Formazione (del Piano) di Sirone

Representation and status

Color RGB

R: 205 G: 200 B: 105

Rank

lithostratigraphic Formation

Validity

Unit is not in Use

Status

local name (informal)

Nomenclature

Deutsch

Piano-di-Sirone-Formation

Français

Formation de Sirone

Italiano

Formazione (del Piano) di Sirone

English

Sirone Formation

Origin of the Name

Sirone (Italia)

Historical Variants

puddingha di Sirone (de Cristoforis 1838), --- (Stoppani 1857), Konglomerat von Sirone (Senn 1924), Konglomerate von Sirone-Olona (Vonderschmitt 1938), Strati di Pian di Sirone (dal Piaz & Trevisan 1956), Piano di Sirone = Sirone Conglomerate (Bichsel & Häring 1981), Conglomerato di Sirone

Nomenclatorial Remarks

Considered as a Member of the Sarnico Formation by Bichsel & Häring 1981.

Components

Hippuriten und Gastropoden (Senn 1924)

Hierarchy and sequence

Superordinate unit

• Gruppo del Flysch Lombardo

Units at roof

• Flysch di Bergamo

Units at floor

• Arenaria di Sarnico
• Flysch di Pontida

Age

Age at top

• Early Santonian

Age at base

• Late Coniacian

Geography

Geographical extent

Lombardia centrale (Brianza, Bergamasco).

Palaenography and tectonic

• Südalpine Flysche

Tectonic unit (resp. main category)

• South Alpine

Kind of protolith

• sedimentary

Conditions of formation

depositi di conoide intermedia canalizzata (Bichsel & Haering 1981)

References

Definition

de Cristoforis G. (1838) : Sulla puddingha di Sirone. Bibl. Ital. 89

Definition

Bichsel Matthias, Häring Markus O. (1981) : Facies evolution of Late Cretaceous flysch in Lombardy (northern Italy). Eclogae geol. Helv. 74/2, 383–420

p.394: We define the Sirone Conglomerate as a member of the Sarnico Sandstone. It is built up by several isolated conglomeratic bodies and is not developed as a continuous layer as described by de Cristoforis (1838). These deposits are concentrated in lenticularly shaped bodies, each 4-7 km wide and 80-200 m thick. Such bodies were recognized in the Sirone. the Pontida. the Bergamo and the Gandosso area respectively. At the Sirone type locality (section 21, p. 401. Fig. 1, E. 11) the conglomerate is estimated to reach 150 m. The youngest planktonic microfossil Dicarinella concavata (Brotzen) found in marly deposits of this member indicates a Late Coniacian to Early Santonian age and is consistent with earlier age determinations (de Alessandri 1899. Venzo 1951) based on ammonites. The Sirone Conglomerate consists of a polygenetic conglomerate of well rounded components with an average grain size of 3 cm and a maximum grain size of 20 cm. The pebbles consist of quartz and crystalline rock fragments (40%). dolomite (22%). chert (21%), pelagic limestone (4%). shallow-water limestone (6%). and coarse biogenic detritus (5%). All components can be attributed to formations of the South- to Austroalpine sequence. The conglomerates show little variation in composition. Massive conglomerate layers, over 20 m thick, with large clay chips, alternate with amalgamated and cross-bedded sandstone layers (Fig. 5). Only thin marly intervals or wavy layer boundaries of amalgamated beds indicate stratification. Imbrication of clasts and inverse to normal grading at the base of the layers is common (Fig. 6). Sometimes, incised channels are cut into the underlying sandstone beds. The individual channel-fill sequences exhibit thinning- and fining-upward cycles (Häring 1978). The Piano
di Sirone represents a classical channelized deposit within the general mid-fan association of the Sarnico Sandstone. Interchannel facies. mudstone dominated sediments with bundles of thin-bedded turbidites (facies D and E) are associated with the channelized bodies.

Important Publications

Gnaccolini M. (1971) : Sedimentologia dei conglomerati di Sirone. Riv. It. Paleont. Strat. 77/1, 1–9

Cadel - (1974) : Composizione e significato paleogeografico del Conglomerato di Sirone. Tesi di laurea inedita, Università degli Studi di Padova