Early Berriasian Research Articles

New record of Brachyoxylon wood from the Lower Cretaceous of Qingyuan, southeastern China and its palaeoclimatic implications

Early Cretaceous was a key period for the evolution of terrestrial ecosystems. In southeastern China, the late Early Cretaceous (Aptian–Albian) floras are relatively well known and characterized by diverse Cheirolepidiaceae, but the early Early Cretaceous floras in southeastern China are poorly known mainly because of the lack of plant fossils. Here we report petrified woods from a new early Early Cretaceous locality in Qingyuan, southern Zhejiang Province, southeastern China. The new fossil woods collected from the Xishantou Formation (earliest Berriasian, earliest Early Cretaceous) are assigned to Brachyoxylon zhejiangense Tian, Zhu, and Wang based on the anatomy of the secondary xylem. The new material of Brachyoxylon zhejiangense from Qingyuan lacks distinct growth rings or resin canals and has mixed type pitting on the radial walls of the tracheids, araucarioid cross-field pitting, and uniseriate rays. It is the earliest record of Brachyoxylon in southeastern China. Brachyoxylon zhejiangense has been regarded as the wood of the extinct conifer family Cheirolepidiceae and grew in arid to semi-arid environments. Evidence also suggests Cheirolepidiaceae played an important role in the vegetation of southeastern China throughout the Early Cretaceous.

No stable coastline in the Monterrey Trough during Late Jurassic to Early Cretaceous! - Comment on Ocampo-Díaz et al. (2022): doi: 10.1016/j.jsames.2022.103759

The following is a comment on the paper: “A wave to tidal influenced deltaic coastline in a carbonate environment: The Late Jurassic to Early Cretaceous La Casita Formation, northeastern Mexico” by Ocampo-Díaz et al. (2022). The authors presented a sedimentological and paleogeographical study of the La Casita Formation, Monterrey Salient, Sierra Madre Oriental. Although this study offers a detailed facies analysis, it shows some need for discussion regarding the study area's stratigraphic and regional geological classification. The article mentions missing or insufficiently treated geological units such as the Carbonera Formation, San Juan Lentil, and Galeana Member. The Coahuila Block, Sabinas Basin, and Tamaulipas Arch are in an erroneous stratigraphic and regional geological context. This comment takes up these weak points and tries to correct them. This comment offers the missing stratigraphic table of the La Casita/Carbonera and the La Casita/Taraises boundary. The siliciclastic deposition of the La Casita Formation ends in the Early Berriasian. Finally, the faulty paleogeographical reconstructions of the authors are countered by an alternative model which shows the pro- and retrograding sedimentation of the La Casita Formation during Tithonian to Berriasian, the development of the San Juan Lentil at Late Berriassian, and the development of the open shelf carbonates of the Taraises Formation, such as the contemporary Carbonera Formation and Galeana Sandstone Member (Valanginian to Hauterivian).

Early Berriasian to Early Barremian Calcareous Nannofossils Biostratigraphy and Paleoecology of Baghamshah Formation (Esfandiar Section, Tabas Block), Eastern Iran

The Baghamshah Formation was previously assigned to Jurassic age in Iran, based on stratigraphic distribution of ammonites. But, recent studies of calcareous nannofossils in the Lut Block show that the age of this formation should be assigned to the Early Cretaceous (early Berriasian to early Barremian). This study analyzed stratigraphic distribution of calcareous nannofossils of the Baghamshah Formation in the Esfandiar section located in the southeast of the Tabas Block (close to the type section). Examinination of samples identified 39 calcareous nannofossil and 6 didemnid ascidian spicules species belonging to 19 genera, corresponding from CC1 to CC5 biozones with the age of early Berriasian to early Barremian. Index nannofossil species in the succession indicate that the sedimentary basin of the Baghamshah Formation in the Esfandiar section was located in low latitudes of the Tethyan realm with warm surface water toward the top of the section. Also, the oceanic basin was an oligotrophic type with low-fertility, as its nutrient supply dropped toward the top of the section. The oligotrophic paleoenvironment during the late Berriasian to early Valanginian in the study area in eastern Iran may have corresponded to a global low sea-level.

Calcareous nannofossil biostratigraphy of Baghamshah Formation in Eastern Iran, Lut Block (Birg Section)

Biostratigraphic studies of the Baghamshah Formation from the Birg section in the northwest of Birjand (Lut Block) are done here for the first time based on the calcareous nannofossils. In the studied section, 82 samples were taken, and smear slides were prepared. The examination of the collected samples resulted in the identification of 65 calcareous nannofossil and 11 didemnid ascidian spicules species belonging to 38 genera corresponding from CC1 to CC4b biozones with the age of early Berriasian to early Hauterivian, according to the Sissingh biozonation. The calcareous nannofossil assemblages are dominated by the following genera: Watznaueria, Nannoconus, Conusphaera, and Cyclagelosphaera. Keywords: Birjand, Baghamshah Formation, biozonation, Biostratigraphy, Early Berriasian, Early Hauterivian.

Biostratigraphy of Baghamshah Formation based on calcareous nannofossils in the Southwest Tabas, Iran

The Tabas Block is part of the Central Iran microcontinent, located between the Lut Block in the East and the Yazd Block in the West. The Baghamshah Formation is the second lithostratigraphic unit from the sedimentary cycle of the Magu Group and the Baghamshah Subgroup in the Jurassic of Tabas Block. This formation is conformably underlaid with the grey pisoidal limestones of the Parvadeh Formation and overlaid with the Pectinid limestones of the Kamar-e-Mehdi Formation (Esfandiar Subgroup). In this research, the biostratigraphy of the Baghamshah Formation in the Rizu and Kamar-e-Mehdi sections, based on calcareous nannofossils, is examined. The thickness of the Baghamshah Formation in the Rizu section is 270 m (mostly including marl and green shales with intercalation of limestones and calcareous sandstones), and in the Kamar-e- Mehdi section is 236 m (composed of gypsiferous marly shales, marl, marly shales and alternation of marl-shale with limestones and calcareous sandstones). According to the taxonomic studies in the Rizu section, 52 species belong to 24 genera, and in the Kamar-e-Mehdi section, 45 species belong to 23 genera of calcareous nannofossils. Based on index calcareous nannofossils, the CC1, CC2, CC3, and CC4 biozones established by Sissinghh in both sections were determined. It is mentioned that CC5 biozone only occur in Kamar-e-Mehdi section. According to the identified biozones, the suggested age of the Baghamshah Formation is early Berriasian–early Hauterivian in the Rizu section, and early Berriasian–late Hauterivian in the Kamar-e-Mehdi section. Keywords: biostratigraphy, Baghamshah, calcareous nannofossils,Tabas, Iran.

Mineralogy and geochemistry of deeply-buried marine sediments of the Vaca Muerta-Quintuco system in the Neuquén Basin (Chacay Melehue section), Argentina: Paleoclimatic and paleoenvironmental implications for the global Tithonian-Valanginian reconstructions

The Vaca Muerta-Quintuco (VM-Q) system of Tithonian-early Valanginian age was studied in the Chacay Melehue section of the Neuquén Basin (western Argentina) by means of sedimentological, mineralogical and geochemical analyses in order to determine the main driving factors that triggered the paleoenvironmental change from a carbonate ramp (Vaca Muerta Formation, VMFm) to a mixed siliciclastic/carbonatic marine environment (Quintuco Formation, QFm). The VMFm was divided into two stratigraphic intervals: Lower VMFm (LVMFm) and Upper VMFm (UVMFm), whereas the QFm is subdivided into the Puesto Barros Member (PBMb) and the Cerro La Visera Member (CVMb), which can be correlated to other sections in the basin (e.g., Puerta Curaco). Isolated, turbiditic sandstone beds, correlated to the Huncal Member, are included in the QFm.The LVMFm (Tithonian) and the UVMFm (Berriasian) are constituted by dark, well-laminated marls, mudstones, calcite concretions and tuffs. The PBMb (earlier early Valanginian) is constituted by marls and sandstones, whereas the CVMb (later early Valanginian) is constituted by marls, mudstones, siltstones, sandstones and coquinas. The LVMFm (Total organic carbon, TOC ~ 1–4 wt%) is characterized by the enrichment of redox sensitive trace elements (RSTE), where the enrichment of Ni and Cu suggest high productivity in the water column, and the enrichment of Mo, U, V points to sea bottom anoxia, with periods of increased oxygenation as deduced from higher P concentrations in marls and mudstones. The clay mineral association is constituted by mixed-layer illite/smectite formed by the transformation of smectitic layers. The predominance of smectite in coeval sucessions, less overprinted by burial diagenesis, suggests a temperate and semi-arid climate in the adjacent continent. The UVMFm (TOC ~ >1 wt%) is characterized by a gradual decrease of the RSTE pointing to a decrease in productivity and a slight increase in the oxygenation of the sea bottom. In addition, a change towards more humid conditions in the continent is inferred by both the increase in the Chemical Index of Alteration and the Al2O3/TiO2 ratio. The PBMb (TOC ~1 wt%) has even lower content of RSTE indicating diminished sea water productivity and a gradual rise of the oxygenation of the sea bottom. In this interval, increased illite contents suggest periods of enhanced physical weathering, probably related to the tectonic uplift of the Huincul Ridge. The RSTE in the CVMb (TOC <1 wt%) documents a fully oxygenated sea bottom, where the productivity of the water column was negligible. The presence of kaolinite and the increment of the detrital sedimentation in the CVMb indicate a change towards more humid conditions in the hinterlands. The enhanced runoff caused by this paleoclimatic change towards more humid conditions that started in the early Berriasian and increased during the later early Valanginian triggered the change from carbonate ramp to mixed siliciclastic/carbonatic to siliciclastic marine paleoenvironments. The organic carbon isotope composition (δ13Corg vs. VPDB) of the VMFm ranges between −30.0 and −23.4‰, whereas in the QFm values range between −29.0 and −23.9‰. Two positive carbon isotope excursions (PCIE) are recorded in the system: PCIE-A in the lower part of the VMFm (early Tithonian) with δ13Corg values ~ −25‰, and PCIE-B in the upper part of the QFm (later early Valanginian) with δ13Corg values ~ −24.5‰. The shift in δ13Corg at PCIE-B is up to +4.2‰ and marks the onset of the Weissert Event. This is the first time that the onset of this event is recorded in the Neuquén Basin, within the Lissonia riveroi ammonite zone. The results of our study confirm that clay mineralogy, trace elements and stable isotopes are valuable proxies of past ocean-climate variability even in sediment deposits that underwent near-surface and deep burial diagenesis.

Macrofauna and biostratigraphy of the Rollrock Section, northern Ellesmere Island, Canadian Arctic Islands – a comprehensive high latitude archive of the Jurassic–Cretaceous transition

The Rollrock Section in the Sverdrup Basin of Arctic Canada is one of the northernmost outcrops where the Jurassic-Cretaceous transition is accessible. The over 500 m thick sedimentary succession exposes the Oxfordian to Valanginian Ringnes and Deer Bay formations. Macrofauna from 15 discrete horizons includes ammonites, Buchia bivalves and belemnites. These fossils improve the biostratigraphy of the Tithonian and Berriasian in the Sverdrup Basin, provide correlation to the remainder of the Boreal Realm and set reliable calibration points. The occurrence of Buchia rugosa in the Ringnes Formation moves the upper formation boundary from the top of the Kimmeridgian into the lower Tithonian. Dorsoplanites maximus and D. sachsi document the middle Tithonian Dorsoplanites maximus Zone in Arctic Canada for the first time. The late Tithonian to early Berriasian Buchia terebratuloides is considered to be the best approximate indicator of the Jurassic-Cretaceous transition in the Rollrock Section. The middle early Berriasian Praetollia maynci and the late early Berriasian Borealites fedorovi tie the respective horizons to the successive Chetaites sibiricus and Hectoroceras kochi zones. Two species of the belemnite Arctoteuthis, collected from an interval with common glendonites, suggest a Valanginian age for the upper Deer Bay Formation. The dearth of Late Jurassic to earliest Cretaceous macrofossils in the Sverdrup Basin is inferred to be predominantly a function of diagenetic carbonate loss. Abundant dropstones and glendonites in the middle Tithonian to middle Valanginian interval suggest cold climatic conditions, and make the Rollrock Section a prime candidate for studying the Arctic environmental perturbations of this time.

A review of the classification of Jurassic aspidoceratid ammonites – the Superfamily Aspidoceratoidea

The aspidoceratid ammonites have been traditionally included in the superfamily Perisphinctoidea. However, the basis of this is unclear for they bear unique combinations of characters unknown in typical perisphinctoids: (1) the distinct laevaptychus, (2) stout shells with high growth rate of the whorl section area, (3) prominent ornamentation with tubercles, spines and strong growth lines running in parallel over strong ribs, (4) lack of constrictions, (5) short to very short bodychamber, and (6) sexual dimorphism characterized by miniaturized microconchs and small-sized macroconchs besides the larger ones, including changes of sex during ontogeny in many cases. Considering the uniqueness of these characters we propose herein to raise the family Aspidoceratidae to the rank of a superfamily Aspidoceratoidea, ranging from the earliest Late Callovian to the Early Berriasian Jacobi Zone. The new superfamily includes two families, Aspidoceratidae (Aspidoceratinae, Euaspidoceratinae, Epipeltoceratinae and Hybonoticeratinae), and Peltoceratidae (Peltoceratinae and Gregoryceratinae nov. subfam.). The highly differentiated features of the aspidoceratoids indicate that their life-histories were very different from those of the perisphinctoids; these ammonites show great promise for studies of developmental and evolutionary patterns and processes, and can be used for bio­stratigraphic-chronostratigraphic purposes and interprovincial correlations.

First report of Sclerobiont Bryozoans in the Maiolica Fm. of the Umbria-Marche Basin (Northern Apennines, Italy)

We describe the first evidence of sclerobiont bryozoans found loose in the pelagic Maiolica Fm. of the Umbria-Marche Basin (Monte Acuto Massif, Northern Apennines, Italy). The material is represented by three small sub-circular colonies with tube-shaped zooecia radially developing from the centre. These characters are not enough for generic or specific classification, consequently, these cyclostomes have been only identified as belonging to the Suborder Tubuliporina.Calpionellid assemblages allow to constrain the bryozoan-bearing rock sample to the early Berriasian. The occurrence of isolated bryozoans in the Maiolica Fm. enriches the knowledge about the fauna of this unit in pure basinal settings, composed by radiolarians, calpionellids, dinoflagellate cysts and rare macrofossils (ammonites and aptychi), including very rare benthic organisms (gastropods, brachiopods and bivalves). Up to date, no sclerobiont organisms in ‘normal’ pelagicMaiolica facies were known, due to the lack of suitable substrates to be colonised. Encrustation of a planktonic or nektonic hard-shelled organism seems the most parsimonious hypothesis based on our material.

PETROLEUM SYSTEMS MODELLING IN A FOLD‐AND‐THRUST BELT SETTING: THE INVERTED CAMEROS BASIN, NORTH‐CENTRAL SPAIN

The Mesozoic Cameros Basin, northern Spain, was inverted during the Cenozoic Alpine orogeny when the Tithonian – Upper Cretaceous sedimentary fill was uplifted and partially eroded. Tar sandstones outcropping in the southern part of the basin and pyrobitumen particles trapped in potential source rocks suggest that hydrocarbons have been generated in the basin and subsequently migrated. However, no economic accumulations of oil or gas have yet been found. This study reconstructs the evolution of possible petroleum systems in the basin from initial extension through to the inversion phase, and is based on structural, stratigraphic and sedimentological data integrated with petrographic and geochemical observations. Petroleum systems modelling was used to investigate the timing of source rock maturation and hydrocarbon generation, and to reconstruct possible hydrocarbon migration pathways and accumulations.In the northern part of the basin, modelling results indicate that the generation of hydrocarbons began in the Early Berriasian and reached a peak in the Late Barremian – Early Albian. The absence of traps during peak generation prevented the formation of significant hydrocarbon accumulations. Some accumulations formed after the deposition of post‐extensional units (Late Cretaceous in age) which acted as seals. However, during subsequent inversion, these reservoir units were uplifted and eroded.In the southern sector of the basin, hydrocarbon generation did not begin until the Late Cretaceous due to the lower rates of subsidence and burial, and migration and accumulation may have taken place until the initial phases of inversion. Sandstones impregnated with bitumen (tar sandstones) observed at the present day in the crests of surface anticlines in the south of the basin are interpreted to represent the relics of these palaeo‐accumulations.Despite a number of uncertainties which are inherent to modelling the petroleum systems evolution of an inverted and overmature basin, this study demonstrates the importance of integrating multidisciplinary and multi‐scale data to the resource assessment of a complex fold‐and‐thrust belt.

High-precision U–Pb ages in the early Tithonian to early Berriasian and implications for the numerical age of the Jurassic–Cretaceous boundary

Abstract. The numerical age of the Jurassic–Cretaceous boundary has been controversial and difficult to determine. In this study, we present high-precision U–Pb geochronological data around the Jurassic–Cretaceous boundary in two distinct sections from different sedimentary basins: the Las Loicas, Neuquén Basin, Argentina, and the Mazatepec, Sierra Madre Oriental, Mexico. These two sections contain primary and secondary fossiliferous markers for the boundary as well as interbedded volcanic ash horizons, allowing researchers to obtain new radioisotopic dates in the late Tithonian and early Berriasian. We also present the first age determinations in the early Tithonian and tentatively propose a minimum duration for the stage as a cross-check for our ages in the early Berriasian. Given our radioisotopic ages in the early Tithonian to early Berriasian, we discuss implications for the numerical age of the boundary.

Dual biozonation scheme (benthic foraminifera and “calcareous” green algae) over the Jurassic–Cretaceous transition. Another plea to revert the system boundary to its historical Orbigny's and Oppel's definition

The Tithonian–Valanginian interval is subdivided into 5 biozones (zones and subzones) combining mostly large benthic foraminifera and “calcareous” green algae, which are typical of photozoan assemblages from the shallow-water carbonate facies of the Tethysian realm. This dual zonation is calibrated on a sequence stratigraphic framework for the Jura Mountains where earlier findings of ammonites and calpionellids are plotted. The microfossil diversity was low in the Tithonian–early Berriasian times; then it significantly increased over the middle–late Berriasian times before a first extinction event at the Berriasian/Valanginian boundary followed by a second extinction event in the early Valanginian times. The lower/middle Berriasian and the Berriasian/Valanginian boundaries can be traced consistently from West to East through the whole Tethysian realm. By contrast, the upper Tithonian and the lower Berriasian cannot be distinguished. Because the location of the Jurassic/Cretaceous system boundary has been pending a decision of the International Commission on Stratigraphy since 1975, this survey provides one more argument to abandon the early 20th century Kilian's view which placed it at the Tithonian/Berriasian stage boundary, and to return it to the original 19th century Orbigny's and Oppel's view, i.e., back at the Berriasian/Valanginian stage boundary.

Upper Jurassic Rock Depositional Settings in the Baidar Valley and Evolution of the Crimean Carbonate Platform

The paper presents results of the lithological study of Upper Jurassic limestones, flyschoids and limestone breccias on the southern side of the Baidar Valley in the Crimean Mountains. Study of the microfacies revealed that the limestones are represented by deposits on lagoons, platform edge shoals, reefs, and forereef aprons on the carbonate platform slope. Flyschoids include deposits in the distributive turbidite channels and hemipelagic sediments in the deep-water part of the basin. Limestone breccias were formed by gravitation flows on the carbonate platform toe-of-slope and slope. The presence of gravitation deposits in the Upper Jurassic carbonate complexes of the Crimean Mountains can testify to the primary clinoform structure of this sedimentary sequence. Comparison of the obtained sedimentological data made it possible to reconstruct the facies model of the Crimean carbonate platform and main episodes of its formation. Development of the carbonate shelf was related to two transgressive-regressive cycles. A dome-shaped reef was formed away from the coast at the initial (Oxfordian) stage. The carbonate platform was formed at the early Kimmeridgian lowstand stage when sediments were deposited in the internal part of the platform adjacent to land. In the late Kimmeridgian and early Tithonian, configuration of the carbonate platform profile resembled a distally steepened ramp, and its active progradation and shelf expansion took place in the course of transgression. Regression in the late Tithonian–early Berriasian led to regressive transformation of the ramp into platform with a flattened shallow-water shelf. Tectonic deformations at the Jurassic/Cretaceous transition promoted the formation of megabreccias on the carbonate platform foreslope. The tectonically reworked rock sequence of the “extinct” carbonate platform was overlapped transgressively by the upper Berriasian or lower Valanginian, relatively deep-water deposits of the Cretaceous platform cover.

Sedimentary architecture, depositional facies and diagenetic response to intracratonic deformation and climate change inferred from outcrops for a pivotal period (Jurassic/Cretaceous boundary, Paris Basin, France)

The aim of this study is to decipher the respective influences of geodynamic and climate disturbances at the Jurassic/Cretaceous boundary on sedimentary facies and carbonate diagenesis in a stable intracratonic basin using isotopic geochemistry and subsidence quantification. Fourteen lithofacies were deposited in a (1) carbonate platform and (2) a delta plain environment. Climate change from cool and wet to warm and semi-arid conditions during the early Tithonian influenced the syn-sedimentary dolomitization process within the carbonate platform during the mid-Tithonian. Architecture and facies reconstructions well-constrained the Jurassic-Cretaceous Unconformity (JCU), which was an important local structural episode marked by (1) an 80 m uplift in the eastern Paris Basin and by (2) the formation of a NW–SE low wavelength 15 km-wide and 30 km-long flexure. This first tectonic event tended to maintain brine ponds and supratidal marsh environments in the platform during the late Tithonian and early Berriasian, forming Purbeckian facies and associated dolomitic facies. A major depositional change occurred between the early and late Berriasian from shallow carbonate platform environments to fluviatile-deltaic clastic deposits (Wealden facies). This facies change is underlain by a major unconformity corresponding to the Ryazanian unconformity. It is marked (1) by erosion processes, karstification of the carbonate substrate, and the development of ferruginous weathering products (goethite), followed by (2) incision processes in a fluvial-deltaic environment. This unconformity is consecutive to a 40 m uplift in the eastern Paris Basin. The rifting phase in the Bay of Biscay, in the Pyrenean Zone, and in the Artic-North Atlantic together with the opening of the Ligurian Sea had a major influence on the northern part of France by causing uplifts (120 m from the Tithonian) and flexuring. Geodynamics played a major role in carbonate demise in the Paris Basin leading to exposure and karstification of the carbonate platform. Added to the generalized uplift, western Tethyan cool and humid conditions from the late Berriasian caused terrigenous influx into large-scale marine domains which was detrimental and unfavorable to carbonate growth.

Magneto- and biostratigraphy across the Jurassic-Cretaceous boundary in the Kurovice section, Western Carpathians, Czech Republic

An integrated magneto- and biostratigraphic study of the Jurassic-Cretaceous (J-K) boundary section at Kurovice, Czech Republic was carried out. The acquired paleomagnetic data showed dual polarity characteristic remanent magnetization (ChRM) with counter-clockwise rotation direction. Rock magnetic data indicated magnetite as the principal carrier of remanent magnetization as well as presence of e.g. hematite and goethite. Magnetozones from M21n up to M17r were identified and dated as early Tithonian (dinoflagellate Semiradiata and nannofossil NJT15b zones) to late early Berriasian (Calpionella elliptica and nannofossil NK-1 (sub)zones).

Sr chemostratigrphy, δ13C, and δ18O of rocks in the Crimean carbonate platform (Late Jurassic, northern Peri-Tethys)

The paper presents the results of study of the Sr, C, and O isotope compositions in Upper Jurassic carbonate rocks of the Baidar Valley and Demerdzhi Plateau in the Crimean Mountains represented by different facies of the carbonate platform at the northern active margin of the Tethys. The 87Sr/86Sr value in them varies from 0.70699 to 0.70728. Based on the Sr chemostratigraphic correlation, the age of massive and layered limestones in the western part of the Ai-Petri and Baidar yailas (pastures) is estimated as late Kimmeridgian–early Tithonian, whereas the age of flyschoids of the Baidar Valley are estimated as late Tithonian–early Berriasian. The nearly synchronous formation of carbonate breccias of the Baidar Valley and Demerdzhi Plateau in late Tithonian–early Berriasian is substantiated. A summary section of Upper Jurassic rocks is compiled based on the Sr chemostratigraphic data. It has been established that δ18O values in the studied carbonate sediments vary from–2.9 to 1.3‰ (V-PDB). At the same time, shallow-water sediments in the internal part and the edge of the Crimean carbonate platform are depleted in 18O (–2.9 to +0.1‰) relative to sediments on the slope and foothill (–0.5 to +1.3‰). It is demonstrated that δ13C values do not depend on the facies properties and decrease in younger carbonate sediments from 3–3.5‰ to 1–1.5‰ in line with the Late Jurassic general trend. The δ13C values obtained for the Crimean carbonate platform turned out to be 0.5–1‰ higher than the values typical of the deep-water marine setting at the western margin of the Tethys. These discrepancies are likely related to peculiarities of water circulation and high bioproductivity in marine waters of the northern Peri-Tethys.

Distribution of organic matter in Callovian-Lower Berriasian deposits of the western part of the Yenisei-Khatanga regional trough and adjacent areas of the West Siberian geosyneclise

This study presents the results of geochemical analysis of organic matter and paleogeographic reconstructions supplemented by data from well log interpretation and cyclostratigraphic analysis for the Vasyugan, Georgiev, and Bazhenov Horizons of the Callovian-Lower Berriasian section in the western part of Yenisei-Khatanga regional trough and adjacent areas of the West Siberian geosyneclise. It was found that each horizon contains zones dominated by terrigenous, mixed, and aquatic organic matter. The distribution of different types of organic matter over the area and throughout the section has been examined. It was shown that the accumulation of aquatic organic matter took place in the deepest parts of the trough during the Callovian-Oxfordian. The area of accumulation of aquatic organic matter expanded considerably and reached its maximum extent within the Bolshaya Kheta megasyneclise during the Kimmeridgian and Early Volgian and in the west Yenisei-Khatanga regional trough during the Volgian and Early Berriasian.

Calpionellid zones of the Tithonian–Berriasian exotic limestone clasts from the Outer Carpathians, Poland

Calpionellids and chitinoidellids were identified from exotic limestone clasts occurring in flysch deposits of the Early Cretaceous to Oligocene age from the Silesian and Subsilesian nappes of the Polish Outer Carpathians. They represent the remnants of carbonate sedimentation along the northern and southern margin of the Severin-Moldavidic Basin, areas which are no longer preserved on the surface. Chitinoidellid and calpionellid assemblages characterize the Chitinoidella, Crassicollaria and Calpionella zones (latest early Tithonian–early Berriasian). The calpionellid zonation for the Western Carpathians was used for the present study, but some difficulties were encountered resulting from the application of this zonation. Cathodoluminescence imaging (CL) was useful for the identification of these microfossils in samples containing sparse and poorly preserved specimens, especially in the studied shallow-water limestone (the so-called Štramberk-type limestones).

Some perisphinctoid ammonites of the Štramberk Limestone and their dating with associated microfossils (Tithonian to Lower Berriasian, Outer Western Carpathians, Czech Republic)

AbstractThe present contribution deals with the taxonomy of seven species of perisphinctoid ammonite from the Štramberk Limestone (Outer Western Carpathians, Czech Republic) deposited in Moravian-Silesian museums. The age of these studied ammonites is compared with that of index microfossils contained in the matrix adhering to or infilling the studied specimens. The ammonites document a stratigraphic range from earliest Tithonian to early Berriasian. In addition to taxonomy and new ontogenetic data on some species, we also present data on their palaeogeographic distribution. The occurrence of Subboreal himalayitids in the Štramberk Limestone of an early Berriasian age is determined by both the microfauna and accompanying ammonites, which indicate connection of the Silesian-part of the Tethyan Carpathian area with the Subboreal Russian Platform Basin. These records also suggest an early Berriasian age (Jacobi Chron) for the lowermost part of the Ryazanian stage in its type area.

Paleoenvironmental conditions across the Jurassic–Cretaceous boundary in central-eastern Mexico

The Padni section of central-eastern Mexico is characterized by pelagic, organic-rich carbonates and shales dated in this study by calpionellid biostratigraphy to the late Tithonian-late Berriasian time interval. Microfacies, pyrite framboid size, spectrometric gamma-ray and mineralogical data are herein integrated in order to reconstruct the paleoenvironmental change during the Jurassic-Cretaceous boundary. Deposits of the late Tithonian–early Berriasian are characterized by laminated, organic-rich facies with abundant radiolarian, tiny pyrite framboids and low Th/U ratios. They are linked to upwelling in a semi-restricted basin, high marine productivity and anoxic bottom waters. The early incursions of Tethyan oceanic waters into the proto-Gulf of Mexico occurred during late Tithonian as attested the appearance of calpionellids. Short and intermittent accumulations of saccocomids during early Berriasian suggest episodes of sporadic connection between the Tethys, the proto-Atlantic and the Pacific ocean during sea-level rise events. A full and stable connection between the Tethys and proto-Gulf of Mexico was established until the late Berriasian. This event is supported by the presence of open marine and bioturbated facies with a framboid population typical of dysoxic conditions, higher Th/U ratios and a decreasing pattern of the total organic carbon content. In addition to highlighting the replenishment of the oxygen supply to the basin, this facies also points to a younger age for the finalization of the Yucatán Block rotation and the end of the Gulf of Mexico opening. Deposition of the studied section occurred mostly during a Tithonian–Berriasian arid phase reported in other Tethyan and Atlantic regions. The similarity between the discrete segments of the standard gamma-ray curve defined in the studied outcrop and those reported from subsurface implies their regional continuity allowing their use for correlation purposes.