Ela-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

Scs Note

TK500 >>> FR: de l'Ela, IT: di Ela

Nomenclature

Deutsch

Ela-Decke

Français

Nappe de l'Ela

Italiano

Falda di Ela

English

Ela Nappe

Origin of the Name

Piz Ela (GR)

Historical Variants

Aeladecke (Zyndel 1912, Ott 1922, Eggenberger 1925, Cornelius 1932, Wilhelm 1933, Stöcklin 1949), nappe de l'Ela (Trümpy 1970), Aela Nappe (Celâl Sengör 1982), Ela-Einheit (Dössegger 1987), Ela nappe (Manatschal & Nievergelt 1997), Ela-Decke (Eberli 1985, Furrer et al. 2015), falda Ela, Ela Nappe (TK500 / Gouffon et al. 2024)

Description

Description

Komplex strukturierte Sedimentdecke zwischen Err-Deckenkomplex und Silvretta-Decke, die vom ehemaligen kristallinen Substrat komplett abgeschert wurde (der basale Abscherhorizont liegt in den Evaporiten des Mora-Members).

Trias tardif ("Dolomites des Grisons centraux") et Jurassique.

Furrer et al. 1985: A décollement sheet of Upper Triassic, Jurassic and locally Cretaceous rocks, affected by thrusts, large ENE-trending folds and post-nappe synforms and antiforms. Generally regarded as an analog to the Ortler nappe, the Ela nappe also contains lower digitations in the Albula pass area, which may represent sediments of Languard or even Lower Austroalpine origin (Gualdauna, Bergüner Stein).

Hierarchy and sequence

Subordinate units

• Kössen-Formation
• Hauptdolomit-Gruppe (Ostalpin)

Upper boundary

Silvretta-Decke

Lower boundary

Err-Deckenkomplex (im Westen) bzw. Bernina-Deckenkomplex (im Osten)

Age

Age at top

• Early Cretaceous

Age at base

• Late Triassic

Geography

Geographical extent

Nordwestlich des Inns (und der Engadin-Störung): von der Ela-Gebirgsgruppe (W Bergün) über die Hänge nördlich des Albulapasses (Piz Üerstch) bis ins Oberengadin bei S-chanf. Kommt auch in der Toissa-Klippe (E des Schams) vor.

Palaenography and tectonic

Tectonic unit (resp. main category)

• Ela

Kind of protolith

• tectonic

References

Definition

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

p.88: The Ela Nappe, which forms the hangingwall of the Madulain Slices and the footwall of the Upper Austroalpine Silvretta Nappe, consists of a sedimentary sequence that was completely detached from its former crystalline substrate during Cretaceous top-W thrusting along Carnian evaporites. Large parts of it were affected by sinistrally transpressive deformation during Cretaceous shortening, followed by an extensional overprint in the latest Cretaceous (Froitzheim 1992) and the N-directed thrusting of the Silvretta Nappe during the Cenozoic orogeny (Froitzheim et al. 1994, Furrer et al. 2015). Hence, the internal structure of the Ela Nappe is highly complex due to its polyphase deformation.
East of Piz Kesch, below the Silvretta basement, a band of Triassic sediments, ending against the Engadin Fault, overthrusts the rest of the Ela Nappe which is dominated by Jurassic deposits. This band is interpreted as representing a thin uppermost slice of the Ela Nappe dragged along the base of the Upper Austroalpine Silvretta Nappe.
The Ela Nappe is assigned to the Lower Austroalpine Bernina Nappe Complex (Furrer et al. 2015) based firstly on the close similarity of its lithofacies to those of the Middle Jurrassic sediments of the Mezzaun Slice (see above; Eberli 1988), secondly on its offset by the Engadine Fault and the difference in structural position between the Ela Nappe and the Ortler Nappe (Schmid & Froitzheim 1993, Froitzheim et al. 1994) and thirdly on the difference in metamorphic grade of these two nappes (Conti 1997). As in the earlier literature, Mohn et al. (2011) instead attribute it to the Upper Austroalpine nappes, based on sedimentological and paleogeographical considerations in comparison with the Upper Austroalpine Ortler Nappe.