The family Rzehakinidae (Foraminifera) from the Upper Cretaceous-Paleogene of the Austral Basin and the adjacent Atlantic continental shelf, Argentina.

The stratigraphic and paleoenvironmental significance of the Rzehakinidae in the widespread Cretaceous-Paleogene agglutinated foraminifera assemblages of southernmost South America, particularly the Austral Basin, is reviewed. Rzeliakina epigona (Rzehak), R. lata Cushman y Jarvis and transitional forms are found in the Bahia Thetis Formation (Upper Campanian-? Lower Maastrichtian); scarce specimens of R. fissistomata (Grzybowski), in the Bahia Thetis Formation, in the Maastrichtian part of the Policarpo Formation and in the Punta Torcida Formation (Lower Eocene). More delicate and small size, evolute and thin walled forms assigned to R. minitria Cushman y Renz occur from the upper Campanian up to the Punta Noguera Formation (uppermost Paleocene/ lowermost Eocene), becoming widespread and abundant in the "Inoceramus Superior", "Arcillas Fragmentosas" and "Senoniano" (Maastrichtian-Paleocene? subsurface beds). Few specimens of Spirosigmoilinella naibensis Turenko ? are recorded from the Lopez de Bertodano Formation (lower Upper Maastrichtian) in the Antarctic Peninsula, the Rio Claro (Upper Paleocene) and Rio Bueno (lower Middle Eocene) Formations in Tierra del Fuego Island. Spirosigniodinella compressa Matsunaga is abundant in Patagonia from the upper Oligocene up to the lower Miocene, and has its oldest record in Tierra del Fuego Island, in the lowest Oligocene, between the last ocurrences of Isthmolithus recurvus Deflandre and Subbotina angiporoides angiporoides (Hornibrook). Silicosigmoilina angiista Turenko is recorded from the Policarpo and the Rio Claro Formations. Typically all these genera are mostly restricted to clastic deep settings of the Andean thrusted and folded belt. The genus Miliammina is recorded in an almost monospecific assemblage of shallow water environment from the Cerro Cazador Formation (Upper Campanian).