Geology Final

relative age

relative age

cronological order of geological events/processes which is determined within field operations

absolute age

time before the present (yrs vs. billions of yrs) assumption is involved

uniformitarianism

processes occuring now that have happened in the past

principle of superposition

younger rocks on top of older rocks (used for dating geological events)

principle of original horizontality

sediments are deposited in flat horizontal layers (meaning tilting/folding must indicate later deformation)

principle of cross cutting relations

features such as dikes, faults, and ignenous rock intrusions are the youngest formation

Principle of Inclusions

included rock is older such as Xenoliths, pebbles and cobbles that are imbedded with in the rock

Principle of faunal sucession

evolutionary fossils can dictate how old a rock is

unconformity

time gap in the sedimentary record; different types such as angular unconformity, nonconformity, and disconformity

angular unconformity

deformation at an angle that results in a gap in sedimentary record

Nonconformity

deformation where younger sedimentary rock overlies eroded “basement” ingenous/metamorphic rocks

Disconformity

a sort of “hidden” unconformity where the layers above and below an eroded boundary have the same orientation

Hadean Eon (a part of the Pre-Cambrian)

• first time period of our planet

• Earth differentiated during this time (core, mantle, primitive crust)

• Moon formed during this period due to a large impact with a Mars-sized planet called Theia. Some of the mantle from Theia combined with some of Earth’s created the moon

• time of major impacts

Archean Eon (Pre-Cambrian)

• “late heavy bombardment”

• records Earth’s earliest life: biomarkers

  • Stromalites - bacterial mounds

• Late Archean: photosynthetic organisms

• Beginning of free oxygen (O2) in atmosphere

  • banded iron formations

    • photosynthetic organisms, which were making oxygen, reacted to iron that was dissolved within seawater to form iron oxide minerals on the ocean floor - creating banded iron formations

Proterozoic Eon (Pre-Cambrian)

• Eukaryotes evolve to have a cell nucleus

• multi-cellular organisms

• carbon films - small, dark compressions most resembling circles, ribbons, or leaves

• “Snowball earth” - amount of greenhouse gas was very little during this time, as global climate becomes colder larger areas of ice begin to form. Ice and snow reflect solar radiation back out into space and the earth becomes colder (positive feedback loop)

Phanerozoic Eon

• rich fossil records

• hard-shelled animals

• plants

• insects, dinosaurs, mammels

• life as we know it

Palaeozoic Era

• hard shelled organisms, vertebrates

• beginnings of life on land - predinosaur

Cambrian Period

• marks first preservation of animal shells

• invertebrates - trilobite

• faunal diversity

• rapid diversification followed by rapid disappearance

  • possibilities for this

    • natural selection

    • preservation

    • global warming

    • supercontinent breakup - Gonwana

      • produced shallow seas

      • expanding environmental niches

Ordovician Period

• first marine vertebrate animals

  • jawless fish - ostracoderm

• mass extinction of organisms near the end of the Ordovician

  • major glaciation centered in Africa → severe drop in sea level

  • 85% of species were lost

Devonian and Silurian

• vascular plants arose

  • mosses, ferns

  • has internal structure to move water and photosynthesis

• spiders, scorpions, insects, crustaceans

• jawed fish

  • sharks

• Silurian → first clear evidence of life on land

• Devonian → armored fish such as Dunkelosteus

  • transition from aquatic to land based organisms

Carboniferous Period

• Made up of Mississippian and Pennsylvanian Epochs

• reptiles

  • laid eggs

• giant insects

• large swamps

• development of limestone and higher concentrations of oxygen in the atmosphere

• Antrhropleura, Meganeura, and Pulmonoscorpian

Permian Period

• supercontinent of Pangea

• age of reptiles

  • lystrosaurus - formed herds

  • dimetrodon - predatory with sail on back

  • postosuchus - ambush predator → thought to be bipedal

• mass extinction at end

  • 90% went extinct

    • reasons:

      • volcanic activity on a massive scale in the Siberian Traps

      • produced carbon dioxide on massive scale

      • global warming followed which may have increased ocean water temperatures which would have been toxic for marine life

Mesozoic Era

“age of the dinosaurs”

Triassic Period

• land vertebrates

• first true dinosaurs

  • Coelophysis

    • plateosaurus

• first mammels

  • Ezostrodon

Jurassic Period

• dinsaur renaissance

• air, land and sea dinos

  • flying reptiles NO BIRDS

    • Pteranodon

• Sauropods

  • evolved from Plateosaurus

  • designed depending upon the type of vegetation that they ate

    • apatosaurus - swallowed large chucks of plants without chewing → consistent with jaw structure

    • Brachiosaurus -swallowed chunks whole as well → consistent with jaw structure

Cretaceous Period

• pangea begins to break apart

• extensive swamps

• flowering plants

• T-rex, Spinosaurus, Argentinosaurus, Deadnoughtus

• ended with mass extinction

  • all dinosaurs

    • possible causes

      • climate change

      • plate tectonics - continental configuration

      • disease

      • competition with mammels

      • volcanic eruptions

      • meteorite impact

        • can cause Tsunami, dust in stratosphere resulting in global cooling

      • Deccan Traps, India → started the climate shift and metorite finished the dinosaurs off

Cenozoic Era

• “age of mammals”

• Paleogene and Neogene

• see early forms of modern mammels in Eocene and Oligocene

• Moerotherium and Deinotherium → Elephants

• Ambulocetus and Basilosaurus → Whales

  • Ambulocetus means “walking whale”

  • ate fish and other animals that strayed into water

  • powerful jaw and bite

• Indricothere

  • rhinocerous is the closest living relative

Quanternary Era

• where we are now in the time period

• glacial cycles

• saber-tooth cats did not exist

• human evolution

  • australopithecus → Homo erectus → Homo sapiens

• Holocene Epoch wraps up the Quaternary

  • proliferation of humans

Drainage

consists of all forms of water reaching Earth’s surface

water shed

collects water from a broader region resulting in catching or drainage basins

permanent

running water all year round

ephemeral

only contains water after rain/melt events. Dried out bed is called a dry-wash

Longitudinal profile

• heavily affected by geology

• steep near headwaters

• affected by resistant rock units

  • waterfalls

meandering

• water flows in a curvy, bendy path like a snake

• gets more exaggerated as time goes on

• process of deposition and erosion

  • point bars

    • a low, curved ridge of sand and gravel along the inner bank of a meandering stream

  • cut banks

    • located on the outside of stream bend. shaped like a small cliff and formed by the erosion of soil as the stream collides with the river bank

  • oxbow lakes

    • starts out as a curve or meander in a river, however, over time the lake finds a shorter course to follow thus cutting off the meander and it becomes a oxbow lake

Floodplains

streams will overtop its banks where the velocity will then suddenly decrease

levees

barriers that formed coarser sediments fall out of suspension

causes of flooding + flood events

excess rainfall, rapid snowmelt, ground saturation, urbanization - prevents movement of water through soils, dam failure

100 yr flood events - reccurence interval of floods - every year has a 1% chance of flooding in any given year

2 yr flood events - 50% chance of flooding in any given year (frequent)

porosity

volume of pore space in rocks or sediment

Permeability

the connectivity of pores in rocks or sediments

water table

boundary between saturated and unsaturated zones

aquifers

• rock or sediment units that store water underground

• confined

  • layers of impermeable material are both above and below the aquifer are called a aquitard

  • water is under pressure

  • when water is penetrated by a well the water will rise above the acquifer

• Unconfined

  • top of the water table

  • able to rise and fall according to atmospheric pressure

  • usually closer to Earth’s surface than confined aquifers

Karst Aquifers, Limestone, and Calcite

• karts aquifers consist of interconnected cracks and caves and forms in the dissolution of limestone

• calcite:

  • carbonic acid passes through joints and cracks in limestone → calcite is dissolved from limestone → water now holds dissolved rock and when exposed to air in the cave it releases carbon dioxide gas → when carbon dioxide gas is release calcite is precipitated on cave ceilings (stalacite) and cave floors (stalagmite) and over time they will grow to meet and make a limestone column

cone of depression

• pumping water from a well in a water table aquifer lowers the water table near the well

• land area above the cone of depression is called the area of influence

• can change the natural direction of groundwater flow within the area of influence around the well

• wells can run dry and contamination could occur

  • acid mine waste, landfills, sewage, etc. can all lead to contamination of groundwater

  • remediation work is required to preserve health

Deserts

• an area of land that recieves no more than 25 cm of precipitation a year

• temperature is not part of the definition

• type and cause of desert aridity varies globally

subtropical deserts

• global atmospheric circulation

  • hadley cells: air rises at the equator → moisture comes from clouds and rains → air cools → air decends about fifteen to thirty degrees north or south of the equator

• descending dry air prevents cloud formation

• example: Sahara

Rain-Shadow deserts

• clouds form as air rises over mountains

• air is rained out by the time the air mass crests the mountain range

• mountains prevent cold air from travelling inward and by the time the air mass crests the mountain range the air is dry

• example: eastern california

coastal deserts

• related to cold ocean currents

• colder air masses with little to no moisture in them is dominant in these areas

• example: Atacama Desert, Chile/Peru

Continental interior deserts

• far from ocean or source of moisture

• moisture has already been used up by the time the air mass reaches the desert

• Example: Gobi Desert, Central Asia

Polar Deserts

• cold, dry air

• example: Antarctica

Dunes

• form when there is a high enough sediment supply and winds that can transport it

• called Eolian Features and is found on other planets such as Mars

Transverse Dunes

• characterized by slipfaces in one direction - representing unidirectional wind regime

Barchan Dunes

• crescent shape

• only one wind direction

Star Dunes

• multiple wind directions

• wind blows from varied directions throughout the year

Glaciers

• slowly moving mass or river of ice formed by the accumulation and compaction of snow on mountains or near the poles

• stream or sheet of recrystalized ice

• mostly frozen all year round

• flows under the influence of gravity

• snow at surface transforms into solid ice

  • snow → firn → ice

    • firn: granular snow not yet pressed into ice

mountain glaciers

• balance on accumulation and loss

• growth/accumulation at high elevation: snowfall

• loss/ablation at low elevation: melting/calving/sublimation

• flow: from high to low

• retreat/advance of glaciers happens at the toe of the glacier NOT at the origin

glacier types

• based on typography

  • cirque glacier

    • bowl-shaped, ampitheater like depressions that glaciers carve into mountains at high elevations

  • valley glacier

    • glacier that is flowing downward between walls of a valley

  • piedmont glacier

    • a valley glacier that spills out of mountains onto the flat foreland - spreading out to form a lobe

continental glaciers

• currently only in Greenland and Antarctica

• used to be on other continents

Glacial distinctive landforms

• glacial erosion

  • movement of glacial ice over bed

    • scrapes away rock

• cirques

  • bowl like structures in mountains (usually left behind by cirque glaciers)

• aretes

  • narrow ridge of rock that seperates two valleys

  • glaciers eroding towards each other

• horns

  • pointed peaks that are bounded on at least 3 sides by glaciers

  • caused by erosion

• hanging valleys

  • glaciers forming a U-shaped valley through erosion

glacial deposits

• glaciers move sediment

  • fine glacial “flour” to boulders

  • results in glacial till - sediment deposited by a glacier

    • supraglacial (on top of ice)

    • englacial (within the ice)

    • subglacial (below the ice)

  • morraines - materials left behind by a glacier

• deposits can be used to determine past glaciers

Creep

• takes place in soil zone

• movement caused by shear stress sufficient to produce permanent deformation

• can be seen in areas that experiene constant alternation of wetting and drying periods

• 3 types

  • seasonal - affected by seasonal changes in soil moisture/temperature

  • continuous - shear stress continuously exceeds strength of material

  • progressive - slopes are reaching the point of failure as other types of mass movements

slumping

• failure along a surface

• takes place in think unconsolidated deposits

• referred to as a rotational slide

  • portion or block of the slope ‘slides’ down as it ‘rotates’ around an axis parallel to the slope

landslides

• forces acting down-slope exceed the strength of the earth materials that compose the slopes

• 5 different modes

  • falls

    • loose material - talus

    • breaking off rocks from steep bedrock slopes

  • topples

    • loose blocks that lean forward before collapsing

  • slides debris/rock

    • debris (unconsolidated) and rock (consolidated)

    • rotational or translational (PICTURE)

  • spreads

    • extension of soil or rock

    • extrusion of underlying material

    • often lateral

  • flows

    • loose material

    • flow mixed with water downslope

    • occurs during rapid snowmelts or heavy rains

    • if the material involved is primarily sand-sized or smaller: mudflow

    • if the material involved is primarily gravel-sized or larger - debris flow

avalanches

• mass movement of snow

• can be caused by

  • heavy snowfall

  • deforestation - makes the slope less stable

  • vibrations - from EQ or noise

  • layering of snow - fresh snow can slide down ice

  • wind direction

slope failure

• angle of repose - slope stability

• depends on types of material

• many factors can trigger slope failure

  • EQ or vibrations

  • undercutting - an erosion of material at the foot of a cliff or steep bank

  • change in slope strength - weakening of slope surface

terracing

rip-rap

forestation

geological resources

• energy resources

  • hydrocarbon

  • oil, gas, coal

  • nuclear fuel

    • uranium

• mineral resources

  • nonmetallic

    • rock, sand salts

• ores

  • primarily in industrialized countries

  • massive amounts per person

ore requirements

• rock must contain ore minerals

• must be abundant enough to be economically extractable

  • depends on

    • concentration of ore minerals

    • ability to extract/extraction process

    • cost of metal

• form through magmatic processes

• concentration determined by crystalization

  • heavy ore minerals crystallize together

    • chromite

    • PGE (platinum group element) sulfides

• ores form via hot water interacting with rock

  • water infiltrates ground → interacts w/ magma → creates future ores

• magmatic intrustions are heat source

  • heat causes water circulation

  • extraction/reprecipitation of metals

    • mineralization (metal sulfides) - formed by hydrothermal processes

ores in sediments

• direct precipitation from waters

  • banded iron formations

• ores are then concentrated by erosion

• stream transport

  • ore vein on cliff side → ore falls and breaks up as it tumbles down → picked up and taken down stream via river current → grains are sorted within the mineral

  • called placer deposits - california gold rush

Energy

• nuclear

• geothermal

• hydrocarbon

  • fossil fuels

oil and gas

• oil forms in sedimentary basin

• burial → heating → migration

• source: oil formation rock

• migration: movement upwards

• reservoir: contains oil deposit

• trap: seals rock and prevents loss

oil reserves

• found in different parts around the world

• accurately measured by drilling

• recoverable economically at current prices with current technology

• must be extracted *

• different than resources

  • resources are geologically proven but not extractable

conventional gas

• trapped with oil

• more bouyant less viscous

unconventional gas

• harder to extract

• found lower in rock where it is harder to extract

• shale gas - unconventional reservoir

• horizontal drilling - fracking

environmental impacts

• emissions

• disruption of wild areas

• oil spills

• Co2 buildup -climate change

• acid rain

  • pyrite in coal releases CO2 when burned, forms sulfuric acid in rainwater and is augmented to form nitric acid

• Acid mine drainage

• contamination of wells and waterways

  • issue in Marcellus Shale region

  • fracking fluid contaminates groundwater

• induced earthquakes

  • from hydraulic fracture process

Venus

• atmosphere 92 times thicker than Earth’s

• dominated by carbon dioxide

• traps more solar radiation as a result

Mars

• 168 times thinner than Earth’s

• dominated by carbon dioxide

• ancient riverbed flows on Mars

  • used to have running water

  • flowing water = thicker atmosphere and higher temperatures

• ice caps - alternating sediments and ice = seasons

Earth

• atmosphere is different from venus because of plate tectonics and the recycling of materials

• venus and mars do not have plate tectonics

• warm periods/ice ages

• variable resolution record

  • poor resolution in distant past

  • better resolution closer to the present

past climate determination

• certain fossils can record climate conditions

  • fossil pollen

    • often in lake sediments

    • grass pollen = warmer

    • tree pollen = colder

  • sea level provides information

    • relative extent (volume) of world’s oceans are preserved in sedimentary record

      • functions of temperature and glacial extent

oxygen isotopes

• reveals past climate through glaciation

• ratio of oxygen 16 to 18

  • oxygen 18 is heavier and harder to evaporate

• non-glacial period

  • ratio of oxygen 16 to 18 is more similar because of water runoff

• glacial period

  • more oxygen 18

  • ocean water is more isotopically heavy

Variation in Earth’s climate

• Short term

• tree rings

  • grow wider in warm, wet years and they are thinner in years when it is cold and dry

• lake cores (varves)

  • seasonal sediment alternations which appear to represent annual cycles

• Long term

  • extensive warm periods

  • ice ages

climate forcing

• plate tectonics - ocean currents, sea levels

• greenhouse gases

• volcanoes

• weathering

• biota

• the CO2 connection

CO2

• greenhouse gas

• traps heat radiating from the Earth’s surface

• CO2 correlates with temperature in the geological record

• depends on the global carbon cycle

solar luminosity

• “faint young sun paradox”

• early sun was smaller and created less energy

Milankovitch Cycles

• explain glacial-interglacial variations

• recent rapid swings in climate

• three types of Earth’s orbital movements

• affect how much solar radiation reaches the top of the Earth’s atmosphere

Eccentricity

• change in the shape of the Earth’s orbit

• 100,000 year periodicity

• affects season length

axial tilt

• change in the Earth’s rotational axis tilt

• 41,000 year periodicity

• less tilt = glacial periods

• more tilt = inter-glaciations

axial precession

• “wobble” of the Earth’s axis

• 23,000 year periodicity

• makes seasonal contrasts more extreme in one hemisphere than the other

zig-zag in graph

• caused by seasons

• winter months pull less CO2

• shows influence of plants in the atmosphere

• CO2 has never been higher in the past millions of years

what can we expect in the future for climate change?

• fossil fuels short circuit the carbon cycle

• exacerbated by deforestation

• higher average global temperatures

• continued loss of ice - sea levels rising

• increased number of extreme storm events