Drilling Project

  The approximately circular geophysical anomaly, now known to define the Chicxulub structure, was originally identified on the northern edge of the Yucatan Peninsula during oil surveys in the 1950's.  Several exploratory wells, all dry, were subsequently drilled in and around the structure, which is buried beneath ~1km of Tertiary carbonate platform sediments.  Two of the boreholes penetrated a crystalline melt rock,
which was initially interpreted to be an extrusive andesite.

Chicxulub Drilling Sites
This map shows the locations of wells drilled into the Chicxulub crater and surrounding impact ejecta. The red circles show boreholes drilled by Petroleos Mexicanos (PEMEX) as part of their oil exploration program and the locations of boreholes from the scientific drilling program conducted by the Universidad Nacional Autonoma de Mexico (UNAM).

Additonal geophysical data, collected many years later, led researchers Penfield and Camargo Z., working for Petroleos Mexicanos (PEMEX),  to suggest the structure might be the result of a mid-plate igneous plume or extrusives associated with an impact event. Later petrologic and geochemical studies by Hildebrand, Kring (now at LPI), and Boynton at the University of Arizona, working with Penfield, Camargo Z.,  Pilkington from the Canadian Geological Survey, and Stein Jacobsen from Harvard University, proved this hypothesis correct.  Seismic, gravity and magnetic data define a structure ~180 km in diameter.

Seismic Reflection Geophysics

The seismic reflection map shows the locations of offshore reflection lines in solid blue. The white dots show the locations of wide-angle seismic receivers. Adapted from  Figure 1 Morgan et al. in Nature (1997).
 

Seismic Refraction Geophysics

The seismic refraction map shows the location of the Leicester Univ. seismic array. Broadband seismometers are indicated by green squares and short period seismometers are shown in blue. Adapted from Figure 1, P.K.H. Maguire et al. in Meteorites: Flux with Time and Impact Effects (1998).

Magnetic Anomaly Geophysics

The magnetic anomaly map shows the location of magnetotelluric profiles as green lines, with each sounding station marked with a green dot. Adapted from Figure 4, Campos-Enríquez et al. inThe Leading Edge (1997).
 

    The Bouguer gravity anomaly at Chicxulub is largely negative and is similar to those at other impact craters which are produced by relatively low-density allochthonous breccia deposits filling the craters and by underlying autochthonous units which have relatively low densities because they were fractured and brecciated during the impact event.  The Chicxulub structure also consists of a centrally-located positive anomaly defined by two concentric negative anomaly troughs with diameters of ~70 and 120 km, reflecting the peak-ring structure typical of complex impact craters.  The central positive gravity anomaly and the surrounding ring(s) are probably produced by relatively high density crystalline rock that was uplifted during the rebound of the crater cavity.

Gravity Anomaly Map
Bouguer gravity data from the northwest corner of the Yucatán Peninsula, Mexico. Adapted from Figure 2, Hildebrand et al. in Geology 1991. The semi-circular blue and yellow feature is produced by the impact crater. The linear blue structure south of the crater is a deeper structural feature in the Earth's crust that existed before the impact event.

    One of the wells, Yucatan-6, penetrated the flank of the ~100 km ring and samples of the polymict breccia and melt rock were recovered.  The polymict breccia consists of igneous-textured microcrystalline clasts with shocked quartz xenoliths, and vesicular and ropy textured phyllosilicate clasts which look like altered fragments of glass, both of which were produced by shock melting.  The breccia also contains clasts of sedimentary carbonates and evaporites, recrystallized sandstone, granitic gneisses and mica schists in a carbonate-rich matrix.

Examples of an unshocked quartz grain (left) and a shock-metamorphosed quartz grain (right). The planar features cross-cutting the shock-metamorphosed grain are essentially microcrystalline faults. The shock metamorphosed grain was ejected from the Chicxulub crater and found in Haiti.
Photo micrograph of unshocked quartz grain (left) and shock metamorphosed quartz grain (right).
 
 

This web site is based on information originally created for the NASA/UA Space Imagery Centerís Impact Cratering Series.
Concept and content by David A. Kring.
Design, graphics, and images by Jake Bailey and David A. Kring.
Any use of the information and images requires permission of the Space Imagery Center and/or David A. Kring (now at LPI).