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Bt2a, Bt2b, Bt2

Material name: Bt2a, Bt2b, Bt2
Synonyms: N/A
Material (geologic): Middle Jurassic (Middle Bathonian) flint from the "limestones with flint" (calcaires à silex) formations

Detail of reticulated flint
Foto: Jehanne Féblot-Augustins, 2005.

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Material description

Introduction: This widespread material originates in the so called "limestones with flint" (calcaires à silex) formations of Middle Bathonian age. Within this group of materials, two subtypes are being distinguished, Bt2a, Bt2b, as well as an undifferentiated group Bt2. The difference between the 2a and 2b types lies in the form, frequency and type of grains, although they share the same basic reticulated ground-mass. The designation Bt2 is used for the general type of material where a finer distinction cannot be made.
Even if the two sub-types seem to be mutually exclusive in primary, and even secondary, sources, and therefore valid types of flint, all materials and sampling-sites within this group are being described on this page. Where necessary, descriptions and sources are marked as to which sub-type they belong.
Mode of occurrence: Abundant large-sized nodules (10 to 20 cm across), generally ovoid but occasionally ramified.
Cortex: Rough, yellowish grey, 0.5 to 1.5 cm, transition more or less sharp.
Colour: Light brownish grey (10YR 7/1, 8/1, 7.5/2), white patina.
Pattern: Generally featureless, to very slightly mottled.
Appearance: Homogeneous material, occasionally jointed, dull and opaque, slightly rough, moderately fine-grained.
Structure: No particular structure.
Texture: Wackestone.
Matrix: Opaque.
Grains: Bt2a: 20 to 20 %, white or pale yellow, rounded to subrounded with high sphericity, well sorted (100-125 µ and 200 µ).
Grain composition: Bt2a: Background consisting of a more or less regularly meshed lattice with round pores of 100 µ; these could be stromatoporoids (Lucas, Cros & Lang 1976), whose transversal pillar sections mimic sponge spicule sections (lacking in these samples); numerous short microfilaments (Posidonomya test sections), pelecypod fragments, rare foraminifera showing as "ghosts" outlined by impurities; a few iron oxides.
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.

Differences between Bt2a and Bt2b subtypes

  In comparison with Bt2a, the Bt2b subtype displays some differences relating to grains and grain composition, although the reticulated background is identical.
Grains: Bt2b: 15 to 30 %, locally 40 %, high to low sphericity, less well sorted (100-300 µ, max. 2 mm).
Grain composition: Bt2b: Foraminifera, microfilaments (Posidonomya test sections) and pelecypod fragments are more abundant; a few serpulids, rare whole sponge spicules.


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Tenay-Upper quarry
Locality: Tenay / Upper quarry, France, Ain department
Synonyms: Sampling site Bugey 19 after Féblot-Augustins
Geographical description: The sample was collected in a quarry near the foot of the Mountain directly to the north of Tenay.
Geographical co-ordinates: east/x 845.9
north/y 2107.8
(Lambert zone II, NTF)

This corresponds roughly with
Lat. 45° 55' 33" N
Long. 005° 30' 27" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, and are within approx. 50 metres of the actual spot.
The latitude/longitude coordinates are a direct transformation of these data on WGS84 and are accurate to the same level, so don't be deceived by the apparently high precision to the second.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: According to the geological map, the exposes the limestones of unit J2 (moy.), of Middle Bathonian age.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Primary.
Other types of flint: No other types of flint apart from Bt2a occur in this exposure.
  Split nodule
Foto: Jehanne Féblot-Augustins, 2005
 
Bathonian chert
Foto: Jehanne Féblot-Augustins, 2005
 
  Reticulate chert
Foto: Jehanne Féblot-Augustins, 2005
 
 


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Col du Nivollet
Locality: Nivollet-Montgriffon / Col du Nivollet (quarry), France, Ain department
Synonyms: Sampling site Bugey 22 after Féblot-Augustins
Geographical description: The material was collected in a quarry alongside the local road that connects Nivollet-Montgriffon with Lupieu, near the highest point of the saddle.
Geographical co-ordinates: east/x 840.45
north/y 2113.65
(Lambert zone II, NTF)

This corresponds roughly with
Lat. 45° 58' 49" N
Long. 005° 26' 25" E
(WGS84)

Co-ordinate precision: The Lambert-coordinates are within 50 metres from the actual sampling point, and were read off a large scale map. The lat/long coordinates were not rounded and within the same margin of error.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: According to the geological map, the substrate belongs to unit J2 (moy.), of Middle Bathonian age.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Primary.
Other types of flint: None but Bt2a.
  Tectonized nodule
Foto: Jehanne Féblot-Augustins, 2005
 
Flake of typical Bt2a flint
Foto: Jehanne Féblot-Augustins, 2005
 


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Résinand
Locality: Résinand / Aranc, France, Ain department
Synonyms: Sampling site Bugey 25 after Féblot-Augustins
Geographical description: The sample-point is located near the hairpin-bends in the departemental road D34 which connects the hamlet of Résinand with the village of Aranc, on a very steep hillside.
Geographical co-ordinates: east/x 844.3
north/y 2115
(Lambert zone II, NTF)

This corresponds roughly with
Lat. 45° 59' 28" N
Long. 005° 29' 27" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, and are within approx. 50-100 metres of the actual spot.
The latitude/longitude coordinates are a direct transformation of these data on WGS84 and lie within the same error-margin.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: The parent-rock of this flint are limestones of Middle Bathonian age, belonging to unit J2 of the local geological map.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Primary.
Other types of flint: This locality doesn't yield any other type of flint apart from Bt2a.
  Flake with typical cortex
Foto: Jehanne Féblot-Augustins, 2005
 
Fine-grained chert
Foto: Jehanne Féblot-Augustins, 2005
 


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Planachat
Locality: Boyeux-St-Jérôme / Planachat, France, Ain department
Synonyms: Sampling site Bugey 20 after Féblot-Augustins
Geographical description: The sample was collected near the departemental road D 12d, between Sous Chaly (see below) and Châtillon de Cornelle.
Geographical co-ordinates: east/x 841.4
north/y 2120.6
(Lambert zone II, NTF)

This transforms to
Lat. 46° 02' 33" N
Long. 005° 27' 22" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, and are within approx. 50-100 metres of the actual spot.
The latitude/longitude coordinates are a direct transformation of these data on WGS84 and are accurate to the same level, so don't be deceived by the apparently high precision to the second.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: According to the geological map, the substrate belongs to unit J2 (Bathonian).

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Primary.
Other types of flint: All flint on this site belongs to the variety Bt2b.
  Fractured nodule
Foto: Jehanne Féblot-Augustins, 2005
 
Piece of rough flint
Foto: Jehanne Féblot-Augustins, 2005
 


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Sous Chaly
Locality: Jujurieux / Cossieux - Sous Chaly, France, Ain department
Synonyms: Sampling site Bugey 21 after Féblot-Augustins
Geographical description: The sampling site is located directly near Sous Chaly, two kilometres east-southeast of Jujurieux.
Geographical co-ordinates: east/x 839.75
north/y 2119.25
(Lambert zone II, NTF)

This corresponds to
Lat. 46° 01' 52" N
Long. 005° 26' 03" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, and are within 50 metres of the actual spot.
The latitude/longitude coordinates are a direct transformation of the Lambert-values and have the same level of accuracy.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: The parent-rock consists of limestones of Middle Bathonian age, unit J2 on the local geological map.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Primary.
Other types of flint: All flints from the Sous Chaly-source are of the Bt2b type.
  Whitish Bt2b chert
Foto: Jehanne Féblot-Augustins, 2005
 
coarse flint with cortex
Foto: Jehanne Féblot-Augustins, 2005
 


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Buges
Locality: St-Rambert-en-Bugey / Buges, France, Ain department
Synonyms: Sampling site Bugey 23 after Féblot-Augustins
Geographical description: This extended primary source is located at the foot of Mont Jud, near the hamlet Buges, which lies a bit over a kilometre to the north of St-Rambert-en-Bugey.
Geographical co-ordinates: east/x 840.45 to 840.65
north/y 2110.2 to 2112.8
(Lambert zone II, NTF)

This corresponds roughly with
Lat. 45° 57' 24" N
Long. 005° 26' 23" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, and because of the size of the area where this material can be found more than good enough to get you near the sampling site.
The latitude/longitude coordinates are a transformation of point near the centre of the area designated by the Lambert coordinates (840.5/2111).

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: According to the geological map, the substrate belongs to unit J2 (Bathonian).

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Primary.
Other types of flint: All flint from this area is of the Bathonian Bt2b variety.
  Jurassic Bt2b flint
Foto: Jehanne Féblot-Augustins, 2005
 
Bathonian chert
Foto: Jehanne Féblot-Augustins, 2005
 


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Mérignat-Pierre-Feu
Locality: Mérignat / Pierre-Feu, France, Ain department
Synonyms: Sampling site Bugey 35 after Féblot-Augustins
Geographical description: The sampling-point is located on a north-facing slope 1 kilometre south of Mérignat, a hamlet/very small village 3 kilometres SSE of Poncin.
Geographical co-ordinates: east/x 840 to 840.2
north/y 2122.3 to 2122.7
(Lambert zone II, NTF)

The centre of these coordinates is
Lat. 46° 03' 36" N
Long. 005° 26' 25" E
(WGS84)

Co-ordinate precision: The area is quite an extended secondary source, so the ccordinates will be good enought to get you were you will have to be.
The latitude/longitude coordinates are a direct transformation of the approximate centre (840.1/2122.5) of the area.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: This source is located on residual loams of the weathering of Middle Bationian limestones.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Secondary.
Other types of flint: All material from Mérignat-Pierre-Feu is of the Bt2b variety.
  slightly patinated flint
Foto: Jehanne Féblot-Augustins, 2005
 
Opaque Jurassic flint
Foto: Jehanne Féblot-Augustins, 2005
 


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Pont de Préau
Locality: Cerdon / Pont de Préau, France, Ain department
Synonyms: Sampling site Bugey 36 after Féblot-Augustins
Geographical description: The sample was collected near the confluence of the Bief de la Fouge with the Veyron, this is where the departemental road D 11 leaves the N84, approx. 3.5 kilometres east of Poncin, one kilometre SW of Cerdon.
Geographical co-ordinates: east/x 841
north/y 2124.1
(Lambert zone II, NTF)

This corresponds with
Lat. 46° 04' 27" N
Long. 005° 27' 10" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, and are within approx. 50 metres of the actual spot.
The latitude/longitude coordinates are a direct transformation of these data on WGS84 and are accurate to the same level, so don't be deceived by the apparently high precision to the second.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: The flint lies in clay-with-flints (Rs), resulting from the weathering of Bathonian (J2) limestones.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Secondary.
Other types of flint: This source doesn't yield other varieties apart from the Bt2b flint.
  chert with neo-cortex
Foto: Jehanne Féblot-Augustins, 2005
 
 


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Le Maupas 2
Locality: Ambérieu-en-Bugey / Vareille - Le Maupas 2, France, Ain department
Synonyms: Sampling site Bugey 28 after Féblot-Augustins
Geographical description: The locality lies at the head of a narrow valley in the Bois d'Ambérieu near the marked footpath GR (Grande Randonné) 59 leading from Vareille/Ambérieu-en-Bugey to Mont Luisandre/Les Allymes.
Geographical co-ordinates: east/x 836.9
north/y 2110.15
(Lambert zone II, NTF)

This corresponds to
Lat. 45° 57' 01" N
Long. 005° 23' 34" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, and are within 50 metres of the actual spot.
The geographical coordinates are a direct transformation of Lambert-values to Lat/Long on WGS84 and are accurate to the same level.

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 substrate consists of residual clay-with-flints formed during the weathering of Middle Bathonian limestones.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Secondary.
Other types of flint: As no criteria are available to decide to attribute the flint from this site to either of the two subtypes, all material is classified as general Bt2-flint.
  Opaque Jurassic chert
Foto: Jehanne Féblot-Augustins, 2005
 
 


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Le Plat-cote 554
Locality: Ambérieu-en-Bugey / Vareille - Le Plat, cote 554, France, Ain department
Synonyms: Sampling site Bugey 29 after Féblot-Augustins
Geographical description: The source is located near the top of a hill, cote (= heighth) 554 in densely wooded country, just 350 metres north of Le Maupas 2
Geographical co-ordinates: east/x 836.9
north/y 2110.5
(Lambert zone II, NTF)

This corresponds with
Lat. 45° 57' 12" N
Long. 005° 23' 35" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, and are within approx. 50 metres of the actual spot.
The latitude/longitude coordinates are a direct transformation of these data on WGS84 and are accurate to the same level, so don't be deceived by the apparently high precision to the second.

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 underground is a clay-with-flint with residual silex from Middle Bathonian formations.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Secondary.
Other types of flint: As the material from this site cannot be further differentiated, all is being lumped into the general Bt2-group.
  Bt2 silex
Foto: Jehanne Féblot-Augustins, 2005
 
 


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Bois d'Ambérieu
Locality: Ambérieu-en-Bugey / Les Allymes - Bois d'Ambérieu , France, Ain department
Synonyms: Sampling site Bugey 32 after Féblot-Augustins
Geographical description: The sample was collected the wooded area of the Bois d'Ambérieu at the foot of a large ridge near the marked Grande Randonné 59 long-distance path, a kilometre and a half south of Les Allymes. This hamlet lies somewhat more than three kilometres NNE of Ambérieu-en-Bugey.
Geographical co-ordinates: east/x 837.4 to 837.5
north/y 2111.1 to 2111.3
(Lambert zone II, NTF)

This corresponds roughly with
Lat. 45° 57' 34" N
Long. 005° 24' 04" E
(WGS84)

Co-ordinate precision: The coordinates given were taken from a large-scale map, but as the source is approx. two hectares in size, they are good enough to get you where you want to be.
The latitude/longitude coordinates point to the eastern side of the centre of the area.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: According to the geological map, the substrate is residual material left behind after the soluble stone was eroded (Rs/J2, clay-with-flint of Bathonian formations).

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Secondary.
Other types of flint: All material belongs to the undifferentiated Bt2 type.
  Residual flint
Foto: Jehanne Féblot-Augustins, 2005
 
 


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Les Boissières
Locality: Nivollet-Montgriffon / Les Boissières, France, Ain department
Synonyms: Sampling site Bugey 39 after Féblot-Augustins
Geographical description: The sample comes from the bottom of a valley near an intermittent stream a few hunderd metres SSW of the village Nivollet-Montgriffon in the heart of the Bugey, 7 kilometres northeast of Ambérieu.
Geographical co-ordinates: east/x 840.2 to 840.4
north/y 2114.2 to 2114.4
(Lambert zone II, NTF)

This corresponds roughly with
Lat. 55° 59' 11" N
Long. 005° 26' 20" E
(WGS84)

Co-ordinate precision: The coordinates are not extremely exact, as they were taken off a larege scale map, but as the site is quite large, you will find yourself in the midst of it by steering towards the centre.
The latitude/longitude coordinates point towards the centre of the area.

The location can be found on the 1:25 000 topographical map sheet 3230 W of the French Institut Géographique National.

Geology: Like most of the secondary material, the flint comes from a residual loam left behind as the encasing (Bathonian) limestone was weathered away.

Map of all sampled localities of Bathonian flint in the Bugey (PDF, 195 KB, opens in new window).

Type of source: Secondary.
Other types of flint: All material from Les Boissières is classified as undifferentiated Bt2 flint.
  Eluvial flint
Foto: Jehanne Féblot-Augustins, 2005
 
 

 

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