Arenaria di Sevinèra
Zurück zu Antigorio-DeckeDarstellung und Status
- Farbe CMYK
- (0%,13%,29%,25%)
- Farbe RGB
- R: 190 G: 165 B: 135
- Rang
- lithostratigraphische Formation
- Gebrauch
- Element ist in Gebrauch
- Status
- informeller Begriff
Nomenklatur
- Deutsch
- Sevinèra-Sandstein
- Français
- Grès de Sevinèra
- Italiano
- Arenaria di Sevinèra
- English
- Sevinèra Sandstone
- Herkunft des Namens
-
Alpe di Sevinèra (TI), E Campo (Val Bavona)
- Historische Varianten
- Triassic marble (Burckhardt 1942, Burckhardt & Günthert 1957, Huber 1981), Sevinèra sandstone (Matasci et al. 2011 p.262), late Mid-Jurassic sandstone
Beschreibung
- Beschreibung
-
grès plus ou moins conglomératiques
Hierarchie und Abfolge
- Hangendes
- Liegendes
- Obergrenze
- Mit scharfer Kontakt zum Sevinèra-Marmor.
- Untergrenze
- Mit scharfer Kontakt über der Ri-d'Antabia-Konglomerat bzw. direkt über den Kristallin.
Alter
- Alter Top
-
- Callovien
- Alter Basis
-
- Bathonien
Geografie
- Geographische Verbreitung
- Lepontin: Val d'Antabia, Val Bavona.
Referenzen
- Erstdefinition
-
(2011) :
The Teggiolo zone: a key to the Helvetic–Penninic connection (stratigraphy and tectonics in the Val Bavona, Ticino, Central Alps). Swiss J. Geosci. 104, 257–283
p.262: 3.3.3 The Sevinèra sandstone
The post-Triassic sequence usually starts with a decameterthick layer of calcareous sandstone. At the Antabia waterfall it rests with a sharp limit upon the conglomerate described above. For this reason, even if the base of the sandstone is itself slightly conglomeratic, we prefer to consider it as a distinct formation. It is well exposed not only at Antabia but also on the eastern bank of Val Bavona, e.g. at the Alpe di Sevinèra (elevation about 2,100 m, E of Campo; from 684.2/141.7 to 685.0/141.5). Therefore, we name this formation the Sevinèra sandstone. In the classical literature (e.g. Burckhardt 1942; Burckhardt and Günthert 1957; Huber 1981) it was incorporated into the ‘‘Triassic marble’’; however, it is a true sandstone and is surmounted with a sharp contact by the marbles of the next formation. On the left bank of Val Bavona E of Campo, where the Triassic is absent, the Sevinèra sandstone always lies directly on the gneissic basement. The Sevinèra sandstone typically is coarse-grained and contains about 30–50% quartz, 20–40% calcite and 20–35% feldspar. Some variations can be observed in the proportions of these minerals, locally causing a thin bedding of this sandstone that usually looks rather homogenous and massive. Rare, extreme cases are decimetric layers of a weakly calcareous quartzite or of a quartzic calcarenite (at its base in the Vanis ravine above Campo). The base of the sandstone is often (but not always) conglomeratic, on a thickness that can reach 1 m, with centimetric to decimetric, sometimes well-rounded pebbles of gneiss or quartzite dispersed in the sandy matrix. Usually their abundance and size decrease gradually upwards. The source of the gneissic pebbles seems to be the underlying Antigorio gneiss, while the source of the quartzitic pebbles seems compatible with the quartzite layer that sometimes forms the base of the Triassic (see above). At several places one observes infiltrations of the sandstone into the underlying gneiss and a kind of progressive transformation of the gneiss into arkosic sandstone immediately below the calcareous sandstone. These features strongly suggest that the Sevinèra formation transgressed on a weathered basement. They have been already described by Burckhardt (1942, p. 166–169) who gave a correct interpretation. On the contrary Reinhard and Preiswerk (1934) and Huber (1981, p. 124–130) proposed a tectonic interpretation of the same features and spoke of ‘‘tektonische Brekzienbildung’’ and ‘‘Pseudokonglomerat’’ generated by a strong shearing along the contact. According to our observations these structures definitely have a sedimentary origin and prove once more the strict autochtony of the Teggiolo zone upon the Antigorio basement. The base of the Sevinèra sandstone displays typical characteristics of a stratigraphic contact, and neither the sandstone nor the immediately underlying gneiss show any sign of a stronger tectonization than the rest of the nappe.