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Chapter 84. Ostracods from non-marine early Cretaceous sediments of Campos Basin, Brazil
1208 J. A. MOURA
1-Study area and location of correlated sections, and location map of Campos, RecBncavo/Tucano
and Sergipe/Alagoas Basins.
The biostratigraphical study of these non-marine sediments can be easily carried out by means
of the ostracods, allowing a better comprehension of the geological history of Brazilian Cretaceous
This paper represents the preliminary step in systematic biostratigraphical studies of this area
based on ostracods. It is devoted to part of the lacustrine-deltaic clastic sequence of the Jiquisl
local stage, also known as the “lake sequence”, and to part of the evaporitic and clastic sequences
of the Alagoas local stage, also called the “gulf sequence” (Pontes and Asmus, 1976).
The ostracods of the Alagoas stage are almost the same as those found in the Sergipe/Alagoas
basin, except for their bad preservation and lesser diversification. The Jiquisl stage is biostratigraphically better refined due to a more diversified ostracod fauna, mainly in its basal portion,
which is comparable to a chronostratigraphically corresponding part of the Rec6ncavo/Tucano
basin. The upper part of the Jiquisl stage is partly comparable to the Rec6ncavo/Tucano basin and
completely comparable to the Sergipe/Alagoas basin in the corresponding sections.
A comparative chronostratigraphical table (Text-fig. 2) provides the local stage correlation and
Text-fig. 3 shows the correlation of biostratigraphical units between the three basins (Campos,
Recbncavo/Tucano and Sergipe/Alagoas) for the referred stages.
The units throughout the study area can be visualized by means of the stratigraphical correlative
sections presented in Text-figs. 4 to 8.
Biochronostratigraphical studies in the Campos basin using ostracods have been carried out
by Petrobrsls personnel and are recorded in private reports existent in Petrobrsls’ files. Moura and
Non-marine Cretaceous Ostracods of Campos Basin, Brazil 1209
C HR 0NO ST RATIGRAPHY
J I Q U l A
B U R A C I C A
stage correlation among
Rec&ncavo/Tucano, Sergipe/Alagoas and
Praca (1985) carried out a biochronostratigraphical study of this interval in the Campos basin.
Ditch and core samples from nineteen selected wells drilled by Petrobris offshore in the Campos
basin were the basic material for taxonomic, biostratigraphical, and correlative studies.
Recognition of the ostracod taxa was accomplished by consulting internal reports and the
papers by Schaller (1969) and Vianna et al. (1971).
The two plates which illustrate this paper were produced using photomicrographs taken by the
Petrobis Research Center’s scanning electron microscope (S.E.M.).
In the Campos basin three biostratigraphical zones have been recognized for the Alagoas and
Jiquii stages. The Alagoas stage is characterized by one single, undivided zone, the “Cytheridea”?
spp. ex. group 201/218 zone, code 011, informally described by Schaller (1969,op. cit.) It is
represented by a poor ostracod assemblage in which only some components are recognizable.
Frequently, a thick sedimentary sequence is representative of this stage. Its upper part is commonly
destitute of ostracods which is a reflection of the environmental restrictions.
The other two zones, corresponding to the Jiquil local stage, are distributed as follows from
top of bottom: Zone Limnocythere troelseni, code 010, represented by a monospecific ostracod
assemblage, occurs in some areas of the basin. This zone was also informally proposed by the
same authors for the Sergipe/Alagoas basin, in the previously mentioned work (Schaller, 1969).
Zone Petrobrasia diversicostata, code 009, with three subzones, is represented by a richer and
more diversified ostracod fauna. It was defined for the Rec6ncavo/Tucano basin (Viana et al.,
1971). This zone can be subdivided into three subzones:
Subzone Cypridea (Pseudocypridina) faveolata, code 009.3, which occurs more frequently,
Subzone Cypridea (Sebastianites) devexa, code 009.2,
Subzone Bisulcocypris postangularis postangularis, code 009.1, occurring less frequently in the
1210 J. A. MOURA
B IOS T R A T IGR A P H Y ( O S T R ACODS)
C HR 0NOS T R AT IGRAPHY
dLAGOAS BASIN TUCANO BASIN
(Schaller, 1969) (Viana
9 4 19711
"Cytheridea 7 "
s p p , gr. 201/211
L. t r o e l s e n i
& C . ( S ) devexa
3-Biochronostratigraphical comparative table of Sergipe/Alagoas, Recancavo/Tucano and Campos
Basins for Alagoas and JiquiP Stages.
Biozones were used exclusively to construct the five sections which illustrate this paper. The
choice of sea level as datum means that the biozones are shown as they occur at present, affected
by all the tectonic disturbances in the basin. With respect to these sections, the following remarks
can be made:
1) Zone 01 1, corresponding to the Alagoas stage, generally encompasses sedimentary sequences
with regular thicknesses along the study area. A tendency for it to thin southward was observed
and it is completely absent in the section E-E'.
2) Zone 010 has an intermittent occurrence throughout the study area. It tends to disappear
in the southernmost part of the basin.
3) Subzone 009.3 is geographically the most widely distributed biozone, encompassing the
thickest sequences along the study area.
4) Subzone 009.2 occurs as the thinnest and most sporadic sequence in the Campos basin.
5) Subzone 009.1 is more regularly distributed in the southernmost portion of the study area,
represented by the section E-E'.
PLATE1-Figs. 1,2. Ostracoda sp. 406. 1. left valve, l-RJS-l17A, 5100-5115m; 2, dorsal view, I-RJS-llgA,
5070-5085m. Figs. 3, 4. Reconcavona aff. R. bateke. 3, left valve, 1-RJS-65, 3065-3,075; 4, dorsal view,
1-RJS-135, 4,740-4,755m. Figs. 5-7. Limnocyprideu subquudruta. 5, left valve, 1-RJS-102A, 4,860-4,875m; 6,
right valve, 1-RJS-135, 4,440-4,445m; 7, dorsal view, l-RJS-l17A, 5100-51 15m. Figs. 8-10. Limnocyrhere
troelseni. 8, right valve, l-RJS-lOZA,4,710-4,725m; 9, left valve; 10, dorsal view, 1-RJS-IOZA, 4,6504,665m.
Fig. 11. Cypridea (Sebastianites) aff. C. (S.)fidafida, right valve, 1-RJS-131, 4,410-4,lSrn. Fig. 12. Bisulcocypris postungduris postangularis, right valve, 1-RJS-131, 4,140-4,155m. (magnification X 33).
Non-marine Cretaceous Ostracods of Campos Basin, Brazil 1213
. . ..
.. .. . ..... ..
TEXT-FIG.&Correlation section A-A‘ (Biostratigraphical units, Campos Basin).
TEXT-ma. 5-Correlation section B-B’ (Biostratigraphical units, Campos Basin).
Originally formalized in the Recdncavo/Tucano and Sergipe/Alagoas basins, the Alagoas and
JiquiP local stages have a problematical position in the international time scale, caused by the
difficulties in correlating international stages. They are best represented in the Sergipe/Alagoas
basin, but they occur in many other continental Brazilian basins, as well as in marginal ones.
The best correlation in terms of a continental approach is with west Mrican basins because of
their common and peculiar origin.
PLATE2-Figs. 1,2. Theriosynoecumpapillaris. 1, right valve, 1-RJS-65, 3,270-3,285m; 2, dorsal view, 1-RJS-65,
3,150-3,165m. Figs. 3,4. Theriosynoecumdorsocallosum. 3, right valve, l-RJS-73B, 3,090-3,105m; 4, dorsal View,
1-RJS-65, 3,330-3,345m. Fig. 5. Petrobrasia diversicostaiu, right valve, 1-RJS-71, 3,495-3,510m. Figs. 6-14.
“Cyprideu” spp. ex. gr. 201/218. 6, left valve, 1-RJS-116, 3,570-3,585m; 7, left valve, l-RJS-l18A, 4,7104,725m; 8, left valve, 1-RJS-125, 3,630-3,645m; 9, right valve, 1-RJS-101, 4,1104,125m; 10, right valve, 1RJS-118, 4,3504,365m; 11, right valve, 1-RJS-101, 4,1104,125m; 12, right, l-RIS-l18A, 4,7104,725m; 13,
right valve, l-RJS-l25m, 3,630-3,645m; 14, right valve, 1-RJS-118, 4,3504,365m. (magnification x 33).
1214 J. A. MOURA
section C-C' (Biostratigraphical units, Campos Basin).
The Alagoas stage is considered as at least partially equivalent to the Aptian, and the Jiquil
stage is considered as pertaining to the late Neocomian, more likely to the Barremian. Therefore,
it is not out of the question that its youngest portion be accepted as belonging to the Aptian stage.
Using uniformitarian concepts, which must be taken as proposals for interpretation, some
palaeoenvironmental inferences were drawn in this work concerning to the faunal content of
the biozones of the Alagoas and Jiquil stages. Caution is needed in adopting those premises,
especially when applied to ancient ecosystems such as the ones analysed in this paper. The inferences drawn may be summarised as follows: the Alagoas stage ostracod fauna in the Campos
Non-marine Cretaceous Ostracods of Campos Basin, Brazil 121 5
section E-E‘ (Biostratigraphical units, Campos Basin).
basin consists of a low diversity, and fairly poor, assemblage. Exclusively smooth ostracods, questionably attributed to the genus “Cytheridea”, are found in the unique zone (011) of the stage.
Associated with them, gastropod and pelecypod shells are recovered at some levels. Marine fossils
are absent. This faunal content disappears upward towards the top of the stage, where the palinomorphs persist. Evaporitic beds are found just above this interval, ending a sedimentary evaporitic
cycle common to the Brazilian and African Atlantic marginal basins. In view of these data, a
transitional lacustrine to lagoonal environment is supposed to have been governing the sedimentary deposition of the Alagoas stage.
The Jiquid stage, represented by five biozones, shows a different environmental pattern with
a tendency for conditions to become brackish to freshwater in the earlier part. Analysing this sequence from top to bottom, zones 010 and 009 are found.
Zone 010, the youngest of the stage, is represented by a monospecific biota, made up of Limnocythere troelseni, a small and weakly ornamented species, which indicates an ecosystem where
conditions of high stress prevailed, probably as a result of strong variations in the physico-chemical
factors. Besides this fact, the intermittent occurrence of this biozone in the study area is observed.
The preceding older zone 009, in its youngest subzone 009.3, bears ostracods among which are
found some fairly ornamented forms. These ostracods generally possess strong carapaces and are
absent in the Rec8ncavo/Tucaco basin, as is the fauna of the Alagoas stage. Both these faunas
represent a sedimentary cycle inhibited in the Rec8ncavo/Tucano, but present in the Campos,
Sergipe/Alagoas and in many other Brazilian and West-African coastal basins.
The lower part of the Jiquid stage, dated by the oldest part of subzone 009.3 and by the entire
009.2 and 009.1 biozones, contains ostracods which are also found in the Rec6ncavo/Tucano basin
and whose morphological characteristics are the same. These forms indicate a lacustrine-deltaic
environment and species of the genera Cypridea, Bisulcocypris, Theriosynoecum and Petrobrasia
are recognized among them.
The aim of this work of refining the biostratigraphical zonation in the Campos basin for this
interval is justified because of the presence of the best source and reservoir rocks within its boundaries (Estrella er al., 1983).
1216 J. A. MOURA
Work on the recognition of the ostracod biozones established in RecbncavolTucano and
Sergipe/Alagoas basins has been continuous in almost all the basins of the Brazilian continental
margins. This has contributed to the understanding of its geological evolutionary history and
improved the stratigraphical correlation of these basins.
The author expresses his gratitude to Petrobrfis’ management for permitting the presentation
and publication of this work and acknowledges the suggestions and comments of his colleagues
Diams Dias-Brito, Jorge Carlos Della Ffivera and Jonas dos Reis Fonseca. He is grateful to HClio
Si Brito and the photographic laboratory personnel for technical work in connection with
the plates. The author also gratefully acknowledges the help of all those colleagues who have
contributed to this paper.
ESTRELLA, G.o., MELLO, M., GAGLIANONI, P.c., AZEVEDO, R.L.M., TSUBONI, K., ROSSETI, E., CONCHA, J. and BRONING,
I.A.M. 1983. The Espirito Santo Basin (Brasil) source rock characterization and petroleum habitat. In DEMAISON,
G. and MURRIS, R.J. (eds.). Petroleum geochemistry and basin evaluation, 253-271. A.A.P.G. Mem., 35, Tulsa.
MOURA, J.A. and PRACA, U.M. (in press). Ostracodes das sequkias ngo marinhas e transicionais mesozdicas
(Andares JiquiP e Alagoas), Bacia de Campos.
1976. The Brazilian marginal basins: current state of knowledge. An. Acud. Brasil. CiZnc.,
SCHALLER, H. 1969. Revisfo estratigrhfica da bacia de Sergipe/Alagoas. Bol. Tkc. Petrobrds, 12(1), 21-86.
VIANNA, c.F.,GAMA JUNIOR, E.G., S I M ~ E S ,I.A., MOURA, J.A., FONSECA, J.R. and ALVES, R.J. 1971. Revisgo estratigrPfica
da bacia RecBncavo/Tucano. Zbid., 14(3/4), 157-192.
PONTE, F.C. and ASMUS, H.E.
Athersuch : Do you consider your biozones to be truly chronostratigraphical or are they
strongly influenced by facies? Do you have a good correlation between your biozones and
Moura: We have recently been concerned with this question. I would say that it depends on the
observed time scale. Great events reflect changes in the environment and the ostracods mark time
lines in this case. The several extinction levels are time lines and the recurrence of species was
never observed. In response to your second question, ostracods are certainly well correlated with
electric markers. I believe that good seismic reflectors are well correlated with ostracod time
Ostracod Evolution and Depositional Characteristics
of the Cretaceous Nenjiang Formation
in the Songliao Basin, China
Research Institute of Exploration and Development, Daqing
Petroleum Administration, P. R. China
In the Cretaceous Songliao Basin, the Nenjiang Formation is the best-developed and is overlain
by the Sifangtai Formation and underlain by the Yaojia Formation. The Nenjiang Formation is
more than 1OOOm thick and forms a great area of dark mudstone and sandstone, where the
oil-bearing beds of the Heidimiao and Shaertu reservoirs Sa-1-Zu and Sa-0-Zu are located. The
formation changes little both in lithology and thickness and mainly consists of grey-dark
mudstones, shales and oil-shales, grey-green mudstones, intercalating grey, grey-white fine silt
sandstones and red mudstones at the upper part of the formation. Upwards, the Nenjiang Formation becomes finer in grain size and richer in fossils. Overall, the Nenjiang Formation can be
divided into five successive members based on the vertical changes in lithology and fossil
During recent years, secondary expioration in the Songliao Basin has taken place. The Hiedimiao reservoir of the Nenjiang Formation is of great interest to the oil industry and as a result,
palaeontologists have also done a great deal of work on it, especially detailed work on ostracods.
OF THE NENJIANG
Ostracods are common in the Nenjiang Formation. Their vertical and horizontal distribution
has been understood through identification and statistics based on more than 2,800 specimens.
According to the regular ostracod distribution, diversity and abundance, the ostracods from the
Nenjiang Formation have been divided into sixteen fossil zones and correspondingly placed in
seventeen beds (Table 1). The fossil ostracod zones can be used for comparison over the whole
basin, and consequently, provide a palaeontological basis for further studies on the sedimentary
facies of the Nenjiang Formation and for the subdivision of the Heidimiao oil-bearing reservoir.
From the characteristics of the fossil zonation, not only have the ostracod bearing strata been
divided into seventeen beds, but it has also been established that the range of the ostracod species
in most of the zones is very short. Some genera and species are limited to one fossil zone where
they pass through all the different evolutionary stages-first appearance, development acme and
1218 D. Q.YE
TABLE THE STRATIFICATXON
IN THE NENJIANG
Fossil ostracod zonation
59 - 2
c " 2
Cypridea gunsulinensis, Cypridea
2 F 2
CHARACTERISTICS OF FOSSILOSTRACODS
IN THE NENJIANG
After the transgression seen in the Qingshankou Formation and the regression of the Yaojia
Formation, the Nenjiang Formation represents a new transgression in the Cretaceous Songliao
basin. With the changing environment, the ostracod ecology of the Nenjiang Formation also
changed considerably. Evolution clearly occurred in such features as the number of genera and
species, the abundance of individuals, the development of ornamentation, etc.
Characteristics of the Evolution of Genera and Species
With the new transgression during the period of deposition of the Nenjiang Formation following
the Yaojia regression, great changes happened in the variety and number of ostracod genera
and species, of which there are more than in the Yaojia Formation, deposited at a time of
The basin transgression began with the deposition of the 1st member of the Nenjiang Formation, when the ostracod fauna consisted of 24 species and 4 main genera: Cypridea, Lycoptero-