Cenomanian to Turonian foraminifera from Ashaka (NE Nigeria): quantitative analysis and palaeoenvironmental interpretation
Abstract
A detailed palaeoenvironmental analysis based on planktonic and benthic foraminifera has been carried out over the Cenomanian/Turonian transition exposed at Ashaka in northeast Nigeria. The predominantly arenaceous benthonic foraminiferal fauna has been divided into four groups. Three of these indicate certain environmental conditions (oxygen deficiency and low salinity, oxygen deficiency and normal salinity, oxygenated water and normal salinity), while the fourth comprises environmentally unrestricted genera. Quantitative analysis, in combination with sedimentological and macrofaunal data, leads to a tripartite division of the section investigated: the thick basal limestones (Gongila Formation) were deposited under well oxygenated, normal marine conditions; the middle part (basal Fika Shale Formation) points to a stratified water body with well oxygenated, normal marine surface water and anoxic/dysoxic but normal marine bottom water; the upper part (Fika Shale Formation) shows alternating normal marine oxic and brackish anoxic/dysoxic conditions. The maximum water-depth probably never exceeded 50 m.
- Publication:
-
Cretaceous Research
- Pub Date:
- February 1997
- DOI:
- Bibcode:
- 1997CrRes..18...17G
- Keywords:
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- Cenomanian;
- Turonian;
- northeastern Nigeria;
- foraminifera;
- quantitative analysis;
- palaeoenvironments;
- oxygenation;
- palaeosalinity;
- water-depth