Abrupt extinction and subsequent reworking of Cretaceous planktonic Foraminifera across the Cretaceous-Tertiary boundary: Evidence from the subtropical North Atlantic

Abstract

An impact ejecta bed containing shoclied quartz and diagenetically altered telitite spherules coincides exactly with biostratigraphic placement of the Cretaceous-Tertiary (K-T) boundary in three drill cores recovered from Ocean Drilling Program Site 1049 (located in the subtropical North Atlantic Ocean). Both the bracketing pelagic ooze and the ejecta bed are undisturbed at Site 1049, allowing detailed examination of the expression of the boundary event in an open ocean setting. The youngest Cretaceous sediments contain a diverse assemblage of well-preserved upper Maastrichtian Tethyan microfossils. The overlying ejecta bed varies laterally in thickness, has sharp lower and upper contacts, and contains features (e.g., presence of a foraminiferal grainstone layer at its base and large chalk clasts in its middle, and dominance of poorly sorted coarse grains throughout) that suggest it was deposited by one or several mass-flow events. The oldest Danian ooze contains abundant, tiny planktonic foraminifera characteristic of the early Danian Pa Zone as well as common, large Cretaceous individuals. The lowermost Danian PO Zone (assemblage dominated by Guembelitria cretacea) is apparently absent. This absence could reflect restriction of the PO assemblage to shallower settings, slow sedimentation rates coupled with bioturbation mixing Tertiary forms into (and thus obscuring) the PO Zone, or an interval of erosion or nondeposition. Cretaceous species decline and last occur in the first several meters of section above the ejecta bed. This pattern could be interpreted as evidence for gradual extinction above the impact bed, but thin-section observations, relative abundance counts, size-distribution analyses, and comparison with species extinctions at other K-T sections demonstrate sudden extinction, nearly all post-K-T occurrences of Cretaceous planktonic foraminiferal species being explained as the result of sediment reworking.

Cretaceous/Paleogene boundary bathyal paleo-environments in the central North Pacific (DSDP Site 465), the Northwestern Atlantic (ODP Site 1049), the Gulf of Mexico and the Tethys: The benthic foraminiferal record

“…1) is at the base of a spherule-bed intercalated between the uppermost Maastrichtian and the lowermost Danian pelagic foraminiferal and nannofossil oozes; paleontological, sedimentological and geochemical information on this layer has been presented by Huber et al (2002), Norris et al (1999), Klaus et al (2000), and Martínez-Ruiz et al (2001). The spherule-bed is overlain by a 3-mm-thick limonitic layer enriched in Ir and a 7-cm-thick dark clay layer with reworked foraminifers (e.g., Norris et al, 1998).…”

“…Biostratigraphic information is from Norris et al (1999) and Huber et al (2002), who identified the upper part of the A. mayaroensis Biozone, and the Danian Pa and P1a Zones. We included the spherulebed into the P0 Biozone, following Arenillas et al (2002).…”

Paleoenvironmental changes across the Cretaceous/Tertiary boundary in the northern Clarence valley, southeastern Marlborough, New Zealand

“…; Olsson et al 1999;Huber et al 2002) or have local records in Zone P0 (Globigerinelloides multispina, G. subcarinatus, and G. volutus;Strong 2000). Paleocene occurrences of these latter species may be due to survival in high-latitudes (Keller 1993;Keller et al 1993) or reworking (Huber et al 2002). Guembelitria cretacea, the nominate species for Zone P0, is common in the sample.…”

“…The planktic assemblage lacks species that are known to die out at the K/T boundary (e.g., Abathomphalus mayaroensis, Globotruncanella petaloidea, Rugotruncana circumnodifer) and is dominated by taxa that are either known to have survived into the earliest Paleocene Foraminiferal Zone P0 worldwide (Guembelitria cretacea, Hedbergella monmouthensis, and Heterohelix spp. ; Olsson et al 1999;Huber et al 2002) or have local records in Zone P0 (Globigerinelloides multispina, G. subcarinatus, and G. volutus;Strong 2000). Paleocene occurrences of these latter species may be due to survival in high-latitudes (Keller 1993;Keller et al 1993) or reworking (Huber et al 2002).…”

Experimental evidence for the global acidification of surface ocean at the Cretaceous–Palaeogene boundary: the biogenic calcite-poor spherule layers

“…The final bed is a 7 cm-thick layer of dark-gray clay from the early Danian overlain by a 15 cm-thick white calcareous plankton ooze (Huber & MacLeod 2000;Alegret & Thomas 2004).…”