首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Modifications to the upper Bathonian zonal scale for northern East Siberia provided by the newly available paleontological record on Middle Jurassic reference sections in the Arctic regions of Yakutia and by the revised earlier collections, are justified. The oldest East Siberian members of Cadoceras are found to be characteristic not of the initial Callovian age as believed by Russian paleontologists, but of the terminal Bathonian age as was previously shown in the biostratigraphic scheme of East Greenland. The succession of zones and index species analogous to that of the latter is revealed in the studied region and the zonal boundaries in Siberia and East Greenland are inferred to be synchronous. Finds of Cadoceras calyx in the upper Bathonian scale permitted, for the first time, the recognition of a corresponding zone. The Bathonian-Callovian boundary is placed between the calyx and anabarense zones. The upper Bathonian zonal scale of northern East Siberia is now in total agreement with the East Greenland zonal scale.  相似文献   

2.
The upper Bathonian Ammonites Cadoceras perrarum Voron. and Kepplerites ex gr. rosenkrantzi Spath are reported for the first time from the western coast of Anabar Bay, loosely collected. Both ammonoids represent index species of two biostratigraphic units: the Cadoceras barnstoni Beds and Cadoceras variabile Zone. The occurrence of genus Kepplerites (Kosmoceratidae) in North Siberia is evidence in favor of the migration of that family into the seas of the Arctic region.  相似文献   

3.
The Oxfordian Stage of West Siberia contains Boreal ammonites Cardioceratidae. The authors’ bank of paleontological data includes ~ 500 definitions of Cardioceratinae, permitting a considerable refinement of the official Oxfordian regional zonal scale. The lower substage is divided into the Cardioceras (Scarburgiceras) obliteratum, C. (S.) scarburgense, and C. (S.) gloriosum Zones instead of beds with C. (S.) spp., whereas the C. (Cardioceras) percaelatum and C. (C.) cordatum Zones are recognized instead of beds with C. (C.) spp. We have found new ammonites typical of the Middle Oxfordian C. (Subvertebriceras) densiplicatum and C. (Miticardioceras) tenuiserratum Zones. The first of these zones is divided into two subzones. The Upper Oxfordian includes the Amoeboceras glosense and A. serratum Zones instead of beds with A. spp., and the A. regulare Zone and beds with A. rosenkrantzi are recognized instead of the A. ex gr. regulare Zone. The genus Ringsteadia (Aulacostephanidae) is observed only in the northwestern part of the region, along the eastern slope of the North Urals; therefore, two upper units of the biostratigraphic scale correspond to beds with Ringsteadia marstonensis.In the Oxfordian, West Siberia and northern Siberia belonged to the North Siberian province of the Arctic realm. Only in the latest Oxfordian did the northwestern West Siberian basin become part of the Boreal-Atlantic realm, as evidenced by the distribution of Ringsteadia on the eastern slope of the Cis-Polar Urals.  相似文献   

4.
In European Russia, the most complete succession of Boreal sediments of the terminal Bathonian and lower Callovian is exposed near the Prosek Settlement. After its revision, the infrazonal division of the upper Bathonian and lower Callovian and position of the Bathonian-Callovian boundary are difined more carefully. The Calyx Zone and bodylevskyi Biohorizon are established in the upper Bathonian. The base of the lower Callovian is defined at the first occurrence level of Macrocephalites jacquoti. Based on four successive ammonite assemblages occurring in lower part of the Elatmae Zone, the breve, frearsi, quenstedti, and elatmae biohorizons are identified. The joint occurrence of Boreal, Subboreal, and Tethyan ammonites in the section facilitate its correlation with the other sections of the Panboreal paleobiogeographic superrealm.  相似文献   

5.
Distribution of ammonites in the Bajocian-Bathonian boundary beds of the Izhma River basin is considered. A new scheme of zonal subdivisions suggested for the Pechora basin includes the Arctocephalites arcticus Zone of the upper Bajocian and the Arctocephalites greenlandicus-Arcticoceras ishmae Zone of the lower Bathonian. The Dreshchanka Formation age (late Bajocian-early Bathonian) and the commencement time of the Boreal sea transgression (Late Bajocian) are specified. Correlation of the Bajocian-Bathonian boundary strata of the northern Caucasus, central and northern Russia with stratigraphic scales of Western Europe and East Greenland are discussed. New infrazonal subdivisions, i.e., the faunal horizons, are described. As is shown, the parkinsoni-zigzag zonal boundary accepted to be the Bajocian-Bathonian boundary in standard scale corresponds to boundaries separating the michalskii and besnosovi zones in the Lower Volga region and the arcticus and greenlandicus zones in the Boreal areas.  相似文献   

6.
The study of new collections from the Urdyuk-Khaya Cape (Nordvik Peninsula) made it possible to specify the taxonomic composition of belemnites from the Volgian and basal Ryazanian in northern East Siberia. Cylindroteuthis knoxvillensis Anderson, 1945, C. cf. newvillensis Anderson, 1945, and Arctoteuthis tehamaensis (Stanton, 1895) known from northern California, as well as the new species C. venusta sp. nov. and A. britanna sp. nov. are first described from the Arctic region. Belemnite stratigraphy of Jurassic-Cretaceous boundary layers is fundamentally revised, allowing a new refined version of their scale to be proposed as a Boreal standard. Two independent successions of biostratigraphic units are defined in the section interval spanning the uppermost Middle Volgian Substage to the basal Ryazanian Stage: (1) Liobelus russiensis Zone, Lagonibelus gustomesovi and Arctoteuthis porrectiformis beds; (2) Lagonibelus napaensis, Arctoteuthis tehamaensis, and Cylindroteuthis knoxvillensis zones.  相似文献   

7.
The Middle Oxfordian to lowermost Upper Kimmeridgian ammonite faunas from northern Central Siberia (Nordvik, Chernokhrebetnaya, and Levaya Boyarka sections) are discussed, giving the basis for distinguishing the ammonite zones based on cardioceratid ammonites of the genus Amoeboceras (Boreal zonation), and, within the Kimmeridgian Stage, faunas–for distinguishing zones based on the aulacostephanid ammonites (Subboreal zonation). The succession of Boreal ammonites is essentially the same as in other areas of the Arctic and NW Europe, but the Subboreal ammonites differ somewhat from those known from NW Europe and Greenland. The Siberian aulacostephanid zones—the Involuta Zone and the Evoluta Zone—are correlated with the Baylei Zone (without its lowermost portion), and the Cymodoce Zone/lowermost part of the Mutabilis Zone (the Askepta Subzone) from NW Europe. The uniform character of the Boreal ammonite faunas in the Arctic makes possible a discussion on their phylogeny during the Late Oxfordian and Kimmeridgian: the succession of particular groups of Amoeboceras species referred to successive subgenera is revealed by the occurrence of well differentiated assemblages of typical normal-sized macro and microconchs, intermittently marked by the occurrence of assemblages of paedomorphic “small-sized microconchs” appearing at some levels preceeding marked evolutionary modifications. Some comments on the paleontology of separate groups of ammonites are also given. These include a discussion on the occurrence of Middle Oxfordian ammonites of the genus Cardioceras in the Nordvik section in relation to the critical review of the paper of Rogov and Wierzbowski (2009) by Nikitenko et al. (2011). The discussion shows that the oldest deposits in the section belong to the Middle Oxfordian, which results in the necessity for some changes in the foraminiferal zonal scheme of Nikitenko et al. (2011). The ammonites of the Pictonia involuta group are distinguished as the new subgenus Mesezhnikovia Wierzbowski and Rogov.  相似文献   

8.
It is proposed to use a Boreal scale based on the succession of cardioceratids (with the Bauhini, Kitchini, Sokolovi, and Decipiens zones) for the subdivision of the Kimmeridgian of Western Siberia instead of the aulacospephanid-based Subpolar Urals scale which was traditionally used in this region. It is shown that the use of the Boreal scale allows a finer subdivision and correlation of the Kimmeridgian of Western Siberia. A complete succession of zones and subzones based on cardioceratids and several biohorizons previously established in western Arctic are confirmed. The infrazonal Kimmeridgian scale of Western Siberia is correlated with the scales of Franz Josef Land, Spitsbergen, and northern Central Siberia. The diagnosis and ranges of Plasmatites zieteni (Rouill.), characteristic of the basal part of the Kimmeridgian (zieteni biohorizon), are given. The new species Amoeboceras (?) klimovae Rogov, sp. nov. and Amoebites peregrinator Rogov, sp. nov. (index species of the biohorizons recognized by the present author) are described.  相似文献   

9.
The first ammonite discovered at the base of the Ghomrassène Member of the Tataouine Formation belongs to a species of Pachyerymnoceras from the Latest Callovian (Solidum Zone) of the Arabian province. The underlying Krechem el Miit Member is also dated Late Callovian, with a fauna of Pachyerymnoceras from the Lower Athleta Zone in Algeria. The associated faunas (echinids, brachiopods) are the same, as well as the faunas of the overlying Ksar Haddada Member, which is dated also Late Callovian, referring to the brachiopods faunal succession in Saudi Arabia. Correlations with other areas in Tunisia, Saudi Arabia and Middle East underline the same sedimentary evolution during a second-order transgressive half-cycle. To cite this article: R. Enay et al., C. R. Geoscience 334 (2002) 1157–1167.

Résumé

La première ammonite découverte à la base du membre Ghomrassène de la formation Tataouine est un Pachyerymnoceras de la partie supérieure du Callovien supérieur (Zone à Solidum) de la province arabique. Le membre Krechem el Miit sous-jacent est aussi daté du Callovien supérieur par des Pachyerymnoceras connus dans la partie inférieure de la Zone à Athleta en Algérie. La faune associée (échinides, brachiopodes) est la même que celle du membre Ksar Haddada sus-jacent, daté également du Callovien supérieur par référence à la succession des brachiopodes en Arabie Saoudite. Les corrélations avec les autres régions de Tunisie, l'Arabie Saoudite et le Moyen-Orient mettent en évidence une même évolution sédimentaire au cours d'un demi-cycle transgressif de deuxième ordre. Pour citer cet article : R. Enay et al., C. R. Geoscience 334 (2002) 1157–1167.  相似文献   

10.
The distribution of calcareous nannofossils and foraminifers occurring in the Callovian-Oxfordian deposits in the southwest of Moscow is studied. Nannoplankton-bearing beds and foraminiferal zones are distinguished. The Retecapsa incompta Beds correspond in range to the Ophthalmidium sagittum-Epistomina volgensis and Ophthalmidium strumosum-Lenticulina brestica foraminiferal zones as well as the lower part of Epistomina uhligi-Lenticulina russiensis Zone. The Watznaueria manivitae, Crepidolithus perforata, and Watznaueria fossacincta (lowermost part) beds span interval of the Epistomina uhligi-Lenticulina russiensis Zone. The Watznaueria fossacincta Beds are concurrent to the Lenticulina ponderosa-Flabellamina lidiae Zone of the foraminiferal scale.  相似文献   

11.
Section of the middle and upper Volgian substages and basal Boreal Berriasian in the Cape Urdyuk-Khaya (Nordvik Peninsula) is largely composed of dark argillites substantially enriched in Corg. Characteristic of the section is a continuous succession of ammonite, foraminiferal, ostracode, and dinocyst zones known also in the other Arctic areas. Boundaries of the upper Volgian Substage are recognizable only based on biostratigraphic criteria. The succession of the middle Volgian Taimyrosphinctes excentricus to basal Ryazanian Hectoroceras kochi zones is characterized. The range of the substage is revised. The lower Exoticus Zone, where ammonites characteristic of the Nikitini Zone upper part in the East European platform have been found, is referred to the middle Volgian Substage. Newly found ammonites are figured. Two possible positions of the Jurassic-Cretaceous boundary in the Arctic region, i.e., at the lower and upper boundaries of the Chetae Zone at the top of the upper Volgian Substage, are discussed.  相似文献   

12.
Eight zonal dinocyst assemblages and three bio stratigraphic units ranked as “beds with flora” are first distinguished in the Danian—lower Lutetian interval of the Paleogene succession, penetrated by the reference borehole Novousensk no. 1, where eight standard and one local nannoplankton zones are simultaneously recognized. The direct correlation of nannoplankton and dinocyst zones is used to refine the paleon-tological substantiation and stratigraphic position of regional lithostratigraphic units, ranges of hiatuses, and the correlation with the general stratigraphie scale. The nannoplankton of the Danian NP2 Cruciplacolithus tenuis and NP3 Chiasmolithus danicus zones is characteristic of the Algai Formation (Fm). The nannoplankton of the NP4 Coccolithus robustus Zone and dinocysts of the D3a Alterbidinium circulum Zone from the Tsyganovo Fm characterizes the Danian top. The Lower Syzran Subformation (Subfm) corresponds to the upper part of the NP4 Coccolithus robustus Zone (Neochiastizygus junctus local zone) and to the D3b (part) Cerodinium depressum Zone of the Selandian dinocysts. The latter spans part of the Upper Syzran Subformation, whose characteristic nannofossils are the nannoplankton of the NP5 Fasciculithus tympaniformis Zone and the dinocysts of the D3b (part) Isabelidinium? viborgense Zone of the Selandian. The Novouzensk Fm is represented by a succession of the dinocyst Cerodinium markovae Beds and the standard D4c Apectodinium hyperacanthum Zone of the upper Thanetian. The coccolitophorids of the lower Thanetian NP6 Heliolithus kleinpelli Zone occur at the formation base. The Bostandyk Fm includes successive bio stratigraphie units of the Ypresian. In the dinocyst scale, these are the D5a Apectodinium augustum Zone, the Pterospermella Beds (DEla Zone of the North Sea scale), and zones DBlb-c Deflandrea oebisfeldensis, D7c Dracodinium varielon-gitudum, and D8 Dracodinium politum—Charlesdowniea coleothrypta, while units of the nannoplankton scale correspond to the NP12 Martasterites tribrachiatus and NP13 Discoaster lodoensis zones. The Kopterek Fm yields Lutetian nannofossils: the nannoplankton of the NP14 Discoaster sublodoensis Zone and the dinocysts of the Wetzeliella coronata—Areosphaeridium diktyoplokum Beds. Three meaningful hiatuses are established at the Danian base, Selandian top, and in the lower Ypresian.  相似文献   

13.
Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47.4–49.0 wt.% SiO2, 13.4–14.9 wt.% Al2O3 and 10.7–14.1 wt.% FeOT. These compositions are lower in FeOT and higher in SiO2 than previous estimates and have distinct La/SmN and Dy/YbN ratios that link them to the lowermost volcanic succession (Milne Land Formation) of the regional East Greenland flood basalt province. New major- and trace element compositions for the FG-1 dyke swarm, previously taken to represent Skaergaard magmas, overlap with the entire range of the regional flood basalt succession and do not form a coherent suite of Skaergaard like melts. These dykes are therefore re-interpreted as feeder dykes throughout the main phase of flood basalt volcanism.  相似文献   

14.
The species Cadochamoussetia aff. subpatruus (Nik.), Cadochamoussetia surensis (Nik.), and Cadoceras cf. simulans Spath are found for the first time in the lower reaches of the Anabar River. The first two species are characteristic of the Lower Callovian Cadochamoussetia subpatruus Subzone of Central Russia, which is equivalent to the Siberian Cadochamoussetia tschernyschewi Zone. Species of the genus Cadochamoussetia, found for the first time in the Arctic, are described. Shells of Siberian representatives of Cadochamoussetia are distinguished from the typical East European species by their larger umbilicus, which is similar to that of the ancestral genus Cadoceras. It is suggested that the Siberian taxa belong to the oldest representatives of this genus, which appeared in the early Callovian Arctic seas and later migrated to seas of Central Europe and England.  相似文献   

15.
Marine and continental deposits from the Tjörnes area in northern Iceland were studied to obtain their pollen/spore content. Six Pollen Zones (PZ) were defined in the Early Pliocene Tjörnes beds and the Early Pleistocene Breidavík Group. The pollen is most diverse during the deposition of the lowest Tapes Zone (PZ 1) and the lower part of the overlying Mactra Zone (PZ 2). Local pollen from marshland, levee and foothill forests was deposited on a large coastal plain. The pollen spectrum reflects transgression and deepening during the second part of the Mactra Zone (PZ 3) and the lower part of the Serripes Zone (PZ 4). Gymnosperm pollen derived from the higher inland plateau increases in PZ 3. This background pollen was of minor importance during periods with an extensive coastal plain (PZ 1, 2, 4, 6). PZ 5 did not yield sufficient pollen for analysis. The pollen analysis allowed refinement of the sea‐level variations based on sedimentology and molluscs. Pollen of warmth‐demanding plants is recorded throughout the Tjörnes beds and the Early Pleistocene interglacial deposits. Warmth‐loving species indicate summers 8°C warmer than today during deposition of the Tapes Zone, and at least 5°C warmer during the rest of the Tjörnes beds. The Pliocene vegetation of Iceland matches well that of the present‐day western European maritime temperate climate. The drastic cooling at the onset of the Quaternary led to a marked vegetation impoverishment, already noticeable in the Early Pleistocene Breidavík Group.  相似文献   

16.
In Russia, the terminal Neoproterozoic formally includes the Vendian of western part of the East European platform and the concurrent Yudoma Group of Siberia. As is shown in this work, the designated subdivisions correspond in the stratotypes only to the upper, Yudomian Series of the Vendian. In the Siberian platform, the Ust-Yudoma and Aim horizons of the Yudomian are tightly interrelated. The lower of them, bearing remains of Ediacaran Fauna, represents the Ediacarian Stage, whereas the upper one containing small-shelled fossils (SSF) corresponds to the Nemakit-Daldynian Stage divided into the trisulcatus and antiqua superregional zones. In more complete sections of the platform periphery, sediments of these subdivisions conformably rest on siliciclastic succession that should be ranked as basal subdivision of the Yudomian. The succession is concurrent to the Laplandian Stage of the East European platform. According to geochronological dates obtained recently, the Yudomian Series spans interval of 600–540 Ma. In the East European platform, the Upper Vendian (Yudomian) begins with the Laplandian basal tillites of synonymous stage. In the west of the platform, tillites are dated at 600 Ma like the Upper Vendian base in Siberia. The next Ediacarian Stage of the East European platform is stratigraphic equivalent of the Redkino Horizon, while summary range of the Kotlin and Rovno horizons is concurrent to that of the Nemakit-Daldynian Stage. The Vendian of Russia is conformably overlain by the Tommotian Stage of the Lower Cambrian. Intense pre-Vendian events constrained distribution areas of the Lower Vendian sediments in Russia. The Lower Vendian deposits of the East European platform are most representative and well studied in the central Urals, where they are attributed to the Serebryanka Group. In Siberia, separate subdivisions representing the Lower Vendian are the Maastakh Formation of the Olenek Uplift, two lower members of the Ushakovka Formation in the Baikal region, and the Taseeva Group of the Yenisei Range. Chronological interval of the Lower Vendian corresponds to 650–600 Ma. The Marinoan Glaciation dated in Australia at 650–635 Ma is concurrent to basal part of the pre-Yudomian interval of the Vendian in Russia, whereas the Laplandian Tillite and Gaskiers Glaciation (600–580 Ma) correspond to onset of the Yudomian Epoch. The new Ediacaran System (Knoll et al., 2004) legalized in the International Neoproterozoic scale is close in range to the entire Vendian (635–544 Ma), although without basal beds (Marinoan Tillite) it deprives the terminal Neoproterozoic of its original sense. Inferiority of the system consists also in its indivisibility into stages. Hence, it is clear that the Vendian System subdivided in detail in Russia should be retained in the rank of terminal system of the Precambrian, one of the basic in general scale of the Neoproterozoic.  相似文献   

17.
Radiolarian biostratigraphic research has been carried out along two continuous sections through the Xialu Chert, one of the accreted sheets included in the Yarlung-Zangbo Suture Zone. Six radiolarian zones have been identified as follows: Laxtorum(?) jurassicum Zone (Aalenian), Tricolocapsa plicarum Zone (Bajocian–lower Bathonian), Stylocapsa(?) spiralis Zone (upper Callovian–Oxfordian), Hsuum maxwelli Zone (Kimmeridgian), Pseudodictyomitra carpatica Zone (upper Tithonian–lower Valanginian), and Turbocapsula costata Zone (Aptian).A reconstructed stratigraphy of the Xialu Chert, based on lithological succession and radiolarian dating, indicates that the chert exhibits a long depositional history, at least from early Middle Jurassic (Aalenian) to late Early Cretaceous (Aptian). The separation of the Lhasa Block from the northern Gondwana margin must, therefore, be dated before the Aalenian. The absence of calcareous sediments in the Xialu Chert indicates that the oceanic basin was deeper than the CCD throughout the depositional history. The transition from chert to siliceous mudstone is recorded sometime in Early Cretaceous, most probably around the Barremian/Aptian boundary. This means that the oceanic plate had already started being consumed at a trench by that time. The accretion of the Xialu Chert occurred after the Aptian time.  相似文献   

18.
《Cretaceous Research》2008,29(1):9-26
An analysis of the stratigraphic distribution of ammonite faunas collected from several sections in the Essaouira-Agadir area (western High Atlas, Morocco) has enabled the establishment of a detailed succession of assemblages for the uppermost Hauterivian to lower Upper Barremian interval. All Mediterranean standard zones of this interval have been identified. The correlation potential of bioevents which define and characterise these units is discussed. Two significant regional hiatuses, one at the Hauterivian/Barremian boundary, the other involving the lower part of the Kotetishvilia nicklesi Zone, are related to third-order sea level falls. Moreover, the upper part of the succession corresponding to the upper Toxancyloceras vandenheckii Zone and the entire Heinzia sartousiana Zone is markedly condensed. The taxonomic composition of the ammonite assemblage reveals a strong Mediterranean character, yet, it shows some peculiar features as well.  相似文献   

19.
20.
To improve regional and intercontinental correlation of the uppermost Devonian–lowermost Carboniferous, we examined the conodont faunas and carbon isotopic records of the Tangbagou Formation in the Qilinzhai section, southern Guizhou, South China. The Tangbagou Formation is a succession of mixed carbonate–siliciclastic rocks that accumulated on a shallow‐water platform under normal marine conditions. Seven conodont zones for shallow‐water biofacies in South China, the Cl. gilwernensis–Cl. unicornis Zone, the Po. spicatus Zone, the Si. homosimplex Zone, the Si. sinensis Zone, the Si. eurylobata Zone, the Ps. multistriatus Zone and the Po. co. porcatus Zone in ascending order, are recognized in the Tangbagou Formation. Although apparently limited in its value for global correlation, this conodont zonation is more applicable to shallow‐water biofacies in South China. Carbonate samples have yielded carbon isotopic signatures consistent with those recorded in Euroamerica sections, in particular showing four distinct characteristics: (1) the peak values of Hangenberg Carbon Isotope Excursion (HICE) during the latest Devonian, (2) a minor positive shift (P1) in the Si. homosimplex Zone during the early Tournaisian, (3) a second minor positive shift (P2) in the Si. sinensis Zone and (4) the middle Tournaisian Carbon Isotope Excursion (TICE) in the middle part of the Tangbagou Formation. The similarity in peak values (~5.5‰) and magnitude of TICE for the Qilinzhai and Belgian sections indicates that the Euro‐asia δ13Ccarb trends may reflect the changes in global mean ocean δ13CDIC, rather than having been overprinted by local carbon cycling. Integration of conodont biostratigraphy and δ13C stratigraphy provides a powerful tool for stratigraphic correlation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号