# Vanguard Formation

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The **Vanguard Formation** is a [stratigraphical](/source/Stratigraphy) unit of [Callovian](/source/Callovian) to [Oxfordian](/source/Oxfordian_(stage)) [age](/source/Geochronology) in the [Western Canadian Sedimentary Basin](/source/Western_Canadian_Sedimentary_Basin).

It takes the name from [Vanguard](/source/Vanguard,_Saskatchewan), and was first defined by R.L. Milner and G.E. Thomas in 1954.[2]

## Lithology

The Vanguard Formation is composed of calcareous [shale](/source/Shale) with a median quartzose [sandstone](/source/Sandstone). [1]

## Distribution

The Vanguard Formation Lateral reaches a maximum thickness of 180 metres (590 ft) in the [Williston Basin](/source/Williston_Basin) along the [Saskatchewan](/source/Saskatchewan)/[Montana](/source/Montana) border.[1]

## Relationship to other units

The Vanguard Formation is [unconformably](/source/Unconformity) overlain by the [Mannville Group](/source/Mannville_Group) and [disconformably](/source/Unconformity) overlays the [Shaunavon Formation](/source/Shaunavon_Formation).[1]

It is equivalent to the [Ellis Group](/source/Ellis_Group) in [Montana](/source/Montana) and [North Dakota](/source/North_Dakota).

## Subdivisions

In south-western Saskatchewan, Vanguard has group status, and includes the following subdivisions (of formation rank):

- [Masefield Shale](/source/Masefield_Shale): calcareous [shale](/source/Shale)
- [Roseray Formation](/source/Roseray_Formation): quartzose [glauconitic](/source/Glauconite) [sandstone](/source/Sandstone)
- [Rush Lake Shale](/source/Rush_Lake_Shale): calcareous shale with [Gryphaea](/source/Gryphaea) and [Kepplerites](/source/Kepplerites) [ammonite](/source/Ammonite) fossils

## References

1. [Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units). ["Vanguard Formation"](http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:015770). Retrieved 2010-01-01.

1. Milner, R.L. and Thomas, G E., 1954. Jurassic System in Saskatchewan. In: Western Canada Sedimentary Basin. [American Association of Petroleum Geologists](/source/American_Association_of_Petroleum_Geologists), p. 250-267

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