Arenaria di Sarnico
Torna a Formazione (del Piano) di SironeRappresentazione e statuto
- Colore RGB
- R: 200 G: 200 B: 125
- Rango
- unità litostratigrafia
- Uso
- Unità in uso.
- Status
- termine informale
Nomenclatura
- Deutsch
- Sarnico-Sandstein
- Français
- Grès de Sarnico
- Italiano
- Arenaria di Sarnico
- English
- Sarnico Sandstone
- Origine del nome
-
Sarnico (Italia)
- Varianti storiche
-
Pietra di Sarnico (de Alessandri 1899), Formazione di Pratolungo (Fernandez 1963), Arenaria di Sarnico = Sarnico Sandstone (de Rosa & Rizzini 1967, Bichsel & Haering 1981)
Gerarchia e successione
- Unità di rango superiore
- Unità sovrastante
- Unità sottostante
Geografia
- Estensione geografica
- Lombardia centrale (Brianza, Bergamasco).
Paleogeografia e tettonica
-
- Südalpine Flysche
- Paleogeografia
- Bacino Lombardo
- Termini generici
- Tipo di origine
-
- sedimentaria
- Condizioni di formazione
-
depositi di conoide esterna fino a conoide intermedia non canalizzata (Bichsel & Haering 1981)
Referenze
- Revisione
-
(1981) :
Facies evolution of Late Cretaceous flysch in Lombardy (northern Italy). Eclogae geol. Helv. 74/2, 383–420
p.393: The term "Pietra di Sarnico" was first mentioned by de Alessandri (1899). Fernandez (1963) described massive sandstones in the Pontida area as "Formazione di Pratolungo". With reference to de Alessandri (1899), de Rosa & Rizzini (1967) adapted the term "Sarnico Sandstone" to all these massive sandstones in the Bergamasco and in the Brianza. The formation crops out from the Brianza (thickness of 500 m) to the Lago d'Iseo (Fig. 1, E-K), where the thickness can be estimated as only 300 m. The lower boundary of the Sarnico Sandstone in the eastern part is with the Scaglia rossa, everywhere else with the Pontida Formation. The upper boundary is with the Bergamo Flysch. The Sarnico Sandstone is poor in fossils. Besides agglutinating foraminifera (Bathysiphon and Rhabdammina), there are only reworked faunal associations from the Albian and Cenomanian (e.g. Ticinella. Pianomalina. Rotalipora). However, in several nannoplankton samples Marthasterites furcatus indicates a Coniacian age. Further stratigraphie control is given by the more precisely dated overlying and underlying formations: In the western Bergamasco, the Sarnico Sandstone lies on sediments dated as Upper Turonian to Lower Coniacian. The onset of the Sarnico Sandstone deposition is obviously earlier in the east than in the west.
The bulk of the formation is composed of grey, massive or coarse-tail graded sandstones separated by thin shale layers. The sandstones consist of quartz (up to 50%). crystalline rock fragments (up to 20%). chert, feldspar, mica, chlorite. (Triassic) dolomite and limestone fragments from older formations. The sandstones have a scarce clayey matrix and a calcareous cement.