Impact and extinction in remarkably complete Cretaceous-Tertiary boundary sections from Demerara Rise, tropical western North Atlantic

Abstract

Ocean Drilling Program (ODP) Leg 207, on the Demerara Rise in the western tropical North Atlantic, recovered multiple Cretaceous-Paleogene boundary sections containing an ejecta layer. Sedimentological, geochemical, and paleontological changes across the boundary closely match patterns expected for a mass extinction caused by a single impact. A normally graded, ~2-cmthick bed of spherules that is interpreted as a primary air-fall deposit of impact ejecta occurs between sediments of the highest Cretaceous Plummerita hantkeninoides foraminiferal zone and the lowest Paleogene PO foraminiferal zone. There are no other spherule layers in the section. In addition to extinction of Cretaceous taxa, foraminiferal abundance drops from abundant to rare across the boundary. Ir concentrations reach a maximum of-1.5 ppb at the top of the spherule bed, and the Ir anomaly is associated with enrichment in other siderophile elements. We attribute the unusually well-preserved and relatively simple stratigraphy to the fact that Demerara Rise was close enough (-4500 km) to the Chicxulub impact site to receive-2 cm of ejecta, yet was far enough away (and perhaps sheltered by the curve of northern South America) to have been relatively unaffected by impact-induced waves.

The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary

“…Detailed investigation of continuous sequences from globally distributed marine and terrestrial sites yield no chemical or physical evidence of a large impact in the last million years of the Cretaceous other than the Chicxulub event (table S1 and fig. S16) (25,37,38 (14) nor a hiatus between the Chicxulub impact and the K-Pg boundary.…”

“…Faunal and floral changes during the Late Cretaceous do occur [e.g., (12,47)] but are clearly distinguishable from the abrupt mass extinction and ecosystem disruption coincident with the K-Pg boundary, as indicated by high-resolution records of marine planktonic microfossils and terrestrial pollen and spores (12,13,25,37,55,57). Productivity proxies (e.g., carbonate content) linked to orbitally tuned stratigraphic time scales provide no evidence for major changes preceding the boundary (39).…”

“…(iii) At intermediate distances from Chicxulub (~1000 to~5000 km), the K-Pg boundary deposit consists of a 2-to 10-cm-thick spherule layer topped by a 0.2-to 0.5-cm-thick layer anomalously rich in PGEs with abundant shocked minerals, granitic clasts, and Nirich spinels (Fig. 3) (12,(24)(25)(26). (iv) In distal marine sections more than 5000 km from Chicxulub, a reddish, 2-to 5-mm-thick clay layer rich in impact ejecta material is usually present at the K-Pg boundary [e.g., (17)].…”

No post-Cretaceous ecosystem depression in European forests? Rich insect-feeding damage on diverse middle Palaeocene plants, Menat, France

“…Jablonski & Raup 1995;Alroy 1999;Pearson et al 2002;MacLeod et al 2006;Benton & Harper 2009). Among the many consequences was substantial turnover for North American plants and herbivorous insects (Tschudy et al 1984;Wolfe & Upchurch 1986;Johnson et al 1989;Hotton 2002;Labandeira et al 2002a,b;Nichols 2002;Wilf & Johnson 2004), expressed in a general pattern of low-diversity floras throughout the 10 Myr of the Palaeocene and a nearly complete loss of specialized insect-feeding damage on leaves until the last approximately 1 Myr of the Palaeocene Labandeira et al 2002a,b;Wilf et al 2006;Currano et al 2008).…”

The Cretaceous-Paleogene boundary and its 405-kyr eccentricity cycle phase: a new constraint on radiometric dating and astrochronology

“…On the contrary, certain oceanic sections provided the K-Pg boundary Ir anomaly and other characteristic objects, reinforcing the idea of sedimentary continuity through the boundary, e.g. : the LL44-GPC3 core in the Pacific (KYTE & WASSON, 1986;BOHOR et al, 1987;KYTE et al, 1993) and the Demerara Rise ODP Leg 207 in western North Atlantic (MACLEOD et al, 2007). Concerning Site 516F, DAILEY (1983) considered the section to be continuous across the K-T boundary.…”