A conspicuous agglutinated new genus of calcareous cemented and perforate wall with remaneicid test morphology from the early Eocene southern high latitudes

MALUMIÁN, N., NÁÑEZ, C., JANNOU, G. Y ARENILLAS, I.

Zaragoza

Workshop; Ninth International Workshop on Agglutinated Foraminifera; 2012

In southernmost South America, the Austral Basin contains a paradigmatic marine Paleogene sequence with representative assemblages of benthic foraminifera in an oceanic hemisphere. These assemblages include several calcareous taxa endemic to high southern latitudes (Malumián and Náñez 2011), such as the conspicuous genera Boltovskoyella and Antarcticella. The latter was originally assigned to a planktonic paleohabit, due to its misleading gross morphology. We add to these taxa of peculiar morphology, a new genus and new species with a wall test agglutinating small foreign particles with very abundant calcareous cement and subdivided chambers that previously led us to misinterpret it as a complex calcareous form (Malumián and Náñez 2002). This peculiar form was found in the early Eocene Punta Noguera Formation, in the Tierra del Fuego Island, from outcrops of very difficult access, so that the gathered material is limited. The new genus has a morphology and paleohabitat similar to those of the subfamily REMANEICINAE Loeblich and Tappan 1964, particularly to the genera Bruneica and Remaneica: It has a low trochospirally coiled small test; the first two or three chambers are globular and undivided; subsequent chambers are semilunate from spiral view, mushroom-shaped from umbilical view, and subdivided by radial secondary septula; the interiomarginal aperture is situated at the end of a median umbilically directed scarcely perforate projection resembling to that of Bruneica. The new genus differs from the organically-cemented REMANEICINAE by the perforate rigid wall, completely calcareous in the initial chambers to very finely agglutinate in the last whorl. It bears scattered perforations, larger on the umbilical side (diameter: 3.75 - 5 µm) and smaller on the spiral side (2.5 - 3.35 µm), mostly situated in the last whorl where the agglutinated foreign particles are more evident. Other smaller perforations are preserved as thin and long gypsum infillings (diameter: 2,5 µm) in the initial chambers of a deeply etched test. Two types of tests are recognized in the general shape: one is the more common watchglass-shaped form that apparently reaches larger sizes (microspheric form?), and the other corresponds to more conical forms with a prominent umbo on the spiral side (megalospheric form?). The paleohabit of this new genus, according to its Holocene homeomorphous Bruneica and Remaneica, would be attached and inhabiting tropical shallow water. This interpretation is also supported by the associated foraminifera, the benthics dominated by attached morphotypes, and the scarce planktonic foraminifera, only represented by small serial forms (Malumián et al. 2009, Malumián and Jannou 2010). Another close homeomorph genus is Abyssotherma, described from the vicinity of deep-sea hydrothermal springs, a contrasting bathymetric but thermally similar paleoenvironment (Brönnimann et al. 1989). The new genus and new species is an exceptional case as calcareous cemented agglutinate foraminifera in the Magallanes Basin, and its occurrence would reflect the early Eocene warm climate in southern high latitudes. According to the most recent systematics proposals (fide Kaminsky 2004), this new genus, despite of the close morphology, would not belong to the organically cemented and imperforate TROCHAMMININA Saidova, 1981, because it has perforate calcareous cemented wall and consequently a firm and resistant test resulting from mineralization of the organic cement by calcium carbonate, and neither to the TEXTULARIINA Delage & Herouard, 1896 because its test gross morphology is uncommon for this suborder. So that, the high systematic location of this new genus will depend whether the chemical composition and structure of the biogenic deposits of the test wall are regarded to be of major systematic importance or the gross morphology must be taken first into consideration. This new genus will be formally described, and its high systematic position will be determined depending on the comments we could harvest in this workshop.