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Chapter 84. Ostracods from non-marine early Cretaceous sediments of Campos Basin, Brazil

Chapter 84. Ostracods from non-marine early Cretaceous sediments of Campos Basin, Brazil

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1208 J. A. MOURA



TEXT-FIG.

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

non-marine basins.

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.



PREVIOUS

WORK

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



I



C HR 0NO ST RATIGRAPHY



J I Q U l A

B U R A C I C A



leY---i

RIO



NEO-



[J”R*SSICI



DA



O



SERRA



OiiO



Tm-no. 2-hcal



stage correlation among

Rec&ncavo/Tucano, Sergipe/Alagoas and

Campos Basins.



Praca (1985) carried out a biochronostratigraphical study of this interval in the Campos basin.



MATERIAL

AND METHODS

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.).



BIOSTR

ATIGRAPHY

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

basin.



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



CAMPOS

BASIN



SERGIPE /

RECONCAVO/

dLAGOAS BASIN TUCANO BASIN

(Schaller, 1969) (Viana



9 4 19711



(this work)



LOCAL STAGES



Zone



AL AGOAS



"Cytheridea 7 "

s p p , gr. 201/211



Zone



L. t r o e l s e n i

C.(F! Ifaveolat



JIQUIA

0 N



-



& C . ( S ) devexa

Subzone

1B.postangulori



TEXT-FIG.

3-Biochronostratigraphical comparative table of Sergipe/Alagoas, Recancavo/Tucano and Campos

Basins for Alagoas and JiquiP Stages.



CORRELATION

SECTIONS

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



A



5



!7



102A



108



A’



5



SE

-



NWJ

-15.5km-



-8.Okm-



. . ..

.. .. . ..... ..

,.. .....,

I



4100



470



TEXT-FIG.&Correlation section A-A‘ (Biostratigraphical units, Campos Basin).



63A



B



sw



A



134



116



131



A



A



&



4200



€3‘



NE



DATUY



= SL



TEXT-ma. 5-Correlation section B-B’ (Biostratigraphical units, Campos Basin).



AGE

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



TEXT-FIG.&-Correlation



sw



section C-C' (Biostratigraphical units, Campos Basin).



86



135



118-A



A



&



&



117



A



Dl



NE



TEX-FIG.



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.



PALAEOECOLOGY

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



E

NW



165



168



A



A



74



63A



E’



210(



270(



310(



TEXT-FIG.

8-Correlation



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.



REMARKS

AND CONCLUSIONS

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.



ACKNOWLEDGEMENTS

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.



REFERENCES

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.,

48 (S~pl.),251-239.

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.



DISCUSSION

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

seismic markers?

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

lines.



Ostracod Evolution and Depositional Characteristics

of the Cretaceous Nenjiang Formation

in the Songliao Basin, China

DE-QUAN

YE

Research Institute of Exploration and Development, Daqing

Petroleum Administration, P. R. China



ABSTRACT

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

ostracods.

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.



OSTRACOD

ZONATION

OF THE NENJIANG

FORMATION

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

extinction.

1217



1218 D. Q.YE



TABLE THE STRATIFICATXON

OF FOSSIL

OSTRACOD

ZONES

IN THE NENJIANG

FORMATION.

Member

c



Reservoir



Oil-bearing

Zu (bed)



sub-bed



Fossil ostracod zonation



2



Cypridea spongvosa

Cypridea magna



1

2



Harbinia hapla

Ilyocyprimorpha inandita



6



1



Cypridea augusta



3

3



4



Cypridea area



3



Cypridea liaukhenensis

Limnocypridea datongzhenensis



2



Ilyocyprimorpha salebrosa



2



5



L T

.*rP



59 - 2



6



7



Lr,



4

-



.

I



0

0



2 3



E



Hei-1-Zu



T 3



Hei-2-Zu



~



.-



-



1



Limnocypridea nova



3



Ilyocyprimorpha portentosa

Cypridea ordinata



c " 2



2



Ilyocyprimorpha netchaevae

Cypridea bella



1



1



6



Upper



Cypridea gunsulinensis, Cypridea

Gunsulinensisvar. carinata



Lower



Cypridea gracila

Cypridea ardua



-0



3



8 8



k



'B



5

-



t



8



4



i -3



1-



L



3

.--



Intercalation

of SO/Sl



Lycopterocypris mediocris

Lycopterocypris vatida



*1



s*



Cypridea anonyma



L:

O



ld



s



2 F 2



1



so



Intercalation

of S1/S2



Upper



Cypridea spingerusa

Cypridea turita



Lower



Cypridea squalid0

Advenocy prisdeltoideus



EVOLUTIONARY

CHARACTERISTICS OF FOSSILOSTRACODS

IN THE NENJIANG

FORMATION

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

regression.

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-



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