The Great Chicxulub Debate -Synchronicity of the Chicxulub impact and the Cretaceous/Tertiary boundary-

Abstract

The Chicxulub crater in the Yucatan Peninsula is now well accepted as an impact crater formed at the Cretaceous/Tertiary (K/T) boundary. Thick K/T boundary breccia and sandstone beds around the impact site are interpreted as K/T boundary tsunami and/or gravity flow deposits. It has been generally believed that the Chicxulub impact was the major cause of the K/T boundary mass extinction. However, G. Keller and others have suspected the synchronicity of the Chicxulub impact and the K/T boundary, and presence of the K/T boundary tsunami and/or gravity flow deposits. In particular, they concluded that the Chicxulub impact predated the K/T boundary by 300 ka based on studies of the K/T boundary deposits in northeastern Mexico, Haiti, and inside the crater, and that the Chicxulub impact had no relation with the K/T boundary mass extinction. The debate on this issue was heated, especially on the web site of Geological Society of London by G. Keller and J. Smit in 2003, and it was called "the Great Chicxulub Debate". In this paper, I review all the arguments on this issue and discuss the timing of the Chicxulub impact. I further take up the recent debate on the sedimentary process of the uppermost part of the impactite in ICDP (International Continental Scientific Drilling Program) Chicxulub drill core (YAX-1 core), which is considered as a conclusive evidence that the Chicxulub impact predates the K/T boundary by G. Keller and others, although other many researchers interpreted that this part was formed by reworking due to the invasion of ocean water into the crater immediately after the impact.