nannofossil abstracts

acvascon at AX.APC.ORG acvascon at AX.APC.ORG
Sun Mar 13 14:52:06 CST 1994


               Light Microscope Revision of the Structure of

      Nannoliths Incertae Sedis Recognized on Paleocene/mid Eocene

                Section of the Espirito Santo Basin

Simone de Oliveira Costa (1)

Rogerio Loureiro Antunes (2)

  Most of the nannolith species described in this paper are of weel-known
biostratigraphic importance both in international and PETROBRAS biozonal
schemes. In the latter, they are used in routine dating of Paleogene strata
in Brazilian marginal basins. The studied nannofossils have all been recovered
from cuttins of the Paleocene-mid Eocene section of boreholes in the Espirito
Santo Basin (eastern Brazilian continental margin). The basic aim of this
study is to present detailed L.M. (light microscope) descriptions of these
calcareous nannofossils in order to optimize their use in the routine
biostratigraphic datations. Altogether, 9 species have been identified, of
which one is new (Ellipsolithus gomidei), and two other recorded for the first
time in Brazil (Ellipsolithus bollii and Trochastrites hohnensis). Other
identified species belong to the following genera: Ellipsolithus, Nannotetrina,
Tribrachiathus, and Trochastrites. All of them are considered incertae sedis,
because they cannot be assigned to any nannofossil families recognized so far.

(1) (2) CENPES/DIVEX/SEBIPE, Cid. Universitaria - Qd. 7 - Pd. 20, Ilha do
Fundao, CEP 21949-900, Rio de Janeiro, RJ, Brasil.



              Calcareous nannofossils from the Paleocene/mid Eocene

                      of Espirito Santo Bay, Brazil

Simone de Oliveira Costa


  This study concerns calcareous nannofossils recovered from cuttings of the
paleocene-mid Eocene section of five boreholes in the Espirito Santo Basin
(eastern Brazilian continental margin). Its basic aim is to present detailed
L.M. (light microscope) descriptions of the calcareous nannofossils in view
of the following reasons: (a) scacity of published papers on the subject;
(b) need of objective criteria for the recognition of relevant species with
the L.M., so as to optimize their use in routine biostratigraphy.

   Altogether, 87 species have been described, of which 5 are new and 9
recorded for the first time in Brazil. They are assembled into the following
structural groups: pentaliths, placoliths, asteroliths, fasciculiths,
helicoliths, helioliths, sphenoliths, nannoliths of Pontosphaeraceae and
Zygodiscaceae, and nannoliths incertae sedis. Taxonomic classifications of
previous workers have been maintained for most species. Descriptive criteria
followed herein include: (a) the build and arrangement of structural units in
the nannolith; (b) the specimen size; (c) the kind of ornamentation; and (d)
optical behavior of the specimen in both cross-polarized and transmitted
light. The terminology employed in this study makes up a glossary aimed to
supplement the descriptions given in this dissertation.

  Biostratigraphic considerations presented herein are based on schemes of
Antunes (1984, 1990) for the Espirito Santo Basin. The nannofossil
biochronostratigraphy of five well investigated allowed introduction of the
following improvements in Antunes (ibid) framework: (a) addition of 25
species of auxiliary value in the identification of the biozones; and (b)
changes in the range of other 11 species.

  CENPES/DIVEX/SEBIPE, Cid. Universitaria - Qd. 7 - Pd. 20, Ilha do
Fundao, CEP 21949-900, Rio de Janeiro, RJ, Brasil.



         Light Microscope Morphostructural Study of Chiasmolithus

     (Coccolithaceae) nannofossils from the Paleocene-mid Eocene interval

      of the Espirito Santo Basin, Eastern Brazilian Continental Margin


Simone de Oliveira Costa

  This paper presents detailed L.M. (Light microscope) descriptions of
nannoliths belonging to the genus Chiasmolithus (family Coccolithaceae).
The research is mainly based on the analysis of Paleocene-mid Eocene
nannofossils from cuttings of 5 boreholes drilled in the emersed portion of
the Espirito Santo Basin. Results of previous biostratigraphic investigations
carried out by Antunes (1984, 1990) on 50 boreholes of this basin have also
been taken into consideration. The reasons for this study are the following:
(a) scarcity of published papers on the subject; (b) need of objective
criteria for the recognition of relevant species with the L.M., so as to
optimize their use in routine biostratigraphy. In most of the specialized
literature nannofossils are currently described with the scanning electron
microscope (S.E.M.), whereas structural features observable with the L.M.
receive too little attention. However, in the oil industry at least, the
equipment most frequently employed in routine work on clacareous nannofossils
is still the light microscope. Descriptive criteria followed herein include:
(a) the built and arrangement of structural units in the nannolith; (b) the
specimen size; (c) the kind of ornamentation; and (d) optical behavior of the
specimen in both transmitted light and cross-polarized light (with the longer
axis of the nannolith either parallel to one of the nichols or rotated 45o
away from them). The terminology employed in this study makes up a glossary
aimed to supplement the descriptions given in the text. The nannoliths
recognized herein comprise the following species: Chiasmolithus bidens,
C. californicus, C. consuetus, C. danicus, C. eograndis, C. expansus
(recorded for the first time in Brazil), C.gigas, C. grandis, C. solitus and
C. titus. The nannofossils mentioned above have proved biostratigraphic
importance both in international biozones (Martini 1971; Okada & Burkry 1980)
and in zonal schemes routinely employed by PETROBRAS for the Paleogene of
Brazilian marginal basins. The biostratigraphic considerations of the present
research are based on the adoption of ranges proposed by Perch-Nielsen (1985),
especially as concerns the first appearance of the species. Also taken into
account are the propositions of Antunes (1984, 1990), followed by Costa (1992),
for the emersed portion of the Espirito Santo Basin. Antunes` biozones are
interval zones of 4C2 type in the sense of the North American Stratigraphic
Code (N.A.C.S.N., 1983, art. 50, fig. 4). All slides investigated in this study
are housed in the nannofossil slide collection of the Biostratigraphy and
Palaoecology Sector (DIVEX/SEBIPE) of PETROBRAS Research Center (CENPES),
Rio de Janeiro, Brazil.

  CENPES/DIVEX/SEBIPE, Cid. Universitaria - Qd. 7 - Pd. 20, Ilha do
Fundao, CEP 21949-900, Rio de Janeiro, RJ, Brasil.




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