Palynology of Middle Tertiary lacustrine deposits

Palynology of Middle Tertiary lacustrine deposits
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Previous palynologic investigation
Not much information is available at all in respect to the biostratigraphic
distribution of palynomorphs in Tertiary sediments of Northern Nigeria, i. e. the
los Plateau. In Niger and Mali the Paleogene section of the Iullemmeden Basin commences
with clay-, marl- and limestones. Certain beds contain marine microfossils
which refer to the Paleocene (Boudouresque et aI., 1982). During the Eocene, the
facies changed drastically to rather marginal marine conditions of sedimentation, immediately
noticeable by the deposition of clayey sediments (palygorskite) and ferruguneous
(Fe-, Mn-oxides) beds. On top of this rests a sequence symptomatically
correlated with the continental Terminal of Kilian (1931; Lang et aI., 1986).
In the arenaceous and pelitic horizons of supposed Eocene age micro- and
macrofossils were encountered and in the northern part of the basin even carbonaceous
and lignitic partings (Lang et aI., 1986). With these remains the status
of the onset of the Continental Terminal might be substantiated stratigraphically, at
least in the Iullemmeden basin (Boudouresque et aI., 1982). Among the palynomorphs
Echiperiporites icacinoides Sal. -Chebold. and Cicatricosisporites dorogensis Pot.
& Gel!. together with Chenolophonidites costatus, Striatopollis bellus and
Bomabacacidt"tes sp. were claimed to reveal a Middle Eocene savanna, but,
elsewhere, C. dorogensis is a rather reliable index-fossil of Eocene-Middle Oligocene
deposits (Takahashi & lux, 1982). A tropical mangrove swamp, vaguely dated with
Ecocene-Miocene appears to be reflected palynologically (Spinozonocolpites echinatus
Muller) at the base of the Gwandu Formation in Nigeria (Kogbe & Sowunmi, 1975;
Kogbe,
1979), the latter being correlated with both the Continental Terminal
(Boudouresque et aI., 1982) and the Kerri-Kerri Formation (Kogbe, 1981).
Palynomorphs are not easily recovered from the clastic sequence of the Gwandu
Formation, but some peaty lenses which were located in a borehole at Kaloye
(lullemmeden Basin, Nigeria), yielded tricolporate and monoporate grains which
perhaps derived from the vegetation of swampy, riverine and tropical forests (Kogbe
& Sowunmi, 1975) : Zonocostites ramonae Germeraad et aI., Spinizonocolpites
echinatus Muller, Monoporites annulatus v. d. Hammen, Retitricolporites irregularis
v. d. Hammen & Wymstra, Tetracolporopollenites sp. together with unidentified
pollen grains which may refer to Mauritia, Arenga, Ken tia, Uapaca and Ravenea. In
spite of the fact that only 70% of this assemblage could be classified systematically a
dominance of dicotyledons (50%) is revealed.
Conifers appear to be missing
whereas monocotyledons and pteridophytes were recognized (each group with ca.
10%). From the species announced the Gwandu Formation can of course only be