Distribution of conspicuous or endemic benthic foraminifera across the K/P boundary in Patagonia

CAROLINA NÁÑEZ Y NORBERTO MALUMIÁN

San Luis, Argentina

Simposio; X Reunión Argentina de Sedimentología, Simposio Límite K/T de Argentina; 2004

Univ. Nac. de San Luis y Asoc. Argentina de Sedimentología

Distribution of conspicuous or endemic benthic foraminifera across the K/P boundary in Patagonia Carolina Náñez1 and N. Malumián1 1.SEGEMAR-CONICET, B. Lavaisse 1194, (1107) Buenos Aires, Argentina. cnaniez@mpgeo1.gov.ar, malumian@mpgeo1.gov.ar          One of the features common to the major extinctions is the preferential disappearance of tropical species over polar species, and of endemic species over cosmopolitan ones. The K/P boundary in northern Patagonia gives the opportunity to verify this feature in mid-latitudes shallow settings. In Patagonia, the K/P transition is characterized by the disappearance or extinction of the endemic benthic foraminifera, passing from a Maastrichtian microfauna of endemic character to a cosmopolitan Danian microfauna, of Midway-type, with few endemic Austral elements (Malumián et al., 1995; Malumián and Caramés, 1995). The turnover between these microfaunas occurs around the K/P boundary, and in order to analyze the nature of the turnover and its paleoenvironmental and paleoceanographic significance, the distribution of endemic species is of particular interest.          Eight species known from the Maastrichtian beds were regarded as endemic to  the Neuquina-Colorado Basin: Alabamina kaasschieteri Bertels, Gavelinella camachoi Bertels, Gavelinella jagueliana Bertels, Gavelinella neuquense Bertels, Praeglobobulimina jaguelensis Bertels, Neobulimina argentinensis Bertels, Buliminella pseudoelegantissima Bertels and Lagenoglandulina neuquensis Bertels, the latter also recorded  in the Danian (Malumián et al., 1995). “Pararotalia” sp., opportunistic, probably endemic, usually occurring in assemblages of high dominance, characterizes some shallow environments of the Maastrichtian of northern Patagonia. Including the entire Patagonia and the Antarctic Peninsula, the following species are also apparently endemic: Favolagena ardolinoi Malumián, Náñez and Caramés, Hiltermannella kochi (Bertels), Favolagena atilai (Bertels), and Buliminella isabelleana Camacho, the two latter species also known from the Danian (Malumián et al., 1995).  Alabamina kaasschieteri should be transferred to the genus Charltonina, and may be a junior synonym of Charltonina acutimarginata (Finlay), a species regarded as endemic to New Zealand. Also, Buliminella isabelleana may be a junior synonym of Buliminella westraliensis Parr (cf. Malumián and Caramés, 2002).          High resolution sampling of the Jagüel Formation in northern Patagonia (eg. Náñez et al., 2002), reveals that Buliminella pseudoelegantissima, a species of marked opportunistic character, survived across the K/P boundary and is very abundant in the finer fractions of the lowermost Danian beds, associated with the also very abundant Buliminella isabelleana. The data obtained up to now indicate that Praeglobobulimina jaguelensis, Neobulimina argentinensis, Gavelinella jagueliana and Favolagena ardolinoi do not cross the boundary, and the first species seems to be restricted to the deepest and dysaerobic settings of the Maastrichtian. Charltonina kaasschieteri, Hiltermannella kochi, Gavelinella camachoi and Gavelinella neuquense were also recorded from the lowermost Danian beds, although they are scarce and the possibility of reworking should be considered. The latter species was also mentioned from the Danian of  the Austral Basin (Caramés and Malumián, 2000).          The genus Praepararotalia, although not exclusive of the southern Hemisphere, is very conspicuous in the Paleocene of Patagonia, developing opportunistic strategies. Scarcely represented in the Maastrichtian of northern Patagonia, it blooms just after the K/P contact, in the lowermost Danian beds, where Praepararotalia cretacea Liu, Olsson and Huber, constitutes up to 50% of the benthic foraminifera. The occurrence of this species is common throughout the Danian of Patagonia, and related forms are found in the Middle Eocene.          Antarcticella and Boltovskoyella are among the few genera conspicuous of or endemic to Patagonia that make their first appearances after the K/P boundary. Both genera become abundant to dominant in the Paleogene of Patagonia (cf. Náñez, 1998; Olivero and  Malumián, 1999). The genus Antarcticella, originally described from the Neogene of Antarctica, was regarded as being of planktonic habit (eg. Loeblich and Tappan, 1988), but isotopic studies indicate a benthic habit confirmed by its distribution restricted to mid and high latitudes of the southern Hemisphere and in shallow settings (Liu et al., 1998).  Antarcticella pauciloculata (Jenkins) is known from the Danian of New Zealand, appearing in the Pα biozone of planktonic foraminifera and ranging through most of the Danian (Hollis and  Strong, 2003). It is also known from the Danian of Antarctica (Liu et al., 1998), the Danian of the Austral Basin (Caramés and Malumián, 2000) and very rare specimens were recorded from the Danian of northern Patagonia. The genus remained in Patagonia, being recorded in the Upper Paleocene of Tierra del Fuego (Malumián and Caramés, 2002) and is very abundant in the Lower Eocene of the Austral Basin (cf. Cañón and Ernst, 1974; Olivero and Malumián, 1999). Its record vanished in the Middle Eocene, and reappeared as Antarcticella antarctica (Leckie and Webb) in the Upper Eocene, becoming a species widely recorded in the Lower Miocene of  Patagonia, in assemblages of Antarctic character (Malumián and Náñez, 1991).             Boltovskoyella, the another typical genus of the Paleocene of Patagonia, appears well after the K/P boundary, in the late Danian, being a conspicuous genus in the late Danian and in the Eocene. References    Cañón, A. and M. Ernst, 1974. Part II, Magallanes Basin foraminifera. In Natland et al., A System of Stages for Correlation of Magallanes Basin Sediments. Geological Society of America Memoir 139: 61-117. Caramés, A. and N. Malumián, 2000. Apéndice 2. Microfósiles calcáreos de la Formación Cerro Dorotea. En Hoja Geológica 5172-III Yacimiento Río Turbio, Provincia de Santa Cruz. Servicio Geológico Minero Argentino, Boletín 247: 79-91. Hollis, C.J. and C.P. Strong, 2003. 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