The Chicxulub structure is not exposed on the surface; thus, only geophysical images give evidence of its presence and extent. This image shows the variations in the magnitude of the gravity field at sea level in the vicinity of the buried Chicxulub impact basin in the northwestern corner of the Yucatán Peninsula, Mexico. In general, lower than normal gravity variations (so-called negative anomalies) indicate that the near-surface crustal rocks have relatively low densities; this could indicate fracturing and other structural disturbances that increase the volume of normal rocks or could be due to infilling by low-density carbonate sediments. Positive gravity anomalies indicate dense rocks such as the low-porosity impact melt sheet or up-thrust deep crustal rocks. A gravity anomaly over the Chicxulub basin ranges from lows exceeding -15 mGals (1 milligal = 10-5 m/s2; magenta) to +54 mGal (red). The Chicxulub basin is expressed as a broad, nearly circular region in which gravity values are 20–30 mGal lower than regional values. A distinct 15- to 20-mGal high occupies the geometric center at 21.3°N latitude and 89.6°W longitude. Surrounding this high are clearly discernible ring-like variations in the gravity field. The pronounced ring that separates the deep annular basin (magenta and deep blue regions) from the basin flanks (cyan and green) has a diameter of ~200 kilometers. A discontinuous, subtle outer ring with a diameter of ~250–280 kilometers can be discerned particularly toward the southern part of the basin. The image has been artificially shaded using a low illumination angle from the north to emphasize broad low-amplitude anomalies. All data have been Bouguer corrected using a model slab density of 2200 km/m3. Numbers along the margins of the image refer to Universal Transverse Mercator coordinates given in meters. The irregular white line marks the shoreline of the Yucatán Peninsula, and the straight lines mark province borders.
Image courtesy of V. L. Sharpton.