geo final

How are fossils formed?

fossilization is the process of forming a fossiloccur in sedimentary rock

some in air-fall ash deposits

Types of fossils

Most commonly the preserved "hard parts" of organisms (shells, bones, etc)

Trace fossils are formed by the action of an organism—footprints, burrows, feeding marks, etc

Can provide great insight into the environment of deposition, climate, etc.

Frozen or dried fossilsCarbonized impressions

Organisms trapped in amber or tarPermineralized materials

Relative age

The age of a rock compared to the ages of rock layers

Numerical age

the age of a geologic feature given in years

Physical Principles - Uniformitarianism

The Principle of Uniformitarianism states that the processes observed today were the same in the past.

Physical Principles - Original Horizontality

settlements settle out of a fluid by gravity so they tend to be horizontaltilted sedimentary rocks must be deformed

Physical Principles - Superposition

In an undeformed sequence of layered rocks, each bed is older than the one above, and younger than the one below

Younger strata are on top, older strata are below

Physical Principles - Lateral Continuity

Strata often form in laterally extensive horizontal sheets

subsequent erosion dissects once-continuous layers

Physical Principles - Cross Cutting relationships

younger features cut across older features

faults, dikes, erosion, etc are older than the material that is faulted, intruded, or eroded

Physical Principles - Baked contacts

An igneous intrusion cools the invaded country rock

the baked rock must have been there first

Physical Principles - Inclusions

Inclusions are always older than the existing enclosing material

weathering must have come from older rock

Unconformity

surface/contact where rock unit above is considerably younger than the rock below

angular unconformity

rocks below the contact are tilted, folded, and most likely eroded

nonconformity

an erosion surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rocks

disconformity

a gap in sequence represents an interruption in deposition or missing rock units that are parallel to another

radioactive decay

the half-life is the time it takes for half of unstable nuclei to decay

the half-life is a unique characteristic of each isotope

physical continuity

Being able to physically follow a rock unit between two places.

Similarity of rock types

identifying similar rock types as continuous between regions; not always accurate; can be strengthened by the identification of a key bed (distinctive layer)

Faunal succession

correlating rocks based on presence of similar fossils; based on concepts of evolution and extinction

standard geologic time scale

eons \> eras \> periods \> epochs

Geologic time scale - Eons

Hadean (oldest)

Archean

Proterozoic

Phanerozoic (542 Ma - present)

Phanerozoic Eon

Paleozoic

Mesozoic

Cenozoic

Paleozoic Era

old life

appearance of complex life

Mesozoic Era

Middle life

dinosaurs abundant

an era ended by mass extinction

Cenozoic Era

New life

mammals and birds are abundant

most recent ice age was during the Pleistocene epoch

Current Era

currently in the Holocene epoch of the quaternary period of the Cenozoic era

Nonrenewable vs renewable

only in restricted geographic settings

form very slowly over millions of years replenished by natural process

fast enough to use continuously

Nonrenewable resources

fossil fuels

Uranium

Renewable resources

Geothermal - heat from the earth's interior

solar - sun

wind - wind turbines

hydroelectric - gravitational energy from falling water

tidal/wave - gravitational energy from waves

biofuels - derived from organic matter

mass movements

downslope motion of rock, regolith, snow, and ice

driven by gravity

important component of the rock cycle

Creep

slow downhill movement of regolith due to seasonal expansion and contraction of regolith

wetting and drying and freezing and thawing

creep operates as grains are moved perpendicularly to the slope as regolith expands and vertically downward by gravity as it contracts

Solifluction

slow downhill movement of tundra

melted permafrost slowly flows over deeper frozen soil

Slumping

mass movement by sliding of regolith as coherent blocks

occurs along a spoon-shaped failure surface

slumps occur in a variety of sizes and have highly variable rates of motion

Lahars

Volcanic ash from recent or ongoing eruptions mixes with water from heavy rains or melted glacial ice

Submarine debris flows

turbidity currents move as a turbulent cloud of suspended sediment that deposit graded beds

Factors affecting slope strength

relief - steeper slopes > more mass movement

climate - more rainfall > larger water problems, accelerates chemical weathering

Landscapes

the landscape is the character and shape of the land surface in a region

Landforms

landforms are the individual shapes that make up landscapes(valleys, cliffs, beaches, etc)

Erosion and Deposition

Erosion - the grinding away and removal of the earth's surface

deposition - the accumulation of transported sedimentboth occur at different rates

energy drives landscape evolution

internal - heat in earth

external - energy from the sun

gravitational - downward pull on material at higher elevation

Anatomy of a slump

slumps have a characteristic head scarp (exposed upper part of the failure surface) and a bulging toe (where material piles up)

Running water

is the most important geologic agent in the erosion, transportation and deposition of sediment in almost all landscapes (even deserts!)

Stream

any body of running water, confined to a channel, that runs downhill under the influence of gravity

Drainage Networks: Dendritic

Drainage networks often form geometric patterns that reflect underlying geology

dendritic networks from when the underlying substrate is generally homogenous

Drainage Networks: Radial

develops from a point uplift (mesa, volcano)

Drainage Networks: Rectangular

where vertical joints break up the ground and streams follow existing fractures and join at right angles

Drainage Networks: Trellis

develops in deformed strata with alternating resistance and weak rocks

Drainage Networks: Parallel

Streams that develop parallel courses on a steep uniform slope

Drainage basin

catchment or watershedland area that drains into a specific trunk stream

Drainage divide

separates adjacent drainage basins

a raindrop flows into one basin or the other, depending on which side of the divide it falls

Continental divide

a continental divide separates flow into different oceans

Factors affecting stream erosion and deposition

velocity

gradient

channel slope and roughness

discharge

Stream transportation of sediment

bed load

suspended load

dissolved load

bed load

large or heavy sediment particles that travel on a streambed

move by traction or saltation

suspended load

sediment light enough to remain indefinitely above the stream bed

dissolved load

soluble products of chemical weathering

Stream valley development

downcutting - process of deepening a valley by erosion of the streambed

narrow slot canyons form when streams downcut their beds

v shaped valley typically form from downcutting combined with mass wasting and sheet erosion

meandering streams

the highest velocity water erodes the outside of a bend (cut bank) the inside of the bend (point bar) is the site of sediment deposition

meandering streams landforms

meander cutoffs occur when cut banks converge and a meander neck thins

meander neck is eroded away

the meander cutoff forms a crescent-shaped oxbow lake

Sediment Deposition

delta - body of sediment deposited at the mouth of a river when flow velocity decreases

shape surface marked by shifting channels

shape of a delta depends on the balance between sediment supply and erosive power of waves/tides

Flooding

Flooding is a natural process on all rivers

Floodwaters are devastating to people and property. Discharge and velocity increase and flow spills out of the stream channel, immersing adjacent land.

Water scours floodplains, altering the landscape and destroying structures.

Recurrence interval: the average time between floods of a given size; "100 year flood" occurs on average once every 100 years (1% probability in any given year)

Types of flooding

seasonal floodin

gurban flooding

flash floods

Common mass movements

slowests

olifluction and creep

slumping

lahars and mudflows

debris flows

rockfalls and rockslides

fastest

Continental Margins

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PassiveActive

Passive continental margins

little movement

continental shelf

continental slope

continental rise

abyssal plain

Active continental margins

active movement

continental shelf

continental slope - extends down into a deep oceanic trench

Features of the Sea Floor

Continental shelf

continental slope

continental rise

Continental shelf

shallow (0-500m)gently sloping

Continental slope

descends from 500m to 4km

Continental rise

transition zone from 4km to 4.5km

abyssal plain

low relief bottom below 4.5kmover 75% of the sea floor

Bathymetry

the measurement of depth of waterocean floor is mostly flat except near plate tectonic structures

Gyres and Eddies

gyres are produces when the coriolis effect causes surface currents to make complete loops

Characteristics of Ocean Waters

ocean water salinity ~35%temperature - sea surface 17CThermocline - a sharp decline in temperature

Ocean water temperatures

temperature changes with depth

oceanic bottom waters are close to the freezing point of freshwater

regional variations in sea surface temperature (linked to overall climate)

ocean currents

surface winds drive currents in the upper ocean

deep below the surface ocean circulation is driven by changes in seawater density (salinity and temperature)

Longshore currents

movement of water near & parrallel to shore

Rip currents

Narrow streams of water that break through sand bars and drain rapidly back to sea

Types of coasts

depositional

erosional

drowned

uplifted

organic

depositional coasts

gently sloping plains with few visible effects of wave erosion

shaped by sediment deposition primarily from longshore drift current

erosional coast

steep, rocky visibly changed by wave erosion

drowned coasts

caused by sea level rise

organic coasts

living organisms control landforms

uplifted coasts

elevated by tectonic forces or crustal rebound after melting ice sheets

depositional coasts - Barrier Islands

waves sculpt sand into elongate offshore bars parallel to the shoreline

in regions with abundant sand, offshore bars can rise above sea level to become barrier islands

barrier islands protect a shallow, quiet water lagoon that accumulates mud

Headland erosion

sea caves form as wave refraction focuses wave attack on a promontory

continued attack forms a sea arch

eventually the sea arch collapses leaving a sea stack

Drowned coasts - estuaries

river valleys that are flooded by sea level risedevelop as river canyons taht cut into the continental shelves during glacial sea-level lowstands

Drowned coasts - fjords

glacially cut valleys flooded by rising sea level

organic coasts - coastal wetlands

Organic coasts are those in which living organisms control landforms along the shore

organic coasts - coastal reefs

coastal reefs grow in tropical marine settings and create largely rocky structures of cemented skeletons

coral reefs are among the most biologically productive ecosystems

Causes of Coastal Variablility - Relative sea-level change

glaciation/deglaciation traps or releases water

during the last ice age, sea level was lower, exposing more land

Coastal stablilization techniques

groins

jetties

breakwaters

Porosity

groundwater resides in subsurface pore spaces, the open spaces within any sediment or rock

total volume of open space

pores can be filled with water, air, mineral cement, or other fluids

Permeability

the ease of water flow due to pore interconnectedness

high permeability material allows water to flow readily

low permeability material allows water to flow slowly

Aquifer

high porosity

high permeability

unconfined - at the surface, easily contaminated

confied - lies beneath an aquitard, less suspectible to pollution

Aquitard

low permeability

low porosity

hinders water flow

Water table

the top of the groundwater reservoir in the subsurface

water table separates the unsaturated (vadose) zone from the saturated (phreatic) zone

capillary fringe forms at the boundary

water table depth

depth varies with the climate and seasons

humid regions - close to the surface

dry regions - deep below the surface

Hydraulic Head

the potential energy driving flow

elevation above sea level.

pressure by the weight of overlying water

flow always moves from high to low hydraulic head

Cone of depression

pumping groundwater affects the water table

if water is extracted faster than it is replaced, a cone of depression develops around the well