Grès des Voirons

Rappresentazione e statuto

Colore CMYK

(0%,17%,43%,18%)

Colore RGB

R: 210 G: 175 B: 120

Rango

Formazione litostratigrafica

Uso

Unità in uso.

Status

termine informale

Discussione del statuto

Nomenclatura

Deutsch

Voirons-Sandstein

Français

Grès des Voirons

Italiano

Arenaria dei Voirons

English

Voirons Sandstone

Origine del nome

Les Voirons (France)

Varianti storiche

Flysch supérieur ou Grès des Voirons (Pilloud 1936), Série des Grès des Voirons (Lombard 1940), Grès des Voirons (Jan du Chêne et al. 1975), Flysch des Voirons proprement dit = Grès des Voirons (Karnay 1980), Flysch gréseux = Grès des Voirons (Charollais et al. 1998), Voirons Sandstones (Ospina-Ostios et al. 2013), Formation du Grès des Voirons (Ragusa 2015)

Descrizione

Potenza

200-300 m (Charollais et al. 1998, Ospina-Ostios et al. 2013, Ragusa 2015).

Gerarchia e successione

Unità di rango superiore

• Flysch des Voirons

Unità di rango inferiore

• Grès des Allinges
• Conglomérat du Signal
• Grès de Bons

Unità sovrastante

• Conglomérat du Vouan

Età

Geomorfologia

• tardo Eocene

Età alla base

• Eocene medio

Metodo di datazione

Nummulites du Paléocène tardif à l'Eocène précoce (Pilloud 1936), voire à l'Eocène moyen ou tardif (Lombard 1940). Palynologie et nannofossiles calcaires: Thanétien précoce à Lutétien (Jan du Chêne et al. 1975, Van Stuijvenberg & Jan du Chêne 1980). Foraminifères benthiques et planctoniques: Eocène moyen à tardif (P13-P19 ; Ujetz 1996, Frébourg 2006, Ospina-Ostios et al. 2013).

Geografia

Estensione geografica

Flanc oriental des Voirons et base du flanc occidental du Mont Vouan.

Regione-tipo

Les Voirons (France)

Sezione-tipo

• La Moutonnière (France)
  Caratteristiche del sito
  • Untergrenze
  • typische Fazies
  Agibilità del sito
  • Strassenanschnitt / Bahnanschnitt
  Coordinate
  • (2519200 / 1123240)
  Nota
  • Ragusa 2015 fig. 6.11 (6,391322 E / 46,255011 N)

Sezione di riferimento

• torrent de Curseille (France)
  Caratteristiche del sito
  • typische Fazies
  Agibilità del sito
  • Bachprofil
  Coordinate
  • (2518645 / 1116400)
  Nota
  • Ragusa 2015 fig. 8.6-8.11

Paleogeografia e tettonica

• Flyschs

Termini generici

• Voirons

Tipo di origine

• sedimentaria

Referenze

Definizione

Lombard Augustin (1940) : Géologie des Voirons. Mém. Soc. Helv. Sc. Nat. 74/1, 112 pages

Revisione

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

Forming the crest and most of the eastern flank of the Voirons ridge (Fig. 2), this formation is between 200 m and 300 m thick, and mainly consists of decimetre-thick to metre-thick beds of sandstone with subordinate calcareous shale, conglomerate and calcilutite. The sandstone beds are grey, with a brown alteration colour, and usually show sharp contacts with the surrounding shales. Grain size in the sandstone ranges from silt to very coarse sand. These rocks can be classified as calcite-cemented arkoses (Fig. 3) with a variable content of bioclasts and lithoclasts. Bioclasts primarily include red-algae fragments, clasts of larger benthic foraminifera (nummulitids and discocyclinids), planktonic foraminifera, bryozoans and rare echinoid debris. Winkler (1984a) found similar compositions in the Gurnigel–Schlieren Flysch group from Central Switzerland to the Lake of Geneva. Shaly intervals are grey to brown; green shale interbeds, very common in the Gurnigel flysch from other areas (Hubert, 1967; Winkler, 1984b), are missing in the Voirons. Metre-thick conglomerate layers mainly occur at localities near the top of the Voirons ridge (Pralere and Signal sections) and are typically clast-supported. The Voirons Sandstones contain igneous, metamorphic and sedimentary lithoclasts. The former include characteristic pink-coloured granite and red porphyry fragments, the parent rocks of which are presently only cropping out in the southern Alps and the Austro-Alpine zone (Sarasin, 1894; Cogulu, 1961). However, they also contain a small percentage of andesite and diabase (Fig. 4) that seem very similar to those found in greater quantities in very external (Helvetic and sub-Alpine) flysch formations (Taveyannaz Sandstones and Val d’Illiez Formation; Martini, 1968; Sawatzki, 1975). The sedimentary lithoclasts, of possible north-Alpine affinity, include micritic limestones with calpionellids, Urgonian-type biosparites, globotruncanid- rich mudstones and spiculites similar to those found in the Helvetic/Ultrahelvetic Wang beds (Villars, 1988). Note that Globotruncana bearing biomicrite was also observed in the Schlieren flysch (Winkler, 1983). Preliminary heavy-mineral analyses (Table 2; Ragusa, 2009; Ospina et al., 2009) show that some exposures (for example, the Moutonnieres section) are characterized by the occurrence of garnet, whereas others (for example, Fillinges quarry) contain a much lower quantity of this mineral. The common occurrence of sole marks (flute and groove casts) and Bouma sequences indicate that the Voirons Sandstones were deposited by gravity-driven mass flows. The thick, flat-based, massive sandstone beds (Fig. 5A) and clast-supported conglomerates exposed along the crest of the Voirons can be assigned to Facies F5 and F3 (Mutti, 1992; Mutti et al., 2003), respectively, whereas the rhythmic alternations of laminated sandstone and shale found in other exposures (for example, Bons quarry; Fig. 5B) appear to be typical of Facies F8 to F9. The planktonic foraminiferal assemblages retrieved from the samples gathered for this study are generally poorly preserved and contain a considerable amount of reworked specimens, including Upper Cretaceous globotruncanids, and Palaeocene and Lower Eocene globigerinids. Providing an accurate age for this formation is thus problematic, as is also the case for the other formations comprising the Gurnigel flysch in this area. The oldest assemblage obtained from one sample collected near the top of the Voirons massif (Signal exposure) includes Acarinina bullbrooki, Acarinina collactea, Acarinina primitiva, Acarinina echinata, Subbotina yeguaensis, Subbotina linaperta, Globigerina officinalis, Truncorotaloides topilensis ?, Turborotalia aff. ampliapertura (Fig. 6H and I), Turborotalia aff. cerroazulensis s.s. (small), Turborotalia frontosa, Turborotalia aff. increbescens, Dentoglobigerina ? (crushed), Morozovella spinulosa and small Catapsydrax sp. indicating a Middle Eocene age (planktonic foraminiferal zones P12 to P14). The youngest assemblage, retrieved from one thin shaly layer on the west flank of the Voirons (Moutonnieres exposure), contains well-preserved, partial internal moulds with fragile, finely preserved remnants of foraminifer walls of Subbotina cf. praeturritilina (Fig. 6A), Subbotina cf. linaperta (Fig. 6D), Catapsydrax aff. unicavus (juv.; Fig. 6E), Globoturborotalita ouachitaensis s.s. (Fig. 6J) and Globoturborotalita cf. ouachitaensis gnaucki (Fig. 6K). This assemblage is consistent with planktonic foraminiferal zones P14 to P19, or younger, indicating that the unit is Upper Eocene to Lower Oligocene. Overall, the planktonic foraminiferal data constrain the deposition of the Voirons Sandstones to between the Middle Eocene and the Early Oligocene. By contrast, nannofossil assemblages obtained from the same samples are Upper Palaeocene to Lower Eocene and, hence, are considered reworked (calcareous nannoplankton zones NP6 to 8, to NP10, corresponding to planktonic foraminiferal zones P4 to P6).

Materiale e vario

15203288