Tải bản đầy đủ - 0 (trang)
Chapter 36. Relationships between ecological models based on ostracods and foraminifers from Sepetiba Bay (Rio de Janeiro, Brazil)

Chapter 36. Relationships between ecological models based on ostracods and foraminifers from Sepetiba Bay (Rio de Janeiro, Brazil)

Tải bản đầy đủ - 0trang

468



-



0



4



I



8km

I



i



i



TEXT-FIG.

l-Study area and sampled points in Sepetiba Bay.



i



I



/



LEGEND



159



0

t



4

1



)



8Rn

h



SAMPLED POINT

1SOBATH

( m 1



I



0



TEXT-FIG.

2-Bathymetry in Sepetiba Bay (after Carvalho et ul., 1979).



43'40'



I



Ecological Models Based on Ostracods and Foraminifers 469



island (Restinga de Marambaia), a lagoon (Sepetiba Bay), a small delta dominated by fluvial

processes (delta of the Guandu River) and a tidal flat, partially covered with mangroves (Guaratiba area). The system has its present configuration tied to events which occurred after the Wurm

glacial interval; more accurately, it is a post-Flandrian transgression. It fits exactly the microtidal

estuary of Hayes (1976). The climate of this area is the tropical type, hot and humid, rainy in the

summer and dry in the winter, belonging to group A of Koppen's classification. Quaternary coastal

plains and pre-Cambrian rocks of the Serra do Mar constitute the neighbourhood of the complex.



Sepetiba Bay: Abiotic Components

This lagoon, with an area of nearly 305 km2,is semi-isolated from the Atlantic Ocean by an

approximately 40 km-long sand bar, which links the metamorphic Pic0 da Marambaia in the

West to the mangrove area of Guaratiba in the East. A string of metamorphic islands, of which

the largest are Jaguanum in the South and Itacurgi in the North, contributes to the isolation of

the bay.

The bathymetry is shown on the map (Text-fig. 2). The depth increases gradually from east to

west and is 8-10m in the central portion; there are deep channels between the Jaguanum and

Itacurugl islands reaching down to 27 m. The water temperature ranges from 19.7' to 251°C;

the pH values range from 7.6 to 8.3. Concerning salinity, adopting Boltovskoy's classification



-



40-3O0/oo



EUHALINE

MIXOHALINE 6 EUHALINE BOTTOM SALINITY

BRACKISH TO MlXOHALlNE



C



30-18°/oo

1 8 - 5 O/oo



\



EUHALINE

MIXOHALINE

BRACKISH WATER



D



U



1.0- 1.5



MUDDY



O-Wo/o SAND



FuEDy



a 26-5O0/0 SAND



~



~



N



~ -75%

y ~SAND

5



SAND 0 7 6 - 1 0 0 % SAND



1



O/o



a 0 . 5 - 1.0 yo

=>

0.5



O/o



Bottom salinity (mod. from Carvalho et al., 1979). B. Surface salinity (mod. from Carvalho

et a1.r 1979). C . Sediment distribution in Sepetiba Bay. D. Organic matter content.



TEXT-FIG.

3-A.



470



TBxr-pra. &System



of currents in Sepetiba Bay based on the distribution of benthic and planktonic micro-



organisms.



M



-



0

I



=

Is3



6QOOO-360.000

10D00- !50.000

1.000- 10.000

1.000



m <;",-



8km



4



I



I



I



I



TBXT-FIG.5-Absolute frequency of foraminifers (per 3000 cm' of wet sediment).



I



1



471



-



TRANSITIONAL ZONE



0



4



8km



a NORMAL MARINE LAGOON

TRANSITIONAL ZONE I



[II]MIXO- EUHALINE B LAGOON



aMIXO-EUHALINE



A LAGOON

I



I



I



I



45

40

35



30

25



PO

15

100



500 1000



5000 1o.Ooo



NORMAL MARINE LAGOON

25100



500 x)o

5000

NUMBER OF SPECIMENS



x).m



NORMAL SEA



MIXO-EUHALtNE LAGOON-A

MIXO-EUHALINE LAGOON-B



TEXT-FIG.

6-Environmental compartments based on specific diversity of foraminifers and specific diversity

in &he environmental compartments (Fisher’s a index).



472 D. DIM-BRITO,

J.A. M o m AND N.WURDIQ



(1976, p. 139), the waters at the bottom are brackish near the mouth of the Guandu River, mixohaline to euhaline in the north-east part as a consequence of the interaction of microtidals (less

than 2 m) and a variable influx of fluvial waters, and euhaline in the main part of the bay. The surface waters are predominantly mixohaline (Text-figs. 3A, B). A salt wedge estuary of Pritchard

(1967) may, thus, be recognized in this area.

The sediments deposited in the lagoon are predominantly fine siliciclastics, with the exception

of the area adjacent to the barrier island and the mouth of the Guandu River, where coarse sediments occur (Text-fig. 3C). The highest content of organic matter, 0.5 to 1.5%, occurs associated

with the most argillaceous sediments (Text-fig. 3D). The CaCO, content in the sediments ranges

from 5 to 25 %, the highest levels being found in the most argillaceous sediments. The granulometry

increases from east to west as a consequence of the progressive, parallel energy increment of the

waters in this direction.

Sepetiba Bay is a relatively calm environment. An ocean stream, however, penetrates the inner

portion of the lagoon, passing between the Jaguanum and Itacurug Islands and heading north;

near the mouth of the Guandu River, the stream suffers a deflection towards the east and proceeds around the bay. Its action causes severe erosion effects in the central portion of the barrier

island. The central area of the bay is calm and, as a consequenceof the main stream, a slow moving

ellipsoidal stream probably exists there (Text-fig. 4).



Cribraetphidium 8ppJA. bemrli

A.bsmPri//Cri&oelphidiun SPP

I';y Goudryino ( ? ) exilis

G*inque/ocufina sp. 1



TEXT--FIG.

7-Biofacies of foraminffers.



Rofshouaenio rofshouseni / Cribroefphidium8 pp

Rafahouscnio rofabausoni

Textulorio r p . l / Texfulorio rp. 2



Ecological Models Based on Ostracods and Foraminvers 473



Sepetiba Bay: Biotic Components

The major microbiological elements present in the Sepetiba Bay include, in addition to Foraminifera and Ostracoda, micromollusca, diatoms, Radiolaria (not common), Archeomonadidae

and sponge spicules (not common). Maps showing their distribution were presented by Moura

et al. (1982). The biotic data, as well as the abiotic, were obtained from 176 sample stations. The

field work was carried out between May and August, 1978.



FORAMINIFERA

Essentially benthic Foraminifera occurred in the area researched. The contents include eury-



Mine and stenohaline species, distributed in specific areas :mixed Lagoon (mixohaline to euhaline

01



z



w



I



I



M-FIG.

&Foraminifera1 frequency/diversity in the 4 environmental divisions (including the biofacies).



-



0



4



8 km



-130

31-130



1-30



TEXC-FIG.0-Absolute frequency of ostracods (per 3000 cm3 of wet sediment).



474 D. DIAS-BRITO,

J.A. M o m AND N. WURDIG



waters), marine Lagoon (euhaline waters) and marine environment (euhaline waters with good

circulation). No distinction between live and dead specimens was made at the time of collection.

Thus, the work was based on total populations existing in the surface sediments collected. Considering that the sedimentation rate in this area is significant and utilizing the results obtained by

Walton (1955), it may be assumed that the maps represent primarily the distribution of live foraminifera.



Frequency

The foraminifers are distributed throughout the lagoon. The highest frequencies occur in the

most unstable environments, where stresses are high and there is a large availability of nutrients.

Rotalids largely predominate and miliolids are rare (Text-fig. 5). Maps showing the distribution

of the three suborders have been published by Bronnimann, Moura and Dias-Brito (1981b).



0



0



0



0



0



0



4



TEXT-FIG.10-Biofacies



0



0



D

O



I



0



0



O



. . , .O



0



0



0



0

D



0



0

0



0

0



8km

I



I



I



I



I



of ostracods in Sepetiba Bay.

I



TEXT-FIG.11-Ostracod biofacies: specific distribution. Remarks concerning the biofacies 9 and 10. In Biofacies 9,

several species that occur in the north, as well as in the south, are not present in the deeper central part (27 m).

This is characteristic of Kangarina sp., Orionina sp., Keijia sp., Morkhovenia sp., Xestoleberis sp. and Bairdidae

(Text-fig. 13). This phenomenon should be related to the presence of the marine current that enters the bay this

way. This is in agreement with the interpretations of Bronnimann, Moura and Dias-Brito (1981). However,

Perissocytheridea sp. 1, Coquimba spp. and Pistocythereis spp. occur in this central area. On the other hand,

Mutilus spp., Callistocythere sp. 3(?), Paracypris sp., Hemicytherura sp. and Padenborchella sp. only occur in the

south of Biofacies 9. This assemblage characterizes a sub-facies under the influence of a more marine water

mass, here called the Mutilus*spp. subfacies after the most common genus in the area. The remarkable

difference between Biofacies 9 and 10 is the insignificant occurrence of Perissocytheridea sp. 1 in Biofacies 10.



475

-



~~



RELAT

FREP.



MAIN SPECIES



(%I

-



OCCURRENCE



Cyprideis riogrondmsis



7 -9c



Widespreod



ffinuythere C L lhinii



4-3c



Widewood



Cytheruro rpp.



4-15



widewwd



Cyprideis spp.



21 -10



Perisoeytheridw sp. 1



5-6(



-



-



WideWidsspmd



21 -10 Eost port

6-10 west port

West port

5-6C lnwst

impmhntl



Cyprideis rtogrondensis

Pcrissocythwideo rp 1



Widespreod



TOM110 Sp 1



51-ia

ClO




Cyprideis riogrondensis

Collistocythen rp. 1

Tondlo r p . 1



-



ASSOCIATED SPECIES



yz

(%)



Perissocytherideo rp. 1



53



16-23



ffinicythere cL beinii



OCCURRENCE



Two slotions



Cyprideis solebroso



1-25

c5



R cf. Rrommelbeini



cf. heinii



ffinicythere



Loaoconcho r p . 2



Widesprad

Widesprwd

Widewrwd



Perisscrytheridw r p . 1



1-35

1-03

8-12

4-13

21



4



Eostern port

Eodern pnt

West port

T h r n staths

four slotions

Wides&neod

Eostern port



P e r i m y t h e r i d w rp. 1



7-80



Widow&



Pistcrythereis rp .



1-05



Very rore



Cyprideis riogrondensis



6 -90



Wideswwd



Neomonocerotino rp.



1-05



Very rore



Widespreod



Collistocythwe ap. 2



1-22



Very rore



Tonello so. 1



0.5-19



Pistorythereis rp.

*kxytheridw



81 - m Widespread



sp. 1



Collistocythere 0 . 1



Cyprideis riogrokiensis



Nwnhmonrotino rp.



Tonello rp. 1



I



TOM/& SP.



Collistocythwe r p . 2

Argilloeoio rp.

Cywideir riowonhnsis



1-05



sovln port



0.1-10

0.1-10



SauH, port



<5



-



6-01



Eost port



Parissocytlhridw rp. 1



0.1 20



25- 70



West port



Pistocythenis sp



11-20



38-50 Fort port

7-25

21 -55

10-50



ScnMmd port

Scorce stotkms

Nortlwst mrt

Widesprd

Sporodic



Tonefio rp. 1



< 10



Rore



West port



Xestokberis rpp.



el0



Widespreod



Widasprood



Cyprideis riogrondmsis



Widewed



Pistmythereis r p .



Widesped



CoIlistocyt&re



SP.



1



Uongorino rp.

Pistocytbereis up.

XestoIe6wis spp.

c o llirtocythue spp.

Collistocythere r p . 1



21-80



- -Boirdidoe

- - - - - - - - __ - -



3



Cyprideis riogrondensis

Pellucistuno r p

Morkhounio 8P.

Hemicytheruro sp.

Poimjenborchello sp.

Porocmris o. &ememis rp.

aeijia rp. Orionino rp.

Mutilus 4. Coudites sp.



.



Coquimbo r p p



Collistocythsr# rp. 3 ?



.5-28 Widespreod



25-80



Widesprwd



Perisscrytheridw rp. 1

Urocythereis sp.

ffutilus rpp.



7-32

1-12

J.1-11



Two stotions

Two stotions

Dispersed



-MorRhonenio

- - -- - - - - - - _ _ _ - - - - - ap.



Coqui&



sm.



Xestoleberis 8pp.



5-25



1-12



Wides,wod



Widesprwd



Hemicytheruro rp.

Orionino sp.

Pellucistomo sp.

Porocytherideo ap.

Coudites sp.



, Aurilo



<5

rp.



0i.werssd



476



-.9-8.4 9 - 8.4



a



.



-



0 --8.3kO 0



!I - 25 25-23

NDDY



SAND



BATHliMETRY ( m )



0-2



0-6



0-3 14-14



SALINITY

BOTTOM WAo!oEoRRs



BRjCK.

M I XOH.



MIXOH.

EUHAL.



!UHAL.



BlOFAClES

0 STR A C O D S

Perissocytherideo sp.

Cyprideis riogrondensis

Minicyihere



L



heinii



CL



Cvfhsruro spp.

Collistocythere spp.

f a n e l l o sp. 1

C y p r i d e i s salebroso



1



Perissocyth.c f. kromelbeini

Loxoconcho sp, 2

Pisfocytherels sp.

Neomonocerotino sp.

Argilloecio s p .

X e s t o l e b e r i s spp.

Coquirnbo spp

Kongorino



.



sp.



P e l l u c i s t m o sp.

Morkhovenio SP.

Hemcyfheruro sp.

Poijimborchello sp.

P o r o c y p r i s sp.

Mocrocypris sp.

K e i j i o sp.

Orionino

Mutilus



sp.

sp.



Coudites



sp.



Urocy th e r d s s p.

Collisfocythere

Aurilo



rp.



Porocy therideo

Eoirdidoe



TgXT-pIo.



124stracod biofacies: specific distribution.



I



5-7



TF

EUHAL.



3



EUHAL.



477



I



I



I



& Collistotytherc sp. 3(? 1

Aurilo sp.

B2 Mutilus p.

Potji?nborche& sp.1

8 Porocypris sp 1



I Hemicytheruro



I



Pamcyfherideo



Coguimbo s p ~

heinti



- Minicythere c f

=



0



Urocyihereis



-



ers riogrondensis



I



I



%r%



Collistocvthere SD 1



e Collistocithere s p 2



Tm-na 13-Distribution of ostracod species in Sepetiba Bay.



SR



0



Orionino s

Kongorino sn



Pistocythere ts spp.



478 D. DIAS-BRITO,

J.A. MOURA

AND N.WURDIG



Specific Diversity

A high dispersion in the specific diversity (Fisher’s a index) was recorded in Sepetiba Bay. Once

this fact was verified, four station groups were recognized where the index varied, respectively, from

1 to 3, 2 to 5, 5 to 10, and > 10. It was then possible to define four environmental divisions, with

two transitional zones: MIXEDLAGOON A, MIXEDLAGOON B, MARINELAGOON and MARINE

ENVIRONMENT (Text-fig. 6). Stations with less than 300 specimens were not taken into account

in the calculations of the index.

Biofacies

In addition to having been divided into four environmental divisions, the lagoon was subdivided

into seven biofacies, the names of which originated from the predominant taxon or taxa (Text-fig.

7).

Text-fig. 8 summarizes the frequency and diversity patterns recognized for Sepetiba Bay. This

is the synthetic, fundamental graph for the distribution of foraminifers in the area studied. The

distribution of the species in the biofacies as well as the parameters controlling such distribution

are shown by Bronnimann, Moura and Dias-Brito (1981b, Text-figs. 4 and 5, p. 1866). The

distribution of the major species, among the 180 found in the bay, is also discussed in this paper.



OSTRACODA

The study of Ostracoda includes a preliminary taxonomic study, which will form the basis of a

more detailed one in the future. Specific differentiation was usually informal, the various species

being given numbers. Such a classification, however, provided good support for the research into

the ecological model of Ostracoda in Sepetiba Bay.

Frequency

The Ostracoda are distributed throughout the area researched. The largest area of the lagoon

contains between 30 and 130 ostracods per 3,000 cm3of wet sediment collected from the lagoon

floor. Some areas are almost destitute of ostracods; there are areas, however, with richer faunal

contents (Text-fig. 9).

Specific Diversity

No diversity index was calculated for Ostracoda in the bay. Nevertheless, the number of species

which occurs in each defined biofacies was recognized based on Ostracoda.



PLATE1-



1. Perissocytheridea sp!l, station BS 4, Biofacies 4. 2. Perissocytheridea sp. 2, station BS 1, Biofacies

3. 3. Perissocytheridea sp. 3(?), station BS 175, Biofaces 9. 4.Perissocytheridea cf. P. Kroemmelbein Pinto

and Ornellas. station BS 22, Biofacies 5. 5. Cyprideis riograndensis Pinto and Ornellas ( q ) ,station BS 37,

Biofacies 4. 6. Cyprideis riograndensis ($), station BS 37,Biofacies 4. 7. Minicythere cf. M . heinii Ornellas,

station BS 5, Biofacies 4. 8. Cytherura sp. 1, station BS 1,Biofacies 3. 9. Cytherura sp. 2 (?), station BS 37,

Biofacies4. 10. Cytherura sp. 3(?), station BS 155, Biofacies 5. 11. Callistocythere sp. 1, station BS 1,

Biofacies 3. 12. Calfistocythere sp. 2, Biofacies 8 (slide 153). 13. Tanella sp. 1, station BS 5,Biofacies 4. 14.

Cyprideis salebrosa Van den Bold ( q ) ,station BS 8,Biofacies 3. 15. Cyprideis salebrosa Van den Bold (8).

station BS 8, Biofacies 3. 16. Loxoconcha sp. 1, station BS 147, Biofacies 9. 17. Loxoconcha sp. 2, station

BS 1, Biofacies 3. 18. Pistocythereis sp. 1, station BS 164, Biofacies 9. 19. Pistocythereis sp. 2, station BS

138, Biofacies 6. 20. Neornonoceratina sp. 1, station BS 150,Biofacies 8. 21. Neomonoceratina sp., station

BS 149, Biofacies 8. 22. ArgTIloecia sp. 1, station BS 157, Biofacies 5.



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

Chapter 36. Relationships between ecological models based on ostracods and foraminifers from Sepetiba Bay (Rio de Janeiro, Brazil)

Tải bản đầy đủ ngay(0 tr)

×