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Bj4a

Material name:	Bj4a
Synonyms:	N/A
Material (geologic):	Middle Jurassic (Late Bajocian) flint/chert.

Foto: Jehanne Féblot-Augustins, 2005.

Sampled sites:

Balme à Juliette 1

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Material description

Mode of occurrence: Occurring in continuous beds 5 to 6 cm thick, highly jointed, jutting out from the compact light brownish grey to light reddish tan limestone. Upper layers of an outcrop at the top of a cliff face.

Cortex: Fresh, rough, grey-white, 1 cm thick, transition sharp.

Colour: Blue-grey (N6).

Pattern: Featureless, rare pale-coloured specks.

Appearance: Homogeneous material, although highly jointed, dull and opaque, moderately smooth, medium to fine-grained.

Structure: No particular structure.

Texture: Wackestone.

Matrix: Opaque.

Grains: 30 to 40 %, white, pale yellow, ochre, black, rounded with high to low sphericity; main grain size 100 µ, with a few grains ranging between 250 and 1000 µ.

Grain composition: Very numerous sponge spicules and foraminifera (frequent black "ghosts" outlined by impurities), pelecypod fragments, serpulids, dispersed entrochi and ooliths, rare pellets, rare Cyclostoma bryozoans.

Further information: Click here for the original French description (opens in a new window), or here for more information on the attributes used in the description (use your browser's "BACK"-button to return here).

Citing: Information on citing this page can be found here.

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Balme à Juliette 1

Locality:	Ambérieu-en-Bugey / Les Balmeaux - Balme à Juliette 1, France, Ain department
Synonyms:	Sampling site Bugey 4 after Féblot-Augustins
Geographical description:	The sample was taken from the upper flint-layers at the top of a cliff approx. 1 kilometre to the east of Vareille, a hamlet at the eastern side of Ambérieu-en-Bugey. For a more precise explanation of the local situation, see the description under Bt4
Geographical co-ordinates:	east/x 836.4 north/y 2111 (Lambert zone II, NTF) This corresponds roughly with Lat. 45° 57' 29" N Long. 005° 23' 13" E (WGS84)
Co-ordinate precision:	The coordinates given were taken from a large-scale map, and are within 50 metres of the actual exposure. The latitude/longitude coordinates are a direct transformation of these data on WGS84 and are accurate to the same level. The high precision to the second is given to prevent the introduction of a rounding-error. The location can be found on the 1:25 000 topographical map sheet 3130 E of the French Institut Géographique National.
Geology:	According to the geological map, the parent-rock belongs to unit J1c of late Bajocian age. Map of all sampled localities of Bajocian flint in the Bugey (PDF, 190 KB, opens in new window).
Type of source:	Primary.
Other types of flint:	In the same exposure the middle and lower banks of flint consist of the coarser Late Bajocian varieties Bj4b and Bj4c.

Foto: Jehanne Féblot-Augustins, 2005

Foto: Jehanne Féblot-Augustins, 2005

Last modified on:
November 15, 2005

Contents primarily by:
Jehanne Féblot-Augustins

Comments to:

Mode of occurrence:	Occurring in continuous beds 5 to 6 cm thick, highly jointed, jutting out from the compact light brownish grey to light reddish tan limestone. Upper layers of an outcrop at the top of a cliff face.
Cortex:	Fresh, rough, grey-white, 1 cm thick, transition sharp.
Colour:	Blue-grey (N6).
Pattern:	Featureless, rare pale-coloured specks.
Appearance:	Homogeneous material, although highly jointed, dull and opaque, moderately smooth, medium to fine-grained.
Structure:	No particular structure.
Texture:	Wackestone.
Matrix:	Opaque.
Grains:	30 to 40 %, white, pale yellow, ochre, black, rounded with high to low sphericity; main grain size 100 µ, with a few grains ranging between 250 and 1000 µ.
Grain composition:	Very numerous sponge spicules and foraminifera (frequent black "ghosts" outlined by impurities), pelecypod fragments, serpulids, dispersed entrochi and ooliths, rare pellets, rare Cyclostoma bryozoans.
Further information:	Click here for the original French description (opens in a new window), or here for more information on the attributes used in the description (use your browser's "BACK"-button to return here).
Citing:	Information on citing this page can be found here.