Editing Hydrogeology of Niger

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||The Chad Basin is a major geological feature: a sedimentary depositional basin that extends over large parts of a number of countries including Chad and Nigeria. In Niger, the Chad Basin covers most of the east and north of the country. The basin contains a great thickness of sedimentary rocks dating from the Cretaceous to Quaternary in age. These are more than 3,500 m thick at the thickest known points, but may be more. These sedimentary rocks are underlain by Precambrian bedrock.  
 
||The Chad Basin is a major geological feature: a sedimentary depositional basin that extends over large parts of a number of countries including Chad and Nigeria. In Niger, the Chad Basin covers most of the east and north of the country. The basin contains a great thickness of sedimentary rocks dating from the Cretaceous to Quaternary in age. These are more than 3,500 m thick at the thickest known points, but may be more. These sedimentary rocks are underlain by Precambrian bedrock.  
  
''Quaternary:'' the uppermost and youngest sediments in the Chad Basin belong to the Chad Formation, and are largely of Quaternary age. These range from a few tens of metres up to many hundreds of metres thick. The Chad Formation consists of unconsolidated fine to coarse grained sands and gravels with sandy clays. These include extensive aeolian (dune) sands, and relatively extensive clayey to sandy aluvial sediments in active and abandoned river channels. There are also lacustrine (lake and lake-margin), alluvial fan and deltaic deposits. Much of the sequence is sandy or gravelly, but there are frequent lacustrine clay layers. Abrupt changes in clay and sand content are common, and the sediments usually occur as overlapping lenses.  
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The uppermost and youngest sediments in the Chad Basin belong to the Chad Formation, and are largely of Quaternary age. These range from a few tens of metres up to many hundreds of metres thick. The Chad Formation consists of unconsolidated fine to coarse grained sands and gravels with sandy clays. These include extensive aeolian (dune) sands, and relatively extensive clayey to sandy aluvial sediments in active and abandoned river channels. There are also lacustrine (lake and lake-margin), alluvial fan and deltaic deposits. Much of the sequence is sandy or gravelly, but there are frequent lacustrine clay layers. Abrupt changes in clay and sand content are common, and the sediments usually occur as overlapping lenses.  
  
''Tertiary:'' the Chad Formation is underlain by the Continental Terminal formation, largely of Tertiary age, which consists of alternating, usually loosely consolidated, sandstones, siltstones, shales and mudstones.
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The Chad Formation is underlain by the Continental Terminal formation, largely of Tertiary age, which consists of alternating, usually loosely consolidated, sandstones, siltstones, shales and mudstones.
  
''Cretaceous:'' below the Continental Terminal there may be consolidated sedimentary rocks of Cretaceous age, dominantly marine but some continental sediments - including sandstones, siltsones, marls/calcareous mudstones and limestones.
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Below the Continental Terminal there may be consolidated sedimentary rocks of Cretaceous age, dominantly marine but some continental sediments - including sandstones, siltsones, marls/calcareous mudstones and limestones.
 
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|Iullemeden (also called Niger) Basin
 
|Iullemeden (also called Niger) Basin
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||The Iullemeden Basin lies immediately west of the Chad Basin and covers most of the western part of Niger. The Basin extends beyond Niger to parts of Mali, Benin and northwest Nigeria (it is called the Sokoto Basin in northwestern Nigeria). The total sedimentary sequence in the basin reaches several thousand metres thick.
 
||The Iullemeden Basin lies immediately west of the Chad Basin and covers most of the western part of Niger. The Basin extends beyond Niger to parts of Mali, Benin and northwest Nigeria (it is called the Sokoto Basin in northwestern Nigeria). The total sedimentary sequence in the basin reaches several thousand metres thick.
  
''Quaternary'': the youngest and uppermost sediments in the basin are unconsolidated Quaternary sediments, including extensive aeolian (dune) sands and alluvial sediments - extensive sands and gravels. and more minor silts and clays. These are often thin, up to few metres thick at most.
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The youngest and uppermost sediments in the basin are unconsolidated Quaternary sediments, including extensive aeolian (dune) sands and alluvial sediments - extensive sands and gravels. and more minor silts and clays. These are often thin, up to few metres thick at most.
  
''Tertiary'': sedimentary rocks of Tertiary age include poorly-consolidated/loosely cemented clays, siltstones and sandstones of continental origin. In some places are chalky limestones. The sandstone parts of this sequence form part of the so-named regional Continental Terminal 3 aquifer, the base of which is formed by a continuous clayey layer of few tens
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Below this are Tertiary sedimentary rocks, including poorly-consolidated/loosely cemented clays, siltstones and sandstones of continental origin. In some places are chalky limestones. The sandstone parts of this sequence form part of the so-named regional Continental Terminal 3 aquifer, the base of which is formed by a continuous clayey layer of few tens
 
of metres thick (Vouillamoz et al, 2007).
 
of metres thick (Vouillamoz et al, 2007).
  
''Cretaceous'': the lower parts of the Iullemeden Basin sequence are of Cretaceous age, including: Upper Cretaceous argillaceous siltstones and clays; Cenomanian to Turonian marine and lagoonal limestones, dolomitic limestones and sandstones; and Middle to Upper Cretaceous coarse grained sandstones.  
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The lower parts of the Iullemeden Basin sequence are of Cretaceous age, including: Upper Cretaceous argillaceous siltstones and clays; Cenomanian to Turonian marine and lagoonal limestones, dolomitic limestones and sandstones; and Middle to Upper Cretaceous coarse grained sandstones.  
 
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|Mesozoic-Palaeozoic
 
|Mesozoic-Palaeozoic

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