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Cretaceous-Paleogene Boundary 1 (Gubyo, Italy Appenines (Section stretches…
Cretaceous-Paleogene Boundary 1
Cause
Huge meteor impact on Earth = cause
bolide = large meteor
Chixculub Crater, Mexico
date correlates to K-T boundary
Impactor ~150 km (modelled size)
expected every ~ 100 Myr
do not find many
crust destroyed via subduction
Discovered by analysis of microfossils & sediment particles
Gubyo, Italy Appenines
Section stretches across K/T boundary (from Cretaceous to Miocene)
Cyclical sedimentation - orbitally controlled
Microfossil content exhibits huge change
along boundary in sedimentary succession
Dated as K/T boundary
Microfossils disappear
Impact Frequency
Impactor ~150 km (modelled size)
do not find many
crust destroyed via subduction
expected every ~ 100 Myr
Dust / small impactors
part of regular ocean floor sedimentation
Alvarez 1960s Appenines, Italy
Microfossils disappear & sediment changes
Paleogene (Above boundary) - lotsa clay
Cretaceous (Below boundary) - carbonate
Iridium spike measured in clay at boundary
Iridium = very rare on Earth
(only small amounts cosmic dust / volcanism)
Inferred
meteorite impact
Many sites globally where boundary & iridium spike discoverd
Coincided with dinosaur extinction
Global-
reaching event
Iridium spike found all around the world
How?
Molten material blown out of atmosphere
Vaporisation of rocks meteor impacted upon
Solidified on re-entering atmosphere
= Tectites
Schmidt
Agost, Spain
Rock with abundant tectites = impact layer
Found evidence of K/T boundary in Spain
Layers (in strat order)
paleogene carbonate
boundary clay
impact/ejecta layer
carbonate
Impact layer
= has abundant tectites (microkrystites)
Carbonate = Microfossil rich sediment
Proposed impact killed off plankton
impact responsible for microfossil disappearance
Importance of Plankton Mass Death
Primary producer extinction
Drove rapid evolutionary change
Effects whole biodiversity
Decreases recovery rate of survivors
Ecological cascade
Provides opportunity for survivors to radiate after impact