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The Late Cretaceous ‘greenhouse’ world witnessed a transition from one of the warmest climates of the past 140 million years to cooler conditions, yet still without significant continental ice. Low-latitude sea surface temperature (SST) records are a vital piece of evidence required to unravel the cause of Late Cretaceous cooling, but high-quality data remain illusive. Here, using an organic geochemical palaeothermometer (TEX86), we present a record of SSTs for the Campanian–Maastrichtian interval (~83–66 Ma) from hemipelagic sediments deposited on the western North Atlantic shelf. Our record reveals that the North Atlantic at 35 °N was relatively warm in the earliest Campanian, with maximum SSTs of ~35 °C, but experienced significant cooling (~7 °C) after this to <~28 °C during the Maastrichtian. The overall stratigraphic trend is remarkably similar to records of high-latitude SSTs and bottom-water temperatures, suggesting that the cooling pattern was global rather than regional and, therefore, driven predominantly by declining atmospheric pCO2 levels.

ABSTRACT. --The planktic foraminiferal mass extinction across the Cretaceous/Tertiary boundary at Agost (Spain) occurred over an extended period, with 7 species disappearing in the late Maastrichtian, 47 species extinct at the K/T boundary and 16 ranging into the earliest Danian. The species that became extinct at the K/T boundary are large, complex tropical and subtropical forms dwelling in deep and intermediate water depths, which constitute only about 20 % of the individuals in the population larger than 63 microns. Nevertheless, their disappearance constitutes the major and sudden extinction event in the history of planktic foraminifera. However, the small cosmopolitan surface dwellers with simple morphologies appear to survive and the last of them gradually disappear in the lower part of the P. pseudobulloides Biozone. This planktic foraminiferal extinction model can be interpreted as a catastrophic mass extinction that centred at the K/T boundary, and was superimposed on a gradual mass extinction which began in the late Maastrichtian and continued into the early Danian. The catastrophic pattern of extinction at the K/T boundary is very compatible with the effect of a large meteorite impact, whereas the gradual and extended pattern of extinction across the Maastrichtian-Danian transition is compatible with temperature and sea level changes that may be related to massive volcanism.R~SUM~. -L'extinction en masse des foraminif~res planctoniques h travers la limite Cr6tac6/Tertiaire h Agost (Espagne) s'est produite au cours d'une certaine p6riode; 7 espbces disparaissant au Maastrichtien sup6rieur, 47 ~ la limite K/T et 16 au Danien inf6rieur. Les esp~ces ayant disparu h la limite K/T sont grandes et complexes, des formes vivant en milieux oc6aniques profonds tropicaux et subtropicaux, qui ne constituent qu'environ 20 % des individus de la population de taille sup6rieure h 63 microns. Cependant, leur disparition repr6sente l'6vbnement d'extinction le plus important et soudain de l'histoire des foraufinif~res planctoniques. Toutefois, les petites formes cosmopolites ayant une morphologie simple et vivant dans les eaux superficielles semblent avoir surv6cu et la phipart ont disparu progressivement darts la partie inf6rieure de la Biozone ~ P. pseudobuUoides. Ce module d'extinction des foraminif~res planctoniques peut ~tre consid6r6 comme une extinction en masse catastrophique eoncentr6e h la limite K/T et superpos6e h une extinction en masse graduelle qui avait commenc6 au Maastrichtien sup6rieur et continua jusqu'au Danien inf6rieur. Le module d'extinction catastrophique h la limite K/T est bien compatible avec les effets de l'in~pact d'un grand m6t6orite, tandis que le patron d'extinction graduelle au cours de la transition Maastrichtien-Danien l'est avec les changements de temp6rature et du nivean de lamer qui pourraient ~tre en rapport avec un volcanisme massif.

A new planktic foraminiferal zonation has been established for the lower Danian, based on some of most expanded and continuous pelagic sections known to date (from Spain, Tunisia and Mexico). This biozonation is considered valid for low and middle latitudes. The maximum stratigraphical distribution of the index-species approximately coincides in all the studied sections. The index-species are abundant and easily recognizable. We propose the following biozones and subzones: Guembelitria cretacea Zone and the Hedbergella holmdelensis and Parvularugoglobigerina longiapertura subzones; the Parvularugoglobigerina eugubina Zone, which is subdivided into the Parvularugoglobigerina sabina and Eoglobigerina simplicissima subzones and the Parasubbotina pseudobulloides Zone with the Eoglobigerina trivialis and Subbotina triloculinoides subzones. A biomagnetostratigraphic correlation and calibration of the stratigraphical ranges of these species suggest that the biohorizons used to de®ne the new biozonation are very isochronous, at least in the geographical areas analysed.

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