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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"

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Sokor 2 Formation

Sokor 2 Fm

Period:

Paleogene

Age Interval:

Oligocene (6, 7b)

Province:
East Niger Rift Basin - Termit Sub-basin, East Niger Rift Basin - Ténéré Sub-basin

Type Locality and Naming

Subsurface: Wells in the Termit and Ténéré Sub-Basins

References: Nasaruddin et al., 2017; Zhou et al., 2017; Lai et al., 2020; Amadou et al., 2021.

Equivalent(s): This sub-surface formation correlates with the surface Zaouzaoua Fm, Dollé Fm, Homodji Fm

Lithology and Thickness

Mainly composed of lacustrine mudstone interbedded by thin sandstone layers. It functions as a regional seal rock for the Sokor 1 reservoirs and the Upper Cretaceous reservoir. The "LV shale marker" layer at the base of the Sokor 2 Fm (improperly known as the "LV Formation"), consisting mainly of pure lacustrine deep-water shale/mudstones, is generally accepted as the regional marker for identifying the top surface of the Sokor 1 Fm (Figure). [Note: The meaning of "LV" in "LV shale marker" is unknown.] These series of lacustrine deep-water shale/mudstones that developed in the semi-deep to deep lake environment indicate that a gradual lake expansion occurred in the Termit Sub-Basin from the Sokor 1 Fm to the LV shale marker. However, the lake level change cycle controlled the deposition process of sediments within a third-order sequence period. The LV shale marker (the seal) thins and fades out north of the Termit Sub-Basin, leaving the Ténéré Sub-Basin with no regional seal due to uplift and erosion. Thickness: 100 m in the proximal and about 500 m in the basin central (Termit Sub-Basin). The LV shale marker in the Termit Sub-Basin ranges in thickness from 50 to 150 m and is not present in the Ténéré Sub-Basin. The Sokor 2 Fm in the Ténéré Sub-Basin ranges from 30 to 1100 meters.

[Figure. Stratigraphic column of the Termit Basin showing the Sokor 1 Fm and Sokor 2 Fm and the LV shale marker at the base of Sokor 2 Fm (Source: Lai et al., 2020).]

Lithology Pattern:

Sandy claystone

Relationships and Distribution

Lower contact

Underlain by Sokor 1 Fm. The "LV shale marker" layer at the base of the Sokor 2 Fm, consisting mainly of pure lacustrine deep-water shale/mudstones, is generally accepted as the regional marker for identifying the top surface of the Sokor 1 Fm.

Upper contact

Overlain by the Chad Fm

Regional extent

GeoJSON

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Fossils

None mentioned

Age

Oligocene [Included " Unnamed post-rift unit" between it and Chad Fm for graphic completeness]

Age Span:

Beginning stage:

Rupelian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

33.90

Ending stage:

Piacenzian

Fraction up in the ending stage:

1.0

Ending date (Ma):

2.58

Depositional setting

Continental (Lacustrine). These series of lacustrine deep-water shale/mudstones that developed in the semi-deep to deep lake environment indicate that a gradual lake expansion occurred in the Termit Sub-Basin from the Sokor 1 Fm to the LV shale marker. However, the lake level change cycle controlled the deposition process of sediments within a third-order sequence period.

Depositional pattern:

Additional Information

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)