Data on Late Cenomanian and Early Turonian foraminiferal assemblages in the northern palaeo biogeographical district of the West Siberian province are summarized in the paper. In addition, the section of borehole 1016 of the Parusovaya area located in the far north of the province is considered. New information on the foraminiferal zones of this stratigraphic level along with the previously known sections of the Tazovskaya, Purpeiskaya, Van-Eganskaya areas provided an opportunity to carry out a correlation of these zones between the West Siberian and the Canadian provinces (Western Canada, Northern Alaska). The West Siberian Late Cenomanian Trochammina wetteri tumida, Verneuilinoides kansasensis and the Early Turonian Gaudryinopsis angustus foraminiferal zones have their analogues as similar zones in the Canadian province. Due to the provided correlation of the micropalaeontological (foraminiferal) zones, their age in the West Siberian province has been clarified. Besides, similarity of the conditions of dwelling within the boundaries of the entire Arctic palaeobiogeographical realm has been observed.
A comparative characteristic of Late Cretaceous West Siberian foraminiferal assemblages and other provinces of the Northern hemisphere has shown that the Cenomanian-Turonian assemblages are significantly distinctive in their systematic composition but correspond to those of the Canadian province (Western Canada, Northern Alaska) within the boundaries of the Arctic palaeobiogeographical realm [
The layers of Cenomanian-Turonian assemblages of Western Siberia had been earlier attributed to the microfaunistic zones (upper Uvatskian, Kuznetsovskian Horizons) by the author of the paper. The assemblages of interest are similar in their systematic composition with time-equivalent assemblages of the analogous zones of Western Canada and Northern Alaska formations attributed to the Canadian province. One should observe a similarity not only at the generic but at specific levels in the Cenomanian and Turonian assemblages. Apparently, it is due to the existence of unimpeded associations between the basins of Western Siberia and Northern America and a similarity of the conditions of existence. In the compared assemblages one can observe almost a general generic composition and a high percent (up to 60%) of similar species, vicariants (geographical substitutes of a related taxon) and geographical subspecies. In all the compared assemblages with the exception of those from the far away areas, agglutinated quartz-siliceous shells are predominant. A similar, specific composition of plankton (pelagic) forms assigned to the lower Turonian stratigraphic level is of great interest. However, a comparison of the Cenomanian-Turonian assemblages of Western Siberia with those of Arctic Canada and the Canadian Arctic Archipelago [
The paper concerned presents results of researching Late Cenomanian and Early Turonian foraminifera from this stratigraphical level of northern palaeobiogeographical district of West Siberian province. This is one of the five districts named according to the cardinal points [
Research of Cenomanian foraminifera from the Uvatskian Horizon in Western Siberia has been carried out since the 50-s of the last century. Only a fragmentary amount of information on isolated foraminifera in this part of the section has
been provided in the works published by [
The Uvatskian Horizon in the northern district consists of grey aleurolites and light-grey millstone grit of the marine genesis. The rocks comprise coarse-grain- ed agglutinated quartz-siliceous foraminifera which are practically the only basis for establishing the Cenomanian age of this Horizon.
The foraminifera of Early Cenomanian of seven sections of Van-Egansky area’s boreholes have been studied in detail, so in the shallow water fascies of the Uvatskian Horizon two foraminiferal zones: Saccammina micra, Ammomarginulina sibirica (lower zone), Trochammina wetteri tumida, Verneuilinoides kansasensis (upper zone) with the layers of Gaudryinopsis nanushukensis at the
Stage | Substage | Western Siberia | Western Canada | Northern Alaska | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Podobina (2000, 2009) | Peace River Alberta (Stelck and Wall, 1954, 1955) | Central Alberta (Wall, 1967) | Vermilion Area, Alberta (Nauss, 1947) | Northern regions (Tappan, 1960, 1962) | |||||||||
Horizon | Micropaleontological zones | Formations and members | Micropaleon-tological zones | Formations and members | Micropaleontological zones | Formations and members | Micropaleon-tological zones | Formations and members | Micropaleontological zones | ||||
Turonian | upper | kusnetzovskian | Pseudoclavulina hastata | Cardium | unknown | Cardium | unknown | Lloydm Inster | unknown | Seabbe | Ayiyak member | Pseudoclavulina hastata, Arenobulimina (?) torula | |
Blackstone | Opabium member | Pseudoclavulina sp. (P. hastata) | |||||||||||
Kaskapau | Haven member | ||||||||||||
lower | Gaudryinopsis angustus | Pelagic, Haplophragmoides spiritensis | Vimy member | Lower Pelagic | Rugoglobigerina, Haplophragmoides (?) collyra | Lower member | unknown | ||||||
Cenomanian | upper | uvatskian | Trochammina wetteri tumida, Verneuilinoides kansasensis | Danvegan | Ammobaculites pacalis | Sunkay member | unknown | Haplophragmoides gigas | Ninuluk | Gaudryina (?) irenensis, Trochammina rutherfordi | |||
Shaftesbury | Gaudryina (?) irenensis | Verneuilinoides kansasensis |
base of the upper zone [
Data on two Turonian foraminifera zones are known in many works of V.M. Podobina [
The determination of the age of the Uvatskian and Kuznetsovskian Horizons is of great practical value because industrial hydrocarbon reserves are assigned to the Uvatskian Horizon and the Kuznetsovskian Horizon is a cap rock which has kept these hydrocarbons from destruction.
Biostratigraphy of upper Cenomanian - lower Turonian deposits of the northern district of Western Siberia has been the object of much experimentation. Twenty core samples selected in the section of borehole 1016 of the Parusovaya area located eastwards of Yamal (
Systematic composition of Late Cenomanian and Early Turonian foraminifera assemblages in the section of borehole 1016 was distinguished and their stratigraphic significance was established, too. The micrograps (Figures 2-4) illustrate several species including index-species of late Cenomanian and two Early Turonian foraminifera assemblages. In
The boundary between the Uvatskian and Kuznetsovskian Horizons is drawn arbitrarily mainly according to the geological data. The lithological and microfaunistic characteristic of the section being studied is made coincident with the biostratigraphic data of both Horizons as well as the identification of index spe- cies of the determined assemblages and the corresponding foraminifera zones (
The Asarotammina genus previously established by P. Bronniman in the Holocene of the Brazilian shelf was first discovered for Western Siberia in the lower Turonian stage of the Parusovaya area.
A new Early Turonian species of the genus concerned―A. antisa Podobina is different from the standard Holocenian one and is found in the lower Turonian stage in the north [
Assemblage with Gaudryinopsis nanushukensis elongatus of Late Cenoman discovered in the section of borehole 1016 of the Parusovaya area differs from that of Van-Eganskaya and other areas [
Early Turonian assemblage with Gaudryinopsis angustus established almost in all the selected samples of the section of borehole 1016 from the bottom of the Kuznetsovskian Horizon is diverse, and index-species is predominant. This assemblage is identical with the complexes studied by V. M. Podobina in many sections of Western Siberia [
Cenomanian stage and its deposits of marine genesis in the northern district were first distinguished by V.M. Podobina [
Upper Substage Uvatskian Horizon
From the rocks with the interval 1031.5 - 1048.8 m (borehole 1016) eight samples from noncalcareous grey aleurolites with sublayers of light-grey millstone grit traced have been selected. Grains of quartz, mica plates, separate agglutinated big-grained foraminiferal shells, black chitinous shell linings in the form of imprints of their former chambers are predominant in the washed-out big-grained fractions. Most of foraminifera shells from the Uvatskian Horizon of the area concerned are poorly preserved so that species character is difficult to distinguish. Along with the indicated remains of organisms, yellowish fragments of diatomaceous flora in the form of small rounded disks are encountered.
In all 8 samples selected from the Uvatskian Horizon hardly distinguishable remains of foraminiferal shells are predominant. Along with them, however, the species of Late Cenomanian mainly without species determinations―Haploph- ragmoides, Ammomarginulina, Trochammina, Verneuilinoides, Gaudryinopsis were established among well preserved forms. Along with them, index-species of one of the assemblages―Gaudryinopsis nanushukensis elongatus―was distinguished (
In some samples studied the following species―Psammosphaera laevigata White, Saccammina micra Bulatova, Rhabdammina discreta Brady, Haplophragmoides cf. variabilis Podobina, Ammomarginulina cf. sibirica Podobina, Ammoscalaria sp. indet, Trochammina aff. wetteri Stelck et Wall tumida Podobina, Gaudryinopsis aff. nanushukensis (Tappan) elongatus Podobina are determined. Flattened remains of the shells of Ammomarginulina and Trochammina genera are the most numerous ones.
Separate pseudomorphoses of calcareous shells of foraminifera Rotaliida order and ostracoda are established. It is necessary to update data on foraminifera and stratigraphy of Cenomanian-Turonian northern district of Western Siberia because industrial and renewable hydrocarbon reserves are assigned to this part of the section.
Lower Substage Kuznetsovskian Horizon
Well-preserved agglutinated quartz-siliceous foraminifera were discovered in 12 samples from the interval 1005.0 - 1019.9 m of the section (borehole 1016). Lithologically, the samples are represented by noncalcareous dark-grey argillite of the Kuznetsovskian Horizon. In the sample at depth 1016.4 m remains of bivalve shells as well as foraminifera were found. In Early Turonian assemblage together with Gaudryinopsis angustus Podobina the representatives of Haplophragmoides, Trochammina and Gaudryinopsis genera are predominant, the number of index-species of shells in some samples attaining 50 and more specimens. In addition to Trochammina wetteri Stelck et Wall, this species significantly prevails in terms of quantity over other species. The species composition of the assemblage together with index-species Gaudryinopsis angustus is the following: Psammosphaera laevigata White, Saccammina complanata (Franke), Lituotuba confusa (Zaspelova), Reophax inordinatus Young, Labrospira collyra (Nauss), Haplophragmoides rota Nauss sibiricus Zaspelova, H. crickmayi Stelck et Wall, Asarotammina antisa Podobina, Ammomarginulina haplophragmoidaeformis (Balakhmatova), Haplophragmium incomprehensis (Ehremeeva), Trochammina subbotinae Zaspelova, Trochammina wetteri Stelck et Wall, Gaudryinopsis angustus Podobina, Pseudoclavulina hastata (Cushman), Uvigerinammina manitobensis (Wickenden). Shells with the exception of completely white azarotammin and lituotrub are of light-grey colour with a predominant fine-grained structure of the wall. Among the enumerated species for the part of the section concerned (lower Turonian), Ammomarginulina haplophragmoidaeformis (Balakhmatova), Uvigerinammina manitobensis (Wickenden), Gaudryinopsis angustus Podobina are the most characteristic ones. In the assemblage Trochammina and Gaudrynopsis are predominant which suggests relatively deep-water and favourable conditions of existence. In one sample at depth 1019.6 m foraminifera shells are coarse-grained, index-species is individual. By and large, the assemblage, however, is Early Turonian although the conditions of shells’ dwelling at the indicated depth were less favourable as compared with Early Turonian foraminifera associations lying above. (
In sample at depth 1019.6 m remains of bivalve shells as well as foraminifera were found.
Unfortunately, between the selection depth of the lower sample from the Kuznetsovskian Horizon and the samples from the upper parts of the Uvatskian Horizon a significant interval in core selection is observed and therefore, we did not manage to trace the boundary between the indicated horizons and hence that of the lower Turonian and upper Cenomanian stages (
The boreal transgression which began in Late Cenomanian significantly expanded in Early Turonian and occupied the territory of not only the Parusovaya area being studied but spread all over Western Siberia: in the south it came to the Kazakhstan hills, in the west-up to the Urals, and in the east it is observed up to the meridian of Napas settlement (on the Tym river) [
Twenty core samples selected from the section of borehole 1016 of the Parusovaya area have been studied. From each sample of the section concerned mainly represented by grey aleurolites and millstone grits (the Uvatskian Horizon) and dark-grey argillites (the Kuznetsovskian Horizon) agglutinated quartz-siliceous foraminiferal shells have been discovered. Late Cenomanian foraminifera were determined in the Uvatskian Horizon.
In contrast to the Late Cenomanian, shells of Early Turonian foraminifera assemblage are well-preserved, and have been found their characteristic species, including Gaudryinopsis angustus Podobina index-species. According to the number of specimens in the assemblage, the representatives of Ataxophragmiida order are predominant which is indicative of a favourable hydrological regime of a marine basin (depth, temperature, salinity, gas composition) which is associated with deepening and expanding Early Turonian boreal transgression.
This transgression, as contrasted to the Late Cenomanian one, occupied almost in the entire territory of Western Siberia that contributed to the foraminiferal assemblage development together with Gaudryinopsis angustus encompassing all species characteristic of the Kuznetsovskian Horizon.
The correlation of the Late Cenomanian-Turonian foraminiferal (micropalaeontological) zones of West Siberian and the Canadian provinces within the boundaries of the Arctic palaeobiogeographical realm is provided (see
Micropalaeontological zones of the Cenomanian-Turonian of the West Siberian province correspond to those of the Canadian province (Western Canada, Northern Alaska ), which suggests a similarity of the conditions of their dwelling. Taxa (genera, species) of agglutinated quartz-siliceous forms are predominant. In the lower Turonian of the Canadian province a layer of pelagic forms (Pelagic, genera Hedbergella) has been observed. Just the same layers have been found at this stratigraphic level within the range of some sections of boreholes (borehole 1002, the Van-Eganskaya area, etc.) of the northern district of the West Siberian province.
Podobina, V.M. (2017) Cenomanian-Turonian Foraminiferal Zones of West Siberian Province and Their Correlation with Canadian Province. Open Journal of Geology, 7, 1176-1187. https://doi.org/10.4236/ojg.2017.78078