High-resolution Biostratigraphy Research Articles

Microfossils, High-Resolution Stratigraphy, Geochemistry and Lithology of the Upper Jurassic and Lower Cretaceous (Urdyuk-Khaya and Paksa Formations) in the Nordvik Peninsula, Anabar Bay, Laptev Sea

Abstract —The goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic–Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed δ13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, δ13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the “subsurface chlorophyll maximum” is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.

Latest Oligocene to middle Miocene low-latitude calcareous nannofossil biostratigraphy and paleoenvironmental interpretations of stratigraphic well 4, Sinú-San Jacinto onshore basin, northwest Colombia

Calcareous nannofossils are one of the main fossil groups used in the petroleum industry to determine the relative age and correlation of lithofacies identified in gas and oil wells. A limited number of biostratigraphic zonation schemes based on nanoplankton and paleoceanographic reconstructions have been suggested to onshore Colombian Caribbean. Most of them are compiled in several publications for the northern Colombian units (Mejía-Molina et al., 2008, 2010). In this study, a medium to high-resolution biostratigraphy study was carried out on one of the best-known Neogene sedimentary successions in the Sinú-San Jacinto onshore Basin, where the Stratigraphic Well 4 (SW4) was drilled by Ecopetrol, the Colombian state-run oil company. The nannoplankton biostratigraphic zonation proposed here constitutes the first calcareous nanoplankton research to construct a biochronologic scheme for the Neogene of northern Colombia, which has direct applications for oil exploration, global energy matrix and the transition to clean energy in the onshore areas of the Sinú-San Jacinto domain. The section studied has a thickness of ∼269 m and comprises mainly a very thick succession of claystone and mudstone with occasional intercalations of silty sandstones corresponding to the El Carmen Formation. The studied interval is assigned to the nannofossils Zones NP25 (CP19) to NN4 (CN3) of Martini (1971) and Okada and Bukry (1980), spanning from the latest Oligocene (latest Chattian) to middle Miocene (early Langhian), approximately 24 Ma to 15 Ma. Intervals without fossil content were identified in the record and could constitute hiatuses, but the nannofloral events, which define the limits of the biozones, can be identified. Global and regional climatic changes which occurred in the Caribbean region at those times are reflected in important changes in the fossil assemblages and abundance pattern of nanoplankton. These could indicate variability in environmental conditions linked to temperature and increased nutrients within the nannofossil communities in this part of the San Jacinto folded belt (SJFB), northwest Colombia. Middle Miocene Climate Optimum (MMCO) episodes of “blooming” intervals of Sphenolithus were identified, accompanied with a drastic reduction in total nannofossil abundance and CaCO3 content. Since the Caribbean geology is framed in a very complex scenario, the data acquired and presented in this research has a potential application to improve the current stratigraphy in the area, targeted to hydrocarbon exploration and studies related to the global energy matrix and the transition to clean energy. It also strengthens the paleoceanographic reconstructions based on these organisms at low latitudes.

Late Miocene biostratigraphy and paleoenvironment of the Sais Basin (southern Rifian Corridor, Morocco): New insights from the Moulay Yakoub area

During the Late Miocene, the Rifian Corridor was one of the two main corridors allowing exchanges between the Atlantic and the Mediterranean Seas. Sedimentary records accumulated along this corridor and specifically, in the Sais Basin, constitute case-study material for understanding the impact of the South Rifian Corridor on the evolution of the fauna, phytoplankton and environment during the Late Miocene. In order to reconstruct the evolution of marine paleoenvironments in the Moulay Yakoub region and to compare this evolution with other areas of the Sais basin, we conducted an integrated biostratigraphic and palynological study of the Upper Miocene of borehole KA 102. High-resolution biostratigraphy based on planktonic foraminifera revised and defined the chronostratigraphic framework of the Upper Miocene sedimentary series of the Moulay Yakoub region providing an age of 7.8 Ma to 6.52 Ma (Late Tortonian to Early Messinian). In the Late Tortonian, the planktonic foraminiferal assemblages suggest an open and relatively deep marine environment. At the Tortonian/Messinian boundary, planktonic foraminiferal and dinoflagellate associations, as well as distal indices, suggest a relatively deep and neritic distal marine environment with a decrease in diversity and an increase in reworked taxa. Surface waters are warm with a minor cooling trend observed just below this boundary. In comparison to previously studied sections in the Sais Basin, the Lower Messinian is characterized by a deeper and more distal marine environment. However, proximal trends and warm surface water conditions persisted in all studied areas from the basin during this period.

CALCAREOUS NANNOFOSSIL TAXONOMY AND BIOSTRATIGRAPHY OF THE TOARCIAN-LOWER BAJOCIAN COLLE DI SOGNO SECTION (LOMBARDY BASIN, SOUTHERN ALPS, ITALY)

Calcareous nannofossil biostratigraphy was conducted in the Toarcian-lower Bajocian interval at Colle di Sogno (Lombardy Basin, Southern Alps, Northern Italy) where the type-section of the Sogno Formation consisting of pelagic marly limestone, marlstone and marly claystone was established. Semiquantitative analyses of calcareous nannofossil assemblages allowed to achieve a high-resolution biostratigraphy based on several biohorizons, including zonal/subzonal markers and additional events. The NJT5 to NJT9 Zones of the standard nannofossil zonation established for the Mediterranean Province were identified. The biostratigraphy obtained at Colle di Sogno was compared to published nannofossil events calibrated with ammonite zones in sections from SE Spain, S France, Portugal and N Algeria. This assessment evidenced some discrepancies in the succession of events of the standard zonation and, furthermore, resulted in the revision of the age of a few datums. Moreover, some new/additional nannofossil biohorizons are proposed as subzonal markers. A morphometric analysis of the genus Watznaueria was conducted to identify diagnostic features for unambiguous species identification. The species W. colacicchii and W. contracta are distinguished on the basis of the coccolith width/central area width ratio, whereas W. britannica britannica is discriminated by the size - as in the original definition of the species - relative to the new subspecies W. britannica minor. The new species W. gaetanii differs from all other Watznaueria taxa by the bridge ultrastructure. In the Toarcian-Aalenian interval a progressive increase in size of Watznaueria specimens is paralleled by the progressive closure of the central area and the modification of the central area structure passing from a cross (W. colacicchii and W. contracta) to a double-button bridge (W. gaetanii) to a single-button bridge (W. britannica). These intrageneric evolutionary innovations accelerated in the Aalenian under stable paleoceanographic conditions and an oligotrophic regime.

Palynofacies Analyses of HA-001 well, Offshore Depobelt, Niger Delta Basin, Nigeria

Palynofacies studies of the strata penetrated by HA-001 well were carried out with the aim to establish palynostratigraphic zones and paleodepositional environments. The standard acid palynological method of sample administration was employed to recover the palynofacies, soaking and washing of samples with water for sedimentological analyses and integration of Gamma Ray Log, palynofacies and sedimentological data for interpretation of paleodepositional environments. The study established two new assemblage biozones namely Cyperaceaepollis sp. – Nympheaepollis clarus, and Stereisporites sp. within the sedimentary intervals penetrated in the wells. The Cyperaceaepollis sp. – Nympheaepollis clarus biozones were further subdivided into Nympheaepollis clarus – Echitriletes pliocenicus and Cyperaceaepollis sp. – Elaeis guineensis subzones. The Late Miocene age is associated with the biozones. The lithologic, textural and wireline log data indicated that the intervals studied in the HA-001 well belong to the Benin Formation and Agbada Formation. Index minerals and accessories are dominated by ferruginous materials, glauconite pellets, carbonaceous detritus, shell fragments and pyrites plus minor mica flakes. Lower delta plain, delta front and prodelta environment of deposition were inferred for the studied well intervals. The research has conformed to international stratigraphic guide for establishment of biozones which serves to increase the knowledge of high resolution biostratigraphy.

The Ordovician of Central Asia (Kyrgyzstan, Uzbekistan and Tajikistan)

Abstract The region of Kyrgyzstan, Tajikistan and Uzbekistan includes five first-order tectonic units with an Early Paleozsoic sedimentary record, comprising North Tien Shan, Karatau Naryn, Turkestan–Alai, Zeravshan–Hissar and the Central Pamirs. Available palaeobiogeographical and palaeomagnetic data suggest that these were widely dispersed in the Ordovician. North Tien Shan, Karatau Naryn, Turkestan–Alai were separate microcontinents located in the low southern latitudes throughout the Ordovician in relative proximity to the western Gondwana margin. Zeravshan–Hissar and the Central Pamirs were also parts of the Gondwana supercontinent but were located in temperate latitudes. The geological literature on the Ordovician of the region is assessed to provide an updated palaeontological record, outline of lithostratigraphy and biostratigraphic correlation based on the International Chronostratigraphic Chart. The Ordovician biostratigraphy of Central Asia is mainly graptolite-based; however, that record is discontinuous, and the absence of detailed faunal logs and lack of monographic studies causes difficulty in precisely locating system and stage boundaries. Although an extensive faunal record has been documented, often it is based on preliminary taxonomical identifications which are not reliable for high-resolution biostratigraphy and tracing biodiversity patterns.

High-Resolution Biostratigraphic, and Paleoenvironmental Analysis of AJAYI-01 Well, Niger Delta, Nigeria

A high-resolution biostratigraphy study and paleoenvironment analysis were carried out on composited fifteen (15) ditch-cutting samples retrieved from AJAYI-01 well, offshore Niger Delta, Nigeria. The studied intervals range from 4060feet – 4960feet and were subjected to foraminifera, calcareous nannofossil and palynological analysis to determine their age, biozonation and environment of deposition. The standard laboratory preparation techniques of wet sieving, simple smear method, and Hydrofluoric (HF) and Hydrochloric (HCl) acids maceration techniques respectively. A sedimentological description of the ditch-cutting samples was carried out.
 Three major foraminifera zones of Turborotalia peripheroacuta/Bolivina mandoroveensis Zone, Praeorbulina glomerosa/Nonion centrosulcatum Zone and Catapsydrax dissimilis/Buliminella subfusiformis Zone and the important marker Heterostegina sp. was recognized in the well based on the critical evaluation of bioevents and correlatable datums. The nannofossil zones of Helicosphaera ampliaperta and Sphenolithus heteromorphus were erected for this well based on the index taxa and fossil assemblage recorded. The palynological data consists of highly diversified assemblages dominated by terrestrial forms such as Zonocostites ramonae, Monoporites annulatus, Laevigatosporites sp., Verrucatosporites sp., Retitricolporites sp., Acrostichum aureum. The important marker recorded was Crassoretitriletes vanraadshooveni (FDO) at 4420feet. The well is dated early to middle Miocene (NN4 –NN5) based on the occurrence of marker species Helicosphaera ampliaperta and Sphenolithus heteromophus which corresponds to Crassoretitriletes vanraadshooveni - Echitricolporites spinosus Zone (P720-P680) subzones.
 A tentative sequence stratigraphic framework for the studied sequences was established. A condensed section that is associated with the Maximum Flooding Surface (MFS) was dated 15.20Ma at 4480 feet based on peak faunal abundance and diversity. The environment of deposition has sediments deposited in the marine environment fluctuating between middle neritic and inner neritic to the littoral, including coastal deltaic settings based on deductions from foraminiferal, palynological and sedimentological data.

Revised planktic foraminiferal biostratigraphy of the early late Albian of northern Tunisia (southern Tethys)

The upper Albian exposed near the Imbrication Zone of northern Tunisia is composed of a pelagic sequence that includes organic-rich beds. High-resolution biostratigraphy based on planktic foraminiferal bioevents across marker beds (i.e., organic-rich beds), allows revision of the lithostratigraphic subdivision and zonal scheme in comparison with late Albian time equivalents recorded in the northern Tethyan margins. In the present study, we proposed a new subdivision of the upper Albian lithostratigraphic section that now includes the Mellegue horizon as an equivalent of theAmadeus Segment rhythmic marl/limestone interval (central Italy). Three studied sections are subdivided into five biozones with the abundance and morphological trends of planktic foraminifera and inferred paleoenvironments: 1) The Biticinella breggiensis Total Range Zone is characterized by the appearance of ticinellids with pinched chambers (i,e., Ticinella praeticinensis) and is recorded a few meters above the first occurrence of Biticinella breggiensis. Agradual increase of trochospiral thick-walled (B. breggiensis, T. roberti, T. raynaudi) and Globigerinelloides taxa, reflecting mesotrophic conditions. 2) The Pseudothalmanninella subticinensis Interval Zone includes the first appearance of keeled forms (Ps.subticinensis), associated with abundant ticinellids with flattened chambers (B.breggiensis, T. roberti) below the base of the organic-rich Mellegue horizon, indicating an oligotrophic environment. 3) The Pseudothalmanninella ticinensis Interval Zone. The continuous occurrence of T. primula and the scarcity of Globigerinelloides throughout the lower part of this zone indicates an oligotrophic to weakly mesotrophic environment. The occurrences of radiolarian-rich horizons and abundant forms with elongated chambers (T. raynaudi) in the lower part of this zone indicate an abrupt shift to enhanced eutrophic and dysaerobic conditions. 4) The Thalmanninella appenninica Zone, which shows a decrease in abundance preceding the extinction of ticinellids, and a gradually increasing number of specialized keeled forms (i.e., Th. appenninica), indicates oligotrophic conditions. 5) The Planomalina buxtorfi Total Range Zone is characterized in its lower part by an increasing abundance of clavate forms with radially elongated chambers (i.e., Clavihedbergella) above the organic-rich bed of the Mouelha Member, indicating low-oxygen, oligotrophic to mesotrophic conditions.

THE APPLICATION OF THE 't' TEST AND MARKOV CHAIN ANALYSIS IN BIOSTRATIGRAPHY OF 'X' WELL

There is no habit in biostratigraphers to apply the statistic methods to solve problems in their jobs, whereas in fact these methods are very useful when conventional ways failed. The use of this method has become very important in reservoir scale where microfossil content is low and indicator species is rare or absent. Applying biozonation in reservoir scale is much less reliable since reservoir layers are mostly below zonal resolution, so that the application of high resolution biostratigraphy is needed. In this case, the integration of biometric study and 't' or 'f' test can be used to define bioevent precisely. In sequence stratigraphy, data of depositional environment in various system tracts that determined using microfossil assemblage are very important. However, for the reasons of barren or no samples, this information might not be obtained by biostratigraphy or other methods. Due to the geological cycle and repeatable nature of depositional sequence, Markov Chain analysis can be used to predict the lost information about environment of deposition.

Carboniferous biostratigraphy of rugose corals

AbstractRugose 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.

Chronostratigraphy of clinothem-filled non-marine basins: Dating the Pannonian Stage

Clinoforms and clinothems are important and common architectural elements in the sedimentary record of many basins worldwide. The influence that they exert on chronostratigraphic interpretations, however, is often underestimated. This is especially true in non-marine basins, such as the Central European to Central Asian Neogene Paratethyan basins, where chronostratigraphic division and correlation is usually based on fossils of environmentally sensitive molluscs recovered from outcrops of shallow-water deposits. In the subsurface, the diachronous boundary between the foreset and topset parts of the shelf-edge scale clinoforms, where significant lithological and paleontological changes can be observed with the transition from deep to shallow water, was routinely identified with one of the regional stage or substage boundaries, inflicting serious confusion in chronostratigraphy. In the late Neogene brackish lacustrine basin fill of the Pannonian basin (Pannonian Stage, 11.6 to 2.6 Ma), where extended endemic radiation and long-term gradual morphological change in various groups of the biota offer good marker species for high-resolution biostratigraphy, molluscs and dinoflagellate algae are used to establish a clinothem chronostratigraphy. The biozone and clinothem boundaries are correlated with the geological time scale through mammal stratigraphic considerations, magnetostratigraphy, and radiometric dating. For the time being, the beginning of lacustrine deposition at 11.6 Ma and the intervals between 8.8 and 7.1 Ma and 4.6–2.6 Ma are accurately dated in drill cores. These time intervals can be correlated through the dense seismic network across the basin. For other time intervals of the late Miocene and Pliocene, the uncertainty of dating remains high on the order of several 100 kys. • Discrepancy between field- or well-based stratigraphy and clinothem geometry is commonly a source of correlation issues. • Such chronostratigraphic misinterpretations are especially common in the non-marine basins of the Paratethys region. • The endemics-based biostratigraphy of the Neogene lacustrine Pannonian basin was adapted to the seismically imaged clinothem sets. • The clionoform-bounded biochronozones of the Pannonian basin are dated by magnetostratigraphy and radioisotopic dating.

Anatomical, morphometric, and stratigraphic analyses of theropod biodiversity in the Upper Cretaceous (Campanian) Dinosaur Park Formation1

The Dinosaur Park Formation (DPF) of Alberta, Canada, has produced one of the most diverse dinosaur faunas, with the record favouring large-bodied taxa, in terms of number and completeness of skeletons. Although small theropods are well documented in the assemblage, taxonomic assessments are frequently based on isolated, fragmentary skeletal elements. Here we reassess DPF theropod biodiversity using morphological comparisons, high-resolution biostratigraphy, and morphometric analyses, with a focus on specimens/taxa originally described from isolated material. In addition to clarifying taxic diversity, we test whether DPF theropods preserve faunal zonation/turnover patterns similar to those previously documented for megaherbivores. Frontal bones referred to a therizinosaur (cf. Erlikosaurus), representing among the only skeletal record of the group from the Campanian–Maastrichtian (83–66 Ma) fossil record of North America, plot most closely to troodontids in morphospace, distinct from non-DPF therizinosaurs, a placement supported by a suite of troodontid anatomical frontal characters. Postcranial material referred to cf. Erlikosaurus in North America is also reviewed and found most similar in morphology to caenagnathids, rather than therizinosaurs. Among troodontids, we document considerable morphospace and biostratigraphic overlap between Stenonychosaurus and the recently described Latenivenatrix, as well as a variable distribution of putatively autapomorphic characters, calling the validity of the latter taxon into question. Biostratigraphically, there are no broad-scale patterns of faunal zonation similar to those previously documented in ornithischians from the DPF, with many theropods ranging throughout much of the formation and overlapping extensively, possibly reflecting a lack of sensitivity to environmental changes, or other cryptic ecological or evolutionary factors.

Tectono-eustatic controls on depositional setting and spatial facies distribution of Coniacian–Santonian sequences of the Zagros Basin in Fars area, S. Iran

New high-resolution biostratigraphy and facies analyses indicate that a Coniacian-Santonian homoclinal carbonate ramp (Ilam Fm.) developed on the subaerially exposed mid-Turonian surface at the top of Sarvak Fm. in Fars zone of the Zagros Basin (northeastern margin of the Arabian Plate). Spatial facies distribution, sequence stratigraphy, and lateral variation in the thickness of Ilam Fm., as well as extend of erosion of the underlying Sarvak Fm. suggest that a combination of regional tectonic activities and global sea-level changes controlled the development of this succession. A major tectonic configuration in the Zagros belt including several basement faults subdivide the belt into different blocks with distinctive sedimentary records. Reactivation of these preexisting basement faults during Late Cretaceous provided a horst and graben geometry due to the closure of Neo-Tethys. Three of our studied sections are located on an upthrown block, bounded between Kazerun and Karebas basement faults, include inner and mid-ramp deposits. These sections represent an eastward deepening trend which correspond to eastward tilting of this fault block. The easternmost section is located in the eastern neighboring downthrown block , bounded between Karebas and Bastak faults, and includes outer ramp and basin deposits confirming a significant paleo-bathymetrical contrast between the two blocks. Furthermore, eastward thickening of the Ilam Fm. independently confirms the increase of accommodation space, as a result of deeper depositional condition, toward center of the Fars zone. Absence of subaerial exposure features at top of the Sarvak Fm. in the downthrown block shows that the global sea-level fall and regional tectonic regime also controlled the extend of unconformity underlying the Coniacian-Santonian platform deposits (Ilam Fm.).

Early Miocene larger benthic foraminifera from the northwestern Tethyan Seaway (NW Iran): new findings on Shallow Benthic Zone 25.

The lower Miocene marine units of NW Iran (Hamedan–Miandoab area) were studied to establish a high-resolution biostratigraphy framework in the context of European standard biozonation (SBZ zonal scheme). The units are dominated by larger and small benthic foraminifera together with coralline algae and corals. Due to its position in the Tethyan Seaway between the Mediterranean and Indo-Pacific, the investigated area has high significance in palaeobiogeography. Seven species of benthic foraminifera were described, including Miogypsina globulina, Amphistegina bohdanowiczi, Elphidium crispum, Elphidium sp. 1, Borelis curdica, Austrotrillina asmariensis, and Peneroplis thomasi. The occurrence of Miogypsina globulina in the shallow-marine carbonates of the studied sections documents the Burdigalian SBZ 25 Zone. Austrotrillina asmariensis and Peneroplis thomasi occur with M. globulina. Simultaneously, their stratigraphical range is extended to the Burdigalian in the Middle East. Based on the discovery of lower Miocene deposits in the Hamedan–Miandoab area (previously mapped as Oligocene–Miocene units), the stratigraphy of northwest Central Iran is revised. The biostratigraphic results also present a more precise chronology for the marine transgression in the study area, initiating in the late early Miocene. The coralline algal assemblages and the abundance and diversity of larger benthic foraminifera indicate that shallow-marine Qom Formation got deposited in tropical to subtropical warm waters.

ITALIAN GEOLOGY AND CLIMATE CHANGE IN THE DEEP PAST

Mesozoic sedimentary rocks, of both deep- and shallow-water character, are present throughout Italy and well exposed in mountains and river valleys. Detailed studies of these sections by Italian geologists, beginning in the nineteenth century and continuing to this day, have produced a high-resolution biostratigraphy that allows identification of increments of geological time of less than a million years. Early work relied largely on ammonites to define biostratigraphy but was applicable primarily to sediments of Jurassic age. Study of deep-marine pelagic limestones and shales of Cretaceous age were subsequently, in the twentieth century, investigated using planktonic microfossils, the size of a sand grain, and even smaller nannofossils of micron scale. Pioneering work on magnetostratigraphy and cyclostratigraphy, undertaken primarily on Cretaceous sediments cropping out in Marche-Umbria, added further refinement to the measuring of small intervals of time in rock. With this stratigraphic background, distinct lithological and chemical signals, discovered first in Italian sequences, could be recognized world-wide and proven to be of global significance. In particular, the involvement of carbon isotopes has underscored the utility of chemostratigraphy, not only as a further aid to correlation, but also as a testimonial to major environmental change. Most significant in this context are the Cretaceous oceanic anoxic events, whose sedimentary record was first documented from Italy. These events were characterized by the development of organic-rich black shales deposited in waters largely lacking in oxygen during times of extraordinarily high temperatures known as hyperthermals. Hyperthermals, likely driven by supply of carbon dioxide from large-scale volcanic eruptions, illustrate the environmental impact on a planet affected by extreme global warming.

First Middle Ordovician conodont record related to key graptolites from the western Puna, Argentina: perspectives for an integrated biostratigraphy and correlation of the Central Andean Basin

Recent biostratigraphic studies on the western argentine Puna recorded the Middle Ordovician conodont Baltoniodus cf. B. navis (Lindström) for first time, related to key graptolite taxa of the Central Andean Basin. The analyzed material comes from the lower and middle thirds of the turbidite succession exposed at the Huaytiquina section, Salta Province, which was previously assigned to the “Coquena” Formation. The conodont fauna was recovered from the calcareous sandstone beds intercalated in the middle portion of this unit, and it is composed by species of the genera Baltoniodus, Gothodus, Trapezognathus, Drepanoistodus, Drepanodus, and Protopanderodus, among others. The conodont association indicates a middle Dapingian (Dp2) age, linking the conodonts of the Argentine Puna with those from Baltoscandinavia and South China. The conodont productive levels also contain graptolites assignable to Tetragraptus bigsbyi (Hall) and Isograptus sp. They are located overlying strata bearing Azygograptus lapworthi Nicholson and underlying deposits with Xiphograptus lofuensis (Lee). The graptolite associations are indicating a Dapingian age (Dp1-Dp2) for the lower and middle portions of the “Coquena” Formation. The current findings from the western Puna, as well as the record of Azygograptus lapworthi related to the early Dapingian (Dp1) index conodont Baltoniodus triangularis in the Argentine Cordillera Oriental, are suggesting that a high-resolution correlation between both geomorphological regions is possible. This also documents that the Cordillera Oriental as well as the Puna were connected parts of the Central Andean Basin, during the interval from the Lower Ordovician (Floian) to the Middle Ordovician (Dapingian), instead of corresponding to the source and infill sectors of the basin, respectively. Furthermore, the regional and global correlations are discussed, and the potential of the Ordovician successions of the Argentine Puna for future advances on conodont-graptolite high-resolution biostratigraphy is highlighted.

Distribution of Alveolina assemblages in the Ypresian (Ilerdian-Cuisian) successions from Iran and Turkey (central and western Tethys): biostratigraphic implications for regional correlation

Benthic foraminiferal assemblages dominated by Alveolina species from the Ypresian (Ilerdian-Cuisian) are studied herein from numerous localities of Iran and Turkey. From these successions, highly diversified assemblage of 58 alveolinid species are identified along with their detailed biostratigraphical application, which resulted in the recognition of eight shallow benthic zones (SBZ5-SBZ12). Our findings are based upon the distribution ranges of Alveolina from the Ilerdian-Cuisian sediments in Iran (Central Tethys) that are considered to have a strong affinity with their coeval fauna in Turkey (Western Tethys). In this study, the wide expansion ranges of Alveolina permit us to achieve a high-resolution biostratigraphy and apply the shallow benthic zones of the peri-Mediterranean region (Western Tethys) to the Ilerdian-Cuisian successions in Iran (Central Tethys). Nevertheless, the distribution of some Alveolina species, even the zonalmarkers consisting of Glomalveolina lepidula, Alveolina ellipsoidalis, A. pisiformis, A. laxa, A. subpyrenaica, A. varians, A. fornasinii and A. canavarii are found occurring at younger stratigraphic levels in Iran and/or Turkey than in the western European shallow marine deposits.

High-resolution biostratigraphy and chemostratigraphy of the Cenomanian stratotype area (Le Mans, France)

The definition of the Cenomanian stage was based on the description of several type sections scattered in the vicinity of Le Mans (Sarthe, France). Despite limited exposures nowadays, the area remains a reference for the palaeontology of the Cenomanian due to its outstanding richness in marine macrofossils, especially molluscs, bryozoans, brachiopods and echinoderms. The publication in 2015 of the volume dedicated to the Cenomanian stratotype yielded the opportunity to restudy the last accessible outcrops. This paper provides a high-resolution stratigraphic scheme and palaeoenvironmental reconstruction for the middle and late Cenomanian interval in its type area. La Garenne Quarry is a window on the middle Cenomanian, where Praeglobotruncana rillella nov. sp. has been identified. The δ13Ccarb and δ18Ocarb record of a Cenomanian–Turonian succession close to Le Mans is correlated with the type section of Pueblo (Colorado). Isotopic and biotic events highlight the presence of several hiatuses in the sedimentary record of Le Mans especially around the Cenomanian–Turonian boundary with a dramatic truncation of the plateau of high δ13Ccarb values. Coiling reversal events among the surface dwellers Muricohedbergella delrioensis, indicate sea surface temperature changes with transient coolings, including the Plenus cold event, and warm conditions at the Cenomanian–Turonian boundary. Sandy to chalky facies have yielded empty, well-preserved shells of foraminifera allowing the description of Dicarinella falsohelvetica nov. sp. Oxygen isotopic analyses performed on right- and left-coiled M. delrioensis reveal a systematic offset during cold events which lead to discuss about the potential occurrence of cryptic species in the Mesozoic.

Morphological variation suggests that chitinozoans may be fossils of individual microorganisms rather than metazoan eggs.

Chitinozoans are organic-walled microfossils widely recorded in Ordovician to Devonian (ca 485–359 Mya) marine sediments and extensively used in high-resolution biostratigraphy. Their biological affinity remains unknown, but most commonly, they are interpreted as eggs of marine metazoans. Here, we provide new insights into their palaeobiology from three lines of inquiry. We examine morphological variation of a new, well-preserved Late Ordovician species, Hercochitina violana; analyse a compiled dataset of measurements on 378 species representing all known chitinozoan genera; and compare these data with the size variation of eggs of both extinct and extant aquatic invertebrates. The results indicate that the magnitude of size variation within chitinozoan species is larger than observed in fossil and modern eggs. Additionally, delicate morphological structures of chitinozoans, such as prosome and complex ornamentation, are inconsistent with the egg hypothesis. Distinct and continuous morphological variation in H. violana is more plausibly interpreted as an ontogenetic series of individual microorganisms, rather than as eggs.