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" Biostratigraphic and Chemostratigraphic Studies of Shales from Akukwa-2 and Amansiodo-1 Wells, Anambra Basin, Southeastern Nigeria "
Haruna, Abdulrasaq Kehinde
Ojo, O J
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Latin Dissertation
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English
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| Record Number
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1057600
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TL56717
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| Main Entry
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Haruna, Abdulrasaq Kehinde
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| Title & Author
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Biostratigraphic and Chemostratigraphic Studies of Shales from Akukwa-2 and Amansiodo-1 Wells, Anambra Basin, Southeastern Nigeria\ Haruna, Abdulrasaq KehindeOjo, O J
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| College
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Kwara State University (Nigeria)
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| Date
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2020
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Ph.D.
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2020
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261 p.
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| Abstract
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Two exploratory wells (Akukwa and Amansiodo) in the Anambra Basin were investigated for biostratigraphy, chemostratigraphy, depositional environment, provenance and weathering history of the shales. Methods used include palynological and foraminiferal studies, XRF, ICPMs, XrD analyses and software such as grapher, tri-plots, r-statistics and illustrator were also used. In Amansiodo well, two broad informal palynological zones were identified whereas, five informal palynological zones were erected in Akukua-2 well. A number of diagnostic marker species such as Ammobaculites coprolithiformis, Lenticulina grandis, Lenticulina pseudomammiligerus, Bolivin aafra, Bolivina explicata, Hedbergella holmdelensis, and Globotruncanita elevate were recovered from Akukwa-2 well and Amansiodo-1 well suggesting predominantly inner neritic, deepening to middle neritic at some horizons. Based on the occurrence and distribution of microflora and microfauna species identified in the Akukwa-2 well, a Late Cretaceous-Paleogene age is suggested for the studied section. In the Amansiodo well, Campanian - Maastrichtian age was assigned. The geochemical data obtained showed that Akukwa well samples contained SiO2, Al2O3 and Fe2O3 with an average values of 35.2wt %; 11.1wt% and 8.21wt% respectively while the Amansiodo well samples contained SiO2 (63.8wt.%); Al2O3(15.9%); Fe2O3(4.74wt%); CaO(0.51wt. %).The CIA and PIA values of shales from Akukwa and Amansiodo wells are very high (78–99 and 97-99 respectively) suggesting that most of the shales were subjected to extreme chemical weathering. K2O/Na2O versus PIA, (K2O+Na2O) versus PIA, Na2O wt% versus PIA, CaO wt.% versus PIA and K2O wt.% versus PIA plots show a substantial decrease in the quantity of Na2O, CaO and K2O with an increase in PIA values also suggesting intense chemical weathering. The plots of TiO2 versus Al2O3 and TiO2 vs. Ni indicate that the shales originated from intermediate to felsic rocks. The Cr/Ni ratios (1.16–5.16 and 1.28–2.77) are low in Akukwa and Amansiodo well samples respectively indicating a felsic provenance. Bivariate discriminant function of the shales indicate passive paleotectonic setting. Binary plot of SiO2wt% vs. (Al2O3 + K2O+Na2O) wt% shows the shales were deposited under humid and partly semiarid conditions.The Ni/Co ratio (average = 1.70) and the Cu/Zn (average = 0.48) obtained from the shales suggest deposition in oxic conditions. The V and Ni cross plots indicate that majority of the Akukwa and Amansiodo samples have input from marine/marine-terrestrial sources under oxic conditions. Four chemostratigraphic zones were identified for each of the wells (AK1, AK2, AK3 and AK4 for Akukwa and AM1, AM2, AM3 and AM4 for Amansiodo). The Sr/Ba ratios in Akukwa ranges from 0.21 - 0.63 indicating a fresh-brackish water while Sr/Ba ratios in the Amansiodo wells ranges from 0.22 - 1.29 (average 0.53), indicating saline conditions. Excess content of silica, Cu/Al and Ni/Al ratios aswell as total Barium (Batot) and biogenic Barium (Babio) reveal high paleoproduction of organic material within the two wells. Mineralogy indicates the enrichment of kaolinite and quartz in the upper intervals of the wells suggesting more continental conditions whereas the lower part is enriched in chlorite but depleted kaolinite indicating seaward contributions. Gypsum and halite occurrence in few intervals in the wells suggest occasional evaporate diagenetic environment and dry conditions.
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| Descriptor
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Geology
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Ojo, O J
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Kwara State University (Nigeria)
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