Voirons Flysch

Datasets of the Voirons Flysch (Voirons-Wägital complex, Chablais Prealps, Haute-Savoie, France)

Geological settings

The Alps are surrounding by several moderate elevated reliefs made of sedimentary covers and usually called Prealps by geographers. The Chablais and Swiss Prealps are located between the Geneva Lake (France) and the Thune Lake (Switzerland). These Prealps are constituted by a stack of Tethyan sedimentary covers (Triassic to Eocene) which were scraped off from their crystalline basement during the Alpine Tethys closure, following a thin-skinned, in-sequence thrusting. The uppermost nappes originate from the Piemont domain, while the lowermost nappe (the Niesen nappe and the Voirons-Wägial complex) derived from the Valais domain. The Chablais and Swiss Prealps represent the former sedimentary accretionnary prism of the Alpine Tethys in the Western to Central Alps. Nowadays, they overlie the Helvetic nappes to the SE and the North Alpine Foreland Basin to the NW throughout a basal Ultrahelvetic nappe.

The Voirons-Wägital complex (formerly named Gurnigel nappe) outcrops along the external edge, in lower position. Four flyschs, spreaded from east to west, compose the Voirons-Wägiral complex. The Voirons nappe is the westernward unit, located at c.a. 20 km to Geneva. It is subdivided into four stratigraphic units: the Voirons Sandstone Fm. (VS), the Vouan Conglomerate Fm. (VC), the Boëge Marl Fm. (BM) and the Bruant Sandstone Fm. (BS). Recent revision of the planktonic foraminiferal biostratigraphy (Ragusa et al., in review) constrains age between Ypresian (Early Eocene) and probably Priabonian (Late Eocene). The provenance analysis (Ragusa et al., 2017) described two major detrital provenances: (1) the Quartzose petrofacies with major quartz component associated with granitic and sedimentary rock fragments, and (2) the Feldspathic petrofacies marked by composition dominated by feldspars and large inputs of metamorphic rock fragments also confirmed by higher garnet content in heavy mineral assemblage.

The palaeogeography of the Voirons-Wägital complex remains a matter of debate. The usual interpretation suggests a South Penninic origin (Winkler, 1983, 1984; Caron et al., 1989). However, the recent revision of the planktonic foraminiferal biostratigraphy (Ospina et al., 2013; Ragusa et al., in review) rejuvenated the Voirons Flysch and indicate a Valais palaeogeographic origin (Trümpy, 2006).

Dataset

The dataset composes the PhD thesis focusing on the petrography, the stratigraphy and the provenance of the Voirons Flysch (Ragusa, 2015).

• GarnetGeoch.csv: garnet (64-125 µm) geochemistry from QEMSCAN (SEM-EDS) at the University of Geneva (Departement of Earth Sciences).
• HeavyMinerals.csv: Heavy mineral populations (64-125 µm) using the QEMSCAN (SEM-EDS) at the University of Geneva (Department of Earth Sciences).
• ModalComposition.csv: dataset of the modal composition following the Gazzi-Dickinson model (Gazzi et al, 1973; Dickinson et al., 1979; Dickinson et al., 1983). Countings include extrabasinal, intrabasinal grains, porosity and overall cementation (Zuffa, 1980). Keys are described in the preambule.
• outcrops: GPS location of outcrops with stratigraphic affiliation. Dataset is available in csv, gpx and geojson files.
• references.bib: list of bibliographic references concerning the Voirons flysch
• StratigraphicColours.gpl: reference colours of the Voirons Flysch stratigraphy for Gimp and Inkscape.
• StratigraphicLog.csv: bed thickness measurements of the studied outcrops
• tectonic.csv: dip and azimut measurements of bed and faults (Ospina-Ostios, 2017).
• TourmalineGeoch.csv: tourmaline (64-125 µm) geochemistry from QEMSCAN (SEM-EDS) at the University of Geneva (Department of Earth Sciences).

Figures

Main figures describing the overall architecture of the Voirons flysch

• CrossSection_Allinges: cross-section of the Allinges Hills based on electric prospects (Buchli, 1976). This relief belongs to the Allinges Sandstone Mb. (Voirons Sandstone Fm.) where three lithological successions were identified: (1) marly interval, (2) sand-marl alternation and (3) sand to conglomerate succession. The Allinges Hills are capped by variable thickness of Quaternary glacial deposits and only a restricted part of the Allinges Sandstone Mb. is exposed, concerning lithology 2 and 3.
• CrossSection_Voirons: cross-section of the Voirons range (Ospina-Ostios, 2017, modified). This section does not cut the Bruan Sandstone Fm.
• GeologicalMap: geological map of the western part of the Voirons flysch (Ospina-Ostios, 2017, modified). Beyond the Dranse river, outcrops disappear beneath Quaternar glacial deposits and only exposed at the Fenalet quarry, near Saint-Gingolph (CH).
• Palaeogeography: successive palaeogeographic models of the Complex Virons-Wägital. Initial model (Hsü and Schlanger, 1971) located the complex in the alpine geosynclinal, along a central cordiellera. The second model is extrapolated from Caron et al. (1989) and involves global tectonic model. The flyschs are deposited in the south part of the Piemont ocean, along the subduction zone of southern TetShyan margin. The third model (Ragusa et al., 2017) also involve the subduction zone but shift the location of the flyschs in the Valais domain.
• StratigraphicLog: Stratigraphic log of the Voirons flysch.
• TectonicMap_Prealps: Tectonic map of the Chablais and Swiss Prealps from the Swiss tectonic map (SwissTopo, 2008).

Main references

• Caron C (1976) La nappe du Gurnigel dans les Préalpes. Eclogae Geologicae Helvetiae 69(2)297-308. doi: 10.5169/seals-164510
• Caron C, Homewood P, Wildi W (1989) The original Swiss flysch: a reappraisal of the type deposits in the Swiss Prealps. Earth-Science Reviews 26:1-45. doi: 10.1016/0012-8252(89)90002-0
• Ospina-Ostios LM, Ragusa J, Wernli R, Kindler P (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. doi: 10.1111/sed.12013
• Ragusa J, Segvic B, Ospina-Ostios LM, Kindler P (2017) Provenance analysis of the Voirons Flysch (Gurnigel nappe, Haute-Savoie, France): Stratigraphic and paleogeographic implications. International Journal of Earth Sciences 106(8):2619-2651. doi: 10.1007/s00531-017-1474-9
• Ragusa J, Ospina-Ostios LM, Spezzaferri S, Kindler P (in review) Revision of the planktonic foraminiferal biostratigraphy of the Voirons flysch (Chablais Prealps, Haute-Savoie, France). Swiss Journal of Geosciences.
• Trumpy R (2006) Geologie der Iberger Klippen und ihrer Flysch-Unterlage. Eclogae Geologicae Helvetiae 99(1):79-126. doi: 10.5169/seals-169227
• Winkler W (1984) Palaeocurrents and petrography of the Gurnigel-Schlieren Flysch: a basin analysis. Sedimentary Geology 40:169-189. doi: 10.1016/0037-0738(84)90045-9