Biostratigraphic Scale Research Articles

Late Cretaceous Planktonic Foraminifera of the Mountainous Crimea in the MSU Earth Science Museum’s Collection

Planktonic foraminifers are widely distributed in the Upper Cretaceous deposits of the Mountainous Crimea. Marker species are of great importance for biostratigraphy and section correlation. Tests Globotruncanita stuarti (De Lapparent, 1918) and Pseudotextularia elegans (Rzehak, 1891) are used as index species for local and regional biostratigraphic scales, and tests of the genus Rugoglobigerina Brönnimann, 1952 are for the faunal layers. The article provides a systematic description of important biostratigraphic species Pseudotextularia elegans (Rzehak, 1891), Rugoglobigerina rugosa (Plummer, 1927), R. hexacamerata Brönnimann, 1952, R. milamensis Smith and Pessagno, 1973, R. macrocephala Brönnimann, 1952 и Globotruncanita stuarti (De Lapparent, 1918), on the basis of which the age of the rocks of five sections of the Mountainous Crimea was determined.

The chronology and rotational kinematics in the South-Eastern Jaca Basin (Southern Pyrenees): Las Bellostas section

Despite the large number of magnetostratigraphic studies in the South Pyrenean Basin aiming to calibrate the basin chronostratigraphy and the biostratigraphic scales, the South Eastern Jaca Basin remains unexplored from this perspective, and its relation with the Ainsa Basin is not fully understood. In this work we contribute with new magnetostratigraphic data from the 950m thick Las Bellostas section, located in the northern hinge of the Balzes anticline. Well-proven primary signal (positive fold test and two pseudo-antiparallel polarities) supported by numerous primary data in the surroundings allow us building a reliable local polarity sequence of eight magnetozones (from R1 to N4). Additionally, seven new biostratigraphic samples (Nummulites and Assilina) in the lower part of the section (marine environment) allows tightening the section to the Geomagnetic Polarity Time Scale (GPTS) and proposing a refined age model for the southeastern Jaca Basin. The section starts in the Boltaña Fm., of Cuisian age (Shallow Benthic Zone, SBZ11), is followed by a sedimentary gap from C22n to C20n as witnessed by biostratigraphic data (SBZ11 underneath the hiatus and SBZ16 just atop). The deltaic Sobrarbe Fm. can be tracked until the C19n (Late Lutetian). From this point (200m) until the top of the section (950m), at least, the entire C18n chron can be recognized within the molassic Campodarbe Fm. (C18n.2n-C18n.1r and C18n.1n) (Bartonian) equivalent to the West to the prodeltaic Arguis marls Fm. The Middle Cusian (SBZ11) to Middle Lutetian (SBZ15) stratigraphic hiatus is, in part, enhanced by the structural position at the hinge of the Balzes anticline. These new chronostratigraphic constraints help refining the W-E and N-S stratigraphic relationships in the eastern Jaca Basin and in the Ainsa Basin. This section also allows us to accurately refine the kinematics of the rotational activity in the eastern External Sierras. The important difference in magnetic declination along the section and neighboring paleomagnetic data from the Balzes anticline (from ≈70º clockwise at the base of the stratigraphic section to non-significant at the top) together with the new age model for the Eastern Jaca Basin help characterizing the rotational activity of the Balzes thrust sheet. The rotation took place between chrons C20r (Middle Lutetian; 45Ma) and C17 (Lower Priabonian 37-38Ma) in agreement to nearby structures (Boltaña, Picodel Aguila anticlines) but clearly diachronic to western ones (Santo Domingo anticline). Besides, the rotational activity seems to follow a linear and continuous pattern (velocity 9-11º/Ma, R: 0.83-0.96) in contrast to closer structures that show two distinct rotational velocities (i.e. Boltaña). These new data still let open the debate on the rotational kinematics along the South Pyrenean basal thrust.

Recent radiometric dating of some Cambrian rocks in southern Australia: relevance to the Cambrian time scale.

The Cambrian time scale is in a state of flux due to a lack of reliable geochronological dates which can be tied to biostratigraphic scales. Most recent Australian dates relevant to the Cambrian geochronologic scale have been determined from the Early Cambrian successions of South Australia and the Middle and Late Cambrian sedimentary and volcanic rocks of western Tasmania. This work has been based on SHRIMP dates using zircon standard SL13. The reliability of these dates is questionable due to doubts as to the reliability of SL13. An analysis of the Lower Cambrian data from South Australia suggests that depending on the standard used the Botoman/Toyonian boundary may be younger than 532.8 ± 4 Ma or 522.8 ± 1.8 Ma. The base of the Botoman is older than 526 ± 4 Ma and may be several million years older, thus suggesting either that the Tommotian and Atdabanian are quite short or that the recently proposed figures of 534 Ma and 528 Ma for the base of the Tommotian and Atclabanian respectively need to be revised to older dates. The Middle Cambrian/Late Cambrian boundary is more likely to have a elate of 505 Ma than 498 Ma. The average time span for a trilobite zone (mainly agnostoid based) in the Middle and Late Cambrian is about 535,000 years. This average time span is such that the error bars of most geochronological dates encompass several trilobite zones.

Carboniferous biostratigraphy of rugose corals

Abstract Rugose corals are one of the major fossil groups in shallow-water environments. They played an important role in dividing and correlating Carboniferous strata during the last century, when regional biostratigraphic schemes were established, and may be useful for long-distance correlation. Carboniferous rugose corals document two evolutionary events. One is the Tournaisian recovery event, with abundant occurrences of typical Carboniferous rugose corals such as columellate taxa and a significant diversification of large, dissepimented corals. The other is the changeover of rugose coral composition at the mid-Carboniferous boundary, which is represented by the disappearance of many large dissepimented taxa with complex axial structures and the appearance of typical Pennsylvanian taxa characterized by compound rugose taxa. The biostratigraphic scales for rugose corals show a finer temporal resolution in the Mississippian than in the Pennsylvanian, which was probably caused by the Late Paleozoic Ice Age that resulted in glacial–eustatic changes and a lack of continuous Pennsylvanian carbonate strata. The Pennsylvanian rugose corals are totally missing in the Cimmerian Continent. High-resolution biostratigraphy of rugose corals has so far only been achieved in few regions for the Mississippian timescale. In most regions, more detailed taxonomic work and precise correlations between different fossil groups are needed.

New Biochronological Scales of Planktic Foraminifera for the Early Danian Based on High-Resolution Biostratigraphy

After the Cretaceous/Paleogene boundary (KPB) catastrophic mass extinction event, an explosive evolutionary radiation of planktic foraminifera took place in consequence of the prompt occupation of empty niches. The rapid evolution of new species makes it possible to establish high-resolution biozonations in the lower Danian. We propose two biostratigraphic scales for low-to-middle latitudes spanning the first two million years of the Danian. The first is based on qualitative data and includes four biozones: the Guembelitria cretacea Zone (Dan1), the Parvularugoglobigerina longiapertura Zone (Dan2), the Parvularugoglobigerina eugubina Zone (Dan3), and the Parasubbotina pseudobulloides Zone (Dan4). The latter two are divided into several sub-biozones: the Parvularugoglobigerina sabina Subzone (Dan3a) and the Eoglobigerina simplicissima Subzone (Dan3b) for the Pv. eugubina Zone, and the Praemurica taurica Subzone (Dan4a), the Subbotina triloculinoides Subzone (Dan4b), and the Globanomalina compressa Subzone (Dan4c) for the P. pseudobulloides Zone. The second scale is based on quantitative data and includes three acme-zones (abundance zones): the Guembelitria Acme-zone (DanAZ1), the Parvularugoglobigerina-Palaeoglobigerina Acme-zone (DanAZ2), and the Woodringina-Chiloguembelina Acme-zone (DanAZ3). Both biozonations are based on high-resolution samplings of the most continuous sections of the lower Danian worldwide and have been calibrated with recent magnetochronological and astrochronological dating.

Models of historical biogeography and continental biochronology

One of the most important contributions of Nieves López Martínez in Palaeobiogeography is the study of the ‘centre of origin of species’ concept and the proposal of the ‘Asymmetric Time Model’ as an alternative to the ‘Symmetric Time Model’, a key concept in dispersalist Historical Biogeography. As a consequence of these ideas, she discussed the methodology to establish biostratigraphic scales, pointing out that the higher number of ‘First Appearance Datum’ (FADs) over that of ‘Last Appearance Datum’ (LADs) in the fossil record supports the Asymmetrical Time Model. In this study we analyse the middle Miocene micromammal appearance and extinction events (FADs and LADs) based on well-calibrated local biostratigraphic scales from different European basins, in order to determine which of the proposed biogeographical models better fits the Miocene European micromammal record. The results support that the Asymmetric Time Model of palaeobiogeography is only applicable in rare cases. The analysed fossil record only shows one event of occurrence and one of extinction that can be considered synchronous at continental level. Finally, the implications of the biogeographic models in the proposition of biochronologic continental scales are also discussed, pointing out that palaeobiogeographic frameworks need robust biochronologies based on extensive local biostratigraphic data with independent temporal correlation

Genus Arcticoceras Spath, 1924 (Ammonidea) and Infrazonal Biostratigraphy of the Lower Bathonian of the Boreal Realm

Analysis of taxonomically significant trait variability in the genus Arcticoceras (Cardioceratide, Arctocephalitinae) enables the assignment of most species of this genus (including A. harlandi) identified earlier and characteristic of the lower Bathonian to the group of synonyms of A. ishmae. Invalidity of the genus Greencephalites is substantiated, and it is proposed to consider the species of this genus as cadiconic morphs of various Arctocephalites and Arcticoceras species. Revision of the genus Arcticoceras enables the abolition of the Harlandi Zone present in the biostratigraphic scales of various regions of the Arctic. The infrazonal volume of the Ishmae Zone of the Boreal (Arctic) standard includes at least three biohorizons, for which the A. ishmae subspecies can be used as indicators.

Stratigraphic scale and geological section

Research subject. The most frequently utilized fundamental notions in stratigraphy are discussed: concrete section, composite section, the stratigraphic scale, the biochronologic scale, the International Stratigraphic Scale. Materials and methods . The conventional content of these concepts is analyzed. The logical invalidity and negative consequences of the identification of subdivisions of the stratigraphic scale and subdivisions of a section are shown. The study of a section provides a way of obtaining information about the stratigraphic sequence of rock formation and the distribution of evidence of the events included in them, which are necessary for constructing stratigraphic scales. The close connection of the source of the actual data and results of its stratigraphic interpretation is the reason for the traditional identification of the subdivisions of the stratigraphic scale and subdivisions of a particular section. Results. The biochronologic scale inherits from a section the time sequence of occurrences of species of a certain group of organisms selected as the basis of a scale. However, special features of the evolutionary development of organisms do not depend on the composition of the containing deposits and the method of the separation of sedimentary rock sequences. This development makes it possible during the study of many specific sections to establish homotaxis in the distribution of fossils, i.e., to build a biochronologic scale. Thus, the understanding of the scale is a model of the biochronologic calculation of geological time. Like any model, a scale cannot be identical to what it simulates. Conclusion. A precise differentiation of the scale and a section is the basis for drawing correct stratigraphic conclusions. A zone is the smallest subdivision of the biostratigraphic scale. Zones are not divided into parts, are discrete (between adjacent zones there are no time passages), equivalent and are characterized by only the place which it occupies on the scale. The construction of a zone scale precedes the establishment of the material equivalent of the zone - of a stratozone - in the section. Any part of a stratozone is dated by the complete zone. The identification of the zonal scale with a sequence of stratozones in the section does not make it possible to understand the minimum dimensionality of a zone subdivision. The International Stratigraphic Scale (ISS) is defined, based on domestic stratigraphic codes and on foreign reference books, as a stratigraphic sequence of rocks (geological bodies) in total volume without passages and overlaps. In this treatment the ISS is not the scale, but is a complete (composite) geological section of the earth’s crust. The biostratigraphic scale serves as a tool of correlation. The ISS gives only the name of that subdivision, with which a concrete section is compared, and the geological age of the deposits of this section is designated by this name.

Benthic foraminiferal assemblages across the Aalenian–Bajocian boundary in the Iberian and Basque-Cantabrian basins (North Spain)

The aim of this work is to describe the benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary (Middle Jurassic) in two sections of the Iberian and Basque-Cantabrian basins (North Spain), well calibrated with the standard ammonite zonation, in order to establish a biostratigraphic scale based on the foraminiferal record, and to infer the palaeoecological conditions that affected their development. A total of 29 samples were collected in the studied sections, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphic interval was analysed using the stratigraphic distribution of the identified species, the quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The studied assemblages are moderately abundant and diverse, and they are constituted by a total of 5435 specimens, corresponding to 5 suborders, 13 families, 25 genera and 51 species. Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. For the studied stratigraphic interval, it was recognised the Lenticulina quenstedti Foraminiferal Zone, in which the recorded assemblages developed in intermediate part of a marine platform environmental conditions, well oxygenated and with normal salinity. In the Aalenian–Bajocian transition, it was possible to identify a sharp decrease in the abundance and diversity of the foraminiferal assemblages that has also been recognised in other coeval basins of the Iberian Plate palaeomargin, thus representing a bioevent of the Northern Hemisphere.

THE REGIONAL STRATIGRAPHIC SCHEME OF MESO-CENOZOIC DEPOSITS OF TRANSCARPATHIAN DEEP BASEMENT

In this article, the first comprehensive stratigraphic scheme of Meso-Cenozoic deposits of Transcarpathian Deep Basement is presented. These deposits spread out in the strip between Pieniny Zone of Carpathians and Pannonian Deep. There are three types of thick rock sections from Triassic to Miocene (Eggenburgian). The scheme is based on new tectonical zoning of Transcarpathian Deep Basement. In first time, there are distinguished the structuralfacial units – Uzhgorod-Solotvino and Pripannonian zones (one includes Berehove and Vyshkiv subzones). The distribution, lithofacial composition, paleontological characteristics, thicknesses, stratigraphic relations of all stratones are described in details. The age of deposits is specified and defined according by analisis of macro- and microfaunistic data (mollusks, foraminifers, tintinnids, nannoplankton, and radiolarians). The biostratigraphic scale is developed. The correlation with International Stratigraphic time Scale (2016), with adjacent territories of Slovakia and Hungary, and with Pieniny Zone of Ukrainian Carpathians is done. The sedimentation model illustrated the geohistorical aspects of forming the deposits of Transcarpathian Deep Basement during the Meso-Cenozoic is added.

Zonal Diatom Scale of the Continental Neogene in Primorye (Most Southern Territory of the Russian Far East)

A significant stratigraphic and micropaleontological problem exists in the development of high-resolution biostratigraphic scales necessary when collecting basic data to construct a modern theory of Biospheric Stratigraphy and in determining the chronozone as a main operation unit. The chronozone should reflect general geobiological events which led to various conditions using the Paleobiosphere, which is a unique instrument used to mimic conditions of the ancient earth. The development and substantiation of zonal continental scales, which also include information on geobiological events, lag behind modern stratigraphy requirements The author's actual materials on the Far East Neogene diatom stratigraphic distribution allow us to decide this problem. The early Miocene is characterized by the intensive development of the Aulacoseira, Alveolophora, Ellerbeckia, Pseudoaulacosira, and Melosira genera. The global climate optimum has appeared between the early and middle Miocene. Many taxa of diatoms as well as the high species diversity of centric diatoms appeared and developed during the Middle–Late Miocene stage of diatom evolution. The Pliocene stage was marked by the appearance of the genera Stephanodiscus, Cyclotella, and Pliocaenicus. The greatest extinction of moderately warm-water species of centric births at the level of 3.6 million years corresponds to the growth and expansion of ice caps at both poles of the planet.

THE MAIN ACHIEVEMENTS AND TRENDS OF THE DEVELOPMENT OF THE DEPARTMENT OF PALEONTOLOGY AND STRATIGRAPHY OF THE PALEOZOIC DEPOSITS OF THE INSTITUTE OF THE GEOLOGICAL SCIENCES OF NAS OF UKRAINE FOR THE PERIOD FROM 1990 TO 2018

The main achievements of the staff of the Department of paleontology and stratigraphy of the Paleozoic deposits of the Institute of the Geological Sciences of the National Academy of Sciences of Ukraine for the period from 1990 to 2018 were highlighted. Their goal was to identify the regularities of the geological structure of the sedimentary cover of different regions of Ukraine, to use the phenomena of the animal and plant world evolution during the Paleozoic to justify the stratigraphic boundaries as boundaries of reorganization of paleoecosystems of different rank. The main directions of research are considered: the study and monographic description of the most important groups of fossils with the aim of construction of zonal biostratigraphic scales and detailed regional stratigraphic schemes for Paleozoic systems of different regions of Ukraine; participation in the research of the international projects of the International Union of Geological Sciences for the improvement of the International Chronostratigraphic Paleozoic Scale; the study of the distribution of facies and formations in the past geological epochs, the compilation of lithofacial and paleogeographical maps. Creation of an independent school of highly qualified internationally estimated stratigraphers and paleontologists, authors of papers and books of the international level and stratigraphic schemes of all the Paleozoic systems of Ukraine, as well as its own Stratigraphic Code are considered as the most important achievements of the Academy of Sciences of Ukraine in the field of paleontology and stratigraphy for 100 years of its existence. The main trends in the development of paleontological and stratigraphic studies throughout the world and the possibilities for their development in the Institute of Geological Sciences of the National Academy of Sciences of Ukraine are indicated.

The Lower Paleogene Biostratigraphic Scale of the Northern Pacific Based on Deep-Water Benthic Foraminifera

Based on the stratigraphic distribution of benthic foraminifera in the lower bathyal–abyssal sediments uncovered by boreholes drilled under the framework of the Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) in the Northern and Southern Pacific, the Lower Paleogene biostratigraphic zonal scale based on deep-water benthic foraminifera is proposed. The proposed scale includes eight subdivisions: six zones and two subzones. The boundaries of the zonal subdivisions are determined by biotic events (appearance or disappearance (extinction)) of stratigraphically important taxa and are correlated to the zonal scales based on planktonic foraminifera and calcareous nanoplankton. Most of these events are considered to be subglobal.

Detailed biostratigraphic scales as based on the palaeobiogenetical approach (an example of the Upper Bajocian – Lower Bathonian ostracod scale of the Russian Platform)

Two new species of ostracods of the family Progonocytheridae Sylvester-Bradley Camptocythere (C.) lateres Tesakova et Shurupova, sp. nov. and C. (C.) angustius Tesakova et Shurupova, sp. nov. from the Michalskii and Besnosovi ammonite zones (Upper Bajocian – Lower Bathonian, Middle Jurassic) of the Sokur section (Saratov) are described. The changes in ontogenesis in the phylogeny of Camptocythere (C.) lateres Tesakova et Shurupova in the stratigraphical interval corresponding to the Palaeocytheridea kalandadzei ostracod Zone, and especially to the beds with C. (C.) lateres, have been studied. The levels of the change in the predominant type of sculpture (corresponding to evolutionary boundaries) are recognized in the sculpture development among the adult representatives of the species in its phylogeny. This palaeobiogenetic (heterochrony) approach allows subdivision of the beds with C. (C.) lateres into three stratigrapical intervals characterized by changes in the type of sculpture.

The rodent succession in the Sifón de Librilla section (Fortuna Basin, SE Spain): implications for the Mio-Pliocene boundary in the Mediterranean terrestrial record

The long and continuous continental section of Sifón de Librilla (Fortuna Basin, southern Spain) provides a detailed biostratigraphic record distributed along eight localities, in which the magnetostratigraphy has been unambiguously established. This section therefore provides a unique opportunity to cross biostratigraphic information with magnetostratigraphic data to establish a reliable frame to date sites. This 800-m-thick sequence extends from the latest Miocene to the early Pliocene, recording more than 2 Myr. Here we provide a complete taxonomic survey of the recovered rodent remains, defining a new cricetid species named as Hispanomys romeroi. We also refine the phylogenetic relationships of the Apodemus, Stephanomys, Paraethomys, Ruscinomys and Apocricetus lineages. Considering the accurate age of the associations, we discuss the chronology of the first and last appearances of some species. In addition, this section clearly records the Mio-Pliocene boundary, allowing us to correlate between the marine and continental biostratigraphic scales. Taking advantage of this opportunity, we explore key biostratigraphic indicators for identifying the beginning of the Pliocene in the continental records, as well as for differentiating the MN13 and MN14 units, most specially the FOD of Occitanomys brailloni. According to this datum, we conclude that the Miocene-Pliocene boundary coincides with that of MN13-MN14 units. http://www.zoobank.org/urn:lsid:zoobank.org:act:BDA60E97-C23B-482D-AD0D-9C25FDF5FA05

New insights on Cricetodontini (Rodentia, Mammalia) from the Duero Basin, Spain

The tribe Cricetodontini is a common cricetid group found in several European basins from the Miocene. Here we present a study of the fossils of this group found in the Duero Basin. We updated the biostratigraphical assignation of some of the localities in which several species of Cricetodontini have been found. Cricetodontini remains from eight localities from the central sector of the Duero Basin have been described, measured and assigned to a species. The presence in these localities of Hispanomys aguirrei, H. lavocati, H. nombrevillae and H. aragonensis has allowed correlating them to the biostratigraphic scale built for the Miocene in Calatayud-Daroca Basin, identifying biozones G3, H and I (MN7/8 – MN10, Late Aragonian – Early Vallesian, Middle – Late Miocene). Furthermore, this study constitutes the first citation of this species in this basin, except H. aguirrei, previously described in the Duero Basin. After this work, the biostratigraphical assignation of the studied sites is now well known. We evidenced the resemblance of Duero and Calatayud-Daroca basins.

Integrated biostratigraphy (Ammonoidea, Foraminiferida) of the Aalenian of the Lusitanian Basin (Portugal): A synthesis

This work reports a synthesis of biostratigraphic outputs resulting from over two decades of comprehensive analysis on the expressive stratigraphic record of the Aalenian of the Lusitanian Basin (Western Iberian Margin; Portugal). The rich and diverse ammonite record studied from ten marly and marlylimestones sections, outcropping in different sectors of the basin ranging from distal to proximal facies, has enabled the establishment of a detailed ammonite-based biostratigraphical framework correlated with other basins located around the Iberian Plate. The study of the benthic foraminiferal assemblages occurring in the basin at the same time interval has allowed the establishment of a biostratigraphic scale based on microfossils accurately calibrated with the ammonite record, an important tool in log interpretation in the context of hydrocarbon exploration activities in sedimentary basins of Jurassic age. The corresponding biostratigraphic units are characterized, as well as the bioevents recognized in the benthic foraminiferal record, which represent another additional proxy of local and/or regional rank that can be used to determine both the age and depositional environment assigned to core samples.

AMMONOIDS FROM THE ZHUGANPO MEMBER OF THE FALANG FORMATION AT NIMAIGU AND THEIR RELEVANCE FOR DATING THE XINGYI FOSSIL-LAGERSTÄTTE (LATE LADINIAN, GUIZHOU, CHINA)

We herein document the various ammonoid faunas, of which 8 are newly described taxa, recently collected from the Falang Formation at Nimaigu (Wusha) near Xingyi (Guizhou, South China) and also define their biostratigraphy, correlation and age. The sampled interval includes the Zhuganpo Member, which contains the world famous Xingyi Fossil-Lagerstatte, and the lowermost part of the overlying Wayao Member. Ammonoids are quite abundant, but preservation is usually very poor. New genera Yangites , Haoceras and Sinomeginoceras are described on the basis of four new species. The new subfamily Haoceratinae (family Trachyceratidae) is erected to accommodate Haoceras and Sinomeginoceras . Xenoprotrachyceras , Detoniceras , Ptychites , Trachyceras and Clionitites are also recognized, together with a specimen attributed with doubt to Parasturia . Most of the faunas are endemic and typical representatives of Upper Ladinian ammonoid zones have not been recognized. A new local biostratigraphic scale is proposed, consisting of the Haoceras xingyiense zone, Trachyceras beds and Trachyceras multituberculatum zone, in stratigraphic order. The Trachyceras beds and the Trachyceras multituberculatum zone are attributed to the Lower Carnian, but most of the bio-chronostratigraphic analysis is focused on the Haoceras xingyiense zone, because it directly overlies the vertebrate-bearing interval. Correlation of the new biozone is discussed and its stratigraphic position is referred, at least in part, to the lower Sutherlandi Zone of the North American scale. This correlation pinpoints the age of the Xingyi Fossil-Lagerstatte as middle Late Ladinian, which until now had been a matter of debate for 30+ years.

Zonal stratigraphy and biogeography of the West Siberian Oxfordian based on ammonites

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.

High resolution ammonite–benthic foraminiferal biostratigraphy across the Aalenian–Bajocian boundary in the Lusitanian Basin (Portugal)

This work describes the ammonite and benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary of the Serra da Boa Viagem II section, located about 6 km to the east of the Bajocian GSSP (Murtinheira, Portugal), and calibrated to the standard ammonite zonation previously established for the Lusitanian Basin. A total of 220 ammonite specimens referred to 30 fossiliferous levels were collected and identified throughout the section, enabling the recognition of the Concavum Zone (Concavum and Limitatum subzones) of the upper Aalenian, and the Discites Zone of the lower Bajocian. A total of 2356 foraminifers were obtained from the 16 samples collected along the section, corresponding to 4 suborders, 8 families, 16 genera and 44 species.The occurrence of Lenticulina quenstedti (Gümbel) has enabled the recognition of the Lenticulina quenstedti Zone, ranging from the Bradfordensis Zone (middle Aalenian) to the lower Discites Zone (lower Bajocian). The first record of Ramulina spandeli Paalzow, whose occurrence, up to now, was limited in the Lusitanian Basin to the Murtinheira section (the Bajocian GSSP), highlights the usefulness of the Ramulina spandeli Zone, with its lower boundary referred to the lower Discites Zone (lower Bajocian). Other bioevents displaying local, basinal or regional biostratigraphic interest have also been identified.The benthic foraminiferal record here presented, accurately calibrated with the ammonite record, aims at contributing to support the recognition of the Lenticulina quenstedti Zone and the Ramulina spandeli Zone as formal biostratigraphic units integrating the biostratigraphic scale based on benthic foraminifers for the Aalenian–Bajocian boundary in the Lusitanian Basin (Portugal). Copyright © 2014 John Wiley & Sons, Ltd.