Tải bản đầy đủ - 0 (trang)
Chapter 88. Biostratigraphical scale in the Toarcian of the Paris Basin (France) by means of ostracod associations

Chapter 88. Biostratigraphical scale in the Toarcian of the Paris Basin (France) by means of ostracod associations

Tải bản đầy đủ - 0trang

1262 A.-M. BODERGAT

AND P. DONZE



Cities

Ouicropl



TJXT-FTG.

1-Location of outcrops.



There is no doubt that the spectacular microfaunistic renewal at the beginning of the Upper Lias

is linked with important changes in palaeogeographic and ecologic conditions. It is noteworthy

to remark here that the adaptive response to ecological changes is faster among ostracod populations than among benthonic foraminifers. While in the TenuicostatumZone the Middle Lias taxonomic stock is only represented by a few species of Metacopina, most of the Domerian foraminifer

species persist in this zone (Ruget, 1983).



OSTRACOD

ASSOCIATIONS

AND THEIR

SUCCESSION

INTO

THE TOARCIAN

STAGE

Association A (Text-fig. 2).

As already noted, most of the Domerian species are not found in the TenuicostatumZone which

can be characterized by the appearance of several species and their disappearance at the top:

Kinkelinella tenuicostati Martin, 1960 (Pl. 1, fig. 4),

Ektyphocythere cf. arcuatocostatum (Martin, 1960) (Pl. 1, fig. 7).

and also by several probably new species, not yet described:

Ektyphocythere sp. A (Pl. 1, fig. 2), with five “chevron” costae arranged,

Ektyphocythere sp. B (Pl. 1, fig. 5), with reticulation between the ribs,

Ektyphocythere sp. C , with numerous fine ribs,

Ogmoconcha sp. A (PI. 1, fig. l), with a strong anterior pad,

Cytherelloideu sp. A p l . 1, fig. 3),

Trachycythere aff. tubulosa serutina Triebel and Klingler, 1959 (Pl. 1, fig. 6).



1263



TOARCIAN



STAGES



-



C

.c

C



Q



F



x



-



2C

al



2

0



2

f



x



C



Q

0

0



Ektyphocythere sp. A. LORD

Gramanella apostolescui

Ogmoconcha controctula

Pseudoheldia etaulensis

Pseudoheldia mouhersensis

Tmchycythere tubululoso semtina

Monoceratina mesdiwsica

Monoceratina ungulina

Trachycythere cf. tubulosa seratina

Ektyphocythere sp. A

Ektyphocyth@resp. B

Ektyphocythere sp. C

Ektyphocythere cf. arcuatocostaia

Kinkelinella tenuicostati

Ogmoconcha sp. A

Ogmoconcha sp.

Cytherelloidea sp. A

Cytherella toarcensis

Cythwelloidea cadomensis

Kinkelinella gr. sennoisensis

Cytheropteron alafast@tum

Ektyphocythererugosa

Ektyphocythere bucki

Monoceratina scrobiculata

Monocemtina striata

CythffOptedMcribra

Fuhrbergiella cf. malzi

Trachycythere sp.

Heurocytherecultrota

heschuleridea bemierensis

Ektyphocythere vitilis

Otocythere callosa

Cytheropterina cribra zieglen’

heschuleridea c f. venm*oaa

A phelocythereundulata

Aphelocythere kuhni



TEXT-FIO.2-Repartition of the main Ostrawd species.



Biostrutigruphy of Toarcian of Paris Basin 1265



We cannot mention any ostracods in the Serpentinum Zone (Text-fig. 2) because this stage is

generally badly represented. So we do not know exactly when the above species become extinct.

However that may be, except for Monoceratina ungulina, we have not found them in the Bifrons

Zone.



Association B (Text-fig. 2).

At the base of the Bifrons Zone, we find three species which also occur in the Aalense Zone:

Cytherelloidea cadomensis Bizon, 1960 (PI. 1, fig. 9),

Cytherella toarcensis Bizon, 1960 (Pl. 1, fig. lo),

Kinkelinella gr. sermoisensis (Apostolescu, 1959). Within this group, it is possible to distinguish

several trends of evolution.

Inside the Bifrons and the Variabilis Zones, some other ostracods also occur:

Cytheropteron alafustigatum Fischer, 1962 (Pl. 1,fig. 1l), still present in the Pseudoradiosa Zone,

Ektyphocythere rugosa (Bizon, 1960) and E. bucki (Bizon, 1960) (Pl. 1, fig. 8), which are

present in the Thouarsense Zone.

The simultaneous occurence of these species enables us to recognize both the Bifrons and the

Variabilis Zones.



Association C (Text-fig. 2).

The Thouarsense Zone is well characterized by the following species association :

Monoceratina scrobiculata Triebel and Bartenstein, 1938, which is also present in the above

Zone,

Monoceratina striata Triebel and Bartenstein, 1938, which already exists at the beginning of

the Thouarsense Zone,

Cytheropterina cf. cribra (Pl. 1, fig. 14), which is probably a precursor of Cytheropterina

cribra ziegleri Wienholz, 1967,

PLATEl-Fig. 1. Ogmoconchu sp. A. RV, lateral view, FSL 171022. Plage de la Mine, Vendee, France. Lower

Toarcian, Tenuicostatum Zone ( x 76). Fig. 2. Ektyphocythere sp. A. RV, lateral view, FSL 171019. Anse StNicolas, Vendee, France. Lower Toarcian, TenuicostaturnZone ( x 68). Fig. 3. Cytherelloideu sp. A. RV, lateral

view, FSL 171024. Plage de la Mine, Vendee, France. Lower Toarcian, Tenuicostutum Zone ( ~ 6 6 ) .Fig. 4.

Kinkelinella tenuicostuti Martin, 1960. RV, lateral view, FSL 171023. Plage de la Mine, Vendee, France. Lower

Toarcian, Tenuicostatum Zone ( x 66). Fig. 5. Ektyphocythere sp. B. RV, lateral view, FSL 171020. Anse St-Nicolas, VendCe, France. Lower Toarcian, Tenuicostutum Zone ( x 65). Fig. 6. Truchycythere cf. tubulosa seratinu

Triebel and Klingler, 1959. LV, lateral view, FSL 171026. Plage de la Mine, VendCe, France. Lower Toarcian,

Tenuicostatum Zone ( ~ 6 7 ) .Fig. 7. Ektyphocythere cf. urcuatocostutu (Martin, 1960). LV, lateral view, FSL

171025. Plage de la Mine, VendCe, France. Lower Toarcian, Tenuicostutum Zone ( x 73). Fig. 8 .Ektyphocythere

bucki(Bizon,1960). LV, lateral view, FSL 17.028. St-Denis, Vendee, France. Middle Toarcian, Bifrons Zone

( X 67). Fig. 9. Cytherelloideu cudomensis Bizon, 1960. C , lateral view, FSL 171029. St-Denis, Vendee, France,

Middle Toarcian, Bifrons Zone (x68). Fig. 10. Cytherella toarcensis Bizon, 1960. RV, lateral view, FSL

171032. St-Denis, Vendee, France. Middle Toarcian, Bifrons Zone ( x 67). Fig. 11. Cytheropteron ulufustigutum

Fischer, 1962. LV, lateral view, FSL 171031. St-Denis, VendCe, France. Middle Toarcian, Bifrons Zone ( ~ 6 8 ) .

Fig. 12. Pleurocythere cultrata Apostolescu, Magne and Malmoustier, 1961. LV, lateral view, FSL 171037. StDenis, Vendee, France. Upper Toarcian, top of the Thouarsense Zone ( X 70). Fig. 13. Trachycythere sp. LV,

lateral view, FSL 171040. St-Denis, VendCe, France. Upper Toarcian, top of the Thouarsense Zone ( X 68).

Fig. 14. Cytheropterina cribru Wienholz, 1967. C , dorsal view, FSL 171039. St-Denis, Vendee, France. Upper

Toarcian, top of the Thouursense Zone ( x 68). Fig. 15. Otocythere callosa Triebel and Klingler, 1959. LV, lateral

view, FSL 171044. St-Denis, VendCe, France. Upper Toarcian, lower part of the Pseudoradiosu Zone ( X 69).

Fig. 16. Ektyphocythere vitilis Apostolescu, Magne and Malmoustier, 1961. RV, lateral view, FSL 171043. StDenis, Vendte, France. Upper Toarcian, Insigne Zone ( x 68). Fig. 17. Praeschulerideu bernierensis(Apostolescu,

1959). LV, lateral view, FSL 171045, St-Denis, VendCe, France Upper Toarcian, lower part of the Pseudoradiosu

Zone (X68). Fig. 18. Cytheropterina cribra ziegleri Wienholz, 1967. RV, lateral view, FSL 171048 St-Denis,

*Vendee, France. Upper Toarcian, Thouursense Zone ( x 68). Fig. 19. Praeschulerideu ventriosu (Plumhoff,

1963). LV, lateral view, FSL 171046. Vergisson, Sa6ne-et-Loire, France, Upper Toarcian, Pseudoradiosu Zone

(X



69).



AND P. DONZE

1266 A.-M. BODERGAT



Furhbergiella cf. malzi Wienholz, 1967,

Trachycythere sp. (Pl. 1, fig. 13), close to T . tubulosa seratina Triebel and Klingler, 1959, but

smaller and with a dorsal margin more sloping.



Association D (Text-fig. 2).

Several species occur at the beginning of the Insigne Zone:

Praeschuleridea bernierensis (Apostolescu, 1959) (Pl. 1, fig. 1 3 ,

Ektyphocythere vitilis (Apostolescu, Magne and Malmoustier, 1961) (Pl. 1, fig, 16),

Otocythere callosa Triebel and Klingler, 1959 (Pl. 1, fig. 15),

Cytheropterina cribra ziegleri Wienholz, 1967 (Pl. 1, fig. 18).

This association and the absence of species of the upper stage enable us to identify the whole

Insigne Zone and the lower part of the Pseudoradiosa Zone. We note that in Germany appearance

of some taxa, for example, Praeschuleridea and Otocythere callosa (Knitter and Riegraf, 1984) seem

to be older. The difference in time of appearance is very small. The fact seems to be important,

and the explanation is perhaps that we have restricted the taxonomic term “Praeschuleridea” to

evoluted forms.



Association E (Text-fig. 2).

In the two last zones of the Toarcian, the genus Praeschuleridea takes predominance in the

population of ostracods. One finds a species close to Praeschuleridea ventriosa (Plumhoff, 1963)

but with a less dense reticulation (Pl. 1, fig. 19). We also note the first appearance of the genus

Aphelocythere with the species A. undulata Triebel and Klingler, 1959, which is succeeded by A.

kuhni Triebel and Klingler, 1959 into the Aalense Zone.

In the Paris Basin, the Aalenian is generally reduced or absent due to erosion. Therefore, it is

difficult, if not impossible, to extend this research into the Dogger.



CONCLUSIONS

Firstly, the study of Toarcian ostracods enables us to recognize five main associations. These

are more or less contemporaneous with the Ammonites Zones and, therefore, they allow to get

some stratigraphic markings. The most important item is the turnover inside the Tenuicostatum

Zone, and the coexistence of the genus Ogmoconcha, heritage of the past, and of the genus Kinkelinella, premise of the future.

Since the Bifrons Zone, the populations are fundamentally different, legitimately justifying

the distinction between the Lower and the Middle Toarcian.

Then three associations allow us to divide the Upper Toarcian:

-the first, at the top of the Thouarsense Zone, encloses Cytheropterina cribra, Fuhrbergiella

cf. malzi, Trachycythere sp. and Pleurocythere cultrata,

-the second, which includes the Insigne Zone and a part of the Pseudoradiosa Zone sees the

appearance of the genus Praeschuleridea s. str.,

-the third begins at the top of the Pseudoradiosa Zone and includes the whole Aalense Zone.

Only an important palaeogeographical event can explain such a microfaunistic renewal :

ostracods populations within the Toarcian find their origin in palaeoenvironmental changes over

very large areas.



Biostratigraphy of Toarcian of Paris Basin 1267



REFERENCES

v. 1956. Correlations dans le Lias marneux des Causses majeurs. Rev. Insf. fianc. Pefrole, Paris,2,

439-451.

- 1959. Ostracodes du Lias du Bassin de Paris. Ibid., 14(6), 795-826.

-, MAGNE, J. and MALMOUSTIER, G. 1961. Quelques espkces nouvelles d’ostracodes du Toarcien de Thouars

(Deux-Skres). Colloque sur le Lias frangais. Mkm. Bur. Rech. gkol. min., Paris, 4, 399-405.

BATE, R.H. and COLEMAN, B.E. 1975. Upper Lias Ostracoda from Rutland and Huntingdonshire. Bull. Geol. survey.

G.B. Lon don, 55,l-42.

BIZON, J.I., 1960. Sur quelques ostracodes du Lias du Bassin Parisien. Rev. Micropalkontol., 2 , 4 , 203-211.

BIZON, G. and OERTLI, H. 1961. Contributions 2i I’ttude micropaleontologique(foraminiferes-ostracodes) du Lias du

Bassin de Paris (septikme partie: conclusions) in Colloque sur le Lias Francais (1961). Mkm. Bur. Rech. gkol.

min., Paris, 4, 107-119.

BRAND, E. and MALZ, H. 1962. Fuhrbergiella n.g. Senckenb. leth., 43 (l), 1-39.

DONZE, P., 1985. Lias inferieur et moyen, In OERTLI, H.J. (ed.). Atlas des Ostracodes de France. Bull. Centres Rech.

Explor.-Prod. Elf-Aquitaine, MBm., 9, 101-1 17.

FISCHER, w . , 1962. Ostracoden der Gattungen Monoceratinu Roth, 1928, Cytheropteron G.O. Sars, 1865 und andere

im Lias Zeta Schwabens. N. Jb. Geol. Palaeontol. Abh., 114, (3), 333-345.

GABILLY, I. 1964. Le Jurassique infkrieur et moyen sur le littoral vendten. Trav. Znst. giol. Antropol. Prkhist. Fac. s c .

Poitiers, 5, 65-107.

GRAMANN, F. 1962. Skulptierte Ostracoden aus dem niederrheinischenLias. Fortschr. Geol. Rheinld. We&, 6, 185198.

HERRIG, E. 1969. Ostracoden aus dem Ober-Domerienvon Grimmen westlich von Griefswald. Geologie, 9,1072-1 102.

KNITTER, H. and RIEGRAF, w. 1984. Ostracod biostratigraphy of the Upper Toarcian in Southern Germany. In

MICHELSEN and ZEISS, A. (eds.). International Symposium on Jurassic Stratigraphy, Erlangen 1984, 1, 252-258.

1984. Neue Ostracoden-Arten aus dem Oberen Pliensbachiurn und Unteren Toarcium Sudwestdeutschlands

und Sudframeichs. Stuttgarter Beitr. Naturk., B, 104, 19 pp.

1984. Biostratigraphie (Cephalopoden, Ostracoden) des Oberen Toarcium von Blumberg-Achdorf/Wutach

und Weilheim/Teck (Baden-Wurttemberg). Jh. geol. Landesamt Baden, 26, 57-97.

LORD, A. 1972. Wicherella and Gramannella, two new genera of Lower Jurassic Ostracoda from England. Palaeontology, 15, 187-196.

1974. Ostracods from the Domerian and Toarcian of England. Ibid., 17(3), 59-22,

1978. The Jurassic. Part 1 (Hettangian-Toarcian). In BATE, R. and ROBINSON, E. (eds.). A stratigwzphical Index of

British Ostracoda. 189-212. See1 House Press, Liverpool.

MALZ, H. 1971. Zur Taxonomie “glattschaliger” Lias-Ostracoden. Senckenbergianu, 52(5/6), 433-455.

-1975. Eine Entwicklunsreihe“vallater” Ogmoconchen (Ostracoda) in S-deutschen Lias. Zbid., 55(6), 485-503.

MARTIN, G.P.R. 1960. Die Zone des Dactylioceras tenuicostatum (Toarcien, LiaS). In HOFFMANN K. and MARTIN, G.P.R.

(eds.). NW-und SW-Deutschland. Palriont. Z., 34(2), 103-149.

MAUPIN, c. 1975. Etude micropaltkntologique de la zone ti Dactylioceras tenuicostaturn du Toarcien de I’anse SaintNicolas (commune de Jard-Vendee). C.R. somm. SOC.gkol. France, 11-1 3.

1978. Deux ostracodes nouveaux du Toarcien de Vendee (France). Geobios, 11, 107-111.

MOUTERDE, R. 1953. Etude sur le Lias et le Bajocien des bordures nord et nord-est du Massif Central franqais. Bull.

Serv. Carte gkol. France. 236, 521 pp.

PLUMHOFF, F. 1963. Die Ostracoden des Oberaalenium und tiefen Unterbajocium (Jura) des Gifhomer Troges,

Norwestdeutschland. Abh. Senckenb. natur. forsch. Ges., 503, 1-100,

-1967. Die Gattung Aphelocythere (Ostracoda) im NW-europalschenJura und zur Entwicklung der Microfauna

am Uberganc Domerium-Toarcium. Senckenbergiana, 48, 549-577.

RIOULT, M. 1968. Contribution a lVtude du Lias de la bordurc occidentalc du Bassin de Paris. Thdse d’Etat, Caen, 564

pp. (ined.).

RUGET, CH. 1983. Les Foraminijiires (NodosariidPs) du Lias de I’Europe occidentale. These d’Etat, Lyon, 248 pp (inkd.).

TRIEBEL, E and BARTENsTEtN, H. 1938. Die Ostracoden des deutschen Juras. 1. Monoceratina -Arten aus dern Lias und

Dogger. Senckenbergiana, 20, 502-51 8.

and KLINGLER w. 1959. Neue Ostracoden-Gattungen aus dem deutschen Lias. Geol. Jb., 76, 335-372.

VIAUD, I. 1963. Les ostracodes desprincipaux bussins liusiquesfrancais. Thkse 3 kme Cycle, Bordeaux, 212 PP. (in6d.I.

WIENHOLZ, E. 1967. Les ostracodes des principaux bassins liaiques franqais. In STOERMER, N. and WIENHOLZ, E.

Mikrobiostratigraphia an der Lias/Dogger-Grenze in Bohrungen nordlich der Mitteldeutschen Hauptscholle.

Jb. Geol., Berlin, 1, 533-591.

APOSTOLESCU,



-



-



-



This Page Intentionally Left Blank



Ostracod Zones and Dispersion of Mesozoic Fossils in

the Scandinavian North Sea Area

OLEBRUUNCHRISTENSEN

GEOLAB, Forus, Statoil, Norway



ABSTRACT

Faulting activities during the Mesozoic strongly affected the development of basins in the

northeastern North Sea. Before the Kimmeridgian, fair ostracod correlation exists between the

Danish Sub-basin and the Polish-German basins. During the Volgian and Neocomian, fair

correlation exists between the Danish Sub-basin and the English basins. A North Sea-Arctic

Seaway during the Jurassic and Lower Cretaceous, probably into lowermost Tertiary, seems to have

some controlling effects on deposition and fossil content in the North Sea area. Mandelstamia

and Galliaecythereidea, characteristic genera for the boreal seas, undergo strong differentiation.

Macrodentina developed in more restricted environments. In shallow areas and in ages with a

strong influx of warm surface water, Cytherelloidea, Bairdia, Protocythere and related genera

occur. Zone index species ought to be selected from among a few genera.



OSTRACOD

ZONESAND TIME-CORRELATION

In a special report on the Jurassic from the Geological Society of London (Cope et al., 1980),

Torrens and Wright reviewed the stratigraphical work on ostracods in the British Isles. They stated

that if there are no better faunas on which to base correlations, ostracods may prove usable. The

proposition, of course, is generally true, but they tell us that ostracods as stratigraphical markers

may not be useful as ammonites, and this is important. It is also important to define ostracod

zones and use these for evaluation of specific stratigraphical events, environments, and timestratigraphical correlation. Ostracod zones are always established in outcrops or by the use of

well-preserved core material from subcrops. Mostly, ostracods have been recognised in apparently

thin beds related to the discontinuous sampling technique, necessary in micropalaeontology, or

to environmental and diagenetic factors. An ostracod zone is often represented in one or a few

samples, related to a slight change of palaeoenvironment for the section. In wells for industrial

investigations in subcrops, finds of useful ostracod faunas are relatively uncommon. The ostracod

zonation in these subcrops has to be looked upon in relation to the total fossil distribution in the

basin. For a common understanding of the limitations and the advances in the use of ostracods,

more general zones of index fossils in specific genera ranges may have a future.



1269



1270 0. B. CHRISTENSEN



STRUCTURAL

EFFECTS

The Scandinavian North Sea area is the northeastern part of the North Sea Basin from the

offshore areas of southern Norway, the entire area of Denmark, through southernmost Sweden

(Scania) and into the islands of Bornholm in the Baltic Sea. From the late Palaeozoic into the

Tertiary, the North Sea areas are characterised by sub-basins of various sizes, relative connections, and with a long-time structural development of complicated faulting events in contrast to

most other areas in the Atlantic Ocean Regions. The area was important for development of

Mesozoic ostracods (Bate, 1977). Strong compression and tension along the Fennoscandian

Sheild affected by the Uralian and the Alpin plate collisions and the initial opening of the North

Atlantic Ocean into the Arctic Ocean, seems to have had strong effects on the biological balance

of the area. Moderate dislocations with some pull-apart basin effects (Baartmann and Christensen,

1975; Christensen 1975) have not been accepted for Latest Jurassic and Lowermost Cretaceous.

Older or younger, minor, but strong structural events with block rotations and dislocations,

however, have been described (Hesledal and Hamar, 1983; Pegrum, 1983).

Permian-Triassic rifting of the North Atlantic intensified a long sea-way, present in the North

Sea area from the Jurassic and renewed by rifting and faulting in various ages. A connection into

the embryonal Artic Ocean is most natural. The older graben structures in the northern North

Sea were elevated in the Middle Jurassic and then subsided as part of a North Sea-Arctic Seaway,

which crosses and follows the trends of the ancient Caledonides. With the sea-floor spreading

sigmoidally developed in the Northern Atlantic during the Late Cretaceous, Tertiary, and

Quarternary, the north-south Arctic Seaway does not necessarily terminate in the North Sea area.

In the eastern North Sea area, the Ringkabing-Fyn High, also elevated during Middle Jurassic,

has a great local effect on the development of the basins and sub-basins in the Scandinavian North

Sea area (Text-fig. 1).



THENORTH

SEA-ARCTIC

SEAWAY

The marine connections between various North Sea sub-basins and other shelf areas and oceans

are generally important for biostratigraphical evaluations. During the Jurassic, Cretaceous and

in the Early Tertiary, the North Sea basins were areas of conversions or interactions between cold,

more or less underset slow moving sea currents from the north and relatively warmer sea water

from the south, diluted in various degrees by runoff. Besides the large epicontinental sea areas in

arctic Alaska, Canada, on the Barents Shelf, and in the Greenland and Norwegian shelf areas, the

structurally downwarped areas most probably followed the central trends of the ancient Caledonian

range into the North Sea, and not into the Fennoscandian Shield. Hydrographical consistency

of the fact that the seaway was rather pronounced and structurally dependant during the Mesozoic,

may explain some paradoxes of the Boreal seas evaluated and referred to by Hallam (1969, 1981,

1983), Gordon (1974) and others. The seaway was defined as epicontinental, but not necessarily

shallow in all parts. In Text-fig. 1, some Mesozoic reconstructions of marine connections between

the arctic areas, the North Sea, and more southern seas are outlined. Influx of polar or boreal water

with contemporary marine effects from connections to basins around the North Sea seems to control much of the depositional environment as well. The eustatic sea-level changes and the structural events initiate the more or less pronounced hydrographical effects.



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

Chapter 88. Biostratigraphical scale in the Toarcian of the Paris Basin (France) by means of ostracod associations

Tải bản đầy đủ ngay(0 tr)

×