strati.ch - Lessico lithostratigrafico della Svizzera

Rappresentazione e statuto

Varianti storiche: Flysch grigio (Vento 1951), Formazione di Pontida (De Rosa & Rizzini 1967, Bichsel & Häring 1981, Bersezio et al. 1990), Pontida Formation (Bernoulli et al. 1981)

Unità di rango superiore

Unità sovrastante

Unità sottostante

Geomorfologia

Età alla base

Termini generici

Tipo di origine

Condizioni di formazione

Deposizione abissala / depositi di piana di bacino (Bichsel & Haering 1981)

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

p.391: The term Pontida Formation was first used by de Rosa & Rizzini (1967) for the succession of turbiditic sandstones and marls in the Pontida area (section 31, p. 406; Fig. 1, G). The expression "Flysch grigio", introduced by Venzo (1951) is a synonym.
The individual turbidites, mainly Tb-e and Tc-e Bouma sequences, ranging from 5 to 100 cm in thickness, have a wide lateral continuity and are bound by even and parallel surfaces. The sandstone/shale ratio is 1:3 (facies D). The turbidites are acyclically arranged; the Pontida Formation displays the diagnostic features of a basin-plain facies association (Fig. 3). The sandstones are grey, brown weathering, of
fine to medium grain. Three main lithologie types can be distinguished: Lithic arenites are composed of siliciclastic fragments such as quartz, crystalline rocks, chert, feldspar and mica. Bioclastic arenites are mainly composed of detrital carbonate particles, such as fragments of echinoderms, molluscs (Inoceramus and rudists), microfossils and lithoclasts derived from the Mesozoic formations of the southern Alps. Foraminiferal arenites: composed mainly of planktonic foraminifera (50-80%) together with silt-sized quartz grains and mica.