218 research outputs found
Upper Cretaceous, K/T boundary, and Paleocene agglutinated foraminifers from Hole 959D (CĂŽte d'Ivoire-Ghana Transform Margin)
Upper Cretaceous agglutinated foraminifer assemblages from Hole 959D of Ocean Drilling Program (ODP) Leg 159, CĂŽte dâIvoire-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 BĂ©doule (SE France): Stable isotope record and orbital cyclicity
International audienceBulk rock stable isotope analysis of La Marcouline section (Cassis-La BĂ©doule area, SE France) revealed a general trend of decreasing ÎŽ13C and ÎŽ18O values from the bottom to the top of the section. The decrease in ÎŽ13C values reflects a global trend in Middle Aptian times, namely a return to pre-excursion values of ÎŽ13C 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 BĂ©doule 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-BĂ©doule 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 (âŒ140â65 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 ForaminifÚres benthiques et planctoniques du Bédoulien sommital et du Gargasien inférieur de La TuiliÚre - St-Saturnin-lÚs-Apt (aire stratotypique de l'Aptien, Vaucluse, SE France)
International audienceFaisant suite aux recherches sur le BĂ©doulien et le Gargasien du secteur de Cassis-La BĂ©doule (B. du Rh., SE France), l'Ă©tude de quatre coupes en relais dans l'aire stratotypique de l'Aptien, situĂ©es dans le secteur du Hameau de la TuiliĂšre (commune de Saint-Saturnin-lĂšs-Apt, Vaucluse, SE France) a permis l'analyse dĂ©taillĂ©e des associations de foraminifĂšres benthiques (30 taxons) et planctoniques (15 taxons) du BĂ©doulien supĂ©rieur et du Gargasien infĂ©rieur. Descriptions, figurations et rĂ©partition stratigraphique sont fournies pour les formes les plus significatives, avec individualisation de plusieurs marqueurs, benthiques et surtout planctoniques. L'Ă©tude de ces derniers dans le cadre privilĂ©giĂ© de coupes dilatĂ©es et dĂ©pourvues de hiatus a permis de conforter la zonation dĂ©finie antĂ©rieurement dans le stratotype de l'Aptien infĂ©rieur de Cassis-La BĂ©doule (succession des zones Ă cabri, luterbacheri, ferreolensis, barri, algerianus) et mĂȘme de l'affiner, par la mise en Ă©vidence d'un horizon Ă Globigerinelloides ferreolensis heptacameratus nov. subsp., chevauchant la limite entre les zones Ă luterbacheri et Ă ferreolensis. Nos rĂ©sultats montrent Ă©galement la quasi-coĂŻncidence temporelle 1) du toit de la zones d'ammonites Ă Furcata, 2) du changement lithologique dit du "changement de couleur" et 3) d'un triple datum micropalĂ©ontologique (FAD de Praehedbergella luterbacheri, LAD de Protocythere bedoulensis et Lenticulina cf. nodosa) dont l'importance avait dĂ©jĂ Ă©tĂ© signalĂ©e dans le stratotype de Cassis-La BĂ©doule. Ces nouvelles donnĂ©es peuvent constituer des Ă©lĂ©ments pour la dĂ©finition de la limite BĂ©doulien-Gargasien. Durant le Gargasien infĂ©rieur (au sein de la Zone Ă luterbacheri), un Ă©pisode probablement d'origine volcanique, que nous sommes tentĂ©s d'assimiler au Niveau Van Gogh (initialement dĂ©tectĂ© dans le domaine vocontien), est marquĂ© par une forte crise de diversitĂ© affectant les foraminifĂšres Ă©pibenthiques, planctoniques, ainsi que les ostracodes. Sur le plan palĂ©oĂ©cologique et palĂ©obiogĂ©ographique, la comparaison des associations de foraminifĂšres benthiques et planctoniques du secteur de La TuiliĂšre avec celles des rĂ©gions voisines fait apparaĂźtre des spĂ©cificitĂ©s liĂ©es Ă la palĂ©o-profondeur et des affinitĂ©s paraissant plus marquĂ©es avec les microfaunes de certaines rĂ©gions borĂ©ales, comme l'Allemagne du Nord, qu'avec le domaine tĂ©thysien
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 ArdĂšche 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 BĂ©doule (SE France)
International audienceRecent biostratigraphic research in the marly limestones of the Cassis-La BĂ©doule 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 BĂ©doule
The Deshayesitidae Stoyanov, 1949 (Ammonoidea) of the Aptian historical stratotype region at Cassis-La BĂ©doule (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 BĂ©doule 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 BĂ©doule, 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 carriĂšre de La Marcouline (secteur de Cassis-La BĂ©doule, SE de la France) a rĂ©vĂ©lĂ© une tendance gĂ©nĂ©rale Ă la dĂ©croissance des valeurs de ÎŽ13C et ÎŽ18O depuis la base jusqu'au sommet de la coupe. La dĂ©croissance des valeurs de ÎŽ13C reflĂšte une tendance globale durant l'Aptien moyen, Ă savoir un retour Ă des valeurs infĂ©rieures Ă celles de l'excursion positive observĂ©e Ă l'Aptien infĂ©rieur, qui correspond Ă l'Ă©vĂ©nement anoxique ocĂ©anique OAE1a. L'analyse spectrale des rythmes de stratification suggĂšre que les cycles de prĂ©cession et les cycles longs d'excentricitĂ© de type MILANKOVITCH ont contrĂŽlĂ© le dĂ©pĂŽt des couplets marne-calcaire. Ceci peut s'interprĂ©ter comme le rĂ©sultat d'un forçage solaire aux basses latitudes qui a engendrĂ© un mode de prĂ©cipitations contrĂŽlĂ© par la mousson, induisant le dĂ©pĂŽt de couches riches en argile. A l'inverse, les niveaux calcaires se sont dĂ©posĂ©s durant les pĂ©riodes de climat plus sec. La plus forte productivitĂ© des eaux de surface durant les pĂ©riodes humides peut avoir Ă©tĂ© causĂ©e par un accroissement des apports venant du continent conduisant Ă une augmentation des Ă©lĂ©ments nutritifs au sein des bassins Ă©picontinentaux. La dĂ©tection d'une cyclicitĂ© orbitale dans les rythmes sĂ©dimentaires de la coupe de La Marcouline fournit l'occasion de calibrer avec la chronologie orbitale la durĂ©e de la zone bien caractĂ©risĂ©e par l'espĂšce de foraminifĂšre planctonique G. ferreolensis. Dans le secteur de Cassis-La BĂ©doule cette zone s'Ă©tage sur 33 cycles prĂ©cessionels et sa durĂ©e peut ainsi ĂȘtre estimĂ©e Ă environ 760.000 ans. Cet intervalle de temps est sensiblement plus bref que les estimations figurant dans certaines Ă©chelles de temps publiĂ©es jusqu'Ă prĂ©sent pour ladite zone. Cette nouvelle donnĂ©e constitue donc un argument qui autorise Ă proposer, pour le sous-Ă©tage Gargasien, une durĂ©e plus brĂšve que celle qui est admise jusqu'ici.Bulk rock stable isotope analysis of La Marcouline section (Cassis-La BĂ©doule area, SE France) revealed a general trend of decreasing ÎŽ13C and ÎŽ18O values from the bottom to the top of the section. The decrease in ÎŽ13C values reflects a global trend in Middle Aptian times, namely a return to pre-excursion values of ÎŽ13C 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 BĂ©doule 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
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