Arenaria di Sarnico
Retour à Gruppo del Flysch LombardoReprésentation et statut
- Couleur RGB
- R: 200 G: 200 B: 125
- Rang
- unité lithostratigraphique
- Usage
- Ce terme est en usage.
- Status
- terme informel
Nomenclature
- Deutsch
- Sarnico-Sandstein
- Français
- Grès de Sarnico
- Italiano
- Arenaria di Sarnico
- English
- Sarnico Sandstone
- Origine du nom
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Sarnico (Italia)
- Variantes historiques
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Pietra di Sarnico (de Alessandri 1899), Formazione di Pratolungo (Fernandez 1963), Arenaria di Sarnico = Sarnico Sandstone (de Rosa & Rizzini 1967, Bichsel & Haering 1981)
Hiérarchie et succession
- Unité hiérarchiquement supérieure
- Unités sus-jacentes
- Unités sous-jacentes
Géographie
- Extension géographique
- Lombardia centrale (Brianza, Bergamasco).
Paléogéographie et tectonique
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- Südalpine Flysche
- Paléogéographie
- Bassin lombard
- Termes génériques
- Type de protolithe
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- sédimentaire
- Conditions de formation
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depositi di conoide esterna fino a conoide intermedia non canalizzata (Bichsel & Haering 1981)
Références
- Révision
-
(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.