New Early Cretaceous sharks (Chondrichthyes,Elasmobranchii) from deep-water deposits of Austria

Early Cretaceous elasmobranchs still are very insufficiently known despite all progress that has been accomplished in recent years. Here, a small elasmobranch assemblage is presented from the Valanginian of Austria that contributes significantly to a better understanding of early Cretaceous elasmobranch diversity. The new assemblage comprises two new carcharhiniform sharks, Altusmirus triquetrus gen. et sp. nov. and Fornicatus austriacus gen. et sp. nov., a new orectolobiform shark, Similiteroscyllium iniquus gen. et sp. nov., and a galeomorph shark tooth of uncertain affinities. The recent identification of Similiteroscyllium gen. nov. has shown that it has strong similarities with Ornatoscyllium rugasimulatum from the Lower Cretaceous of France. Significant differences of the tooth morphology of O. rugasimulatum and the type specimen O. freemani justify full reconsideration of the systematic position of O. rugasimulatum and require it to be reassigned to Similiteroscyllium gen. nov. described in this paper. The new assemblage described here, and those from the Valanginian of France and Poland comprising 30 additional taxa, indicates that Early Cretaceous elasmobranch diversity was significantly higher than previously assumed. Consequently, the supposed diversity decline of elasmobranchs across the Jurassic-Cretaceous boundary represents a collecting bias rather than a real pattern.     

First Lower Cretaceous record of Podocarpaceae wood associated with dinosaur remains from Patagonia,Neuquén Province,Argentina

The first Podocarpaceae wood record is described from the Mulichinco Formation (Valanginian, Lower Cretaceous), Neuquén Basin, Argentina. The specimen was directly associated with a middle caudal vertebra of a diplodocid sauropod dinosaur. A new species – Podocarpoxylon prumnopityoides – is proposed based on features that include the presence of abietinean wood type (tracheid radial pitting), plus podocarpoid (cupressoid type) and some dacrydioid (taxodioid type) cross-field pits, diffuse axial parenchyma and low rays. This combination of anatomical characters is comparable to both Prumnopitys and Podocarpus, whereas the type of pits in the cross-fields resembles some members of the extant Prumnopitys. This is the first unequivocal record of the Family Podocarpaceae in the Valanginian of South America and confirms the hypothesis that the divergence between the “Podocarpoid-Dacrydioid” and “Prumnopityoid” clades occurred earlier than the Early Cretaceous.     

The Early Valanginian ammonite, brachiopod and crustacean fauna of the Mecsek Mts. and its relationships with the embryonic shallow water hydrothermal vent at Zeng?várkony (Mecsek Mts., South Hungary)

Early Cretaceous development of the Mecsek Mts. (South Hungary) is characterized by continental rifting that produced mixed volcano-sedimentary rocks in the Tihonian/Berriasian and built up a volcanic edifice in the earliest Cretaceous of ankaramite-alkaline basalts. During the Valanginian, marl sedimentation occurred in the basinal part containing rich pelagic fauna dominated by ammonites. Beside phylloceratids, lytoceratids and haploceratids, Kilianella roubaudiana, K. lucensis, Sarasinella eucyrta, Thurmanniceras pertransiens, Th. (Clavithurmannia) foraticostata, Busnardoites campylotoxus, Olcostephanus drumensis, O. densicostatus, and Sabbaiceras stefanescui are indicating the Early and Late Valanginian Thurmanniceras pertransiens, Busnardoites campylotoxus and Saynoceras verrucosum zones. The Early Valanginian is also supported by Calpionellites darderi indicating the calpionellid “E” zone. The marl sequence contains a turbidite bed with rich fauna of shallow marine origin from the volcanic slope of lagoonal, reef, and tidal environs, however it contains metasomatized limestone olistoliths of different origin. Source of these olistoliths is the near iron-ore deposit, which is considered an embryonic shallow water hydrothermal vent. It includes a remarkable fauna of rich crustacean coprolite ichnospecies of Favreina dispentochetarius, F. hexaochetarius, F. octoochetarius, Palaxius decaochetarius, P. tetraochetarius, P. triochetarius. In the neighbourhood of the embryonic vent, a remarkable megafauna occurs, which is an almost monospecific brachiopod fauna dominated by Lacunosella hoheneggeri. Other brachiopods as Nucleata veronica, Moutonithyris moutoniana, Karadagithyris sp., and Zittelina pinguicula also occur as stray individuals. Together with benthic megafauna, nektonic elements as Nautiloidea gen. et sp. ind, phylloceratid- and lytoceratid ammonites and echinoid spines of Balanocidaris rysacantha occur.     

The first definite record of a Valanginian ichthyosaur and its implications on the evolution of post-Liassic Ichthyosauria

A complete ichthyosaur rostrum, with 124 associated teeth, was recently discovered in Laux-Montaux locality, department of Drôme, southeastern France. The associated belemnites and ammonites indicate a late Valanginian age (Neocomites peregrinus Zone, Olcostephanus nicklesi Subzone) for this fossil, which consequently represents the first diagnostic ichthyosaur ever reported from Valanginian strata. This specimen also represents the first occurrence of Aegirosaurus outside the Tithonian (Upper Jurassic) lithographic limestones of Bavaria (southern Germany). Tooth morphology and wear pattern suggest that Aegirosaurus belonged to the “Pierce II/ Generalist” feeding guild, which was hitherto not represented in post-Liassic ichthyosaurs. Most Late Jurassic ichthyosaurs actually crossed the Jurassic-Cretaceous boundary.     

The Upper Valanginian (Early Cretaceous) positive carbon-isotope event recorded in terrestrial plants

Our understanding of the ancient ocean-atmosphere system has focused on oceanic proxies. However, the study of terrestrial proxies is equally necessary to constrain our understanding of ancient climates and linkages between the terrestrial and oceanic carbon reservoirs. We have analyzed carbon-isotope ratios from fossil plant material through the Valanginian and Lower Hauterivian from a shallow-marine, ammonite-constrained succession in the Crimean Peninsula of the southern Ukraine in order to determine if the Upper Valanginian positive carbon-isotope excursion is expressed in the atmosphere. δ¹³C_plant values fluctuate around − 23‰ to − 22‰ for the Valanginian-Hauterivian, except during the Upper Valanginian where δ¹³C_plant values record a positive excursion to ∼− 18‰. Based upon ammonite biostratigraphy from Crimea, and in conjunction with a composite Tethyan marine δ¹³C_carb curve, several conclusions can be drawn: (1) the δ¹³C_plant record indicates that the atmospheric carbon reservoir was affected; (2) the defined ammonite correlations between Europe and Crimea are synchronous; and (3) a change in photosynthetic carbon-isotope fractionation, caused by a decrease in atmospheric pCO₂, occurred during the Upper Valanginian positive δ¹³C excursion. Our new data, combined with other paleoenvironmental and paleoclimatic information, indicate that the Upper Valanginian was a cool period (icehouse) and highlights that the Cretaceous period was interrupted by periods of cooling and was not an equable climate as previously thought.     

西西伯利亚东南部早凡兰吟期孢粉地层学,古环境和植被再造

分析了西西伯利亚东南地区的下凡兰吟阶的两个剖面的陆相孢粉型化石的分布。依据西伯利亚北部已经定年的剖面中动物群建立起来的孢粉组合的对比,确定了孢粉标志层的定义,并与北方区的菊石带相对应的孢粉组合进行了对比。这一工作为早凡兰吟期与气候变化息息相关的植被和景观的短期变化以及周边古盆地变迁的重建,提供了地层依据。欧亚大陆中部和东部地区凡兰吟期孢粉组合的横向对比显示:西西伯利亚东南地区的植被具有印度欧洲和西伯利亚加拿大两大古植物地理区的过渡性质,显有这两区的典型特征。     

Cyclostratigraphic calibration of cretaceous magnetic polarity events (Cismon, Southern Alps, Italy)

In an introductory section the problems of constructing a geologic time scale and the role of magnetic reversals and Milankovitch cycles in geochronology are outlined. Results of a detailed cyclostratigraphic and magnetostratigraphic study of the Valanginian/Hauterivian part of the pelagic limestone section at Cismon in the Southern Alps are presented and used in conjunction to estimate the duration of magnetic subchrons between CM10N and CM8. The new estimates are shorter than in most published time scales by a factor of two to three. More research along these lines may make a revision of the Early Cretaceous time scale necessary.     

Revision of Valanginian Steinmanellinae bivalves from the Neuquén basin,West-central Argentina,and their biostratigraphic implications

We present a new species of Steinmanella Crickmay from the Valanginian of the Neuquén Basin, west-central Argentina, and at the same time update a Valanginian–earliest Barremian bivalve zonation which is integrated into the local, Chilean and European standard ammonoid zonations. Steinmanella caicayensis sp. nov. presents a moderately inflated shell, a subtriangular outline, well-developed carinae and a straight to moderately convex anterior margin. Steinmanella is very abundant in the Tithonian–Barremian interval in the basin and thus provides an ideal opportunity to perform detailed taxonomic and stratigraphic studies; a former zonation based on these trigonioids is here revised and expanded with a thorough revision of Valanginian occurrences based on new material. Two new zones are proposed, namely the S. quintucoensis and S. caicayensis zones, encompassing Valanginian times. The proposed bivalve zonation encompassing the Valanginian–earliest Barremian time interval can be useful in correlating with other southwestern Gondwanan regions, such as Perú, Chile, South Africa, Tanzania, and India, where Steinmanella has been recorded.     

Sea‐level reconstructions from the Peri‐Vocontian Zone (South‐east France) point to Valanginian glacio‐eustasy

The Valanginian is a period of global environmental change as illustrated by sedimentary, palaeontological, geochemical and climatic perturbations. A production crisis in most of the carbonate platforms suggests important changes in palaeoenvironmental conditions. During the same time interval, a major positive excursion in δ¹³C, the Weissert Event, suggests perturbations of the carbon cycle from the latest Early Valanginian to the Early Hauterivian. In order to better understand the link between these changes, sea‐level fluctuations have been reconstructed in detail from the Middle Berriasian to the earliest Hauterivian. Sections from the Peri‐Vocontian Zone (South‐east France) have been investigated because of the good quality of outcrops on the carbonate platforms, their margins and in the Vocontian Basin. Sections ranging from the most proximal zone (Swiss Jura) to the basin were interpreted in terms of sequence stratigraphy and cyclostratigraphy, and correlated at high resolutions. Using the identified small, medium and large‐scale sequences as well as depositional geometries, sea‐level fluctuations were reconstructed. Two main trends are evidenced during the studied interval: (i) the peak amplitude (magnitude) of the sea‐level fluctuations increased gradually from the Middle Berriasian to the Early Valanginian, and reached a maximum (more than 50 m) from the middle Early Valanginian to the Valanginian/Hauterivian boundary; and (ii) sea‐level variations were quite symmetrical during the Late Berriasian, slightly asymmetrical during the Early Valanginian and strongly asymmetrical (fast sea‐level rise, slow fall) from the latest Early Valanginian to the earliest Hauterivian. Moreover, three orders of sea‐level fluctuations were recognized in the sedimentary rocks of the Peri‐Vocontian Zone. Platform‐basin correlations and cyclostratigraphic interpretations of the basinal sections evidence an astronomical control on the sea‐level variations, mainly by the two eccentricity cycles of 100 and 400 kyr. The increase in the amplitude of the sea‐level fluctuations and their change from symmetrical to asymmetrical can be related to the onset of a major cooling event in the Early Valanginian. Fast transgressions followed by slower regressions would correspond to waxing and waning of high‐latitudinal ice during most of the Valanginian, especially from the latest Early Valanginian to the latest Late Valanginian. Glacio‐eustatic sea‐level fluctuations in tune with the 100 and 400 kyr eccentricity cycles are in agreement with glaciations during the Valanginian.     

Astronomical calibration of the Valanginian “Weissert” episode: The Orpierre marl–limestone succession (Vocontian Basin,southeastern France)

A high-resolution, biostratigraphic (calcareous nannofossils, calpionellids), chemostratigraphic (C-isotope) and cyclostratigraphic (magnetic susceptibility) study was performed on the marl–limestone alternations of the Upper Berriasian–Valanginian Orpierre section, deposited in the hemipelagic setting of the Vocontian Basin (SE France). The main aims of this study were to detect orbital forcing, to estimate the duration of the Valanginian “Weissert” episode, and to discuss the palaeoenvironmental implications. Detailed calcareous nannofossil biochronology allowed the recognition of Upper Berriasian–Lower Hauterivian biohorizons. The general trends of the δ¹³C curve and the major positive C-isotope excursion (amplitude of 1.8‰) recorded at the Orpierre section are very similar to those found in other sections worldwide. Spectral analysis applied on high-resolution magnetic susceptibility (MS) variations coupled with frequency ratio method reveals a strong cyclic pattern related to the Earth's orbital parameters (precession, obliquity and eccentricity). The prominent 405 kyr eccentricity cycle in the MS signal and has been used as a geochronometer to time calibrate the section. The duration of the Weissert episode was estimated as 2.08 Myr. This duration is coherent with those obtained from the Umbria Marche Basin (∼2.3 Myr) and from the Angles section (∼2.14 Myr). Durations of more than 2 Myr suggest that a long perturbation in the dynamic of the global carbon cycle that is not compatible with the rapid and intense volcanic activity. Our cyclostratigraphic study indicates a minimal duration of 4.29 Myr for the Valanginian stage. The comparison between the MS signal at Orpierre and the spectral gamma-ray signal recently obtained in two composite sections of the Vocontian Basin allows to propose a revised duration for the Valanginian stage of 4.695 Myr instead of 5.08 Myr.