Chicxulub Gravity Survey Update
Final Update on the Chicxulub Gravity Survey
Meteorite and Impacts Advisory Committee (MIAC) / Gravity Measurements over the Chicxulub Crater

Extinction Crater to be Mapped

In September and October of 1996 the Geodetic Survey Division (GSD) collaborated with the Geological Survey of Canada (GSC) to play a key role in marine geophysical surveys designed to map the seaward extension of the Chicxulub Crater in the Gulf of Mexico. The Chicxulub Crater is considered by many scientists, including the team led by Alan Hildebrand of the GSC, to be the signature of the comet whose impact with Earth triggered the extinction of the dinosaurs 65 million years ago.

Chicxulub Crater in the Gulf of Mexico

Previous Work

Previous gravity and magnetic surveys on the Yucatan Peninsula have revealed the circular pattern of the crater's structure and drill core has helped to define the stratigraphy within the crater. A piece of the puzzle is missing, however, as about half of the crater lies offshore under the Gulf of Mexico. To fill this gap in data coverage, a marine geophysical survey, sponsored by the British Institutions Reflection Profiling Syndicate (BIRPS), the University of Texas (U of T), National Geographic Society (NGS), the Pan American Institute of History and Geography (PAIGH), and Geological Survey of Canada (GSC) will be launched in September from the U of T vessel "Longhorn". Seismic, gravity, and magnetic data will be collected.

The primary role of the U of T vessel "Longhorn" will be collecting seismic refraction data in an experiment organized by Richard Buffer of U of T's Institute for Geophysics, however the "longhorn will collect gravity and magnetic-field data between ocean bottom seismometer deployment and recovery. The GECO "Sigma" will shoot conventional reflection seismic while a team led by Michael Warner and Joanna Morgan of the Imperial College of Science, Technology and Medicine collects wide-angle seismic data on land.

Geodetic Survey's Role

John Halpenny and Roy Cooper of GSD were responsible for collecting gravity, bathymetry and magnetic data. They used GPS for positioning the profiles. In a second phase of the survey the gravimeter, digital depth sounder, and magnetometer was transferred to a smaller vessel to map the near-shore gravity and magnetic fields.

Chicxulub Gravity Survey Update

The deep-water phase of the gravity survey was completed on October 8, 1996. The ship's tracks are shown on the accompanying map. A total of 3809 line kilometres of gravity data was collected. Initial results indicate that gravity gradients associated with the crater margin have been mapped.

The gravimeter has been transferred from the RV "Longhorn" to a 35 foot (10.7m) cruiser. "Aye Aye Sir" for the near-shore phase of the survey which commenced on October 11. The near-shore survey is expected to take fourteen days.

Magnetic data could not be collected as the magnetometer fish was lost at sea during mobilization. On a more positive note, the seismic survey was completed as planned.

Ship's tracks

Final Update on the Chicxulub Gravity Survey - November, 1996.

Following completion of the deep water phase of the marine gravity survey on October 8, 1996 (3800 line kilometres), the near shore phase of the survey is now complete (October 27).

A total of 1300 line kilometres of nearshore track data was collected by the Geodetic team. A total of 5000 land gravity stations were also collected by GSC in October.

Despite many equipment and weather problems most of the survey objectives were achieved and initial indications suggest that the crater signal has been mapped offshore.

Final data reduction will reveal a more complete picture of the crater.