Provenance and tectonic setting of the Eocene Nanka Sandstone, Anambra Basin, Nigeria

Abstract

The Anambra Basin is a Cretaceous intracratonic basin, trending NE–SW in the southern part of Nigeria. The basin is believed to have been formed during the Santonian tectonic episode, which affected the entire Benue Trough. Inorganic geochemical data of the Nanka Sandstone was applied in studying its tectonic setting and provenance. The sandstones have fractionated chondrite-normalised rare earth element (REE) patterns, enriched light rare earth elements (LREE) and nearly horizontal REE with negative europium (Eu) anomalies. These patterns as well as a wide range of LREE/HREE (heavy rare earth elements) ratios and negative Eu anomalies suggest a felsic and/or mixed rock type source. A provenance discriminant function diagram utilising major oxides indicates a quartzose recycled sedimentary source. A plot of La/Th vs. Hf suggests a mixed felsic/basic source; a plot of Cr/Th and Th/Sc indicates contributions from felsic and basic end members, suggesting a mixed-source provenance. A Th/Co vs. La/Sc diagram, V-Ni-Th*10 ternary plot and Th/Co vs. La/Co suggest mixed source rock. Provenance investigations allude to sediment derivation from felsic, intermediate and mafic components and probably inputs from recycled older sediments. Tectonic discrimination based on major and trace elements indicates a passive margin setting.

Keywords:

• Nanka
• sandstone
• provenance
• tectonic setting
• mafic
• felsic

ACKNOWLEDGEMENTS

The author thanks the students (2016/2017 session) who partook in the field exercise and Dr Akin Eluwole for preparation of the location map.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author.