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Questions and Answers
Where are rocks of the Tarkwaian Group concentrated mainly in Ghana?
What is the approximate width of the Tarkwaian belt stretching from Axim to the edge of the Voltaian basin?
What type of sediments are mainly found in the lower members of the Tarkwaian Group rocks?
What is the believed origin of the Tarkwaian Group rocks in terms of water depth?
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In which type of basin are the Tarkwaian sediments believed to have been deposited?
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What geological event is responsible for the inter-folding of the metasedimentary Birimian and Tarkwaian rocks in some places?
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Which minerals are common in the Tarkwaian sediments?
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Which of the following is not a subdivision of the Tarkwaian Group according to Junner, Hirst and Service (1942)?
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What lithology characterizes the Kawere Group within the Tarkwaian sediments?
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What is the most persistent conglomerate bed in the Tarkwa Goldfields area?
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At what metamorphic facies have the Tarkwaian sediments been subjected to according to the text?
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Which division of the Tarkwaian is described as an accumulation of high-energy, coarse clastics?
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Study Notes
Geology of the Tarkwaian Group
- The Tarkwaian Group is concentrated mainly in the southwestern part of Ghana, stretching from Axim to the edge of the Voltaian basin near Agogo, covering a distance of about 250 km.
- The belt has a width of about 16 km.
- Elsewhere in Ghana, the Tarkwaian occupies a portion of the Bui Syncline parallel to the Côte d'Ivoire border at 8º N latitude, with a length of about 140 km and an average width of 0.8 km.
Characteristics of Tarkwaian Rocks
- Tarkwaian rocks consist of thick series of argillaceous and arenaceous sediments, mainly arenaceous.
- The rocks are of shallow water continental origin, derived from the Birimian and associated granites.
- They were deposited in elongated intracratonic basins bordered by granite-greenstone belts of the Birimian Supergroup.
Depositional Environment
- The sediments were deposited in high-energy alluvial fans entering a steep-sided basin filled with fresh water.
- They consist of coarse, poorly sorted, immature sediments with low roundness, typical of a braided stream environment.
Relationship with Birimian
- The Tarkwaian is thought to rest unconformably on the Birimian, although in some places, the metasedimentary Birimian and the Tarkwaian are inter-folded due to post-Tarkwaian orogenic activity.
- In some localities, no angular unconformity can be observed between the Birimian and the Tarkwaian.
Metamorphism
- The Tarkwaian sediments have been subjected to low-grade metamorphism, i.e., middle greenschists to middle almandine-amphibolite facies.
- The common minerals are chlorite, sericite, zoisite, calcite, quartz, limonite, and chloritoid.
Divisions of the Tarkwaian Group
- The most accepted subdivisions of the Tarkwaian are provided by Junner, Hirst, and Service (1942), including:
- Huni Sandstone (and Dompim Phyllite)
- Tarkwa Phyllite
- Banket Series
- Kawere Group
Descriptions of Tarkwaian Units
Kawere Group
- The Kawere Group consists of shallow water greenish grey, feldspathic, carbonate-spotted quartzites, grits, breccias, and conglomerates.
- The conglomerates normally consist of closely packed pebbles of very fine-grained, silicified Birimian greenstones in a matrix of quartz, feldspar, chlorite, carbonate, epidote, and magnetite.
Banket Series
- The Banket Series represents a fluviatile series with a thickness varying between 120-600 m.
- It is essentially an accumulation of high-energy, coarse clastics, represented by conglomerates, grits, and quartzites, which have suffered low-grade metamorphism.
- Four reefs or conglomerate bands have been identified in the western and southern parts of the Tarkwa Goldfields.
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Description
Explore the geological features of the Tarkwaian Group in Ghana, particularly its concentration in the Southwestern part of the country. Learn about the distribution and characteristics of the Tarkwaian rocks and their significance in the region's geology.
