2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 200-6
Presentation Time: 9:25 AM


KELLER, Gerta, Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544 and ADATTE, Thierry, Institute of Earth Sciences, Université de Lausanne, Géopolis, Lausanne, 1015, Switzerland, gkeller@princeton.edu

The Chicxulub impact is commonly believed to have struck Yucatan precisely at the Cretaceous-Tertiary boundary (KTB or KPG) and caused the mass extinction. This claim has been controversial because a wealth of data contradicts this belief. Chicxulub impact glass spherules are the most reliable and least controversial impact signals in sediments. By applying the same global biostratigraphic and mass extinction criteria to about 100 sections with impact glass spherules surrounding the Chicxulub impact crater from the North Atlantic through Central America and the USA a remarkably distinct spherule age distribution pattern emerges. In NE Mexico, Texas and the Chicxulub crater core Yaxcopoil-1 impact glass spherules and melt rock are invariably found in planktic foraminiferal zone CF1, which spans the last ~160 ky of the Maastrichtian. Impact spherule deposition coincides with the latest Maastrichtian global warming that began in the upper part of CF2 about 200 ky before the KTB and ended in the middle of CF1 about 80 ky before the mass extinction. Based on this data the Chicxulub impact predates the KTB by about 100-150 ky. In all other localities from the North Atlantic, New Jersey, Caribbean, Belize, Guatemala and southern Mexico a major KTB unconformity spans from early Danian through late Maastrichtian sediments. Impact spherule layers are reworked above the hiatus in early Danian zone P1a about 100 ky after the mass extinction. This geographic pattern of erosion and impact spherule redistribution appears linked to an intensified Gulf Stream and Caribbean tectonic activity.

The recent discovery of the mass extinction directly between major Deccan volcanic eruptions has fundamentally changed the impact controversy. Questions now concern the role of Chicxulub in Deccan volcanism and the mass extinction. It has been suggested that Chicxulub triggered the massive Deccan eruptions that led to the mass extinction. Deccan eruptions totaling as much as 3000 m of lava flows occurred over the last 200 ky of the Maastrichtian. With Chicxulub correlating to about the middle of this eruption phase its potential trigger role in Deccan volcanism or the subsequent mass extinction remains highly doubtful and impossible to verify.