Upper Cretaceous, K/T boundary, and Paleocene agglutinated foraminifers from Hole 959D (Côte d'Ivoire-Ghana Transform Margin)

Upper Cretaceous agglutinated foraminifer assemblages from Hole 959D of Ocean Drilling Program (ODP) Leg 159, Côte d’Ivoire-Ghana Transform Margin, reflect the subsidence history and paleoceanography of the widening equatorial Atlantic gateway. Five benthic foraminifer assemblage types are recognized: (1) Santonian and the lowermost Campanian assemblages (Cores 159-959D-65R and 64R) are characterized by the occurrence of bathyal calcareous benthic foraminifers with an increasing proportion of agglutinated foraminifers. The disappearance of calcareous foraminifers and assemblages exclusively composed of organically cemented agglutinated forms in Section 159-959D-65R-3 reflects the subsidence of the seafloor below the calcite compensation depth (CCD); (2) lower Campanian "biofacies B" assemblages (Cores 159-959D-63R through 61R) are exclusively composed of low-diversity agglutinated foraminifers, accompanied by abundant and occasionally well-preserved radiolarian assemblages; (3) middle Campanian to upper Maastrichtian deposits (Cores 159-959D-59R through 49R) contain an exclusively agglutinated Rzehakina epigona biofacies, which is well-known from middle to deep bathyal sites along the North Atlantic margins; (4) a change in agglutinated foraminifer assemblage composition toward morphologies commonly observed in present infaunal habitats and the common occurrence of the presumably infaunal genus Spiroplectammina are observed in Core 159-959D-48R. This change in agglutinated foraminifer assemblages corresponds to the Tethyan early Paleocene "Spiroplectammina event;" (5) a diversified Paleocene "Lizard Springs type" assemblage is characterized by several diverse Rzehakina, Saccamina, and Haplophragmoides species. Assemblages from Cores 159-959D-48R through 44R display high species diversity and reflect the deepest (lower bathyal to upper abyssal) paleobathymetry. Ranges of agglutinated foraminifer marker species and occurrences of paleoceanographic events within this biostratigraphic framework are almost identical to those observed in the North Atlantic, in the Western Tethys, and along the conjugate Brazilian margin. These observations lead us to confirm that a deep-water circulation system common to the North and South Atlantic has been active at least since the Santonian

The Gargasian (Middle Aptian) of La Marcouline section at Cassis-La Bédoule (SE France): Stable isotope record and orbital cyclicity

International audienceBulk rock stable isotope analysis of La Marcouline section (Cassis-La Bédoule area, SE France) revealed a general trend of decreasing δ13C and δ18O values from the bottom to the top of the section. The decrease in δ13C values reflects a global trend in Middle Aptian times, namely a return to pre-excursion values of δ13C values following a major, positive excursion in the Early Aptian, which is a reflection of the Oceanic Anoxic Event (OAE) 1a. Power spectra of the bedding rhythms suggest that precessional and long eccentricity cycles of the Milankovitch band controlled the deposition of marl-limestone bundles. This can be interpreted as the result of a forcing by insolation at low latitudes which resulted in a monsoon-controlled precipitation pattern, that in turn induced the deposition of clay-rich beds. Conversely, limestone beds were formed in periods of dryer climate. Higher sea-surface productivity during wet periods may have been caused by an increase in continental runoff and a consequent enhancement in the delivery of nutrients to epicontinental basins. An orbital cyclicity in the sedimentary patterns in La Marcouline section provides the opportunity to calibrate the duration of the well-established G. ferreolensis foraminiferal Zone with that of orbital chronology. The G. ferreolensis Zone at Cassis-La Bédoule spans 33 precessional cycles and its duration is thus estimated to be approximately 760 ka. This length of time is significantly shorter than the estimates of published timescales for this zone and thus may be an argument for proposing that the Gargasian substage is significantly shorter than its currently accepted range

Characterisation of the organic matter of upper Bedoulian and lower Gargasian strata in the historical stratotypes (Apt and Cassis-la-Bédoule areas, SE France)

International audienceThe Total Organic Carbon (TOC) content of the Gargasian strata studied in their historical stratotype area is rather low (0.3% on average). Only a few levels show TOC values approaching 1.2%. This small amount of preserved organic matter, associated with low hydrogen index values (10 to 115 mg hydrocarbons/g TOC), argues for deposition in fully oxic conditions. This organic content is a mixture of land-derived organic particles and deeply oxidized marine organic matter. The organic flux was strongly diluted by the autochthonous carbonate input

Drilling of Early Cretaceaous Oceanic Anoxic Event 1a in southern France

The massive concentration of black, laminated, organic carbon-rich shales at certain time periods during the Cretaceous period (∼140–65 Ma) led to the concept of Oceanic Anoxic Events (OAEs). These events are characterized by unusually enhanced preservation of organic matteracross environments ranging from the deep oceans to shelf seas. Enhanced productivity of siliceous and organic-walled primary producers and/or strongly dysaerobic or anoxic conditions in all major oceans were both suggested as likely causes (Meyer and Kump, 2008). Fundamental chemical and biological changes in the world ocean must have been associated with these events

Associations et biostratigraphie des Foraminifères benthiques et planctoniques du Bédoulien sommital et du Gargasien inférieur de La Tuilière - St-Saturnin-lès-Apt (aire stratotypique de l'Aptien, Vaucluse, SE France)

International audienceFaisant suite aux recherches sur le Bédoulien et le Gargasien du secteur de Cassis-La Bédoule (B. du Rh., SE France), l'étude de quatre coupes en relais dans l'aire stratotypique de l'Aptien, situées dans le secteur du Hameau de la Tuilière (commune de Saint-Saturnin-lès-Apt, Vaucluse, SE France) a permis l'analyse détaillée des associations de foraminifères benthiques (30 taxons) et planctoniques (15 taxons) du Bédoulien supérieur et du Gargasien inférieur. Descriptions, figurations et répartition stratigraphique sont fournies pour les formes les plus significatives, avec individualisation de plusieurs marqueurs, benthiques et surtout planctoniques. L'étude de ces derniers dans le cadre privilégié de coupes dilatées et dépourvues de hiatus a permis de conforter la zonation définie antérieurement dans le stratotype de l'Aptien inférieur de Cassis-La Bédoule (succession des zones à cabri, luterbacheri, ferreolensis, barri, algerianus) et même de l'affiner, par la mise en évidence d'un horizon à Globigerinelloides ferreolensis heptacameratus nov. subsp., chevauchant la limite entre les zones à luterbacheri et à ferreolensis. Nos résultats montrent également la quasi-coïncidence temporelle 1) du toit de la zones d'ammonites à Furcata, 2) du changement lithologique dit du "changement de couleur" et 3) d'un triple datum micropaléontologique (FAD de Praehedbergella luterbacheri, LAD de Protocythere bedoulensis et Lenticulina cf. nodosa) dont l'importance avait déjà été signalée dans le stratotype de Cassis-La Bédoule. Ces nouvelles données peuvent constituer des éléments pour la définition de la limite Bédoulien-Gargasien. Durant le Gargasien inférieur (au sein de la Zone à luterbacheri), un épisode probablement d'origine volcanique, que nous sommes tentés d'assimiler au Niveau Van Gogh (initialement détecté dans le domaine vocontien), est marqué par une forte crise de diversité affectant les foraminifères épibenthiques, planctoniques, ainsi que les ostracodes. Sur le plan paléoécologique et paléobiogéographique, la comparaison des associations de foraminifères benthiques et planctoniques du secteur de La Tuilière avec celles des régions voisines fait apparaître des spécificités liées à la paléo-profondeur et des affinités paraissant plus marquées avec les microfaunes de certaines régions boréales, comme l'Allemagne du Nord, qu'avec le domaine téthysien

About the stratigraphic position of the Lower Aptian Roloboceras hambrovi (Ammonoidea) level

International audienceIn the stratotype of the Lower Aptian substage the position of the assemblage that includes Roloboceras spp. and Megatyloceras spp. has been clearly established as being in the middle part of the upper Bedoulian. Some authors have erected this horizon as a subzone, or even a zone, with R. hambrovi as species-index. In other areas (southern England, eastern Spain, the Ardèche in southeastern France), where taphonomic conditions are not always as favourable as they are in the stratotype, the level at which this assemblage occurs seems to be confined to the upper part of the lower Bedoulian. Various hypotheses are considered in an attempt to explain this divergence

The Douvilleiceratidae (Ammonoidea) of the Lower Aptian historical stratotype area at Cassis-La Bédoule (SE France)

International audienceRecent biostratigraphic research in the marly limestones of the Cassis-La Bédoule area (SE France) provided a rich macrofauna of Douvilleiceratidae Parona & Bonarelli, 1897. From the uppermost Barremian (Pseudocrioceras waagenoides Subzone) to the middle Aptian (Parahoplites melchioris Zone), specimens of Procheloniceras, Cheloniceras, Roloboceras, Megatyloceras and Epicheloniceras were collected in succession. In this paper we describe the various genera and species from this material and delimit precisely their stratigraphic positions. Our study shows that each genus or subgenus characterizes a discrete stratigraphic interval. In addition, the Cheloniceras meyendorffi (upper Bedoulian), Epicheloniceras debile, Epicheloniceras gracile, and Epicheloniceras buxtorfi (Gargasian = middle Aptian) subzones, originally defined in England by Casey (1961a), are identified for the first time in the Lower Aptian stratotypic area of Cassis-La Bédoule

The Deshayesitidae Stoyanov, 1949 (Ammonoidea) of the Aptian historical stratotype region at Cassis-La Bédoule (SE France)

International audienceOne of the significant results of the multidisciplinary investigations carried out during recent years in the Lower Aptian historical stratotype of the Cassis-La Bédoule region (South-Eastern France) was a proposal to update the local Upper Barremian/Lower Aptian ammonite biozonation in order to be more consistent with the standard Mediterranean zonal subdivisions. So the lower and upper boundaries of the Lower Aptian (= Bedoulian substage of most French authors) as well as the boundaries of four biozones (Paradeshayesites tuarkyricus, P. weissi, Deshayesites deshayesi, Dufrenoyia furcata zones) and two subzones (Roloboceras hambrovi and Paradeshayesites grandis subzones) were identified and formally defined in the stratotype. However, to support this zonal scheme additional descriptions and illustrations of the ammonites collected bed by bed in the several sections studied were still required. In this paper we describe the members of the most significant ammonite family found in the Lower Aptian of Cassis-La Bédoule, i.e. the Deshayesitidae, and delimit precisely their stratigraphic positions. As regards zonation, we have replaced the index ammonite of the earliest Bedoulian Zone, i.e. Paradeshayesites tuarkyricus (Bogdanova, 1983), by Paradeshayesites oglanlensis (Bogdanova, 1983), and re-established the Pseudocrioceras waagenoides Zone as a subzone

Le Gargasien (Aptien moyen) dans les stratotypes historiques de l'Aptien (SE France) : Introduction générale

version française de l'article hal-00142240International audiencepas de résum

Le Gargasien (Aptien moyen) de la coupe de La Marcouline à Cassis-La Bédoule (SE France) : enregistrement des isotopes stables et cyclicité orbitale

Une analyse sur roche totale des isotopes stables de la coupe de la carrière de La Marcouline (secteur de Cassis-La Bédoule, SE de la France) a révélé une tendance générale à la décroissance des valeurs de δ13C et δ18O depuis la base jusqu'au sommet de la coupe. La décroissance des valeurs de δ13C reflète une tendance globale durant l'Aptien moyen, à savoir un retour à des valeurs inférieures à celles de l'excursion positive observée à l'Aptien inférieur, qui correspond à l'événement anoxique océanique OAE1a. L'analyse spectrale des rythmes de stratification suggère que les cycles de précession et les cycles longs d'excentricité de type MILANKOVITCH ont contrôlé le dépôt des couplets marne-calcaire. Ceci peut s'interpréter comme le résultat d'un forçage solaire aux basses latitudes qui a engendré un mode de précipitations contrôlé par la mousson, induisant le dépôt de couches riches en argile. A l'inverse, les niveaux calcaires se sont déposés durant les périodes de climat plus sec. La plus forte productivité des eaux de surface durant les périodes humides peut avoir été causée par un accroissement des apports venant du continent conduisant à une augmentation des éléments nutritifs au sein des bassins épicontinentaux. La détection d'une cyclicité orbitale dans les rythmes sédimentaires de la coupe de La Marcouline fournit l'occasion de calibrer avec la chronologie orbitale la durée de la zone bien caractérisée par l'espèce de foraminifère planctonique G. ferreolensis. Dans le secteur de Cassis-La Bédoule cette zone s'étage sur 33 cycles précessionels et sa durée peut ainsi être estimée à environ 760.000 ans. Cet intervalle de temps est sensiblement plus bref que les estimations figurant dans certaines échelles de temps publiées jusqu'à présent pour ladite zone. Cette nouvelle donnée constitue donc un argument qui autorise à proposer, pour le sous-étage Gargasien, une durée plus brève que celle qui est admise jusqu'ici.Bulk rock stable isotope analysis of La Marcouline section (Cassis-La Bédoule area, SE France) revealed a general trend of decreasing δ13C and δ18O values from the bottom to the top of the section. The decrease in δ13C values reflects a global trend in Middle Aptian times, namely a return to pre-excursion values of δ13C values following a major, positive excursion in the Early Aptian, which is a reflection of the Oceanic Anoxic Event (OAE) 1a. Power spectra of the bedding rhythms suggest that precessional and long eccentricity cycles of the MILANKOVITCH band controlled the deposition of marl-limestone bundles. This can be interpreted as the result of a forcing by insolation at low latitudes which resulted in a monsoon-controlled precipitation pattern, that in turn induced the deposition of clay-rich beds. Conversely, limestone beds were formed in periods of dryer climate. Higher sea-surface productivity during wet periods may have been be caused by an increase in continental runoff and a consequent enhancement in the delivery of nutrients to epicontinental basins. An orbital cyclicity in the sedimentary patterns in La Marcouline section provides the opportunity to calibrate the duration of the well-established G. ferreolensis foraminiferal Zone with that of orbital chronology. The G. ferreolensis Zone at Cassis-La Bédoule spans 33 precessional cycles and its duration is thus estimated to be approximately 760 ka. This length of time is significantly shorter than the estimates of published timescales for this zone and thus may be an argument for proposing that the Gargasian substage is significantly shorter than its currently accepted range