- © 2000 by AASP Foundation
The paper presents a new study of the Paleogene dinoflagellate cysts from a borehole in central Western Siberia. The presence of stratigraphic markers from the European zonations permitted recognition of six dinoflagellate zones in this section: the Cerodinium speciosum, Apectodinium hyperacanthum and Apectodinium augustum zones in the Paleocene interval; and the Dracodinium varielongitudum, Charlesdowniea coleotrhypta and Charlesdowniea clathrata angulosa zones in the Eocene section. This sequence permits precise age assignment of the Siberian lithological formations, as well as interpretation of the presence of stratigraphic gaps in the marine Siberian Paleogene section. The Late Eocene–Oligocene boundary is characterized by the successive disappearance of the Siberian marine basin and by a significant floristic change.
The first studies of fossil dinoflagellates from Western Siberia were made by Vozzhennikova in the 1960s (Vozzhennikova, 1963, 1965, 1967). The principal goal of these works was the morphological study of the dinoflagellate cysts. The stratigraphic application of dinoflagellates in this region started only at the end of the 1980s when a few boreholes were investigated and the first dinoflagellate zones were identified (Kulkova, 1988; Kulkova and Shatsky, 1990; Ilyina et al., 1994). During the 1990s, new bore-holes have been investigated in the northern part of Western Siberia; these datasets have provided new insight regarding the distribution of dinoflagellate cysts in the Paleogene sediments of this region (Iakovleva et al., in press; Iakovleva and Kulkova, in press). This microfossil group is of particular interest for the detailed Paleogene stratigraphy in Western Siberia and adjacent regions. In fact, during the Paleocene and Eocene, the Western Siberia plain was a wild epicontinental basin connected to the southern and boreal seas. Consequently, at that time the exchange of plankton between the Siberian sea and the world ocean was possible.
The wide development of non-carbonated facies in this area during the Paleocene–Eocene excludes the use of planktonic foraminifers and calcareous nannoplankton for correlation of Siberian sediments with deposits of other regions (Shatsky, 1989). Therefore, other fossils have been used for regional stratigraphic frameworks (Text-Figure 1⇓) (Shatsky, 1984). Indeed, numerous palynological studies have been carried out over the entire western Siberian area. Eight pollen assemblages are recognized in the western Siberia Paleogene section, and six diatom and silicoflagellate assemblages have been established in the Paleocene–Eocene section (Krotov and Shibkova, 1961; Glezer, 1974, 1978; Strelnikova, 1992). The number of radiolarian zones recognized varies between four and eight according to different authors(Lipman et al., 1960; Kozlova and Gorbovetz, 1966; Kozlova and Strelnikova, 1984). The insufficient basis for the dating of the diatom assemblages — one of the principal groups in the first stratigraphic diagrams of Western Siberia —however should be noted. According to Strelnikova (1992), the age determination of the diatom assemblages in the 1970s was based on the similarity between the taxonomic composition of the Siberian associations and those from other regions of the Former Soviet Union (where the age of formations had not been unequivocally established, or had been subsequently modified). After the definition of a regional Paleogene zonation of Western Siberia, numerous authors have questioned the validity of these biochronological subdivisions. However, the questionable basis for the age interpretations has largely been ignored and at present the stratigraphic ages of the regional formations are, for the most parts, accepted without reservation. The diatoms, radiolaria and silicoflagellates of Western Siberia belong to the Paleogene boreal province (Strelnikova, 1992). Therefore, the direct correlation of these assemblages with their low latitude homologues seems highly unlikely (Strelnikova, 1992). Moreover, these microfossil groups only partly characterize the Siberian Paleocene–Eocene section (Text-Figure 1⇓). Finally, the problem of the different number of subdivisions in the various zonations based on the radiolaria and, especially on the diatoms, remains to be resolved.
Given the large geographic extent of the Siberian area, one of the main problems with the study of Siberian Paleogene sediments is there cognition of the precise chronostratigraphic age of the lithological formations. Therefore, the dinoflagellates (organic-walled planktonic algae), which occur in both carbonate and clastic marine sediments, are of special interest to the resolution of these problems. The dinoflagellates typically have relatively rapid rates of morphological evolution and they apparently adapt very quickly to different aquatic conditions. These characteristics give the dinoflagellates significant potential to solve these regional biostratigraphic problems in Western Siberia. Additionally, the simultaneous presence of dinoflagellates, pollen grains and spores in the same samples makes possible the direct correlation of marine and nonmarine sediments.
The purpose of this article is to present new results regarding Paleogene dinoflagellates in Western Siberia and to document more precisely the stratigraphic position of regional lithologic units (formations).
GEOGRAPHIC AND GEOLOGICAL SETTING
Lithology and Geographic Location
Six formations have been defined in the Paleocene–Eocene section of Western Siberia and the adjacent Ural region. These formations are Talitskaya, Serovskaya, Irbitskaya, Nurolskaya, Tardinskaya, and Atlimskaya (Text-Figure 1⇑) (Vereshagin, 1982).
The Talitskaya Formation was defined by Aleskerova and Osyko (1956) in the Sverdlovsk region of the southern Ural region. The lower part of the unit consists of marly clay with benthic foraminifers belonging to the Ammoscalarya inculta assemblage. The upper part of the formation is composed of clay containing the Cibicidoides favorabilis assemblage. The thickness of this formation varies from 100 m to 180 m. The Talitskaya Formation overlies the Upper Cretaceous sediments by a stratigraphic discordance.
The Serovskaya Formation was established by Eremeeva et al. (1956) in the Serov region of the Eastern Urals. This formation consists mainly of clay and diatomite. It contains the diatom assemblage with Triceratium mirabilis and Dictyochia lamellifera, and the pollen assemblage with Triporopollenites robustus. The thickness of this formation varies from 2 m to 35 m.
The Irbitskaya Formation was defined by Sigov (1956) in the Irbit River region of the Ural. Its lower part (up to 40 m thick) consists of argillaceous diatomite, occassional marly diatomite, clay and sandstone. The Irbitskaya Formation contains the Dictyocha frengelli and Coscinodiscus uralensis diatom assemblages. The middle section of the formation (up to 75 m thick) is composed of argillaceous diatomites with intercalations of sandstone, and it is characterized by the Coscinodiscus payeri and Dictyocha deflanderi diatom assemblage. The upper part of the Irbitskaya Formation is made up of clay with argillaceous diatomite and can be up to 150 m thick.
The Nurolskaya Formation was defined by Shatsky (1969) in the Nurolka River region of Western Siberia. This formation consists of clay with marly intercalations, and it contains the Ellipsoxiphus chabakovi, Heliodiscus lentis and Pyxilla gracilis diatom assemblages. The thickness of the unit varies between 15 m and 80 m.
The Tavdinskaya Formation was defined in 1944 by Bogdanovich (see Rostovtsev, 1955) in the Tavda region of the Ural. The lower part is composed of green clay and attains a maximum thickness of 100 m. The middle section is made up of 30 m of sand and clay with lignite intercalations. The upper part (100 m) consists of green clay with sand intercalations and siderite inclusions. According to the Stratigraphical Dictionary (Vereshagin, 1982), the lower section contains the diatoms Pelecyora incrassata,Pelecyora tenuis and Cibicidoides khabaensis.
The marine sediments of the Tavdinskaya Formation are overlain by the terrestrial sediments of the Atlimskaya Formation, which contains the Carya spackmania pollen assemblage in its lower section.
Borehole No. 4, the subject of this article, is located in the Vasugan Basin (eastern part of the Irtysh–Ob area, in central part of Western Siberia; Text-Figure 2⇓). The marine section of this borehole is represented by the sediments of the Talitskaya, Serovskaya, Irbitskaya, Nurolskaya and Tavdinskaya formations. The lithological succession (Text-Figure 3⇓), from top to bottom, is:
Atlimskaya Formation (169.0–170.0 m): gray sand with brown clay intercalations
Tavdinskaya Formation (170.0–252.9 m): green–gray clay with marl lenses
Nurolskaya Formation (252.9–310.0m):green–yellowclay with few marly beds
Irbitskaya Formation (310.0–342.0 m): gray diatomite/ gray–green marly clay
Serovskaya Formation (342.0–405.3 m): gray and dark gray clay with diatomite intercalations
Talitskaya Formation (405.3–416.0 m): dark gray marly clay
The palynological samples were processed using the palynological techniques of the Russian Academy of Sciences (Grichuk, 1940; Petrova, 1986). The processing steps are as follows: (1) sample is processed with 10% HCl until the calcium carbonate is dissolved; (2) solution of 10% NaH4OH is added to the sample in a water-bath, followed by several washes until argilleous elements are eliminated; (3) sample is centrifuged with a heavy liquid [K2(CdI4)] with density of 2.25, followed by dehydration in pure acetic acid and several washings in water; (4) the acetolysis solution (9:1 acetic anhydride to sulphuric acid) is prepared and immediately used; (5) this mixture is distributed into test tubes, and the samples are placed in a boiling water-bath for 2 minutes; (6) this reaction is stopped with acetic acid, followed by centrifugation and several washes in water; the liquid fraction is decanted and the sample is mounted in glycerine jelly.
The ubiquitous distribution of dinoflagellate cysts in the Paleocene–Eocene section in Borehole No. 4 permitted the recognition of six dinoflagellate zones originally described from western Europe (Cavelier and Pomerol, 1986; Powell, 1992). The distribution of phytoplankton is illustrated in Text-Figure 3⇑.
This zone is recognized in the interval from 354.0 m and 416.0 m (Talitskaya and Serovskaya formations) by the presence of the marker species C. speciosum and the absence of other younger marker taxa. The dinoflagellate assemblage consists of many taxa that typically occur in the Paleocene section of Europe. These include, among others, Alterbidinium acutulum, Areoligera coronata, A. senonensis, Cerodinium speciosum, C. striatum, Glaphyrocysta ordinata, Membranosphaera maastrichtica, Rhiptocorys veligera, Senegalinium obscurum, and Palaeocystodinium benjaminii. The species Cerodinium markovae is particularly abundant at 374.0 m.
Pollen and spores are also present in this assemblage, and consist primarily of Normapolles with somewhat less abundant Postnormapolles. The pollen Anacolosidites insignis, Comptonia rotunda, Platycaryapollis sp., Pterocarya sp., Ulmoideipites sp., Pinus sp., Haploxylon, Cedrus sp., and Taxodiaceae, as well as the spores Sphagnum sp., Selaginella sp. and Gleichenia sp., occur in this interval.
This zone is recognized between 344.5 and 354.0 m (Serovskaya Formation and lowermost part of the Irbitskaya Formation) and is defined by the first occurrence of the marker Apectodinium homomorphum. This assemblage is characterized by very high numbers of members of the genera Deflandrea and Cerodinium.
The pollen assemblage in this interval is sparse and contains few species, which include Trudopollis menneri Zaklinskaya, Comptonia rotunda Kulkova and Castanopsis sp.
This zone is recognized between 339.5 m and 344.5 m (Irbitskaya Formation). This section is characterized by the first occurrence of the zonal marker A. augustum and of the species A. quinquelatum and A. parvum.
This zone is recognized between 308.0 m and 339.5 m (Irbitskaya Formation) and is defined by the first occurrence of D. varielongitudum. In addition to the zonal marker, the dinoflagellate assemblage is characterized by Wetzeliella meckelfeldensis, W. articulata, W. lobisca, Dracodinium simile, and D. solidum. An unusually high abundance of W. meckelfeldensis occurs at 357.0 m, while the abundance peak of D.varielongitudum occurs at 310.0 m.
The predominance of “tricolporates” such as Castanopsis sp. and Tricolporopollenites sp. is chararcteristic of the pollen assemblage. The pollen Psilatricolporites sp., Rhoipites villensis Boïtzova, R. pseudocingulum (Krutzsch) Pflug, Triatriopollenites aroboratus Pflug, Myrica sp., Castanea sp., Pterocarya communis Kulkova, Alnus quadropollenites Rouse, among others, are also present in this interval.
This zone is recognized between 252.9 m and 308.0 m (Nurolskaya Formation) and is defined by the first occurrence of Charlesdowniea coleothrypta. The first occurrences of the species Deflandrea phosphoritica and Dracodinium politum occur simultaneously with C. coleothrypta at the base of this interval. The species C. tenuivirgula, C. coleothrypta rotundata, Wetzeliella coronata, and W. echinulata occur within this interval. The genus Charlesdowniea is very abundant at depths of 266.0 m, 271.0 m, and 291.0 m. The species Soaniella granulata, which is known only from Western Siberia, occurs at 256.0 m.
Angiosperms are dominant in the pollen assemblage of this interval. The most common species are Araliaceoipollenites euphorii Potonié, Pompeckjoidaepollenites subhercynicus Krutzsch, Sapotaceoidaepollenites manifestus Potonié, and Castanopsis pseudocingulum (Potonié) Boïtzova.
Charlesdowniea clathrata angulosaZone.
The zone is recognized between 187.0 m and 252.9 m (Tavdinskaya Formation) and is defined by the first occurrence of C.clathrata angulosa. The interval does not have abundant phytoplankton; species present in the assemblage include Areosphaeridium diktyoplokum, Wetzeliella irtyschensis, C. fasciata, Gochtodinium spinula, among others. The interval is also characterized by the presence of Pterospermella sp., Tasmanites sp. and Tytthodiscus sp.
The samples between 228.5 m and 251.0 m are rich in pollen and spores; the assemblage is characterized by high numbers of Castanopsis pseudocingulum, Rhoipites pseudocingulum, Castanea sp., Quercus gracilis Boïtzova, Alnusquadropollenites, Tiliapseudinstructa (Mai)Kulkova. An increase in the percentage of conifers (Cedrus, Podocarpus, Pinus) is observed below 238.0 m.
The assemblage between 170.0 m and 218.0 is very poor in phytoplankton, with only the following species present: Deflandrea phosphoritica, Cordosphaeridium inodes, Hystrichosphaeridium tubiferum, Pterospermella sp., Tasmanites sp. and Tytthodiscus sp. The abundance of the aquatic fern Hydropteris indutus is recorded in the samples between 208.0 m and 230.5 m. The pollen Quercus gracilis–Quercus graciliformis assemblage is recognized at these depths.
Carya spackmania Assemblage.
Phytoplankton become absent at 169.0 m and above (Atlimskaya Formation). Concurrently, a significant change in the composition of the pollen assemblage occurs; this is the Carya spackmania pollen assemblage. The assemblage is characterized by the dominance of deciduous pollen grains such as Carya, Juglans, Betula, Tilia, Corylus, Alnus, Ulmus and by the conifers.
The six dinoflagellate zones recognized in Borehole No. 4 permit the direct correlation between the Siberian stratigraphy and the sediments of Western Europe. Consequently, it is possible now to more precisely estimate the relative ages of the Siberian marine sediments.
Cerodinium speciosum zone.
This zone, recognized in the the Upper Talitskaya Formation and the Serovskaya Formation, corresponds to its European homologue in the zonation of Powell (1992). According to Powell (1992), this zone is calibrated with the calcareous nannoplankton biozone NP5 (pars) of Martini (1971) and planktonic foraminiferal biozones P3b (pars)–P4 (pars) (Berggren et al., 1995). Therefore, the sediments in Western Europe that comprise the C. speciosum zone are attributed to the Selandian–Early Thanetian. Because we did not recognize the base of the C. speciosum in Borehole No. 4, this interval in the Talitskaya and Serovskaya Formations can be estimated to be early Thanetian in age. We note that the C. speciosum Zone was also recognized in other regions of the former Soviet Union, including Crimea–Caucasus (Andreeva-Grigorovich, 1991) and the Southern Ural region (Vasilieva, 1990).
Apectodinium hyperacanthum Zone.
This zone in the Serovskaya Formation in Borehole No. 4 corresponds to the European A. hyperacanthum Zone of Powell (1992) and to the Apectodinium homorphum Zone in the former Soviet Union (Andreeva-Grigorovich, 1991; Vasilieva, 1990). According to Powell (1992), the zone is calibrated to nannoplankton biozone NP9 (pars) and planktonic foraminiferal biozones P4 (pars)–P5 (pars). Hence, we assign this interval in the Serovskaya Formation a Thanetian age.
Apectodinium augustum Zone.
This zone is recognized for the first time in the former Soviet Union, and corresponds to its European analogue (Powell, 1992). According to Powell (1992), this zone is calibrated in Western Europe to nannoplankton biozone NP9 (pars) and planktonic foraminiferal biozones P6A–P6B (pars). Consequently, the sediments of the Serovskaya and Irbitskaya formations with the A. augustum assemblage are dated as Thanetian–earliest Ypresian.
Dracodinium varielogitudum Zone.
The zone in Borehole No. 4 is recognized using the same criteria as in Western Europe: its zonal boundaries are the first occurrence of D. varielongitudum and the first occurrence of Charlesdowniea coleothrypta. In Western Europe, the D. varielongitudum zone is calibrated using nanno-plankton biozones NP11 (pars)–NP12 (pars) and planktonic foraminiferal biozone P7 (pars), and is dated as Ypresian (Berggren et al., 1995). In the south regions of the former Soviet Union, this zone is also dated as Ypresian (Andreeva-Grigorovich, 1991). Consequently, the sediments of the Irbitskaya Formation containing the D. varielongitudum assemblage are assigned to the Ypresian.
Charlesdowniea coleothrypta Zone.
This zone occurs in the Nurolskaya Formation in Borehole No. 4 and corresponds to the Powell’s (1992)Charlesdowniea coleothrypta Zone. According to Powell (1992), the C. coleothrypta Zone is calibrated with nannoplankton biozone NP12(pars) and planktonic foraminiferal biozone P8 (pars). Its age is Ypresian (pars).
Charlesdowniea clathrata angulosa Zone.
This zone occurs in the Tavdinskaya Formation in Borehole No. 4 and corresponds to its homologue in the Paris Basin (Cavelier and Pomerol, 1986). In the Paris Basin the zone corresponds to nannoplankton NP18–NP21 biozones. Therefore, the sediments from the Tavdinskaya Formation that contain the C. clathrata angulosa assemblage can be dated as Priabonian.
Comparison of the Paleogene dinoflagellate zones in Borehole No. 4 with Powell’s (1992) dinoflagellate zonation for Western Europe suggests the absence of several zones in the Paleogene record of Borehole No. 4 (Text-Figure 4⇓).
The Paleocene part of the European Alisocystamargarita dinoflagellate Zone is not recognized in Borehole No. 4, however it is recognized in other regions of Western Siberia (Iakovleva and Kulkova, in press). This fact can be explained either by the presence of a hiatus within the Serovskaya Formation, or by an insufficient sampling regime to resolve this zone through this section.
The absence of three dinoflagellate zones (G. ordinata, W. astra, and W. meckelfeldensis zones) which characterize the Paleocene–Eocene transition in western Europe. These zones are absent in the interval which corresponds to the boundary between the Serovskaya and Irbitskaya formations in Borehole No. 4. The possibility of an unconformity between the two formations, which represents the time interval for these three zones, is therefore suggested.
The dinoflagellate zones which characterize the Lutetian and Bartonian in Western Europe are not recognized in the borehole section. This event coincides with the boundary between the Nurolskaya and Tavdinskaya formations. We suggest the presence of a hiatus and, consequently, the interruption of marine sedimentation in the Vasugan Basin during the Lutetian–Bartonian.
The disappearance of phytoplankton at the boundary between the Tavdinskaya and Nurolskaya formations has been observed in other regions of Western Siberia (Kulkova and Shatsky, 1990; Ilyina et al., 1994). This event corresponds to the end of marine sedimentation in the West Siberia area. The simultaneous important floristic change (predominance of temperate deciduous broadleaf plant pollen such as Betula, Corylus, Tilia, Ulmus, along with gymnosperms such as Pinus) indicates that the climate began a cooling trend at this time. This cooling event at the Eocene–Oligocene transition is globally recognized (Prothero, 1994).
Borehole No. 4, located in the central part of Western Siberia, contains a rich Paleocene–Eocene record of dinoflagellate cysts. The dinoflagellate cysts are abundant in the lower and middle parts of the section, but the abundance decreases in the upper parts of the section. Six dinoflagellate zones from the Western European zonations are recognized in the borehole section; these are the Cerodinium speciosum, Apectodinium hyperacanthum and A. augustum zones in the Paleocene section, and the Dracodinium varielongitudum, Charlesdowniea coleotrhypta and C. clathrata angulosa zones in the Eocene section. The presence in Borehole No. 4 of key stratigraphic markers used in the European zonations permitted the reasonably detailed correlation of marine sections in West Siberia and western Europe. As a result, the following ages for the Siberian regional formations in this area are proposed:
Tavdinskaya Formation – Priabonian
Nurloskaya Formation – Ypresian
Irbitskaya Formation – late Thanetian–early Ypresian
Serovskaya Formation – Thanetian (pars)
Upper Talitskaya Formation – early Thanetian
The absence of several dinoflagellate zones in the Paleocene–Eocene section indicates the presence of stratigraphic hiatuses at several places in the section. The boundary between the marine sediments of the Tavdinskaya Formation and the terrestrial deposits of the Atlimskaya Formation are characterized by an important floristic change that supports the climatic cooling event and termination of marine deposition in the Siberian Sea during the time of the Eocene–Oligocene boundary.
By increasing the number of studies focusing on dinoflagellates from Western Siberia, we shall expand the available data sets to interpret more precisely the relative ages of Siberian stratigraphic sections, and to reconstruct more accurately the paleoenvironments of the Siberian area during the Paleogene.
Achomosphaera sagena Davey & Williams 1966 (Plate 2, figs. 3, 4⇓)
Adnatosphaeridium robustum (Morgenroth 1966) De Coninck 1975
Alterbidinium acutulum (Wilson 1967) Lentin & Williams 1985
Apectodinium augustum (Harland 1979) Lentin & Williams 1981 (Plate 1, figs. 7, 8⇓)
Apectodinium homomorphum (Deflandre & Cookson 1955) Lentin & Williams 1977
Apectodiniumhyperacanthum (Cookson & Eisenack 1965) Lentin & Williams 1977
Apectodinium parvum (Alberti 1961) Lentin & Williams 1977 (Plate 2, fig. 2⇓)
Apectodinium quinquelatum (Williams & Downie 1966) Costa & Downie 1979
Areoligera coronata (O.Wetzel 1933) Lejeune-Carpentier 1938
Areoligera senonensis Lejeune-Carpentier 1938
Areosphaeridium diktyoplokum (Klumpp 1953) Stover & Williams 1981
Cerodinium diebelii (Alberti 1959) Lentin & Williams 1987
Cerodinium markovae (Vozzhennikova 1967) Lentin & Williams 1987
Cerodinium speciosum (Alberti 1959) Lentin & Williams 1987
Cerodinium striatum (Drugg 1967) Lentin & Williams 1987
Charlesdowniea clathrata (Eisenack 1938) Lentin & Vozzhennikova 1989
Charlesdowniea aff. clathrata (Eisenack 1938) Lentin & Vozzhennikova 1989 (Plate 1, figs.2, 5⇑)
Charlesdowniea clathrata subsp. angulosa (Châteauneuf & Gruas-Cavagnetto 1978) Lentin & Vozzhennikova 1989 (Plate 2, fig. 1⇑)
Charlesdowniea coleothrypta (Williams & Downie 1966) Lentin & Vozzhennikova 1989
Charlesdowniea coleothrypta subsp. rotundata (Châteauneuf & Gruas-Cavagnetto 1978) Lentin & Vozzhennikova 1989
Charlesdowniea fasciata (Rozen 1965) Lentin & Vozzhennikova 1989
Charlesdowniea tenuivirgula (Williams & Downie 1966) Lentin & Vozzhennikova 1989
Chlamydophorella cf. wallala Cookson & Eisenack 1960
Cometodinium whitei (Deflandre & Courteville 1939) Monteil 1991
Cordosphaeridium exilimurum Davey & Williams 1966
Cordosphaeridium inodes (Klumpp 1953) Eisenack 1963
Deflandrea andromiensis Vozzhennikova 1967
Deflandrea arcuata Vozzhennikova 1967
Deflandrea denticulata Alberti 1959
Deflandrea dissoluta Vozzhennikova 1967
Deflandrea phosphoritica Eisenack 1938
Diphyes colligerum (Deflandre & Cookson 1955) Cookson 1965 (Plate 1, figs. 3, 9⇑)
Dracodinium politum Bujak in Bujak et al. 1980
Dracodinium simile (Eisenack 1954) Costa & Downie 1979
Dracodinium solidum Gocht 1955
Dracodinium varielongitudum (Williams & Downie 1966) Costa & Downie 1979 (Plate 1, figs. 1, 4⇑)
Glaphyrocysta ordinata (Williams & Downie 1966) Stover & Evitt 1978 (Plate 2, fig. 6⇑)
Gochtodinium spinula Bujak 1979
Hafniasphaeraseptata (Cookson & Eisenack 1967) Hansen 1977
Homotryblium cf. pallidum Davey & Williams 1966
Hystrichokolpoma eisenackii Williams & Downie 1966 (Plate 2, figs. 8, 9⇑)
Hystrichosphaeridium tubiferum (Ehrenberg 1838) Deflandre 1937
Hystrichostrogylon membranophorum Agelopoulos 1964
Impagidinium dispertatum (Cookson & Eisenack 1965) Stover & Evitt 1978
Laciniadinium furmum (Harland 1973) Morgan 1977
Lingulodinium machaerophorum (Deflandre & Cookson 1955) Wall 1967
Membranosphaera maastrichtica Samoilovich 1961
Microdinium kustanaicum Vozzhennikova 1967
Microdinium reticulatum Vozzhennikova 1967
Palaeocystodinium benjaminii Drugg 1967
Palaeocystodinium golzowense Alberti 1961
Palaeotetradinium minusculum (Alberti 1961) Stover & Evitt 1978
Phthanoperidinium alectrolophum Eaton 1976
Phthanoperidinium eocenicum (Cookson & Eisenack 1965) Lentin & Williams 1973
Pierceoites pentagonus (May 1981) Habib & Drugg 1987
Rhombodinium glabrum (Cookson 1956) Vozzhennikova 1967
Rhiptocorysveligera (Deflandre 1937) Lejeune-Carpentier & Sarjeant 1983
Samlandia chlamydophora Eisenack 1954
Senegalinium obscurum (Drugg 1967) Stover & Evitt 1978 (Plate 1, fig. 6⇑)
Soaniella granulata Vozzhennikova 1967
Spiniferella coronata (Gerlach 1961) Stover & Hardenbol 1993
Spiniferites membranaceus (Rossignol 1964) Sarjeant 1970
Spiniferites porosus (Manum & Cookson 1964) Harland 1973
Spiniferites pseudofurcatus (Klumpp 1953) Sarjeant 1981
Spiniferites ramosus (Ehrenberg 1838) Loeblich & Loeblich 1966
Spiniferites ramosus subsp. granosus (Davey & Williams 1966) Lentin & Williams 1973
Spiniferites scabrosus (Clark & Verdier 1967) Lentin & Williams 1975
Systematophora placacantha (Deflandre & Cookson 1955) Davey et al. 1969
Thalassiphora pelagica (Eisenack 1954) Eisenack & Gocht 1960
Wetzeliella articulata Eisenack 1938
Wetzeliella coronata (Vozzhennikova 1967) Lentin & Williams 1976
Wetzeliella echinulata Vozzhennikova 1967
Wetzeliella irtyschensis Alberti 1961
Wetzeliella lobisca (Williams & Downie 1966) Jolley & Spinner 1989 (Plate 2, figs. 5, 7⇑)
Wetzeliella meckelfeldensis Gocht 1969
Paucilobimorpha incurvata (Cookson & Eisenack 1962) Prössl 1994
We are grateful to Dr. Kulkova (Institute of Geology, Geophysics and Mineralogy, Novosibirsk) and Dr. Akhmetiev (Geological Institute, Moscow) for their advice and insightful discussions. This is an ISEM (Institut des Sciences de l’Evolution, Montpellier) Contribution 2000-109.