Tải bản đầy đủ - 0trang
Chapter 89. Ostracod zones and dispersion of Mesozoic fossils in the Scandinavian North Sea area
1270 0. B. CHRISTENSEN
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).
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.
NORTH SEA AREA
r n J
. I '
h V A I L & TODD)
of ostracod zones
i n the t e x t .
TEXTFIG. l-outline of stratigraphic relations between sea level changes (Vail and Todd, 1981). basin develop
ments, and ostracod distribution referred to and numbered in the text.
1272 0.B. CHRISTENSEN
Generally, the ostracods comprise a minor part of other calcareous fossils recognised in the
Scandinavian Mesozoic. They are most well-preserved in the Late Mesozoic deposits and in the
southern and eastern areas. Only a few sections with pure ostracod assemblages are found in the
Triassic and in Purbeck-Wealden beds. Marine and brackish assemblages dominate. Secondary
diagenetic effects on the distribution of calcareous microfossils are seldom greater than the effects
of poor life conditions in the northwestern areas. There calcareous ostracods are present, but
scarce, compared with other groups of fossils, but very poor compared with the southeastern
areas in the Scandinavian North Sea. Solution plays a role in many coarse sediments. In these
beds, diagenetic calcite is rather common. Further south and in the eastern areas, probably not so
deeply exposed, rich calcareous faunas are relatively common between beds devoid of calcareous
fossils. These faunas are mostly very well-preserved, the most important, established through
the Scandinavian Upper Jurassic and Lower Cretaceous are noted (refer to numbers in Text-fig. 1).
7 . Mandocythere harrisiana Zone
Cythereis luermannae hannoverana Zone
Cythereis folkestonensis Subzone
? Cythereis 1. luermanniae-Neocythere ventrocostata Zone
Saxocythere notera senilis Subzone
Protocythere albae-Dolocythereidea bosquetiana Zone
Protocythere albae-Dolocytheridea vinculum Zone
Zsocythereis fissicostis Subzone
Cythereis corrigenda Subzone
Protocythere nodigera Zone
? Unnamed Zone
Protocythere intermedia Zone
Protocythere triplicata Zone
Mandocythere frankei Zone
Protocythere hannoverana Zone
Cytherella valanginiana Subzone
Stravia crossata Subzone
Paranotacythere globosa Subzone
Galliaecytheridea teres Zone
8. Fabanella boloniensis-Pachycytheridea compacta Zone
Cypridea aha formosa Zone
Cypridea inversa-C. valdensisprecursor Zone
9. Macrodentina reticulata Zone
? Galliaecytherideapolita Zone
? Unnamed Zone
Eocytheropteron aquitanum Zone
? Unnamed Zone
Mandelstamia maculata Zone
Mandelstamia horria'a Zone
? Unnkned Zone
10. Mandelstama inflata Zone
Dicrorygma brotzeni Zonule
Ostracod Zones and Dispersion of Mesozoic Fossils 1273
11. Macrodentina steghausi Zone
Galliaecytheridea elongata Zone
Galliaecytherideamandelst. kilenyi Subzone
Amphicythere semisulcata-Schuleridea tribeli Zonule
13. ? Nophrecythere crusiata oxfordiana Zone
? Lophocythere interrupta Zone
The Triassic deposits in Scandinavian are mostly devoid of fossils. Red, oxidised continental
clastics are most common. An epicontinental sea occupied large areas in central Europe during
most of the Triassic. On strong mature landscape plains, a legacy from the Permian Period, marine
and lacustrine transgressions may reach large areas in the Scandinavian North Sea, but charophytae recognized in many wells in Denmark and Scania (Sorgenfrei and Buch, 1964; Brotzen, 1950)
indicate lacustrine environments in most areas.
Middle Triassic ostracods (e.g. Triassinella pulcra, Speluncella teres) are recognised with marine
fossils, indicating that the Muschelkalk sea reached the southernmost Danish area (Christensen,
1972). Late Triassic ostracods (Darwinula spp., Christellocythere sp., Speluncella vulgaris, S.
piriformis) were collected in outcrops of red to greenish fine clastics in Bornholm and are relatively
common in many localities in North Germany and Poland.
An arctic epicontinental sea north of the northern North Sea was hardly connected with the
Central European sea through the North Sea grabens, where fine clastics most probably indicate
some large lacustrine environments. In the Norian, contemporary with a change to a humid climate,
the deposits in the southern areas from the Central Graben into Denmark became rich in fossils.
A cyclical development in the sedimentation has been interpretated as due to eustatic sea level
changes (Bertelsen, 1978). The initial major transgression, marked by oolitic beds in most areas in
Denmark (Christensen, 1972), is probably not marine, but interpreted as lacustrine based on
the ostracods, below the Rhombocythere penarthensis Zone and beds with Rhaetavicula contorta,
The Late Triassic ostracod assemblage is useful for zonation. Closely connected with the general
climatic change, a transgression, probably lacustrine, reached most Danish onshore areas. Later,
with a sea connection, marine faunas invaded. The zonation in England proposed by Anderson
(1964) is mainly based on marine ostracods. A zonation from Northwest Germany by Will (1969)
published after his death, it most useful for the Danish area. Anderson seems to have included
species from Germany in Rhombocythere penarthensis. Using the work of Will, it is easy to evaluate
some of those, as well as a number of Anderson's mistaken synonyms for Triassic ostracods in
Denmark, illustrated by Christensen (1962). R . penarthensis is similar to Notocythere magna
maritina Will. It occurs in the N . elegans Zone of Will with most species of the R. penarthensis
group and with N. hechti Zongu Will of the R. ruegeri group (Plate 1-I), but also above in marine
1274 0. B. CHRISTENSEN
beds. Anderson established his new genus Rhombocythere on studies of a small number of English
and German species. Will used in his work the genus name Notocythere in a wide sense. The genera
Rhombocythere and Notocythere (parts) are closely related to the genus EmphasiaMa ndelstam, 1956,
but the genera and species Rhombocythere penarthensis Anderson and Notocythere hechti Will are
established, and some genera (Notocythere), species, and subspecies need to be re-established. A
biostratigraphy close to the intentions of Will and for the Danish formations, revised by Bertelsen
(1978) is useful in Denmark:
Late Norian (Rhaet-Keuper)
Member G3 of Gassum Formation with megaspores (e.g. Trieletes),
Lepidopteris ottonis Flora.
Member G2 of Gassum Formation with agglutinated foraminifera
(e.g. Ammodiscus parva) and marine molluscs (e.g. Rhaetavicula contorta) and R . pernarthensis.
Early Norian (Steinmergelkeuper)
Beds of Gassum Formation G2 and G1 and Vinding Formations with ostracods.
Rhombocythere penarthensis Zone (Gassum Formation).
Rhombocythere wicheri-R. penarthensis Subzone. (P1.l fig.1)
2. Notocythere media Zone (Vinding Formation).
Rhombocythere ruegeri Subzone.
Notocythere media Subzone (Pl. 1 fig. 2).
The R . pernarthensis Subzone is most probably brachyhaline to euhaline. The older Subzones
are probably of lacustrine origin. The Rhombocythere wicheri-R. penarthensis Subzone has been
identified far north of the northern North Sea.
In a great variety of Jurassic environments, poor ostracod assemblages have been collected from
Late and Middle Jurassic in the Viking Graben, more well-preserved assemblages at the margin.
In the Central Graben, rich Late Jurassic and scarce Middle Jurassic ostracod assemblages are
found. Rather well-preserved Lower Jurassic Ogmoconcha and Kinkelinella faunas are common in
most southern and eastern Scandinavian North Sea areas, but are also present in the Viking Graben.
Scarce and poorly preserved Middle Jurassic ostracods are present in some western and southern
parts of the Scandinavian North Sea grabens. During the Middle Jurassic most of the Scandinavian
areas were uplifted and the Rinksbing-Fyn High was created as a permanent structure. Volcanic
activities in the Central North Sea and in Scania illustrate a trend of faulting activities north of
the Ringksbing-Fyn High. There, fine to coarse clastics often with coal beds but altogether very
poor in fossils, are sandwiched between the fine clastics of the marine Early and Late Jurassic.
During the Late Jurassic strong rifting activities continued, with subsidence of most axial parts
of the Central and Viking Grabens. Poor benthonic faunas in the deepest part and common occurTriassic and Jurassic samples from the Danish Sub-basin. Fig. 1 . Assemblage from Rhombocythere
wicheri-R. penarthensis Subzone with R. penarthensis.R. elegans, R. cf. R. wicheri. R. ruegeri longa, Notocythere
media tuberculata a.0. Fig. 2. Assemblage from Notocythere media Subzone with Limnocythere keuperiana,
Notocythere media Subzone with Limnocythere keuperiana. Notocythere media prima, Darwinula spp. a.0.
Fig. 3. Monotypic assemblage of Polydentina? quadricostata.
1276 0. B. CHRISTENSEN
rences in some shallow areas are more an effect of poorly oxygenated seawater than diagenesis.
Agglutinated foraminifera1 assemblages with a low diversity are common in some intervals. A huge
number of more or less pyritized radiolarians in the grabens and along the margins indicate anaerobic to dysaerobic bottom conditions, and a stratified water column with space for a high production of heterotrophic plankton. In the Danish Sub-basin, Late Jurassic radiolarians are uncommon.
Calcareous foraminifera occur in certain horizons among the agglutinated foraminifers. They
are most common in the shallowest areas, but there also, most intervals are scarce in foraminifera.
Ostracods are most common in samples from horizons which also contain mollusc fragments.
An ostracod zonation for the Early Jurassic Fjerritslev Formation was established by Michelsen
(1975) for the Danish Sub-basin and for the Central Graben (Michelsen, 1978):
3. Ogmoconchella adenticulata-Nanacythere simplex Zone (Late Pliensbachian)
Grammannella apostolescui-Kinkelinella foveolata Subzone (Early Pliensbachian)
Progonoidea reticulata Subzone (Early Late Sinemurian)
Ogmoconchella danica Zone (Late Sinemurian-Early Pliensbachian)
Cristacyrhere betzi-C. crassireticulata Zone (Late Sinemurian)
6. Ogmoconchella aspinata Zone (Hettangian-Early Sinemurian)
In Scania the C. betzi-C. crassireticulata Zone and the Ogmoconchella danica Zone are recorded
by Sivhed (1980). Ammonites and foraminifera investigated in the Danish wells and in Scania
directly support the establishment and general use of these ostracod zones. The affinity between
the Danish Sub-basin and the North German Basin is very high for the Lower Jurassic ostracods,
except in the Early Sinemurian (Michelsen, 1975).
Marine ostracods (Camptocythere praecox, Kinkelinella aff. adunca. K. oblonga. Pseudomacrocypris subaequabilis) found along the Fennoscandian Border Zone (Christensen, 1972) from Scania
to the Danish Sub-basin indicate Toarcian-Aalenian in the upper part of the Fjerritslev Formation,
below the non-marine Haldager Formation, which is difficult to correlate.
From wells in southwestern Scania and in the Hano Bay east of Scania, Norling (1981) indicates marine ostracods from the Bathonian (Oligocythereis woodwardi, 0. fullonica), from the
Callovian (Lophocythere interrupta interrupta, Ostracod Nos. 4,5,6 Lutze), and from the CallovianOxfordian (Lophyocythere scabra, L. cruciata spp. oxfordiana, Paracypris sp. A Schmidt). These
may indicate that during the Middle Jurassic, Scania had a close marine connection with the Polish
and North German Basins, east and south of the Ringksbing-Fyn High. Marine Ostracods from
the Middle Jurassic have not been reported from the Danish Sub-basin, but in most parts of the
North Sea Grabens ostracods of Bathonian-Callovian age (Praeschuleridea quadrata, P. batei, P.
subtrigonia, Pleurocythere borealis, Lophocythere bradiana, Macrodentina bathonica and others)
can be collected at some horizons. Along the eastern margins of the North Sea-Arctic Seaway, in
the northern North Sea, deltaic and coastal deposits successively built up during the Middle Jurassic
and closed the Seaway for long intervals after the Toarcian. High deposition rates, and erosion with
re-deposition and diagenesis probably resulted in the reduced ostracod assemblage during the
Middle Jurassic in Scandinavia.
Oxfordian transgressive events with opening, rifting and successive subsidence of the North
of boreal ostracod samples from the Danish Sub-basin. Fig. 1. Assemblage from
Galliaecytheridea spinosa Zone with G. spinosa sensu lato, Mandelstamia n. sp., Polydentina rudis, P. cf. P.
wicheri, Aaleniella (pro Pyrocytherura) inornata, A. gracilis a.0. Fig. 2, Assemblage from Mandocytherefiankei
Zone with M . jiankei fiankei, Acrocythere hauteriiana. Rehacythereis senckenbergi a.0.
1278 0.B. CHRISTENSEN
Sea-Arctic Seaway renewed the hydrographical conditions in the North Sea basins. Changes to
boreal conditions reached the Danish Sub-basin successively from Late Oxfordian to Early Kimmeridgian. At least on one occasion during the Late Oxfordian and Lowermost Kimmeridgian, and
contemporary with the deposition of coarser clastics (Flyvbjerg Member), the Danish Sub-basin
was part of a Danish-Polish Trough and probably also connected with the North German Basin.
A Jurassic ostracod, probably Polydentina quadricostata (Pl. 1 fig. 3), known from the Early Kimmeridgian in Central Poland, occurs monotypically (Pl. 2) and is found centrally in the Subbasin
and in the western euhaline areas belonging to the G. dissimilis Zone, as well. In the Fennoscandian
Border Zone an Amphicythere semisulcata-Schuleridea triebeli Zonule occurs in Scania and northermost Denmark. It includes a few Galliaecytheridea dorsetensis. In the North German basin of
Denmark, the zonule is found below the G. dissimilis Zone. In the Early Kimmeridgian (G. dissimilis
and G. elongata Zones) an open marine multi-lateral connection was established.
During the Volgian, the Norwegian-Danish Basin seems to have been exposed to the west as the
ostracod assemblage is closely related to the English Mandelstamia and Galliaecytheridea assemblages. The Polish and German Basins were cut off from the deeper boreal sea. Evaporites indicate
a warm, perhaps a more arid climate. In Scania, on the Fennoscandian Border Zone, and in the
North German Basin immediately south of the Rinksbing-Fyn High, an ostracod assemblage of
Macrodentina retirugata and limnophile genera was found. Fresh to brackish water environments
continued during the Portlandian and Berriasian. In Scania and Bornholm, Cypridea assemblages
are common (Christensen, 1968,1974). In the Fennoscandian Border Zone, not far from the boreal
sea and below the island of Anholt in Kattegat, Cypridea assemblages also, seem to be present
(Baartmann and Bruun Christensen, 1975).
The author and Tom Kilenyi (1970) developed a proposal for a basic ostracod zonation for the
Northwest European Kimmeridgian based on the type section in Dorset in which a great deal
of the Danish Middle Volgian (Upper Kimmeridgian) could be included. Wilkinson quite understood our review and gave valuable new information in his recent paper (Wilkinson, 1983),
also based on a parallel ammonite zonation. In the Scandinavian Upper Jurassic a great
number of Galliaecytheridea and Mandelstamia species have been collected, but this unfortunately
did not include a parallel investigation of other fossil groups. Variation in reticulation and the
peripheral outline are important features for determinations in these genera. The species of Mandelstarnia and Galliaecytheridea are most common in open sea deposits in the North Sea (Pl. 2, fig.
1). Species of Macrodentina dominate in more restricted environments. Most of the species of
these three genera have been observed in the North Sea area. This indicates that they are most
indigenous to the boreal sea. Mandelstarnia and Galliaecytheridea (from G. denticula Sharapova)
are also characteristic genera for the boreal Early Cretaceous in the USSR (Andreev and
Mandelstam, 1971), as well.
The species of Mandelstamia vary in outline and are in some degree environmentally or regionally dependant. As an example, two smooth species occur in the Danish Sub-basin. One of
these is closely related to, perhaps identical with, Limnocythere? infata (Steghaus). I have used it
as an index for the Mandelstamia infata Zone at the Kimmeridgian-Volgian boundary above the
A . sernisulcata-S. trebeli Zone in the Fennoscandian Border Zone.
The specimens of Galliaecytheridea are in many cases difficult to define as species in samples
without specimens of both sexes larval individuals. Dorsal views are virtually a necessity for descriptions and illustrations of an acceptable standard.
Species of the thermophilic Cytherelloidea have been found reither in the Early nor the Late
Jurassic in the Norwegian-Danish Basin. Lack of this genus in the Early Jurassic is also
characteristic of the North German Basin, but in England it is relatively common.
Ostracod Zones and Dispersion of Mesozoic Fossils 1219
A zonation of the Early Cretaceous in the Scandinavian North Sea follows that from England by
Neale (1978), Wilkinson and Morton (1983), and from Germany. It is characteristic of the boreal
ostracod assemblages, that they are so alike, but with differences, at least in the earliest ages, easy
to determine as slight environmental variations mostly related to hydrographical rather than
local structural factors.
Effects of an influx of boreal water on the ostracod assemblages are mostly secondary in the
Early Cretaceous. Influx of warm surface water quickly stabilized in the Valanginian with a high
eustatic sea-level and a relatively thick surface layer of warm seawater in which the various ostracod
assemblages developed. I have recognised Acrocythere hauteriviana further north in the North
Sea-Arctic Seaway than other species. In the Danish area there is no evidence for a specific seaway
through the Danish Sub-basin and into a Danish-Polish Trough in the Earliest Cretaceous. Across
the submerged central parts of the Ringkobing-Fyn High, an early connection between the northeast
German Basin and the Danish Sub-basin seems to have been established in the Valanginian.
Barremian limestones, rich in Bairdia, Pontocyprella, Bythocypris and related genera, from
higher levels in some North Sea areas and far north along Norway, is an example of a warm surface
influx of seawater in the North Sea during the Early Cretaceous. Hydrographically more stable
conditions were established in the Late Cretaceous.
The Late Cretaceous ostracod assemblages in the Scandinavian North Sea Area vary from
open sea conditions to mangrove in Scania, and are relatively rich in ostracods, but a few have
been studied more intensively. In Denmark the outcrops from the Campanian and Maastrichtian
have been studied by Jorgensen from various aspects. He has established (1979) two biozones for
ostracods in the homogeneous chalk sequence : Bythoceratina danica Zone for the uppermost Maastrichtian, and Bythoceratina umbonatoides Zone for the Lower and lowermost part of Upper
The ostracod assemblages from the Mesozoic in the Scandinavian North Sea area have been
studied to varying degrees. The exploration for oil and gas in the area provoked intensive studies
of the Jurassic and Lower Cretaceous. During this geological period, strong faulting activities with
various basin configurations and many ostracod assemblages were developed in the area, dominated
by boreal fauna elements. Differences between the deepest parts of the basins (graben areas) and
“more” epicontinental areas (e.g. the Norwegian-Danish Basin) seem to be related to hydrographical and structural factors. In many intervals only agglutinated foraminifera are present and
recognising or establishing an ostracod zonation is difficult without zonal parallels in other fossil
groups for reference to other areas with ostracods in the boreal faunal province. Gulliaecytherideu
and Mandelstamia are typical boreal ostracods which migrated along the North Sea-Artic Seaway.
This Seaway is considered to have been of great importance in the hydrographical and geological
development in the North Sea basins.
1280 0. B. CHRISTENSEN
ANDERSON, F.w. 1964. Rhaetic Ostracoda. Bull. Geol. Surv. G. B., 21, 133-174.
ANDREEV, YU N. and MANDELSTAM, M.I. 1971. Biogeographical associations of Cretaceous ostracods in the USSR.
In OERTLI, H.J. (ed.). Paleoecologie Ostracodes. Bull. Centre Rech. Pau.-SNPA, 5 suppl., 615-629.
BAARTMANN, J.C. and CHRISTENSEN, 0. BRUUN, 1975. Contribution to the interpretation of the Fennoscandian
Border Zone. Dann. geol. Unders., 11, 102, 1-47.
1977. Jurassic ostracoda of the Atlantic Basin. In M. SWAIN, F.M. (ed.). Stratigraphic micropaleontology of
Atlantic Basin and Borderlands. 23 1-242, Elsevier, Amsterdam.
BERTELSEN, F. 1978. The Upper Triassic-Lower Jurassic Vinding and Gassum Formations of the Norwegian-Danish
Basin. Danm. geol. Unders., B, 3, 1-26.
BROTZEN, F. 1950. De geologiska resultaten fran borrningarna vid Hollviken, Del 11. Undre Kritan och Trias. Sver.
geol. Unders., C 505, 1-48.
CHRISTENSEN, 0.B. 1962. Ostracodtyper fra Keuper-Rhaet lagserien i dybdeboringerne Harte og Ullerslev. Medd.
Geol. Foren., 15, 90-103.
- 1972. Det danske Senkningsomrades udvikling i det mellemste Mesozoikum. Xansk geol. Foren., Arskrift for
- 1974. Marine communication through the Danish Embayment during Uppermost Jurassic and Lowermost
Cretaceous. Geosci. and Man, 4, 99-115.
-1975. Remarks about Displacements of the old rift systems in the North Sea areas. Norgesgeol.
-and KILENYI, T.I.
1970. Ostracod biography of the Kimmeridgian in northern and western Europe. Geol. Surv.
Denmark, II,95, 1-73.
DUFF, K.L., PARSON, c.A., PARSON, c.A., TORRENS, H.s., WIMBLEDON, W.A. and WRIGHT, J.K. 1980.
A correlation of Jurassic rocks in the British Isles. Part Two: Middle and Upper Jurassic. Geol. SOC.Lond.
Spec. Rep., 15, 1-109.
GORDON, W.A. 1974. Physical controls on marine biotic distributions in the Jurassic period. Soc. Econ. Paleont. Miner.,
Spec. Pub., 21, 136-147.
HALLAM, A. 1969. Faunal realms and facies in the Jurassic. Palaeontology, 12, 1, 1-18.
- 1981. Facies interpretation and the stratigraphic record. 1-291. W.H. Freeman & Co. Oxford.
-1983. Early and Mid-Jurassic molluscan biogeography and the establishment of the central Atlantic Seaway.
Palaeogeogr. Palaeoclimatol. Palaeoecol., 43, 181-193.
HESJEDAL, A. and HAMAR, G.P. 1983. Lower Cretaceous stratigraphy and tectonics of the south-southeastern Norwegian offshore. In KAASCHIETER and REIGERS, T.J.A. (eds.) Petroleum geology of the southern North Sea
and the a4acent onshore areas. Geologie en Mijnbouw. Leidschendam.
N.O. 1979. The ostracod fauna from the Maastrichtian white chalk of Denmark. Bull. geol. Soc. Denmark, 27,93-98.
KILENYI, T. 1978. The Jurassic, Part 111,Callovian-Portlandian. In BATE, R.H. and ROBINSON, F. (eds.). A stratigraphical
index of British Ostracodu, 259-298. Seel House Press, Liverpool.
MICHELSEN, 0.1975. Lower Jurassic biostratigraphy and ostracodes of the Danish Embayment. Danm. geol. Unders.,
11, 104, 1-287.
-1978. The Lower Jurassic of the Danish Nordsd 0-1 boring. Central Trough. Danm. geol. Unders., Arbog
1978. The Cretaceous. In BATE, R.H. and ROBINSON, E. (eds.). A stratigraphical index of British ostracoda,
325-384. Seel House Press, Liverpool.
NORLING, E. 1972. Jurassic stratigraphy and foraminifera of western Scania, southern Sweden. Sver. geol. Unders.,
Ca 47, 1-119.
- 1981. Upper Jurassic and Lower Cretaceous geology of Sweden. Geol. Foren. Forth., 103 (2), 253 269.
PEGRUM, R.M. 1984. Structural development of the southwestern margin of the Russian-Fennoscandian Platform. In
SPENCER, A.M. (ed.). Petroleum Geology of the North European Margin, 359-369. Graham & Trotmann Ltd.,
SIVHED, u. 1980. Lower Jurassic ostracodes
and stratigraphy of western Skane, southern Sweden. Sver. geol. Unders.,
Ca 50, 1-61.
SORGENFREI, T. and BUCH, A. 1964. Deep tests in Denmark 1935-1959. Danm. geol. Unders., 111, 36, 1-146.
V A L , P.R. and TODD, R.G. 1981. Northern North Sea Jurassic unconformities, chronostratigraphy and sea-level
changes from seismic stratigraphy. In ILLING, L.V. and HOBSON, G.D., Petroleum geology of continental shelf of
north-west Europe, 216-235, Institute of Petroleum. London.
1983. Kimmeridge Clay Ostracoda of the North Wootton Borehole, Norfolk, England. J. Micropalaeontol.. 2, 17-29.
WILKINSON, I.P. and MORTER, A.A. 1981. The biostratigraphical zonation of the East Anglian Gault by ostracoda.