Steps taken to understand the Chicxulub basin since the Jalisco meeting in 1993, have heightened interest in and sharpened the focus of a deeper drilling program inside the basin. A continuous section of the impact-generated rock sequence and samples of the underlying, downfaulted Mesozoic platform rocks will provide considerably better controls than are presently available over the original target lithologies and how those rocks were brecciated, shocked, mixed and emplaced on the crater floor as a consequence of the Chicxulub basin-forming event. Gathering a complete section through the impact sequence is essential because excavation and ejecta deposition result in a vertically, as well as, radially stratified impact sequence: Weakly shocked rocks from the upper flanks of the excavation cavity are exhumed and deposited first followed progressively by the deeper and more heavily shocked materials. A characteristically abrupt boundary separates the lower unit of weakly shocked (‘Bunta Breccia' equivalent; [Hörz et al., 1983]) and the overlying, highly shocked ‘suevite'. The exact sequence and its specific characteristics (bearing on the nature of excavation and ejecta emplacement) for such a large crater as Chicxulub remains unknown. It is a fundamental goal of this project to recover the samples necessary to address this issue.
To evaluate these characteristics, the drilling must take place over a portion of the basin that is outside the central zone of intense deformation, excavation, and deep structural uplift associated with the so-called transient crater. Although we have developed a strategy that will maximize the diversity, quality, and the quantity of science returned from this project, a single drill hole into the Chicxulub crater will not address all the outstanding problems of Chicxulub's formation. Given that limitation, we believe that issues that contribute to a better understanding of the nature of the breccia and melt rock units within Chicxulub, particularly those that shed new light on large body impact and how it could induce environmental change, take precedence over those of melt rock formation and evolution, central uplift, and the nature of deep crustal materials in Northern Yucatan. Consequently, such topics must await future opportunities for deeper and, quite frankly, much more costly drilling. We can only hope that the enhanced knowledge of the Chicxulub crater arising from this project will
serve to mobilize support for such a project in the years to come. The cores recovered from this project would represent the first continuous section through the allogenic impact deposits within the Chicxulub basin, or for that matter, within any impact crater greater than ~100 km in diameter. In addition to the principal goals summarized above, these samples provide a valuable record of the long-termevolution of the Yucatan structural block. Within the impact breccias are clasts of deep basement materials recording Pan-African deformation styles and crustal characteristics. Furthermore, the Mesozoic through Cenozoic platform sequence provides an almost uninterrupted lithological, biostratigraphic, and paleoenvironmental record of the evolution of this platform sequence. After cores are extracted during the drilling phase, downhole techniques will measure geophysical and rock properties to tie this hole into the stratigraphic framework from existing Pemex wells.
