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End Cretaceous Mass Extinction (Impact Evidence (Crater found in 1990s…
End Cretaceous Mass Extinction
Cause = Comet/Asteroid Impact ?
Impact Evidence
Iridium spike
in clay layer at K-T boundary
found Appenines (Italy) & Agost (Spain)
Global correlatable pattern
Shocked Quartz
Mineral planes collapse from high T & P
Only observed in meteor sites / nuclear bomb craters
Quartz crystal deformed by high P & T
Tectites
Blobs of vaporised rock
Solidify & cool rapidly on falling back to Earth
Aerodynamic shapes (teardrops etc)
Crater found
in 1990s
Much of it underwater
sediment covered in Gulf of Mexico
revealed by seismic data from oil industry
over 100 miles across
Chixculub Crater, Mexico
Confidently dated to 66 Myr
Confirmed impact theory
1980s spent looking for evidence to prove impact theory
Fossil Pattern
El Mimbral, Mexico
Paleogene
Only small planktonic forams
Low diversity
Cretaceous
Abundant large specialised planktonic forams
Terrestrial Change
Dinosaurs disappear
Timescales
Events = sudden, shortlived
Weeks to hundreds yrs max - not kyr
Recovery = faster than Permian (discrete impact event)
Impact Effects
= Rapid
Domino effect =
over shorter period than End-Permian
Chixculub Impact
Tsunamis
Heat pulse sweeps across globe
causing wildfires
charcoal / charred wood in geological record
Dust blocks out sun
for near decade ?
Photosynthesis shutdown
Acid rain devastates plants
Ecosystem collapse as plants extinct
Huge amount
CO2 released
Carbonate platform hit
Some global warming
Impact Effects on Life
Sudden extinctions
coincide w iridium spike
mass kill Cretaceous plankton
dinosaurs disappear
Negative excursion C isotope
ecosystem instability
Ocean Disequilib for ~10kyr
Low diversity
Strange plankton develop
Collapse of ocean food chain
End of Mesozoic Oceans
Most Forams Extinct
Sone 'disaster species' radiate
blooms & adaptive radiation
Ecological Cascade
Planktic extinction
propagating effect through food chain
i.e. marine reptiles & ammonites extinct
Deccan Traps, India
Extensive LIPS volcanism at end Cretaceous before asteroid impact
Could Deccan Traps have caused mass extinction?
End Cretaceous - Envmt in Flux before impact
Deccan Traps
Climate Shifts - cold spell at end Cretaceous
Sealevel change (regression)
Was asteroid just final straw or incorrectly accused?