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1.
This work is a study of the ammonite record of a new stratigraphic section of Aptian age, at the Mina Texali (Puebla State, Central Mexico). A detailed biostratigraphic analysis was carried out on 309 specimens systematically sampled on a bed-by-bed basis. An Aptian ammonite zonation is proposed for the Mina Texali (= MT) section with two interval zones, Dufrenoyia justinae and Caseyella sp., and one informal biostratigraphic unit represented by the Huastecoceras trispinosoides beds. We also analyze the taxonomic composition, paleoecology and some systematic issues of the ammonite record of the MT section. The first record in Mexico of the genera Pseudosaynella, Xerticeras and the nautiloid Heminautilus is identified in this section. The ammonite assemblage is assigned to the proximal part of the outer neritic region of the continental shelf. The ammonite record of the studied section is diagnostic in establishing the lower-upper Aptian transition, and the local zonation of the MT provides important data for the development of an Aptian standard ammonite zonation for the Central Atlantic province.  相似文献   

2.
Fossil diatoms from the Milky River Formation of the Sandy Ridge section, Alaska Peninsula are analyzed. Data on stratigraphic distribution of diatoms and silicoflagellates are presented. Based on presence of stratigraphically important forms (Neodenticula kamtschatica, Thalassiosira oestrupii, Cosmiodiscus insignis), the assemblages studied are correlated with the North Pacific Cenozoic diatom zones. An assemblage similar to that of subzone “b” of the Neodenticula kamtschatica Zone (Barron and Gladenkov, 1995) indicates the latest Miocene-initial early Pliocene (5.5-4.8 Ma) age of its host deposits. Additional species of biostratigraphic importance (Thalassiosira temperei, Th. latimarginata, and others) refine ages of different parts of the section. In particular, age of stratigraphically lowest beds bearing Astarte (mollusks valuable for establishing the Bering Strait opening) were dated at 5.5-5.4 Ma. Some paleogeographic inferences are made from analysis of composition of the diatom assemblages.  相似文献   

3.
The first data on the distribution of Radiolaria and planktonic Foraminifera in the section at Biyuk-Karasu River in central part of the Crimean Mountains, are presented. Based on the study of radiolarian findings, the upper Cretaceous deposits of Biyuk-Karasu section are subdivided into the following biostratigraphic units: Alievium superbum-Phaseliforma turovi (middle Turonian), Dactylodiscus longispinus-Patulibracchium (?) quadroastrum (upper Turonian), and Orbiculiforma quadrata-Patellula sp. B (Turonian-Coniacian boundary deposits). The stratigraphic interval of Alievium superbum-Phaseliforma turovi has been previously characterized by the complex of Alievium superbum-Phaseliforma sp. A (middle Turonian, Mt. Chuku section, SW of the Crimean Mountains, and middle Turonian, Mt. Ak, central part of the Crimean Mountains). Based on the study of Foraminifera findings, the following biostratigraphic subdivisions were identified: Whiteinella paradubia (lower-lower part of the middle Turonian), Marginotruncana pseudolinneiana (uppermost middle Turonian), and Marginotruncana coronata (upper Turonian). The complex of beds with Marginotruncana pseudolinneiana and Marginotruncana coronata are comparable to the deposits of zones of same name in the Crimean-Caucasian region.  相似文献   

4.
Data on spores, pollen, and dinoflagellate cysts studied in composite section of Oligocene-Miocene deposits in southern part of West Siberia are presented. Eleven biostratigraphic units distinguished in the section are ranked as palynozones and beds with palynological assemblages. Palynological data substantiate age of deposits and specify ranges and boundaries of palynozones. Based on dinocyst assemblages first studied in sediments of the Zhuravka and Abrosimovo horizons (upper Oligocene, lower Miocene), the Pseudokomewuia Beds are included into local stratigraphic scheme. According to results of comparative analysis, similar and distinctive features of Oligocene-Miocene dinocyst assemblages from West Siberia, China and North America are elucidated. Based on palynological data, the local stratigraphic scheme of higher resolution is suggested for subdivision of Oligocene and Miocene deposits in southern part of West Siberia (Baraba and Kulunda lithofacies regions).  相似文献   

5.
The most complete Hungarian Valanginian perisphinctid ammonite fauna of the Mecsek Mountains (South Hungary) consists of 14 species is reported. Thurmanniceras sp. aff. otopeta, Fuhriella michaelis, F. cf. hoheneggeri, Sarasinella cf. ambigua, Neocomites (Neocomites) subtenuis, Neocomites (Eristavites) platycostatus are reported for the first time from Hungary. The fauna comprises 23 ammonite species and is reported from Valanginian tuffaceous marl, alternating marl–limestone beds and loose limestone blocks. Two studied sections represent the Lower Valanginian Thurmanniceras pertransiens and partly the Busnardoites campylotoxus Zones while ammonites from loose blocks indicate the latter and possibly the Upper Valanginian Saynoceras verrucosum Zone. Variations in the faunal composition of the marl beds and the limestone blocks respectively, refer to the contrast between the ammonite ecological demands. Phylloceratid and lytoceratid ammonites prevail the marl beds, while olcostephanid and neocomitid ammonites prevail the shallower platform-like limestones. Sediment accumulation rate in that palaeo volcano related environment was high and bottom currents frequently washed together ammonite shells or filled their body chambers with smaller ammonite shell fragments. Due to the fast sedimentation the sections represent only partially the recognized ammonite zones therefore long-term or even infra-regional correlation was not possible. Palaeobiogeographically, the ammonite fauna has Mediterranean character and it shows close relationships to the Valanginian faunas of the Bakony Mts. (Hungary), Western Carpathians (Slovakia), Northern Calcareous Alps (Austria), and SE Spain. The presence of Fuhriella species is remarkable and enlarges our knowledge on the distribution of this enigmatic ammonite taxon adding new data to its Valanginian stratigraphic position and geographic distribution.  相似文献   

6.
Benthic foraminiferal fauna are analyzed quantitatively and qualitatively at three stratigraphic sections in Eastern Desert of Egypt (Serai, Duwi, and Um El Huetat). These sections embrace the Paleocene–Eocene Thermal Maximum (PETM) interval which is represented by the occurrence of five distinctive beds. These beds constitute the Dababiya Quarry Member at the lower part of Esna Formation. The occurrence of them indicates an expanded and relatively continuous record across the P/E boundary. The organic-rich clay layer (bed no. 1 of the Dababiya Quarry Member) marks the start of the PETM event. This bed is characterized by the extinction of all benthic foraminiferal fauna except for the occurrence of rare agglutinated foraminiferal species. The presence of these species indicates an oceanic anoxic event at the sea floor. High concentration of phosphatic contents including fish remains occurred in the middle part of the PETM (bed nos. 2 and 3 of the Dababiya Quarry Member) with the continuous absence of benthic foraminiferal fauna except for few specimens at the top of bed 3. Bed nos. 4 and 5 of the Dababiya Quarry Member represent the upper part of the PETM and the initial stage of sea floor recovery. Low diversity and abundance of benthic foraminiferal taxa occurred within these beds, represented by Valvulineria scrobiculata, Lenticulina midwayensis, Loxostomoides appliane, and Siphogenerinoides eleganta. This phenomenon continues upward during the post-PETM event. The Paleocene velasco-type benthic foraminifera Angulogavelinella avnimelechi and Coryphostoma midwayensis species are extinct within the advent of the PETM event. The benthic foraminiferal assemblages at the studied sections are dominated by midway-type fauna with little representative of velasco-type fauna. The velasco-type species are represented with high abundance at Serai section and with low densities at Um El Huetat section, while at Duwi section, they rarely occurred. This suggests outer neritic-upper bathyal (150–400 m) setting at Serai section and mostly middle-outer neritic (50–150 m) setting at Um El Huetat and Duwi sections.  相似文献   

7.
Upper Hauterivian deposits in the Kurilovo area, Kamenica 1 section, NE of Niš, are described based of abundant and diverse orbitolinids. So far, the interval was assigned to the Barremian–Aptian on the geological map. Such a new age assignment results from the first detailed study carried out on the orbitolinid fauna contained in the Lower Cretaceous (upper Hauterivian) shallow-water limestones of eastern Serbia. The upper Hauterivian is documented on the basis of two key stratigraphic markers, specifically Valserina primitiva and Paleodictyoconus beckerae.In addition to these late Hauterivian index fossils, the studied section bears orbitolinids having a larger stratigraphic distribution: Cribellopsis neoelongata, Cribellopsis thieuloyi?, Montseciella glanensis, Orbitolinopsis debelmasi, Orbitolinopsis cf. debelmasi, Orbitolinopsis sp., Paleodictyoconus cuvillieri, Paleodictyoconus cf. cuvillieri, Paleodictyoconus cf. beckerae, Paleodictyoconus cf. actinostoma, Paleodictyoconus sp., Paracoskinolina? jourdanensis, Paracoskinolina cf. hispanica, Urgonina alpillensis, Valserina sp. The microfossil assemblage includes other foraminifers such as Charentia cuvillieri, Mayncina bulgarica, Nautiloculina cretacea, Pfenderina globosa, Pseudocyclammina cf. lituus, Pseudolituonella gavonensis, Ammobaculites sp., Bolivinopsis sp., abundant trocholinids, various miliolids, other foraminifers and sparse algae which will be presented separately.  相似文献   

8.
The Middle Cambrian succession of the Parahio Valley in general and Debsakhad section in particular is dominated by trilobites. Genus Opsidiscus, along with other trilobite forms dominates the lower Middle Cambrian succession. In the present study two new species of Opsidiscus, Opsidiscus wadiai and Opsidiscus srikantiai are reported from the lower Middle Cambrian succession of Debsakhad section. The species were differentiated on their morphological features and their multivariate analysis. The multivariate analysis applied here is used as a supplement method to qualitative analysis in order to differentiate between the cranidial characters of Opsidiscus. The qualitative study of each species studied individually shows more or less close affiliation as is observed by different quantitative methods. The presence of Opsidiscus has a great stratigraphic significance in this region, as they first appear from informal Stage 5 of Series 3 and goes up to the Drumian Stage of Series 3 of the Cambrian System in the Debsakhad section, which helps to correlate this section with other well known sections of the Middle Cambrian.  相似文献   

9.
This paper presents the benthic foraminiferal biostratigraphy of the lower and middle Campanian of the Polish Lowlands based on the study of Wierzchowisko, Jeżówka and Rzeżuśnia sections in the Wolbrom-Miechów area (southern Poland) and the Mielnik section (eastern Poland).The ranges of twenty two selected stratigraphically useful taxa of the genera Gavelinella, Bolivinoides, Cibicidoides, Globorotalites and Stensioeina are presented in relation to macrofossil zonation, previously established in the same successions. The evolutionary changes within selected lineages of the studied genera and major foraminiferal bioevents are discussed. The taxa ranges recorded in the Polish Cretaceous are compared with the ranges described from western Europe. Most of the studied events seem to be readily applicable for stratigraphic correlation all over Europe.  相似文献   

10.
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11.
New collections at the Induan/Olenekian boundary GSSP candidate at Mud (Himachal Pradesh, Northern India) lead to the recognition of several well preserved ammonoid faunas that significantly improve the biostratigraphic resolution in the beds underlying the proposed GSSP level. In ascending order, the new biostratigraphical sequence comprises: the Ambites lilangense beds, the Fuchsites markhami beds, the Kingites lens beds, the Prionolobus rotundatus beds, the Flemingites bhargavai beds, the Kashmiritidae gen. nov. A beds and the Vercherites cf. pulchrum beds. The faunas from Bed 10, located about 1 m below the proposed GSSP level, contain certain ammonoids with typical early Smithian affinity (Flemingitidae, Kashmiritidae) and thus reflect the beginning of the early Smithian evolutionary radiation. Seen from an evolutionary point of view, the Dienerian/Smithian boundary can therefore be placed just below Bed 10. Ideally, the stage boundary should also be intercalibrated with other biological, chemical or physical proxies as additional tools for world-wide correlations.Four new species (Flemingites bhargavai, Kingites korni, ?Kingites parkashi and Xenodiscoides variocostatus) and two new genera (Mudiceras, Vercherites) are described.  相似文献   

12.
Baripada Marine Beds (BMB) have been studied extensively in terms of its mega fossil content. However, not much has been discussed about the foraminiferal content and the organic matter assemblage in these beds. The fossiliferous sequence of BMB consists of sandstone, shale and limestone units. The present study is persued on the limestone unit of BMB. Foraminiferal, thin section and rock-eval pyrolysis studies were performed on the 33 surface samples collected from five sections of Jamdapal and Mukurmatia region along the Budhabalang river bank. Foraminifera are less abundant in the samples of Jamdapal, whereas Mukurmatia is comparatively rich. First appearance datum of Globorotalia menardii[ranges since middle Miocene (12.6 Ma); FAD at planktic foraminiferal zone N12] and last appearance datum of Neogloboquadrina continuosa [ranges between early Miocene (23.2 Ma) to late Miocene (8.3 Ma); FAD at planktic foraminiferal zone N4B and LAD at N16] together suggest that the limestone unit was deposited in between 12.6 to 8.3 Ma within the upper Miocene. Also, the association of shallow water benthic foraminifera (Species of Ammonia, Asterorotalia, Bolivina, Buliminella, Cibicides, Challengerella, Criboelphidium, Cribononion, Elphidium, Hanzawaia, Nonionella) and planktic foraminifera (Globigerina falcoensis, Globigerina woodi, Globorotalia menardii, Neogloboquadrina continuosa) together with oyster bank and shark teeth suggest deposition of limestone within well oxygenated, tropical, shallow water, open marine condition (within 40m water depth). Lithological and thin section studies together with global sea level fluctuation history advocate that upper Miocene marine transgression promoted the formation of this unit. Bulk organic geochemical data obtained by the rock-eval pyrolysis studies on selected samples indicate a low total organic carbon (TOC), with low hydrogen index (HI), high oxygen index (OI). The organic facies is characterised by type-IV kerogen with major contribution from near shore terrestrial plants. This also suggests deposition in shallow, oxygenated environments that did not promote significant accumulation and preservation of organic content in sediments.  相似文献   

13.
A stratigraphic section may be divided into lithologic units which in turn may be divided into beds. This paper gives a mathematical formulation of stratigraphic sections that takes these two levels into account and uses bed properties to yield the thickness and number of beds in lithologic units. The model is a semiMarkov chain in which the succession of lithologic bed types forms a Markov chain and is an independent random variable. The model is tested against stratigraphic data obtained from micrologs. There is close agreement between the observed and calculated thicknesses of lithologic units. Tests for the degree of agreement between observed and calculated numbers of beds in lithologic units are hampered by inability to observe thin beds on micrologs. Some implications of this limitation to stratigraphic analysis are noted.  相似文献   

14.
The Early Cretaceous (latest Hauterivian) Faraoni Oceanic Anoxic Event (F-OAE) in the Río Argos section (Caravaca region, southern Spain), the candidate for the Global Boundary Stratotype Section and Point (GSSP) of the Hauterivian–Barremian transition, has been studied. Its ichnological bed-by-bed analysis allows for interpretation of oxygenation changes through the Faraoni Level interval and improvement upon previous characterization of oxygen conditions prior, during and after the F-OAE. The trace fossil assemblage belongs to the Zoophycos ichnofacies and it includes Chondrites intricatus, Chondrites targionii, Halimedides isp., Palaeophycus isp., ?Patagonichnus isp., Planolites isp., Rhizocorallium isp., Taenidium isp., Thalassinoides isp., Trichichnus linearis, Zavitokichnus fusiformis, and Zoophycos isp. Their diversity in particular beds fluctuates. Beds with four to six ichnotaxa reflect a multi-tiered macrobenthic trace maker assemblage living in good oxic and trophic conditions. In one bed below and one bed above the Faraoni Level (both marls without primary lamination), there are only two or three, mostly opportunistic ichnotaxa (Trichichnus, Chondrites, Planolites). They record dysoxic conditions. At the base of the Faraoni Level, one thicker and two thinner beds of marly mudstones (21.2 and 3.5 cm thick, respectively) are characterized by primary lamination. At the top and in the basal part of the thicker bed and in the thinner beds some trace fossils are present. These beds were deposited under anoxic conditions and later colonized by trace makers either from overlying beds deposited under oxic conditions or from the level of a greenish lamina in the lower part of the thicker bed, recording short episodes of dysoxic conditions. The thinner anoxic beds are separated by marls deposited under dysoxic conditions.  相似文献   

15.
This work deals with the study of the ammonoid record of a classical stratigraphic section of Aptian age, the Francisco Zarco Dam (Durango State, northeast Mexico). A detailed biostratigraphical analysis considered 1281 specimens systematically sampled on a bed-by-bed basis. Taphonomy, taxonomic composition and paleocology of the studied assemblage, were also stressed. We formally propose an ammonite zonation for this section, which consists of two interval zones, Dufrenoyia justinae and Gargasiceras? adkinsi, one taxon range zone Caseyella aguilerae, and one biohorizon Huastecoceras trispinosoides. Among those biostratigraphic units, three are of new definition. Another topic discussed herein concerns to the problematic definition of the Lower-Upper Aptian boundary using the first stratigraphical appearance of the genus Epicheloniceras. From a paleoecological point of view, we recognized the ammonoid assemblage of the Francisco Zarco Dam section, to be representative of a distal platform environment. Finally, we compared the zonation built for this section with that considered the standard zonation for the Tethyan Domain, concluding that the differences are so substantial that an independent zonation for the Central Atlantic is necessary.  相似文献   

16.
This study of the upper Maastrichtian to Danian sedimentary succession from the northern part of the Romanian Eastern Carpathians (Varniţa section) aims to establish an integrated biostratigraphy based on calcareous nannofossils, organic-walled dinoflagellate cysts (dinocysts) and foraminiferal assemblages, and to reconstruct the depositional environments of the interval. The stratigraphic record across the studied section is incomplete, considering that an approximately 16 m thick strata interval from the top of the Maastrichtian to lowermost Danian cannot be analyzed due to a landslide covering the outcrop. The upper Maastrichtian is marked by a succession of biostratigraphic events, such as the First Appearance Datum (FAD) of the nannoplankton taxon Nephrolithus frequens and FAD of the dinocyst species Deflandrea galeata and Disphaerogena carposphaeropsis, and the Last Appearance Datum (LAD) of Isabelidinium cooksoniae in the lower part of the section. These bioevents are followed by the LAD of the Dinogymnium spp. and Palynodinium grallator dinocyst markers in the top of the Maastrichtian deposits analyzed. In terms of foraminiferal biostratigraphy, the upper Maastrichtian Abathomphalus mayaroensis Zone is documented in the lower part of the studied section. Some bioevents, such as the bloom of the calcareous dinoflagellate genus Thoracosphaera and the FAD of the organic-walled dinocysts Damassadinium californicum, Senoniasphaera inornata, Xenicodinium lubricum and X. reticulatum suggest an early Danian age for the middle part of the section. From the Danian deposits in the Varniţa section, we describe a new organic-walled dinocyst species, Pentadinium darmirae sp. nov., which is until now the only species of the Pentadinium genus discovered in the Paleocene. The occurrence of the global Danian dinocyst marker Senoniasphaera inornata in the top of the section, suggests an age not younger than middle Danian (62.6 Ma) for the analyzed deposits.The palynofacies constituents, as well as the agglutinated foraminiferal morphogroups, used to reconstruct the depositional environments, show that the late Maastrichtian sediments were deposited in an outer shelf to distal (bathyal) environment, followed by a marine transgression during the Danian.  相似文献   

17.
新疆准噶尔盆地是中国油气、煤炭等能源矿产的重要储集场所。本次研究对搜集到的准噶尔盆地东缘五彩湾地区20个煤田钻孔资料进行二次开发利用,通过提取钻孔坐标、高程、地层分层厚度、颜色、测井曲线解译数据等重要信息,重新建立了钻孔数据集。数据集共包含20个钻孔资料的Excel数据库型数据,每个Excel数据库由“钻孔基本信息”、“测井解释岩性分层”、“地质编录柱状分层”、“综合柱状信息”、“钻孔岩性分层”、“地层名称及代号表”、“地层颜色”、“测井曲线配置”、“测井曲线数据”、“数据字典”等10个工作表组成。利用石文软件可读取数据集信息,绘制地层沉积三维立体图,该成果能够对准噶尔盆地东缘五彩湾地区砂体的空间展布、三维地质结构等提供更加直观的认识,对研究准噶尔盆地东缘五彩湾地区的沉积环境具有重要意义。  相似文献   

18.
《Sedimentology》2018,65(6):1918-1946
In southern Patagonia, outcrops of the Upper Cretaceous Cerro Toro Formation preserve a >150 km long deep‐water axial channel belt in the Magallanes–Austral Basin, providing a unique opportunity to investigate longitudinal variations in the depositional characteristics of a deep‐water channel system. This study documents sedimentological, stratigraphical and geochronological data from the Cerro Toro Formation in the Argentine sector of the basin. New results are integrated with previous work from the Chilean basin sector to conduct a basin‐scale comparison of the timing of deposition, provenance and lithofacies proportions. The Cerro Toro channel belt includes a nearly 1000 m thick section characterized by high‐density turbidites and mass‐wasting deposits. Two ash beds from the base of the section yield U–Pb zircon ages of 90·4 ± 2 Ma and 88·0 ± 3 Ma, indicating similar initiation ages as documented in the Chilean sector. The U–Pb detrital zircon age spectra from samples in the study area reveal similar provenance trends to samples from the Chilean basin sector, with peak age populations at 310 to 260 Ma, 160 to 135 Ma and 110 to 82 Ma. The maximum depositional age of the channel belt in the Argentine sector is 87·8 ± 1·5 Ma and all new geochronology data corroborate an 86 to 80 Ma depositional age for the main Cerro Toro channel belt. Statistical analyses of 7370 beds from nearly 8000 m of new and previously published stratigraphic sections along the entire outcrop belt suggest progressive variations in the down‐system proportion of lithofacies. In the up‐slope region, lithofacies representing mass wasting processes (for example, debris‐flow and mass‐transport deposits) account for ca 29% of the stratigraphic thickness, as opposed to 5% in the down‐slope region of the channel belt, where turbidity current deposits are more prevalent. The proportion of beds >1 m thick also decreases systematically down slope, particularly for conglomeratic turbidite deposits. This work highlights that: (i) the proportion of thick beds and distribution of lithofacies are key down‐system changes in the stratigraphic fill of this deep‐water channel belt; (ii) detrital zircon trends suggest a relatively well‐mixed longitudinal depositional system; and (iii) geochronology of the main Cerro Toro outcrop belt supports but does not necessitate the model of a single, roughly age‐equivalent, channel system. This study has implications for understanding the downslope variability in depositional processes, stratigraphic architecture and reservoir quality of submarine channel systems.  相似文献   

19.
The Upper Cretaceous Qingshankou Formation (K2qn) and Nenjiang Formation (K2n) in the Songliao Basin (SLB), China, contain discrete ostracod-bearing deposits. The ostracod-bearing layers range in thickness from 5 to 380 cm. Based on integrated analysis of seismic, drilling, core and logging data, the sedimentary characteristics, distribution patterns and hydrocarbon implications of the ostracod-bearing beds have been studied. Compared with mudstone and sandstone in lacustrine settings, ostracod-bearing beds have distinctive characteristics in terms of seismic response and logging features. Three types of depositional pattern of ostracod-bearing beds are recognised in different facies: mixed siliciclastic–ostracod deposits in the delta front, sheeted ostracod deposits, and dotted ostracod deposits in shallow or semi-deep lacustrine settings. In plan view, ostracod-bearing beds mainly occur in the Daqing area, the Longhupao–Honggang terraces and the Heidimiao depression, and are relatively less developed in the east of the SLB. Shallow and semi-deep lacustrine settings were favourable environments for the survival of ostracods. In the stratigraphic succession, ostracod-bearing beds mainly occur in the upper K2qn1, K2qn2, lower K2qn3 and K2n1 units. High-frequency sequence cycles controlled ostracod reproduction and death, and mass mortalities of ostracods commonly occurred during periods in which the lake base-level fell, leading to water shallowing, increasing salinity and sand intrusion into the shore-shallow lakes. Ostracod mortality was not associated with expansion of the lake area, marine transgression or volcanic eruptions. The ostracod-bearing beds were widely formed in shallow and semi-deep lacustrine settings in the SLB. Tight oil/gas reservoirs can be developed in thick ostracod-bearing beds. In addition, areas containing ostracod can be regarded as sweet spots for mud or shale oil/gas exploration, because extensive ostracods can improve the content of brittle minerals in mudstone.  相似文献   

20.
The stratigraphic distribution of ammonoids was analyzed in the Daxatina canadensis Subzone of the Trachyceras Zone distinguished in the Dolomites of Italy. It was established that ammonoids of the Daxatina and Trachyceras genera are confined to the lower and upper parts of the canadensis Subzone in the Stuores-Wiesen section, which was suggested as a global stratigraphic section of the lower boundary of the Carnian Stage. Owing to discreteness of the ammonoid complex and absence of the Trachyceras genus, the lower part of the canadensis Subzone was excluded from the Trachyceras generic zone and is considered as the independent Daxatina canadensis Zone, which overlies the Frankites regoledanus Zone. On the basis of the principle of priority and similar ammonoids of the canadensis and regoledanus zones, the lower boundary of the Carnian Stage was accepted in the basement of the Alpine Trachyceras aon Zone and coincides with appearance of the Trachyceras genus. The main problems of the Boreal-Tethyan correlation of the Lower Carnian and adjacent stratigraphic levels are reviewed. The composition and distribution of the Lower Carnian ammonoids of northeastern Asia are specified taking into account the results of the revision of the Early Carnian trachyceratids of this region. Being the traditional biomarkers of the basal beds of the Carnian Stage in the Tethys, the ammonoids of the Trachyceras genus, which were unknown before in the Boreal Realm, were identified for the first time in the Lower Carnian of northeastern Asia. The Lower Carnian rocks of northeastern Asia, British Columbia, and the Alps were zonally correlated and the Lower Carnian boundaries were substantiated in the Boreal Realm. The Boreotrachyceras omkutchanicum Zone correlates with the Alpine Trachyceras aon Zone by the presence of the Trachyceras genus and stratigraphic position over the Stolleyites tenuis Zone and its analogs in British Columbia. The ammonoid complex of the Neosirennites armiger Zone includes Sirenites s.s., in particular, Sirenites ovinus Tozer species, known in the upper zone of the Lower Carnian of British Columbia (Sirenites nanseni), which allows comparison of the armiger and nanseni zones and, through it, with the upper part of the Alpine Austrotrachyceras austriacum Zone.  相似文献   

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