Stratotype Section Research Articles

The problem of ammonoid substantiation of the Artinskian–Kungurian boundary in Western Verkhoyanie

Kungurian ammonoids had high taxonomic diversity, but were distinguished by an extremely high level of endemism and sharp geographic differentiation. Therefore, outside the regions containing the most important conodont taxa, the Artinskian-Kungurian boundary based on ammonoids must be established through indirect evidence due to the lack of common species with potential global stratotypes of the lower boundary of the Kungurian. A long-term study of the reference sections of the Echian and Tumarian regional stages and their ammonoids made it possible to change the understanding of the bio- and lithostratigraphy of the Artinskian-Kungurian boundary deposits of the Kuranakh structural-facies zone of Western Verkhoyanie. Clarification of the upper boundary of the Khabakh Formation in the stratotype section led to the fact that the ammonoids previously belonging to this formation began to be considered in the lower part of the Orol formation. They characterize the Paratumaroceras? sp. nov. biostratigraphic beds of the lower part of the Tumarian Regional Stage. At the current level of knowledge, the ammonoid substantiation of the Artinskian–Kungurian boundary in Verkhoyanie is difficult due to the existing hiatus corresponding to the Khabakh formation and its age analogues. However, the appearance at the base of the Tumarian Regional Stage of the first paragastrioceratids with a ventral sinus in transverse sculpture (Paratumaroceras? sp. nov.) suggests that the boundary in question is located near the base of the indicated regional stage or even combined with it. For further clearer identification of the Kungurian lower boundary in Verkhoyanie, new studies of the Echian–Tumarian boundary deposits in typical sections, independent of paleontology, are necessary. Such research should primarily include isotope-stratigraphic subdivision and high-precision U-Pb dating.

Calcareous Nannofossil variability controlled by Milankovitch and sub-Milankovitch periodicity in the Monte San Nicola section (Gelasian GSSP / MIS 100–104)

The Quaternary marks the beginning of the ice ages, with the establishment of a stable Northern Hemisphere ice sheet. The Monte San Nicola section, southern Sicily (Italy) is the Global Boundary Stratotype Section and Point of the Gelasian Stage of the Lower Quaternary Subseries and is attracting new attention for providing valuable information on paleoclimate evolution.Here we present a paleoenvironmental reconstruction based on new data from calcareous nannoplankton, the phytoplankton organisms that are sensitive to sea surface changes and water column dynamics. We adopt statistical and signal analysis to support our paleoenvironmental model. The most evident paleoenvironmental signal throughout the investigated interval is the contrast between the abundance patterns of placoliths and Florisphaera profunda, the former pointing to surface productivity (water column mixing, shallow nutricline), the latter to the establishment of a deep nutricline. The observed nutricline depth shift occurred with a regular precessional pace, following Northern Hemisphere summer insolation and, likely, North African monsoon activity. A significant periodicity of 8 kyr, in tune with late Quaternary Heinrich events, is also observed in nannoplankton taxa, supporting previous findings on the existence of suborbital climatic variability even at the Pliocene-Pleistocene transition.

Stable carbon isotope chemostratigraphy of the base of the Callovian in Greenland

D’Orbigny named the Callovian stage after Kellaways in Wiltshire, UK, in the 1850 s. However, agreement on its boundaries and, more recently, on the position and location of the Global Boundary Stratotype Section and Point (GSSP) for the base of the Callovian has proven difficult for the last 170 years. This is mainly due to the lack of agreement on the appropriate index fossil and its regional and global correlations, as well as the location of the stratotype section. Stable carbon isotope chemostratigraphy and event stratigraphy are now essential tools for aiding in the definition of GSSPs. In this study, stable carbon isotopic analysis of 91 samples from east Greenland’s Middle Jurassic shallow marine sandstones of the Pelion Formation (Store Koldewey and Hold with Hope) and correlative and well-dated offshore siltstones and mudstones of the Fossilbjerget Formation (Jameson Land) is used to discriminate several isotopic events previously observed in other European basins and propose the early Callovian (δ13CTOC) positive carbon isotopic excursion as a secondary marker for defining the Callovian GSSP. The early Callovian (δ13CTOC) positive carbon isotopic excursion is a fundamental tool for superregional correlation between candidate GSSPs and Standard Auxiliary Boundary Stratotypes. It can also help establish a chronological order (synchronous vs diachronous) of species occurrences between different locations.

Late Quaternary history of the Kerch Strait — the stratotype region for the Black Sea

The Kerch Strait has periodically connected to the Black, Azov, and Caspian seas throughout its Late Quaternary history. The strait's deposits reflect the changes in the natural environment of the entire Ponto-Caspian region, which are a response to global climate change. Several studies have been done on the region's stratigraphy, biostratigraphy, geomorphology, and paleogeography. However, most of the current knowledge about the paleogeography of the area is based on the analysis of empirical data collected more than 25 years ago, and due to the lack of detailed geochronological studies, many palaeogeographical problems remain unresolved.This paper presents a reconstruction of environmental change in the Kerch Strait during the Late Quaternary. The reconstruction is based on the results of a comprehensive study of the sedimentary sequences in the Kerch Strait carried out by the author and colleagues over the past ten years. The study examines the deposits of two stratotype sections of the Karangatian (Eemian) transgression and the four boreholes’ sections in Tuzla Island in the central part of the strait.A biostratigraphic division of the Upper Quaternary deposits of the Kerch Strait was carried out based on a malacofaunal study. Mollusc assemblages corresponding to various paleogeographic stages of development were identified, and their paleoecological characteristics were described. Luminescence and radiocarbon ages made it possible to determine the time intervals of established paleogeographic stages in the strait's history. Detailed luminescence dating of the Karangatian transgression sediments of the Eltigen and Tuzla stratotype sections has been carried out for the first time.Six main stages in the Kerch Strait natural environment development were established in the Late Quaternary and correlated with global and regional climatic events: Karangatian, with three stages (MIS 5e-c); Tarkhankutian (MIS 5a); Post-Karangatian (MIS 4); Surozh (MIS 3); Neoeuxinian, with two stages (MIS 2); and Chernomorian (MIS 1). Two episodes of the Caspian waters flowing through the Kerch Strait into the Black Sea were identified in MIS 5c and at the end of MIS 2.

Cyclostratigraphy of late Cambrian marine sedimentary records and reconstruction of Earth-Moon system parameters

The Cambrian period is an important era in geological history, marked by numerous major geological and biological events. To better understand these events, it is important to establish a high-precision chronostratigraphic framework. An astronomical time scale can be created by the identified Milankovitch cycles in well-preserved stratigraphic successions. Duibian B section in Jiangshan (Zhejiang Province, China) is the global stratotype section and point (GSSP) for the Jiangshanian Stage, and this section provides well-preserved records covering the upper Paibian to lower Jiangshanian stages. In this study, we use high-resolution magnetic susceptibility record to conduct cyclostratigraphic analysis of the Duibian B section. Our results indicate that the 2.44 m, 0.84–0.73 m, 0.20–0.19 m, and 0.12–0.09 m sedimentary cycles may represent long-eccentricity, short-eccentricity, obliquity, and precession cycles, respectively. Using the stable 405-kyr eccentricity cycles, we constructed an ∼5.96 Myr floating astronomical time scale to calibrate agnostoid trilobite zones. In addition, we reconstructed the precession rate k from geological records, and our result provides an insight into the Earth-Moon distance and length of day in the late Cambrian (Paibian–Jiangshanian, ∼494.2 Ma). It enriches our understanding of the Earth-Moon evolutionary history in deep time.

Calcareous nannofossil biostratigraphy, bioevents, and palaeoecological interpretation of the lower-middle Miocene outcrops in west central Sinai (Egypt)

The Burdigalian/Langhian (B/L) boundary has not yet been designated as a Global Stratotype Section and Point (GSSP), despite various proposed zonal schemes. In the Gulf of Suez region of Egypt, the Burdigalian-Langhian successions are notable for hosting significant hydrocarbon reservoirs within a tectonic rift setting. Therefore, biostatigraphy plays a crucial role in exploration endeavors in this area. The nannofossil biostratigraphy is investigated in two sections, Wadi Baba and Wadi Gharandel, of the lower-middle Miocene from west-central Sinai. Three biozones, NN3 (Sphenolithus belemnos) Zone, NN4 (Helicosphaera ampliaperta) Zone, and NN5 (Sphenolithus heteromorphus) Zone, are identified from the studied interval. The NN4 Zone could be divided into MNN4a/b and MNN4c. Important biovents are discussed, such as the S. heteromorphus paracme interval and the first occurrence and evolution of the Discoaster exilis and Discoaster variabilis groups. Based on the cluster analysis, the recorded taxa can be subdivided into four groups that reflect their palaeoclimatic preferences. The paleoecological interpretation of the studied Rudies Formation indicates prevailing cool and eutrophic nutrient conditions based on the dominance of taxa such as Coccolithus pelagicus, Reticulofenestra minuta, and Cyclicargolithus floridanus. The nannofossil taxa responses to sea level curve are interpreted. Fluctuations in taxa abundance and diversity indicate a slight rise in the sea level at the base of the Burdigalian followed by sudden drop in the sea level at the middle Burdigalian. High sea-level conditions prevailed again until the B/L boundary. During the Langhian period, many small-scale fluctuations in sea-level curve are detected.

Palaeoenvironmental and palaeoclimatic study of the Olazagutia (Spain) and Ten Mile Creek-Arbor Park (USA) sections during the Coniacian–Santonian interval

The mechanisms and palaeoenvironmental conditions leading to and occurring through the Coniacian–Santonian Ocean Anoxic Event 3 (OAE3) are poorly known, particularly with regard to the marine phosphorus cycle and the climatic conditions in general. To explore these issues further, two famous locations have been studied, Olazagutia (Spain) and Ten Mile Creek–Arbor Park (TX, USA), which are located in different palaeogeographical areas and deposited at different palaeodepths. The study of these two locations is based on mineralogy (bulk and clay), geochemistry (stable isotopes, organic matter, phosphorus and major element) and high-resolution biostratigraphy (nannofossils) to infer changes in climate and primary productivity across OAE3. The investigated sections were both previously proposed as candidates for the base Santonian global boundary stratotype section and point (GSSP). The Olazagutia section was ratified in 2013, where the base of the Santonian was defined by the first appearance datum of the inoceramid Platyceramus undulatoplicatus . Both sections, deposited in oxygenated conditions, record the δ 13 C patterns which characterized the Coniacian–Santonian OAE3 interval, in particular the positive carbon-isotope excursions comprising the K2, Michel Dean and Bedwell events. New nannofossil biostratigraphy for both sections is presented including new occurrences. Significant diachronism of marker taxa is observed between the Spanish and Texan sections. Based on a weathering index and mineralogy, similar climate changes are observed in all sections. The climate shifted synchronously from relatively drier to warmer and wetter conditions above the Coniacian–Santonian boundary from the Michel Dean event to above the Bedwell event during the early Santonian. Fluctuations in total phosphorus contents appear mainly to have been driven by changes in detrital input and consequently by climate change in Spain and Texas. Several bentonite layers were observed in Texas close to the Coniacian–Santonian boundary, but only one located 7 m above the Coniacian–Santonian boundary provided sufficient well-preserved zircon minerals, and gives an age of 86.24 ± 0.12 Ma based on U–Pb geochronology, consistent with an early Santonian age.

Carbonate-siliciclastic deposits of the Lower Uk Subformation (Neoproterozoic) in the stratotype section and its correlation within Bashkirian Mega-Anticlinorium of the Southern Urals

Research subject. Carbonate-siliciclastic deposits of the Lower Uk Subformation were thoroughly studied in the section along the Yuryuzan river (near Ust-Katav town, Chelyabinsk region) and correlated with subformation sections along the Basu, Zilim and Bolshoy Inzer rivers. Material and methods. A detailed description of the stratotype section was carried out; sandstones, siltstones and limestones were studied in thin sections. The sections were correlated with each other. Results. Relationships between the Lower Uk Subformation and the underlying deposits are studied. The petrographic characteristics of rocks are presented. The Lower Uk Subformation sequences are traced between sections of various structural-tectonic zones of the Bashkirian Mega-anticlinorium (BMA). Conclusions. The set of features supports the idea about the presence of a sedimentary hiatus at the base of the formation, even in the most complete sequences (which contain the locally developed Shubino Member of the Minyar Formation). In the stratotype and in other reference sections, the Lower Uk Subformation has a pronounced three-membered structure; it is subdivided into the lower (siliciclastic) Yamashta, middle (substantially carbonate) Akkostyak, and upper (siliciclastic-carbonate) Avdyrdak members. The lithofacies analysis results suggest a change in environments from coastal-marine siliciclastic to shallow-marine siliciclastic-carbonate (middle and inner ramps) due to fluctuations in the relative sea level and, probably, climate change. It was established that the area of the Suleimanovo anticline at latest Riphean corresponded to the distal sedimentary environments in comparison with the southern and western zones (Alatau anticlinorium) of the BMA.

Lithogeochemical characteristics and sedimentary environments of the Uk Formation limestones (upper Riphean, Southern Urals)

The lithogeochemical characteristics of the Uk Formation limestones (Uppermost Unit of the Riphean stratotype section in the Southern Urals) are considered. Data points of limestones (40 samples) accumulated in the middle and inner ramp environments have a quite contrasting distribution on diagrams with parameters (La/Sm)sh, (La/Yb)sh and (Sm/Yb)sh, proposed based on the systematization of a significant amount of analytical data on carbonate sequences formed in various platetectonic (in the broad sense of the word, paleogeographic) environments (according to [Zhang et al., 2017]) was established. The data points of the limestones of the Medved Member of the Uk Formation, which was formed, according to a detailed lithological-facies analysis, in the middle ramp environment, in the indicated diagrams located towards the field of limestones of the open ocean, while the limestones of the Manaysu Member (inner ramp deposits) in their geochemical characteristics are more consistent with the limestones of the near-coastal environments. Thus, the geochemical characteristics of the Uk Formation limestones seem to confirm the conclusions of the previous reconstructions. It has been suggested that in the example we described, the distribution of trace elements in the inner ramp limestones was apparently controlled by fine-grained siliciclastic material coming from the continent, while in the geochemical features of deeper-sea middle ramp limestones the influence of the open ocean environment is already perceptible.

Jurassic–Cretaceous boundary in the Dedina section (Serbian Carpathians): Effects of remagnetization on magnetostratigraphy

The Upper Tithonian to Lower Berriasian carbonate sequence of the Getic Nappe system was studied near Golubac (eastern Serbia) using rock-magnetic and paleomagnetic methods to verify the age of the magnetization and to correlate magnetostratigraphy with biostratigraphy. A major part of the Dedina section shows the presence of authigenic goethite, hematite and magnetite as carriers of remagnetization. The youngest overprint, residing in goethite, sometimes carrying up to 90 % of natural remanent magnetization, was probably received after 18 Ma. The remagnetization residing in hematite and magnetite, attributed to the late Early Cretaceous collision, was obtained during long normal polarity Chron C34 (118–82 Ma). The mean direction implies a clockwise post-remagnetization rotation by about 57°. The normal (Dn) and reverse (Er) polarity components, heavily affected by the chemo-remanent magnetization overprint, can be tentatively interpreted in terms of polarity zones. Thus, the obtained data enabled a preliminary identification of M17r to M19n.2n magnetochrons. The correlation of magnetostratigraphy with biostratigraphy of the Dedina section contributes to the stratigraphic framework necessary for the definition of the Berriasian Global Boundary Stratotype Section and Point.

Sedimentary DNA reveals phytoplankton diversity loss in a deep maar lake during the Anthropocene

AbstractAnthropogenic‐driven environmental change, including current climate warming, has influenced lake ecosystems globally during the Anthropocene. Phytoplankton are important indicators of environmental changes in lakes and play a fundamental role in maintaining the functioning and stability of these ecosystems. However, the extent to which lake phytoplankton were affected by anthropogenic or climatic forces during the Anthropocene remains unclear. Here, we investigated the 160‐yr‐long dynamics of the phytoplankton community (cyanobacteria and eukaryotic microalgae) in response to anthropogenic forcing in Sihailongwan Maar Lake—a candidate for a Global boundary Stratotype Section and Point for demarcation of the Anthropocene—using DNA metabarcoding and traditional paleolimnological approaches. Our results show a significant decline in phytoplankton diversity and an abrupt shift in community composition around the 1950s, corresponding to the beginning of the “Great Acceleration” period. Specifically, phytoplankton taxa coexistence patterns, niche differentiation, and assembly mechanisms changed significantly after the 1950s. Overall, increases in air temperature and anthropogenic forcing appear to be the dominant controls for community reorganization and diversity decline of the phytoplankton from this deep maar lake. A neutral community model suggests that phytoplankton community composition was mainly controlled by stochastic processes before the 1950s; however, as time progressed, deterministic effects driven by anthropogenic global warming increased. The results of this study imply that anthropogenic perturbations have led to a loss of phytoplankton diversity and a further decline in ecological resilience in deep lakes, with likely knock‐on effects on the productivity and function of lake ecosystems.

A Hyperactive Geomagnetic Field in the Late Visean (Early Carboniferous) From the Late Asbian Stratotype Section in Northwest England, UK

Plain Language SummaryNearly synchronous global changes in geomagnetic polarity give both a detailed irregular pacing to geological time and provide a glimpse into heat transfer processes across the core—mantle boundary which drives the Earth's geodynamo. Although the Late Carboniferous is characterized by some well‐studied reversals, details of the tempo of polarity changes in the Early Carboniferous are unknown. This work addresses this by providing a detailed record of polarity changes over a ∼2 million year interval at around 334.5–332.5 million years ago‐from the Trowbarrow Quarry section in NW England. We demonstrate that these limestones likely preserve magnetization from close to their time of formation and record at least 31 polarity reversals. These observations support the idea that the Earth's dynamo was in a hyperactive reversing state similar to those sustained for tens of Myr in the Late Jurassic, parts of the Cambrian and the Late Ediacaran. It further corroborates a ∼200 Myr cyclicity in paleomagnetic field behavior since the Precambrian, potentially linked to variable core heat flow forced by mantle convection.

Katav, Inzer and Minyar formations of the Avdyrdak anticline along the Ufa – Inzer –Beloretsk highway (Alatau anticlinorium, Southern Urals)

Object of study: sections of deposits of the Katav, Inzer and Minyar formations of the Karatau series of the Upper Riphean of the Avdyrdak anticline of the Alatau anticlinorium (Southern Urals). For the first time, detailed descriptions and sketches of sections of sediments of the Katav, Inzer and Minyar formations of the Avdyrdak anticline along the highway (80K-031) Ufa – Inzer – Beloretsk are presented. The study of deposits in natural outcrops and road quarries and excavations made it possible to clarify the material composition of the deposits in question, their ratio and thickness in the westernmost sections of the outer zone of the folded Urals. It has been established that the main features of the material composition and structure of the sections of the Katav, Inzer and Minyar formations of the Avdyrdak anticline are similar to the deposits of these formations in the reference and stratotype sections, which makes it possible to use the obtained data for stratigraphic correlation of sediments and reconstruction of sedimentation conditions in different parts of the paleobasin.

Stratotypic section of the Wenlockian Voyvyv horizon (Western slope of the Subpolar Urals)

Research subject. The paper presents the results of a study into the carbonate-terrigenous section of 197.8 m-thick Wenlockian section in the Shchugor River basin, which is proposed as the stratotype of the regional horizon. Materials and methods. The study was based on numerous samples from Lower Silurian deposits collected by the authors in different years during fieldwork on the Western slope of the Circumpolar Urals and the Chernov and Chernyshev uplifts, as well as the biostratigraphic, paleontological, lithological, and C-isotopic data obtained during these works. Results. The obtained data allowed revising some of the established ideas about the structure of the Lower Silurian section and the position of the boundary level between the Llandoverian and Wenlockian in the Subpolar Urals and to identify a new regional subdivision with the name “Voyvyv”. The traced formation conditions of shallow carbonate sediments of the Voyvyv horizon and the consistent change of zonal taxa of marine fauna in the stratotype section indicate similarity with coeval strata on the Chernov and Chernyshev uplifts and Dolgy Island. Conclusions. The results of the study of Wenlockian Voyvyv deposits in the Timan-North Urals region showed that the section in the Shchugor River basin in outcrop 10c can be considered the most informative in the Northern Urals region in terms of exposure degree, established stratigraphic completeness, and preservation of macro- and microfauna.

ERRATUM: Stratigraphy of the Cretaceous/Paleogene (K/Pg) boundary at the Global Stratotype Section and Point (GSSP) in El Kef, Tunisia: New insights from the El Kef Coring Project

“X-ray diffraction (XRD)” rather than “X-ray fluorescence (XRF)” was printed in the captions to Figure 7, Figure 9, and Figure 10. See PDF file for details.

Early Cretaceous continental sedimentatary environments, palaeogeography and biota of southeastern Western Siberia

Abstract The Ilek Formation was distinguished by Ragozin in 1936 in the SE of Western Siberia, as a sequence of continental deposits accumulated in the alluvial and lacustrine environments, dating Barremian–Early Albian. At the end of the twentieth century a series of sites, comprising rich and diverse Early Cretaceous vertebrates, was discovered, which forced an intensive comprehensive research of the Ilek Formation. The stratotype section of the Bolshoi Ilek represents an abnormal section of the Ilek Formation, comprising the deposits of prodelta, delta front and mouth bars. Three regions within the area of the Ilek Formation reflect the evolution of the fluvial system. The eastern region represents the oldest part of the section, preliminarily dated to the Barremian based on spore and pollen analysis in addition to lithological characteristics. The western region was probably deposited during ocean anoxic event (OAE) 1a. The central region represents the final stage of the tectonic cycle, deposited within the environments of the calm plain river and fluvial delta. The vertebrate assemblages distinguished for the Kiya and Bolshoi Kemchug basins have specific features, which can support the heterochrony of the Ilekian deposits.

The Central South Atlantic: The origin of its waters, its evolution and effects beyond

The primitive sea that occupied the Central South Atlantic (CSA), part of the intra-Gondwana rift during the Early Cretaceous, allowed precipitation of an extensive and thick layer of evaporites, the Ibura Salt, followed by the deposition of a prominent Albian carbonate package. Although the shallow platform facies do not contain classical benthic Tethys markers, the pelagic open sea carbonates are essentially dominated by planktonic elements coming from the Tethys Realm. This condition led some researchers to think that Tethys waters also contributed to salt formation, an idea that clashes with the geotectonic model of northward separation of Africa and South America and ingression of predominantly Austral marine waters. Now, a new controversy arises as to the age of this salt layer when trying to position bio-events and lithological and chemostratigraphic markers from these rocks with respect to established data for the Global Boundary Stratotype Section and Point for the Aptian/Albian boundary (GSSP-Alb). Biochronostratigraphic information on planktonic foraminifera points to an Aptian age as opposed to the earliest Albian traditionally accepted for the carbonate section that overlies the giant salt layer. On the other hand, stratigraphic and geochronological data suggest an age of 113 Ma for the base of the salt, very near to the 113.2 ± 0.1 Ma arbitrated for the GSSP-Alb. In this study, we adopt the base of the evaporite bed as the Aptian/Albian boundary in the CSA, Equatorial South Atlantic (ESA), and northeastern Brazilian interior basins (BNE) as well. Based on these criteria, a broad review and the integration of available information have led to new interpretations regarding the earliest phase of these segments of the South Atlantic and adjacent areas. Initially, during the Aptian-Albian transition, an ephemeral interior sea within Brazil, drawing its waters from the north, would have contributed to salt deposition in the intra-Gondwana rift (evaporitic stage of the CSA). Afterward, but still within the earliest Albian, the evaporitic system evolved into a carbonate gulf when the northern barrier, the Exception Zone (EZ), disappeared. The lagoonal circulation pattern that then formed in the CSA created a hypersaline and warm outflow plume that swept across the marine bottom of the ESA and part of the Tethys Sea. Paleoceanographic events registered at Site 545, Mazagan Plateau, support this new hypothesis and illustrate the potential complexity of correlation of organic-rich deposits in which local influences have been greater than global ones. This long, narrow, and continuous carbonate gulf disappeared at the end of the Albian with the arrival of southern waters from the Meridional South Atlantic (MSA), and the South Atlantic became consolidated as a proto-ocean.

The integrated biostratigraphy and palaeoenvironments across the Jurassic–Cretaceous boundary in the Dedina section (eastern Serbian Carpathians)

Upper Tithonian to lower Berriasian carbonate sequence of the Getic Nappe System was studied near Golubac using an integrated biostratigraphy approach based on calpionellid, calcareous dinoflagellate, nannofossil, foraminifer, and palynomorph record. Calpionellids allowed subdivision of the section to standard calpionellid zones including the Colomi and Alpina subzones on the Tithonian–Berriasian transition. Nannofossil Nannoconus wintereri proves the presence of the NC0 Zone. Foraminifer fauna on the Tithonian–Berriasian transition contain zonal marker Globospirillina neocomiana and some other potential stratigraphic markers, whose range and taxonomy have to be fixed yet. Poor palynomorph spectra consist of long-ranging Lower-Cretaceous spores and pollen, and a few dinoflagellate cysts known from the Berriasian. Integrated biostratigraphy of the Tithonian–Berriasian oligotrophic open-marine carbonate facies of the Dedina section contributes to the stratigraphic framework necessary for the definition of the Berriasian Global Boundary Stratotype Section and Point.

Integrated study on the base of the Coniacian Stage in the Caucasus

The continuous Turonian–Coniacian succession, exposed in the Shapsug quarry (northwestern Caucasus) composed of rhythmic carbonate strata of the hemipelagic and pelagic type, have been studied comprehensively. Foraminiferal zones, corresponding to the zonation recognized in the Coniacian Global Boundary Stratotype Section and Point (GSSP), have been identified. Chemostratigraphic (isotope) studies determine the levels of abiotic events traced in this section and in the GSSP for the base of the Coniacian Stage. The Shapsug section may be proposed a possible auxiliary section of the base of the Coniacian for the Russian Federation.

Biostratigraphy of Liminic Ostracoda (Crustacea) from the Quiricó Formation, Lower Cretaceous of the São Francisco Basin, Minas Gerais State, Brazil: An approach on paleozoogeographic evolution of Gondwana

The present study is the first biostratigraphic framework based on limnic ostracods for the Quiricó Formation, São Francisco Basin, Brazil. Three sections located at Minas Gerais State were approached: 1. Stratotype section of the Quiricó Formation, Presidente Olegário County; 2. Hypostratotype section of the Tereza Farm, João Pinheiro County; and 3. São Bento Farm section, Carmo do Paranaíba County. After ostracod taxonomic analysis and integration with previous studies, six biostratigraphic units are described, one superzone and five zones. From the lower to the upper part of the Quiricó Formation, zones are: Zone Brasacypris ovum, OSF-0; Zone Timiriasevia sanfranciscanensis, OSF-1.1; Zone Cypridea hystrix, OSF-1.2; Zone Alicenula longiformis, OSF-1.3; and Zone Harbinia spp., OSF-1.4. Superzone Penthesilenula pintoi, OSF-1, comprises zones Timiriasevia sanfranciscanensis, Cypridea hystrix, Alicenula longiformis and Harbinia spp, and is attributed to the Berriasian–Albian? interval. The Brasacypris ovum Zone is attributed to the Berriasian; the Timiriasevia sanfranciscanensis Zone is attributed to the Berriasian; the Cypridea hystrix Zone is attributed to the Valanginian–Hauterivian interval; the Alicenula longiformis Zone is attributed to the Barremian; and the Harbinia spp. Zone is attributed to the Aptian. A paleozoogeographic analysis showed faunal similarities with several sedimentary basins in Brazil, Argentina, Gabon, Gamba, Congo and Cabinda during the late assemblage of Gondwana previous to the complete breakup of the supercontinent.