STRATIGRAPHY OF THE EASTERN GONGOLA BASIN, NORTH-EASTERN NIGERIA, WITH SPECIAL EMPHASIS ON THE TURONIAN GULANI FORMATION
STRATIGRAPHY OF THE EASTERN GONGOLA BASIN, NORTH-EASTERN NIGERIA, WITH SPECIAL EMPHASIS ON THE TURONIAN GULANI FORMATION
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Date
2012-12
Authors
JEREMIAH, AYOK
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Abstract
The stratigraphy of the eastern part of the Cretaceous Gongola Basin comprises the Bima Group (which is
subdivided into the Lower Bima Sandstone, the Middle Bima Sandstone and the Upper Bima Sandstone), the
Yolde Formation and the Pindiga Group (comprising the Kanawa Formation and the Gulani Formation).
Dolerite sills intrude the Kanawa Formation, while the Neogene Biu Basalt caps the entire Cretaceous
succession to the east. The “Kanawa Member” and the “Gulani Member” of previous authors are upgraded to
the Kanawa Formation and the Gulani Formation, respectively. The greater part of the “Pindiga Formation”
of previous authors is herein regarded as the Pindiga Group consisting of the Kanawa Formation, Gulani
Formation, “Deba Fulani Member”, “Dumbulwa Member” and “lower Fika Member”, the last being the pre-
Santonian portion of the “Fika Member”. A type section is proposed for the Gulani Formation some 1 km
north-east of the village of Dogon Zaga. Here the unit is made up of a lower part comprising Kanawa
Formation-type shales and thin sandstones with Thalassinoides burrows, interpreted as a sublittoral facies
deposited on a ramp-like margin. The major part of the Gulani Formation is made up of repetitive cyclic
arrangements of a similar but thinner subfacies overlain by large-scale tabular cross-bedded, coarse-grained
quartz arenite, and granulestones, the formation showing a generally coarsening-upwards or progradational
character. The cross-bedded sandstone facies are interpreted as small- scale Gilbert-type deltas prograding
over a shallow sublittoral facies into a hyposaline sea. The extreme rarity or absence of feldspar in the
sandstones of the Gulani Formation, the presence of sedimentary rock fragments and the low-diversity heavy
mineral assemblage suggests a sedimentary source, perhaps reworked Late Cenomanian to Early Turonian
littoral sands deposited during a preceeding transgressive interval. Palaeocurrent directions for the Gulani
Formation show a westerly-directed radiating pattern, suggesting the main point of sediment influx was
located around latitude 10o46' north. The type section of the Gulani Formation is interpreted as comprising
parts of two sequences. The lower part of the Kanawa Formation has a retrogradational parasequence stacking
pattern suggesting that it belongs to the transgressive systems tract of the first sequence. The maximum
flooding surface is here interpreted to be within that part of the section containing a number of condensed
horizons. The upper part of the Kanawa Formation, shows an aggradational parasequence stacking pattern
suggesting that it belongs to the lower part of the highstand systems tract of the first sequence. The lower 20
m of the Gulani Formation shows a progradational stacking pattern and probably represents the continuation
of the lower part of the highstand system tract of the first sequence. The greater part of the Gulani Formation
comprises parasequences with a progradational stacking pattern suggesting that it belongs to the lowstand
systems tract of a second sequence. The sequence boundary between the two sequences is interpreted to occur
at the base of the lowest cross-bedded sandstone since it represents the abrupt beginning of new subfacies. An
interpreted sea-level curve for the Late Cenomanian to Early Turonian section in the Ashaka Quarry shows a
good fit with the Exxon curve as regards the timing of the overall Cenomanian-Turonian sea-level peak with
both of them occurring in the Early Turonian. The most pronounced sea-level trough shown by the Exxon
curve around the Middle-Late Turonian boundary cannot at present be matched with any particular level at
Ashaka or anywhere else in the Gongola Basin though, the possibility that maximum regressive conditions
occurred in the Gongola Basin at a comparable interval cannot be excluded. Comparison of the levels of the
maximum flooding surfaces identified at Dogon Zaga and the Ashaka Quarry coupled with available
biostratigraphic information suggests that they are isochronous but that the Kanawa Formation is diachronous,
both its base and top being younger at Dogon Zaga than at Ashaka.
Description
A DISSERTATION SUBMITTED TO THE POSTGRADUATE SCHOOL,
AHMADU BELLO UINIVERSITY, ZARIA, NIGERIA IN PARTIAL
FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF THE
DEGREE OF DOCTOR OF PHILOSOPHY (Ph.D.) IN GEOLOGY
Keywords
STRATIGRAPHY, EASTERN, GONGOLA, NORTH-EASTERN, NIGERIA, EMPHASIS, TURONIAN, GULANI, FORMATION