In southernmost South America, several ephemeral Atlantic transgressions flooded the Patagonian Platform: in the Maastrichtian‐Danian, late Mid‐Eocene, Late Oligocene‐Early Miocene, and Middle Miocene; only in the Fuegian Andes did marine conditions remain continuously from the Maastrichtian up to the Middle Miocene. In the Maastrichtian, the calcareous foraminiferal benthic assemblages contain endemic species, and most of them disappear in the Cretaceous–Palaeogene transition. The Palaeocene carries the extinct cosmopolitan Midway type assemblage with few endemic taxa such as Buliminella isabelleana, and the genera Antarcticella and Boltovskoyella. The Palaeocene/Eocene turnover gives room to assemblages of modern and marked Austral aspect: Elphidiidae dominates in shallow environments, including genera endemic to high and mid‐high southern latitudes such as Cribrorotalia. The Late Middle Eocene transgression is characterized by large nodosarids in the Fuegian area and the spreading of Elphidium saginatum. The Late Oligocene transgression is of limited extension and shallow waters, with abundant Buccella and the conspicuous genus Discorotalia. The Early Miocene transgression carries the extinct and typical Antarctic genus Ammoelphidiella and witnesses the origin of the modern Patagonian coastal assemblage, characterized by its pauperism and the dominance of the genus Buccella. The Middle Miocene transgression covers mainly northern Argentina. Considering that the late Middle Eocene and Middle Miocene transgressions are coeval with relative climatic optima, and in comparison with assemblages at similar palaeolatitudes elsewhere in the Southern Hemisphere, the absence of larger foraminifera or thermophilic forms in the Patagonian and Fuegian assemblages is outstanding. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 269–288. En el extremo austral de América del Sur, varias transgresiones efímeras inundaron la Plataforma Patagónica: en el Maastrichtiano‐Daniano, Eoceno Medio Tardío, Oligoceno Tardío‐Mioceno Temprano, y en el Mioceno Medio; sólo en los Andes Fueguinos las condiciones marinas permanecieron desde el Maastrichtiano hasta el Mioceno Medio. En el Maastrichtiano, las asociaciones de foraminíferos bentónicos contienen especies calcáreas endémicas, que en su mayoría desaparecen en la transición Cretácico/Paleógeno. El Paleoceno porta la asociación cosmopolita extinta del tipo Midway, con pocos taxones endémicos tales como Buliminella isabelleana, y los géneros Antarcticella y Boltovskoyella. El recambio del límite Paleoceno/Eoceno da lugar a asociaciones de aspecto moderno y marcadamente austral: los Elphidiidae dominan en los ambientes someros, incluyendo géneros endémicos de altas y medias altas latitudes australes tales como Cribrorotalia. La transgresión del Eoceno Medio Tardío está caracterizada por grandes nodosáridos en el área fueguina y por la dispersión de Elphidium saginatum. La transgresión del Oligoceno Tardío, de limitada extensión y de aguas someras...

the Magallanes or Austral basin is shared by Argentina and Chile; both countries developed the knowledge on foraminifera in different timing and ways. these differences delayed the integration of the stratigraphical information from both parts of the basin. in Chile, the studies began in the ´40s in the national oil company EnAP and most of its reports remained unpublished until 1974, when a system of stages for correlation was proposed. this system, particularly for the Paleogene, was based on benthonic foraminifera because of the scarcity of planktonic forms. in Argentina, a first study on the Paleogene foraminifera from the Austral basin is published in the late 60s, and after several years devoted to publish and illustrate the Cretaceous foraminifera, the research has been again focused on the Paleogene since the end of the century. the integration of the knowledge from both sides of the international boundary, and particularly the gathering of the data on the scarce planktonic forms, have helped to correlate Argentinean and Chilean formations, pointing out the great difference between the thick Paleogene sequences in the Chilean Peninsula brunswick and the reduced Paleogene sequence, including more manifest and amplified unconformities, in the Argentinean Atlantic fuegian coast.the contact between the Maastrichtian and the danian by means of foraminifera is recognized in the northern part of the basin (Cerro dorotea formation), whereas in the southern part is not evident due to an unconformity in the mid-Paleocene and the dominant, not age diagnostic, flysch type assemblages. the Paleocene/Eocene turnover in calcareous assemblages exhibits a contrast between a cosmopolitan Midway type assemblage in the upper Paleocene (la barca/Chorrillo Chico formations) and an endemic early Eocene Austral assemblage that includes the first appearance of the genus Elphidium (Punta noguera/lower Agua fresca), and the genus Cribrorotalia in the Punta noguera formation. the lower 1 Consejo nacional de investigaciones Científicas y técnicas, Argentina. n.malumian@yahoo.com 2 laboratorio de Micropaleontología, instituto de la Patagonia, universidad de Magallanes, Chile. 3 servicio geológico Minero Argentino. Middle Eocene unconformity separates disaerobic and turbiditic paleoenvironments of the Paleocenelower Middle Eocene (la barca, Punta torcida/Chorrillo Chico, Agua fresca) from the aerobic shallow marine settings of the late Middle Eocene (leticia/tres brazos, boquerón). the sediments underlying the unconformity were deposited in a turbiditic marine paleoenvironment, with both restricted circulation and connection with the open sea, which was dominant from the Campanian up to the lower Eocene. the paleoenvironmental turnover is clearly reflected by the dominance of agglutinated and generally small foraminifera in the Campanian-lower Eocene in contrast with dominant large nodosariidae foraminifera associated to a bloom of crinoids in the late Mid Eocene. this turnover reveals changes in the morphology of the basin t...

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