FORAMS 2014 ABSTRACT VOLUME
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paleogeographical distribution, the abundant microspheric tests are considered the typical form, and the megalospheric ones are informally named: A. pauciloculata forma primitiva, from the Danian of the Colorado and San Jorge basins; A. cecionii f. noguerense, from the Fuegian lower and lower middle Eocene; and A. antarctica f. incognita, from the Fuegian late mid-Eocene. The benthic habit previously assigned to Antarcticella is confirmed by: the accentuated dimorphism, unknown in planktonic foraminifera; the opportunistic behavior suggested by its distribution in different paleoenvironments, and by its abundance in organic-rich settings in correspondence with the preferences of similar modem spherical infaunal morphotypes. Ammoelphidiella, originally described from the Antarctic Pliocene, is recorded by a new species from the early Miocene of the Austral Basin up to the late early Miocene in the Colorado Basin. The geographic distribution of Antarcticella and Ammoelphidiella reveals the major penetration of Antarctic waters in the early Miocene on the Patagonian Platform. The tests of both genera share a preferential bioerosion among associated foraminifera and could be one of the causes that contributed to their disappearance in the late Pliocene. Projects PIP 0820 (CONICET, Argentina); CGL20ll-230n and CGL20l1-229l2 (Spanish Ministerio de Economía y Competitividad, co-founded by FEDER funds).
Microperforate planktonic foraminifera from the late Maastrichtian-Danian of Bajada del Jagüel, Neuquén, Argentina Carolina Náñezl, José A.
Arz2,
Ignacio Arenillas2 and Norberto Malumián1
¡Servicio Geológico Minero Argentino and CONICET, Buenos Aires, Argentina. e-mail:
[email protected] 2Dpto. Ciencias de la Tierra and IUCA, Universidad de Zaragoza, Zaragoza, Spain Microperforate planktonic foraminifera characterize the late Maastrichtian and Danian of the Bajada del Jagüel section, Neuquén Basin, a shallow marginal basin at mid southem latitudes. The late Maastrichtian is characterized by the abundance of the tris erial genus Guembelitria, represented by G. cretacea Cushman, G. blowi Arz, Arenillas and Náñez and G. dammula Voloshina. This genus absolutely dominates the planktonic assemblages in the last two meters of the Maastrichtian, except for a small peak of biserial species at ca. 40cm below the Cretaceous/Paleogene (K/Pg) boundary. The associated benthic assemblages are relatively diverse, suggesting stable conditions. The first meter of Danian sediments, including the KlPg boundary bed, contains foraminiferal assemblages of a very low p/b ratio, where planktonics are represented by the serial genera Guembelitria and Woodringina/ Chiloguembelina. Planktonic species indicative of the Parvularugoglobigerina eugubina biozone were not found. Towards the upper part of this first meter, biserial planktonic foraminifera (Woodringina/ Chiloguembelina) increase in abundance relative to triserials and are associated with a low diversity benthic assemblage dominated by Antarcticella pauciloculata (Jenkins). This small opportunistic species endemic to southem high latitudes and apparently of polar origin, was originally assigned a planktonic habit, and later regarded as a benthic species. At Bajada del Jagüel, it abruptly appears just after the KlPg boundary. This assemblage characterized by Antarcticella and planktonic biserials occurs in a horizon with diffuse lamination suggesting deficiency in oxygen content. An acme of biserial planktonics has been described elsewhere in the Danian but local factors cannot be disregarded. Upwards in the section, p/b ratio increases and planktonic assemblages become more diverse suggesting a relative increase in sea level. They inclúde abundant low trochospiral, normal perforate taxa; among microperforate taxa, Globoconusa daubjergensis (Bronnimann) is dominant; serial planktonic foraminifera are also common, including "Guembelitria" spp. and Trochoguembelitria alabamensis (Liu and Olsson). These planktonic assemblages are associated with the cosmopolitan Midway-type benthic
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assemblage. Thus the section provides opportunity to analyze the paleoecology and evolution of the wall texture of microperforate planktonic foraminifera in the late Maastrichtian-Danian from southern mid latitudes. Funded by projects PIP 0820 (CONICET, Argentina); CGL2011-23077 and CGL20l1-22912 (Spanish Ministerio de Economía y Competitividad, both co-founded by FEDER funds).
Variations of benthic foraminiferal biomass in response to gradients of organic matter and redox conditions off the Central Peruvian coast Dennis
Romero1,2,
Dimitri Gutiérrezl,2 and Jorge Cardich2,3
lInstituto del Mar del Perú. e-mail:
[email protected] 2Universidad Peruana Cayetano Heredia 3Universidade Federal Fluminense, LMI PALEOTRACES, Niteroi, RJ, Brazil One ecological aspect in the upper Central Peruvian margin still not well known is the contribution of foraminiferal biomass to the benthic communities within the OMZ, which would furnish valuable information in terms of energy flux and carbon cycling. The presence of strong phytodetrital carbon fluxes and extreme dysoxic bottom waters, make for high densities ofbenthic foraminiferal communities. Diversity and vertical distribution of benthic foraminifera on the continental shelf off Callao appeared to be governed by redox conditions and labile organic matter. Clearly, those controlling factor s might rule biomass as well and could be very useful to explore differences in foraminiferal communities. Thus, the benthic foraminiferal biomass was assessed in two bathymetric transects off Callao (12° S) and Pisco (14° S) during April 2009, 2010 and 2011 in relation to bottom-water dissolved oxygen (BWDO), quantity (chlorophyll a and chloroplastic pigment equivalents (CPE)) and quality (chlorophyll a/phaeopigments ratio, carbohydrates (CHO), proteins (PRT)) of sedimentary organic matter (OM) and bulk properties (total organic carbon and total nitrogen) for the top 1cm of sediment. Pore water sulfide (H2S) was used as a proxy of redox condition for their vertical microhabitat. Calcareous and agglutinated foraminiferal biomass was estimated based on maximum length of the cell applying the carbon/diameter ratio for species of similar shape and size previously calibrated. For allogromids, we considered the calculation of the volume of the test by approximating the cell shape to a sphere or pro late spheroid and elongated shapes. Highest values of total biomass (~ 2000 mg.C m-2) were found which are close to the estimates of previous studies recorded for this region suggesting an important budget in terms of organic carbono Total carbohydrates on sediment showed different profiles correlated with biomass in both areas. Biomass in Nonionella auris correlated better with pore water sulfide firming up the importance in other processes such denitrification due to their large biomass. We concluded that biomass as well as the other community parameters seems to be governed by quality of organic matter.
Preliminary analysis of the latitudinal distribution of the Holocene planktonic foraminifera from the Southern Brazilian continental margin: The water masses influence Eduardo da Silva Aguiar1, Guilherme KrahlJ and Micael Lua Bergamaschi2 lUniversidade do Vale do Rio dos Sinos, Instituto Tecnológico de Micropaleontologia FOSSILlUNISINOS), Sao Leopoldo, Brazil. e-mail:
[email protected] 2Research Center ofPetrobras, Fundayao Gorceix (BPA/CENPES), Rio de Janeiro, Brazil
(ITT
