Cenozoic

Mesozoic

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Galhak Formation

Galhak Fm

Period:

Cretaceous

Age Interval:

Cenomanian to Campanian

Province:
SouthSudan, Sudan S

Type Locality and Naming

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 thickness of this formation averages 290m and it is characterized by the predominance of medium- to fine-grained sandstones and claystones. In the Rawat Basin, it is subdivided into an Upper Galhak Fm and a Lower Galhak Fm, with a possible unconformity between them. There, the Upper Galhak Fm is about 288m thick, composed of mainly composed of shale, mudstone, siltstone and occasionally sandstone. The claystone comprises the dominant lithology of the formation (Mohammed et al., 2017). Its top is characterized by an upward change from a predominantly argillaceous section to a more arenaceous interval at the base of the Melut Fm (Mohammed et al., 2017). The Lower Galhak Fm in the Rawat Basin is estimated to be about 613m thick at well M-1, and 538m at well M-2 (Mohammed et al., 2017). It is mainly composed of sandstone, shale, and siltstone. The sandstone is transparent to translucent quartz grains, occasionally moderately- to well-consolidated, fine to coarse-grained, subangular to rounded, moderately sorted, poor to fair porosity (Mohammed et al., 2017).

Lithology Pattern:

fine-grained sandstone

Relationships and Distribution

Lower contact

Galhak Fm unconformably rests on the Al Renk Fm in the Melut Basin. In the Rawat Basin, it comprises the oldest sedimentary rocks overlying the basement.

Upper contact

Melut Fm conformably rests on the Galhak Fm.

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

Upper Galhak Fm in the Rawat Basin has Pollen (Triorites minor, Buttunia andreevi, Cycadopites ovatus, Foveotriletes margaritae, Gemmamonocolpites sp.); and the Lower Galbak Fm has Pollen (Triorites minor, Buttunia andreevi, Cycadopites ovatus, Foveotriletes margaritae, Gemmamonocolpites sp.) (Mohammed et al., 2017)

Age

Cenomanian to Campanian (interpreted as Cenomanian through Santonian in Melut Basin; but only as Campanian in Rawat Basin)NOTE: Age span as estimated for the Melut Basin used here for graphic and paleogeographic display purposes.

Age Span:

Beginning stage:

Cenomanian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

100.50

Ending stage:

Santonian

Fraction up in the ending stage:

1.0

Ending date (Ma):

83.65

Depositional setting

Braided delta and shallow lake (Dou et al., 2007) in Melut Basin. In the Rawat Basin, the Upper Galhak Fm is interpreted as Fluvio-lacustrine environments; and the Lower Galhak Fm is interpreted as lacustrine but rapidly changed upward to braided river (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