Characteristics, Source Area-weathering, Sedimentary Processes, Tectonic Setting and Taxonomy of Vertisols Developed on Alluvial Sediments in the Benue Trough of North Cameroon

Abstract

Although Vertisols have been highly documented owing to technological breakthroughs, numerous aspects are still not fully understood such as implication of geochemistry on source area-weathering, provenance, tectonic setting and sedimentary processes as well as problems of classification and management. This work aims to highlight the geochemical characteristics of Vertisols formed on alluvial deposits in the Benue Basin of North Cameroon and to highlight their source area-weathering, sedimentary processes, tectonic setting, taxonomic level and possible management strategies. The work was done in the field and in the Laboratory. The main results showed that smectite is the predominant clay mineral. Chemical composition revealed high Si, Al and Fe contents. Heavy minerals contents are of plutonic (augite, aegerine and aegerinic augerinic augite), metamorphic (kyanite, sillimanite and andalusite) and volcanic (tourmaline) origin. This agrees with the Al2O3/TiO2 ratio of 8.72 to 30.40 reflecting sediments from felsic rocks and minor mafic rocks. The CIA (chemical index of alteration: 70 to 85), PIA (plagioclase index of alteration: 66 to 82) and Ruxton’s index (SiO2/Al2O3: 2.27 to 3.55) suggest a warm and humid climate during moderate to intense chemical weathering probably prevailing during a more humid pre-depositional period. The K2O/Na2O ratio <1 suggests high sediments chemical maturity. The predominance of angular quartz grains suggests short fluvial transport distance and low sorting. The tectonic setting discrimination ternary diagram indicates that alluvial sediments, parent material of Vertisols, originate from an Active Continental Margin while the discriminant function-based multidimensional tectonic diagram indicates an arc-collisional setting suggesting that parent materials are from the Pan-African basement of the Central African Fold Belt. The Vertisols are classified as Ustic Haplusterts Clayey Isohyperthermic (United States Department of Agriculture) and as Gleyic Stagnic Vertisols (Pellic, Hypereutric, Clayic) (World Reference Base for Soil Classification).