Grava-Decke

Representation and status

Color CMYK

N/A

Color RGB

R: 241 G: 239 B: 237

Rank

nappe

Validity

Unit is in Use

Status

valid

Nomenclature

Deutsch

Grava-Decke

Français

Nappe de la Grava

Italiano

Falda della Grava

English

Grava Nappe

Origin of the Name

Alp Grava (GR), Valser Tal

Historical Variants

Grava Nappe (Berger & Mercolli 2007, Berger et al. 2017), Grava-Decke (Wyss & Wiederkehr 2017)

Nomenclatorial Remarks

Die Grava-Decke bildete ursprünglich die nördliche Fortsetzung der Tomül-Decke.

Description

Description

Unterpenninische Decke der Ostschweiz. Wie die hangende Tomül-Decke ist sie aus einer eher monotonen Abfolge von schiefrigen tonigen und kalkigen Metasedimenten («Bündnerschiefer») aufgebaut.

Components

• carpholite

Hierarchy and sequence

Units at roof

• Tomül-Decke

Units at floor

• Aul-Decke

Age

Age at top

• Cretaceous

Age at base

• Cretaceous

Geography

Geographical extent

... bis zum Safiental, dann gegen NE Richtung Chur.

Point of interest

• Turischtobel (GR), Safiental
  Site particularities
  • Untergrenze
  Site accessibility
  • Bachprofil
  Coordinates
  • (2742100 / 1181840)
  Note
  • Steinmann 1994, Wyss & Wiederkehr 2017

Palaenography and tectonic

Paleogeography

Valaisan Basin

Tectonic unit (resp. main category)

• Grava

Metamorphism

monocyclic

Metamorphic facies

• blueschist facies

Note on facies

Durch das häufige Auftreten von Fe/Mg-Karpolith charakterisiert (Goffé & Oberhänsli 1992, Oberhänsli et al. 1995, Bousquet et al. 2002)

References

Definition

Gouffon Yves (Editor) (2024) : Tectonic Map of Switzerland 1:500000, Explanatory notes. Federal Office of Topography swisstopo, Wabern

p.72: The Grava Nappe overlies the Aul Nappe with a basal mélange zone, which contains Early Jurassic Gryphaea-bearing limestones (Nabholz 1945), metabasalts and dark shales. The rest of the nappe consists of Cretaceous “Bündnerschiefer” (Steinmann 1994). This nappe is folded around the front of the Adula Nappe and the Lunschania Antiform. In an overturned tectonic position, it can be followed all the way into a synform located between the Simano and Leventina-Lucomagno nappes (Wiederkehr et al. 2008). Westward it is found as a klippe in the core of the Molare Syncline (see § 5.7). Further west, an outcrop of “Bündnerschiefer” pinched in the Piora-Peiden Slice Complex (located between Lago Ritom and Airolo) is attributed to the Grava Nappe based on lithological and structural analogy. This latter occurence closes the nappe to the southwest above Airolo. However, the Quaternary cover hides this possible closure and it could instead connect with the Sion-Courmayeur Nappe that passes just south of this locality and contains similar rocks (Probst 1980).

Important Publications

Voll Gerhard (1976) : Structural studies of the Valser Rhine valley and Lukmanier region and their importance for the nappe structure of the Central Swiss Alps. Schweiz. mineral. petrogr. Mitt. 56/3, 619-626

Probst Philippe (1980) : Die Bündnerschiefer des nördlichen Penninikums zwischen Valser Tal und Passo di San Giacomo. Beitr. geol. Karte Schweiz (N.F.) 153, 66 Seiten

Nabholz Walter K. (1945) : Geologie der Bündnerschiefergebirge zwischen Rheinwald, Valser- und Safiental. Eclogae geol. Helv. 38/1, 1-119

Steinmann M. (1994) : Die nordpenninischen Bündnerschiefer der Zentralalpen Graubündens: Tektonik, Stratigraphie und Beckenentwicklung. Diss. ETH Zürich Nr.10668