Lower and Middle Cenomanian ammonites from the Morondava Basin, Madagascar

Lower and Middle Cenomanian ammonite assemblages have been collected on a bed-by-bed basis from localities at Vohipaly and Mahaboboka, Madagascar, as well as from outcrops around Berekata, all in the Morondava Basin, southwest Madagascar. These collections demonstrate the presence of the upper Lower Cenomanian Mantelliceras dixoni Zone and the lower Middle Cenomanian Cunningtoniceras inerme Zone of the north-western European standard sequence. These records indicate that the striking anomalies in the zonal assemblages of the classic divisions of the Madagascan Cenomanian are based on mixed assemblages, rather than a succession that differs radically from that elsewhere in the world. The dixoni Zone fauna is: Desmoceras cf. latidorsatum (Michelin, 1838), Pachydesmoceras kossmati Matsumoto, 1987, Forbesiceras sp., F. baylissiWright & Kennedy, 1984, F. largilliertianum (d'Orbigny, 1841), Mantelliceras cantianum Spath, 1926a, M. dixoni Spath, 1926b, M. mantelli (J. Sowerby, 1814), M. picteti Hyatt, 1903, M. saxbii (Sharpe, 1857), Sharpeiceras sp., S. falloti (Collignon, 1931), S. mocambiquense (Choffat, 1903), S. cf. florencae Spath, 1925, Acompsoceras renevieri (Sharpe, 1857), A. tenue Collignon, 1964, Calycoceras sp., Mrhiliceras lapparenti (Pervinquičre, 1907), Mariella (Mariella) stolizcai (Collignon, 1964), Hypoturrilites taxyfabreae (Collignon, 1964), Turrilites scheuchzerianus Bosc, 1801, Sciponoceras cucullatum Collignon, 1964, and Sciponoceras antanimangaensis (Collignon, 1964). The presence of Calycoceras in a Lower Cenomanian association represents a precocious appearance of a genus typically Middle and Upper Cenomanian in occurrence, and matches records from Tunisia. The inerme Zone yields a more restricted assemblage: Pachydesmoceras kossmati, Forbesiceras baylissi, Acanthoceras sp. juv., Cunningtoniceras cunningtoni (Sharpe, 1855) and Hypoturrilites taxyfabreae

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

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Integrated stratigraphy of the Upper Hauterivian to Lower Barremian Agua de la Mula Member of the Agrio Formation, Neuquén Basin, Argentina

The Upper Hauterivian to Lower Barremian Agua de la Mula Member of the Agrio Formation (Neuquén Basin, Argentina) was studied applying an integrated stratigraphic approach and facies analysis. The ammonite biostratigraphy of the member has been improved based on bed-by-bed collecting. The already defined biozones (S. riccardii, C. schlagintweiti, C. diamantensis and P.groeberi) were recognized, precisely related to the succession, and further refinement was proposed. Sequences of different order are built by stacked starvation/dilution (S/D) sequences, regarded here as sixth order sequences with only two components that can be unequivocally distinguished: the lower starvation hemisequence and the upper dilution hemisequence. Pro- and retrogradational stacking pattern of S/D sequences define supra-ordinate sequences. The sequence-stratigraphic analysis resulted in the subdivision of the member into four main depositional sequences (DSAM-1 to -4) and several subordinate sequences. Previously published sequence stratigraphic charts of the Neuquén Basin did not relate sedimentary sequences to biozones, and are hence not comparable to the scheme presented here and other charts. Our study shows a good agreement with the sequence-chronostratigraphic scheme of European basins, thus arguing in favour of a predominantly eustatic control on sequence development during the Late Hauterivian to Early Barremian. A latest Early Barremian age is proposed for the almost ammonite-barren upper part of the Agrio Formation, based on correlations of sequence boundaries.Fil: Archuby, Fernando. GeoZentrum Nordbayern; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Wilmsen, Markus. Museum für Mineralogie und Geologie; AlemaniaFil: Leanza, Hector Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentin

Biostratigrafie spodní křídy manínské jednotky (lom Butkov, Strážovské vrchy, Západní Karpaty)

This paper is a continuation of systematic stratigraphical research of Lower Cretaceous sequence of the Manín Unit excavated in the Butkov quarry. Calcareous deposits are significant especially by richness of ammonites. Attention is focused on the parts enabling the definition of ammonite zones. The following ammonite zones were determined: the Campylotoxus Zone (Early Valanginian), the Furcillata Zone (Late Valanginian), the Balearis Zone (Late Hauterivian) and boundary between the Pulchella Zone and the Compresissima Zone (Early Barremian). Non-calcareous and calcareous dinoflagellates, calpionellids and calcareous nannoplankton were analysed in the same places to provide a correlation of their ranges with ammonite zones.Tato práce je pokračováním systematických stratigrafických výzkumů spodnokřídových uloženin manínské jednotky těžených v lomu Butkov. Tamější karbonátové uloženiny se vyznačují bohatým výskytem amonitů. Pozornost je věnována úsekům umožňujícím definování amonitových zón. Zjištěny byly následující amonitové zóny: zóna Campylotoxus (spodní valangin), zóna Furcillata (svrchní valangin), zóna Balearis (svrchní hauteriv) a hraniční uloženiny mezi zónou Pulchella a zónou Compressissima (spodní barrem). Ve stejných úsecích byly studovány vzorky na nevápnitá a vápnitá dinoflageláta, kalpionely a vápnitý nanoplankton za účelem jejich korelace s příslušnými amonitovými zónami

The distribution of the ammonite Gravesia (Salfeld, 1913) in the Kimmeridge Clay Formation (Late Jurassic) in Britain

Species of the ammonite Gravesia (Salfeld, 1913) have a widespread distribution in Europe over a relatively narrow stratigraphical range in the late Kimmeridgian and early Tithonian stages. The genus is a warm-water form that reaches its maximum stratigraphical range in the Submediterranean faunal province in central France and south Germany where six species have been recognised. Four of these, G. gigas (Zieten, 1830), G. gravesiana (d’Orbigny, 1850), G. irius (d’Orbigny, 1850) and G. lafauriana Hantzpergue, 1987 have been recorded in the Kimmeridge Clay Formation. A few examples have been found in cored boreholes, but most have come from the cliff and foreshore outcrops at Brandy Bay and Kimmeridge Bay in Dorset. The distribution of Gravesia in Britain is mostly restricted to the more calcareous parts of the succession where they represent migrations of a warmer water fauna into a region in which the ammonite assemblages were dominated by Subboreal forms of Aulacostephanus and Pectinatites. The palaeogeography of the late Jurassic in central and North West Europe comprised relatively small land areas separated by seaways that became progressively more restricted with time. In late Kimmeridgian and early Tithonian/Volgian times, migrations of warmer- and cooler-water ammonites through these seaways gave rise to mixed assemblages that enable correlations to be made between the local zonal schemes in the Submediterranean and Subboreal faunal provinces. Gravesia is one of the few ammonites that has a stratigraphical range that crosses the Kimmeridgian-Tithonian and Kimmeridgian-Volgian boundaries, and which has a large geographical distribution which includes much of North West and Central Europe and as far east as the Subarctic Urals. The known distribution of the genus in Britain is summarised herein, along with the first detailed account of its occurrence in the Kimmeridge Clay Formation in the Dorset type section