Formation du Pralet

Representation and status

Color CMYK

(0%,29%,55%,4%)

Color RGB

R: 245 G: 175 B: 110

Rank

lithostratigraphic Formation

Validity

Unit is in Use

Scs Note

Ratifié par le SKS.

Scs Date

27.04.2017

Nomenclature

Deutsch

Pralet-Formation

Français

Formation du Pralet

Italiano

Formazione del Pralet

English

Pralet Formation

Origin of the Name

Creux du Pralet (VD), au nord du Rocher Plat

Historical Variants

Cycle III = Pralet Formation (Baud et al. 2016)

Nomenclatorial Remarks

Bereich der spätigen Lumachellen und überlagernden Dolomite, gelben Schiefer und Dolomitbreccien (Genge 1958), Cycle IV + Cycle V (Baud & Mégard-Galli 1975), Cycle III

Description

Thickness

150 m am Seehorn (Genge 1958), 90 m à la localité-type (Baud et al. 2016).

Components

• Conodonts

Sephardiella truempy (Hirsch)

Hierarchy and sequence

Subordinate units

• «Obere Rauhwacke» (des Penninikums)
• Membre des Erpilles
• Membre du Balmi (-grabe/-wald)

Units at roof

• Formation de Clôt la Cime

Upper boundary

Surface érosive (Rocher Plat, Seehorn) ou contact tectonique. La Fm. de Clot-la-Cime sus-jacente n'est présente que dans la région de Briançon (France).

Lower boundary

Contact transgressif sur les dolomies claires du sommet de la Fm. du Wiriehorn.

Age

Age at top

• Late Ladinian

Age at base

• Earliest Ladinian

Dating Method

Conodontes (Sephardiella truempy) et comparaisons de faciès (Baud et al. 2016)

Geography

Geographical extent

Ecailles du Rocher Plat (SE Château-d'Oex) et du Seehorn (Diemtigtal).

Type area

Pays d'Enhaut (VD), écaille du Rocher Plat

Type locality

• Rocher Plat - Rocher Pourri (VD)
  Site particularities
  • Obergrenze
  • Untergrenze
  • typische Fazies
  Site accessibility
  • Grat
  Coordinates
  • (2581000 / 1145370)
  Note
  • Baud et al. 2016 ; base dolomitisée

Type profile

• Rocher Plat - Rocher Pourri (VD)
  Site particularities
  • Obergrenze
  • Untergrenze
  • typische Fazies
  Site accessibility
  • Grat
  Coordinates
  • (2581000 / 1145370)
  Note
  • Baud et al. 2016 Suppl. Mat. Fig. f3/g ; base dolomitisée

Point of interest

• Röti am Seehore (BE)
  Site particularities
  • typische Fazies
  Site accessibility
  • Grat
  Coordinates
  • (2602060 / 1157480)
  Note
  • Genge 1958: 150 m, avec base calcaire non dolomitisée

Palaenography and tectonic

• Triassic of the Briançonnais

Paleogeography

Briançonnais Domain :
microcontinent briançonnais

Tectonic unit (resp. main category)

• Médianes rigides :
  nappe des Préalpes Médianes rigides

Kind of protolith

• sedimentary

Sequence

Base = transgression majeure de la limite Anisien/Ladinien (Baud et al. 2016).

References

Definition

Baud Aymon, Plasencia Pablo, Hirsch Francis, Richoz Sylvain (2016) : Revised middle Triassic stratigraphy of the Swiss Prealps based on conodonts and correlation to the Brianc¸onnais (Western Alps). Swiss J. Geosc. 109/2, 365-377

p. 368: 2.3 Cycle CIII: ‘‘Formation du Pralet ‘‘ (Online Resources 1 and 3)

Mégard-Galli and Baud (1977) having not provided a formation name for this cycle, we propose herein the Pralet Formation for the Prealps. This ‘‘Formation du Pralet’’

overlies conformably the Wiriehorn Formation.

It encompasses two members: the new Balmi and Erpilles Members. Transgressive from the bottom, the Balmi Member (Online Resources 1 and 3) starts with light

coloured dolo-grainstone, followed by the large transgressive unit of the ‘‘Couches à Costatoria goldfussi’’ that represents the peak of the transgression (MFS). It ends with the sudden appearance of crinoidal limestone, with a brown dolomite at its top.

The second member, the Erpillles Member, starts with terrigenous yellowish clay (mudstone). This sudden terrigenous input was previously interpreted as the base of a new cycle (Cycle IVa, Mégard-Galli and Baud 1977). But it is at present interpreted as the continuation of the high-stand deposit of Cycle III that consists of the thick, partly brecciated, dolomite of the Erpilles Member. We propose a Ladinian age for the Pralet Formation time interval, with the Balmi Member being Early Ladinian (Fig. 3 and Online Resources 1, 2 and 3 for further details).

Material and varia

15203277