High-resolution chemostratigraphy of Maastrichtian/Paleocene transition in Texas, USA, and Brazil

点击翻译按钮获取中文摘要

The ICDP drilling of the Chicxulub crater on Yucatan and K-T outcrop studies throughout NE Mexico have revealed stratigraphic, geochemical, mineralogical, paleomagnetic and paleontological evidences that this impact predates the K-T boundary by about 300,000 years and hence could not have been responsible for the end-Cretaceous mass extinction as commonly believed. The major purpose of this project is to contribute by means of geochemical methods on newly sampled and cored material in Brazos and Brasil to the solution of the current controversy over the age of the Chicxulub impact and its relationship to the K-T boundary mass extinction within an interdisciplinary, international research project. The debate is not a matter of who is right or wrong it is more a matter of tremendous implications that go way beyond the mere age of the Chicxulub impact, with tremendous bearing on the nature and cause(s) of mass extinctions during the Earth´s history. Preliminary results of the first project year combined with a comparative, critical evaluation of the latest literature, seems to reinforce the conclusion that the Chicxulub impact and the biostratigraphic K-T boundary of the sections of Brazos and Brazil are not coincident in time. However, a series of key features are still debatable and must be answered before reached to an irrefutable conclusion. Among others, these include (i) the nature of the “event deposits”, (ii) the deposition time of the sediments intercalated above the “event deposits” and the biostratigraphic K-T boundary, (iii) whether the recently discovered “yellow clay layer” below the event deposits at Brazos corresponds or not to the original Chixculub impact ejecta layer, or (iv) whether the Ir anomaly in sediments of Danian age at Poty Quarry, Brazil is reworked or marks a different, younger impact event. Of further major interest is to clear the possible role of other stress factors than impact (e.g. “super-volcanism”, anoxia) to the end-Cretaceous mass extinction.