavy rain

Where deserts form and why

Near 30 degrees latitude where dry air sinks; also rain shadows behind mountains and along cold coastal currents

Evidence of climate change

Rising CO2 and global temperature, retreating glaciers and sea ice, rising sea level, ocean warming and acidification, ice cores and sediment records

Reasons for studying the seafloor

Understanding plate tectonics, resources (oil, gas, minerals), climate records in sediments, hazards (earthquakes, tsunamis)

Seafloor age pattern

Youngest at mid-ocean ridges, older with distance; oldest about 180 million years

Seafloor sediment pattern

Thin or absent at ridges; thickens toward the continents

Mid-ocean ridge

Where new oceanic crust forms by seafloor spreading

Trench

Deep seafloor depression where oceanic plates subduct

Abyssal plain

Flat, deep seafloor covered by sediment

Seamount

Underwater volcano

How atolls form

Volcanic island gets a fringing reef; as the island subsides the reef grows upward into a barrier reef; when the island sinks, a reef ring (atoll) remains around a lagoon

Small seas of the Pacific and Eurasia

Marginal or back-arc basins formed behind subduction zones as the overriding plate stretches and thins (e.g., Sea of Japan)

Passive margin structure

Within a plate; wide shelf, gentle slope and rise, thick sediment wedge, little earthquake or volcanic activity (e.g., U.S. East Coast)

Active margin structure

At a plate boundary; narrow shelf, steep slope, deep trench, frequent earthquakes and volcanoes (e.g., U.S. West Coast)