Conglomérat du Vouan

Représentation et statut

Couleur CMYK

(0%,13%,50%,22%)

Couleur RGB

R: 200 G: 175 B: 100

Rang

Formation lithostratigraphique

Usage

Ce terme est en usage.

Status

terme informel

Discussion du statut

Nomenclature

Deutsch

Vouan-Konglomerat

Français

Conglomérat du Vouan

Italiano

Conglomerato del Vouan

English

Vouan Conglomerate

Origine du nom

Mont de Vouan (France)

Variantes historiques

Conglomérats du Vouan (Lombard 1940), série des grès et conglomérats du Vouan (Rutsch et al. 1966), Flysch du Vouan (Karnay 1980), Vouan Conglomerates (Ospina-Ostios et al. 2013), Conglomérat du Vouan (Cogulu 1961, Charollais et al. 1998), Formation des Conglomérats du Vouan (Ragusa 2015)

Description

Description

galets à blocs métriques: fragments cristallins "sudalpins" (Sarasin 1894) et sédimentaires briançonnais (Frébourg 2006)

Géomorphologie

Falaises.

Épaisseur

300-400 m (Coppo 1999).

Hiérarchie et succession

Unités sus-jacentes

• Marne de Boëge

Limite inférieure

Limite biostratigraphique [???] avec les Grès des Voirons, visible au torrent de Cruseilles et au nant de Manant.

Âge

Âge au sommet

• Oligocène précoce

Âge à la base

• Eocène tardif

Méthode de datation

Lutétien tardif à Priabonien (Vial 1975) ; Eocène tardif à Oligocène précoce (P16-P20 ; Frébourg 2006).

Géographie

Extension géographique

Mont Vouan, flanc oriental des Voirons et col de Saxel. Probablement encore présent au nord de la Grande Combe et de la Tête de Char, voire jusqu'aux collines d'Allinges.

Région-type

Les Voirons (France)

Typusprofil

• meulière de Grande Gueule (France)
  Particularités du site
  • typische Fazies
  Accessibilité du site
  • geschützter Geotop
  Coordonnées
  • (2518000 / 1114325)
  Note
  • <p>Ragusa 2015 (6,380586 E / 46,168069 N)</p>

Paléogéographie et tectonique

Termes génériques

• Voirons

Type de protolithe

• sédimentaire

Conditions de formation

Faciès proximaux de séquences turbiditiques (Frébourg 2006, Ospina-Ostios et al. 2013).

Références

Révision

Ospina-Ostios Lina M., Ragusa Jérémy, Wernli Roland, Kindler Pascal (2013) : Planktonic foraminifer biostratigraphy as a tool in constraining the timing of flysch deposition: Gurnigel flysch, Voirons massif (Haute-Savoie, France). Sedimentology 60, 225–238

Between 300 m and 400 m thick, the Vouan Conglomerates occur along the eastern flank of the Voirons ridge, but are best exposed in the western cliffs of the Mont Vouan along the Menoge River (Figs 2 and 5C), where they have been mined for millstone. These cliffs consist of plurimetric beds of matrix-supported conglomerates (cobbly and pebbly sandstones) that are occasionally highly weathered and friable, probably due to poor cementation (Fr
ebourg, 2006). Shaly intervals are extremely rare in this formation. The conglomerate matrix is a feldspar-rich arkose (Fig. 3). The centimetre-sized to metre-sized lithoclasts are angular to well-rounded and derive from sedimentary, metamorphic and igneous rocks. The former include Triassic dolostones, crinoidal-rich, bryozoan-rich and oolite-rich limestones of possible Late Jurassic age (Frébourg, 2006), and orbitolinid limestone dating to the Aptian (Cogulu, 1961). Metamorphic blocks comprise dark schists, sandstones and conglomerates, possibly derived from Carboniferous-age strata from the Zone Houillere (Lombard, 1940) which are generally absent in the Voirons Sandstones. In contrast, the pink granite clasts, so typical of the coarse-grained lithologies observed in the Voirons Sandstones, are missing in the Vouan Conglomerates. Preliminary analyses (Table 2; Ragusa, 2009) show that the heavy-mineral assemblage is dominated by garnet. The thick cobbly/pebbly sandstone beds are massive and commonly show erosional bases and load casts. Normal and inverse grading occur, but clasts are, in general, randomly distributed within beds. Facies F1 to F7 of Mutti (1992) have been observed in the Vouan Conglomerates, Facies F1, F2 (Fig. 5D) and F5 being the most frequent ones. As mentioned above, shaly intervals are scarce in the Vouan Conglomerates and only one sample from the Curseilles creek has so far yielded a sizeable planktonic foraminiferal assemblage. It includes Acarinina sp., A. cf. bullbrooki (reworked), Globigerina cf. officinalis, Globoturborotalita ouachitaensis s.s., Globigerina cf. praebulloides, Globoturborotalita cf. ciperoensis (Fig. 6L) and Globoturborotalita ouachitaensis gnaucki indicating a Late Eocene to Early Oligocene age (planktonic foraminiferal zones P15 to P19).