Sur l'attribution générique d'une ammonite de l'Aptien du Mexique: Megatyloceras casei HUMPHREY, 1949 (Ammonoidea, Ancyloceratina)

Dans ce travail, nous révisons l'attribution générique de l'espèce mexicaine d'ammonite Megatyloceras casei HUMPHREY, 1949. Grâce à un examen minutieux de l'holotype conservé à l'Université du Michigan et grâce aussi aux nouvelles données bio-stratigraphiques obtenues dans la localité-type, cette révision nous permet d'inclure maintenant cette espèce dans le genre Epicheloniceras CASEY, 1954.In the present work we review the generic attribution of the Mexican ammonoid species Megatyloceras casei HUMPHREY, 1949, through a careful examination of the holotype housed in the Uni-versity of Michigan and with reference to new biostratigraphic data from the type locality. We assign here this species to the subfamily Cheloniceratinae and to the genus Epicheloniceras CASEY, 1954

Revisión de algunos ammonites aptienses colectados por Gaston Astre en la Provincia de Lérida, Cataluña, España

We study the three best preserved ammonites collected by Astre in 1924-1925 in Lleida Province, Catalonia, Spain, in order to assess their taxonomic assignment. We also include images of these ammonoids since they were not illustrated in Astre's original 1934 work. This taxonomic review allows us to identify these lower Aptian ammonites as Pseudohaploceras liptoviense, Deshayesites sp. and Dufrenoyia sp.Nous avons étudié les trois ammonites les mieux préservées parmi celles récoltées par Astre en 1924-1925 dans la Province de Lérida (Catalogne, Espagne) afin d'en ré-évaluer plus sûrement l'attribution taxinomique. Nous figurons ces ammonoïdés puisqu'il n'y avait aucune illustration dans la publication originale de Astre en 1934. Ce ré-examen taxinomique nous permet d'attribuer ces trois ammonites de l'Aptien inférieur à Pseudohaploceras liptoviense, Deshayesites sp. et Dufrenoyia sp.Se estudian los tres ammonites mejor conservados colectados por Astre en 1924-1925 en la Provincia de Lérida, Cataluña, España, con la finalidad de mejorar su asignación taxonómica. También incluimos imágenes de estos ammonites ya que no se figuraron en el trabajo original de Astre, 1934. Esta revisión taxonómica nos permite identificar los ammonites del Aptiense inferior: Pseudohaploceras liptoviense, Deshayesites sp. y Dufrenoyia sp

Mesozoic stratigraphy and new Aptian cephalopods of el Vendrell, southwest of the Garraf Massif (Catalonia)

En aquest treball es mostra l'estratigrafia del Mesozoic de l'extrem sud-oest del massís del Garraf i es dóna a conèixer per primera vegada una associació de cefalòpodes procedents de l'Aptià (Cretaci inferior) de l'entorn del municipi del Vendrell. El Mesozoic que aflora a l'est del Vendrell esta format per roques fonamentalment carbonàtiques del Kimmeridgià-Berriasià a les que se li superposen de forma discordant els dipòsits del Barremià i l'Aptià. En l'Aptià del Vendrell s'identifiquen uns ammonits i nautiloïdeus trobats a la part baixa de la unitat Margues de Vallcarca (Salas & Moreno, 2008) i se'n realitza una anàlisi biostratigràfica. També s'analitza l'estratigrafia deis materials del Cretaci inferior (Barremià superior-Aptià superior) d'aquest sector de la conca de Salou-Garraf mitjan<;:ant una correlació amb la conca veïna del Maestral. Entre els cefalòpodes estudiats destaca la presencia de l'ammonit Pseudosaynella bicurvata (Michelin, 1838), ja que és la primera vegada que aquesta espècie se cita al massís del Garraf, i un exemplar ben conservat del nautiloïdeu Heminautilus lallierianus (d'Orbigny, 1841), el segon exemplar conegut d'aquesta espècie al Garraf. Des d'un punt de vista biostratigrafic, els cefalòpodes aptians estudiats constitueixen un dels registres més antics coneguts per a la unitat Margues de Vallcarca, essent atribuïble a les biozones Deshayesites forbesi i Deshayesites deshayesi (Aptià inferior). La correlació efectuada entre les unitats litostratigràfiques del Barremià superior i l'Aptià de les conques veïnes de Salou-Garraf i del Maestrat permet assignar al Barremià terminal la part basal de la unitat Margues de Vallcarca, quan c1assicament aquesta unitat de la conca de Salou-Garraf havia estat atribuïda íntegrament a l'Aptià.The current work shows the Mesozoic stratigraphy of the southwestern part of the Garraf Massif and reports for the first time an Aptian (Lower Cretaceous) cephalopod assemblage from the surroundings of the town of el Vendrell. The Mesozoic out craps to the east of el Vendrell primarily consist of carbonate rocks of Kimmeridgian-Berriasian age, which are uncorformably overlain by Barremian and Aptian deposits. In the Aptian of el Vendrell, we identify ammonoids and nautiloids that were collected in the lower part of the Vallcarca Marls Unit (Salas & Moreno, 2008), and we carry out a biostratigraphic analysis. We also analyze the stratigraphy of the Cretaceous materials (upper Barremian to upper Aptian) of this area of the Salou-Garraf Basin and establish a correlation with the neighboring Maestrat Basin. Among the cephalopods studied, the presence of the ammonite Pseudosaynella bicurvata (Michelin, 1838) is remarkable because it is the first time that this species is quoted in the Garraf Massif. In addition, we report a well-preserved specimen of the nautiloid Heminautilus lallierianus (d'Orbigny, 1841), which is the second specimen of this species known in the Garraf area. Fram a biostratigraphic point of view, the Aptian cephalopods studied herein are some of the oldest known records of the Vallcarca Marls Unit being attributed to the Deshayesites forbesi and Deshayesites deshayesi biozones (lower Aptian). The correlation between the upper barremian and Aptian lithostatigraphic units among the neighboring basins Salou-Garraf and Maestrat allows us to ascribe for the first time the basal part of the Vallcarca Marls Unit to the uppermost Barremian. This latter lithostatigraphic unit of Salou-Garraf Basin has been classically attribued to the Aptian

Ammonites de l'Aptien inférieur de la Sierra de Parras, État de Coahuila, au nord du Mexique

We report an interesting Aptian ammonite record from the La Peña Formation in the Sierra de Parras, Coahuila State. This assemblage is analyzed from a paleoecological perspective. It contains the first reported occurrence of a macroconch of Dufrenoyia from Mexico, and the largest known specimen of 'Gargasiceras' adkinsi. Such an assemblage yielding large ammonites is unusual in deposits of this age in Mexico. To properly document this ammonite record, we review 'Gargasiceras' adkinsi, formerly misidentified as Rhytidoplites robertsi, and allied taxa. From our analysis, we conclude that 'Gargasiceras' adkinsi exhibits strong intraspecific variability. We also analyze in detail the differences that exist between 'Gargasiceras' adkinsi and Rhytidoplites robertsi, and emend the concept of the genus Rhytidoplites. These revisions are important from a biostratigraphic point of view since 'Gargasiceras' adkinsi is an index species for the lower Aptian ammonite zonation of Mexico.Ce travail fait état d'une intéressante faune d'ammonites de l'Aptien de la Formation de La Peña, dans la Sierra de Parras, État de Coahuila, analysée ici d'un point de vue paléoécologique. Il permet également de signaler pour la première fois au Mexique la présence d'un macroconque de Dufrenoyia, ainsi que le plus grand spécimen connu de 'Gargasiceras' adkinsi. Une telle association livrant de grandes ammonites est inhabituelle dans les dépôts aptiens du Mexique. Afin de bien caractériser cette ammonitofaune, il est procédé à une révision de l'espèce 'Gargasiceras' adkinsi, autrefois confondue avec Rhytidoplites robertsi, ainsi que des espèces proches. Notre analyse montre que 'Gargasiceras' adkinsi présente une forte variabilité intraspécifique. Les différences entre 'Gargasiceras' adkinsi et Rhytidoplites robertsi sont également analysées en détail, ce qui permet d'émender le concept du genre Rhytidoplites. Ces révisions sont importantes sur le plan biostratigraphique puisque 'Gargasiceras' adkinsi constitue l'une des espèces-index de la zonation de l'Aptien inférieur du Mexique

Lower Cretaceous (Hauterivian-Albian) ammonite biostratigraphy in the Maestrat Basin (E Spain)

A review of the stratigraphic distribution of ammonoid species in the Lower Cretaceous (Hauterivian-Albian) of the Maestrat Basin (E Spain) was carried out. The specimens were mainly collected in the field by us and are stored in university or museum collections. Specimens from private collections and figured in the literature were also studied. We recognized 73 species that are distributed, in accordance with the latest version of the standard Mediterranean ammonite zonation for the Lower Cretaceous, in 14 ammonite zones: Acanthodiscus radiatus, Crioceratites loryi, Lyticoceras nodosoplicatum (Lower Hauterivian); Pseudothurmannia ohmi (Upper Hauterivian); Imerites giraudi (Upper Barremian); Deshayesites oglanlensis, Deshayesites forbesi, Deshayesites deshayesi, Dufrenoyia furcata (Lower Aptian); Epicheloniceras martini, Parahoplites melchioris, Acanthohoplites nolani (Upper Aptian); Leymeriella tardefurcata and Douvilleiceras mammillatum (Lower Albian). The recognition of these biozones allows a precise age calibration of the Maestrat Basin's lithostatigraphic units that contain ammonoids as well as an associated indirect age calibration of the formations without ammonoids. Consequently, this report provides an updated, comprehensive and precise biostratigraphic framework, which aims to become a reference for the analysis of the Lower Cretaceous strata of the Maestrat Basin. The results are also relevant for the analysis of coeval ammonite-bearing sedimentary successions found in other Tethyan basins

Uppermost lower aptian transgressive records in mexico and spain: chronostratigraphic implications for the Tethyan sequences

A widespread marine transgression, which began at the very end of the Early Aptian, is well recorded in Mexico and Spain. In Mexico, this transgression was the most important Aptian transgressive event and its record begins in the Dufrenoyia justinae Zone, whereas in Spain the corresponding transgression is registered in the uppermost part of the Dufrenoyia furcata Zone. The basal age of this Tethyan transgression does not correspond exactly to any of the Lower Aptian third-order sequences as reported in the literature. In Spain, the most important Aptian transgressive event was earlier, corresponding to the Tethyan sequence Ap3, which is well-defined below this transgression reported herein. Consequently, it is possible to correlate this later transgressive event with the third-order Ap4 sequence, which has commonly been attributed to the Upper Aptian. The available ammonoid data allow us to correct the basal age of the transgression, and to correlate the start of the ammonite record in Mexico with the Tethyan sequence Ap4

Well-preserved cuticle of Atherfieldastacus magnus (Decapoda, Glypheida) from the Aptian of Mexico

The cuticle structure of fossil decapod crustaceans is an important tool, not only for palaeocological and taphonomic interpretations, but also as a potential way to characterise systematically genera and even species the cuticle of which has not been severely altered by diagenetic processes. Localities with abundant decapod crustacean remains can be interpreted either as reflecting mass mortality events or just simple accumulations of exuviae, on the basis of completeness and comparison of cuticle structures between specimens of the same species from different localities. Association with anoxic events by microfacies analyses can offer clues to explain the unusual abundance of decapod crustacean remains. This is the case for the Early Cretaceous lobster Atherfieldastacus magnus (M’Coy, 1849), which is found in large numbers in different Lower Cretaceous (mainly Aptian) lithostratigraphic units across the globe. In this case, we document the well-preserved cuticle structure of specimens from the upper Aptian of Chihuahua (Mexico), preserved three-dimensionally, mainly in concretions, which were studied in different transverse sections showing the cuticle in diverse portions of the lobster body. Thin cuticle layers show the typical crustacean cuticular structure that suggest these are corpses preserved in an anoxic environmen

Aptian and Albian (Early Cretaceous) ammonites from Lampazos and the Bisbee groups (Sonora State, northwest Mexico)

A taxonomic study was carried out of 34 ammonites collected from the Agua Salada and Nogal formations (Lampazos Group) and the Mural Limestone (Bisbee Group) in the Sonora State, northwest of Mexico. Twenty-one taxa are described, with 13 being endemic of the Central Atlantic province: Puzosia (Anapuzosia) sp. juv. cf. tucuyensis, Parasilesites cf. bullatus, Beudanticeras parandieri, \textquotedblleftBeudanticeras\textquotedblright newtoni, Beudanticeras sp., Desmoceras (Pseudouhligella) cf. vetus (en=endemic), Engonoceras complicatum (en), Engonoceras stolleyi, Protengonoceras gabbi (en), Protengonoceras neolobitoides (en), \textquotedblleftEodouvilleiceras cf. adkinsi\textquotedblright (en), Huastecoceras? sp. (en), Hypacanthoplites sp., Immunitoceras immunitum (en), Immunitoceras cf. trinitensis (en), Kazanskyella minima (en), Kazanskyella spathi (en), Quitmanites ceratitosus (en), Quitmanites fosteri (en), and Quitmanites sp. (en), between them we erected one new species: Protengonoceras neolobitoides. The record of Aptian-Albian ammonites in Sonora is scarce, therefore the ammonites herein studied are valuable due to the number of endemic taxa that could be used in future biostratigraphic works. In addition, these taxa allow a revision of the stratigraphic frame: The Agua Salada Formation is now considered from late Aptian to early Albian; the Nogal Formation is confined to late Albian; the Cerro Las Conchas succession is limited to middle Albian; and the age of the Cerro La Ceja Member is late Aptian. (C) 2018 Elsevier Ltd. All rights reserved

Chronostratigraphy of the barremian-early albian of the maestrat basin (E Iberian Peninsula): Integrating strontium-isotope stratigraphy and ammonoid biostratigraphy

A revised chronostratigraphy of the Barremian-Early Albian sedimentary record of the Maestrat Basin (E Iberian Peninsula) is provided based on a comprehensive synthesis of previous biostratigrahic data, a new ammonoid finding and numerical ages derived from 87Sr/86Sr values measured on shells of rudists, oysters and brachiopods. The succession, which comprises eight lithostratigraphic formations, is arranged into six major transgressive-regressive sequences and plotted against numerical ages, geomagnetic polarity chrons, ammonoid zones and the stratigraphic distribution of age-diagnostic ammonoids, orbitolinid fora - minifera and rudist bivalves. The oldest lithostratigraphic unit sampled, the marine Artoles Formation, is Early to Late Barremian. Above, the dinosaur-bearing deposits of the Morella Formation and its coastal to shallow-marine equivalent, the Cervera del Maestrat Formation, are of Late Barremian age and span at least part of the Imerites giraudi ammonoid zone. 87Sr/86Sr ratios from oyster shells in the upper part of the overlying marine Xert Formation are consistent with a latest Barremian-earliest Aptian age, while an ammonite belonging to the Late Barremian Martelites sarasini Zone was collected within the lowermost part of this latter formation. The Barremian-Aptian boundary is tentatively placed close above the base of the succeeding transgressive marls of the Forcall Formation by analogy with nearby Tethyan basins, where major transgressive records contain latest Barremian ammonoids in their basal parts. The rest of the Forcall Formation and the platform carbonates of the Villarroya de los Pinares Formation are of Early Aptian age. The transition from the Barremian into the Aptian occurred in the course of a wide transgression, which was accompanied by the proliferation of Palorbitolina lenticularis. This transgressive event drowned Late Barremian carbonate platforms (Xert Formation) throughout the basin. Extensive carbonate platforms (Villarroya de los Pinares Formation) recovered coevally with a post-OAE 1a late Early Aptian major regression of relative sea level. The last lithostratigraphic unit analyzed, the marine Benassal Formation, spans the terminal Early Aptian- Late Aptian interval. Based on ammonite distributions, the lower part of the overlying coastal to continental coal-bearing Escucha Formation is Early Albian in age. This improved chronostratigraphic knowledge allows a more precise correlation of the sedimentary record studied with other coeval successions worldwide

Révision de la "Falaise de Blanche" (Crétacé inférieur) au Liban et définition de l'Étage Régional Jezzinien

International audienceThe "Falaise de Blanche" is a prominent cliff, consisting mostly of Lower Cretaceous limestones that extends as linear outcrops over most of the Lebanese territory and provides geologists a remarkable reference for stratigraphic studies. However, until now, this unit was lacking a clear definition. We introduce herein the Jezzinian Regional Stage, the type-locality of which is at Jezzine. It equates as an unconformity-bounded unit and, per definition, it is framed by two discontinuities. Because we identified an additional, median sequence-boundary, poorly-expressed in the type-section but better at Aazour, only 4.5 km westward of Jezzine, the new regional stage implicitly spans two sequences. The lithostratigraphic framework being properly redefined, we were able to investigate time-constrained micropaleontological assemblages, consisting mostly of benthic foraminifers and calcareous algae. Typically Southern Tethysian, these assemblages contribute to high-resolution, holostratigraphic correlations with the Persian Gulf area, on the eastern part of the Arabian Plate. The Jezzinian interval correlates with the upper part of the Kharaibian Regional Stage (also known as "Thamama II" reservoir unit in the oil industry). In turn, the Jezzinian is indirectly correlated with the Northern Tethysian Urgonian stratigraphic units where it corresponds to a rather short interval encompassing the standard Barremian - Bedoulian stage boundary. Locally the upper discontinuity is associated to a significant intra-Bedoulian hiatus. The macrofossil assemblages found in the Jezzinian (echinids) and above it (ammonites) support, or at least do not contradict, our micropaleontological dating.Les calcaires du Crétacé inférieur de la "Falaise de Blanche" affleurent sur une grande partie du territoire libanais. Ils apparaissent dans le paysage sous forme d'escarpements linéaires saillants constituant autant de points d'ancrage remarquables pour tout recalage stratigraphique. Toutefois, jusqu'à très récemment, cette unité était piètrement caractérisée : il lui manquait notamment une définition rigoureuse. Nous introduisons ici l'Étage Régional Jezzinien, dont la localité-type est sise à Jezzine. Il s'agit d'une unité stratigraphique particulière, aussi appelée U.B.U. (pour "unconformity-bounded unit"), une unité qui, par définition, est encadrée par deux discontinuités. Parce que nous avons identifié une limite de séquence supplémentaire, en position médiane, peu exprimée dans la section-type, mais beaucoup mieux à Aazour, à 4,5 km à peine à l'ouest de Jezzine, le nouvel étage régional devrait implicitement couvrir deux séquences. Le canevas lithostratigraphique étant clairement redéfini, nous avons pu étudier les associations micropaléontologiques, constituées essentiellement de foraminifères benthiques et d'algues calcaires, associations dorénavant relativement bien contraintes du point de vue de leur âge. Typiquement sud-téthysiennes, elles facilitent les corrélations holostratigraphiques à haute résolution avec la région du Golfe persique, sur le côté oriental de la Plaque arabique. L'intervalle Jezzinien correspond ainsi à la partie supérieure de l'Étage Régional Kharaibien (aussi connu comme unité réservoir "Thamama II" dans l'industrie pétrolière). À son tour, le Jezzinien est indirectement corrélé avec les unités stratigraphiques urgoniennes nord-téthysiennes où il correspond à un intervalle relativement court comprenant la limite des étages standards (internationaux) Barrémien et Bédoulien. Localement la discontinuité sommitale est associée à un hiatus intra-Bédoulien significatif. Les associations macropaléontologiques reconnues dans le Jezzinien (échinides) et au-dessus de cette unité (ammonites) viennent à l'appui de notre datation micropaléontologique ou tout au moins ne la contredisent pas