Abstract Larger foraminifera occur today in marine infra-littoral environments whose mean annual temperature (TAM) is at least 22-23 °C, and are situated in a circum-equatorial belt between latitudes 30° North and 30° South. Throughout the Middle Eocene (around 40 Ma), the carbonate platform, which lay along the whole length of the Atlantic front of Europe, supported diverse populations of larger foraminifera as far north as the Paris and Hampshire basins, which at that time were situated at latitude 42° North. Larger foraminifera only disappear around 45° North. During the same period, in the carbonate platform which borders the African and Madagascan shores, larger foraminifera were well diversified as far south as palaeolatitude 35° South, before diminishing and finally disappearing near 45° South. Thus in the Middle Eocene, the equatorial belt of near-surface warm waters lay between parallels 45° North and 45° South, and was therefore somewhat extended compared to the present day. In fact, it covered a distance of 1500 km, North to South. The global latitudinal thermal gradient, as a consequence, was very much reduced (in the order of 15-20 °C), and only contained three main climatic zones: an expanded equatorial belt (TAM > +22/23 °C), flanked by two circumpolar caps with a temperate climate. Abstract Résumé: Les grands Foraminifères se rencontrent actuellement dans les environnements marins infralittoraux dont la température moyenne annuelle (TAM) est au moins égale à +22/23 °C, et situés dans la ceinture équatoriale circumterrestre comprise entre les latitudes 30° nord et 30° sud. Au cours de l'Éocène moyen (vers 40 Ma), la plate-forme carbonatée qui s'étend le long de la façade atlantique de l'Europe héberge de grands Foraminifères formant des associations diversifiées jusque dans les Bassins de Paris et du Hampshire, situés à l'époque à la latitude 42° nord. Plus au nord, les grands Foraminiféres se font rares et disparaissent vers le parallèle 45°. Pendant la même période, dans la plate-forme carbonatée qui borde les littoraux africain et malgache, les grands Foraminifères sont bien diversifiés jusque vers la paléolatitude 35° sud. Ils diminuent ensuite pour disparaître vers le parallèle 45°. Ainsi, à l'Eocène moyen, la ceinture équatoriale d'eaux superficielles chaudes, comprise entre les parallèles 45° nord et 45° sud, est dilatée par rapport à l'actuelle. Elle déborde de quelques 1.500 km à la fois en direction du nord et en direction du sud. Le gradient thermique global latitudinal très réduit (de l'ordre de 15 à 20 °C) n'autorise que trois zones climatiques majeures: une ceinture équatoriale (TAM > +22/23 °C) dilatée et flanquée de deux calottes circumpolaires au climat tempéré.

Abstract Sampling Bracklesham Group sediments of the WhitecliffBay (Isle of Wight) succession has led to the discovery of an assemblage of marine diatoms in a series of clays previously thought to be barren of microfossils. Although preserved as pyritized steinkerns, there is enough detail present to enable identification to generic and even species level in nearly all cases. The flora includes the stratigraphically restricted species Brightwellia hyperborea Grunow, Aulacodis-cus singiliewskyanus Barker & Meakin and Aulacodiscus subexcavatus Hustedt, which allow the assemblage to be placed within the Triceratium kanayae Diatom Zone of the Middle Eocene. This is equivalent to Calcareous Nannoplankton Zone NP15 and confirms a Lutetian age. The assemblage is dominated by the large centric species Fenestrella antiqua (Grunow) Swatman, previously unknown from strata later than earliest Eocene age in NW Europe, and this occurrence thus extends the range of this species. The diatoms include both low-latitude planktic species and more cosmopolitan coastal and nearshore taxa, attesting to strong connections to both southerly, warmer waters as well as to the north and east. Palaeoecological evidence from the diatom assemblage suggests the presence of water stratification, with eutrophic, nutrient-enriched surface water conditions encouraging the blooming of centric diatoms. This event may coincide with a worldwide increase in biogenic silica, coincident with a pulse of cooling and sea-level lowstand, all of which are related to the initiation of thermohaline circulation, as Antarctica split away from Australia and began to cool down. Mass sedimentation of the diatoms occurred at the end of this period, as improved water circulation led to mixing of the water mass and the return of larger calcareous benthic foraminifera. The presence of relatively nearshore, fairly shallow conditions during deposition of the diatomac-eous interval is indicated by the presence of several benthic diatom genera such as Aulacodiscus and Triceratium .