home ]


Material name: Bj4b
Synonyms: N/A
Material (geologic): Middle Jurassic (Dogger, Late Bajocian) flint.

Detail of Bj4b packstone chert
Foto: Jehanne Féblot-Augustins, 2005.

top ] [ home ]

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. Middle layers of an outcrop at the top of a cliff face.
Cortex: Fresh, rough, grey-white, 1 cm thick, transition sharp.
Colour: Grey-brown (10YR 4/1).
Pattern: Flecked with pale-coloured specks.
Appearance: Homogeneous material, although highly jointed, dull and opaque, moderately smooth, medium-grained.
Structure: No particular structure
Texture: Packstone.
Matrix: Subtranslucent.
Grains: 50 %, white, pale yellow, ochre, rounded with high sphericity; balanced distribution of grains measuring100 µ (sponge spicule sections) and ranging between 500 and 1000 µ (ooliths, entrochi); rare grains of 3 mm max.
Grain composition: Rare foraminifera, numerous sponge spicules, ooliths (occasional aggregates, entrochi, fragments of pelecypods and of 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.

top ] [ home ]
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 middle 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

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: At this exposure, three types of flint can be found, all of Late Bajocian age, in the upper layers Bj4a flint, in the middle layers the Bj4b-type descibed on this page, and in the lower part the Bj4c variety.
  Split nodule of Bajocian packstone
Foto: Jehanne Féblot-Augustins, 2005
Flake of typical Bj4b-flint
Foto: Jehanne Féblot-Augustins, 2005


Last modified on:
November 15, 2005
Contents primarily by:
Jehanne Féblot-Augustins
Comments to: