Saint-Vaast Chalk Formation

The information on this page is a summary description.
The full formal description is available here: Saint-Vaast Chalk Formation

Abbreviation SVA
Parent unit Chalk group
Child units
Lithological description White togreyishchalk, containing clay minerals but notmarly, difficult to break. The lower part (“Craie de Saint-Vaast inférieure” auct.) contains sponges and grey to black flints but only in the eastern part of the Mons Basin. At the base, a thin conglomerate with phosphatised chalk pebbles, phosphatised and glauconitised sponges and glauconitic grains.
The upper part (” Craie de Saint-Vaast supérieure” auct.) is not flinty but chalky with pyritic spheroids. The top is sometimes marked by a hardground. Sponges are more abundant than other fossils.
Age The lower part of the St.-Vaast Fm. is of Coniacian age on the basis of: Micraster decipiens, Volviceramus involutus, the foraminifer Dicarinella gr. concavata. It also contains numerous specimens of Hyotissa semiplana.
The upper part of the St.-Vaast Fm. is of Santonian age on the basis of: Micraster coranguinum, Actinocamax verus, Gibbaster belgicus, Sphenoceramus digitatus, and foraminifers: Stensioeina exsculpta gracilis, Gavelinella clementiana, Bolivinoides strigillatus…
Thickness 15 to 25 m on the southern and northern margins of the Basin, about 50 m on the eastern margin near the village of Trivières.
Area of occurrence Mons Basin. The upper part seems to be transgressive over the lower part of the Saint -Vaast Fm. or the Maisières Fm. or Devonian bedrock.
Type locality Stratotype: The quarry at St. Vaast where the “Craie de Saint Vaast” was originally defined has been filled in. Still visible in the old quarry “des crayères” at Thieu.
Alternative names
Authors Robaszynski, F., Dhondt, A.V. & Jagt, J.W.M.
Date 01/01/2001
Cite as Robaszynski, F., Dhondt, A.V. & Jagt, J.W.M., 2001. The Saint-Vaast Chalk Formation, 01/01/2001. National Commission for Stratigraphy Belgium. https://ncs.naturalsciences.be/lithostratigraphy/Saint-Vaast-Chalk-Formation
Additional information At this moment (2000) there are no good outcrops exposing the Saint-Vaast Chalk Fm.
Reference: Godfriaux & Sigal (1969).

Lithostratigraphy Cretaceous

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