Cenozoic

Cretaceous

Jurassic

Triassic

Permian

Paleozoic

Compiled by: Jacques LeBlanc (2022), Stratigraphic Lexicon: The Sedimentary Formations of The Republic of Niger, Africa. Colnes Publishing (Tallin, Estonia), 365 pp. For more information see "About"

Select Region(s) to search
Hold Ctrl (Windows/Linux) or Command (Mac) to select multiple

Assaouas Formation

Assaouas Fm

Period:

Jurassic

Age Interval:

Middle Jurassic (1)

Province:
Iullemmeden Basin - Tim Mersoï Sub-basin

Type Locality and Naming

Joulia, 1951-1957. Higher formation in Agadez Gr

References: Joulia, 1951-1957; Valsardieu, 1971; Fabre et al., 1983.

Synonym: Grès d’Assaouas (not to be confused with the In-Azaoua Fm of Cambrian-Ordovician)

Lithology and Thickness

Intercalations of argillites in silty sediments. Valsardieu (1971, page 221) describes the formation between the Irhazer Fm and the Tchirezrine Fm as brown argillites dotted with medium to fine sandstone, isogranular, feldspathic, micaceous, clayey, with abundant calcareous cement, brown. The existence of oblique micro-stratifications is reminiscent of the existence at the time of deposition of an oriented sedimentation not so intense. The sandstones occupy stratiform lenses isolated in the argillites, or sporadic layers overlaid on the Tchirezrine 2 sandstones. The sandstones are beige to greenish, coarse, heterogranular, feldspathic, film-cemented, phyllite (p. 221). Its thickness is 0-30 m.

Lithology Pattern:

Sandy claystone

Relationships and Distribution

Lower contact

Underlying unit is Tchirezrine 2 Mbr of the Tchirezrine Fm.

Upper contact

Overlying unit is the Irhazer Fm.

Regional extent

GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[8.12,16.79],[8.54,17.19],[8.37,17.72],[8.16,18.66],[8.06,20.13],[8.54,21],[9.37,21.18],[9.09,21.81],[7.34,23.1],[6.93,23.64],[6.08,23.47],[5.84,20.17],[5.56,19.4],[6.37,19.07],[7.34,18.31],[7.84,17.41],[7.82,16.68],[8.12,16.79]]]]}}

Fossils

Invertebrates, vertebrate tracks, abundant plant imprints in sandstones, fish, dinosaurs. Estheries (Euestheria lamberti, E. margínata, DEFRETIN et al., 1956), lamellibranchs (Cuneopsis, Unio, Cyrena, MONGIN, 1963), vertebrate remains (Sauropods, Theropods, Crocodiles, fish) and pentadactyles and tridactyles tracks (de Lapparent et al., 1966) have been found in the unit of Assaouas Fm and the Irhazer Fm.

Age

Age Span:

Beginning stage:

Bajocian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

170.90

Ending stage:

Bajocian

Fraction up in the ending stage:

1.0

Ending date (Ma):

168.17

Depositional setting

Lacustrine

Depositional pattern:

Additional Information

The Assaouas Fm is not always present between the Irhazer Fm and Tchirezrine Fm. Sometimes it is reduced to small lenses of channel sandstones.

Compiler:

Jacques LeBlanc (2022), Stratigraphic Lexicon: The Sedimentary Formations of The Republic of Niger, Africa. Colnes Publishing (Tallin, Estonia), 365 pp. https://doi.org/10.47909/978-9916-9760-6-7 (or via https://sites.google.com/site/leblancjacques)