Conglomerato del Ri d'Antabia

Back to Antigorio nappe

Representation and status

Color CMYK
Color RGB
R: 175 G: 125 B: 125
lithostratigraphic Formation
Unit is in Use
informal term


Conglomérat du Ri d'Antabia
Conglomerato del Ri d'Antabia
Ri d'Antabia Conglomerate
Origin of the Name

Ri d'Antabia (TI), SW San Carlo

Historical Variants

Ri d'Antabia conglomerate (Matasci et al. 2011 p.261)


Max. 20 m (Matasci et al. 2011).

Hierarchy and sequence

Upper boundary


Lower boundary

Antigorio-Kristallin bzw. relitkische Trias


Age at top
  • Middle Jurassic
Age at base
  • Early Jurassic
Dating Method

Post-triasique (Matasci et al. 2011).


Geographical extent
Lepontin: Val d'Antabia, Val Bavona (Campo).

Palaenography and tectonic

Kind of protolith
  • sedimentary


Matasci Battista, Epard Jean-Luc, Masson Henri (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.261: 3.3.2 The Ri d’Antabia conglomerate:

The second sedimentary cycle starts sporadically with a coarse conglomerate. It is best developed at the cascade of the Ri d’Antabia (2.5 km SW San Carlo; 681.4/138.8) where it reaches a thickness of 20 m. There it consists of several m-thick layers of variable composition that represent distinct successive detrital events, with rapid lateral variations. In broad lines they show an inverse reconstitution of the eroded series: the first layers contain mixed calcareous and dolomitic pebbles; the source of the dolomitic clasts is obviously Triassic, while the limestones, that are unknown in the underlying stratigraphic column, presumably originate from the erosion of a post-Triassic and pre-conglomeratic, completely destroyed part of the column. Some layers show a weak graded-bedding with an increasing upwards proportion of sandy matrix. It also contains a layer of biotite-rich micaschist that might represent a metapelitic intercalation. Gneissic elements appear higher up, first as rare clasts dispersed in the mainly calcodolomitic conglomerate. The top of the conglomerate is formed by a 4 m thick layer entirely made of gneissic pebbles in an abundant arkosic matrix. At first sight this gneissic conglomerate might look like a genuine gneiss and has indeed been mapped as a tectonic slice of basement by Burckhardt and Günthert (1957) and by Huber (1981). The Ri d’Antabia conglomerate extends to Campo where it is exposed in the bed of the Bavona river. Here it rests upon the lower layers of the Triassic dolomite. It consists in an often purely dolomitic, monomict conglomerate or breccia that, at first sight, could easily be confused with genuine Triassic dolomite. However, the clastic structure is often well recognizable. At several places it also contains a few pebbles of gneiss. It clearly represents a basal conglomerate, transgressive on the partially eroded Triassic dolomite that it reworks with a smaller amount of elements eroded from the granitic basement. Above Campo a conglomerate has been mapped by Schmidt and Preiswerk (1908a) but is no longer visible today. It never reappears (nor the Triassic) farther E on the left bank of Val Bavona, where the Sevinèra sandstone (see below) is always transgressive on the Antigorio gneiss. Other conglomerates occur in a similar position at several places along the base of the Teggiolo zone in Italy. Good examples are found at the NW foot of the Teggiolo mountain where they have already been noted by Schmidt and Preiswerk (1908a) and by Spring et al. (1992, their cross-section D). At the base of the slope (near Véina), in the inverse limb of the nappe, a very demonstrative and easily accessible outcrop shows a conglomerate formed of well rounded boulders of Antigorio granite, occasionally accompanied by pebbles of marble and quartzite, filling an (overturned) small depression eroded into the gneiss. Following the contact uphill towards the hinge of the nappe, several other channels of decametric width and 5–10 m depth occur at the top the gneiss and are filled by mainly gneissic conglomerates. They pass upwards to the sandstones and marbles that usually form the base of the Teggiolo zone in this area. On the other side of the valley, on Monte Cistella, Milnes (1964) observed similar conglomerates at the base of the metasediments. They contain aplitic and granitic pebbles and blocks, identical to the underlying Antigorio granite. Although sporadic, these conglomerates are of prime importance for the interpretation of the Teggiolo zone: (1) for stratigraphy: as they can in no case be Triassic (see below Sect. 3.3.6), they prove the post-Triassic age of the rest of the series (including the overlying marbles, generally considered as Triassic); (2) for tectonics: they are like pins that fix the Teggiolo sedimentary cover on the Antigorio gneiss. At Antabia, the confusion of the gneissic conglomerate with a basement slice gave rise to suggestions of intense shearing at the base of the Teggiolo zone. Just on the contrary the conglomerates demonstrate the autochtony of the sedimentary cover with respect to its gneissic basement.

Back to top