FORAMINIFERS FROM THE IRIGOYEN FORMATION, NEOGENE, TIERRA DEL FUEGO, ARGENTINA: THEIR PALEOBIOGEOGRAPHIC SIGNIFICANCE. Two shallow-water assemblages of benthic foraminifers of strong austral character are recognized in the Irigoyen Formation (Upper Miocene-Pliocene, Rio Irigoyen transtensive Basin, Atlantic coast of the Tierra del Fuego Island). The lower assemblage, dominated by Angulogerina angulosa fueguina (Malumian), is in general similar to the assemblage known from the Carmen Silva Formation; it contains "Trochoelphidiella" sp., previously described from the Antarctic Oligo-Miocene. The upper assemblage is dominated by Nonion hancocki Cushman and McCulloch, a species previously known only from the modern Peruvian coast, and contains frequent Cribrorotalia meridionalis (Cushman and Kellett), which is abundant from the Beagle channel up to the Peruvian coast as a living species, giving both species a Pacific aspect to the assemblage. This Pacific aspect, together with coincident morphoestructural features, suggest a direct shallow connection between the Atlantic and Pacific Oceans by means of a Pliocene paleochannel, here called the "paleocanal de Hoces", similar to the modern Beagle channel. The Hoces paleochannel was running on the areas occupied now by depressions such as the Seno Almirantazgo, the Fagnano Lake and the Irigoyen Basin, related to the Magallanes-Fagnano fault.
