Editing Hydrogeology of Guinea Bissau

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|Devonian
 
|Devonian
||Shales and sandstones over a large area in the east of the country, forming a northwest/southeast syncline.  
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||Shales and sandstones over a large area in the east of the country, forming a northwest/southeast syncline. The base of the series is sandstones of Lower Devonian age in the Cusselinta-Saltinho area, which are mostly well consolidated micaceous and feldspathic sandstones. Overlying this is the Middle to Upper Devonian Bafata Group, comprising argillaceous schists with intercalactions of fine grained quartz sandstone.  
 
 
At the base of the series are Lower Devonian sandstones, seend in the Cusselinta-Saltinho area. These are mostly well-consolidated micaceous and feldspathic sandstones.  
 
 
 
Overlying this is the Middle to Upper Devonian Bafata Group, comprising argillaceous schists with intercalactions of fine grained quartz sandstone.  
 
 
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|Silurian
 
|Silurian
||The Buba Group: mostly sandstones with some organic rich/carbonaceous black shales. Drilling in the southeast of the country showed very compact black, carbonaceous schists with fine grained sandstone intercalations, and some doloritic layers. In the northeast, schists interbedded with dolerite were seen, with varying indications of metamorphism, and fine grained, clay-rich sandstones at the top at the transition to the overlying Devonian rocks.  
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||Rocks of the Buba Group, including sandstones with some organic rich/carbonaceous black shales. Drilling in the southeast of the country showed very compact black, carbonaceous schists with fine grained sandstone intercalations, and some doloritic layers. In the northeast, schists interbedded with dolerite were seen, with varying indications of metamorphism, and fine grained, clay-rich sandstones at the top at the transition to the overlying Devonian rocks.  
 
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|Ordovician and Cambrian
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|Cambrian-Ordovician  
 
||Sandstones, shales, conglomerates and rare limestones. These are found in the northeast of the country, overlying older Neoproterozoic metamorphic rocks.  
 
||Sandstones, shales, conglomerates and rare limestones. These are found in the northeast of the country, overlying older Neoproterozoic metamorphic rocks.  
  
The Ordovician rocks distinguished on the geology map are dominated by the Canjufa-Canjadude series of quartz-arenites. The other dominant Ordovician series is the Gabu sandstone series, thought to be mostly steeply dipping at up to 50 degrees. At its base is a white, coarse grained sandstone unit up to 170 m thick, overlain by less compact, sandier strata of considerable thickness, and then by a fine grained sandstone unit that is 10-30 m thick (UN 1988).  
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The Ordovician rocks distinguished on the geology map are dominated by the Canjufa-Canjadude series of quartz-arenites. The other dominant Ordovician series is the Gabu sandstone series, which is thought to be mostly steeply dipping at up to 50 degrees. At its base is a white, coarse grained sandstone unit up to 170 m thick, overlain by less compact, sandier strata of considerable thickness, and then by a fine grained sandstone unit that is 10-30 m thick (UN 1988).  
  
 
Cambrian rocks are dominated by fine grained sandstones and shales, including shales of Pirada and Canquelifa, schist-sandstones of Cantari, and the younger Caium sandstones of Upper Cambrian age.
 
Cambrian rocks are dominated by fine grained sandstones and shales, including shales of Pirada and Canquelifa, schist-sandstones of Cantari, and the younger Caium sandstones of Upper Cambrian age.

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