The Cretaceous-Tertiary boundary (KTB) transition in NE Brazil

TitleThe Cretaceous-Tertiary boundary (KTB) transition in NE Brazil
Publication TypeJournal Article
Year of Publication2013
AuthorsGertsch, B, Keller, G, Adatte, T, Berner, Z
JournalJournal of the Geological Society
Pagination249 - 262
Date Published01/2013

The Cretaceous-Tertiary boundary (KTB) transition of the Poty Quarry near Recife, NE Brazil, is the most distant locality (7800 km from Yucatan) with reported Chicxulub impact-tsunami deposits, impact spherules and Ir anomaly. Investigations based on sedimentology, biostratigraphy, mineralogy, stable isotopes and elemental geochemistry failed to confirm these reports. The KTB is at an unconformity marked by erosion and bioturbation. Latest Maastrichtian planktic foraminiferal zones CF1 below the unconformity and early Danian zone P1a(1) above indicates a short hiatus with the KTB clay (zone P0), Ir anomaly and characteristic negative d13C excursion missing. Above the unconformity is an upward-fining micro-conglomerate with abundant reworked Cretaceous foraminifera, sub-angular phosphate clasts, calcitic and phosphatic spheroids along with an early Danian zone P1a(1) assemblage.

This deposit has previously been interpreted as impact-tsunami with impact spherules. However, the spheroids are common throughout the late Campanian-Maastrichtian and appear to be chamber infillings of the benthic foraminifer Dentalina alternata. The unconformity coincides with the latest Maastrichtian sea level fall, which is widely recognized globally. The upward fining micro-conglomerate is likely a gravity-flow deposit associated with the early Danian sea level rise. Two minor Ir anomalies (<0.7 ppb) in thin clay layers of zone Pla are unrelated to the Chicxulub impact. Although there is no evidence of the Chicxulub impact in the Poty Quarry, this section remains a very important distant example of the complex global environmental and sea level changes, including gravity flows, observed in KT sequences from North America through Mexico, Central America and the Caribbean and commonly misinterpreted as impact tsunami event.  PDF

Short TitleJournal of the Geological Society