Cenozoic

Mesozoic

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Adar Formation

Adar Fm

Period:

Paleogene

Age Interval:

Eocene-early Oligocene

Province:
SouthSudan, Sudan S

Type Locality and Naming

It is exposed at the margin of the basin

Melut Basin (NE South Sudan - W Ethiopia), and the Rawat Basin (SE Sudan), which are the southeastern and the northwestern basins of the greater White Nile rift basin.

Reference: Dou et al., 2007; Dou et al., 2023 (Melut Basin); Mohammed et al, 2017 (Rawat Basin)

[Fig. 1: Simplified map of the West and Central African Rift System (WCARS) showing the major features discussed in the text and the location of the Melut Basin in South Sudan (modified from Genik, 1993)]

[Fig. 2: Comprehensive stratigraphic columns in the Melut Basin (from Dou et al., 2023)]

[Fig. 3: Rawat Basin- Block 25 in southern Sudan (after Ministry of Petroleum & Gas-OEPA, 2015, Extracted from Mohammed et al., 2017).]

[Fig. 4: Summary of Tectono-stratigraphy of the Rawat Basin (from Mohammed, 2016).]

Lithology and Thickness

In the Melut Basin, the formation is characterized by the dominance of shales with thin siltstones and sandstones in the interior of the basin. Toward the margin of the Melut Basin, in the areas of major sediment influx, the Adar Formation is composed of coarse alluvial sediments. The maximum thickness of the unit is 900m (Dou et al., 2007). In the Rawat Basin, the Adar Fm consists predominantly of greyish-green to dusky-yellow green mudstone with greyish siltstone and poorly consolidated, fine- to medium-grained sandstone, subrounded to rounded, well to moderately sorted, quartz sandstone, occasionally argillaceous matrix, trace kaolinite cement, fair to good porosity (Mohammed, 2016). Mohammed (2016) placed the total thickness of the formation at 323m in well M-1, and 538m in well M-2.

Lithology Pattern:

Sandy claystone

Relationships and Distribution

Lower contact

Adar Fm conformably overlies the Yabus Fm

Upper contact

In Melut Basin (only), a Lau Fm unconformably overlies the Adar Fm. In Rawat Basin, the Jimidi Fm overlies it.

Regional extent

Melut Basin (NE South Sudan - W Ethiopia), and the Rawat Basin (SE Sudan), which are the southeastern and the northwestern basins of the greater White Nile rift basin.

GeoJSON

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Fossils

In Rawat Basin, it has Pollen-Spores (Praedapollis flexibilis, Deltoidospora cf. africana, Triplanosporites sp.)

Age

Eocene-early Oligocene (estimated span of entire Eocene in Melut Basin; but assigned entirely to Oligocene in Rawat Basin)NOTE: Age span as estimated for the Melut Basin used here for graphic and paleogeographic display purposes.

Age Span:

Beginning stage:

Ypresian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

56.00

Ending stage:

Priabonian

Fraction up in the ending stage:

1.0

Ending date (Ma):

33.90

Depositional setting

In Melut Basin, it is interpreted as shallow to semi-deep lacustrine environments (Dou et al., 2007); but in Rawat Basin wells, it is mainly deep lacustrine (Mohammed et al., 2017).

Depositional pattern:

Additional Information

Compiler:

Enam O. Obiosio, Solomon Joshua Avong and Henry Nasir Suleiman (2024) - Stratigraphic Lexicon compiled from the following publications:

Dou L., Xiao K., Cheng D., Shi B., Li Z. (2007): Petroleum Geology of the Melut Basin and the Great Palogue Field, Sudan. Marine and Petroleum Geology, 24, pp.129-144

Dou L., Xiao K., Wang J. (2023): Petroleum Geology and Exploration of the Bongor Basin. Petroleum Industry Press.

Mohammed H. Z. A., Awad M. Z., Eisawi (2017): Upper Cretaceous to Neogene Palynology of the Rawat Basin, White Nile State, Sudan. Journal of Earth Science & Climatic Change. 08 (04)

Robertson Research International “RRI”, Geological Research Authority of Sudan “GRAS” (2016): The Geology and Petroleum Potential of Southern, Central, and Eastern Sudan. Unpublished Report. Vol. 1-4