Ammonite Zones Research Articles

A Bajocian event of global coral reef growth: Record from northern Switzerland

Following the extinction event at the Triassic – Jurassic boundary and during the Pliensbachian – Toarcian events, coral reef builders were severely affected, and the number of reef domains during the early Middle Jurassic was at an all-time low. However, new and updated data seem to show that corals were more widespread than previously thought, particularly during the Bajocian (170–168 Ma), but biostratigraphic markers are lacking to constrain the precise timing of reef evolution of this interval. A recently discovered 40 m-thick carbonate unit in northern Switzerland, on the northern Tethys margin, documents this rapid growth. Two cores from this unit display a reef with a high number of specimen but a low coral diversity, dated as Bajocian, which likely grew at a considerable water depth (upper limit of the mesophotic zone or 20–30 m). Additionally, it developed on top of clay mineral-rich accumulation characterised by low relief. Twelve different coral genera were identified, with a strong predominance of Periseris, Isastrea, Thamnasteria and Dendraraea. In the absence of other biostratigraphic markers, palynomorphs were used to provide accurate dating, which shows that palynology is a powerful tool for dating reef deposits. The results show reef growth during the early Bajocian, in the Sauzei and Humphriesianum ammonite zones, based on the palynological data, yielding similar ages to other Bajocian reef localities in the Eastern Paris Basin in France and Luxembourg dated simultaneously. These results indicate that the Middle Jurassic and more specifically the last two ammonite zones of the early Bajocian were periods suitable for coral reef builders, and that global regrowth of coral reefs occurred more rapidly than expected. A new Bajocian reef distribution is presented, showing no reefs at latitudes below 15°. This distribution pattern is probably due to the fact that water temperature was too elevated (> 25 °C) towards the equator for corals, which prevented reef growth. This would tend to favour a scenario in which the global climate, in particular temperature, is a determining factor for coral reef growth.

Intra-Turonian stratigraphic reorganization on the Arabian Plate

Shallow-marine carbonate deposition was widespread across the Arabian Plate during much of the Late Permian–Mesozoic but was significantly interrupted by a major tectonically driven stratigraphic reorganization that took place within the Turonian. Published literature terms this the ‘Wasia–Aruma Break’, the ‘mid-Turonian Unconformity’, or the ‘K150 Sequence Boundary (SB)’. It is widely understood that this event relates to subduction in a closing Neotethys Ocean and obduction onto the continental margin, especially in the southeastern part of the plate. As well as a change in facies, a hiatus of variable duration is present, associated with erosion of the underlying stratigraphy. Despite the event being known for several decades, precision on its timing has been lacking due to the limitations of biostratigraphic data and because few other chronostratigraphic proxies have been employed. In order to rectify this, all relevant biostratigraphic data from across the Arabian Plate have been synthesized and evaluated in the context of a review of chronostratigraphic calibration of standard biozones from multiple fossil groups. This shows that the youngest preserved rocks beneath the K150 SB can be assigned to the middle Turonian Helvetoglobotruncana helvetica planktonic foraminifera zone or Collignoniceras woollgari ammonite zone. The oldest rocks above the K150 SB can be assigned to the same biozones, supporting the assertions that it is a very short duration event. Whilst obduction may have initiated earlier (as supported by the recognition of precursor events), crustal loading was sufficient by 91.5 Ma to develop a forebulge in the eastern part of the plate with associated uplift and erosion. A review of relative sea-level change during the Turonian has been carried out to investigate eustatic signals during this time. In multiple sections around the world, a sea-level fall in the upper part of the woollgari Zone of European usage can be detected. This appears to coincide with an episode of climate cooling. However, despite there being correspondence between the K150 SB and a significant eustatic event, this seems mostly coincidental as the tectonic drivers at this time across Arabia were much more dramatic. This is especially true in southeastern Arabia. In northwestern Arabia, tectonic quiescence may have allowed eustasy to dominate. In any case, a eustatic fall would have amplified the effects of tectonics across the entire region.

Lower Valanginian ammonite biostratigraphy of the Cañón de la Vaca section, Taraises Formation, Coahuila state, northern Mexico

The present work carries out a biostratigraphic analysis of the Valanginian ammonite record from the Cañón de la Vaca section in the Sierra de Parras, Coahuila, Mexico. The collection of ammonites exhibits an abundance of specimens, representing a biodiverse range of taxa, and numerous occurrences throughout the biostratigraphic section. This record in the Taraises Formation allowed a solid identification and diagnosis of the ‘Thurmanniceras’ pertransiens, Neocomites neocomiensiformis and Karakaschiceras inostranzewi zones, along with the Neocomites premolicus, Neocomites neocomiensiformis, Busnardoites campylotoxus, Karakaschiceras inostranzewi and Neocomites platycostatus subzones. These biostratigraphic units corresponds to the lower Valanginian of the Standard Mediterranean Ammonite Zonation. Among the collected ammonites, numerous specimens of significant biostratigraphic importance remain scarcely known or lack a proper taxonomic identification. This situation has been already observed in other sections, such as Peña del Águila, Zacatecas, Mexico, and in the Betic Cordillera, southeast Spain. Fortunately, these unknown taxa can be compared with other sections in Mexico and with lower Valanginian ammonites from Spain, facilitating a more comprehensive biostratigraphic analysis. The present biostratigraphic analysis is expected to contribute to an increased understanding of lower Valanginian strata, thereby enabling future taxonomic and biostratigraphic research on the lower Valanginian in Mexico and globally.

Early Jurassic extrinsic solar system dynamics versus intrinsic Earth processes: Toarcian sedimentation and benthic life in deep-sea contourite drift facies, Cardigan Bay Basin, UK

The Cardigan Bay Basin (UK) may have functioned as a deep and narrow strait, and thereby influenced Early Jurassic oceanic circulation through the northern and southern Laurasian Seaway, and between Boreal and Peri-Tethys domains. Toarcian hemipelagic deposits of the basin in the Mochras borehole show strongly bioturbated contourite facies. Trace fossils are strongly dominated by Phycosiphon incertum (represented by four morphotypes), which was produced by opportunistic colonizers. Thalassinoides, Schaubcylindrichnus and Trichichnus are common (the latter is a deep-tier trace fossil produced by filamentous sulfide-oxidizing bacteria with a high tolerance for dysoxia), accompanied by less common Zoophycos, Planolites, Palaeophycus, Teichichnus, Rhizocorallium, Chondrites, and dwelling and resting structures, such as cf. Polykladichnus, Siphonichnus, Skolithos, Arenicolites, Monocraterion and Lockeia. Ichnological and lithological signals suggest repetitive fluctuations in benthic conditions attributed to a hierarchy of orbital cycles (precession and obliquity [4th order], short eccentricity [3rd order], long eccentricity [2nd order] and Earth–Mars secular resonance [1st order]). The Pliensbachian–Toarcian transition appears to be a significant palaeoceanographic turning point in the Cardigan Bay Basin, starting a CaCO3 decline, and with the most severe oxygen crisis of the Tenuicostatum Zone (here dysoxic but not anoxic) ending at the onset, in the early Serpentinum Zone (Exaratum Subzone), of the Toarcian negative carbon isotope excursion (To-CIE—linked with the Toarcian Oceanic Anoxic Event occurring in the lower part in the Serpentinum Zone). This trend contrasts with the prevalence of anoxia synchronous with the To-CIE in many other settings. Minor dysoxia returned to the Mochras setting in the latest Thouarsense to Dispansum zone interval. Extreme climate warming during the To-CIE may have enhanced and caused a reversal in the direction of deep marine circulation, improving oxygenation of the sea floor. Spectral analysis of binary data on ichnotaxa appearances gives high confidence in orbital signals and allows refined estimation of ammonite zones and the duration of the Toarcian (minimum ~ 9.4 Myr).

Late Cretaceous Sevier Versus Laramide Orogenies in Wyoming‐Utah‐Colorado, USA: New Insights From Basin Subsidence History

AbstractVariability in subsidence rates within Upper Cretaceous strata of the Western Interior Basin offers crucial insights into the response of surface sedimentation styles to Sevier‐to‐Laramide tectonics and related deep mantle processes. The formation mechanisms of the Late Cretaceous Western Interior Basin in North America have long been a subject of debate. A re‐evaluation of the basin's subsidence history reveals rapid subsidence pulses lasting ca. 2 Myr within longer‐term (average 5.7 Myr) progradational or aggradational clastic wedges. The timing of these wedges, especially the widespread marine flooding resulting from subsidence, is constrained through the calibration of ammonite zonation with absolute dates. Sevier wedges exhibit a different architecture compared to the Laramide wedges. The former recorded initial rapid and widespread marine transgressions followed by long‐term coastal progradation, whereas the latter developed by initial erosional and progradational growth followed by aggradation and long‐term coastal transgression. The Sevier clastic wedges, initially accumulated within a N‐S elongated, long‐wavelength tectonic subsidence zone close to the thrust belt, gradually migrated cratonward. Starting in the early Campanian (ca. 82 Ma), the Laramide Orogeny developed along a NW‐SE trend and then migrated northeastward, roughly consistent with coeval long‐wavelength frontal basin subsidence. The spatio‐temporal variations in long‐wavelength tectonic subsidence indicate a shift in the dynamic subsidence's migration direction from eastward to northeastward, driven by changes in Farallon subduction direction and mode. Our work shows how repeated subsidence behavior in the Sevier‐to‐Laramide transition records evolving architectural responses and the trajectory of coeval dynamic topography.

Duration of ammonite zones and characteristic Jurassic fossil taxa from the Pliensbachian–Aalenian successions of Bulgaria

The relative durations of ammonite biozones and selected ammonite taxa, as well as some bioevents associated with coeval Lower–Middle Jurassic benthic taxa are represented herein. Based on linked Sr-isotope data, we found a notable difference in the time spans of the zones and in the relative longevity of the guiding ammonite genera around the Pliensbachian/Toarcian (P/T) boundary. The last occurrences of the well-known late Pliensbachian bivalve taxa Gryphaea gigantea and Pseudopecten aequivalvis were dated at 184 Ma and 183.8 Ma, respectively. Recently defined Toarcian–Aalenian autochtonous brachiopod taxa (Bulgariarhynchia and Capillirhynchia brezenensis) were found to have significant taxonomic durations (2 Ma and 5 Ma). The Sr-isotope data also revealed ~2 Ma duration of seawater warming and 0.2 Ma fossil hiatus around the P/T boundary.

The Neogondolella constricta (Mosher and Clark, 1965) group in the Middle Triassic of North America: speciation and distribution

AbstractNeogondolella constricta (Mosher and Clark, 1965) from the Prida Formation at Fossil Hill in central Nevada was the first conodont described from Middle Triassic strata in North America. The species has since been widely reported from elsewhere despite uncertainties about its taxonomic scope and that of similar related taxa. Poor definition of these taxa has spawned a diverse nomenclature and inhibited use of the group in biozonation. Starting with a growth series of topotype N. constricta, we reassess allied contemporaneous taxa from North America. In Nevada, 11 conodont taxa are identified: N. constricta, N. aldae Kozur, Krainer, and Mostler, 1994b, N. cornuta Budurov and Stefanov, 1972, N. ex gr. mesotriassica (Kozur and Mostler, 1982), N. postcornuta (Kovács, 1994), N. posterolonga Kozur, Krainer, and Mostler, 1994b, N. quasiconstricta n. sp., N. quasicornuta n. sp., and three subspecies of N. excentrica Budurov and Stefanov, 1972. Successive associations of taxa display symmetry transition in posterior platform configuration. Subdivision of the upper Anisian–lower Ladinian is provided by dominant N. constricta plus relatively uncommon N. quasiconstricta n. sp. and N. excentrica primitiva n. subsp. in the Rotelliformis ammonoid zone. This is followed in the Meeki through the Subasperum zones by dominant N. cornuta, associated N. posterolonga, plus relatively uncommon N. quasicornuta n. sp., and a variety of asymmetric elements: the Meeki Zone includes N. aff. N. cornuta; the Occidentalis Zone adds N. e. excentrica; and finally, N. e. sigmoidalis n. subsp. appears in the Subasperum Zone. In British Columbia, the three subspecies of N. excentrica are recognized in, respectively, the Deleeni, Chischa, and Matutinum (and younger) ammonoid zones.UUID: http://zoobank.org/7d58c8c8-cd68-498f-bb84-5d43de47f779

Re-Os geochronology of the Middle to Upper Jurassic marine black shales in the Agardhfjellet Formation, Central Spitsbergen, Svalbard: A cornerstone for global faunal correlation and Os isotopic change

Ammonite provincialism makes it difficult to link the Boreal and Tethyan realms during the Late Jurassic to Early Cretaceous time. Absolute ages through radiometric dating offer new age information that is independent and complementary to relative ages based on biostratigraphy. In this study, we report seven new Re-Os ages for black shales from the Agardhfjellet Formation, Svalbard. We also report pyrolysis results, carbon and sulfur stable isotopic data, and initial 187Os/188Os ratios to evaluate the paleoenvironment during organic-rich shale deposition. Re-Os ages are derived from three Boreal ammonite zones: (1) 159.2 and 160.1 Ma from the shale intervals containing Cadoceras sp.; (2) 149.6, 149.9, 150.8, and 151.9 Ma from the Rasenia cymodoce Zone in the Early Kimmeridgian, which is the equivalent of the Sutneria platynota and Ataxioceras hypselocyclum zones in the Tethyan realm; (3) 146.8 Ma from an upper Volgian interval above the occurrence of Laugeites sp.. Within this 14.5 Myr interval, the initial Os profile shows a gradually increasing trend from 0.335 (one of the lowest shale values throughout the Phanerozoic) to 0.529, consistent with previous initial Os studies and Sr isotopic ratio chemostratigraphic studies. The trend of increasing initial Os ratios indicates an increase in continental runoff relative to unradiogenic Os input from mantle sources, such as seafloor hydrothermal activity or ultramafic source rocks. We provide new Re-Os geochronological anchors in the Late Jurassic with new Re-Os ages and propose correlations of specific Late Jurassic ammonite zones between the Tethyan and Boreal realms. In turn, the gradual increase in seawater Os isotopic ratios may signal climate change in the Late Jurassic, indicating the increase of radiogenic Os or decrease of unradiogenic Os, induced by high continental runoff or less hydrothermal/volcanic activity.

Report on the 7th International Meeting of the IUGS Lower Cretaceous Ammonite Working Group, the Kilian Group (Warsaw, Poland, 21st August 2022): State of the art on the current Standard Ammonite Zonation of the Western Tethyan Mediterranean Province

The 7th meeting of the IUGS Lower Cretaceous Ammonite Working Group the ‘Kilian Group (KG)’ was held in Warsaw, Poland, on 21st August 2022. Need of major changes for the Jurassic/Cretaceous transition, namely to the uppermost Tithonian and lower Berriasian, and for the upper Aptian and Albian schemes is a long-known issue, which are finally conceptualized and hereby introduced into the Standard Mediterranean Ammonite Zonation (SMAZ, Western Tethys). Besides, refinements were added to the Valanginian and Hauterivian stages, discussion on some zonal indices and units are also provided. The KG highlights again the exclusive use of interval zones and subzones.Most important changes of the uppermost Tithonian–Berriasian stages are the followings: i) use of two folded Berriasian is agreed, to be in better accordance with ammonite turnovers and microfossil framework; ii) uppermost Tithonian Lopeziceras chaperi, top-uppermost Tithonian to lowermost Berriasian Praedalmasiceras progenitor and lower Berriasian Pseudosubplanites grandis Zones are accepted to be introduced into the SMAZ, these three zones to cover the former ‘Berriasella’ jacobi Zone auctorum which is formally abandoned; iii) lower Berriasian Delphinella delphinensis Subzone is accepted as a reliable marker level of the upper Praedalmasiceras progenitor Zone; iv) Strambergella jacobi Zone is established and discussed. Tirnovella occitanica Zone and Tirnovella subalpina Subzone are discussed.Modifications on the Valanginian zonation are the followings: i) Neocomites premolicus Subzone is re-defined, ii) Neolissoceras (Vergoliceras) salinarium Subzone is introduced; iii) Neocomites neocomiensiformis Zone is divided into two subzones, the lower N. neocomiensiformis and the upper Busnardoites campylotoxus Subzones. Modifications on the Hauterivian stage are the followings: i) all horizons are deleted; ii) Olcostephanus (Olcostephanus) variegatus Subzone is introduced; iii) Balearites angulicostatus Subzone is introduced; iv) all subzonal index-species of the B. balearis Zone are assigned to genus Balearites; v) Pseudothurmannia mortilleti is considered as a senior synonym of P. catulloi, therefore its nominal subzone also changed its name to mortilleti.No change in the Barremian scheme, however the base of Toxancyloceras vandenheckii Subzone and Zone is defined by the first appearance of the genus Toxancyloceras.Most important changes of the upper Aptian zonation are the followings: i) Nolaniceras nolani and 'Hypacanthoplites jacobi' zones are retained from the SMAZ; ii) re-introduction of Diadochoceras nodosocostatum Zone is given. For the Aptian–Albian transition interval, introduction of ‘Hypacanthoplites’ elegans Zone is accepted, where the Aptian/Albian boundary lies within.Most important zonal changes of the Albian stage are: i) the Leymeriella-based succession is abandoned from the SMAZ and replaced by the cosmopolitan Douvilleiceras-based succession; ii) Douvilleiceras leightonense Zone is introduced; iii) middle Albian Hoplites dentatus, Euhoplites loricatus, Euhoplites lautus Zones and Hoplites spathi Subzone are retained from the SMAZ and restricted to the Boreal ammonite scheme; iv) Lyelliceras lyelli Subzone arisen to zonal rank defining the basal middle Albian; v) Oxytropidoceras (Oxytropidoceras) roissyanum Zone is introduced; vi) upper Albian zonation based on the phyletic lineage of Mortoniceratids is kept, however generic names of the indices are modified to Pervinquieria; vii) Pervinquieria pricei Zone is divided into three subzones of Hysteroceras varicosum, H. binum and H. choffati from the oldest to youngest; viii) Pervinquieria inflata Zone is divided into two subzones of Hysteroceras bucklandi and Cantabrigites spp.The KG tributes to our recently deceased ammonitologist colleagues in the Supplement, a discussion on the future work is provided. The next Kilian Group meeting will be held in Hannover, prior to the first day of the 12th International Symposium on the Cretaceous System.

Upper Cenomanian caprinulid-radiolitid rudists (Bivalvia) from the Gattar Member of Jebel el Kebar (central Tunisia): Stratigraphical implications and palaeobiogeographical relationships with coeval rudist-assemblages from carbonate platforms of the southern Tethyan margin

The Gattar Member (upper part of the Zebbag Formation) is a prominent dolomitic limestone unit in Tunisia, the age of which was ascribed either to the Turonian, the Cenomanian, or the Cenomanian−Turonian. Here, we present the discovery of a Caprinulidae-Radiolitidae rudist asssemblage in the Gattar Member of Jebel el Kebar (central Tunisia). This consists of Caprinula cf. boissyi, Sauvagesia cf. sharpei, Durania arnaudi, Neocaprina sp. and Eoradiolites sp. The detailed description of two sections of the Gattar Member in Jebel el Kebar allows us to define the sedimentological and palaeoecological attributes of the rudist-bearing carbonates and their sequential relationships with the Zebbag and Rouana stratigraphical units respectively. The caprinulid-radiolitid assemblage is age-calibrated, based on the ammonite standard zonation of the Cenomanian stage from Portugal, South-Eastern France, and Oman, where rudist, benthic foraminifera and ammonite Zones have been correlated. Its age is late Cenomanian. The correlations of the Gattar Member between central Tunisia and the Gafsa-Chotts area are established on the base of ammonite and rudist biostratigraphical markers. The age of the Gattar Member of southern Tunisia and of its stratigraphical counterpart in western Libya is discussed. At last, we analyze the palaeobiogeographical distribution of the upper Cenomanian caprinulid-radiolitid assemblages from coeval carbonate platforms of the North African margin (Algeria, Morocco) and of the North Arabian margin (Levant region: Syria, Jordan, Lebanon, Israel, North Sinai).

Microcrinoids (Roveacrinidae) from the middle–upper Cenomanian Grey Chalk Subgroup, Dover (Kent, United Kingdom): biostratigraphy and re-evaluation of cup structure in roveacrinids

New material of Roveacrinidae from the middle–upper Cenomanian Grey Chalk Group of the Kent coast (Folkestone-Dover) is described. The fauna includes 10 taxa, including a new genus and species ( Dubrisicrinus minutus) and three new species ( Styracocrinus shakespearensis, Roveacrinus aboudaensis and Dentatocrinus serratus). The biostratigraphical significance of roveacrinid faunas is placed in a global context, and it is demonstrated that the roveacrinid zone CeR5, previously recorded only from Morocco, is approximately equivalent to the upper middle Cenomanian Acanthoceras jukesbrownei ammonite Zone, and zone CeR6 – to the Calycoceras guerangeri ammonite Zone. The new material also provides novel information on the cup structure of roveacrinids, which is reviewed and placed in a phylogenetic context.

Integrated biostratigraphy (orbitolinids, calcareous nannofossils, and palynomorphs) of the Lower Cretaceous Sarcheshmeh Formation, western Koppeh-Dagh Basin, NE Iran

An integrated biostratigraphy using orbitolinids, calcareous nannofossils, and dinoflagellate cysts was conducted on the Lower Cretaceous Sarcheshmeh Formation in two stratigraphic sections from the western Koppeh-Dagh Basin (NE Iran). The analyzed successions consist mainly of deep-marine shales and marlstones with intercalations of thin-bedded orbitolinid-bearing limestones. These strata yielded common to abundant and fairly well to well-preserved calcareous nannofossil assemblages. The aforementioned assemblages led to the identification of parts of the NC6 and NC7a biozones that can be correlated with parts of the CC7a and CC7b zones. The organic-walled dinoflagellate cysts also show well-preserved and relatively diverse assemblages in the studied sections that corresponded to the Odontochitina operculata Zone. Additionally, within the limestone intercalations of the Sarcheshmeh Formation, two index species of orbitolinids, Praeorbitolina cormyi Schroeder, and P. wienandsi Schroeder, were recorded, indicating the presence of the Praeorbitolina cormyi Zone. According to the literature, these recognized biozones are compatible with the ammonite zones of Deshayesites forbesi, Deshayesites deshayesi, and Dufrenoyia furcata, as well as the Globigerinelloides blowi and Leupoldina cabri planktonic foraminiferal zones. By the compilation of all acquired data, an age of late early Aptian (late Bedoulian) is deduced for the Sarcheshmeh Formation in the studied sections.

Les ammonites les plus récentes du Luxembourg et de la région frontalière franco-luxembourgeoise : Sonniniidés, Stephanoceratidés et Sphaeroceratidés du Bajocien (Jurassique moyen).

The youngest Mesozoic sediments in Luxembourg are those of the Bajocian in the southwestern part of Luxembourg along the French border. The “Marnes sableuses d’Audun-le-Tiche” and the “Calcaire de Nondkeil“ units had previously been dated from the Lower Bajocian Humphriesianum ammonite zone, based on sporadic ammonite findings reported in the literature. Re-studying material from the collection of the Luxembourg National Museum for Natural History allowed identifying 17 ammonite species from the families Sonninidae, Stephanoceratidae and Sphaeroceratida. The herein described ammonites provide evidence that all three subzones of the Humphriesanum Zone, namely the Romani, Humphriesianum and Blagdeni subzones, are present in the Rumelange area. The stratigraphically youngest ammonite from the Grand-Duchy is represented by one specimen of Teloceras from the plateau south of Differdange.

New Insights into the Platform-to-basin Anatomy of the Urgonian Bas-Vivarais Domain (Lower Cretaceous; SE France)

This paper offers a new contribution to our ongoing harmonization efforts concerning the chronostratigraphic model of the southern France Urgonian-type carbonate platforms, which surrounded the Vocontian Basin during the Early Cretaceous. A multi-stratigraphic approach on the classical sections of the Ardèche River gorges and the Saint-Remèze Plateau have been used for reconstructing the evolution of the Bas-Vivarais Urgonian domain along an inner-to-outer platform profile; the latter being nearly perpendicular to the eastern Vocontian platform margin. In our transect, the installation and first developments of the Urgonian platform domain occured during the early Barremian Taveraidiscus hugii and Kotetishvilia nicklesi ammonite zones. This first platform stage was interrupted at a brief emersion episode that lasted through the Nicklesia pulchella ammonite zone, and resulted in the deposition of a sedimentary wedge with limited gradual downward, basinward shift in inner platform facies. This was followed by the regional deposition of shallow-water communities dominated by corals, echinoids, and orbitolinids, which passes basinward into open-marine, ammonite-bearing marly deposits in the Saint-Remèze Plateau outcrops. This change in facies was previously referred to as the Serre de Tourre Beds (STB), and dated to the Kotetishvilia compressissima and Moutoniceras moutonianum ammonite zones. The STB are further identified to as the local sedimentary expression of the Mid-Barremian Event recording a brief warming climate pulse testified by the presence of Offneria simplex, a caprinid rudist of Caribbean origin. Above, there is a regional recovery of inner platform Urgonian facies during the early late Barremian showing a striking progradational basinward trend. The latter, and its subsequent developments are in need of investigations. Taken together, the general evolution of the Urgonian Bas-Vivarais domain shows strong similarities with the sedimentary context of the nearby Subalpine Urgonian platform during the early Barremian. The finding of common sedimentary signals is more difficult with the Provence platform domain at that time.

A new lower Turonian mosasaurid from the Western Interior Seaway and the antiquity of the unique basicranial circulation pattern in Plioplatecarpinae

We describe and name a new mosasaur taxon, Sarabosaurus dahli gen. et sp. nov., from the lower Turonian part of the Tropic Shale in Utah, USA. The holotype specimen preserves significant portions of the skull and axial postcranial skeleton. It was found in the upper part of the Watinoceras devonense Ammonite Zone, bounded by radioisotopic dates above and below, and is thus about 93.7 Ma, the oldest mosasaurid taxon known from the Western Interior Seaway. The new taxon possesses a vascular pattern of the basisphenoid heretofore only seen in late diverging plioplatecarpine mosasaurids. Reevaluation of the morphology of the basisphenoid of previously described Turonian mosasaurs using μCT techniques reveals the derived condition is also present in Yaguasaurus and the incipient condition in Tethysaurus and Russellosaurus. In these two taxa, the canals enter the basisphenoid, but do not pass into the basioccipital. Instead, they exit only high on the posterior wall of the sella turcica, in a position similar to the basilar artery of other lizards. This vascular pattern, both in its incipient and derived states, is unique among squamates and supports inclusion of the aforementioned taxa in a monophyletic Plioplatecarpinae, for which we provide an emended diagnosis. Phylogenetic analysis recovers Sarabosaurus dahli gen. et sp. nov. as the sister taxon to Yaguarasaurus and all other later diverging plioplatecarpines, with Russellosaurus and Tethysaurus as successive sister taxa. Tylosaurine mosasaurids retain the primitive condition of the basisphenoid vascularization pattern and implies a tylosaurine-plioplatecarpine divergence in the late Cenomanian or earliest Turonian.

Astronomical timescale for the early Toarcian (Early Jurassic) Posidonia Shale and global environmental changes

Lower Toarcian sediments (Early Jurassic, c. 183 Ma) record the Toarcian Oceanic Anoxic Event (T-OAE), which represents a period of profound environmental changes. The event involved the widespread deposition of organic carbon-rich strata in oxygen-depleted paleo-shelf settings, global warming, and is characterized by a negative Toarcian carbon-isotope excursion (T-CIE). The T-CIE provides a global time-correlative chemostratigraphic marker; however, its age, duration and underlying causes remain uncertain in the absence of an accurate early Toarcian timescale. This article presents a cyclostratigraphic framework for the lower Toarcian Posidonia Shale Formation from the Dotternhausen Quarry (South German Basin), one of the best-studied sediment archives that record early Toarcian environmental and ecosystem changes. The Posidonia Shale in the study site was deposited in the deeper part of the epicontinental shelf sea, where sediment accumulation rates were relatively uniform and major hiatuses unlikely. These factors are rarely found in most sections, and favor obtaining accurate cyclostratigraphic results at the study site. Our astronomical timescale indicates that black shale deposition at the site lasted about ∼3.2 Myr, a remarkably long period for sufficient primary productivity in stagnant bottom-water conditions. The estimated durations of the tenuicostatum and falciferum ammonite zones, and the T-CIE are ∼0.9, ∼1.8 and ∼ 1.2 Myr, respectively. Early Toarcian global warming, accompanying the T-CIE, occurred over a period of ∼400 kyr. Early Toarcian 3rd-order sea-level cycles correlate to 1.2 to 1.6 Myr orbital cycles, reflecting long-term obliquity and eccentricity periods. Orbitally-forced 3rd-order sea-level cycles, in combination with 405 kyr long-eccentricity, and potentially 100 kyr short-eccentricity cycles, controlled sea-floor oxygenation and deposition of black shales. Short-term environmental changes (e.g., redox cycles), responding to long- and short-eccentricity cycles were most pronounced during 3rd-order sea-level lowstands, when the depositional environment was most susceptible to short-term environmental instabilities. Our results highlight orbital-forcing as a key driving mechanism for early Toarcian environmental conditions.

Biostratigraphy of Bajocian–Oxfordian strata based on dinoflagellate cysts and ammonites from the Dalichai Formation, northeastern Iran

The Bajocian–Oxfordian Dalichai Formation of the Binalud Mountains (northeastern Iran) consists of marls, marly limestones and limestones that were sampled and studied in detail for their palynomorph and ammonite contents. Palynological studies enabled differentiation of three marine biozones (Cribroperidinium crispum, Dichadogonyaulax sellwoodii, and Ctenidodinium continuum) within the lower interval of the formation. The palynofacies analysis shows a gradual sea-level rise during the depositional period of the rock unit, while terrestrial palynomorphs (spores and pollen grains) revealed a predominantly tropical climate for the time interval. Furthermore, a large number of ammonites were recovered from the formation, based on which 12 families, 22 genera, 30 species and 12 biozones (Zigzag, Aurigerus, Retrocostatum, Discus, Bullatus, Gracilis, Anceps, Coronatum, Athleta, Transversarium, Bifurcatus, and Bimammatum) were differentiated. When comparing the dinoflagellate cyst zones with the ammonite zones, the Dichadogonyaulax sellwoodii dinoflagellate cyst zone was correlated with the ammonite zones of Zigzag, Aurigerus, Retrocostatum, Discus, Bullatus, and Gracilis and the Ctenidodinium continuum dinocyst zone was correlated with the Gracilis and Anceps ammonite zones. The dinocyst and ammonite assemblages of the Binalud Mountains are similar to assemblages described from northern and northeastern Iran (Alborz and Koppeh-Dagh basins) as well as Northwest Europe. This suggests marine connections between these sedimentary basins during the Bajocian–Oxfordian. Consequently, the integrated dinocyst and ammonite zonation established here can be utilized also in other parts of the northern Tethyan Realm. The diachroneity of the upper boundary of the Dichadogonyaulax sellwoodii Zone between the Binalud Mountains and Northwest Europe is however revealed by comparison with the ammonite zones.

Stratigraphy, palaeontology and sedimentology of the Upper Cretaceous of northern Tademait (Sahara, Algeria)

Thorough sedimentological and palaeontological analyses of four expanded Upper Cretaceous sections in northern Tademait had allowed us to address and reconsider the stratigraphical framework of the so-called ‘Continental Intercalary’ and ‘Hamada series’ in this remote Saharan area. These four sections (i.e., Meguidene, Gara Samani, Oued El Mezaourou-Gour Louazouaza, and El Menia) document Upper Cretaceous strata overlying post-Palaeozoic substrata and ranging from the clastic Gara Samani Formation (of supposed early Cenomanian age), through the El Golea Clays (lower–middle Cenomanian), the Gour Louazouaza Formation (lowermost upper Cenomanian, with the Oued El Mezaourou Limestone Member ranging from the Neolobites vibrayeanus to the Vascoceras gamai ammonite zones of the uppermost Cenomanian, and the Marls of Gara Mta El Mar Member of the Choffaticeras sinaiticum ammonite Zone in the lower, but not lowermost, Turonian), to the Ain El-Hadjaj Formation (of alleged Campanian age). Most efforts have concentrated on the ‘mid’-Cretaceous deposits that yield vertebrates and diversified ammonite and macrofossil assemblages. In spite of these improved correlations, further bio-chronostratigraphical data are needed in order to constrain the stratigraphical gap within the Gour Louazouaza Formation at the Cenomanian–Turonian boundary (C/TB) better. The succession studied can be correlated with other similar-aged sections in North Africa and illustrates the development of braided fluvial and aeolian dune-interdune environments followed by a ramp depositional system in response to the early Late Cretaceous second-order sea level rise along the southern margin of the Tethys.

Upper Oxfordian (Upper Jurassic) radiolarians from Rybaki Section, Moscow Region, Central Russia

A well-preserved radiolarian assemblage was recovered from the Upper Jurassic section near the Rybaki village, Moscow Region, Central Russia. The radiolarians were found within the Amoeboceras serratum ammonite zone (upper Oxfordian), in phosphatized body chambers of ammonite shells. The radiolarian assemblage is represented by 23 species of 11 genera and displays Boreal affinity. It is characterized by abundance of Praeparvicingula: P. blackhorsensis (Pessagno and Whalen), P. donnae Bragin, P. elementaria (Carter), P. enormis (Yang) and by presence of the characteristic boreal family Echinocampidae (genera Echinocampe and Nordvikella). Five new species are described.

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.