Chicxulub Impact Crater: The Dinosaurs Didn't Have a Chance

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Chicxulub Impact CraterThe Dinosaurs Didn't
Have a Chance!

• Gail Christeson, UTIG

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WHY STUDY CHICXULUB?

• It is associated with the K/T boundary impact
• It is the best-preserved large impact crater on
  Earth

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Talk Overview

• General Crater Morphology
• Background on Chicxulub Crater
• Seismic Experiments

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simple crater
Meteor Crater, Arizona
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complex crater central peak
Tycho crater, Moon
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complex crater peak ring
Wheatley crater, Venus
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multi-ring basin
Meade Crater, Venus
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crater mechanics
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transient crater, fate of target material
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Talk Overview

• General Crater Morphology
• Background on Chicxulub Crater
• Seismic Experiments

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• Chicxulub Discovery Timeline
• 1948 - zone of concentric anomalies recognized in
  gravity surveys of the Yucatan Peninsula
• 1950s - exploratory drilling program by Pemex
• mid-1970s - completion of Pemex drilling program
  - found unusual occurrences of Upper Cretacious
  crystalline rocks and breccias, thought at the
  time to indicate a large volcanic field
• 1980 - Alvarez et al. propose a K/T impact event
• 1981 - Penfield and Camargo propose that
  Chicxulub structure could be buried impact crater
  (SEG meeting)
• 1988 - 2 potential solutions to absence of a
  large recognized K/T crater
• 1. Impact on ocean floor destroyed during 65
  million years of plate recycling
• 2. Many smaller impact events occurring either
  simultaneously or in a narrow time window
• 1991, 1992 - papers published in Geology
  (Hildebrand et al., 1991), Nature (Sharpton et
  al., 1992) naming Chicxulub structure as the KT
  impact basin
• 2003 - General consensus that Chicxulub is the
  site of KT impact

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• Environmental change agents
• Proximal to regional fireball irradiance -
  minutes
• Regional thermal pulse from re-entering ejecta -
  hour
• Proximal wind - hours
• Proximal giant waves - hours
• Dust veil (darkness and cold) - months
• Acid rain (nitrogen and sulfer based) - year
• Stratospheric aerosols (cold) - decades
• Ozone layer depletion (ultraviolet exposure) -
  decades
• H2O greenhouse - decades
• CO2 greenhouse - millennia
• Poisons and mutagens - years to millenia?
• Oscillatory/dirupted climate - million years
• (Wolbach et al., 1990 Hildebrand et al., 1998)

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Environmental Effects
From Hildebrand et al., 1998
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Talk Overview

• General Crater Morphology
• Background on Chicxulub Crater
• Seismic Experiments

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1996 Seismic Experiment
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Chicx-A
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Shallow Structure

• Most prominent feature shallow velocities
  associated with Tertiary impact basin
• The edge of the Tertiary impact basin correlates
  well with steep gravity gradient on eastern end
  of profile
• High velocities at crater flanks are interpreted
  as reefal buildups at margins of Tertiary basin
• Lowered velocities beneath the Tertiary impact
  basin within the transient cavity are interpreted
  as melt breccias

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• Velocity contours are uplifted near the crater
  center, indicating central basement uplift with a
  diameter of 40-60 km. The central uplift is
  associated with a central gravity high
• Shallow basement is observed along the northwest
  portion of the profile, and is associated with a
  prominent northwest trending high in the gravity
  field

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Moho relief of 1-1.5 km is associated with deep
crustal faulting. The Moho topography may be
related to deformation processes associated with
the formation of the outer ring.
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Seismic Cruise Feb 28 - April 1, 2004
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THE END