Cenomanian ammonites from the condensed deposits of the Helvetic Domain (western Alps, France and Switzerland)

The Cenomanian ammonites of the Helvetic Domain (French-Swiss Western Alps) are revised and illustrated for the first time since the middle of the Nineteenth Century. The faunas occur in remarkable condensed hemipelagic glauconite-rich biomicrites that also contain planktic foraminifera and small stromatolites. Thirty-three ammonite species referred to 15 genera are described; the assemblage extends from the lower part of the Lower Cenomanian Mantelliceras mantelli Zone (Neostlingoceras carcitanense Subzone) to the lower part of the Middle Cenomanian Acanthoceras rhotomagense Zone (Turrilites costatus Subzone). The assemblage comprises 57 percent trachyostracous forms, 41 percent heteromorphs of the standard N.W. European sequence, and 2 percent leiostracous forms, which inhabited an external shelf biome. The biogeographic affinity of this fauna is essentially cosmopolitan (69 percent), but 31 percent of the specimens belong to the European Boreal biota, with no Tethyan tax

Lyelliceratidae and Flickiidae (Ammonoidea) from the Upper Albian of the Helvetic Shelf (western Alps, France and Switzerland)

The condensed Upper Albian to Lower Cenomanian deposits of the Helvetic Shelf of France and Swtizerland yield diverse ammonite fauna includings representatives of the family Lyelliceratidae, subfamily Stoliczkaiinae that is the origin of the Upper Cretaceous Acanthoceratidae and its descendants, as well as representatives of the dwarf stoliczkaiine offshoot, the family Flickiidae, subfamily Salaziceratinae. -from Author

Cenomanian ammonites from the condensed deposits of the Helvetic domain (western Alps, France and Switzerland)

The Cenomanian ammonites of the Helvetic Domain (French-Swiss Western Alps) are revised and illustrated for the first time since the middle of the 19th century. The faunas occur in remarkable condensed hemipelagic glauconite-rich biomicrites that also contain planktic foraminifera and small stromatolites. Thirty-three ammonite species referred to 15 genera are described; the assemblage extends from the lower part of the Lower Cenomanian Mantelliceras mantelli Zone (Neostlingoceras carcitanense Subzone) to the lower part of the Middle Cenomanian Acanthoceras rhotomagense Zone (Turrilites costatus Subzone). The assemblage comprises 57% trachyostracous forms, 41% heteromorphs of the standard NW European sequence, and 2% leiostracous forms, which inhabited an external shelf biome. The biogeographic affinity of this fauna is essentially cosmopolitan (69%), but 31% of the specimens belong to the European Boreal biota, with no Tethyan taxa. -Author

Aptian to Cenomanian deeper-water hiatal stromatolites from the northern Tethyan margin

A suite of deeper-water hiatal (DWH) stromatolites has been identified in the phosphatic and glauconitic sediments of Aptian to Cenomanian age in the alpine Helvetic thrust-and-fold belt, which represents the former northern Tethyan margin. The most important occurrences date from the latest Early to Late Aptian, the late Early to early middle Albian, and the Early Cenomanian. They are invariably associated with condensed phosphatic beds and occur preferentially on top of hardgrounds or on reworked pebbles and fossils. The zone of optimal stromatolite growth and preservation coincides with the zone of maximal sedimentary condensation, in the deeper parts of phosphogenic areas. The DWH stromatolites show variable morphologies, ranging from isolated laminae ("films") to internally laminated columns and crusts. They reach thicknesses of maximal 10 cm and are either preserved in phosphate or micrite. In the latter case, they may show peripheral impregnations of phosphate or iron oxyhydroxides. The quasi-complete lack of macroscopic sessile organisms suggests that the DWH stromatolites grew close to the upper boundary of an oxygen-minimum zone. Electron-scanning microscopic images show that the Early Cenomanian examples preserved in micrite consist of filamentous structures, which form spaghetti-like assemblages. They are. interpreted as the remains of poikiloaerobic, heterotrophic microbes. Coeval DWH stromatolites are known from the entire European segment of the northern Tethyan margin, and shallow-water counterparts are commonplace on Tethyan carbonate platforms. This indicates that, in general, paleoceanographic and paleoenvironmental conditions were appropriate for stromatolite growth and preservation. The here-described DWH stromatolites proliferated especially in time windows, which followed upon the oceanic anoxic periods OAE la (Early Aptian), lb (latest Aptian and earliest Albian), and Id (latest Albian). They may represent pioneer ecosystems, which thrived during the recovery phases following the "mid"-Cretaceous OAEs

Le gouffre Jean-Bernard (-1602 m, Haute-Savoie), écoulements souterrains et formation du réseau

With its depth of 1602 m and development of more than 20 km, the lean-Bernard network provides a clear view of an alpine karst system : with a steep gradient and reduced watershed (4 km2). Over the last 30 years, hundreds of explorations led by the caving club Vulcain (Lyon) have resulted in a thorough knowledge of the cave. The network develops in a syncline formed from urgonian limestone (Lower Cretaceous). Two parts may be distinguished : a complex upper network with numerous dry phreatic tubes, and a lower network which restricts itself to a high meander. A tracing carried out in 1992 has allowed us to locale the outlet in the bed of the Clévieux (alt. 780 m). The I former spring of the upper network : must have been situated on the level of the lower entrances (about 1800 | m) and could date back to the end of the Tertiary when the valley was less deep. The Quaternary period is responsible for the hollowing of the old galleries, for the destruction of speleothems and the genesis of the lower "subterranean delta", between , -1400 and -1600 m.Avec 1602 m de profondeur et plus de 20 km de développement, le réseau Jean-Bernard permet d'avoir une vision directe sur un système karstique alpin à forte dénivellation et à bassin d'alimentation réduit (4 km2). La bonne connaissance spéléologique résulte de centaines d'explorations accomplies depuis 30 ans sous la direction du groupe spéléo Vulcain. La cavité se développe dans une gouttière | synclinale armée par les calcaires urgoniens. On distingue deux parties : un réseau amont complexe avec de nombreuses conduites forcées fossiles et un réseau aval se limitant à un haut méandre. Un traçage a permis de situer l'exutoire dans le lit du Clévieux (ait. 783 m). L'ancien exutoire du réseau amont devait se situer au niveau des | entrées inférieures (vers 1800 m) et pourrait remonter à la fin du Tertiaire lorsque la vallée était moins profonde. Le creusement : | quaternaire est responsable de sur : creusements de galeries, de destructions de concrétions et de la genèse du "delta souterrain" aval, entre ! -1400 et -1600 m.Lips Bernard, Gresse Alain, Delamette M, Maire Richard. Le gouffre Jean-Bernard (-1602 m, Haute-Savoie), écoulements souterrains et formation du réseau. In: Karstologia : revue de karstologie et de spéléologie physique, n°21, 1er semestre 1993. pp. 1-14

Lyelliceratidae and Flickiidae (Ammonoidea) from the Upper Albian of the Helvetic Shelf (western Alps, France and Switzerland)

The condensed Upper Albian to Lower Cenomanian deposits of the Helvetic Shelf of France and Swtizerland yield diverse ammonite fauna includings representatives of the family Lyelliceratidae, subfamily Stoliczkaiinae that is the origin of the Upper Cretaceous Acanthoceratidae and its descendants, as well as representatives of the dwarf stoliczkaiine offshoot, the family Flickiidae, subfamily Salaziceratinae. -from Author