A revised ammonoid biostratigraphy for the Aptian of NW Africa:Essaouira-Agadir Basin, Morocco

International audienceA revised ammonoid biostratigraphy is presented for the Aptian of NW Africa, Essaouira-Agadir Basin (EAB), Morocco, based on detailed analysis of 5 key sections. A number of bio-events are documented and 26 genus and 43 species fully documented, forming the largest published Aptian ammonite collection made from NW Africa. The section at Tiskatine is documented as the type section, and 8 zones and subzones are defined, of which 5 are new. This work allows correlation of the Aptian of the EAB to the Standard Mediterranean Ammonite Scale (SMAS). Two main hiatuses are identified at the scale of the basin scale: a major one that includes most of the lower Aptian and the base of the upper Aptian and a second one encompass the top of the upper Aptian and the base of the lower Albian. The ammonite fauna displays a clear Tethyan palaeobiogeographic character affected by a fairly high degree of endemism at the genus and species level. The new genus and species Elsaisabellia tiskatinensis is introduced.(C) 2017 Elsevier Ltd. All rights reserved

Architecture séquentielle des dépôts marins à continentaux sur une marge passive (Cénomanien, marge Atlantique marocaine, transversale d'Agadir)

Seven sections, covering the upper Albian to lowermost Turonian, have been correlated from full-marine to continental-dominated deposits across a passive margin, along a transect 425 km long, from the present-day Atlantic coast to the "Pre-African Trough" between the Anti-Atlas and the High-Atlas. The thickness of the Cenomanian succession changes from around 500 metres in the fully marine sections to 250 metres in mostly continental facies in the western High-Atlas, about 150 km updip, to a few tens of metres in the Bou Tazoult area. The strata thicken again eastwards into the Pre-African Trough where they can be traced without major facies changes to the Kem Kem embayment and to the Bechar area in Algeria. Over all this eastern area, continental facies are overlain by the fully-marine shallow-water deposits of the Cenomanian-Turonian boundary interval. A first major conclusion is that fluvial aggradation in high-frequency transgressive-regressive sequences is coeval with the seaward-shift of the shoreline, in accordance with the genetic sequence stratigraphic model of Galloway (1989). Both the flatness of the depositional profile and the corresponding very low energy of the marine environment during the transgressions account for the blanket of red continental clays on top of marine facies in updip depositional sequences, which is then preserved under the marine transgressive surface of the next sequence. A second major conclusion is that the high-frequency transgressive-regressive (T-R) sequences do not look like classical parasequences bounded by transgression surfaces. They usually exhibit a surface created by a sea-level fall within the regressive half-cycle. This is interpreted in the following way: regressions did not operate through a regular seaward-shift of the shoreline, but through stepped sea-level falls. The very low slope of the depositional ramp is thought to have enhanced the sequence stratigraphic record of such stepped regressions. Short-term, high-frequency sequences are organized into medium-frequency T-R sequences (seven in the Cenomanian) which show an overall aggrading and slowly retrograding pattern along the whole transect. Comparisons with other basins show that medium-frequency sequences do not fit the third-order depositional sequences described elsewhere, casting doubts about a eustatic mechanism for their deposition.Sept coupes couvrant l'intervalle Albien supérieur-Turonien inférieur ont été corrélées sur plus de 400 km, des faciès entièrement marins jusqu'aux dépôts presque exclusivement continentaux, depuis la côte atlantique et le sillon pré-africain, entre le Haut-Atlas et l'Anti-Atlas marocains. L'épaisseur des dépôts cénomaniens varie d'environ 500 m dans les séries entièrement marines de la côte actuelle, à 250 m dans les séries principalement continentales du Haut-Atlas, pour s'amincir à quelques dizaines de mètres (Bou Tazoult), sur environ 250 km. La série s'épaissit à nouveau vers l'est dans le sillon pré-africain où elle peut être suivie sans changements notables vers le golfe des Kem-Kem et le secteur de Béchar en Algérie. Sur toute la partie orientale de la transversale, les faciès continentaux ou mixtes sont recouverts par les dolomies marines du passage Cénomanien-Turonien. Une première conclusion majeure est que, dans les séquences transgression-régression (T-R) à haute fréquence, l'aggradation fluviatile accompagne sans hiatus le déplacement de la ligne de rivage au cours du demi-cycle régressif, en accord avec le modèle génétique de Galloway (1989). La platitude extrême du profil de dépôt ainsi que la faible énergie correspondante de l'environnement marin expliquent la préservation de la faible couche de dépôts continentaux rouges de fin de séquence au cours de la transgression suivante. Une seconde observation majeure est que ces séquences T-R à haute fréquence ne sont pas organisées comme les "paraséquences" du modèle de stratigraphie séquentielle "d'Exxon", en principe limitées les unes des autres par des surfaces de transgression. Elles comportent toutes en plus une surface de chute du niveau marin relatif dans le demi-cycle régressif. Ceci est interprété de la façon suivante : les régressions de la ligne de rivage ne sont jamais régulières, elles s'effectuent par l'intermédiaire de chutes étagées qui emboîtent vers l'aval les prismes côtiers successifs. Là encore, la pente extrêmement faible du profil de dépôt explique la distorsion géométrique de l'enregistrement stratigraphique du demi-cycle régressif. Les séquences à haute fréquence sont organisées en séquences T-R à moyenne fréquence dont l'empilement au cours du Cénomanien est globalement aggradant-lentement rétrogradant sur la transversale. La comparaison avec d'autres bassins montre que les séquences à moyenne fréquence ne correspondent pas aux séquences de 3º ordre décrites ailleurs, mettant ainsi en doute un mécanisme eustatique pour leur mise en place

Revision of Toxoceratoides royeri (d'Orbigny, 1842) and its bearing on the systematics of the Aptian Acrioceratidae Vermeulen, 2004 (Ammonoidea, Ancyloceratina, Ancyloceratoidea)

The acrioceratid ammonite genus Toxoceratoides Spath has long been used to accommodate any late Barremian or Aptian species that show morphological similarities with its type species Toxoceratoides royeri (d'Orbigny). The revision of T. royeri and its allied species T. rochi Casey has convinced us that new genera should be introduced for some Aptian forms that were previously referred to Toxoceratoides. These are Klingerites gen. nov. (type species: Toxoceratoides? haughtoni Klinger & Kennedy), Richardreymentella gen. nov. (type species: Ancyloceras patagonicum Stolley), Immelites gen. nov. (type species: Tonohamites multituberculatus Immel & Guoxiong), Jenslehmannella gen. nov. (type species Jenslehmannella bangestanense gen. et sp. nov.). This contribution also reconsiders the taxonomic value of Tonohamites Spath, Colomboceratoides Etayo Serna and Raymondcaseyites Avram. The new taxonomic treatment proposed herein outlines the diversity and provincialism of the Acrioceratidae during Aptian times and questions the alleged cosmopolitan distribution of Toxoceratoides

Revision of Toxoceratoides royeri (d'Orbigny, 1842) and its bearing on the systematics of the Aptian Acrioceratidae Vermeulen, 2004 (Ammonoidea, Ancyloceratina, Ancyloceratoidea)

The acrioceratid ammonite genus Toxoceratoides Spath has long been used to accommodate any late Barremian or Aptian species that show morphological similarities with its type species Toxoceratoides royeri (d'Orbigny). The revision of T. royeri and its allied species T. rochi Casey has convinced us that new genera should be introduced for some Aptian forms that were previously referred to Toxoceratoides. These are Klingerites gen. nov. (type species: Toxoceratoides? haughtoni Klinger & Kennedy), Richardreymentella gen. nov. (type species: Ancyloceras patagonicum Stolley), Immelites gen. nov. (type species: Tonohamites multituberculatus Immel & Guoxiong), Jenslehmannella gen. nov. (type species Jenslehmannella bangestanense gen. et sp. nov.). This contribution also reconsiders the taxonomic value of Tonohamites Spath, Colomboceratoides Etayo Serna and Raymondcaseyites Avram. The new taxonomic treatment proposed herein outlines the diversity and provincialism of the Acrioceratidae during Aptian times and questions the alleged cosmopolitan distribution of Toxoceratoides

New and poorly known Aptian Acrioceratidae (Acrioceratidae, Ammonoidea) from Cassis - Roquefort-la-Bedoule (Bouches-du-Rhone, France)

Brainaella marcoulinense gen. nov. et sp. nov. is described on the basis of new material from the Upper Aptian of the reference succession of Cassis - Roquefort-la-Bedoule (Bouches-du-Rhone, France). The morphological features of this new taxon suggest affinities with the late Early Aptian Toxoceratoides rochi CASEY, a poorly understood species revised in the present contribution. The study of these two taxa sheds new light on the taxonomic status, content and evolution of the long-debated families Helicancylidae HYATT and Acrioceratidae VERMEULEN

Controls and timing of Cenomanian-Turonian organic enrichment andrelationship to the OAE2 event in Morocco, North Africa

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Upper Tithonian ammonites (Himalayitidae Spath, 1925 and Neocomitidae Salfeld, 1921) from Charens (Drôme, France)

This contribution focuses on the Perisphinctoidea ammonite taxa from the Upper Tithonian at Charens (Drôme, south-east France). Emphasis is laid on five genera that belong to the families Himalayitidae and Neocomitidae. We document the precise vertical range of the index-species Micracanthoceras microcanthum, and a comparative ontogenetic- biometric analysis sheds new light on its range of variation and dimorphism as compared to the bestknown Spanish populations. As herein understood, the lower boundary of the M. microcanthum Zone (base of the Upper Tithonian) is fixed at the FAD of its index species. The faunal assemblages and species distribution of the P. andreaei Zone are rather similar to those described at the key-section of Le Chouet as confirmed by the co-occurrence of the genera Protacanthodiscus, Boughdiriella and Pratumidiscus. New palaeontological evidence supports the view that the basal Neocomitidae Busnardoiceras busnardoi was derived from Protacanthodiscus andreaei in the upper part of the P. andreaei Zone

Systematic palaeontology of the Perisphinctoidea in the Jurassic/Cretaceous boundary interval at Le Chouet (Drome, France), and its implications for biostratigraphy

International audienceThis study describes ammonite taxa of the Perisphinctoidea in the Jurassic/Cretaceous boundary interval at Le Chouet (Drome, France). Emphasis is placed on new and poorly known Himalayitidae, Neocomitidae and Olcostephanidae from the lower part of the Jacobi Zone auctorum. Significant results relate the introduction of Lopeziceras gen. nov.. grouping himalayitid-like forms with two rows of tubercles, and Praedalmasiceras gen. nov.. grouping the early Berriasian Dalmasiceras taxa. Study of the ontogenetic sequences of both genera show that they were derived from late Tithonian Himalayitidae. This supports the distinction between the subfamilies Himalayitidae and Dalmasiceratidae subfam. nov. Content, variation, dimorphism and vertical range of the Neocomitidae Borriasella, Pseudoneocomites. Elenaella and Delphinella are discussed. A conservative use of the Olcostephanidae Proniceras is followed herein

Fishing in the Central Atlantic, an earliest Cenomanian ichthyodectiform from DSDP Site 367, Cape Verde Basin

International audienceThe discovery of the ichthyodectiform specimen in a borehole sample collected ca. 400km offshore the West African Atlantic Margin at 699.9 m measured depth is an exceptional event that deserves to be recorded. Although its systematic assignment is too uncertain to draw precise palaeobiogeographical implications, the fish bears a strong similarity to Chiromystus, which would indicate a late marine connection ofthis genus (or a related representative of this lineage), which has been described on both sides of the opening South Atlantic in the Early Cretaceous. If the fish is related to Gillicus, with which it also shares characteristics, it extends southward the known geographical distribution of that genus, currently known from the North Atlantic only