Origin and emplacement of the impact formations at Chicxulub, Mexico, as revealed by the ICDP deep drilling at Yaxcopoil‐1 and by numerical modeling

Abstract

We present and interpret results of petrographic, mineralogical, and chemical analyses of the 1511 m deep ICDP Yaxcopoil‐1 (Yax‐1) drill core, with special emphasis on the impactite units. Using numerical model calculations of the formation, excavation, and dynamic modification of the Chicxulub crater, constrained by laboratory data, a model of the origin and emplacement of the impact formations of Yax‐1 and of the impact structure as a whole is derived. The lower part of Yax‐1 is formed by displaced Cretaceous target rocks (610 m thick), while the upper part comprises six suevite‐type allochthonous breccia units (100 m thick). From the texture and composition of these lithological units and from numerical model calculations, we were able to link the seven distinct impact‐induced units of Yax‐1 to the corresponding successive phases of the crater formation and modification, which are as follows: 1) transient cavity formation including displacement and deposition of Cretaceous “megablocks;” 2) ground surging and mixing of impact melt and lithic clasts at the base of the ejecta curtain and deposition of the lower suevite right after the formation of the transient cavity; 3) deposition of a thin veneer of melt on top of the lower suevite and lateral transport and brecciation of this melt toward the end of the collapse of the transient cavity (brecciated impact melt rock); 4) collapse of the ejecta plume and deposition of fall‐back material from the lower part of the ejecta plume to form the middle suevite near the end of the dynamic crater modification; 5) continued collapse of the ejecta plume and deposition of the upper suevite; 6) late phase of the collapse and deposition of the lower sorted suevite after interaction with the inward flowing atmosphere; 7) final phase of fall‐back from the highest part of the ejecta plume and settling of melt and solid particles through the reestablished atmosphere to form the upper sorted suevite; and 8) return of the ocean into the crater after some time and minor reworking of the uppermost suevite under aquatic conditions. Our results are compatible with: a) 180 km and 100 km for the diameters of the final crater and the transient cavity of Chicxulub, respectively, as previously proposed by several authors, and b) the interpretation of Chicxulub as a peak‐ring impact basin that is at the transition to a multi‐ring basin.

Volume 364: Chicxulub: Drilling the K-Pg Impact Crater

“…Unfortunately, its location on a steep slope meant studies of the post-impact section were plagued by coarse-grained redeposited carbonates and lithification, and the very basal Paleocene appears to be missing (Arz et al, 2004;Smit et al, 2004;Rebolledo-Vieyra and Urrutia-Fucugauchi, 2004;Whalen et al, 2013). The 100 m thick melt-rich impactite sequence is complex and composed of six distinct units (Claeys et al, 2003;Kring et al, 2004;Stöffler et al, 2004;Wittmann et al, 2007), which were modified by post-impact hydrothermal circulation . The Cretaceous rocks appear to be formed from a number of megablocks composed of dolomite, limestone, and about 27% anhydrite that have rotated relative to each other, probably during the crater modification stage .…”

Geochemistry of drill core samples from Yaxcopoil‐1, Chicxulub impact crater, Mexico

“…With the diameter of ~170-180 km, the Chicxulub impact crater on the Yucatán Peninsula, Mexico, is the third largest impact structure known on Earth and is linked to the 65 Ma-old Cretaceous/Tertiary boundary that is well-known to mark a worldwide mass extinction (Alvarez et al 1980;Smith and Hertogen 1980;Hildebrand et al 1991Hildebrand et al , 1998Hildebrand et al , 1999Sharpton et al 1992Sharpton et al , 1993Sharpton et al , 1996Swisher et al 1992;Koeberl et al 1994;Pilkington et al 1994;Schuraytz et al 1994;Morgan et al 1997Morgan et al , 2000Morgan et al , 2002Dressler et al 2003;Stöffler et al 2004). The key to the understanding of this mass extinction lies in the Cretaceous target rock sequence of the Yucatán Peninsula and in the composition of proximal and distal ejecta deposits from the Chicxulub crater (Smit 1999;Dressler et al 2003).…”

“…1). The Yax-1 drill core exposes 795 m of Tertiary sediments and only 100 m of a suevite unit resting on 616 m of obviously displaced Cretaceous sediments that are cut by several impact-generated dikes (Dressler et al 2003;Stinnesbeck et al 2003;Wittmann et al 2003aWittmann et al , b, 2004Kenkmann et al 2004;Stöffler et al 2004). The suevite unite was subdivided by Dressler into six subunits based on a macroscopic inspection of the drill core (Dressler et al 2003).…”

“…The suevite unite was subdivided by Dressler into six subunits based on a macroscopic inspection of the drill core (Dressler et al 2003). These suevite subunits were later renamed by Stöffler et al (2004) and the depth intervals were slightly modified based on an inspection of the drill core (see Table 1). …”

Impact cratering — fundamental process in geoscience and planetary science

“…Mineralogical and geochemical studies of impact breccia deposits, in combination with geological investigation of their spatial distribution, are still required to refine our understanding of their formation, depositional processes, and post-impact alteration. Since several years the International Continental Scientific Drilling Program (ICDP) has undertaken large-scale drilling projectsalways in conjunction with detailed pre-drilling geophysical analysis -at Chicxulub (Mexico), Bosumtwi (Ghana) and Chesapeake Bay (USA), with the aim to provide complete cross-sections through impact breccia fills of these structures (e.g., Stöffler et al 2004;Urrutia-Fucugauchi et al 2004;Gohn et al 2006). A further ICDP impactdrilling project will soon take place at El'gygytgyn crater (18 km diameter, 3.5 Ma age) in northeastern Siberia.…”