Geoscience Reference
In-Depth Information
FIGURE 14
The cenote
ring at Chicxulub (dark
circles) superimposed on
the gravity anomaly map.
Note how the cenotes to
the middle and left trace
out part of a nearly perfect
circle. [Photo courtesy
of Alan Hildebrand and
Geological Survey of
Canada. For this and other
images, see web page at
uquebec.ca/-mhiggins/
MI AC/chicxulub. htm. ]
S
IZE
AND
S
HAPE
Although the Chicxulub structure lies buried beneath a kilometer
of younger sedimentary rocks, gravity anomaly maps clearly reveal it
(see Figure 14). (Structural domes, which often contain petroleum
deposits, also produce concentric geophysical patterns, thus explain-
ing the decades-long interest that Chicxulub held for PEMEX.) The
edge of the gravity anomaly indicates a structure at least 170 km in
diameter, consistent with an impactor of 10 km in diameter. If Chic-
xulub is of impact origin, and if the outer perimeter of the gravity
pattern represents the true outer rim of the crater, then that is its
diameter. On the other hand, if the edge of the gravity pattern in-
stead represents one of the inner concentric structures of a complex
crater, for example, a collapsed terrace rim, then the structure might
be larger, even much larger.
Still another possibility is that Chicxulub is not a complex crater
of the kind shown in Figure 7 but something more: a giant, multi-
ringed basin like the Orientale Basin on the moon. In any case, the
original Alvarez calculation of 10 km was sufficiently imprecise that
a greater radius for the crater is certainly possible. Virgil "Buck"
Sharpton and his colleagues at the Lunar and Planetary Institute
