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78 Cards in this Set
- Front
- Back
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Zone Fossils
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can be used to correlate zone successions
short stratigraphical range wide geographical distribution abundant graptolites + cephalopods (ammonoids + nautiloids) |
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Graptoloid Graptolites (zone fossils)
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colonial
planktic - float/drift in water have a lophophore to filter-feed with morphoseries Ordovician-Devonian |
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Cephalopods (zone fossils)
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not colonial
benthonic - live on sea floor siphuncular tube runs through chambers to control gas suture line → joint between two or more hard elements of an organism morphoseries - coiling of shell Jurassic - Cretaceous |
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Fossil modes of life
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benthonic - on sea floor
planktic - float in water epifaunal - on top of sea-floor sediments infaunal - filter-feed within sea-floor sediments |
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Correlation
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Process of defining the age relationships between rocks at different localities
Often based on fossils as they are preserved in the rocks |
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Trace Fossils
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Organisms travel over or through sediment & leave their mark
Tracks - imprints left by feet/appendages Trails - continuous markings Burrows - a hole or excavation dug for feeding/protection into soft substrates Boring - digging into hard substrates |
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Mold Fossil
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Forms when an organism is buried in sediment and then decays and dissolves leaving a mould the shape of the animal (negative shape)
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Cast Fossil
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Forms when the empty shape of a mold fossil is filled with precipitate minerals (positive shape)
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Body Fossil
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Fossilised remains of the actual animal/organism
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Preservations
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Enhancers
→ rapid burial in fine substrate → minimal transport → anoxic environment Limitations → decay → physical destruction/ scavenging |
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Preservational Traps
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inhibit decay
rapid burial in very fine sediment early mineralisation of soft tissues → amber → permafrost → peat-bogs |
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ontogeny
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the origin and development of an organism from embryo to adult
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ecdysis
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the process of shedding the old skin (in reptiles) or casting off the outer cuticle (in insects and other arthropods)
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holaspis
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A stage in the development of a trilobite where the creature has gained their adult segmentation, but continues to molt and grow
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coprolite
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fossilised dung
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hermatypic corals
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build reefs
live in shallow waters have symbiotic algae → ahermatypic do not build reefs |
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corals
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a hard skeleton left behind by marine polyps
solitary → live alone compound → live in groups, contain many corallites overall shape of colonies is strongly influenced by environmental conditions shape and interrelationships of the individual corallites is genetically defined |
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coral reefs
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formed by growth of corals and other organisms which create a framework for sediment to be trapped in
restricted to the tropics wave resistant complex ecological and sedimentological systems atolls - island consisting of a ribbon reef that nearly or entirely surrounds a lagoon |
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coral reef formation
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larvae settle on sea floor, some distance from shore
scattered mounds of larvae develop and become substrates for further colonisers mounds join up and sediment is trapped between them growth continues into the wave zone storms break off parts of colonies and transport them shoreward regrowth keep pace with loss, as wave energy increases the biological diversity increases due to more nutrients + light this causes the coral colony shape to change |
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camels → cambrian
shelled animals + mineralised parts ordinarily → ordovician fish-like vertebrates + teeth sit → silurian land plants down → devonian large trees carefully → carboniferous forests + reptiles their → triassic dinosaurs, first mammals perhaps → permian huge extinction |
joints → jurassic
birds creak → cretaceous extinction of dinosaurs possibly → palaeocene age of mammals early → eocene oiling → oligocene might → miocene prevent → pliocene permanent → pleistocene rheumatism → recent (holocene) age of humans |
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terranes
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a fault-bounded area or region with a distinctive stratigraphy, structure, and geological history
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orogeny
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a process in which a section of the earth's crust is folded and deformed by lateral compression to form a mountain range
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solifluction
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the gradual movement of wet soil or other material down a slope, especially where frozen subsoil acts as a barrier to the percolation of water
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percolation
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to filter gradually through a porous surface/substance
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aquifer
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An underground body permeable rock which can contain or transmit groundwater
→ confined - between layers of impermeable rock and thus under pressure → unconfined - at the same level as the water-table and not under pressure → groundwater spring - a location where groundwater naturally emerges from the Earth's subsurface |
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water-table
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Level below the earth's surface at which the ground becomes saturated with water. The top of an unconfined aquifer
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Calcite compensation depth (CCD)
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the depth in the oceans below which the rate of supply of calcium carbonate lags behind the rate of solvation, such that no calcite is preserved
reflects the amount of carbon dioxide present in the atmosphere, and thus gives clues about climate on geological timescales |
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Snowball Earth
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late Proterozoic
ice + snow reflects suns rays = colder = more ice + snow.... continuous if oceans were frozen = no snow/rain → no glaciers as no water would evaporate to create clouds → less weathering → CO2 build up as volcanoes continue to produce CO2 → greenhouse effect would heat up Earth (this may be how snowball earth ended) |
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Life in Ice ages
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A few life forms can survive in the dark frozen ocean as hot springs contain many minerals
after snowball earth there was huge empty spaces for evolution → change from single to multi-cellular organism occurred after this event |
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ablation + accumulation
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Ablation
→melting →evaporation →calving → split off →sublimation → change from solid to gas or vice versa without becoming liquid Accumulation →snow+ice →avalanches →re-freezing of melt water |
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Glacier Climate indicators
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fossil distribution
pollen insects micropalaeontology coral reefs |
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Milankovitch Cycles - orbital forcing mechanisms
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describes the collective effects of changes in the Earth's movements upon its climate
eccentricity → orbit shape changes tilt → angle towards the sun precession → wobble of the Earth around its axis |
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Evidence of past glaciers
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u-shaped valleys
glacial deposits → dropped when glacier melts, very poorly sorted glacial striation → scratches caused by moving ice lakes, bogs and mires sea level change, river terraces |
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Erosion + Weathering sediment types
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Clastic
→ fragments of weathered rocks rich in silica + carbonates Chemical and Biochemical → dissolved products of weathering occurs when there are changes in the chemical environment → precipitation → evaporation → biological activity → organic sedimentation - oil+gas chemical weathering – CO2 combines with silicates to form calcite/quartz less CO2 in atmosphere if more weathering = colder |
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Event Horizon
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A thin, distinctive layer of soil in a vertical cross-section of land useful for stratigraphic correlation
volcanic ash → travel very far by winds magnetic reversals → magnetic minerals align themselves to the magnetic field of the Earth mass extinctions → change in the abundance or type of fossils present meteor impacts → creates crater and layer of impact projecta, melted rock spreads widely The Human Event Horizon → agriculture, construction, climate change, pollution + fossils |
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oxygen isotope evidence of ice age
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oxygen occurs naturally in two different isotopes (oxygen 16 and oxygen 18)
glaciers absorb oxygen 16 most as it is lighter → change the ratio of oxygen animals use oxygen from water to create shells → they absorb the oxygen ratio as it is → through their fossils we can figure out what the oxygen isotope ratio was at that time |
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Dating processes
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Isotopes → radioactive decay
half live = decay rate 2 main types of carbon isotopes → carbon-12 (6 neutrons, 6 protons) and carbon-13 (7 neutrons, 6 protons) organisms prefer 12C, if life become difficult the 13C/12C ratio drops → less 12C Magnetic → some rocks record the Earth's magnetism when they form, you can then work out where they were formed |
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supercontinent cycle
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the continents drift together and form one supercontinent and then break up again, this is a continuous process – cycle
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Slope failure
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slope stability depends on the balance of stress v strength
stress as the driver of the failure strength as the resister of the stress → gravity → wet soil = more mass → water between the pores is under more pressure and so the particles get pushed apart releasing friction → seismicity – earthquakes the shaking decreases the frictional resistance and cohesion → erosion at base of slope |
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Slope failure movement processes
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→ creep - slow, deforms over time
→ debris - fast, large particles, mix of water and sediment → slumping - slope fails due to failed base and leave a curved scar → mudflow - watery + fast → lahars – very destructive Angle of repose - steepest angle at which a slope is stable |
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meandering rivers
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single thread → one channel
sinuosity > 1.5 → down channel distance/straight line distance → where one sin curve is complete lower slopes + lower discharges finer grained sediment → harder to erode oxbow lakes |
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braided rivers
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multiple channels which divide and rejoin
→ unstable, migrating islands higher discharges + steeper slopes → erodes easily = unstable coarser grain sediment in banks and bed |
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anastomosing rivers
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relatively little with small discharge
similar to braided rivers but the islands are stable multi-thread channel |
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river discharge
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discharge = cross-sectional area . avVelocity
→ Q=A * avV |
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river sediment transport
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suspension
→ suspended particles carried along by current saltation → particles bouncing along river bed traction → particles sliding and rolling along river bed |
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bedforms
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sedimentary structures on the bed of the channel
ripples small → low velocities move down stream internal structure is inclined → cross bedding dunes larger → high velocities may have ripples climbing up the back of the dune also cross bedded due to sediment falling down the slope at the angle of the slope can figure out the river flow direction from this cross bedding |
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river competence + capacity
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Competence
→ maximum particle size that it is able to transport capacity → how much water + sediment it can hold |
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Erosional forces on a river
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Hydraulic action → the force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.
Abrasion → rocks carried along by the river wear down the river bed and banks. Attrition → rocks being carried by the river smash together and break into smaller, smoother and rounder particles. Solution → soluble particles are dissolved into the river |
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floodplain
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An alluvial plain that experiences occasional or periodic flooding.
Features - landforms produced by stream erosion, sediment transport, and deposition → point bars sand and gravel that accumulates on the inside bend of streams and rivers → oxbow lakes crescent-shaped lake that results from the meandering course of a river → terraces remnants of earlier floodplains at a higher elevation → meander scars scars left by previous meanders which occur when a river alternates its direction of flow due to the downward slope of a valley |
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desert types
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→ subtropical
dry air above and below equator → rain shadow mountainous regions cause air to rise and condense, dropping its moisture as it passes over the mountains → coastal cold upwelling seawater cools the air and decreases its ability to hold moisture → continental interior far from source of moisture → polar cold dry air prevails and moisture available remains frozen |
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dune formations
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→ barchans
resemble crescent moons – tips point towards wind direction form where there is a limited supply of sand, relatively flat ground, and a fairly constant flow of wind from one direction → blow outs similar shape to barchan but opposite direction occur when vegetation stabilizes sediments and a U-shaped blowout forms between clumps of plants → transverse Long asymmetrical dunes that form at right angles to the wind form when there is an abundant supply of sand and relatively weak winds → linear forms where sand is abundant and strong cross winds converge from at least two directions, pushing the sand into long lines or ridges |
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desert locations
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→ pressure belts
descending aid warms + dries → interior of large continent far from ocean → poles |
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desert erosion
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Air near the surface is heated and rises, cooler air comes in to replace hot rising air and this movement of air results in winds.
Arid regions have little or no soil moisture to hold rock and mineral fragments |
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desert sediment
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transport → aeolian → eroded or carried by wind
well sorted + rounded due to repeated transport |
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fluvial desert
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→ Alluvial Fans and Bajadas - forms where a mountain stream enters a broad flat valley and deposits sediment
→ Playa Lakes - Lakes that form during the rare periods of rainfall, quickly evaporate, leaving a dry lake bed behind → braided streams |
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glacial motion
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→ slide
warm based water moving around at the base of the ice picks up + erodes sediment from the bed → creep ice is deformed by its own weight → internally cold based-glaciers they are frozen to the bed → the base of the glacier is stuck to the ground |
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glacial moraines
→ An accumulation of rocks and debris carried and deposited by a glacier |
→ end moraine - the deposited material created by glacial processes at the end of the glacier snout
very poorly sorted → terminal - left at the maximum extent of the ice → lateral - from rocks falling and being picked up + scraped off of valley sides → medial moraines - where two lateral moraines meet and join from 2 separate valleys coming together → ground moraine (till) - lodged into ground below the glacier, created by glacier sliding over ground and churning up the ground below |
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glacier mass balance
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Equilibrium Line - the border between where ice accumulates or ablates
→ Accumulation - at top end +ve net balance glacier advances → Ablation - at bottom end -ve net balance glacier retreats could be due to less snowfall higher temperatures |
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thermohaline circulation
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movement of warm ocean (salt) water
warms northern and southern oceans |
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glacial features
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→ dropstones
fall into the marine environment when ice burg melts → drumlins tear-drop shaped hills left by glaciers which are aligned and show flow direction → eskers sub-glacial tunnels of sediment moving in a faster flow, better sorted → braided streams on outwash planes → ice dammed lakes in areas down glacier which do not receive snowfall and where streams flow onto ice and get blocked by ice in valley |
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delta cross section
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cross section → graded sediment profile
as the river meets the sea it loses power to transport sediment Coarsest material deposited first at river mouth - topset beds Finer sands further out - foreset beds clay - bottomset beds |
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delta
a triangular sedimentary landform at the mouth of a river where it empties into a body of water – sediment deposit |
→ fan shaped created by new channels forming in different directions
→ procreational phase when the delta is producing sediments → abandonment phase the channel is breached and the water takes a shorted path to sea |
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carbonate oozes
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Foraminifera are single celled floating organisms
they record the salinity and temperature of water in it's shell when the forams die they create a calcium carbonate ooze with clay minerals |
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wave formation
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high winds create waves
wave hight increases as - wind speed increases - wind blows for longer - wind blows water over further distance |
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wave motion
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wave forms travel but the water stays in the same place
orbital motion crest → the highest point trough → lowest point |
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wave refraction + longshore drift
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refraction - waves are turned parallel when they hit shallow shore
long shore drift controls the shape, extent and deposition of the beach a process when sand is transported by swash and backwash |
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waveform characteristics
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velocity = wavelength X wave speed
wavelength → distance between crests period (T) → time for successive waves to pass energy is strongest at the waters surface |
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how do waves break?
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in shallow water, as they hit the shelf
wave shape is deformed and squashed and so the waves steepen then ultimately breaks |
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beach sand budget
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→ inputs
backshore cliffs eroded by waves upcurrent beach eroded by longshore drift and current brought in by rivers → outputs transported to backshore dunes by offshore winds transported downcurrent by longshore drift and current transported to deep water by tidal currents and waves |
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way-up evidence (structural geology)
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unconformities
bedding mudcracks + ripple marks pillow lavas |
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Cretaceous – Paleogene Boundary Meteor Impact
a layer of clay found globally, in many different environments |
Around time dinosaurs died out, crater found in mexico - 10km meteor
Ejecta layer - contain tektites (glass droplets) Fireball layer → globally distributed small minerals grains with evidence of shock impact contains shock metamorphosed quartz, soot, small diamonds |
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impact of meteor on the atmosphere and temps
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fine material can stay in atmosphere for a while and move all over the world
this causes a short obscuring of the sun, reflects the rays → it gets dark and cold and causes a shut down of photosynthesis for 3-6 months and temps will change dramatically → first it will be extremely hot for a few hours and then for it will be cold below zero for about 3 months longer term → greenhouse effect causes the elevation off temperatures |
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slope stability
F=w . sin0 (stress) |
water in pores creates cohesion → how well locked together the particles are
damp sand is most cohesive as the water particles are drawn in together creating surface tension |
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fluvial ripples
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On beach sand – back & forth waves – symmetrical
On dunes & river banks – asymmetrical |
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delta location
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largest deltas near equator as heat speeds up chemical erosion
and at largest river basins and near large mountain outcrops as more sediment available very fertile agricultural lands has a profound effect on human activities |
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plate boundaries
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→ divergent - plates moving away from each other
can create oceans, smaller and fewer earthquakes → convergent boundaries - plates moving together creates mountain ranges, largest earthquakes → conservative boundaries - plates sliding past each other magnitude of Earth quake not as high, but generatex many sheer surface waves which are most destructive to buildings |
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fault types
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→ Dip-slip
normal → when crust is extended, land drops reverse → crust is compressed, land rises → Strike-slip → land slides left/right → Oblique-slip → has a component of dip and strike slips listric → spoon shaped |
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Earth future
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ice covering - most glaciers are retreating
today 10% of Earth is covered in ice 20,000 yeas ago → Cape Cod, most recent ice age snow/ice covered 30% sea level changes Pangaea Ultima - super continent expected to form |
