The Fluviovolcanic Series (= FVS) of the Jos plateau, Central Nigeria
are an upper Eocene to middle Miocene time-equivalent to the Continent
al Terminal of the surrounding basins. It can be divided into a lower
part with mafic to intermediate and even felsic volcanic rocks (accord
ing to the Zr/TiO2), fluvial or limnic sediments and an upper part of
mafic volcanic rocks with intercalated transported pisoids and quartz
grains. Palynomorphs of a limnic clay reflect a subtropical to montane
tropical vegetation rich in plant species. The lower part of the FVS
often shows distinct tilting as a result of neotectonic movement along
a reactivated conservative plate boundary in continuation of the tran
satlantic Romanche fracture zone. The various rocks have been complete
ly converted into deep (often > 80 m) polygenetic soils which consist
of repetitive sequences of saprolite, mottled horizon and ferricrete.
The ferricrete represents a paleosurface and protects the profiles aga
inst erosion. The mineralogy of 3 profiles consists essentially of kao
linite with various amounts of goethite and hematite; gibbsite appears
in one confined horizon, whereas anatase and residual (weathered) ilm
enite and quartz occur as accessories. The presence or absence of ilme
nite, quartz and anatase in the various sections of the profiles were
taken as an indicator for different parent rocks. The crystallinity of
kaolinite (Hinckley index), the crystal size and Al substitution of g
oethite and hematite varied sectionwise indicating different weatherin
g environments. For example, the goethite in laminar-massive ferricret
es appearing at the base of all 3 profiles had lower Al substitution a
nd somewhat larger crystals than that of the pisolitic-vermiform ferri
cretes and was associated with redoximorphic conditions. On the basis
of mineralogical, paleontological, sedimentological and absolute K/Ar
age of basalts, the profiles were placed into the transition from Pale
ogene to Neogene and stratigraphic correlation was suggested.