Eric Fourcade

The disappearance of the “Ammonitico Rosso”

Abstract Results of the research for the reconstruction of the Tethys paleoenvironments show that the Ammonitico Rosso disappeared in the late Berriasian. No typical analogues have been recorded so far in younger levels. The Ammonitico Rosso basically developed during the rifting of the continental margins pointing up the phases of the Tethys opening. It is found on tilted-block tops and slopes as well as in the related basins. The Ammonitico Rosso developed especially in areas characterized by a complex paleogeography such as Apulia or southern Iberia. Few occurrences are reported from the central Atlantic margins, although the information is scarce and only available by Deep Sea Drilling cores. The maps 1:20,000,000 of middle Toarcian, early Kimmeridgian and late Tithonian paleoenvironments of the Tethys illustrate the gradual disappearance of this characteristic facies. This disappearance in the Berriasian is correlated with: (1) the increase of biogenic (e.g., the bloom of nannoplankton) and clastic sediment supply (development of flysch facies); (2) the establishment of an oceanic circulation, which was not suitable for the AR formation, from the Himalayan branch of the Tethys to the Caribbean; (3) the end of the rifting of the western Tethys continental margins, around Late Jurassic-Early Cretaceous times, which began to sink because of thermal subsidence; (4) the evolution of oceanic chemistry. However, these factors were controlled by the global paleogeographic evolution. The Tethys ocean occupied a triangle-shaped area bounded by huge continental masses situated in roughly tropical latitudes. The gradual fragmentation of Pangaea and Cretaceous-Tertiary continental collisions definitely modified the global paleogeography never again producing this kind of ocean.

Foraminifères et algues du Permien du Guatemala

Resume Les calcaires de la Formation Chochal du Permien du Guatemala (Amerique Centrale) sont riches en algues et foraminiferes. Les especes suivantes de dasycladales: Clavaporella americana, Connexia slovenica , de petits foraminiferes: Neoendothyra sp. et de fusulines Eoverbeekina americana, Pseudoreichelina discoidea, Schubertella muellerriedi, Pseudofusulinoides chixoyensis nov. sp., Skinnerella gruperaensis, Parafusulina australis, P. sapperi, P. guatemalaensis, P. fountaini, P. durhami et Skinnerina latina nov. sp. sont decrites. Lensemble de la Formation Chochal est dâge leonardien-roadien et presente des diachronismes importants. Les fusulines permettent detablir la paleogeographie dun golfe qui setendait du Texas au Venezuela et confirment les reconstitutions geodynamiques ou la region du lac de Maracaibo est juxtaposee au Nord du Guatemala (bloc Maya). La dispersion des fusulines a travers la Panthalassa semble avoir ete favorisee par des courants de surface, des radeaux de vegetaux flottants et la presence de relais ecologiques constitues par des plates-formes carbonatees installees sur des guyots et “terranes”.

New Early Permian fusulinid assemblage from Guatemala

Abstract A Latest Sakmarian–Earliest Artinskian (i.e. Late Wolfcampian) fusulinid assemblage, mainly composed of Levenella (?) and Pseudofusulinoides , has been discovered in the Purulha area, Guatemala. It contains some Tethyan species never described in America, mixed with more classical cratonic North American species. Palaeobiogeographically, this association allows improved correlations between the American and Tethyan faunistic provinces, and provide evidence of repetitive fusulinid and alga migrations during the Permian through Palaeopacifica, from the eastern Asian Blocks to the Chortis Block.

Age of the Guatemala breccias around the Cretaceous-Tertiary boundary: relationships with the asteroid impact on the Yucatan

Abstract The upper part of the near K/T boundary limestone breccia deposits which crop out in Guatemala near 16 °N contains impact remains: altered glass spherules (tektites) and elevated concentrations of iridium. This suggests that these deposits could result from the impact of the K/T boundary asteroid on the Yucatan. However, their matrix contains foraminifers of the Eugubina Zone and calcareous nannofossils of the CP1a Zone, an association characterizing Early (but not the earliest) Danian. This unusual assemblage of K/T and Danian components suggests that the upper part of the breccia was reworked several thousands of years after the K/T event.

Contribution à la datation de la croûte océanique de l'Atlantique central: Age valanginien inférieur des basaltes océaniques et âge néocomien des calcaires Maiolica de Maio (Iles du Cap Vert)

Abstract The discovery of calpionellids and radiolarians in thin sedimentary layers intercalated in the upper part of MORB tholeiitic pillow basalts allows us to date the oceanic crust of Maio Island (Capo Verde Islands) as early Valanginian instead of, as was hitherto believed Late Jurassic. This new dating fits better with reconstructions of the geological history of the Central Atlantic based on magnetic anomalies. The overlying light-coloured pelagic limestones (Maiolica facies) with radiolarians, aptychi and ammonites are Valanginian-Barremian in age. These limestones are lithologically similar to the white limestones drilled at several DSDP sites in the Central Atlantic.

La limite Crétacé/Tertiaire dans le Sud-Ouest du Petén (Guatemala)

Resume Au Peten, entre les calcaires a grands foraminiferes, algues et rudistes du Maastrichtien et les calcaires, marnes et argiles a foraminiferes planctoniques et nannofossiles calcaires du Danien inferieur, affleurent soit des breches a clastes de calcaires de plate-forme comme a El Caribe, soit une surface ferrugineuse comme a El Ceibo. Lorigine des breches a fait lobjet de controverses: tsunami du a limpact de la meteorite de la limite Cretace / Tertiaire sur le Yucatan versus baisse du niveau marin. La coupe dEl Ceibo fournit des donnees qui nincitent pas a retenir pour ces breches une origine liee a la vague dimpact. La comparaison des deux coupes plaiderait en faveur dune origine tectonique.

Paleogeography and Paleoenvironment of the Tethyan Realm During the Jurassic Breakup of Pangea

To reconstitute the evolution of the paleogeography and paleoenvironments of Tethys from 201 Ma until 135 Ma, five maps at a 1:20,000,000 scale were used, four of which were incorporated into the Tethys Atlas of Dercourt et al. (1993). They are (1) the Late Sinemurian map (unpublished), (2) the Mid-Toarcian (Bassoullet et al., 1993), (3) the Callovian (Enay et al., 1993), (4) the Early Kimmeridgian (Cecca et al., 1993), and (5) the Late Tithonian (Fourcade et al., 1991a, 1993). The first and last show periods of relatively low sea level, whereas the three others correspond to periods of relatively high sea level.

Radiolarians and Tethyan Radiolarites from Primary Production to their Paleogeography

Paleogeography is established using mainly plate kinematics and unfolding mountain belts, but basinal paleodepths are defined using specific facies, among which radiolarites can provide key information. The common equation radiolarites = deep oceanic basin is obviously too simple to be correct; and to infer from the geological message (e.g., radiolarites), the original, environmental, biological signal requires a good knowledge of the successive filters that have changed it and the originators of these signals (e.g., the radiolarians).

Levantinella nov. gen. et révision du genre Mangashtia HENSON, grands foraminifères du Jurassique et du Crétacé du Moyen-Orient

The presence of a young planispiral stage in the genus Mangashtia Henson, foraminifer from UpperCretaceous limestones of Iran is not demonstrated as it seems in the original description of the genus. The analysis of many topo types of Mangashtia viennoti Henson, from Upper Cretaceous of Kuh-e-Mangasht (Zagros Mountains) in Iran and the revision of the type-material enable to precise the characteristics of this genus and to consider it as unknown in the Jurassic. Its stratigraphic distribution must be, in this case, limited to the Upper Cretaceous in the best days knowledge. In fact, the revision of Mangashtia viennoti Henson from the type-locality and its comparison with the larger foraminifer wrongly attributed to Mangashtia Henson and coming from the Upper Jurassic limestones of Iran, Syria, Lebanon and Egypt allow us to include the Jurassic form into a new genus Levantina with as type-species Mangashtia egyptiensis Fourcade, Arafa & Sigal.

Origine, évolution et systématique de Praechubbina n. gen., foraminifères alveolinacea du crétacé supérieur du Guatemala et du Mexique

Resume Six nouvelles especes sont decrites qui, toutes anterieures a lapparition du genre Chubbina, permettent detabhir les origines de ce genre et de comprendre la structure de la sous-famille Chubbininae, largement repandue dans les plates-formes carbonatees peu profondes du Sud-Est du Mexique et du Guatemala, au Campanien-Maastrichtien. Lune de ces especes, Pseudonummoloculina pecheuxi n. sp., bien que depourvue de cloisonnement, semble a lorigine de toutes les autres par lensemble de ses caracteres, qui la placent parmi les Miliolacea. On montre en particulier que son ouverture en « fente crenelee est susceptible de donner naissance aux rangees douvertures multiples caracterisant les Chubbininae (super famille Alveolinacea), dont le nouveau genre Praechubbina fait partie. Les 5 autres especes nouvelles sont reunies avec “ Boretis ” cardenasensis Barker et Grimsdale dans ce nouveau genre. Lune delles, Praechubbina breviclaustra n. sp., montre une transition entre Pseudonummoloculina pecheuxi n. sp. et ses 5 congeneres; louverture a lorigine comparable a celle de P. pecheuxi n. sp. passe a une organisation en rangees douvertures multiples; la meme espece montre lapparition concomitante dun cloisonnement discret. Les autres especes, P. cardenasensis ( Barker et Grimsdale ), P. compressa n. sp., P. obesa n. sp., P. ovoidea n. sp. et P. streptospira n. sp., egalement caracterisees par des rangees douvertures multiples, offrent toute une gamma de differenciations de lenroulement et de lendosquelette (avec apparition de planchers chez certaines) independantes de la taille du proloculus. Il sagit done dun complexe foisonnant au sein duquel les especes du genre Chubbina prennent leurs racines.