In contrast to many other biota, benthic foraminifers living over a wide depth range did not suffer significant extinction at the Cretaceous/Paleogene (K/Pg) boundary. Their assemblages show temporal faunal restructuring (changes in relative abundance and diversity) that has been related to severe decrease in food deliver to the benthos on the ocean floor, either as the result of collapse of the pelagic food web or to the extinction of pellet-producing zooplankton and thus transport of organic matter to the seafloor rather than decreased productivity. We quantitatively analyzed benthic foraminiferal assemblages from the northwest Pacific (Shatsky Rise, Ocean Drilling Program Site 1210) in order to infer paleoenvironmental changes across the K/Pg boundary in the largest ocean on Earth, and to evaluate the different hypotheses regarding the nature of the biotic turnover. The sedimentary succession includes uppermost Maastrichtian white to pale orange nannofossil ooze overlain by lowermost Paleocene, grayish-orange foraminiferal ooze (10 cm) that grades upwards into a white foraminiferal nannofossil chalk (20 cm), and then into a grayish-orange nannofossil ooze. Abrupt changes in nannofossil and planktonic foraminiferal assemblages have been documented across the K/Pg boundary, although intense bioturbation disturbs the record. At Site 1210, calcareous nannoplankton shows a catastrophic mass extinction at the K/Pg boundary, followed by a recovery interval where survivors such as calcispheres (calcareous dinoflagellates) were abundant, followed by successive acmes (rapid colonization) of Danian nannofossil taxa (Bown, 2005). Benthic foraminiferal assemblages at Site 1210 contain abundant representatives of the cosmopolitan lower bathyal-abyssal Velasco-type fauna. Assemblages are diverse and the percentage of buliminid taxa increases towards the uppermost Cretaceous, then show a sudden decrease in diversity and heterogeneity across the boundary. In contrast to the oligotrophic seafloor environment due to extinction of primary producers ("Strangelove Ocean") or the biotic pump ("Living Ocean"), benthic foraminifers point to a high food supply during the earliest Danian, as indicated by the strong dominance of buliminids (45% of the assemblages; e.g., Bulimina kugleri, Aragonia aragonensis), as earlier observed at Pacific Site 465 (Alegret and Thomas, 2005). We suggest that high-food taxa such as buliminids may have bloomed at least at some locations when the vacant niches of calcareous nannoplankton producers were rapidly filled by other producers (e.g., dinoflagellates, prokaryotes), leading to reorganization of the planktic ecosystems, but not to a severe decrease in delivery of food to the seafloor.

West: 158.1600 East: 158.1600 North: 32.1300 South: 32.1300

Expedition: 198

Site: 198-1210

Provider: SEDIS Publication Catalogue

Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=2010-071321 (c.f. for more detailed metadata)

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