In the last four years the KT boundary debate took a drastic new turn with the recognition
that the Chicxulub crater located at the tip of the Yucatan Peninsula [ Penfield and Camargo,
1981] was in fact the long sought KT crater [ Hildebrand et al., 1991]. The crater is buried
under roughly 1 km of Cenozoic sediments rendering geophysical exploration methods essential
for describing its structure and morphology. There is some ongoing debate as to the size and
morphology of the Chicxulub structure. Hildebrand et al. [1991] based on gravity and
magnetic data viewed Chicxulub as a roughly circular 
180 km diameter, central peak ring
crater. Bouger gravity profiles across the structure show two symmetrical negative anomalies
with a central high comparable to the gravity anomaly profile across the Manicouagan crater in
Quebec. Magnetic field modeling performed by Pilkington et al. [1994] indicates that the
melt volume is
20,000 km
and the collapsed transient crater cavity around 90 km
in diameter. Sharpton et al. [1993] reprocessed the gravity data and interpreted Chicxulub
as a multiring impact basin with a distinct 15 to 20 mGal gravity high at the center, three major
concentric rings expressed as local gravity highs and evidence for a fourth fragmentary outer
ring extending to almost 300 km in diameter. These results point towards a diameter of 
170 
25 km for the transient crater and a depth of 45 to 60 km. Pope et al. [1993]
proposed that the formation of the Yucatan Cenote ring, a ring of sink holes important for
Yucatan water ressources, may be linked to the Chicxulub structure by slumping at the crater
rim or solution collapse within impact deposits. Chicxulub is certainly one of the largest impact
structure on Earth and if the 300 km size estimate is proven correct, perhaps one of the largest
produced in the inner solar system in the last 4 billion years.
The crater stratigraphy is known only from a few preserved core fragments from petroleum
exploration wells drilled over twenty years ago by the Mexican National Oil Company
(PEMEX). The Chicxulub crater stratigraphy consists of 
900 m of Cenozoic sediments
underlain by a 
300 m thick impact-breccia unit. This polymictic breccia contains
abundant minerals (quartz, feldspar, zircon) providing unequivocal evidence of shock
metamorphism [ Sharpton et al., 1992; Swisher et al., 1992; Shuraytz et al.,
1994]. Below the breccia is a melt-rock unit composed mainly of a fine grained (<10 
m) groundmass of alkali and plagioclase feldspars with clasts of roughly granophyric texture.
The Chicxulub melt-rock is dated by 
Ar-
Ar at 65.07 
0.1 Ma, an age
indistinguishable from that obtained on impact glass found at the KT boundary in Mexico and
Haiti [ Swisher et al., 1992].
Chicxulub may also have some economic potential as a mineral resource or hydrocarbon habitat. The similar size Sudbury crater in Ontario contains large deposits of copper and nickel. Chicxulub breccias and melt-rock have hydrothermal alteration patterns comparable to those of the Sudbury Onaping formation; which may indicate the presence of mineral resources deeper within the structure [ Shuraytz et al., 1994]. The Late Cretaceous-Paleocene ages oil-filled thick breccias from Southern Mexico may have been generated by slope disturbance and/or submarine slumping caused by the nearby Chicxulub impact [ Limòn et al., 1994]. The newly discovered Ames crater in Oklahoma and Avak crater in Alaska are known to contain proven commercial amounts of hydrocarbons [ Kuykendall and Carlson, 1994] and the Red Wing Creek crater in North Dakota has been producing hydrocarbons for 20 years.
It is of utmost importance that the well-preserved Chicxulub impact crater be re-drilled. A complete series of cores will provide ample information on the magnitude of the event, better document the formation of large impact craters and will help constrain the global consequence of this event, that modified the environment and devastated the biota.