Niger or Benue Delta: A New Insight

Orji O. Akaa, Uisdean Nicholson, Peter Clift, and David Macdonald
Geology & Petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom

A radical shift in the drainage pattern of River Niger is being investigated, following suggestions that the course was different from what it is now over geological time. An ancient upper Niger system is believed to have risen from the Guinea Highlands and flowed north-eastward, emptying into Lake Araouane, southwest of Timbuktu (Mali). In Quaternary times a completely separate, stronger lower Niger flowing southeast-ward cut its valley head-wards, captured the other river and drained off the lake, leaving only shallow pools, marshes, swamps and alluvial and lake deposits to mark where it once existed. While most of the sediments that originated before the capture and subsequent elongation of the Niger remained trapped in the inland lakes, the Benue, a far older river, related to early rifting of the Gondwana supercontinent, supplied its sediment to the “Niger” delta unhindered.

This study affords the opportunity to test competing hypotheses to better understand the provenance of the sediments that comprise the Niger Delta through geological time: have they come down the present-day Niger, or from the Benue River? The study involves the use of combined proxies, including light and heavy mineral studies, augmented by geochemical techniques. A compelling analogue is exposed around the area west of the Salton Sea, California, where deltaic sediments of the Colorado River occasionally inter-finger with locally derived sediments enable the generation of a framework for the reconstruction of the paleo-drainage system that may have controlled the depositional mechanisms of the evolving delta.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas